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A Survey on Power-Amplifier-Centric Techniques for Spectrum- and Energy-Efficient Wireless Communications
Abstract
In this paper, we provide a survey on techniques to improve the spectrum and energy efficiency of wireless communication systems. Recognizing the fact that power amplifier (PA) is one of the most critical components in wireless communication systems and consumes a significant fraction of the total energy, we take a bottom-up approach to focus on PA-centric designs. In the first part of the survey, we introduce the fundamental properties of the PA, such as linearity and efficiency. Next, we quantify the detrimental effects of the signal non-linearity and power inefficiency of the PA on the spectrum efficiency (SE) and energy efficiency (EE) of wireless communications. In the last part, we survey known mitigation techniques from three perspectives: PA design , signal design and network design. We believe that this broad understanding will help motivate holistic design approaches to mitigate the non-ideal effects in real-life PA devices, and accelerate cross-domain research to further enhance the available techniques.
... In the comparison the states of AAS u = 1, 2, and 3 are same. The total direct current (DC) power consumption in Watt scale of the PAs [36]- [40] of active sub-array connected to one RF chain of GBS AAS type u to compensate for the RF power loss L u and to radiate power P T is ...
... where G A (k, l) is RF power gain of PA [36]- [40] connected to antenna element (k, l) in dB scale, η(k, l) is the power-added efficiency (PAE) of the PA [36]- [40] connected to antenna element (k, l), a u is the number of active PAs of GBS AAS type u, L u is in Watt scale, P T is in Watt scale, for AAS u = 1 proposed in this work the a 1 = 2 (α+β) , for AAS u = 2 [13] the a 2 = 2 (α+β) , and for AAS u = 3 [14] the a 3 = 2 (α+β) . Also, in (18) to radiate power P T and to compensate AAS loss L u , the condition is ...
... where G A (k, l) is RF power gain of PA [36]- [40] connected to antenna element (k, l) in dB scale, η(k, l) is the power-added efficiency (PAE) of the PA [36]- [40] connected to antenna element (k, l), a u is the number of active PAs of GBS AAS type u, L u is in Watt scale, P T is in Watt scale, for AAS u = 1 proposed in this work the a 1 = 2 (α+β) , for AAS u = 2 [13] the a 2 = 2 (α+β) , and for AAS u = 3 [14] the a 3 = 2 (α+β) . Also, in (18) to radiate power P T and to compensate AAS loss L u , the condition is ...
A ground base station (GBS) antenna array system (AAS) geometry and feed technique are proposed for 360 degree azimuth beam scan, elevation beam scan, azimuth beam-width control, elevation beam-width control, and in existing AASs these four capabilities do not coexist. Firstly, the results confirm that the number of active radio-frequency (RF) switches in the proposed AAS feed network is reduced by more than 99 %, and the AAS achieves a power consumption reduction of up to 50 % without fully connected (FC) architecture and 35 % with FC architecture compared to the existing AAS. Also, an independent GBS AAS azimuth and elevation plane beam-width control can be achieved from 65 to 0.01 degrees which makes it suitable for GBS-assisted wireless back-hauling plus wireless charging of unmanned aerial vehicle base stations (UAV-BSs), dynamic GBS sectorisation order control, and millimeter wave beam tracking. Also, a parallel concurrent UAV-BS battery charging configuration with power source swap capability is proposed to charge UAV-BS using the GBS back-haul and onboard power amplifier (PA) system as the power sources. The results show that the proposed charging configuration improves hovering time by 180.7 % compared to the existing onboard PA system configuration for battery charging. Furthermore, the proposed charging configuration can recharge the battery of the inactive state UAV-BS to increase the state of charge of two 16 Ampere hour batteries to 80 % in 180.13 minutes, and UAV-BS’s inactive state charging was not proposed in the existing onboard PA system configuration for UAV-BS’s battery charging.
... The PA power consumption depends on many factors, including transmitted waveform, utilized PA architecture, or the PA operating point. The two main architectures to be considered are class A and class B PAs [16]. Most importantly, the PA nonlinearity influences the emitted waveform that, e.g., for class B PA, influences power consumption. ...
... There are various types of PAs, each characterized by different power consumption. A comparison of various commercial PAs efficiencies is provided in [16]. However, the two most common in wireless transceivers, because of their linearity, are classes A and B PAs [22]. ...
... While for low SNR SAT values, perfect PA requires higher IBO values resulting in lower SNDR values, after exceeding a SNR SAT of about 20 dB, it is a class B PA that requires higher IBO values and obtains lower SNDR values. This observation is important in the context of the next generations of highly efficient PAs, e.g., class B PAs with adaptively changed supply voltage using so-called Envelope Tracking (ET) [16,23]. Their ultimate design goal is characteristic of the perfect PA considered here. ...
While Orthogonal Frequency Division Multiplexing (OFDM) is a dominating spectrum access technology in modern, wideband access networks, it is important to maximize its transmission efficiency considering the underlying radio front-end characteristics. A practical front-end contains nonlinear components, e.g., a Power Amplifier (PA), resulting in nonlinear distortion being injected into OFDM band deteriorating symbols detection. A PA operating point, defined here by Input Back-Off (IBO), can be adjusted to balance the wanted signal power and nonlinear distortion power. While it is the most common to maximize the spectral efficiency (SE), recently, energy efficiency (EE) maximization gained momentum. However, EE maximization requires, in addition to PA nonlinearity modeling, modeling of the power consumption of the PA and all other transmitter components. While it is commonly overlooked, if a battery is used to power the transmitter, its model should be considered as well. This paper derives mathematical expressions for EE and SE of an OFDM transmitter considering Rapp and soft-limiter models of PA nonlinearity, class A, class B, and perfect PA power consumption models, and two battery models: perfect and worst-case. While closed-form expressions cannot be obtained for most of the derived integrals, numerical methods have been used to obtain the optimal IBO value in each case. The numerical results show, in addition to optimal IBO values, the expected Signal-to-Noise and Distortion Ratios (SNDRs). It is shown that the optimal IBO value changes significantly with the wireless channel properties, utilized hardware architecture, or the utilized optimization goal. As such, the proposed optimization is an important topic for 5G and beyond transmitters.
... In the prior works [34]- [38] the UAV's radiated RF output power is controlled for the reasons such as to mitigate interference [34], to minimize the aerial vehicle assisted IoT system power consumption [35], to secure UAV communication using coordinated multipoint [36] reception, to secure the UAV communication using intelligent reecting surface [37] and to secure UAV communication [38]. Realistically, the radiated output power of UAVs [34]- [38] is controlled by the PAs [10]- [14], and PAs are well-known as a power-hungry component. ...
... RF PAs [10]- [14] control the radiated RF output power by tuning its Direct Current (DC) power supply, and PAs are power-hungry because of poor PAE η. The PAE η decreases with the reduction of PA's RF output power [12], so for specic RF output power levels of PA, the PAEs are distinct, so PA's output RF power control uctuates the PAE η, realistically, η ≈ 0.2 [10], and η ≈ 0.27 [15]. ...
... RF PAs [10]- [14] control the radiated RF output power by tuning its Direct Current (DC) power supply, and PAs are power-hungry because of poor PAE η. The PAE η decreases with the reduction of PA's RF output power [12], so for specic RF output power levels of PA, the PAEs are distinct, so PA's output RF power control uctuates the PAE η, realistically, η ≈ 0.2 [10], and η ≈ 0.27 [15]. Also, the non-linearity [10]- [14] of RF output power levels of PAs is a well known challenging problem. ...
A simple and energy-efficient communication system configuration is proposed for Unmanned Aerial Vehicle
Energy Transmitters (UAV-ETs) for Wireless Power Transfer (WPT) applications. The results show that the
proposed UAV-ET’s hardware configuration improves WPT time by 9.305%, and reduces UAV-ET’s power
consumption by 7.47% compared to the UAV Base Stations (UAV-BSs). Also, in the prior works on UAVenabled
WPT the UAV-ET’s communication system configuration was not proposed, and UAV-ET’s radio
frequency component’s real-world imperfections were ignored. Therefore, the work proposes a holistic energy
efficiency optimization framework for UAV-ETs and hardware design parameters for qualifying the UAV-ET’s
hardware components to maximize UAV-ET’s WPT time. Additionally, a three-dimensional UAV-ET placement
optimization is proposed for maximizing WPT time, and results show that higher UAV-ET heights above the
Wireless Energy-Receivers (WERs) decrease the WPT time by 4.75%. Besides, the results suggest that Antenna
Array (AA) losses and the power amplifier’s power added efficiency variation reduce UAV-ET’s WPT time by
16.48%. Finally, a 115 g crossed-slotted waveguide AA for UAV-ET is manufactured using laser cutting, and
the experiments confirm that the AA’s total loss is 0.72 dB, therefore, the AA qualifies requirements according
to the proposed UAV-ET’s hardware component design optimization framework.
... In this way, it is important to determine an appropriate rate of sampling bandwidth in the presence of memory effects (MEs) to meet the target performance of intra-band (within carrier), and inter-band (outside carrier) signal modulations [28], [29]. It is also worth highlighting that the worst-case scenario of ambient MEs occurs in the wideband systems, where the inter-band distortion coincides with DPD modulated intra-band signal [15], [30]. Therefore, another variant of the PD scheme, known as analog predistortion (APD), with its wideband operating capability, can target the out-of-band (OOB) distortions more effectively than DPD [31]. ...
... BACKGROUND: FROM AN EYE OF RECENT SURVEYS The objective of this section is to familiarize the reader with the fundamental background, state-of-the-art proposals, approaches, and application scenarios of the three PD paradigms when developing MIMO technology for 5G BS modules. The summary of general and relevant surveys [15], [44]- [48] and magazine articles [19], [49]- [52] pertaining directly or indirectly to the PD linearization schemes or technology can be found in Table I and III, respectively. ...
... An exhaustive survey has been presented in [15] to investigate distortion-free PA architectures' system requirements in conventional 3G/4G communications. This survey carries an extensive research study to validate the energy efficiency (EE) and SE trade-off. ...
The next-generation (5G/6G) wireless communication aims to leapfrog the currently occupied sub-6 GHz spectrum to the wideband millimeter-wave (MMW) spectrum. However, MMW spectrums with high-order modulation schemes drive the power amplifier (PA) at significant back-off, causing severe nonlinear distortions, thus deteriorating the transceiver’s (TRXs) modulation process. Typically, the TRX efficacy is quantified with standardized linearization matrices, which take advantage of different predistortion (PD) schemes to handle deep compression of the PA. In this regard, TRX baseband signals are mostly linearized in the digital domain, where digitally controlled linearization needs higher sampling rates due to increasing MMW bandwidths to compensate for intermodulation (IMD) products, resulting in increased system cost and power consumption. Alternately, the digitally controlled analog-based linearization, i.e., the hybridization of digital predistortion (DPD) and analog predistortion (APD), is highly productive and cost-effective for fulfilling the linearized energy-efficient design vision of MMW networks. Therefore, this paper puts an extensive spotlight on the progress in PD-based linearization for 5G and beyond communications. It first provides background information on the advancements of PD schemes through recent surveys, then classifies the general roadmap of PD waveform processing across the TRX system models as preliminary. After this, we present three prominent PD architectures and their design approaches with intrinsic performance metrics. Finally, we explore four case studies encompassing PD operation under certain nonlinear constraints of different communication schemes. We examine the suitability of PD-based linearization solutions, both existing and proposed till the first quarter of 2022, and identify the potential prospects in this domain.
... 5) Works on UAV's radiated RF power control: The UAV's radiated radio frequency (RF) output power is controlled for the reasons such as to mitigate interference [33], to minimize the aerial vehicle assisted internet of things system power consumption [34], to secure UAV communication using coordinated multipoint [35] reception, to secure the UAV communication using intelligent reflecting surface (IRS) [36] and to secure UAV communication [37]. Realistically, the radiated output power of UAVs [33]- [37] is controlled by the power amplifiers (PAs) [14]- [18], and PAs are well-known as a power-hungry component. ...
... 6) Works on RF power amplifier: RF power amplifiers (PAs) [14]- [18] control the radiated RF output power by adjusting its direct current (DC) power supply, and PAs are power-hungry because of poor power added efficiency (PAE) η m . The PAE η m decreases with the reduction of PA's RF output power [16], so for specific RF output power levels of PA, the PAEs are distinct, so PA's output RF power control fluctuates the PAE η m , realistically, η m ≈ 0.2 [14], and η m ≈ 0.27 [19]. ...
... 6) Works on RF power amplifier: RF power amplifiers (PAs) [14]- [18] control the radiated RF output power by adjusting its direct current (DC) power supply, and PAs are power-hungry because of poor power added efficiency (PAE) η m . The PAE η m decreases with the reduction of PA's RF output power [16], so for specific RF output power levels of PA, the PAEs are distinct, so PA's output RF power control fluctuates the PAE η m , realistically, η m ≈ 0.2 [14], and η m ≈ 0.27 [19]. Also, the non-linearity [14]- [18] of RF output power levels of PAs is a well known challenging problem. ...
A radio frequency (RF) power amplifier (PA) system configuration for on-board energy conversion is proposed for unmanned aerial vehicle base station's (UAV-BS's) battery charging. Firstly, the PA system utilizes the internal radio-frequency source for energy conversion, so that perpetual battery charging is possible without external power sources. Therefore, continuous battery charging of UAV-BS is possible while providing wireless network coverage by hovering over the target location. In addition, the proposed PA system offers higher RF power control resolution than the existing PA works, which is desirable for precise power control of UAV-BS. The objective of simultaneous RF power control and battery charging by the PA system is achieved by activating one Wilkinson power divider (WPD) with a specific power splitting ratio in the power divider bank. The simulations show that the dynamic activation of 10 distinct unequal split WPDs of the proposed PA system improves the RF power control resolution by 157 % and 396 % compared to the existing PAs. Additionally, the simulations show that the PA's power added efficiency fluctuation is reduced by 54 % and 82 % compared to the existing PAs. In addition, it will be shown that the proposed on-board battery charging increases the hovering time by 7.4 %. Furthermore, an energy-efficiency optimization framework for UAV-BS's is proposed considering real-world communication system hardware imperfections, and the proposed result suggests that UAV-BS's flight time may decrease by 50 % depending upon the type of UAV-BS RF components.
... W tym celu wykorzystuje się różne podejścia do architektury układów wzmacniaczy [7], które mają na celu osiągnięcie jak najbardziej liniowego wzmocnienia sygnału przy jednoczesnej minimalizacji zużycia energii. Śledzenie obwiedni (ang. ...
... Istnieje wiele publikacji naukowych [4,7,10,21], które szeroko omawiają podstawowe modele behawioralne. Niektóre modelują tylko efekty bezpamięciowe (Soft limiter, Rapp, Saleh). ...
The work aims to propose a new nonlinear characteristics model for a wideband radio amplifier of variable supply voltage. An extended Rapp model proposal is presented. The proposed model has been verified by measurements of three different amplifiers. This model can be used to design frontend-aware 6G systems. -- Praca ma na celu zaproponowanie nowego modelu dla nieliniowej charakterystyki wzmacniacza radiowego ze zmiennym napi\k{e}ciem zasilania pracuj\k{a}cym w szerokim zakresie cz\k{e}stotliwo\'sci. Przedstawiona zosta{\l}a propozycja rozszerzonego modelu Rappa. Zaproponowany model zweryfikowano na podstawie pomiar\'ow charakterystyk trzech r\'o\.znych wzmacniaczy. Model ten mo\.ze by\'c wykorzystany do projektowania system\'ow 6G "\'swiadomych" niedoskona{\l}o\'sci uk{\l}ad\'ow wej\'sciowo-wyj\'sciowych.
... We then rely on the WLAN multipath fading 'Model C' proposed by the HT Task Group for n-channel (TGn) waveform propagation [23] and modify it 1 for generation of 1 Note that both the HT baseband transmission of 802.11n and the generation of h SI [k] are simulated using the WLAN Toolbox of MATLAB [28]. Nonlinearities of PA and LNA&A/D in Fig. 1 are assumed to be memoryless [22] with only amplitude-to-amplitude (AM/AM) distortion [29]. The respective nonlinear functions are thus given as ...
... The last dimension merely refers to a single input channel. Cartesian s[k] is then split into magnitude and phase to resemble a physically motivated nonlinear PA in the magnitude [29,31]. Nonlinear modeling f (s) on the magnitude is here represented by a multilayer perceptron (MLP) where the number of units per layer is here implemented by the number of filters P of convolutional layers. ...
Neural network modeling is a key technology of science and research and a platform for deployment of algorithms to systems. In wireless communications, system modeling plays a pivotal role for interference cancellation with specifically high requirements of accuracy regarding the elimination of self-interference in full-duplex relays. This paper hence investigates the potential of identification and representation of the self-interference channel by neural network architectures. The approach is promising for its ability to cope with nonlinear representations, but the variability of channel characteristics is a first obstacle in straightforward application of data-driven neural networks. We therefore propose architectures with a touch of "adaptivity" to accomplish a successful training. For reproducibility of results and further investigations with possibly stronger models and enhanced performance, we document and share our data.
... At the same time, it is expected that new transceivers will be highly energy-efficient [3]. Most importantly, up to 80% of energy consumption at the base station can be attributed to the power amplifier [4]. In the case of a PA, the highest signal quality, characterized by minimal self-distortion, is obtained when the PA is linear in the whole range of transmitted signal samples. ...
... These models can be distinguished based on whether they account for the memory effect, such as the Volterra series, Wiener, or Hammerstein models, or if they only characterize static nonlinearities, like those by Saleh, Rapp, or Ghorbani [19]. Considerable effort has been devoted to reviewing, analyzing, or comparing basic available models such as [1,4,7]. However, for contemporary, solid-state power amplifiers used in 5G systems, the Rapp model has been proposed [20]. ...
Next-generation wireless systems require increased spectral and energy efficiency in terminals. This can only be achieved if the nonlinear characteristics of the radio front-end, primarily the power amplifier (PA), are known and considered while designing algorithms or optimizing radio links. PA datasheets contain limited information, and wideband PA measurements typically require advanced equipment and software. This paper proposes a measurement and signal processing framework that enables the acquisition of nonlinear PA characteristics using generic complex sample transmitters and receivers, e.g., software-defined radio (SDR). This paper also proposes a multistage signal calibration and synchronization procedure that allows obtaining nonlinear PA characteristics that are non-distorted by other phenomena. The correctness and usefulness of the proposed framework are demonstrated by measuring three PAs, each under varying supply voltage and carrier frequency. At the same time, the high variability of the obtained nonlinear characteristic justifies the need for PA measurements to obtain awareness of nonlinear characteristics.
... Moreover, the signal amplification in the HPA requires a DC power source, which accounts for the majority of the power consumption. Notably, the HPA introduces non-linear signal distortion that requires precise modeling [17], [18]. The significant drawback of the fully-digital architecture is the high complexity and cost, making it impractical for applications requiring massive MIMO (mMIMO) implementations. ...
... Herein, we focus on the low-power regime, for which it was demonstrated in [13], [32] that truncating the Taylor expansion at n 0 = 4 is accurate enough. Therefore, (17) can be written as ...
Radio frequency (RF) wireless power transfer (WPT) is a promising charging technology for future wireless systems. However, low end-to-end power transfer efficiency (PTE) is a critical challenge for practical implementations. One of the main inefficiency sources is the power consumption and loss of key components such as the high-power amplifier (HPA) and rectenna, which must be considered for PTE optimization. Herein, we investigate the power consumption of an RF-WPT system considering the emerging dynamic metasurface antenna (DMA) as the transmitter. Moreover, we incorporate the HPA and rectenna non-linearities and consider the Doherty HPA to reduce power consumption. We provide a mathematical framework to calculate each user's harvested power from multi-tone signal transmissions and the system power consumption. Then, the waveform and beamforming are designed using swarm-based intelligence to minimize power consumption while satisfying the users' energy harvesting (EH) requirements. Numerical results manifest that increasing the number of transmit tones enhances the performance in terms of coverage probability and power consumption since the HPAs operate below the saturation region in the simulation setup and the EH non-linearity is the dominant factor. Finally, our findings demonstrate that a properly shaped DMA may outperform a fully-digital antenna of the same size.
... It is shown that 16-CPM is the least sensitive to HPA nonlinearities compared to APSK and QAM. Several techniques have been proposed to combat the effect of nonlinear distortions at the transmitter side in the form of predistortion and post-distortion at the receiver side through nonlinear equalization (Ding et al., 2004;Beidas, 2011;Beidas et al., 2015;Joung et al., 2015). Authors in (Joung et al., 2015) provide a summary of HPA centric techniques with an emphasis on the design of HPAs, signals, and networks to improve HPA linearity and efficiency. ...
... Several techniques have been proposed to combat the effect of nonlinear distortions at the transmitter side in the form of predistortion and post-distortion at the receiver side through nonlinear equalization (Ding et al., 2004;Beidas, 2011;Beidas et al., 2015;Joung et al., 2015). Authors in (Joung et al., 2015) provide a summary of HPA centric techniques with an emphasis on the design of HPAs, signals, and networks to improve HPA linearity and efficiency. It should be noted that the extent to which nonlinearity affects the communications system is mainly dependant on the power requirement and modulation scheme in use (Corazza, 2007). ...
The unrelenting technological advancement in the generation of wireless networks in recent years has awakened the motion concerning the inclusion of satellites in personal communications. Leveraging their ability to provide wide coverage, uniform services, wide bandwidth, and so forth, Satellite systems will be expected to co-exist with the current state-of-the-art infrastructure of terrestrial networks. Herein, we present a comparative study on the representative digital modulation techniques for use in personal satellite communications. We discuss the advantages and limitations of different modulation techniques, such as phase shift keying, continuous phase modulation, amplitude phase shift keying, and quadrature amplitude modulation. We also perform evaluations based on spectral efficiency, power efficiency, modulation error ratio, error vector magnitude, and peak-to-average power ratio in the presence of high power amplifier nonlinearities and Doppler effects. Comparisons in the form of tables, illustrations, and curves are also presented. In correspondence to the comparisons made basing on the aforementioned metrics, we conclude that continuous phase modulation is the best candidate modulation scheme for personal satellite communications since it outperforms other schemes by compromising the trade-off between power efficiency, bandwidth efficiency, and immunity to errors. We further present open issues that would reinforce personal satellite communications in terms of reliability, throughput and latency, other than power and spectral efficiency, if combined with appropriate modulation schemes.
... To get a reasonably tractable and accurate power consumption model, the power amplifier model from [36] is used to characterize the power consumption of the reflection amplifier for active elements. The power consumed by m number of identical active elements during energy harvesting is expressed as follows: ...
To enhance wireless communication in IoT systems using reconfigurable intelligent surfaces (RISs), efficient control of programmable passive and active elements is essential. However, increasing RIS elements requires more microcontrollers, raising complexity and cost. This paper proposes a modular approach ("Module"), where each microcontroller controls a module of optimal active or passive elements. The module size is determined using a non-linear energy harvesting model, where a batteryless IoT (b-IoT) sensor harvests energy from base station (BS) RF signals. We optimize the number of modules (microcontrollers) to minimize energy consumption while satisfying energy harvesting and information causality constraints. Simulations show that RIS module-assisted energy harvesting improves IoT system performance by ~100% compared to models without RIS panels.
... Attention has been given to the energy-efficient design of power amplifiers [143], [144], both through direct circuit design and through signal design techniques aimed at peak-to-average-power ratio reduction. The use of simplified transmitter and receiver architectures, including the adoption of coarse signal quantization (e.g. one bit quantization) and hybrid analog/digital beamformers, is another technique that is being proposed for increasing hardware energy efficiency, especially in systems with many antennas such as massive MIMO systems and mmWave systems. ...
After about a decade of intense research, spurred by both economic and operational considerations, and by environmental concerns, energy efficiency has now become a key pillar in the design of communication networks. With the advent of the fifth generation of wireless networks, with millions more base stations and billions of connected devices, the need for energy-efficient system design and operation will be even more compelling. This survey provides an overview of energy-efficient wireless communications, reviews seminal and recent contribution to the state-of-the-art, including the papers published in this special issue, and discusses the most relevant research challenges to be addressed in the future.
... Moreover, high PAPR in OFDM-IM signals may result in nonlinear distortions and degrade system performance [13]. As next-generation communication technologies transition from centimeter waves to millimeter waves [14], addressing the high PAPR issue becomes increasingly crucial, particularly given that HPAs are major contributors to energy consumption in cellular networks [15]. ...
Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a promising technique for next-generation wireless communications due to its superior error performance and flexibility. However, as a type of multi-carrier modulation, it suffers from a high peak-to-average power ratio (PAPR), which can compromise transmission reliability. Therefore, in this paper, a polar-coded PAPR reduction scheme based on hybrid index modulation (PC-HIM) for OFDM-IM is proposed. Also, the proposed framework employs sets of various frozen bits and spatial modulation (SM) to solve the high PAPR issue in OFDM-IM systems. At the receiving side, the detection of the activated antennas status facilitate the recovery of selected frozen bit set, whose indices are embedded in the SM operations. Therefore, the need for transmitting side information, which is a necessary process in probabilistic PAPR reduction schemes, can be eliminated. Further, to enhance detection accuracy, a construction method for frozen bit sets based on Hadamard matrix is proposed. Additionally, to address the high complexity inherent in the proposed PC-HIM PAPR reduction framework, a low-complexity version, termed LC-PC-HIM, is proposed. This framework simplifies both the transmitting and receiving operations through a redesign of the information processing procedures and the selected frozen bit set detection step. Simulation results demonstrate that the proposed PAPR reduction scheme (PC-HIM and LC-PC-HIM) outperforms existing polar code-based PAPR reduction schemes by at most 12.5%, delivering the most effective PAPR reduction performance. Furthermore, the proposed receiving approach achieves error performance comparable to that of a receiver utilizing perfect side information.
... In comparison to the passive RIS, each RE of the active RIS is added a reflection amplifier (RA), which can be implemented by a tunnel diode circuit. Then, we adopt the conventional power amplifier model [20] to characterize the power consumption of the mth RE, denoted by P RE,m , as follows: ...
Wireless devices can be easily attacked by jammers during transmission, which is a potential security threat for wireless communications. Active reconfigurable intelligent surface (RIS) attracts considerable attention and is expected to be employed in anti-jamming systems for secure transmission to significantly enhance the anti-jamming performance. However, active RIS introduces external power load, which increases the complexity of hardware and restricts the flexible deployment of active RIS. To overcome these drawbacks, we design a innovative self-sustainable structure in this paper, where the active RIS is energized by harvesting energy from base station (BS) signals through the time dividing based simultaneous wireless information and power transfer (TD-SWIPT) scheme. Based on the above structure, we develop the BS harvesting scheme based on joint transmit and reflecting beamforming with the aim of maximizing the achievable rate of active RIS-assisted system, where the alternating optimization (AO) algorithm based on stochastic successive convex approximation (SSCA) tackles the nonconvex optimization problem in the scheme. Simulation results verified the effectiveness of our developed BS harvesting scheme, which can attain higher anti-jamming performance than other schemes when given the same maximum transmit power.
... The large unused available bandwidth in the mm-Waves and sub mm-Waves bands (24-100 GHz) has driven a higher demand for high data rate, high efficiency, and high integration transceiver systems that are able to deliver high output power. Intrinsically, Power Amplifiers (PAs) consume the most power in a transmitter system; their performance and design is instrumental to the overall performance and reliability of the system [1]. The challenge with designing PAs is maintaining high efficiency while delivering high output power [2]. ...
Using the stacking technique in CMOS technology for Power Amplifiers (PAs), allows the use of a higher supply voltage. This facilitates achieving a higher voltage swing, and delivering more output power while maintaining a high efficiency. This work presents an improved 2-stacked cascode class-E PA at 28 GHz. Unlike existing topologies, a switching input signal is not only applied at the input transistor, but also at the cascode transistor with an added delay. The design was fabricated in 22 nm FDSOI CMOS technology by GlobalFoundries that offers high performance especially at mm-wave frequencies. Measurement results of the cascode Class-E Power Amplifier achieves a peak PAE of 28%, and 41% DE. The switched-cascode topology showed an improved peak PAE of 35% and DE of 45%. Measured power gain was 8.5 dB with saturated output power (P
sat
) of 13 dBm. This work reports the best Drain Efficiency (DE) and FoM for a fully integrated PA at 28 GHz in 22 nm FDSOI.
... Finally, the power consumed by the radar transmitter can be modeled as P tot r = ρ r + η −1 r,all P r , where ρ r is the static power [32] and η r,all is the overall efficiency of the RF amplifier [33,Eq. (10)]. ...
In this paper, we consider a monostatic radar and study the joint detection and localization of a prospective target when the receiver is assisted by a reconfigurable intelligent surface (RIS). To mitigate the multiplicative path loss in the target-RIS-radar hops, we resort to an active RIS, which allows both redirecting and amplifying the incident signal. Upon choosing the array gain factor of the radar transmitter and the RIS to uniformly cover the inspected region, the joint target detection and localization is formulated as a composite hypothesis testing problem, which is solved via a generalized likelihood ratio test (GLRT). Numerical examples are provided to show the merits of the proposed architecture.
... where P e is the power dissipation of each unit cell due to the circuit consumption required for adaptive phase shifting. For the power consumption of ARIS, the typical power amplification model of ARIS [39] can be represented as ...
Due to the serious path loss of millimeter-wave (mmWave), the signal sent by the base station is seriously attenuated when it reaches the indoors. Recent studies have proposed a glass-based metasurface that can enhance mmWave indoor signals. The transparent reconfigurable intelligent surface (RIS) focuses on the mmWave signal to a specific location indoors. In this paper, a novel RIS-assisted mmWave indoor enhancement scheme is proposed, in which a transparent RIS is deployed on the glass to enhance mmWave indoor signals, and three assisted transmission scenarios, namely passive RIS (PRIS), active RIS (ARIS), and a novel hybrid RIS (HRIS) are proposed. This paper aims to maximize the signal-to-noise ratio (SNR) of the received signal for the three assisted transmission scenarios. The closed-form solution to the maximum SNR is presented in the PRIS and the ARIS-assisted transmission scenarios. Meanwhile, the closed-form solution to the maximum SNR for the HRIS-assisted transmission scenario is presented for given active unit cells. In addition, the performance of the proposed scheme is analyzed under three assisted transmission scenarios. The results indicate that under a specific RIS power budget, the ARIS-assisted transmission scenario achieves the highest data rate and energy efficiency. Also, it requires very few unit cells, thus dramatically reducing the size of the metasurface.
... For a 5G network using massive multiple-input multiple-output (mMIMO), the energy consumption can be broken down into two major parts: the antenna unit and BBU, in which the antenna unit requires about 90% of the total energy consumption. The HPA efficiency has been indicated as a key component of network energy efficiency during the 3G/4G era [85,86]. However, HPA efficiency has improved over time, in which Doherty PA architecture with envelope tracking and Gallium Nitride (GaN) semiconductor material has been introduced, resulting in an HPA efficiency of more than 50% [87]. ...
... The effect depends not only on the chosen PA back-off but also on the PA characterstics or on the properties of the OFDM signal being amplified. There are tens of different models of nonlinear PA ranging from some complicated Volterra-series, through polynomial representation with or without memory, to a simple clipper having linear AM/AM characteristic in a given range of input power and saturation above this range [110]. It has been shown in [111] that a PA of clipper-like characteristic guarantees the highest Signal to Noise and Distortion power Ratio (SNDR). ...
In this paper, we review radio resource optimization methods for energy-efficient wireless communication in links and networks using the Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) techniques. We first consider the energy-efficiency metrics and optimization goals. We discuss the increasingly complex systems, starting from (i) a single OFDM link, (ii) an OFDMA single-hop network to (iii) multi-hop relay OFDMA interference networks. In each case, we elaborate on the transmission rate estimation, power consumption modelling, existing optimization constraints and the optimization solutions. Specifically, in the power-consumption modelling, we include the signal-processing (and related computing) power.We discuss the practicality of the considered solutions. We also touch upon the problem of nonlinear power amplifier characteristics (causing distortions typical for OFDM signals) to be taken into account for energy-efficient resource allocation. We discuss trade-offs and provide recommendations for future energy-efficient OFDM networks design. We also discuss the future works and challenges in the context of energy efficiency resource allocation for OFDM/OFDMA and their derivative techniques.We conclude that the presented design practices should include computational awareness in the networks to trade-off between information communication, information processing and the required network management energy-efficiency.
... Accurate behavioral models of RFPAs also enables us to estimate the BER due to nonlinear PA on the system behavior of various communication systems and helps to formulate techniques to reduce the BER [11]. In addition, data-driven strategy also helps us to derive accurate inverse models of the PA, for designing digital pre-distorters which decreases signal distortions and increases power added efficiency (PAE) of RFPAs [12]. ...
This paper, investigates and presents the behavioral modeling and digital pre-distortion (DPD) of radio frequency power amplifiers (RFPAs) using a time-delay kernel ridge regression (KRR) algorithm. The KRR is an advanced machine learning algorithm that can be effectively used for modeling the baseband characteristics of the RFPA considering both the effects of memory and transistor non-linearity. Compared to the traditional artificial neural network (ANN) based approach which is computationally intensive, the proposed approach using KRR with radial basis kernel function and min-max normalization method, extracts the PA behavioral and DPD model in a short time and yield consistently better results. The performance of the proposed approach in extracting PA and DPD model is demonstrated experimentally on a GaN based class AB power amplifier. The experimental results illustrates that, when compared to ANN based model, the proposed approach yields more accurate PA and DPD models, with an improvement in modeling performance by 2 dB in terms of normalized mean square error (NMSE). In addition, compared to the ANN based approach, the DPD model developed using the proposed approach exhibit improved linearization performance in suppressing spectral regrowth due to PA non-linearity.
The wireless communication systems has made significant progress since its inception, revolutionalizing the way people communicate. A great leap in communication systems was observed when wireless communication was introduced, in which the world witnessed the transition from wired to wireless operation.
Peak-to-average-power ratio (PAPR) and power amplifier (PA) nonlinearity are significant challenges that limit the performance of orthogonal frequency division multiplexing (OFDM) systems. Various techniques have been proposed to address these two issues separately. In this letter, we propose a unified framework for PAPR reduction and digital predistortion (DPD) by optimizing the waveform of the OFDM signal. We develop two effective and low-complexity algorithms to address the joint PAPR and DPD optimization problem. Simulation results demonstrate that the proposed algorithms surpass existing approaches in terms of error vector magnitude (EVM), PAPR, and power spectral density (PSD).
Thanks to the customization of channel propagation, reconfigurable intelligent surface (RIS)-aided cell-free (CF) massive multiple-input multiple-output (MIMO) is recognized as a competitive candidate technique for the future communication system. However, only the limited performance gain can be afforded by passive RIS due to the double-fading effect in RIS-aided links. In this paper, we consider the cell-free massive MIMO system with the assistance of the active RIS, which is capable of reflecting and amplifying the incident signal, to enable the Internet of Things network. We analyze the trade-off between the number of active RIS reflecting elements (REs) and the amplification coefficient. Considering the power constraint at the active RIS, we formulate a sum-rate maximization problem to jointly optimize the user transmission power, the receive beamforming, and the RIS reflecting precoding. Since the original problem is non-convex, we decouple it into three subproblems and then design an alternating optimization algorithm to solve them iteratively. Using the Lagrangian dual reformulation and generalized Rayleigh quotient theory, we derive the closed-form solutions for both the user transmission power and the uplink receive beamforming. We also develop a low-complexity method to acquire the RIS reflecting precoding based on the primal-dual subgradient theory. Compared to the passive RIS, the active RIS can significantly improve the system performance with fewer REs. Moreover, the proposed optimization scheme effectively mitigates the drawbacks of the active RIS under the high transmission power regime and enhance its benefits. Finally, the proposed alternating optimization algorithm is validated by numerical results.
Widespread deployment of relays can yield a significant boost in the throughput of forthcoming wireless networks. However, the optimal operation of large relay networks is still infeasible. This paper presents two approaches for the optimization of large relay networks. In the traditional approach, we formulate and solve an optimization problem where the relays are considered linear. In the second approach, we take an entirely new direction and consider the true non-linear nature of the relays. Using the similarity to neural networks, we leverage deep-learning methodology. Unlike previous applications of neural networks in wireless communications, where neural networks are added to the network to perform computational tasks, our deep relay optimization treats the relay network itself as a neural network. By exploiting the non-linear transfer function exhibited by each relay, we achieve over 15dB gain compared to traditional optimization methods. Moreover, we are able to implement part of the network functionality over the relay network. Our findings shed light on the potential of deep relay optimization, promising significant advancements in future wireless communication systems.
Wireless devices can be easily attacked by jammers during transmission, which is a potential security threat for wireless communications. Active reconfigurable intelligent surface (RIS) attracts considerable attention and is expected to be employed in antijamming systems for secure transmission to significantly enhance the antijamming performance. However, active RIS introduces external power load, which increases the complexity of hardware and restricts the flexible deployment of active RIS. To overcome these drawbacks, we design an innovative self-sustainable structure in this article, where the active RIS is energized by harvesting energy from base station signals through the time dividing based simultaneous wireless information and power transfer scheme. Based on the above structure, we develop the BS harvesting scheme based on joint transmit and reflecting beamforming with the aim of maximizing the achievable rate of active RIS-assisted system, where the alternating optimization algorithm based on stochastic successive convex approximation tackles the nonconvex optimization problem in the scheme. Simulation results verified the effectiveness of our developed BS harvesting scheme, which can attain higher antijamming performance than other schemes when given the same maximum transmit power.
The goal of “double carbon” (namely “peak carbon dioxide emissions” and “carbon neutrality”) proposed by China for the first time is an important layout in the Tenth Five-Year Plan, and it is also the key goal to realize the green and sustainable development of mobile communication networks in the future, and it is also the foundation for China’s international carbon asset pricing right and the world carbon trading platform. Among them, the difficulty in realizing green communication lies in maintaining the growth of business volume. Reduce network energy consumption and carbon emissions. This paper studies the green communication technology from the perspective of energy saving and emission reduction on the mobile communication network side and the perspective of the integrated architecture of communication network and multi-energy energy network. The research results show that the key to realize green communication technology lies in the mutual matching of network resources, energy resources and business distribution, while the existing technology can only achieve one-way matching of network resources and business distribution. Or the one-way matching of energy resources and service distribution. Based on this, this paper proposes a native green grid architecture with communication, perception and energy fusion, which has the ability of energy perception and service perception, supports the two-way matching method of network resources, energy resources and service distribution, and realizes the continuous growth of service while significantly reducing the energy consumption and carbon emissions on the mobile communication network side by eliminating the randomness and suddenness of service distribution and energy distribution.
Due to the substantial path loss inherent to millimeter-wave (mmWave) frequencies, the signal sent by the outdoor base station is seriously attenuated when it reaches the indoors. Recent research has introduced a glass-based metasurface to enhance mmWave signals in indoor settings. While a transparent reconfigurable intelligent surface (RIS) can focus signals in specific areas, achieving ideal coverage is hindered by constraints such as building structures. To address this limitation, we propose a novel RIS-assisted mmWave indoor enhancement scheme in which a transparent RIS is deployed on the glass, and a reflection RIS is introduced to enhance signal connectivity, ensuring mmWave coverage across indoor spaces. Three distinct assisted transmission scenarios are considered in this proposed scheme: passive RIS (PRIS), active RIS (ARIS), and hybrid RIS (HRIS). This paper aims to maximize the signal-to-noise ratio (SNR) of the received signal for the three assisted transmission scenarios. The closed-form solution is presented in the PRIS and the ARIS-assisted transmission scenarios. In addition, the performance of the proposed scheme is analyzed under three assisted transmission scenarios. The results indicate that the ARIS-assisted transmission scenario achieves the highest data rate and energy efficiency under a smaller transmit power while demanding minimal unit cells.
Enhancing Internet of Things (IoT) communications through Reconfigurable Intelligent Surfaces (RIS) necessitates novel approaches that go beyond the conventional deployment of passive elements. This paper introduces an efficient method to enhance IoT system performance by combining active and passive functionality in RISs: an active and passive integrated approach. One identified enhancement area is efficiently managing signal throughput and exchanges in IoT systems, which is essential for supporting numerous devices. For this challenge, we propose a thorough process model that describes channel gains, develops a nonlinear energy harvesting, and identifies device-to-device communication schemes without violating information causality. The innovative component of our work is the utilization and strategic application of RIS panels that benefit from the advantages of active and passive components synergism to solve thermal noise issues and optimize signal reflection and transmission. An advanced optimization mechanism is developed based on mixed-integer nonlinear programming: an enabling approach between performance efficiency and maximum service utilization. Our simulation analyses show that developed RIS panels optimize IoT system performance and surpass existing performance indicators in conventional RIS-less systems.
In this letter, we study a downlink communication system with symbol level precoding (SLP) technique, which guarantees low peak to average ratio (PAPR) signal transmission, thus reducing the energy consumption of power amplifiers (PAs) and improving the energy efficiency (EE). However, the low PAPR precoding design may lead to a decrement in data rate, which shrinks the EE performance gain of SLP. In order to avoid data rate decrement in the SLP system, an reconfigurable intelligent surface (RIS) is deployed, which is capable to adjust the propagation environment according to the result of the low PAPR precoding design. We formulate a joint BS precoding and RIS configuration optimization problem to minimize the energy consumption of the system. A novel algorithm is proposed to solve the formulated problem, and its complexity and convergency are analysed. Simulation results show that the RIS-assisted SLP communication system improves the EE for over 40% when compared to the zero forcing (ZF) precoding scheme in both sparse-user equipment (UE) and dense-UE scenarios.
One of the most prominent physical aspects of mobile communication systems is that they are inherently non-equilibrium systems. Traditional researches on the energetic costs of communication systems pay little attention to the relationship between the energy and the information transmitted and processed by the system. On the other hand, recent breakthroughs in nonequilibrium thermodynamics have led to a deeper understanding of the thermodynamics of information. To investigate the energetic costs of a mobile communication system at a fundamental level, in this paper, an entropy-based energy dissipation model based on nonequilibrium thermodynamics is first proposed for mobile communication systems. The energy dissipation model relates the energy and information through the common concept “entropy” from thermodynamics and information theory. Moreover, the theoretical minimal energy dissipation limits are derived for typical modulations in mobile communication systems. Simulation results show that the practical energy dissipation of information processing and information transmission is three and seven orders of magnitude away from the theoretical minimal energy dissipation limits in mobile communication systems, respectively. The energy dissipation model and results derived in the paper provide guidelines on how to design future mobile communication systems to minimize the thermodynamic costs.
In satellite communications, the power amplifier (PA) plays a vital role in enhancing the transmission performance of signals. However, the non-linearity of PAs often distorts the transmitted signals, degrading communication performance. Digital pre-distortion (DPD) is one of the most effective linearization technologies to address the abovementioned issue and improve PA performance. Neural networks (NNs) outperform traditional models in PA behavioral modeling and linearization due to their strong nonlinear fitting capability, but the lack of learning data distributions limits the performance. Hence, this paper proposes a novel behavioral and linearization model for PA, utilizing the residual generative adversarial network (Res-GAN). The proposed model can extract deep features of the PA with enhanced accuracy, thereby improving PA linearization performance. Simulation results show that the proposed Res-GAN behavioral model achieves the normalized mean squared error (NMSE) of -55.737 dB. Additionally, the Res-GAN DPD outperforms traditional DPD models by a reduction in the NMSE of about 2 dB and the adjacent channel power ratio (ACPR) of about 2-4 dBc.
In this paper, a permutated partial transmit sequence (PTS) scheme is proposed to reduce the peak-to-average-power ratio (PAPR) in polar-coded orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems without side-information (SI) transmission. For generating candidate signals, the proposed PTS method combines two operations of phase rotations and frequency-domain permutations by implementing circular shifting and factor multiplications in time domain, where the phase rotation factors are determined by the frozen bits of polar codes. Additionally, according to the transmitting and polar-coded structures, an SI-free decoder based on successive cancellation lists (SCL) algorithm is developed at the receiving end. Compared with conventional PTS and existing PAPR reduction schemes, the proposed PTS scheme exhibits significantly higher PAPR reduction performance with less complexity. Based on stimulation results, the proposed SI-free receiver is able to achieve error performance similar to that with the receiver utilizing perfect side information in both Additive White Gaussian noise (AWGN) and frequency selective channels.
Digital pre-distortion (DPD) has recently been developed to compensate for in-phase and quadrature (IQ) imbalance and crosstalk, as well as power amplifier (PA) nonlinearity distortions in multi-input multi-output (MIMO) transmitters (TXs). Despite its limitations, most DPD models still use a simple non-iterative framework called the indirect learning architecture (ILA). This paper proposes a novel integrated DPD solution supported by iterative learning control (ILC) and a neural network (NN) model to compensate for all of these impairments simultaneously. Compared to the state-of-the-art DPD models, our proposed scheme achieves excellent in-band and out-of-band (OOB) performance. In addition, it has a significantly lower running complexity than other polynomial-based models, with 50% fewer floating-point operations (FLOPs).
While electric vehicle users enjoy the convenience of electrified transportation, their random driving characteristics and disorderly charging will cause traffic congestion and aggravate the peak valley difference of power grid load. An electric vehicle charging navigation strategy that takes into account the idle rate and dynamic tariff is proposed in this paper, which improves the load characteristics and reduce traffic congestion. Firstly, the electric vehicle charging navigation model with the integration of “four networks and four flows” is established. The interaction effect between the charging demand of electric vehicle users and the information network, traffic network, power grid is analyzed. Secondly, the multi-dimensional spatial and temporal characteristics of the empty-loading ratio of the electric taxi are studied. The optimal charging period for electric vehicle users is determined by the intelligent charging navigation terminal based on real-time road condition information. The path planning is carried out with the goal of minimizing the comprehensive cost of charging time and dynamic charging cost, and the electric taxi is guided to the optimal charging station to achieve orderly charging in space. Finally, taking the coupling system of traffic network and power grid in an urban area as an example, the proposed strategy is simulated and analyzed. The results show that this strategy can effectively balance the load of each charging station, improve the load characteristics of distribution network, which can effectively divert traffic flow, alleviate traffic congestion, and improve the operating income of electric taxi.
Spectrum congestion has motivated the recent introduction of integrated sensing and communication (ISAC) systems where radar and communications functionalities co-exist and share the same spectrum. This is accompanied by extensive research in the area of reconfigurable intelligent surfaces (RIS), thanks to their ability to improve the ISAC systems. In this paper, the physical layer security of a multiuser multiple-input single-output (MU-MISO) ISAC system is investigated when the system is subject to eavesdropping by a malicious unmanned aerial vehicle (UAV). In particular, we propose using an active RIS to maximize the achievable secrecy rate of the system through jointly designing the radar receive beamformers, the active RIS reflection coefficients matrix and the transmit beamformers at the dual-function base station of the ISAC system. This is done while taking into account a minimum radar detection signal-to-noise ratio (SNR) and total system power budget constraints. The resulting non-convex optimization problem is tackled by exploiting fractional programming (FP) and majorization-minimization (MM) techniques to achieve a solution. Our numerical results show the superiority of active RIS to achieve the goal when compared with passive RIS or with an ISAC without an RIS. Results also show that passive RIS could still be a viable solution to achieve this goal but at the expense of a much larger needed size especially when lower power budgets are available.
Hybrid beamforming multiple-input multiple-output (MIMO) system has attracted a lot of attention in recent years since it significantly reduces the hardware cost compared to the fully digital beamforming system. However, with hybrid beamforming, the one-to-one mapping between the radio frequency (RF) chain and the nonlinear power amplifier (PA) is destroyed. The PA nonlinearity cannot be compensated by conventional digital predistortion (DPD) algorithms. In this paper, we propose a novel multiple-input DPD model for hybrid beamforming MIMO systems. An extra digital compensation block is introduced in the feedback path. With the feedback compensation block, the proposed DPD can linearize the PA output signal as well as the aggregated far-field signal. What is more, we propose a DPD estimation algorithm with much reduced complexity. Comparing to existing solutions, the proposed scheme achieves satisfactory performance for hybrid beamforming system. It does not rely on the measurement of the channel or the assumption of massive antennas. Simulation results demonstrate the effectiveness of the proposed DPD scheme.
The frequency and spatial characteristics of nonlinear distortion from a MIMO-OFDM (multiple-input multiple-output orthogonal frequency-division multiplexing) base station with memoryful nonlinear amplifiers (modeled by a generalized memory polynomial) is studied herein. We prove a theorem about a linear representation of the amplified signal from which the nonlinear distortion is obtained. Our measurement results demonstrate that the generalized memory polynomial can provide better accuracy of the nonlinear distortion than the memoryless and memory polynomial models. Furthermore, it is shown that in contrast to the memoryless amplifier, the amplifier with memory can distort the useful linear signal and introduce interference in a wider range of subcarriers. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the in-band and out-of-band radiation, and to schedule users in the frequency plane to minimize the effect of nonlinear distortion.
Estimates indicate that about 80% of the power consumption of cellular networks must be supplied by operators. It is thus becoming of paramount importance to improve the energy efficiency of cellular networks at the operator side for an economic and environmentally-sustainable traffic growth. The introduction of discontinuous transmission - or sleep mode - at the base stations can enable a reduction of power consumption. To further enhance the reduction, this paper proposes to coordinate the sleep scheduling among neighboring cells. The sleep schedule coordination allows the inter-cell interference reduction, during the sleep periods. This paper assesses the performance of different sleep schedules (uncoordinated, coordinated orthogonal and coordinated partially-orthogonal) applied to cellular networks based on Long Term Evolution (LTE) protocol. Simulation results show that only by coordinating the sleep schedules it is possible to significantly improve the throughput and the energy efficiency. In particular, the coordinated orthogonal sleep schedule is able to reduce the energy consumption by over 80%, achieving a gain of about 13%.
The objective of this survey is to provide the readers and practitioners in the industry with a broader understanding of the high peak-to-average power ratio (PAPR) problem in orthogonal frequency division multiplexing (OFDM) systems and generate a taxonomy of the available solutions to mitigate the problem. Beginning with a description of OFDM systems, the survey describes the most commonly encountered impediment of OFDM systems, the PAPR problem and consequent impact on power amplifiers leading to nonlinear distortion. The survey clearly defines the metrics based on which the performance of PAPR reduction schemes can be evaluated. A taxonomy of PAPR reduction schemes classifies them into signal distortion, multiple signaling and probabilistic, and coding techniques with further classification within each category. We also provide complexity analyses for a few PAPR reduction methods to demonstrate the differences in complexity requirements between different methods. Moreover, the paper provides insights into the transmitted power constraint by showing the possibility of satisfying the constraint without added complexity by the use of companding transforms with suitably chosen companding parameters. The rapid growth in multimedia-based applications has triggered an insatiable thirst for high data rates and hence increased demand on OFDM-based wireless systems that can support high data rates and high mobility. As the data rates and mobility supported by the OFDM system increase, the number of subcarriers also increases, which in turn leads to high PAPR. As future OFDM-based systems may push the number of subcarriers up to meet the higher data rates and mobility demands, there will be also a need to mitigate the high PAPR that arises, which will likely spur new research activities. The authors believe that this survey will serve as a valuable pedagogical resource for understanding the current research contributions in the area of PAPR reduction in OFDM systems, the - ifferent techniques that are available for designers and their trade-offs towards developing more efficient and practical solutions, especially for future research in PAPR reduction schemes for high data rate OFDM systems.
The widely accepted OFDMA air interface technology has recently been adopted in most mobile standards by the wireless industry. However, similar to other frequency-time multiplexed systems, their performance is limited by inter-cell interference. To address this performance degradation, interference mitigation can be employed to maximize the potential capacity of such interference-limited systems. This paper surveys key issues in mitigating interference and gives an overview of the recent developments of a promising mitigation technique, namely, interference avoidance through inter-cell interference coordination (ICIC). By using optimization theory, an ICIC problem is formulated in a multi-cell OFDMA-based system and some research directions in simplifying the problem and associated challenges are given. Furthermore, we present the main trends of interference avoidance techniques that can be incorporated in the main ICIC formulation. Although this paper focuses on 3GPP LTE/LTE-A mobile networks in the downlink, a similar framework can be applied for any typical multi-cellular environment based on OFDMA technology. Some promising future directions are identified and, finally, the state-of-the-art interference avoidance techniques are compared under LTE-system parameters.
Reducing energy consumption in wireless communications has attracted increasing attention recently. Advanced physical layer techniques such as multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM), cognitive radio, network coding, cooperative communication, etc.; new network architectures such as heterogeneous networks, distributed antennas, multi-hop cellulars, etc.; as well as radio and network resource management schemes such as various cross-layer optimization algorithms, dynamic power saving, multiple radio access technologies coordination, etc. have been proposed to address this issue. In this article, we overview these technologies and present the state-of-the-art on each aspect. Some challenges that need to be solved in the area are also described.
We consider the joint resource allocation and admission control problem for Orthogonal Frequency-Division Multiple Access (OFDMA)-based femtocell networks. We assume that Macrocell User Equipments (MUEs) can establish connections with Femtocell Base Stations (FBSs) to mitigate the excessive cross-tier interference and achieve better throughput. A cross-layer design model is considered where multiband opportunistic scheduling at the Medium Access Control (MAC) layer and admission control at the network layer working at different time-scales are assumed. We assume that both MUEs and Femtocell User Equipments (FUEs) have minimum average rate constraints, which depend on their geographical locations and their application requirements. In addition, blocking probability constraints are imposed on each FUE so that the connections from MUEs only result in controllable performance degradation for FUEs. We present an optimal design for the admission control problem by using the theory of Semi-Markov Decision Process (SMDP). Moreover, we devise a novel distributed femtocell power adaptation algorithm, which converges to the Nash equilibrium of a corresponding power adaptation game. This power adaptation algorithm reduces energy consumption for femtocells while still maintaining individual cell throughput by adapting the FBS power to the traffic load in the network. Finally, numerical results are presented to demonstrate the desirable operation of the optimal admission control solution, the significant performance gain of the proposed hybrid access strategy with respect to the closed access counterpart, and the great power saving gain achieved by the proposed power adaptation algorithm.
Over the last few years, data traffic over cellular networks has seen an exponential rise, primarily due to the explosion of smartphones, tablets, and laptops. This increase in data traffic on cellular networks has caused an immediate need for offloading traffic for optimum performance of both voice and data services. As a result, different innovative solutions have emerged to manage data traffic. Some of the key technologies include Wi-Fi, femtocells, and IP flow mobility. The growth of data traffic is also creating challenges for the backhaul of cellular networks; therefore, solutions such as core network offloading and media optimization are also gaining popularity. This article aims to provide a survey of mobile data offloading technologies including insights from the business perspective as well.
In this paper, the trade-off between energy efficiency (EE) and spectral efficiency (SE) is analyzed for both the uplink and downlink of the distributed multiple-input multiple-output (DMIMO) system over the Rayleigh fading channel while considering different types of power consumption models (PCMs). A novel tight closed-form approximation of the DMIMO EE-SE trade-off is presented and a detailed analysis is provided for the scenario with practical antenna configurations. Furthermore, generic and accurate low and high-SE approximations of this trade-off are derived for any number of RAUs in both the uplink and downlink channels. Our expressions have been utilized for assessing both the EE gain of DMIMO over co-located MIMO (CMIMO) and the incremental EE gain of DMIMO in the downlink channel. Our results reveal that DMIMO is more energy efficient than CMIMO for cell edge users in both the idealistic and realistic PCMs; whereas in terms of the incremental EE gain, connecting the user terminal to only one RAU is the most energy efficient approach when a realistic PCM is considered.
The proliferation of internet-connected mobile devices will continue to drive growth in data traffic in an exponential fashion, forcing network operators to dramatically increase the capacity of their networks. To do this cost-effectively, a paradigm shift in cellular network infrastructure deployment is occurring away from traditional (expensive) high-power tower-mounted base stations and towards heterogeneous elements. Examples of heterogeneous elements include microcells, picocells, femtocells, and distributed antenna systems (remote radio heads), which are distinguished by their transmit powers/ coverage areas, physical size, backhaul, and propagation characteristics. This shift presents many opportunities for capacity improvement, and many new challenges to co-existence and network management. This article discusses new theoretical models for understanding the heterogeneous cellular networks of tomorrow, and the practical constraints and challenges that operators must tackle in order for these networks to reach their potential.
Efficiency and linearity of the power amplifier contained in second-generation (2G) CDMA cellular mobile radios are critical parameters. Further system application of power control where the mobile unit transmits output power levels ranging from maximum to tens of decibels in back-off emphasizes the importance of optimizing the efficiency/linearity trade-off over a wide output power range to extend battery life of the radio. This article discusses improvements obtained using a switched gain stage power amplifier where the second stage (of a two-stage power amplifier) is bypassed at lower output power levels, thereby substantially improving performance in power back-off operation. Improvements in efficiency and battery lifetime are calculated with performance compared to traditional single-ended operation.
We study resource allocation for energy-efficient communication in multi-cell orthogonal frequency division multiple access (OFDMA) downlink networks with cooperative base stations (BSs). We formulate the resource allocation problem for joint BS zero-forcing beamforming (ZFBF) transmission as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate. We transform the considered problem in fractional form into an equivalent optimization problem in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. In each iteration, a low-complexity suboptimal semi-orthogonal user selection policy is computed. Besides, by using the concept of perturbation function, we show that in the considered systems under some general conditions, the duality gap with respect to the power optimization variables is zero despite the non-convexity of the primal problem. Thus, dual decomposition can be used in each iteration to derive an efficient closed-form power allocation solution for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations, and unveil the trade-off between energy efficiency, network capacity, and backhaul capacity: (1) In the low transmit power regime, an algorithm which achieves the maximum spectral efficiency may also achieve the maximum energy efficiency; (2) a high spectral efficiency does not necessarily result in a high energy efficiency; (3) spectral efficiency is always limited by the backhaul capacity; (4) energy efficiency increases with the backhaul capacity only until the maximum energy efficiency is achieved.
In this paper, we consider a distributed transmitter (D-TX) system, in which each TX has a dissimilar power amplifier with different maximum output power, and different number of transmit antennas. To improve energy efficiency (EE) of the D-TX system, we design a multiuser multiple-input multiple-output (MU-MIMO) precoding matrix, a transmit antenna selection (AS) matrix, and a power control (PC) matrix. A conventional zero-forcing based MU-MIMO precoding is shown to be EE optimal for given AS and PC. Optimal and heuristic PC methods are proposed for given AS and MU-MIMO precoding. For the AS, we also propose heuristic algorithms. Average transmit power, outage probability, and EE performance are evaluated to compare three AS algorithms, and to observe the performance gap between the optimal and heuristic PC methods. From the numerical results, we discuss a tradeoff between AS complexity and EE performance and provide a useful guide for energy efficient D-TX system design.
To improve the energy efficiency (EE) of an orthogonal frequency-division multiple access system with multiple transmit antennas supporting multiple single-receive-antenna users, we propose an EE-aware multiple access (EMA) scheme. The EMA selects an energy-efficient channel access method that is either time-division multiple access (TDMA) or space-division multiple access (SDMA) for each subband. For the SDMA, the near optimal number of SDMA time slots is derived. Numerical results verify that the EE of pure TDMA and SDMA can be significantly improved through the proposed EMA scheme.
In this paper, resource allocation for energy efficient communication in multi-cell orthogonal frequency division multiple access (OFDMA) downlink networks with cooperative base stations (BSs) is studied. The considered problem is formulated as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate for joint BS zero-forcing beamforming (ZFBF) transmission. By exploiting the properties of fractional programming, the considered non-convex optimization problem in fractional form is transformed into an equivalent optimization problem in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. For each iteration, the optimal power allocation solution is derived with a low complexity suboptimal subcarrier allocation policy for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations, and unveil the trade-off between energy efficiency and network capacity.
The mobile handset is well established as a business and consumer device, expanding beyond the foundation built on earlier mobile handset technology. The functions and capabilities of the handset are continually evolving. Handset providers, application developers and users are putting ever greater demands on handsets which simultaneously strain limited battery power and require higher data transfer. This results in ever more challenging requirements on the RF front-end of the handset. At the same time there are cost pressures that require functions to be provided ever more economically. This paper discussed these trends, the implications in front-end architecture, and some of the advanced implementations that address these dynamics.
We propose a time division duplex (TDD) based network architecture where a macrocell tier with a “massive” multiple-input multiple-output (MIMO) base station (BS) is overlaid with a dense tier of small cells (SCs). In this context, the TDD protocol and the resulting channel reciprocity have two compelling advantages. First, a large number of BS antennas can be deployed without incurring a prohibitive overhead for channel training. Second, the BS can estimate the interference covariance matrix from the SC tier which can be leveraged for downlink precoding. In particular, the BS designs its precoding vectors to transmit independent data streams to its users while being orthogonal to the subspace spanned by the strongest interference directions; thereby minimizing the sum interference imposed on the SCs. In other words, the BS “sacrifices” some of its antennas for interference cancellation while the TDD protocol allows for an implicit coordination across both tiers. Simulation results suggest that, given a sufficiently large number of BS antennas, the proposed scheme can significantly improve the sum-rate of the SC tier at the price of a small macro performance loss.
We propose a time-slot-based transmission strategy, referred to as coordinated napping (CoNap) for energy saving in cellular networks. In CoNap, multiple base stations (BSs) form a cluster and each BS operates in a transmit mode (TM) and a nap mode (NM) independently through an implicitly coordinated manner. The implicit coordination is implemented by the binary matrices to assign TM and NM to each BS in the cluster. CoNap can effectively reduce the network energy consumption and reduce the inter-cell interference, especially during the non-peak traffic load hours. Our numerical results based on a realistic energy consumption model in a cellular network show that as high as 50% saving can be achieved without compromising the quality of service to users.
This paper introduces a novel approach in increasing the capacity of LTE cellular networks. The solution is based on massive deployment of small cells by leveraging high frequency reuse at high frequency bands in conjunction with a Macrocell. The presence, discovery and usage of the small cells are controlled dynamically by a Macrocell in a master-slave configuration hence they are called Phantom Cells. To realize this concept, a new method of managing the connections between mobile terminals and small cell nodes is introduced. It is achieved by splitting the Control and User (C/U) planes of the radio link. The combination of C/U-plane split and Phantom Cells can achieve high capacity enhancement using small cells at the same time taking into consideration mobility, scalability and flexibility requirements for massive deployment. The advantages of this approach as well as the implementation aspects are described in the paper. Simulations were also conducted to verify the concept and the results show some promising capacity enhancements. The rest of the paper describes the Phantom Cell concept as well as the challenges of deploying small cells in LTE networks.
Spectral efficiency (SE) and energy efficiency (EE) are key measures for wireless communication systems. In OFDM systems, the non-linear effects and inefficiencies of power amplifiers (PAs) have posed practical challenges for system design. In this paper, we analyze the impact of the PA on the SE and EE tradeoff of OFDM systems. We also propose a PA switching technique which achieves a better SE-EE tradeoff, e.g., the EE can be improved by 323% with 15% SE reduction.
In this paper, we evaluate the Energy Efficiency (EE) for Amplify-and-Forward (AF) protocol based two-way relay system with different types of practical power amplifier models, namely Traditional Power Amplifier (TPA) and Envelope Tracking Power Amplifier (ET-PA). We show how to choose or configure PA from the perspective of EE optimization. We use two coefficients, Max-Power-Offset (MPO) and PA-Dependent- Parameter (PADP), to describe PA characteristics, and coefficients Data-Average (DA) and Fluctuation-Coefficient (FC) to describe the realistic 24 hours data traffic behavior. It is shown that the PA selection depends on its configuration and the data traffic model. With coefficients MPO and PADP increasing, TPA gets more energy efficient with nearly 15% energy saved in the simulations. While with DA and FC decreasing, ET-PA performs better with 8% energy saved. The results demonstrate that the PA selection is heavily dependent on the assumed traffic model and that ET-PA may not always be more energy-efficient than TPA.
In this paper, we survey two essential and practical characteristics of radio-frequency power amplifier (PA), namely, linearity and efficiency. Nonlinear amplification yields significant distortion of the transmit signals and strong interference for cochannel users. Imperfect efficiency of the PA causes an overhead of the systems resulting in energy efficiency (EE) degradation. Therefore, the linearity and efficiency of the PA should be precisely characterized in the system design. We first survey the linearity and efficiency models of PA, and then introduce commonly used technologies for improving the EE according to three approaches: i) transmitter architecture, ii) signal processing, and iii) network protocols. We then introduce our recent work on a multiple PA switching (PAS) architecture, in which one or more PAs are switched on at any time to maximize the EE while satisfying the required spectral efficiency (SE). We consider the case where either full or partial channel state information is available at the transmitter (CSIT). Since the transmitter selects the most efficient PA that satisfies a target rate with the least power consumption, EE is improved, and a Pareto-optimal SE-EE tradeoff region can be enlarged as verified in the numerical results with real-life device parameters. For example, we observe around 323% and 50% EE improvements for a single antenna system with a full CSIT and for a transmit antenna selection and maximum ration combining system with a partial CSIT, respectively; as a result, we can surmise that the PAS is one promising technology for green, i.e., energy efficient, wireless communication systems.
Energy consumption of next generation radio access network is posing a deep impact on CO2 emission and network operating cost. In a macro site, radio equipment dominates the power consumption. Specifically, the power amplifiers consume 70% of the total input power. In case of WCDMA and OFDMA, the Traditional Power Amplifier (TPA) suffers from low efficiency due to the non-constant envelope signals. To improve efficiency in case of these kinds of signals, deployment of Envelope Tracking Power Amplifier (ET-PA) is a viable solution. In this paper, the efficiency vs. output power characteristics of the ET-PA has been modeled. Moreover, by carrying out system level simulation in WCDMA network scenario, we show that 7-15% energy can be saved by replacing TPA by ET-PA.
In this paper, a power consumption model for both macrocell and microcell base stations is proposed. This model is validated by temporal power measurements on actual base stations, and an excellent agreement is obtained. Furthermore, the power consumption's evolution during the day is investigated by means of these measurements. The energy efficiency of three different wireless technologies is compared namely mobile Worldwide Interoperability for Microwave Access, Long Term Evolution and High Speed Packet Access. With the model proposed, the deployment tool Green Radio Access Network Design is implemented, which allows to design an energy-efficient access network for a predefined area. In general and with the assumptions made, a macrocell base station consumes about 4.4 times more than a microcell base station. However, a microcell base station is less energy efficient than a macrocell base station because of its lower coverage range. Despite this, it is still useful to introduce them in the network as the same coverage can be obtained with a lower total power consumption than with a network where only macrocell base stations are used. Copyright © 2012 John Wiley & Sons, Ltd.
In this paper, we develop an uplink pilot and downlink link adaptation approach to improve the energy efficiency (EE) of mobile users in time division duplexing (TDD) multi-user multiple input and multiple output (MU-MIMO) systems. Assuming reciprocity between uplink and downlink channels, the downlink transmission is based on uplink channel estimation. While more uplink pilot power ensures more accurate channel estimation and better downlink performance, it incurs higher energy consumption of mobile users. This paper reveals the relationship and tradeoff among pilot power, channel estimation, and downlink link adaptation that achieves the highest energy efficiency for mobile users. We show that the energy efficiency of different users can be decoupled because the downlink average throughput of each user is independent of the pilot powers of other users and energy-efficient design can be done on a per-user basis. Based on the analysis, we propose an uplink pilot and downlink link adaptation algorithm to improve the EE of mobile users. Simulation results are finally provided to demonstrate the significant gain in energy efficiency for mobile users.
We compare the downlink energy efficiency of spatial diversity multiple transmit antenna schemes. We determine the minimum required transmit power for a given outage probability. Our analysis shows that antenna selection is in general the most energy efficient option as it requires a single radio-frequency chain. We also investigate the limiting distances up to which the antenna selection technique outperforms the transmit beamforming scheme for different numbers of transmit antennas.
Distributed transmitter (D-TX) system with multiple distributed TXs is considered. To support multiple users, the D-TX system employs a zero-forcing based multiuser multiple-input multiple-output precoding. An energy efficiency (EE) maximization problem is formulated under constraints on {per-user data rate} and per-antenna instantaneous transmit power. The latter constraint is to avoid severe distortion of transmit signals at a power amplifier, i.e., the clipping effects. A low-complexity and performance-effective power control method is then proposed by solving the modification of the original, intractable optimization problem. Transmit antenna selection is elucidated with respect to the EE. Numerical results verify the efficacy of D-TX system employing the proposed EE-aware power control and antenna selection with respect to both system EE and outage performance, and also impart the importance of equal power output capability, i.e., equal maximum output power of the distributed TXs, for energy efficient D-TX systems.
We propose a sequential linear assignment algorithm (SLAA) for resource allocation of OFDMA systems consisting of M users and N (N >; M) resource blocks, with the aim of achieving near optimal energy consumption with polynomial complexity. The proposed SLAA allocates subchannels through a linear assignment algorithm (LAA), sequentially; thus, it requires O(MN2(N - M)2) complexity. From numerical results, the required power from the proposed assignment is observed to be within around 0.4 % of the lower bound of minimum possible power required to achieve the same target rates.
Green wireless communications has recently attracted a lot of attention. Most recent work on green wireless communications focuses on energy efficiencies and sustainable/renewable energies. In a broader sense, however, green wireless communications could also include wireless communications using environmentally sustainable materials, occupying less land space, accompanying less electromagnetic pollution, together with waste recycling and reducing wastes, and cost reductions.
We propose a power amplifier (PA) switching/selection (PAS) method to improve the energy efficiency (EE) of a transmit antenna selection and maximum ratio combining (TAS-MRC) system. A PAS transmitter has a PA bank consisting of multiple dissimilar PAs, which operate with different output power levels, and selects the most efficient PA and its power level that satisfies a target rate. If there is no PA supporting the target rate, the transmitter is set to an off-mode (i.e., all PAs are turned off). The receiver feeds back the choice of PA and its power level to the transmitter, similar to the feedback in a conventional power control system with a single PA. Numerical results show that the system EE can be improved by using the PAS. This letter is the first study to investigate and verify the potential capability of PAS for the system EE improvement in wireless communications.
In this work, we investigate the properties of energy-efficiency (EE) and spectrum-efficiency (SE) for video streaming over mobile ad hoc networks by developing an energy-spectrum-aware scheduling (ESAS) scheme. To describe a practical mobile scenario, we use a random walk mobility model, in which each node can choose its mobility direction and velocity randomly and independently. Through rigorous analysis and extensive simulations, we demonstrate that the node mobility is beneficial to EE but not to SE. The contributions of this work are twofold: 1) We propose an ESAS scheme with a dynamic transmission range, which significantly outperforms the previous minimum-distortion video scheduling in terms of joint EE and SE performance; 2) We derive an achievable EE-SE tradeoff range and a tight upper/lower bound with respect to energy-spectrum efficiency index for various node velocities. We believe that this work helps to shed insights on the fundamental design guidelines on building an energy and spectrum efficient mobile video transmission system.
We propose a time slot based transmission strategy, referred to as adaptive coordinated napping (CoNap), for energy saving in cellular networks under time-varying traffic demand. In adaptive CoNap network, multiple neighboring base stations (BSs) form a cluster and each BS operates in either a transmit mode (TM) or a nap mode (NM) in each time slot. The dynamic assignment of TM and NM to each BS is implicitly coordinated among multiple BSs. This implicit coordination is realized by a binary general flickering pattern matrix (FPM) through adaptively selected mapping matrix (MM). To track the time-varying traffic demand, we develop an adaptive algorithm to dynamically select the appropriate MM from a predefined MM set by taking into account the network quality of service (QoS) requirement. Our numerical results based on a realistic energy consumption model in a cellular network show that as high as 40% saving can be achieved without compromising the network QoS.
A combined approach to digital predistortion (DPD) and crest factor reduction (CFR) is proposed. The new CFR is structured similar to DPD and is implemented by introducing a steady-state offset into the DPD coefficients. The DPD and CFR coefficients are estimated using separate adaptive processes but applied to the transmission path in a common module. The DPD/CFR module provides the means to exploit margins in the transmitter performance, allowing the tradeoff between peak-to-average-power ratio (PAPR), error vector magnitude, and adjacent channel power ratio (ACPR). The proposed approach applies CFR to the predistorted signal instead of the input signal. This allows the envelope clipping module, which is typically present to protect the power amplifier (PA), to be removed, thereby avoiding divergence problems during the iterative closed-loop estimation of the DPD coefficients. Results show that post-CFR lowers the PAPR of the predistorted signal by 5 dB, which reduces the stress on the peaking transistor in a Doherty PA. The combined DPD/CFR reduces the ACPR of the transmitter by 21 dB compared with the unlinearized PA.
In this paper, resource allocation for energy-efficient communication in an orthogonal frequency division multiple access (OFDMA) downlink network with a large number of transmit antennas is studied. The considered problem is modeled as a non-convex optimization problem which takes into account the circuit power consumption, imperfect channel state information at the transmitter (CSIT), and different quality of service (QoS) requirements including a minimum required data rate and a maximum tolerable channel outage probability. The power allocation, data rate adaptation, antenna allocation, and subcarrier allocation policies are optimized for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). By exploiting the properties of fractional programming, the resulting non-convex optimization problem in fractional form is transformed into an equivalent optimization problem in subtractive form, which leads to an efficient iterative resource allocation algorithm. In each iteration, the objective function is lower bounded by a concave function which can be maximized by using dual decomposition. Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations and demonstrate the trade-off between energy efficiency and the number of transmit antennas.
Coordinated multipoint (CoMP) transmission is a promising technique to mitigate intercell interference and to increase system throughput in single-frequency reuse networks. Despite the remarkable benefits, the associated operational costs for exchanging user data and control information between multiple cooperating base stations (BSs) limit practical applications of CoMP processing. To facilitate wide usage of CoMP transmission, we consider in this paper the problem of joint network optimization and downlink beamforming (JNOB), with the objective to minimize the overall BS power consumption (including the operational costs of CoMP transmission) while guaranteeing the quality-of-service (QoS) requirements of the mobile stations (MSs). We address this problem using a mixed integer second-order cone program (MI-SOCP) framework and develop an extended MI-SOCP formulation that admits tighter continuous relaxations, which is essential for reducing the computational complexity of the branch-and-cut (BnC) method. Analytic studies of the MI-SOCP formulations are carried out. Based on the analyses, we introduce efficient customizing strategies to further speed up the BnC algorithm through generating tight lower bounds of the minimum total BS power consumptions. For practical applications, we develop polynomial-time inflation and deflation procedures to compute high-quality solutions of the JNOB problem. Numerical results show that the inflation and deflation procedures yield total BS power consumptions that are close to the lower bounds, e.g., exceeding the lower bounds by about 12.9% and 9.0%, respectively, for a network with 13 BSs and 25 MSs. Simulation results also show that minimizing the total BS power consumption results in sparse network topologies and reduced operational overhead in CoMP transmission and that some of the BSs are switched off when possible.
The resource allocation problem of minimising transmission power with per user rate constraint is studied for energy efficiency of multiuser multicarrier systems. The authors introduce an algorithm that deploys a flow-based decomposition strategy, called the network-flow-based algorithm (NFBA), to circumvent the NP-hard complexity of the resource allocation problem. The authors prove global optimality of the algorithm for the case of a flat-fading channel. For the general frequency selective channel, the flow size is adjusted adaptively to minimise the transmission power. Also, a compact integer programming formulation is developed to provide tight lower and upper bounds of the minimum power. Numerical results show that the authors' proposed NFBA achieves near-optimal performance with polynomial complexity even for large-scale systems.
Femtocell technology has been proposed to offload user data traffic from the macrocell to the femtocell and extend the limited coverage of the macrocell in mobile communications networks. In existing commercial femtocell/macrocell networks, a widely accepted solution to configure the location areas (LAs) is to partition the femtocells overlapped with a macrocell into small groups and to assign each group with a unique LA ID different from that of the macrocell. Such configuration can reduce the paging cost in the mobility management, but increases registration signaling overhead due to discontinuous coverage of femtocells. To reduce signaling overhead in the femtocell/macrocell network, we propose a delay registration (DR) algorithm that postpones the registration until the delay timer expires when the mobile station (MS) moves into the overlapped femtocell. Analytical models and simulation experiments are proposed to investigate the performance of the DR algorithm. Our analytical models are generally enough to accommodate various MS mobility behaviors. Our study can provide guidelines for the operators to set up a delay timer to reduce signaling overhead while sustaining the traffic offloading capability of the femtocell.
This paper introduces a figure-of-merit to investigate tradeoffs between amplifiers and modulation waveforms in complex digital communications systems. Class-AB amplifiers are investigated with a variety of modulation schemes to better understand the relations between amplifier efficiency, amplifier distortion, signal in-band and adjacent channel interference, and power consumption. The goal is to better understand the tradeoffs needed to design low-energy communications systems.
Large-scale distributed-antenna system (L-DAS) with very large number of
distributed antennas, possibly up to a few hundred antennas, is considered. Two
major issues of the L-DAS, namely high delay and energy consumption, are
identified, and L-DAS's potential capability is illuminated in terms of an
energy efficiency (EE) throughout the paper. We firstly and generally model the
power consumption of an L-DAS transmitter, and formulate an EE maximization
problem to find an active antenna set, to design a preprocessing matrix, and to
allocate transmit power, under constraints on per-antenna transmit power and
per-user rate. To obtain a tractable solution, we propose a channel-gain-based
antenna selection and an interference-based clustering. The original problem is
then divided into multiple subproblems by a cluster, and each subproblem is
solved in parallel for EE-aware precoding and power control. Simulation results
on an EE verify the proposed method complied with clustering, precoding, and
power allocation outperforms a non-clustering L-DAS and colocated antenna
system, and underpins the EE merit of the proposed L-DAS.
Earlier works studied the tradeoff between sensing performance and throughput of secondary users (SUs) for cooperative spectrum sensing. However, The tradeoff between sensing performance and energy consumption has not been well investigated in cognitive radio (CR) networks with relays. In this paper, the issues on cooperative spectrum sensing in a CR network with amplify-and-forward relay are studied. In particular, an optimization problem is formulated to analyze the tradeoff between sensing performance and energy consumption. The objective is to minimize energy consumption for spectrum sensing under given detection probability and false alarm probability constraints. We do so via finding an optimal pair of the parameters, i.e., the number of samples (proportional to sensing time) and the amplification gain. First, the case of fixed amplification gain is considered, in which the minimum number of samples is identified. Then, the case of varying amplification gain is further discussed, where an appropriate amplification gain is found such that the energy consumption is minimized while the sensing performance is kept above a threshold and the required throughput of the SU can be satisfied. The analytical and simulation results show that there exists an optimal pair of the number of samples and the amplification gain to strike the best tradeoff between sensing performance and energy consumption.
Resource allocation in orthogonal frequency division multiple access (OFDMA) relay cellular networks (RCN) has been investigated. We introduce an orthogonal frequency-and-time transmission (OFTT) protocol, in which orthogonal frequency and time resources are allocated to different communication modes and phases, respectively, and propose a simple algorithm for resource allocation. Communication modes (one- and two-hop modes), subchannels, and relay transmit power are sequentially allocated to enhance the power efficiency of the OFDMA RCN. We show an achievable quality-of-service tradeoff between one- and two-hop users. Furthermore, we show that the relays consume proportional power to their own second hop channel gains, whereas a single selected relay uses its full available power. Network power and system throughput are evaluated to confirm that the proposed OFTT protocol with the sequential resource allocation is power efficient in OFDMA RCN.
art 1 of this series introduced basic concepts, discussed the characteristics of sig- nals to be amplified, and gave background infor- mation on RF power devices. Part 2 reviews the basic techniques, rat- ings, and implementation methods for power amplifiers operating at HF through microwave frequencies. 6a. BASIC TECHNIQUES FOR
High-frequency power amplifiers operate most efficiently at saturation, i.e., in the nonlinear range of their input/output characteristics. This phenomenon has traditionally dictated the use of constant envelope modulation methods for data transmission, resulting in circular signal constellations. This approach has inherently limited the admissible data rates in digital radio. In this paper we present a method for solving this problem without sacrificing amplifier power efficiency. We describe and analyze an adaptive linearizer that can automatically compensate for amplifier nonlinearity and thus make it possible to transmit multilevel quadrature amplitude modulated signals without incurring intolerable constellation distortions. The linearizer utilizes a real-time, data-directed, recursive algorithm for predistorting the signal constellation. Our analysis and computer simulations indicate that the algorithm is robust and converges rapidly from a blind start. Furthermore, the signal constellation and the average transmitted power can both be changed through software.
The realization of high data rates in LTE technology over an all IP network means an ever increasing load on packet data networks. 3GPP has defined data offloading as a key solution to cope with this challenge. Data offloading has been a critical area of study in 3GPP Release-10. The 3GPP Evolved Packet Core (EPC) has been defined to be expansive; for example, it is designed to work in conjunction with non-3GPP access networks, femto cells etc., This diversity causes more scenarios to tackle, but it also provides solutions in the ways of offloading data from the EPC. This article is a tutorial on three such mechanisms, namely Local IP Access (LIPA), Selected IP Traffic Offload (SIPTO) and IP Flow Mobility (IFOM). The article starts with an overview of data offloading methods. The basics and key concepts of each method are summarized before giving the requirements, architecture and procedures with high-level message flows. The article ends with a brief evaluation of the mechanisms and references for the reader interested in further reading.