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Adaptive Polarization Transmission of OFDM Signals in Channels with Polarization Mode Dispersion and Polarization-Dependent Loss
Abstract
A 2times2 multiple-input multiple-output (MIMO) architecture using dual-polarized antennas (DPAs) is considered with orthogonal frequency division multiplexing (OFDM). The performance of DPAs is evaluated for adaptive polarization (AP) transmission techniques in time-varying multipath channels impaired by polarization mode dispersion (PMD) and polarization-dependent loss (PDL). AP transmission techniques considered include power gain maximization, polarization dispersion minimization for interference avoidance, polarization multiplexing with water-filling, and a suboptimal multiplexing strategy that enables direct recovery of the polarization multiplexed streams, thereby simplifying the design of the receiver. Measured time-varying dual-polarized channel realizations from mobile-to-mobile experiments are used to estimate the capacity, diversity, and interference avoidance performance of the adaptive approaches.
... However, regardless, in optical and wireless communications, depolarization has not been investigated. In a realistic wireless channel, the polarized signals are distorted by depolarization, polarization-dependent loss (PDL), polarization mode dispersion (PMD) [18] and cross polarization discrimination (XPD) [19]. XPD is the power coupling between different polarizations, which can be canceled out by, for example, zero-forcing or pre-coding methods. ...
... x y ⋅ = P P [18]. Then, the orthogonal polarized time-continuous analog signals passed through the multi-path channel are disturbed by phase noise and AWGN which can be written as follows: ...
... Depolarization effects caused by the wireless channel are XPD, PMD and PDL [18]. XPD is the ability to separate the vertical and horizontal polarizations resulting in interference from one polarization to another. ...
In orthogonal frequency-division multiplexing (OFDM) systems, phase noise introduced by the local oscillators can cause bit error rate (BER) performance degradation. To solve the phase noise problem, a novel orthogonal-polarization-based phase noise self-cancellation (OP-PNSC) scheme is proposed. First, the efficiency of canceling the phase noise of the OP-PNSC scheme in the AWGN channel is investigated. Then, the OP-PNSC scheme in the polarization-dependent loss (PDL) channel is investigated due to power imbalance caused by PDL, and a PDL pre-compensated OP-PNSC (PPC -OP-PNSC) scheme is proposed to mitigate the power imbalance caused by PDL. In addition, the performance of the PPC-OP-PNSC scheme is investigated, where the signal-to-interference-plus-noise ratio (SINR) and spectral efficiency (SE) performances are analyzed. Finally, a comparison between the OP-PNSC and polarization diversity scheme is discussed. The numerical results show that the BER and SINR performances of the OP-PNSC scheme outperform the case with the phase noise compensation and phase noise self-cancellation scheme.
... Polarization mode dispersion (PMD) is the polarizationsensitive frequency-selective fading effect of the channel in wideband environments; for example, the channel depolarization effects on different frequencies are distinct. In [1], it is shown that the output polarization states (PS) of the channel exhibit frequency-dependent dispersion if the channel has polarization-diverse multipath delay spreads. ...
... An LTE frame usually contains environment learning and data transmission phases. As shown in Fig. 3, the frame length is T. The learning time for each cluster with N samples is ε, then the overall learning time for all clusters is ( 1 ) ...
... Then, the desired and interference signals' power are is the power of additive noise at LR. It is noteworthy that1 is a generalized Rayleigh entropy problem, whose solution is well-known as where M is the subcarrier number of the operation band. The channel depolarization effects are frequency-selective as a result of PMD. ...
Polarized spectrum sharing (PSS) exploits the spectrum opportunities in a polarized domain. However, when it comes to wideband environments PSS is impaired by the frequencydependent polarization mode dispersion (PMD); thus, the effective throughput of PSS drops. To combat the PMD effect, this work proposes a cluster-based PSS approach to enable PSS on a narrower frequency span. Simulation results show that the effective throughput of PSS on cluster basis outperforms that of PSS on bandwidth and subcarrier basis.
... • The second challenge is the complex depolarization effects introduced by the open wireless channels, which is different from the traditional wired and closed propagation channels in optical communication [8], [9]. For example, there are some serious depolarization effects such as polarization mode dispersion (PMD) and PDL, which respectively show the dispersion of the polarizations with frequency and power coupling behavior with the polarizations [2]. ...
... where T rC and DetC are the trace and the determinant of the matrix C, respectively. Then the PDL effect is identified by the eigenvalue ratio as [8] P DL = 10 log 10 (λ 1 /λ 2 ) , ...
Facing the challenges of spectrum shortage and complex depolarization effects in wireless communication, a multilevel continuous polarization modulation (MCPoM) scheme is investigated to achieve high spectral efficiency and improve the symbol error rate performance in the practical depolarization channels. The principle of the MCPoM modulation is stated in details on the basis of the MCPoM system model. Then a noncoherent and a coherent MCPoM demodulation methods are proposed as the differential demodulation and the suboptimum sequence detection based demodulation, respectively. Furthermore, considering the depolarization effect of polarization-dependent loss in the practical wireless channels, MCPoM is evaluated with two influences of power attenuation and polarization difference distortion. After that, we propose a polarization pre-compensation algorithm for MCPoM to mitigate the influences of polarization-dependent loss. The performances of the proposed scheme are evaluated with symbol error rate and spectral efficiency. Simulations results demonstrate that higher spectral efficiency and enhanced symbol error rate of the proposed MCPoM scheme are guaranteed in the depolarization channels.
... To solve the problem, we can counteract the depolarization effect of the received signals by precompensating the polarization distortion of the transmitted signals on the transmitter side (49). In addition, the depolarization effect of wireless channels makes them more diverse and random, which can be used to encrypt the digital information, achieving the concealed communication links (50). Second, because the reflection-type metasurface transmitter is bulky due to the need of a horn antenna for feeding, dynamic metasurface antennas (51-53) and radiation-type programmable metasurfaces (54,55) with integrated feed can be explored to serve as the transmitters in the future, so as to achieve compact transmitter architectures. ...
Information metasurface has shown great potential in wireless communications owing to its ability to flexibly control electromagnetic waves. However, it is still a big challenge to achieve high-security and large–channel capacity wireless communications by a simple system. Here, we propose a space-polarization-division multiplexing secure wireless communication system with information camouflage capability based on the information metasurface, which can realize multichannel encrypted wireless communications with different polarization coding strategies independently and simultaneously. A polarization mask key is introduced to encrypt the target message, and the cipher message is further concealed behind a cover image with steganography and sent to the user by using the polarization modulation strategy. Different polarization mask keys can be adopted in each individual communication by changing the polarization coding strategy to enhance the system security. The proposed scheme integrates computational algorithm encryption and physical layer security together and thus has the advantages of high security, large channel capacity, and strong camouflage ability.
... Based on the CSI obtained, the transmitting polarization state can be pre-compensated, i.e., multiplying each polarization state by a pre-compensation matrix. Some other depolarization suppression methods can be used to fight against the depolarization effect of the received signals [47,48]. ...
Directional modulation (DM), as an emerging promising physical layer security (PLS) technique at the transmitter side with the help of an antenna array, has developed rapidly over decades. In this study, a DM technique using a polarization sensitive array (PSA) to produce the modulation with different polarization states (PSs) at different directions is investigated. A PSA, as a vector sensor, can be employed for more effective DM for an additional degree of freedom (DOF) provided in the polarization domain. The polarization information can be exploited to transmit different data streams simultaneously at the same directions, same frequency, but with different PSs in the desired directions to increase the channel capacity, and with random PSs off the desired directions to enhance PLS. The proposed method has the capability of concurrently projecting independent signals into different specified spatial directions while simultaneously distorting signal constellation in all other directions. The symbol error rate (SER), secrecy rate, and the robustness of the proposed DM scheme are analyzed. Design examples for single- and multi-beam DM systems are also presented. Simulations corroborate that (1) the proposed method is more effective for PLS; (2) the proposed DM scheme is more power-efficient than the traditional artificial noise aided DM schemes; and (3) the channel capacity is significantly improved compared with conventional scalar antenna arrays.
... Based on the CSI obtained, the transmitting polarization state can be pre-compensated, i.e., multiplying each polarization state by a pre-compensation matrix. Some other depolarization suppression methods can be used to fight against the depolarization effect of the received signals [47,48]. ...
Directional modulation (DM), as an emerging promising physical layer security (PLS) technique at the transmitter side with the help of an antenna array, has developed rapidly over decades. In this study, a DM technique using a polarization sensitive array (PSA) to produce the modulation with different polarization states (PSs) at different directions is investigated. A PSA, as a vector sensor, can be employed for more effective DM for an additional degree of freedom (DOF) provided in the polarization domain. The polarization information can be exploited to transmit different data streams simultaneously at the same directions, same frequency, but with different PSs in the desired directions to increase the channel capacity, and with random PSs off the desired directions to enhance PLS. The proposed method has the capability of concurrently projecting independent signals into different specified spatial directions while simultaneously distorting signal constellation in all other directions. The symbol error rate (SER), secrecy rate, and the robustness of the proposed DM scheme are analyzed. Design examples for single- and multi-beam DM systems are also presented. Simulations corroborate that 1) the proposed method is more effective for PLS; 2) the proposed DM scheme is more power-efficient than the traditional artificial noise aided DM schemes; and 3) the channel capacity is significantly improved compared with conventional scalar antenna arrays.
... We have proposed the differential polarization shift keying, which is a special PM, to cancel phase noise for the OFDM system in our prior work [34]. In a realistic wireless channel, the polarized signals are distorted by depolarization, such as cross-polarization discrimination (XPD) [35,36], polarization-dependent loss (PDL), and polarization mode dispersion (PMD) [37]; some papers propose the channel compensation methods to improve the PM performance [29][30][31][32][38][39][40]. In this paper, we extend the phase noise cancelation scheme for a larger number of antenna scenarios under XPD effect. ...
In massive multiple-input multiple-output (MIMO) systems, phase noise introduced by oscillators can cause severe performance loss. It leads to common phase error and intercarrier interference in massive MIMO-OFDM uplink. To solve the issue, a novel phase noise cancelation scheme based on polarization modulation for the massive MIMO-OFDM system is proposed. We first introduce the polarization modulation (PM) exploited in massive MIMO-OFDM uplink. Then, by exploiting the zero-forcing detection, we analyze the asymptotically ICI and the distribution of the transformed noise under different XPD values. Furthermore, we demonstrate that phase noise can be asymptotically canceled and only the transformed additive white Gaussian noise exists as the number of antennas at the base station is very large. Moreover, we derive the instantaneous signal-to-noise ratio (SNR) on each subcarrier and analyze the ergodic capacity. To increase the ergodic capacity performance further, a joint modulation scheme combining the PM and 2PSK is proposed and the ergodic capacity performance of the joint modulation is discussed. The simulation results show that the proposed scheme can effectively mitigate phase noise and achieve a higher ergodic capacity.
... Then a full-band APQAM algorithm with low complexity and considerable EE improvement can be designed in this case, where the whole signal band is modulated with the same modulation order for both QAM and PM. In another case, when the depolarization effect exists, the degree of depolarization effect such as power dependent loss (PDL) is related to the frequency of subcarriers in OFDM systems, and adjacent subcarriers suffer similar degree of depolarization effect due to its slowfrequency changing characteristic [18]- [19]. Therefore, all the subcarriers can be divided into several subgroups while considering the subgroup as the minimum adaptive modulation unit to build a sub-band APQAM algorithm [20]. ...
In this paper, an adaptive polarization-QAM modulation (APQAM) scheme is proposed to improve the power amplifier (PA) energy efficiency (EE) in OFDM systems. Since we found that polarization modulation (PM) has better EE performance than QAM in the nonlinear region of PA while QAM outperforms PM in the linear region, we can combine these two modulation schemes together and adjust their modulation orders adaptively to obtain higher EE performance. First, a truncated Taylor series model is used to represent PA nonlinearity, so the effects of both the in-band distortions and the out-of-band emissions on the OFDM signals can be analyzed. Second, two APQAM algorithms are investigated in both AWGN channel and depolarization channel with power dependent loss. Further, symbol error rate performance of the APQAM scheme is obtained in different channel conditions, and the influence of channel estimation error is analyzed to testify the robustness of the proposed APQAM scheme. Simulation results show that, if perfect channel state information is obtained, the EE of the proposed scheme is nearly fifty percent more than that of the traditional QAM scheme in OFDM systems.
... cos 2γ l,n,T sin 2γ l,n,T cos φ l,n,T sin 2γ l,n,T sin φ l,n,T (2) P l,n,T is deflected during transmission due to depolarization effect of fading channels. In this paper, the channels are modeled as 2 × 2 dual-polarized frequency-selective fading channels incorporating depolarization effect according to the method in [22]. Channel matrix H m l ,l,n represents the downlink channel from the lth SBS to the m l th SUE at subcarrier n, and is denoted as ...
Ultra-dense deployment of small cell networks is widely regarded as a key role to meet the increasing demand for huge capacity of wireless communication systems. Meanwhile, network densification will result in severe inter-cell interference and thus impair system performance. Traditional radio resource management schemes pay attention to interference mitigation through resource allocation in time, frequency, space and power domains, or a mix of them. In this paper, polarization, an important and underutilized property of electromagnetic waves, is exploited as a novel means to enhance system capacity. We propose a multicell joint polarization, power and subcarrier allocation (MC-JPPSA) scheme to maximize system capacity through joint optimization of transmitting polarization states, power and subcarriers with an iterative approach. Though the iterative solution is suboptimal, simulation results demonstrate that MC-JPPSA scheme can strike a balance between performance and complexity compared with the optimal exhaustive search. Furthermore, the proposed scheme outperforms traditional joint power and subcarrier allocation schemes by means of exploiting polarization in ultra-dense small cell networks.
... Recently, co-located orthogonally dual-polarized antennas (ODPAs) have become a promising cost-and space-effective configuration and have been widely used in practical deployed wireless communication systems [19] [20]. The use of dual-polarized antennas enables receivers to obtain polarization information derived from the amplitude ratio and relative phase between two orthogonally polarized branch signals [21]. Since polarization is an independent parameter of waves, it can be used to design several technologies, such as polarization-based modulation [22], polarization-based signal sensing [23], polarization-based orthogonal transmission [24] and polarization-based filtering [25]. ...
A fast dual polarization hopping (FDPH) system is designed to enhance the physical layer secure transmission in fixed down-link satellite communications (SATCOM). In order to prevent the eavesdropper from detecting transmitted signals, a pair of dual polarization states is chosen to carry the modulated signal by the designed FDPH pattern. The polarized signal is transmitted through orthogonal dual polarized parabolic antennas (ODPPAs) by virtual polarization technique. Due to the assumption that the designed FDPH pattern is synchronous among the legitimate users, the legitimate receivers apply oblique projection polarization filter (OPPF) to suppress one of dual polarization states, and then have a polarization match to recover the scalar modulated signal and demodulate the scalar signal. Whereas, the eavesdropper can’t match the right polarization state. Therefore, the eavesdropper receives random amplitudes signal owing to the fast polarization hopping. If the modulation scheme is ASK and QAM, the demodulation performance of the eavesdropper would be very poor, resulting in a high bit error rate (BER). Moreover, there is severe distinction in orthogonal dual polarized channel. The legitimate users would have a prelinear compensation with perfect channel state information (CSI), which further worsen eavesdropping. Thus, the eavesdropper can’t even demodulate the PSK signal because of the time varying orthogonal dual polarized channel and auxiliary polarized angle. Simulation results demonstrate the secure performance of our design.
... Recently, co-located orthogonally dual-polarized antennas (ODPAs) have become a promising cost-and space-effective configuration and have been widely used in practical deployed wireless communication systems [19] [20]. The use of dual-polarized antennas enables receivers to obtain polarization information derived from the amplitude ratio and relative phase between two orthogonally polarized branch signals [21]. Since polarization is an independent parameter of waves, it can be used to design several technologies, such as polarization-based modulation [22], polarization-based signal sensing [23], polarization-based orthogonal transmission [24] and polarization-based filtering [25]. ...
A poly-polarization multiplexing (PPM) system applying orthogonal dual polarized antennas (ODPAs) is designed to enhance the spectrum efficiency for narrow-band wireless communication in this letter. In order to minimize the cochannel interference, we apply the multi-notch oblique projection polarization filters (OPPFs) to separate parallel streams at the same frequency at the receiver. Due to the polarization dependent loss (PDL) effects of the narrow-band polarized channel, the precompensation method is proposed to mitigate the impairment of the signal-to-interference ratio (SIR) in OPPFs. Whereas the signal-to-noise ratio (SNR) of the polarized channel is decreasing after pre-compensation. Therefore, the optimal pre-compensation coefficient is calculated to obtain maximum capacity of the multiplexing system by signal to interference plus noise ratio (SINR). Simulation results demonstrate the performance of our design.
... Further results showed the potential of space savings with cross polarization discrimination (XPD) at both transceiver ends compared to conventional space diversity [4], also in the context of long term evolution (LTE) [5]. In LTE, the orthogonal frequency division multiplexing (OFDM) air interface technology is applied [6], which offers additional degrees of freedom concerning adaptive polarization on a subcarrier basis [7]. Problems about the significant mean signal power difference of unequally polarized branches and principles to overcome this by means of circular polarization are discussed, e.g., in [3], [8], but are beyond the scope of this contribution. ...
The performance of multiple-input multiple-output (MIMO) systems is affected by the spatial correlation properties, which depend on the array configuration and the channel characteristics. The configuration can be influenced by manipulating the radiation patterns of the antennas, the antenna spacing and the array geometry. To decrease the spatial correlation effects, e.g., the antenna spacing can be increased, which is usually undesirable in mobile devices. Here, the utilization of polarization diversity techniques comes into consideration. This paper deals with the application and comparison of different polarized transmit/receive array setups in indoor environments using a multiple antenna demonstrator in uncoded adaptive MIMO-OFDM scenarios. Measurement results indicate a decreased correlation of the spatial subchannels, a higher MIMO capacity for cross-polarized antenna arrays and lower bit error rates with bit and power loading algorithms.
... In an onthe-field deployment, this polarization controller would be automatic [24]. Also, adaptive polarization can be used to remove the tracking at the receiver as it was proposed in Advances in Optical Technologies [25]. Different optical PDM receiver architectures that can be used to eliminate the necessity of conventional polarization tracking are presented in [26] for both intensity modulation direct detection and coherent receivers. ...
This paper describes the state-of-the-art of polarization multiplexing for optical networks transmission. The use of polarization division multiplexing (PDM) permits to multiply the user capacity and increase the spectral efficiency. Combining PDM and orthogonal frequency division multiplexed (OFDM) modulation allows maximizing the optical transmission capacity. The experimental demonstration of transmitting OFDM signals following ECMA-368 ultrawide band (UWB) standard in radio-over-fiber using PDM in passive optical networks is herein reported. The impact of cross-polarization and cochannel crosstalk is evaluated experimentally in a three-user OFDM-UWB subcarrier multiplexed (SCM) configuration per polarization. Each SCM uses up to three OFDM-UWB channels of 200 Mbit/s each, achieving an aggregated bitrate of 1.2 Gbit/s with 0.76 bit/s/Hz spectral efficiency when using PDM transmission. The experimental results for the polarization-multiplexed SCM indicate that a 4 dB additional polarization crosstalk interference can be expected compared to a nonpolarization-multiplexed transmission system which translates to 2.4 dB EVM penalty in the UWB signals. The successful PDM transmission of SCM multiuser OFDM-UWB over a passive optical network of 25 km standard-single mode fiber (SSMF) reach is demonstrated.
As the technical trends for the next-generation wireless network significantly extend the near-field region, a performance reevaluation of integrated sensing and communications (ISAC) with an appropriate channel model to account for the effects introduced by the near field becomes essential. In this paper, a near-field ISAC framework is proposed for both downlink and uplink scenarios based on an accurate channel model. A uniform planar array is equipped at a base station, where the impacts of the effective aperture and polarization of antennas are considered. For the downlink case, three distinct designs are studied: a communications-centric (C-C) design, a sensing-centric (S-C) design, and a Pareto optimal design. Regarding the uplink case, the C-C design, the S-C design and a time-sharing strategy are considered. Within each design, sensing rates (SRs) and communication rates (CRs) are derived. To gain further insights, high signal-to-noise ratio slopes and rate scaling laws concerning the number of antennas are examined. The attainable near-field SR-CR regions of ISAC and the baseline frequency-division S&C are also characterized. Numerical results reveal that, as the number of antennas in the array grows, the SRs and CRs under our accurate model converge to finite values, while those under conventional far- and near-field models exhibit unbounded growth, highlighting the importance of precisely modeling the channels for near-field ISAC.
Polarization modulation is playing an increasingly important role in wireless communications. However, the research on polarization modulation system channels mostly focuses on the modeling of the channel’s channel depolarization effect. As a key component of the polarization modulation system, dual-polarized antennas have rarely been studied. In this paper, we proposed a 2*2 MIMO channel with taking the dual-polarization antennas posture into account. With the help of this channel model, we derived the directional sensitivity and symbol error rate. Through the simulation results, we demonstrated the direction-sensitive nature of polarization modulation systems, which can be used for physical layer security.
This paper proposes a method to represent and predict received signal instantaneous polarization states as a function of arbitrary transmit polarization states for time-dispersive channels. The model incorporates frequency-dependent characterizations to represent the polarization dispersion behavior of a received signal across its bandwidth in a multipath channel. The representation takes advantage of signal dispersion features typical of depolarized signals, and employs subbanded characterizations to achieve polarization representations exhibiting high degrees of polarization in each subband. Experiments are conducted that demonstrate the utility of the modeling approach to predict polarization dispersion responses for arbitrary transmit polarizations based on measurements from two orthogonal transmit polarizations.
In this paper, a spectrum efficient spatial polarized quadrature amplitude modulation (SPQM) scheme for physical layer security in dual-polarized satellite systems is proposed, which uses the carrier's polarization state, amplitude, phase and the polarization characteristics of the transmitting beams as information bearing parameters, which can improve the transmission efficiency and enhance the transmission security at the same time. As we know, the depolarization effect is the main drawback that affects the symbol error rate performance when polarization states are used to carry information. To solve the problem, we exploit an additional degree of freedom, time, in the proposed scheme, which means that two components of the polarized signal are transmitted in turn in two symbol periods, thus they can be recovered without mutual interference. Furthermore, orthogonal polarizations of the transmitting beam are used as spatial modulation for further increasing the throughput. In addition, in order to improve the transmission security, two transmitting beams are designed to transmit the two components of the polarized signal respectively. In this way, a secure transmission link is formed from the transmitter to the receiver to prevent eavesdropping. Finally, superiorities of SPQM are validated by the theoretical analysis and simulation results in dual-polarized satellite systems.
Polarization is an important property of electromagnetic waves. It has shown the great application potential in optical fiber, radar, and satellite communications, where polarization has been exploited to be a promising means of enhancing channel capacity. The existing research has shown that, in theory, it has great potential to sixfold the channel capacity by using six co-located orthogonally polarized electric and magnetic dipoles. Wireless communications exploits the electromagnetic medium, which is also intrinsically polarization-sensitive. In the past decades, wireless communications have mainly exploited the dimensions of time, frequency, and space, and most wireless channels, technologies, and applications have been devised without explicit consideration of polarization. To keep up with the recent exponentially growing network capacity, as such, leveraging polarization for wireless communications is a logical next step. However, exploiting polarization in wireless communications involves many challenges that differentiate it from conventional polarization applications in terms of optical fiber, radar, and satellite communications due to complex depolarization effects, restriction on additional gain offered, and limited degrees of freedom in the polarization domain. These challenges have inspired recent advances, particularly related to polarization channels, polarization technologies (such as polarization-based modulation, polarization-based signal sensing, polarization-based orthogonal transmission, and polarization-based filtering), and their applications to emerging communication scenarios including energy-efficient communications, cognitive radio networks, and in-band full-duplex transmission. This paper thoroughly surveys these recent advances and presents the state-of-the-art research progress on each aspect. Furthermore, open research issues and challenges are discussed in order to provide perspectives for future research directions.
To adapt to variation of polarization dependent loss (PDL) in depolarization channel, an adaptive polarization modulation scheme which can improve the spectral efficiency of polarization modulation system is proposed. In the proposed scheme, the transmitter adapts the optimal constellation size to the variation of the channel due to PDL while fulfilling a fixed target BER constraint, which is based on the received feedback information of channel state information estimated at the receiver. Our simulation results and analysis show that, adaptive polarization modulation (APM) can achieve higher spectral efficiency (SE) than nonadaptive polarization modulation, subject to the same fixed target BER constraint.
Common remote-sensing techniques of analyzing received radio frequency (RF) signals, such as amplitude envelope detection and frequency Doppler shift, may work fine when the transmitted RF signal is precisely known and available. But, some remote-sensing applications may not permit such control over the RF transmission. Another technique, RF polarization, offers satisfactory results in some of those situations-when multipath and/or bandwidth-delay spread can be kept low. However, a new technique leveraging the polarization mode dispersion (PMD) inherent in most RF channels promises better results (accuracy, precision, and sensitivity) for most remote-sensing applications. The PMD technique adds a frequency-subband dimension to the analysis that the other methods overlook. This paper will present the data analysis techniques for several methods of RF signal processing aimed at the general remote-sensing application of vibrometry (the measurement of vibrations). Using model simulations calibrated to laboratory results, the PMD-based approach is shown to out-perform more common techniques by one or more orders of magnitude for typical indoor environments. Such performance gains (up to 30 dB on average) could allow for the successful detection of a vibrator or target within an RF field simply by adopting these PMD-based data analysis techniques on the received RF signals.
Spectrum sensing exploiting polarization can be leveraged to improve detection performance. In this paper, we present an optimal likelihood ratio test (LRT) which serves as the upper bound on the performance of all methods that exploit polarization under Gaussian assumption. However, the performance of LRT for realistic blind sensing is unclear since the practical implementation of polarization sensing has to face several challenges, which is the focus of this paper. Four practical sensing algorithms utilizing polarization are considered in this work, that is, a generalized likelihood ratio test (GLRT) for polarization sensing using maximum likelihood estimate (MLE) method when any prior knowledge is unknown, an optimal test when the noise of channel between primary user and secondary user is partially polarized, a realistic detector considering that the received polarization wave arrived with a specific direction rather than is almost perpendicular to the receiver dual-polarized antennas, and a more practical blind detector for polarization channel exhibiting polarization mode dispersion (PMD) phenomenon especially in wideband system. The simulation results show the performance gains possible with proposed detectors and how well the proposed detectors are expected to perform in practice.
A Polarized Phase Shifting Keying/Quadrature Amplitude Modulation(PPSK/PQAM) scheme in the wireless depolarized channel is proposed. Such scheme uses the carrier's polarization state, amplitude and phase as the information bearing parameters, and can further improve the traditional modulation methods' spectrum efficiency. The impairment to PPSK/PQAM from the wireless depolarized channel is quantitatively analyzed. To mitigate such impairment, a constellation compensation algorithm is also presented. Furthermore, the PPSK/PQAM's symbol error rate is derived on the basis of the proposed constellation compensation; then to maximize the PPSK/PQAM's link spectrum efficiency (LSE), the optimal modulation ratio, which is defined as the ratio of the data rata achieved by the polarization state and amplitude-phase, is also calculated. Finally, simulations show that PPSK/PQAM's SER and LSE performance have significant advantage over the traditional PSK/QAM modulation methods.
In this paper, we propose a self-interference cancellation scheme for the full duplex communication in the polarization domain. The proposed scheme cancels self-interference first by orthogonal projection to the null space of the self-interference before the analog to digital converter (ADC). Then, the theory of virtual polarization adaptation is used to maximize the desired signal power. Different from the existing schemes in the polarization domain, the scheme proposed in this paper is based on the virtual polarization technologies so that it's more flexible than the existing schemes in polarization domain. This paper conducts theoretical analysis and simulation under the condition of Ricean channel. Analysis and simulation results verify that the proposed scheme has better cancellation performance and more adaptive to the Ricean fading channel than the existing schemes in the polarization domain.
In cognitive radios, the biggest challenge is spectrum sensing. It usually makes use of the amplitude, frequency or space dimension of the received signal to differentiate signal from background noise. Polarization, also as an inherent characteristic of signals, provides an additional degree of freedom in signal space. Polarization-based spectrum sensing has been identified as an effective method for improving detection performance. In this paper, various polarization-based spectrum sensing methods including the optimal polarization likelihood ratio test using Neyman–Pearson theorem, virtual polarization detection utilizing maximum signal to noise ratio method and blind polarization detectors based on generalized likelihood ratio test method are reviewed. Then, a comprehensive comparison of various polarization-based sensing methods in terms of detection performance and computational complexity is detailed. Finally, challenges and possible future studies on polarization-based spectrum sensing are described. Copyright © 2015 John Wiley & Sons, Ltd.
In this paper, we consider the problem of spectrum sensing in cognitive radios by exploiting Stokes subvector, which can completely describe energy and polarization information of the received vector signal captured by dual-polarized antennas. We first find that both component correlation between Stokes variables (i.e., the elements of Stokes subvector) and vector correlation between Stokes subvectors containing signal and noise are different from that of noise only with high probability. Therefore, two new blind detectors, namely, component-correlation-based energy-polarization detection (CCB-EPD) and vector-correlation-based energy-polarization detection (VCB-EPD), are proposed, respectively. The analysis results reveal that CCB-EPD and VCB-EPD are all constant false alarm rate detectors, and the VCB-EPD method achieves better performance than CCB-EPD when channel is low depolarized and vice versa. Simulations show that the proposed two methods exhibit better performances than other multiantenna-based detectors whether priori polarization information of primary user is known or not. We also show that the two proposed methods have performance improvement with respect to existing polarization-based detectors due to the exploitation of both energy and polarization information and the unaffectedness by noise uncertainty. The experimental results verify that the proposed two methods can satisfy the performance requirement specified by the IEEE 802.22 standard.
Polarization-enabled Spectrum Sharing (PSS) that exploits the spectrum opportunities in polarization domain is deployed to balance between avoiding interference at the incumbent receiver and optimizing the throughput of secondary user. However, when it comes to wideband environments, PSS is impaired by the frequency-dependent Polarization Mode Dispersion (PMD) effect, thus the spectrum efficiency of PSS drops. Different from previous studies on PSS without taking the frequency-dependent depolarization effect into consideration, this work firstly analyzes the PMD effect and then proposes a cluster-based PSS approach to enable PSS on a narrower frequency span for LTE user. Since the width of the frequency span impacts both the environment learning time overhead and the PMD effect suffered by PSS, we analytically incorporate the PMD effect into LTE throughput and the interference at the incumbent receiver. By this means, the optimal number of subcarriers is derived to maximize the effective throughput for LTE users, subject to the interference power constraint at the incumbent receiver.
SUMMARYA new spectrum sensing algorithm-degree of polarization (DoP) sensing algorithm is proposed in this paper. By exploiting a pair of dual-polarized antenna at the receiver, DoP of the received vector signal is estimated and utilized to detect the presence of primary users based on the polarization characteristics of electromagnetic waves. The dual-polarized narrowband and broadband systems are both considered for DoP detection. In theoretical analysis, we derive the probability of detection, the probability of false and detection threshold of the proposed algorithm. It is shown that our algorithm overcomes the noise uncertainty problem. Considering the polarization-sensitive channel impairments, the impact of polarization mode dispersion on DoP detector is discussed. This method can be utilized for various signal detection applications without requiring the knowledge of signal, transmission channel, and noise power. In simulations based on wireless microphone signals, by applying polarization information signal carries, DoP achieves a better detection performance than arithmetic-to-geometric mean detector, the maximum-to-minimum ratio eigenvalue detector, and energy detector with noise uncertainty. The simulations based on digital video broadcasting-terrestrial signals are also presented, which may show the detection performance of the proposed method may be affected by polarization mode dispersion. Copyright © 2013 John Wiley & Sons, Ltd.
A cellular down-link polarization division multiple access (PDMA) scheme with collaborative transmitter-receiver-polarization adjustment and polarization filtering detection is proposed for polarized wide-band non-line-of-sight (NLoS) wireless fading channels. The fundamental novelty of the proposed scheme is that it can adjust transmit polarization to yield more desirable per-subcarrier complex cross-polarization discrimination (XPD) observed at the receivers. This is a significant difference between the proposed scheme and conventional multiple-input multiple-output (MIMO) systems. The capacity analysis of the proposed PDMA scheme is provided, and the feasibility and satisfactory performance of the scheme are demonstrated even when serious time-variant channel depolarization and polarization mismatch between receivers occurs. The proposed cellular down-link PDMA scheme uses synchronous orthogonal frequency division multiple access (OFDMA) with an equally spaced pilot symbol allocation and a channel estimator. Excellent symbol error rate (SER)/effective signal-to-interference plus noise ratio (SINR) performance is shown despite the presence of substantial channel depolarization. The scheme can be used to extend the capacity of any cellular system that uses uni-polarized antennas and can be extended and applied to MIMO arrays as well.
In wireless communications, wideband polarization dependent loss (PDL) has become significant with the development of signal processing in wideband polarization domain. Aiming at deriving PDL statistical characteristic, a polarized time-variant multipath channel transfer function matrix H which considers azimuth power spectra, power delay profile (PDP), polarization power imbalance and polarization correlations is proposed. Closed-form expressions have been derived for various autocorrelation functions and cross-correlation functions for the polarized channel to fully characterize its statistical property. PDL is defined as the ratio between maximum and minimum eigenvalues of HHH at frequency f. However, due to the difficulty to analytically derive PDL's statistical characteristic, i.e., the distribution of PDL, numerical sum-of-sinusoids simulator is realized to accurately emulate the channel correlations derived above. Inspired by Weibull distribution, the probability density function (PDF) of PDL is well curve fitted using raw data from numerical simulator. The function is parameterized by scale factor, shape factor and normalization factor which all relate to polarization power imbalance and polarization correlations of the polarized channel. Results show that the degree of attenuation unbalance towards eigen-polarizations is in the descending order as: NLOS macrocell > NLOS microcell > NLOS picocell.
An Energy Efficient Subcarrier-power Allocation (EESA) scheme is proposed to improve the Power Amplifier (PA) energy efficiency. The proposed scheme is applied for the Polarization-Amplitude-Phase Modulation (PAPM) in the channel with Polarization Mode Dispersion (PMD). Considering a multiuser downlink system, utilizing the diversity of the polarization characteristic on each subcarrier caused by PMD, EESA scheme can make PA energy efficiency optimal under the constraint of each user terminal's data demand. To reduce the allocation's computationally complexity, the EESA scheme performs the subcarrier allocation and power allocation separately. Firstly, by assuming the equal power distribution, the subcarrier is allocated through Differential Evolution (DE); then based the obtained subcarrier allocation method, a two-step allocation algorithm is presented to distribute the PA input power on each subcarrier. Through numerical calculation, the optimal parameters setting of DE is examined. Our results show that the EESA scheme is able to achieve significant improvement in PA energy efficiency.
A Polarization Mode Dispersion Tolerant Subcarrier-power Allocation (PMDTSA) scheme is proposed to improve the Power Amplifier (PA) energy efficiency. The proposed scheme is applied in the multiuser downlink system based on Joint Polarization-Amplitude-Phase Modulation (JPAPM). Dut to the wireless channel's polarization mode dispersion effect, the polarization based impairment to JPAPM on each subcarrier will be diverse. Through the optimal subcarrier-power allocation, such diversity can be utilized to make PA energy efficiency optimal under the constraint of each user terminal's data rate demand. To reduce the allocation's computationally complexity, the PMDTSA scheme performs the subcarrier allocation and power allocation separately. Firstly, assuming the equal power distribution, the subcarrier is allocated through Particle Swarm Optimization (PSO); then based the obtained subcarrier allocation method, a two-step allocation algorithm is presented to distribute the PA input power on each subcarrier. Through numerical calculation, the optimal parameters setting of PSO is examined. Our results show that the proposed PMDTSA scheme is able to achieve significant improvement in PA energy efficiency.
To improve the Power Amplifier (PA) energy efficiency, a Polarization Modulation (PM) scheme that uses the Polarization State (PS) as the information bearing parameter is proposed. Since the PS determined by orthogonally dual-polarized antennas is unaffected by PA, PM can let PA operate in nonlinear region without suffering the distortion. Furthermore, to mitigate the wireless channel depolarization impairment to PM from the polarization dependent loss and the polarization mode dispersion, an Optimal Constellation Pre-compensation (OCP) algorithm is also presented. The simulation results show, with same symbol error rate, PM can reduce the energy consumption per bit by 25% at most compared with the traditional multi-phase shift keying.
A Joint Polarization-Amplitude-Phase Modulation (JPAPM) scheme in wireless communication is proposed to improve the Power Amplifier (PA) energy efficiency. The proposed scheme introduces the signal's Polarization State (PS), amplitude and phase as the information-bearing parameters. Thus, the data rate can be further enhanced on the basis of the traditional amplitude-phase modulation. Also, since the transmitted signal's PS completely manipulated by orthogonally dual-polarized antennas is unaffected by the PA, JPAPM can let PA work in its nonlinear region to acquire high PA conversion efficiency. Furthermore, to mitigate the polarization-based impairment to JPAPM caused by the wireless channel's polarization dependent loss effect, the optimal pre-compensation algorithm is also presented. Simulation under the same symbol error rate and channel state shows the JPAPM can improve the PA energy efficiency significantly compared with the traditional quadrature amplitude modulation.
In this paper, we propose a new blind spectrum sensing method based on the polarization characteristic of the received signal, which is completely represented by the orientation of a polarization vector. We first discuss a spectrum sensing model based on polarization vectors' orientation. Then we develop the directional statistics of polarization vectors that contain both the signal and noise or noise only. The distinctive difference between the two statistics can be used to decide whether the primary signal exists or not. Based on this, by using the well-known generalized likelihood ratio test (GLRT) paradigm, a new polarization sensing algorithm GLRT-polarization vector (GLRT-PV) is proposed. By applying directional statistics, we derive closed-form expressions for the probability of false alarm and the probability of detection under both dual-polarized additive white Gaussian noise (AWGN) and Rayleigh-fading channels. Our numerical simulation and experimental results show that the proposed method exhibits better performance than other existing methods in the case of unknown primary transmitter polarization and/or presence of noise power uncertainty.
The analysis of rotating machines during their test and characterization phases provides information essential for their design. Afterward, the monitoring of rotating machines operating in production is increasingly popular for condition based maintenance programs. Typically, contact accelerometers or strain gauges are physically attached to rotating machine parts (rotors, stators, housing, etc.) and/or proximity sensors are mounted very near to rotating shafts to capture data on periodic motions and vibrations. Radio frequency signals offer a noncontact, remote-sensing alternative. The temporally changing polarization of a reflected or scattered radio frequency signal can be analyzed to provide suitable information for rotating machine analysis. This paper will present the theory and practical application for using radio frequency polarimetry in analyzing rotating machines. A common desktop fan will be measured in normal operating condition and in simulated faulty conditions to demonstrate this technology's remote-sensing capabilities.
This paper presents a novel, noncontact vibration transducer system using radio frequency (RF) polarimetry, which allows for vibration measurements to be collected remotely and nonintrusively at a distance. Movement or vibration of an object within the RF propagation channel can alter the combined direct, reflected, and multipath RF signals, thereby changing the received signal's polarization. This paper presents the theory to analyze a RF signal's polarization for used as a vibration transducer. The proposed transducer leverages the entire bandwidth of the RF signal using the frequency-dependent polarization mode dispersion phenomenon that occurs in multipath channels. To analyze the approach, a software model has been constructed and used to simulate and characterize the transducer's performance. A feasibility comparison of this RF polarimetry technique to similar vibration transducers, including laser Doppler vibrometry, shows this new transducer to be easier and less expensive to implement without significant tradeoffs in performance. Finally, laboratory experiments verify the software model and demonstrate a real-world prototype implementation. The pure-tone vibration of tuning forks, the forced and free vibrations of a ringing telephone, and the rotational motion of a desktop fan have been measured and are presented as an evidence of this RF polarimetry transducer's diverse capabilities in vibrometry.
To improve the power amplifier (PA) energy efficiency, a polarization–amplitude–phase modulation (PAPM) scheme in wireless communication is proposed. The proposed scheme introduces the signal’s polarization state (PS), amplitude, and phase as the information-bearing parameters. Thus, the data rate can be further enhanced on the basis of the traditional amplitude–phase modulation. Also, since the transmitted signal’s PS completely manipulated by orthogonally dual-polarized antennas is unaffected by PA, PAPM can let PA work in its nonlinear region to acquire high PA efficiency. To further optimize the PA energy efficiency based on PAPM, a constrained optimization problem regarding the output back-off value and the ratio between the data carried by the PS and the amplitude–phase is formulated, and the distribution of the optimum solutions is presented. The simulation results show that PAPM can improve the PA energy efficiency significantly.
Methods for detecting object translation and/or motion using differential polarization-based sensing are described. Both time and frequency-based polarimetric sensing strategies are considered. The time-based detection statistic is formed using the differential time-averaged received signal polarization state. This approach suffers from the impact of polarization-sensitive channel impairments, especially polarization mode dispersion (PMD). As PMD effects become more prominent, the variability of the time-domain signal polarization increases and the average polarization over a detection interval may be substantially different from the instantaneous signal polarization states, detracting from the overall sensitivity of the detection statistic. Frequency-domain approaches, on the other hand, can leverage the relatively stable polarization-frequency signature of the received signal, and can be designed to easily exploit PMD using differential detection in the subbands. Integration of the detections over the full complement of subbands is then used to arrive at a final detection statistic. Using indoor measurements, the resulting subbanded architecture is found to provide improved detection sensitivity in comparison to the time-based version as well as to more conventional power-based techniques, including a subbanded power-based architecture.
This paper proposes an adaptive transmission power control scheme between cross-polarized transmission antennas for mul-tiple-input multiple-output (MIMO) diversity using polarization diversity in orthogonal frequency division multiplexing (OFDM), in order to mitigate the degradation due to the effect of cross polarization discrimination (XPD). In the proposed scheme, the transmission power of each cross-polarized channel is controlled so that it is proportional to the instantaneous received signal power of the cross-polarized channel measured at each polarized branch of a receiver. It is shown by computer simulation that the required average signal energy per bit-to-noise power spectrum density ratio (E b /N 0) at the bit error rate of 10 -3 using the pro-posed method is reduced by approximately 1 dB compared to that of the conventional polarization diversity without using transmission power control in MIMO-OFDM radio access.
A three-dimensional reference model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) channels is reviewed. To validate the reference model, an experimental MIMO M-to-M channel-sounding campaign was conducted for M-to-M vehicular communication with vehicles travelling along expressways in a metropolitan area. The measured data is processed and the channel statistics obtained from the reference model and from the empirical measurements are compared. The close agreement between the analytically and empirically obtained channel statistics confirms the utility of the proposed reference model.
A three-dimensional reference model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) channels is reviewed. To validate the reference model, an experimental MIMO M-to-M channel-sounding campaign was conducted for M-to-M vehicular communication with vehicles travelling along surface streets of a metropolitan area. The measured data is processed and the first- and second-order channel statistics obtained from the reference model and from the empirical measurements are compared. The close agreement between the analytically and empirically obtained channel statistics confirms the utility of the proposed reference model.
In real single-mode optical fibers, imperfections cause the two possible polarizations to propagate at different phase velocities. This birefringence leads to different group velocities. We have measured the resulting mode dispersion in short fiber lengths (0.5–2.5 m) from the depolarization of broad-bandwidth light. In a typical fiber we found 30 psec/km at 0.69-μm wavelength, in good agreement with the observed birefringence. The effect of mode dispersion can be compensated by a ±68° double twist midway along the fiber, interchanging the fast and slow modes.
In this paper polarization adaptivity on transmit has been used to enhance the received signals directed to a pre-selected receiver in a near-field multi-input multi-output (MIMO) environment. The objective here is to select a set of weights on the transmitting antennas adapted to each receiver based on the principles of reciprocity. Using the polarization properties, when the number of receiving antennas is greater than the number of transmitting antennas, the transmitted signal may be directed more to a particular receiver location while simultaneously minimizing the reception signal strength at other receivers. A numerical simulation has been made to illustrate the novelty of the proposed approach.
Many methods have been developed and are continuing to evolve in recent years, to enhance reception of signals in a multi-input multi-output (MIMO) environment [1,2]. For mobile communication, the development of a methodology that mitigates the deleterious effects of multipath fading, near-field scatterers (buildings, trees, platforms), etc. is necessary for improved reception. To achieve such enhancements, the authors believe that transmit/receive configurations with spatial diversity are required as shown in Figure 1. Unfortunately, the small footprint of a mobile receiver precludes spatial diversity. In contrast, spatial diversity on transmit is obtainable at a base station, if that station has multiple antennas and the signals being fed to each one of the transmitting antennas corresponding to a particular receiver are weighted. So this paper addresses the of what can be done in terms of adaptivity on transmit so as to enhance the field strength of the signal at a pre-specified receiver while simultaneously minimizing the reception signal strength at the remaining receivers. In this way, the transmitted signals would be received essentially at the designated receiver while it would be canceled at the other locations. By providing spatial diversity on transmit it is possible to mitigate the effects of multipath fading, as the directed energy from the transmitted antennas, would combine vectorially at the selected receiving antenna element either to produce a maximum or a minimum.
The past decade has seen many advances in physical layer wireless communication theory and their implementation in wireless systems. This textbook takes a unified view of the fundamentals of wireless communication and explains the web of concepts underpinning these advances at a level accessible to an audience with a basic background in probability and digital communication. Topics covered include MIMO (multi-input, multi-output) communication, space-time coding, opportunistic communication, OFDM and CDMA. The concepts are illustrated using many examples from real wireless systems such as GSM, IS-95 (CDMA), IS-856 (1 x EV-DO), Flash OFDM and UWB (ultra-wideband). Particular emphasis is placed on the interplay between concepts and their implementation in real systems. An abundant supply of exercises and figures reinforce the material in the text. This book is intended for use on graduate courses in electrical and computer engineering and will also be of great interest to practising engineers.
Use of multiple antennas in wireless links with appropriate space-time (ST) coding/modulation and demodulation/decoding is rapidly becoming the new frontier of wireless communications. In the past few years, the theory of ST wireless communications has grown so large. An attempt is made to provide a coherent overview of the key advances in this field emphasizing basic theory and intuition.
The past decade has seen many advances in physical-layer wireless communication theory and their implementation in wireless systems. This textbook takes a unified view of the fundamentals of wireless communication and explains the web of concepts underpinning these advances at a level accessible to an audience with a basic background in probability and digital communication. Topics covered include MIMO (multiple input multiple output) communication, space-time coding, opportunistic communication, OFDM and CDMA. The concepts are illustrated using many examples from wireless systems such as GSM, IS-95 (CDMA), IS-856 (1 × EV-DO), Flash OFDM and ArrayComm SDMA systems. Particular emphasis is placed on the interplay between concepts and their implementation in systems. An abundant supply of exercises and figures reinforce the material in the text. This book is intended for use on
This paper is motivated by the need for fundamental understanding of ultimate limits of bandwidth efficient delivery of higher bit-rates in digital wireless communications and to also begin to look into how these limits might be approached. We examine exploitation of multi-element array (MEA) technology, that is processing the spatial dimension (not just the time dimension) to improve wireless capacities in certain applications. Specifically, we present some basic information theory results that promise great advantages of using MEAs in wireless LANs and building to building wireless communication links. We explore the important case when the channel characteristic is not available at the transmitter but the receiver knows (tracks) the characteristic which is subject to Rayleigh fading. Fixing the overall transmitted power, we express the capacity offered by MEA technology and we see how the capacity scales with increasing SNR for a large but practical number, n, of antenna elements at both transmitter and receiver. We investigate the case of independent Rayleigh faded paths between antenna elements and find that with high probability extraordinary capacity is available. Compared to the baseline n = 1 case, which by Shannon’s classical formula scales as one more bit/cycle for every 3 dB of signal-to-noise ratio (SNR) increase, remarkably with MEAs, the scaling is almost like n more bits/cycle for each 3 dB increase in SNR. To illustrate how great this capacity is, even for small n, take the cases n = 2, 4 and 16 at an average received SNR of 21 dB. For over 99%
This chapter begins with a brief history of wireless systems and standards, including cellular systems, cordless telephone systems, and wireless local and personal area networks (LANs and PANs). The discussion of cellular standards includes GSM, IS-54/136, IS-95, PDC, cdma2000, UMTS, and WiMAX. The discussion of cordless phones includes DECT and PHS, and the discussion of IEEE802.11a/b/g, IEEE802.15 and Bluetooth. The chapter then introduces frequency reuse and the cellular concept, and discusses the propagation phenomenon that are found in land mobile radio environments along with additive impairments such as co-channel interference (CCI) and noise. Afterwards, the cellular land mobile radio link budget is considered, including the effects of interference loading, shadow margin and handoff gain that are peculiar to cellular frequency reuse systems. The chapter concludes with a discussion of coverage and capacity issues for cellular radio systems.
The throughput that a MIMO channel can support is a function of different array parameters. Another technique, for miniaturized antenna designs, is polarization/pattern diversity where the antennas are designed to radiate with orthogonal radiation patterns and polarizations as a means to create uncorrelated channels across different array elements. The benefits of pattern diversity have been shown by L. Dong et al. (2003). That analysis, however, did not use realistic channel models. We aim to extend the analysis of Dong et al. to clustered channel models, adopted by the IEEE 802.11n standard body for wireless local area networks (WLANs). We analyze MIMO arrays consisting of circular microstrip antennas to enable pattern diversity and compare their performance against conventional uniform linear arrays. We also model the effect of mutual coupling and measure the performance degradation produced by the near-field effects. We briefly review the channel model and the properties of circular microstrip antennas. Then, we analytically compute the spatial correlation coefficients and evaluate the MIMO channel capacity. Pattern diversity yields better performance than space diversity.
Spatial multiplexing and space-time block codes are promising techniques that effectively exploit multiple-input multiple-output (MIMO) transmission to achieve a higher data rate and more reliable communication, respectively. On the other hand, the use of dual-polarized antennas in MIMO systems has emerged as a cost- and space-effective alternative, where two spatially separated uni-polarized antennas can be replaced by a single antenna element employing orthogonal polarizations. In this paper, we investigate the use of dual-polarized antennas in a combined spatial multiplexing and space-time block coded system. We present a hybrid transmission scheme that employs transmit diversity over the same polarization of the two transmit dual-polarized antennas and transmits the co-channel space-time coded signals on the orthogonal polarizations. We evaluate the system performance for both the Rayleigh fading channel and the suburban environment of a personal communication system (PCS) at 1800 MHz. It is shown that the performance of PM-STBC approaches that of STBC in the correlated Ricean fading environment and it saves one receive antenna.