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An overview of air interface multiple access for IMT-2000/UMTS
Abstract
The basis for any air interface design is how the common
transmission medium is shared between users (i.e., multiple access
scheme). The underlying multiple access method for all mobile radio
systems is FDMA. The performance of TDMA and CDMA has been subject to
vigorous debate, without any definitive conclusions. This article gives
an overview of worldwide research and standardization activities related
to the multiple access schemes for third-generation mobile
communications systems IMT-2000 and UMTS
... Telecommunications System (UMTS) [1,2]. UMTS typically provides low to high data rate services for multimedia applications such as voice, audio/video, graphics, data, inter-net acce"" and e-mail with a significant maximum data rate of 2 Mb/s. ...
... Firstly, duplex procedures and multiple access techniques commonly used in mobile radio communications are explained and compared in Sec. 2.1 and Sec. 2.2 respectively. ...
... Secondly, the general technique of spreading a signal over a wide band of frequencies is presented in Sec. 2. 3. ...
p>In this thesis, we propose a new robust and simple blind multiuser equaliser for downlink DS-CDMA systems, the so-called filtered-R multiple error CM algorithm (FIRMER-CMA) equaliser. The latter has a relatively low computational complexity, shows good convergence behaviour and a BER performance close to the MMSE solution. The FIRMER-CMA is further modified to be readily reconfigured to different modes such as partial loading schemes, multi-rate transmission, and semi-blind adaptation employing the aid of pilots. A considerable complexity reduction is achieved by adopting a novel strategy based on considering a new small virtual population of active users.
The robustness of the FIRMER-CMA to carrier frequency offset is addressed whereby a combined scheme based on FIRMER-CMA equaliser and a blind carrier frequency offset estimator is introduced. Furthermore, convergence speed of the proposed algorithm is increased by introducing an affine projection scheme, and steady state MSE is lowered by adopting a concurrent FIRMER-CMA and decision directed (DD) mode. A system relying on both latter principles is derived whereby substantial performance improvements can be gained over either technique on its own. Finally, a significant gain in data rate and spectrum efficiency is achieved by adopting a new homogeneous burst type and a semi-blind approach based on the proposed algorithm for the UMTS TDD component.</p
... Wireless communications networks enable the provision of both mobile and fixed services to serve a variety of commercial and business applications and services. Nowadays, third generation (3G) mobile cellular systems [3]- [5] have enabled access to advanced services, such as video communications, multimedia, and high-speed internet access. Typical example of 3G standards is the Universal Mobile Telephone System (UMTS) [3]- [5], especially supplemented with High-speed Downlink Packet Access (HSDPA) [6], [7]. ...
... Nowadays, third generation (3G) mobile cellular systems [3]- [5] have enabled access to advanced services, such as video communications, multimedia, and high-speed internet access. Typical example of 3G standards is the Universal Mobile Telephone System (UMTS) [3]- [5], especially supplemented with High-speed Downlink Packet Access (HSDPA) [6], [7]. In addition, Fixed Wireless Access (FWA) [8]- [10] communications systems attempt to provide a set of reliable, cost-effective and secure communications services in case where existing wired infrastructure is impractical, expensive or temporary. ...
... The angles n T a and n R a denote the azimuth angle of departure (AoD) of the waves that impinge on the scatterer n S and the azimuth AoA of the waves scattered It is assumed that ,max S R is much smaller than D, i.e., ,max S R D. 3 Then, one ...
High altitude platforms (HAPs) are one of the most promising alternative infrastructures for realizing next generation high data-rate wireless communications networks. Considering the continuous demand for enhanced spectral efficiency, increased channel capacity, and improved link reliability, multiple-input multiple-output (MIMO) technology is the leading candidate for future communications systems. The development of MIMO-based communications networks depends on a proper characterization and modeling of the propagation channel. To enable the successful design and performance evaluation of broadband wireless HAP-MIMO systems, this doctoral thesis focuses on modeling of HAP-MIMO channels.
Novel three-dimensional (3-D) geometry-based reference models for Ricean fading channels are proposed that encompass narrowband and wideband HAP-MIMO channel scenarios with line-of-sight (LoS) and non-line-of-sight (NLoS) connections at L and S frequency bands licensed for mobile communications through HAPs. From these models, the statistical properties and the capacity performance are analytically and thoroughly studied in terms of various parameters, such as the elevation angle of the platform, the antenna array configuration, the Doppler and delay spread, and the 3-D non-isotropic distribution of the local scatterers. Using the theoretical expressions one can easily evaluate numerically the HAP antenna inter-element spacing required to achieve uncorrelated responses in the HAP-MIMO channel matrix.
Moreover, novel 3-D deterministic and statistical simulation models for HAP-MIMO channels based on the reference narrowband and wideband models are developed by using the sum-of-sinusoids (SoS) method, which has been widely accepted by academia and industry. The efficiency, the accuracy, and the complexity of these models are thoroughly investigated with respect to the statistical properties. The results indicate that the proposed simulation models yield high-performance and satisfactorily approximate the statistical properties of the reference models.
Finally, a novel geometrical design approach to construct high-capacity HAP-MIMO communications systems in LoS propagation environments is proposed, considering the Ka and V frequency bands licensed for fixed broadband communications through HAPs. In these mm-wave frequencies, the rain has a significant effect on the quality of the link. The potential channel capacity gain of the optimized LoS-HAP-MIMO architecture is investigated, under clear sky and rain conditions.
The proposed models for HAP-MIMO channels would provide other researchers a convenient framework and guidelines for the characterization, analysis, test, and design of future mobile and fixed HAP-MIMO communications systems.
... Direct-sequence/code-division multiple access (DS/CDMA) has been widely used in multiuser cellular wireless communications (e.g., 2G, 3G, and ultra-wideband systems) due to efficient spectrum utilization, release from frequency management, low mobile station's transmit power through power control [1], and high multipath resolution, and so forth [2][3][4][5][6][7][8]. With growing demands for multimedia services in wireless communication systems, there has been a need to provide a platform of high-speed multirate for the transmission of image, video, voice, and data such as variable chip rate (VCR), variable processing gain (VPG) (which is also called variable sequence length), and multicode (MC) DS/CDMA systems [9][10][11][12][13][14][15][16][17]. ...
... For MC systems, high-rate users are accommodated by multiplexing their data sequences onto several commonrate data sequences (virtual users) through subsampling, and then a distinct spreading sequence is assigned to each virtual user, and these spreading signals are superimposed before transmission [12,13]. The VPG and MC access schemes have been adopted for 3G wireless communication systems [4,5]. ...
... where w[n] is a white Gaussian noise vector, (R1) One can observe, by (4) and (17) to (23), that h (l) i j,−1 = 0 P+q for all 2 ≤ l ≤ N i and h (l) i j,1 = 0 P+q for 1 ≤ l ≤ N i − 1 for the VPG system. Therefore, by removing these zero column vectors in H , the channel matrix H reduces to a (P+q)×(K+2K) matrix instead of a (P+q)×(3K) matrix, and then the associated signal vector u[n] consists of only (K +2K) (≤ 3K) components out of all the 3K sources ...
... However, MT-CDMA suffers from inter-subcarrier interference due to the fact that the subcarriers are not orthogonal to each other. Since MC-DS-CDMA is capable of providing backward compatibility with the existing IS-95 DS-CDMA system, a specific form of MC-DS-CDMA has been chosen as one of the Third Generation (3G) mobile communication standards [312]. ...
... Part II of the book concentrated on investigating the MC-CDMA scheme of [70,71,73], which constitutes a specific family of the three different multi-carrier CDMA types often used in the literature [90]. This technique was advocated, because MC-CDMA results in the lowest BER among the three schemes investigated in a similar scenario [312]. Our investigations concentrated on the downlink, because in the uplink stringent synchronisation of the mobile terminals has to be met. ...
... 16(b) gives an overview of the resulting BER per subcarrier for the data-bearing subcarriers for SNR values from 0 dB up to 50 dB. It can be seen that the residual bit errors are concentrated in four bursts, comprising the six symbols with subcarrier indices136,137,312,401, 477, and 478. At 50 dB SNR the symbols in the outer two bursts have a bit error rate of 1/3, corresponding to one bit error per D8PSK symbol. ...
IntroductionPrinciples of QAM-OFDMModulation by Discrete Fourier Transform [165, 166]Transmission via Bandlimited ChannelsGeneralised Nyquist CriterionBasic OFDM Modem ImplementationsCyclic OFDM Symbol ExtensionReducing MDI by Compensation [15]Decision-Directed Adaptive Channel EqualisationOFDM Bandwidth EfficiencyChapter Summary and Conclusion
... Harry Nyquist, working in the early 1920s on optimizing the performance of telegraph systems, published a paper in 1924 [1], which defines optimum signal shapes to be used over band limiting telegraph wires. Nyquist inter symbol interference (ISI) criteria, as well as his 1928 published sampling theorem [2], are the foundations in all of today's communication systems [3], [4], [5], [6], [7]. ...
... At stage-I, a fully connected neural network, based on the principle in (5), is trained to approximate signals using the training data. To ensure a low-complexity architecture, the neural network at Stage-I is designed without any hidden layers and only input and output layers are stacked. ...
Signal waveform is the basic physical layer element that fundamentally determines the most important key performance indicator in communication systems, namely spectral efficiency. Traditional waveforms rely on orthogonal Nyquist shaping but result in restricted spectral efficiency. Non-orthogonal waveforms have been proposed to enhance spectral efficiency via compressing either time or frequency resources. However, beyond 25% efficiency improvements in this way, classical Mazo theory states that performance will start to degrade. Here we use a robust and low-complexity neural network modulator to create asymmetric sub-carrier shapes, for multi-carrier non-orthogonal frequency shaping (NOFS) signals. The result is a non-Nyquist waveform which achieves 150% spectral efficiency improvement and still operates well with simple receiver processing. We set up a hardware communication link with over-the-air image transmission that practically validates the spectral efficiency improvement. This spectral efficiency will save communication resources for future communications systems such as 6G services.
... In the downlink scenario of spread spectrum systems several spreading codes may be simultaneously assigned to one user in order to support a high data throughput [42]. A specific example of this concept, namely a multi-code MC-CDMA scheme, was introduced in Section 4.5.1. ...
... The thesis concentrated on investigating the MC-CDMA[1, 2, 35] scheme, which is one of the family of three different multi-carrier CDMA techniques[42]. This technique was advocated, becauseMC-CDMA results in the lowest BER among the three schemes investigated in a similar scenario [42]. Our investigations concentrated on the downlink, because in the uplink stringent synchronisation of the mobile terminals has to be met. ...
p>Multi-Carrier Code Division Multiple Access (MC-CDMA) exploits the joint benefits of Direct-Sequence (DS) CDMA and Orthogonal Frequency Division Multiplexing (OFDM). Hence, MC-CDMA exhibits high spectral efficiency and substantial benefits from the frequency diversity provided by frequency selective fading channels. This dissertation investigates several aspects of MC-CDMA. Firstly, the Peak-to-Average Power Ratio (PAPR) of the MC-CDMA signal is analysed. It was shown that the PAPR is characterised by the aperiodic correlation properties of the spreading sequences employed. Several orthogonal spreading codes were investigated in terms of their PAPR and it was found that the PAPR can be upper bounded by 3dB when employing orthogonal complementary codes in the context of low number of sub-carriers. Secondly, the application of adaptive modulation to MC-CDMA was studied. The optimum mode switching levels for generic adaptive modulation schemes were derived first and then, the performance of adaptive-modulation assisted MC-CDMA was analysed for transmission over various propagation scenarios. When space-time block codes were combined with adaptive-modulation assisted MC-CDMA, as expected the SNR gains of adaptive modulation over fixed-mode modems were found to decrease. Lastly, three types of reduced-complexity despreading schemes were proposed with an application to MC-CDMA in mind and the BER performance as well as the achievable complexity reduction were investigated.</p
... The relationship between the chip rate, R c , roll-off factor, cc, and channel separation, Af, is given by (7) The channelization codes for the forward link from cell to mobile station are the modified Walsh codes, which are variable-length orthogonal sequences. For the reverse link from mobile station to cell, the codes are also variable-length orthogonal sequences. ...
... This section briefly describes the development of CDMA communication systems based on the channelization schemes proposed in Section 5. Figure 6 illustrates a proposed transceiver for the mobile terminals. The architecture for the mobile terminal transceiver is very similar to the one being used by the CDMA-IS-95 system [7,10]. Figure 7 presents the satellite payload architecture for the baseline channelization scheme shown in Figure 4. ...
Recently, a satellite-based system has been proposed in [1] that integrates mobile communication and navigation (NavCom) capabilities using the Code Division Multiple Access (CDMA) concept. This paper describes various communication architectures using wideband CDMA 2000+ standards for NavCom systems. Estimates of weight and power along with the link performance are presented for these architectures. Link performance for various propagation conditions, satellite antenna sizes, and mixed services with different data rates are presented. Effects of coding schemes, such as convolutional code and Turbo code, Adjacent Channel interference (ACl), and nonlinear power amplifier on the communications link are included in the link performance evaluation. In addition, a brief description of the mobile-satellite communications propagation model is also discussed.
... In this context, it is worth mentioning that orthogonal multiplexing/transmission has been the key to the wireless communications realm regardless of ever-increasing interference sources. In particular, frequency division multiplexing (FDM), time division multiplexing (TDM), code division multiplexing (CDM), and lastly orthogonal frequency division multiplexing (OFDM) represent the basic signal formats that have been used and modified within the industry of wireless communications up to 4G [47]. ...
Interference represents one of the most common barriers for the wireless communications society to bring the fully connected world to life, where everybody and everything is connected at any time, aiming to support a wide range of services and applications with increasing demand in terms of data rate with a higher degree of reliability and security, while keeping an affordable overall system capacity, complexity, and latency. Essentially, interference clearly explains the primitive nature of the wireless communications systems, where there is always an unwanted physical signal that disrupts the communication link, occurring from the physical layer (PHY) architecture of transmission signal, its interaction with the wireless channel and transceiver architecture in particular. Therefore, in past wireless technologies, waveform design along with wireless channel impairments and handset architecture define the main sources of interference, leading to inter-symbol interference (ISI), inter-carrier interference (ICI) and co-channel interference (CCI) types. In this line, recent advances in wireless technologies have revealed unprecedented interference types including inter-numerology interference (INI), inter-antenna interference (IAI), inter-waveform interference (IWI), cross-link interference (CLI) and inter-Doppler interference (IDI), while additional unique interference types are expected in near future. Consequently, a broader view of the interference has become a crucial need in order to avoid and relax its impact towards beyond 5G radio access technologies. Despite the extensive research in the literature performed by academia and industry, to the best of the authors’ knowledge, there is no work that provides a comprehensive taxonomy framework of interference sources and types, and a review of management techniques from the perspective of the PHY layer. This work aims to fill this gap in the literature. With this notation, in this survey, we propose an intuitive, generic, and expandable framework that categorizes the interference sources and their corresponding management solutions. In particular, we split the interference sources into two main groups by taking into account the user of interest such as self-user-interference (SUI) and other-user-interference (OUI), which we further classify considering the user’s intention about the presence of interference named intentional SUI (I-SUI), unintentional SUI (U-SUI), intentional OUI (I-OUI), and unintentional OUI (U-OUI). In line with this, we offer a classification of the interference management techniques regarding the source of interference. Lastly, the survey presents open research perspectives for beyond 5G wireless systems and concluding remarks.
... Harry Nyquist, working in the early 1920s on optimizing the performance of telegraph systems, published a paper in 1924 1 , which defines optimum signal shapes to be used over band limiting telegraph wires. Nyquist inter symbol interference (ISI) criteria, as well as his 1928 published sampling theorem 2 , are the foundations in all of today's communication systems [3][4][5][6][7] . ...
Signal waveform is the basic physical layer element that fundamentally determines the most important key performance indicator in communication systems, namely spectral efficiency. Traditional waveforms rely on orthogonal Nyquist shaping but result in restricted spectral efficiency. Non-orthogonal waveforms have been proposed to enhance spectral efficiency via compressing either time or frequency resources. However, beyond 25% efficiency improvements in this way, classical Mazo theory states that performance will start to degrade. Here we use a robust and low-complexity neural network modulator to create asymmetric sub-carrier shapes, for multi-carrier non-orthogonal frequency shaping (NOFS) signals. The result is a non-Nyquist waveform which achieves 150% spectral efficiency improvement and still operates well with simple receiver processing. We set up a hardware communication link with over-the-air image transmission that practically validates the spectral efficiency improvement. This spectral efficiency will save communication resources for future communications systems such as 6G services.
... A seguir apresentamos uma visão geral dos serviços a se considerar em futuros sistemas "wireless", segundo [Rape95], [Kni98a] Os sistemas de terceira geração, IMT-2000, liderado pela ITU e UMTS, da ETSI, vem sendo amplamente discutidos, tendo como principais propostas para padronização, os sistemas cdma2000 (americano) e WCDMA (europeu). Uma comparação dessas propostas, incluindo, também, as características da interface de segunda geração IS-95 pode ser encontrada em [Ojan98] e [Kni98a]. Referências adicionais sobre o assunto são: [Dahl98], [Fuka96], [Adac98] e [Kni98b]. ...
The objective of this work is to study multi-rate DS/CDMA systems, an important access technology for the third generation mobile systems, which specifications have been discussed internationally. The work focuses on capacity and resource optimization aspects of this system. From user specifications, as maximum transmission power and minimum rate and quality of service (QoS) requirements in a multi-class environment, a capacity expression is derived, which can be optimized to result the minimum total transmission power solution or the maximum total throughput one, as was investigated, initially for a single cell, next for multi-cell environment. Furthermore, the work studied a modification in the multi-rate CDMA transmission scheme (single-user detection with all users transmitting at same time) that proposes to time schedule the signals of delay-tolerant users and also maximize their rates in this situation, resulting throughput gains, when compared with the conventional transmission mode. These throughput gains were also compared with the ones obtained with SIC (Successive Interference Cancellation) multi-user approach, which was also modelled in this work.
... A third access method is known as Code Division Multiple Access (CDMA) [36]. In a CDMA system, the available spectrum is not channelized in frequency or in time as that in FDMA and TDMA systems, respectively. ...
... Long spreading (scrambling) codes have been included in several leading standard proposals for 3G cellular networks [13,14]. The use of long codes ensures that all the users achieve on the average the same performance. ...
In this thesis, we study iterative detection, decoding and channel parameter estimation algorithms for asynchronous direct-sequence code division multiple access (DS-CDMA) systems employing orthogonal signalling formats and long scrambling codes. Multiuser detection techniques are widely used to combat the detrimental effects of multipath fading and multiple access interference (MAI), which are the major impairments in CDMA communication systems. Although the emphasis is placed on nonlinear interference cancellation schemes, several linear interference filtering techniques are also discussed in the first part of the thesis. The multi-stage parallel interference canceler (PIC) is evaluated analytically and compared with simulation results. To prevent performance degradation of PIC due to error propagation, some soft cancellation schemes using soft decision feedback are presented. Most multiuser detectors rely on accurate channel information, which needs to be estimated in practice. For the purpose of channel estimation, both classic and Bayesian methods are considered in this thesis, depending on whether prior knowledge about the parameters to be estimated is available or not. We focus on the decision directed approach when estimating the fading channel gains. That is, the receiver estimates the channel parameters based on the detected data, no training sequences are needed. The estimated channel coefficients are also used to regenerate the signal of each user for the purpose of interference cancellation. Another essential channel parameter to be estimated is the propagation delay. Many studies show that multiuser detectors need very accurate delay estimates to perform well. We propose some suboptimal synchronization algorithms that achieve good acquisition performance in presence of MAI and have reduced complexity compared to the optimum maximum likelihood estimator. In the second part of the thesis, we employ the turbo processing principle and study iterative demodulation and decoding of a convolutionally coded and orthogonally modulated asynchronous DS-CDMA system. Several iterative schemes based on soft demodulation and decoding algorithms are presented. The performance of different strategies are evaluated and proved to achieve substantial performance gains compared to the conventional hard decision based scheme, iii especially when the soft demodulator is assisted by decision directed channel estimation and interference cancellation techniques, and also when demodulation and decoding are performed jointly in an iterative manner. It is also shown that iterative decoding with properly corrected extrinsic information or with non-extrinsic/extrinsic adaptation enables the system to operate reliably in the presence of severe multiuser interference. Additional gain is noticed when soft information rather than hard decision feedback is used for channel estimation and interference cancellation.
... Hence the signals are spread over the complete bandwidth. Supporting bandwidth on demand (BoD) service [5]. Hence a narrow band (data) code modulates a wide band code (PN-sequence), resulting into a noise like wide band signal and then undergoes phase shift keying [1]. ...
The performance of any communication system is assessed by its bit error rate (BER). Energy to Noise ratio plays an important role in evaluation of a communication system. The application of chaos based communication system is very popular. To check the relationship between energy to noise ratio and BER, WCDMA downlink simulation model as per 3gpp specification is used with chaos codes along OVSF spreading codes. Simulation is done in the presence of an additive white Gaussian noise (AWGN) channel along with QPSK modulation. The simulations and Bit Error Rate (BER) evaluation with respect to Energy-To-Noise ratio are performed using MATLAB.
... In these systems, a large variety of users have a wide range of high-speed data rate service. So, these systems are required to have large capacity, ability to transfer data with various rates, and flexibility to support a wide range of environments [1], [2]. IMT-2000 systems will support voice, video,and low to high speed data services. ...
As mobile communication systems have been widespread and the needs for new service grows, IMT-2000 systems have largely been researched and developed for standardization. Among them, Wideband CDMA (WCDMA) solution is standardized in the 3rd Generation Partnership Project. In WCDMA system, voice and high data rate services are supported through dedicated traffic channels, however other packet based services with short duration are provided by using common channels. Data users are allowed to transmit a short message based on a contention manner via the reverse common channels. The basic Common Packet Channel (CPCH) mechanism has been proposed and adopted for accessing common channels. It consists of three phases: Random Access Phase, Collision Resolution Phase, and Data Transmission Phase. To enhance the resource usage efficiency, the CPCH mechanisms with channel assignment or status monitoring have been proposed. They can improve the performance. however increase the system complexity. Up to now, performances of the CPCH mechanisms have been discussed and studied based on computer simulations. Numerical results have been obtained by using S-G analysis, but they are different from simulation results. In this paper, we analyze the CPCH mechanisms by using the Equilibrium Point Analysis (EPA). And we compare computer simulation results with analytical results.
... The wireless module is responsible for communicating with mobile terminals within the coverage of a base station (i.e., cell ). The protocol between the base stations and the mobile terminals can be, but not restrict to, GSM [11], IMT 2000 [12] or IEEE 802.11 [2]. The function of the W/C converter is to interchange the data format (such as: modulation, cell format, and frequency spectrum) between the wireless module and the cable module. ...
The cable TV (CATV) network is an ideal backbone for PCS due to its prevalent and broadcast nature. This significantly reduces the implementation costs and the handoff overheads. This paper proposes two architectures for the CATV-based PCS system. In the first architecture, each base station is equipped with multiple fixed receivers to provide fast and seamless handoffs for mobile users. Nevertheless, the hardware cost for this implementation is relative expensive. To overcome this, in the second architecture, each base station is equipped with only one tunable receiver. This simple and economic architecture suffers from the possibility of offset conflict when mobile terminals handoff between cells. Three offset assignment algorithms based on the concepts of random assignment, neighbor usage, and clustering, respectively are proposed to solve the offset conflict problem. Simulation results indicate the one with the concept of clustering performs much better than the other two schemes in terms of offset conflict probability.
... The general trend CDMA IS-95 A works on " GSM, IS-95 B works on GPRS and 1XRTT/3XRt CDMA2000 works on W-CDMA and the technology that worked behind all these standards are TDMA, EDGE and UWC- 136 " [1]. Although the air interface is significantly different in the case of CDMA compared with the TDMA technique, the core fixed network infrastructure that supports the wire interface is very similar to the structure of the GSM core network [4]. In fact, the core networks for North American CDMA and TDMA systems are more or less identical [5] ...
This work deals on simulation and evaluation of the performance of physical layer of wireless communication system of CDMA-2000 requirement using radio configuration-3 under forward fundamental channel 1x in terms of bit error rate (BER) by using MATLAB 7.9.0 (2009b). Built-in functions in MATLAB 7.9.0(2009 b) version was used to achieve this. A signal simulator was employed according to the physical layer requirement of the IMT-2000 CDMA system. The data was transmitted in a frame by frame basis through a time-varying channel. The transmitted signal was degraded by AWGN at the front end of the receiver. A rake receiver was employed at the receiver in order to down samples and de-correlates pilot bits and data. On the basis of simulated result of CDMA2000 Physical layer under AWGN channel it was found out that at gated transmission rate of (1/4) a better system performance was obtained looking at the BER than that at gated transmission rate of (1/2).
... The general trend CDMA IS-95 A works on "GSM, IS-95 B works on GPRS and 1XRTT/3XRt CDMA2000 works on W-CDMA and the technology that worked behind all these standards are TDMA, EDGE and UWC-136" [1]. Although the air interface is significantly different in the case of CDMA compared with the TDMA technique, the core fixed network infrastructure that supports the wire interface is very similar to the structure of the GSM core network [4]. In fact, the core networks for North American CDMA and TDMA systems are more or less identical [5]. ...
This work deals on simulation and evaluation of the performance of physical layer of wireless communication system of CDMA-2000 requirement using radio configuration-3 under forward fundamental channel 1x in terms of bit error rate (BER) by using MATLAB 7.9.0 (2009b). Built-in functions in MATLAB 7.9.0(2009 b) version was used to achieve this. A signal simulator was employed according to the physical layer requirement of the IMT-2000 CDMA system. The data was transmitted in a frame by frame basis through a time-varying channel. The transmitted signal was degraded by AWGN at the front end of the receiver. A rake receiver was employed at the receiver in order to down samples and de-correlates pilot bits and data. On the basis of simulated result of CDMA2000 Physical layer under AWGN channel it was found out that at gated transmission rate of (1/4) a better system performance was obtained looking at the BER than that at gated transmission rate of (1/2).
... The general trend CDMA IS-95 A works on " GSM, IS-95 B works on GPRS and 1XRTT/3XRt CDMA2000 works on W-CDMA and the technology that worked behind all these standards are TDMA, EDGE and UWC- 136 " [1]. Although the air interface is significantly different in the case of CDMA compared with the TDMA technique, the core fixed network infrastructure that supports the wire interface is very similar to the structure of the GSM core network [4]. In fact, the core networks for North American CDMA and TDMA systems are more or less identical [5] ...
This work deals on simulation and evaluation of the performance of physical layer of wireless communication system of CDMA-2000 requirement using radio configuration-3 under forward fundamental channel 1x in terms of bit error rate (BER) by using MATLAB 7.9.0 (2009b). Built-in functions in MATLAB 7.9.0(2009 b) version was used to achieve this. A signal simulator was employed according to the physical layer requirement of the IMT-2000 CDMA system. The data was transmitted in a frame by frame basis through a time-varying channel. The transmitted signal was degraded by AWGN at the front end of the receiver. A rake receiver was employed at the receiver in order to down samples and de-correlates pilot bits and data. On the basis of simulated result of CDMA2000 Physical layer under AWGN channel it was found out that at gated transmission rate of (1/4) a better system performance was obtained looking at the BER than that at gated transmission rate of (1/2).
... En Europe, quatre interfaces radio candidates ont été étudiées, toutes basées sur des techniques d'accès multiple différentes présentées dans [OP98a]. L'une d'elles, basée sur l'OFDM (Orthogonal Frequency Division Multiplexing) a été rapidement abandonnée du fait de son importante complexité et de sa relative inadéquation à un environnement d'accès multiple non 4 Gaussian Minimum Shift Keying 5 Modulation De Phase à 8 états. ...
UMTS is a new radiocommunication standard aimed at solving today's second generation networks' problems that are local saturation and slow bitrates. UMTS and previous networks sharing close to nothing regarding the radio link, network equipments as well as user equipments must be rebuilt from scratch. User equipments, in particular, must embed a lot more processing power than their older counterparts. After having introduced UMTS and the first to-be-deployed of its radio interfaces, the Wideband CDMA, we determined that the channel estimation prior to the Rake combining, assuming the receiver uses this well-known receiver structure, is the most complex task to be performed by the user equipment. An algorithmic solution to this problem is proposed through an iterative channel estimation algorithm which suppresses identified paths before trying to find new ones in the considered time window. This algorithm has a major drawback : its computational complexity varies quadratically with the oversampling factor, and thus forbids to work with high oversampling factors, which are the key to a precise channel delay estimation. An optimized version of this algorithme is proposed, whose complexity scales linearly with the oversampling factor, against a quadratic variation for the original one, and who does not cause a noticeable performance loss. The optimized channel estimation algorithm is therefore suitable for a constrained environment such as a user equipment. Furthermore, the performed optimization has the side effect of making the proposed algorithm much more suitable for a hybrid hardware-software implementation than for a pure software one. A system-level design flow is then proposed to realize this hybrid architecture while kee- ping a fast prototyping approach in mind. This methodology revolves around CoWare's N2C environment and uses a superset of the C language called CoWareC. CoWareC includes several constructs needed to describe partitionned systems and hardware structures. The proposed al- gorithm is mapped onto a hybrid architecture composed of a ST100 DSP core and a hardware coprocessor. Due to major software issues, this hybrid implementation could not be developped following the proposed methodology, but interesting results were nonetheless obtained from a pure software implementation. The application of the first steps of the proposed methodology to the channel estimation algorithm yielded interesting results and suggestions for the improve- ment of the N2C tool. Then, hints are given for the development of a real hybrid prototype and the adequation of the proposed methodology to a fast prototyping environment is discussed.
... The basis for any mobile system is its air interface design, and particularly the way the common transmission medium is shared between users, that is, multiple access scheme [12]. Multiple access scheme defines how the radio spectrum is divided into channels, and how the channels separate the different users of the system. ...
The performance of DS-CDMA cellular radio networks, such as UMTS, is highly dependent on the amount of interference in the system. High interference reduces cell size and increases the outage probability of mobile users. Interference is increased as the number of admitted users grows in the system. This means that there is a trade-off between capacity and coverage and between capacity and quality of service (QoS). The system load is controlled by the radio resource management (RRM). The optimization and adaptivity of RRM is of great importance both for the operators and for manufacturers, since RRM has a lot to answer for when it comes to the stability and the utilized capacity of mobile network. In this thesis, uplink admission control and closely related concepts such as CDMA and RRM are studied. The focus is on interference based admission control. A strategy to improve the system effectiveness in terms of QoS, by tuning the threshold limiting the total amount of received uplink power, is proposed. The impact of the proposed autotuning algorithm on the system performance is investigated by system simulations. Both real time circuit switched speech traffic and non-real time interactive packet traffic is studied. The quality indicators used are call blocking probability, bad call probability and call dropping probability. These quality indicator...
... Moreover, in January 1998 ETSI (European Telecommunications Standards Institute) decided to specify two air interfaces for the European candidate of the 3rd generation mobile telecommunications systems: UMTS (universal mobile telecommunications system). The UMTS terrestrial radio access (UTRA) is divided into a FDD and a TDD mode [38]. The UTRA-TDD mode employs a hybrid form of CDMA and TDMA [39] which is referred to as TD-CDMA [40]. ...
... The upcoming wireless cellular infrastructures such as third generation (3G and fourth generation (4G) are deemed to support bandwidth requirements, faster data rates with different quality of services for multimedia applications. Wideband Codedivision multiple accesses (WCDMA) has emerged as one of the most promising multipleaccess techniques for future wireless multimedia networks and has been selected for IMT-2000 systems by standardization bodies all around the world [1].Compared to the narrow-band CDMA, wideband CDMA can support services with much higher rate. It is also flexible to deliver multimedia traffic. ...
This article presents a survey on medium access control protocols for wireless multimedia networks. Abasic overview of MAC protocol concepts is presented, and a framework is developed for comparisons.The MAC protocols covered in this article include Random Access protocols, Contention less protocols,TDMA CDMA, third-generation WCDMA schemes and Hybrid protocols proposed for wirelessMultimedia Networks. The operation of each protocol is explained, and its advantages and disadvantagesare presented. Finally, a qualitative comparative outline of the discussed protocols is provided.
... Mobile learning is a distance learning combined with modern mobile communication technology [1]. The use of mobile terminal equipment in mobile learning is the progress of distance learning technology, at the same time due to the personalization introduced by mobile learning such as scene interaction, wireless communication, time space randomness， it has many differences compared with the distance learning relying on wired network and the portable terminal device. ...
Augmented reality can create a learning environment to learners, combining the actual condition of let them around to see the real environment at the same time, also can see a computer, virtual information generated by mobile phones as the implementation of the augmented reality application platform, due to the mobility, portability, and human-computer interaction, etc, has strong advantage, and therefore more mobile learning application prospect, this paper discusses the structure of augmented reality based on mobile phone key technology and main function features, on the basis of to augmented reality based on mobile phone and its application in mobile learning has a deeper understanding.
... But the UAV as a relay platform needs to meet the following requirements: first, it needs to have a large throughput and high speed to ensure real-time network; second,it needs to have a good anti-jamming capability to ensure the reliability of the network. Most communication system designs try to either reduce or avoid interference (e.g., through receiver design or transmission scheduling [2]). However, instead of treating interference as a nuisance to be avoided, we can actually embrace interference to improve throughput performance. ...
In order to improve the network throughput and anti-jamming capability of UAV communications, physical layer network coding is applied in the UAV communications. Simulation results show that: the use of physical layer network coding can not only improve network throughput greatly, reduce the error rate of communication, but also enhance its anti-jamming capability,which satisfy UAVs’ requirements in modern warfare.
... Transmission solutions have been developed to deal with the problem aforementioned by avoiding interference or reduce the interference received. These techniques include the use of Request to Send (RTS) and Clear to Send (CTS) transmissions [3], scheduling transmissions or designing the receiver interface so as to limit the interference received [4]. In order to increase the throughput harnessed by the network, network coding schemes on the bit level [5]- [7] has been devised to maximize the use of the non-interfering transmissions by encoding multiple frames or packets in one transmission from the sending node. ...
In this paper, PNCR, a routing framework based on Physical Network Coding is proposed. PNCR enables shared utilization of the channel during the broadcast and multiple access phases of transmissions. These additional transmission opportunities can be observed as performance gains in terms of less packet delays and better network throughput. In this paper, we discuss the details of our proposed framework to utilize the virtues presented by Physical Network Coding. Existing work on Physical Network Coding is theoretic and does not present itself as a tool for multi-hop network deployment except for limited network topologies. Our work in this paper is an effort to utilize such techniques for networks of arbitrary structure. We evaluate the performance of our proposed framework using simulations and show that it achieves better throughput and less delivery delay per packet than conventional wireless routing solutions without Physical Network Coding.
As a result of mass digitization during the pandemic, businesses were able to automate business processes, giving people and brands a deeper connection. A proactive strategy, however, is the next step for organizations to implement AI during crisis situations by going one step further. In spite of this, most organizations still do not adequately address this growing problem. After Covid outbreaks, consumer behavior is unlikely to return to pre-pandemic levels. Consumers will increasingly buy goods and services online, and more people will work remotely. In the post-Covid-19 world, as economies slowly begin to open up again, artificial intelligence (AI) will be extremely valuable as companies begin to adapt to the new environment. Similar to other global crises, several major trends that were already underway before Covid are likely to accelerate as a result of the pandemic. Companies must continue to invest in artificial intelligence initiatives during the recovery phase. A conceptual framework for marketing and user engagement is presented in this paper that uses artificial intelligence and automation in ways that are user-centric, integrating traditional marketing practices into an overarching framework that can be implemented by structured artificial intelligence. Embedded technologies, artificial intelligence, and automation have had a significant impact on the four Ps of marketing and will continue to do so.
This paper aims to examine how mobile applications relate to learning and development. It will determine whether these two factors are properly intertwined and whether these two factors are fully justified in being related. As a result of examining the literature, and reviewing the results of our survey, we have developed a framework for research. This framework will provide evidence that mobile technologies have a positive impact on classroom performance both directly and indirectly. These technologies foster the learning and development process at all levels, which ultimately enhances the individual's competency by equipping him or her with a more comprehensive skill set. A total of one hundred and eighty interviews were conducted with educators during the research process. These interviews were conducted to develop the findings presented in this article on the impact of mobile applications in the classroom as a result of the research process. There is a growing body of research that suggests the use of mobile apps can be an effective tool for fostering creativity, learning, and development in a variety of settings, both formal and informal. They have been shown to be beneficial in a number of ways when it comes to promoting learning and development. When compared to traditional methods of teaching, mobile apps have shown to be more effective in promoting holistic learning and increasing learning speed than traditional methods of teaching, especially when it comes to promoting holistic learning and increasing learning speed. With the introduction of mobile applications to the education sector, many novel learning strategies have been developed within this sector as a result of the introduction of mobile apps. The use of mobile devices in the classroom has resulted in a number of changes in this respect. The use of mobile apps can provide students with a variety of games that are designed to encourage them to engage in a positive thought process as well as allow them to gain a deeper understanding of what they are learning as they interact with the games and become engaged with them on a more personal level. "Mobile learning" refers to the use of mobile devices and apps in order to facilitate the learning process in an attempt to facilitate the learning process mobile devices and apps in order to facilitate the learning process. The term may also refer to the way in which mobile technology can be used to support a continuous learning environment.
p>This thesis investigates the employment of Radial Basis Function (RBF) networks in the context of multilevel channel equalisation. The RBF-based Decision Feedback Equaliser (DFE) was found to outperform the conventional DFE at the cost of an increased computational complexity. The RBF DFE was studied in the context of a wideband Burst-by-Burst (BbB) Adaptive Quadrature Amplitude Modulation (AQAM) scheme, where the modulation modes of no transmission (NOTX), Binary Phase Shift Keying (BPSK), 4-QAM, 16-QAM and 64-QAM were invoked by the transmitter, depending on the prevalent channel quality. The 'short-term BER' of the received burst quantifies the channel quality, which was used as the mode switching criterion in order to switch between different modulation modes. The Bit Per Symbol (BPS) throughput improvement for the proposed AQAM scheme designed for a target Bit Error Rate (BER) of 1% was up to a factor of two in comparison to the fixed constituent modulation modes.
The logarithmic version of the RBF equaliser referred to as the Jacobian RBF equaliser was derived, which has a reduced computational complexity. Turbo codes were invoked for improving the BER and BPS performance of the BbB AQAM scheme. The Jacobian RBF equaliser provides a logarithmic-domain output, which can be used to provide soft outputs for the channel decoder. We proposed employing the average magnitude of the Log-Likelihood Ratio (LLR) of the bits in the received burst as the channel quality measure for our adaptive scheme. The system exhibited a better BPS performance, when compared with the uncoded AQAM/RBF DFE system at low to medium channel SNRs and also showed an improved coded BER performance at higher channel SNRs.</p
In this paper, we present a method to detect and identify mobile network signals. The method relies on features extracted from the power spectral density of the signals. The performance of the proposed method is evaluated using over-the-air measurements acquired in various cellular bands, in different geographical areas, and in rural and urban settings. Results verify the high detection and identification accuracy of the method.
Bridging the gap between the video compression and communication communities, this unique volume provides an all-encompassing treatment of wireless video communications, compression, channel coding, and wireless transmission as a joint subject. WIRELESS VIDEO COMMUNICATIONS begins with relatively simple compression and information theoretical principles, continues through state-of-the-art and future concepts, and concludes with implementation-ready system solutions. This book's deductive presentation and broad scope make it essential for anyone interested in wireless communications. It systematically converts the lessons of Shannon's information theory into design principles applicable to practical wireless systems. It provides in a comprehensive manner "implementation-ready" overall system design and performance studies, giving cognizance to the contradictory design requirements of video quality, bit rate, delay, complexity error resilience, and other related system design aspects. Topics covered include • information theoretical foundations • block-based and convolutional channel coding • very-low-bit-rate video codecs and multimode videophone transceivers • high-resolution video coding using both proprietary and standard schemes • CDMA/OFDM systems, third-generation and beyond adaptive video systems. WIRELESS VIDEO COMMUNICATIONS is a valuable reference for postgraduate researchers, system engineers, industrialists, managers and visual communications practitioners. © 2001 by the Institute of Electricaland Electronics Engineers, Inc. All rights reserved.
The coherent RAKE reception of wideband code division multiple access (Wideband CDMA) signals with complex spreading is considered in this chapter. A general multipath-fading channel model is assumed. A dedicated pilot channel, which is separate from data channels, is used for the purpose of channel estimation. Based on a digital implementation, the coherent demodulation scheme is presented. Pilot channel estimation error due to multiple access and multipath interference is studied. System performance is evaluated by means of bit error rate. The analysis shows that the error of channel estimation significantly degrades system performance and can be effectively suppressed by low pass filters (LPFs). A discussion on the envelope variation of complex spread signals is also included, which illustrates that the complex spread signal has more stable envelope than the dual-channel spread signal. The power ratio of pilot to data channels should be chosen in the range of 0.2 to 0.4 (−7 dB to −4 dB) in order to achieve maximum system capacity.
In this paper we propose a multistage nonlinear blind interference cancellation (MS-NL-BIC) receiver for direct-sequence code-division multiple-access (DS-CDMA) systems. The receiver uses higher order statistics of the received baseband signal. Specifically, we use the second and fourth moments of the received signal to determine a component of the received vector that has significant mean energy and low variability of the energy, both of which are favorable characteristics for application in an interference cancellation scheme that uses hard decisions. The structure of the receiver is multidimensional and can be viewed as a matrix of receivers. Each row in the matrix consists of receivers that perform (hard decisions) cancellation of successive components that have significant mean energy and low variability of the energy. The columns of the matrix essentially resemble multistage receivers that iteratively refine performance from earlier stages. Simulation results show that unlike linear receivers, the MS-NL-BIC is exceptionally efficient in systems with strong and highly correlated interferers, as may be the case in overloaded DS-CDMA systems.
A K-user multi-rate code is proposed for a Gaussian multiple access channel with binary inputs, equal-power, and symbol synchronisation. In this multi-rate transmission, K users are equally divided into M groups. For each user in the mth group, a rate-1/qm regular repeat-accumulate code serially concatenated with a length-Lm spreading is employed. The transmitted rate of each user in the mth group is 1/(qmLm). At the receiver, iterative joint decoding (IJD) and hybrid interference cancellation (HIC) schemes are considered. For each decoding scheme, a bivariate fixed-point analysis is applied to explicitly represent (qm,Lm) as a function of mutual information outputs. On the basis of these basic explicit representations, a united unreliable region is given, where users in at least one group are undecodable. The complementary set of the united unreliable region gives an optimal rate profile that achieves the maximum sum rate. Numerical results show that, for the IJD scheme with M increments, the maximum sum rate increases, approaches the Shannon limit, and exceeds that in conventional equal rate transmission. The maximum sum rate of the HIC scheme, which provides much lower decoding complexity than the IJD scheme, is superior to the conventional successive interference cancellation scheme.
This chapter describes the circuit design of two evolution versions of continuous-time opamp-RC low-pass filters that were implemented in this work as a part of two single-chip multicarrier UTRA FDD WCDMA base-station receivers. Hereafter UTRA FDD WCDMA is called simply WCDMA. The two opamp-RC low-pass filters that were designed, implemented, and measured and are included in this chapter are original work in this book, previously published in [1] and [2]. The corresponding versions of the multicarrier receiver IC implementations were previously reported with experimental results in [3] and [4]. To the best of the authors’ knowledge, the former is the first published single-chip multicarrier WCDMA receiver implementation. Since the main interest in this book is in the design and implementation of continuous-time low-pass filters for integrated radio receivers, rather than concentrating on stand-alone filter circuits, both multicarrier receiver implementations are also briefly presented in this chapter. Moreover, since the operation of the opamp-RC low-pass filters that were designed being embedded in a single-chip radio receiver affects the overall performance of the receiver, the experimental results of both the low-pass filters and the multicarrier receivers are shown at the end of this chapter. This chapter is mainly based on the contents of the four publications cited above.
CPCH is an uplink common channel that is used by 3GPP to support reliable packet transport. In this paper, we propose a new access scheme by using the discrimination of backoff timer for providing a prioritized service. We also present a simple system model of CPCH for EPA and use it to derive mathematical results. The results show that multi-class services with different priorities can be served effectively and easily by the proposed scheme.
In this paper, two types of multi-stage partial parallel interference cancellation (PIC) receivers are considered for multi-rate DS-CDMA system: multi-stage PIC receiver with partial cancellation factors and multi-stage PIC receiver with decision thresholds. Bit error rate (BER) of the multi-stage partial PIC receivers is obtained by simulation in a Rayleigh fading channel. It is shown that the multi-stage partial PIC receivers achieve smaller BER than the matched filter (MF) receiver, multi-stage PIC receiver, group-wise successive interference cancellation (GSIC) receiver, and extended GSIC receiver (EGSIC) for the multi-rate DS-CDMA system in a Rayleigh fading channel.
In this paper, a sub-optimal Rake receiver combined with a Wiener Filter is investigated for use in an indoor environment. Inner-Chip-interference is dominant when the application is indoors, so the inner-chip-interference rejection function becomes critical for the receiver. Pilot symbols in each slot are used for channel estimation and weight calculation of Rake combining through Wiener Filter. Compared to conventional combining which uses maximum ratio combining, Wiener combining using IRC (Interference rejection combining) achieves better ICI (Inner-chip-interference) rejection. This paper clarified that the sub optimal Rake receiver using Wiener Filter is 4 dB better than the conventional Rake receiver under the indoor application.
A novel stochastic gradient descent frequency-domain (FD) space-frequency (SF) semiblind multiuser receiver with an adaptive optimal mixing parameter is proposed to improve performance of FD semiblind multi-user receivers with a fixed mixing parameters and reduces computational complexity of suboptimal FD semiblind multiuser receivers in SFBC downlink MIMO MC-CDMA systems where various numbers of users exist. The receiver exploits an adaptive mixing parameter to mix information ratio between the training-based mode and the blind-based mode. Analytical results prove that the optimal mixing parameter value relies on power and number of active loaded users existing in the system. Computer simulation results show that when the mixing parameter is adapted closely to the optimal mixing parameter value, the performance of the receiver outperforms existing FD SF adaptive step-size (AS) LMS semiblind based with a fixed mixing parameter and conventional FD SF AS-LMS training-based multiuser receivers in the MSE, SER and signal to interference plus noise ratio in both static and dynamic environments.
Mobile Broadband: Including WiMAX and LTE provides an overview of IP-OFDMA technology, commencing with cellular and IP technology for the uninitiated while providing a foundation for OFDMA theory and emerging technologies, such as WiMAX, LTE, and beyond. Features include: A coherent and systematic discussion of all aspects of Mobile Broadband Wireless, Thorough information on OFDMA and All-IP Networking with its present technology in 4G, Information to assist industry professionals in understanding the convergence of core access networks, device convergence and service convergence. Throughout the book the author also discusses several wireless standards based on OFDMA such as UMB, IEEE 802.16j (Mobile Multihop Relay) and 802.16m (Gigabit WiMAX), IEEE 802.20 (MBWA), and IEEE 802.22 (Cognitive Radio). The book brings a good balance of theory, technology and practice of mobile broadband. © Springer Science+Business Media, LLC 2009. All rights reserved.
Wireless communications has witnessed a tremendous growth during the past decade and further spectacular enabling technology advances are expected in an effort to render ubiquitous wireless connectivity a reality. Currently, a technical in-depth book on this subject is unavailable, which has a similar detailed exposure of OFDM, MIMO-OFDM and MC-CDMA. A further attraction of the joint treatment of these topics is that it allows the reader to view their design trade-offs in a comparative context. Divided into three main parts: Part I provides a detailed exposure of OFDM designed for employment in various applications. Part II is another design alternative applicable in the context of OFDM systems where the channel quality fluctuations observed are averaged out with the aid of frequency-domain spreading codes, which leads to the concept of MC-CDMA. Part III discusses how to employ multiple antennas at the base station for the sake of supporting multiple users in the uplink. By providing an all-encompassing self-contained treatment this volume will appeal to a wide readership, as it is both an easy-reading textbook and a high-level research monograph.
The new frequency bands that will be allocated to W-CDMA cellular networks might open the possibility to use higher bandwidths than the 5 MHz specified in 3GPP. In this paper the temporal channel properties, i.e., power delay profile, in terms of number of Rake receiver fingers and their characteristics, are analyzed for 5, 10, 20, and 30MHz bandwidths. The lower bandwidth impulse responses are obtained by filtering measurement results obtained with a channel sounder having a bandwidth of 30 MHz.
Third generation mobile communication systems are currently being developed. The use of DS-CDMA in these systems leads to a multiple access interference limited system. Due to cross-correlation between the codes used for spreading the system performance is degraded. Multiuser detection techniques have been developed to limit the impact of this interference. In this paper an overview of Multiuser detection techniques is given. Interference cancellation receivers, such as decorrelator, MMSE receiver, parallel interference cancellation receiver and successive interference cancellation receiver are discussed. The importance of parameter estimation is stessed and the complexity of different multiuser detection schemes is analysed.
Augmented reality can create a learning environment to learners, combining the actual condition of let them around to see the real environment at the same time, also can see a computer, virtual information generated by mobile phones as the implementation of the augmented reality application platform, due to the mobility, portability, and human-computer interaction and so on, has strong advantage, and therefore more mobile learning application prospect, this paper discusses the structure of augmented reality based on mobile phone key technology and main function features, on the basis of to augmented reality based on mobile phone and its application in mobile learning has a deeper understanding.
Cloud storage technology has become a research hotspot in recent years, while the existing cloud storage services are mainly designed for data storage needs with stable high speed Internet connection. Mobile Internet connections are often unstable and the speed is relatively low. These native features of mobile Internet limit the use of cloud storage in portable consumer electronics. The Network Attached Flash File System (NAFFS) presented the idea of taking the portable device built-in NAND flash memory as the front-end cache of virtualized cloud storage device. Modern portable devices with Internet connection have built-in more than 1GB NAND Flash, which is quite enough for daily data storage. The data transfer rate of NAND flash device is much higher than mobile Internet connections[1], and its non-volatile feature makes it very suitable as the cache device of Internet cloud storage on portable device, which often have unstable power supply and intermittent Internet connection. In the present work, NAFFS is evaluated with several benchmarks, and its performance is compared with traditional network attached file systems, such as NFS. Our evaluation results indicate that the NAFFS achieves an average accessing speed of 3.38MB/s, which is about 3 times faster than directly accessing cloud storage by mobile Internet connection， and offers a more stable interface than that of directly using cloud storage API. Unstable Internet connection and sudden power off condition are tolerable, and no data in cache will be lost in such situation.
This paper focuses on the performance of cochannel interference (CCI) which is the primary
factor to limit the capacity of wireless communication systems. Several cellular network
architectures have been proposed in the literature to reduce the cochannel interference, but none
of them appears to effectively tackle this problem. Microzoning is the technique, where the cells
are further divided into smaller zones. The advantage of this technique is that the cochannel
interference in the cellular system is reduced because the cell maintains a particular coverage
radius. The objective of this paper is to analyze the performance of cochannel interference on the
forward channels of the proposed microzone based CDMA cellular systems operating with
perfect power control in an effort to reduce the cochannel interference. Simulation results
showed that the proposed technique can effectively minimize cochannel interference and the
proposed architecture can be used for practical applications.
This paper presents a novel methodology in planning the PN-offsets
of a highly non-uniform CDMA network and discusses the major related
issues. The strategy is applicable to any real life PCS and cellular
networks. It is shown that by optimally choosing/arranging parameters,
it is not only possible to mitigate the co- and adjacent PN-offset
interferences, sufficient PN-offset values can also be reserved for new
cells to be added into existing clusters for future network development
A design of a DS-CDMA system based on multiuser detection is
presented. Key features of the system include a flexible transport
scheme, large 5.1 MHz bandwidth, coherent demodulation and fast mobile
controlled handover with interfrequency handover capability.
Furthermore, the major trade-offs and design choices are explained
The feasibility of four TDMA based radio interfaces for UMTS to
provide up to a 2 Mbit/s service is studied. GSM compatible multicarrier
and single carrier solutions with binary and multilevel offset QAM
modulation are shown to be feasible for micro-cells and indoor cells.
Instead, in a macro-cell environment, relatively poor capacity (2
users/cell/24 MHz operator band) for 2 Mbit/s users can be achieved with
the limited cell size (<2 km). In a micro-cell (dense urban linear
street), and in an indoor cell environment with good isolation between
cells, the system with quaternary offset QAM modulation provides a
larger capacity than the system with binary offset QAM modulation and
reasonable cell range. Interference cancellation seems to have great
potential especially in a micro-cellular network
We address the problem of combining two potential capacity
enhancing techniques in the future TDMA mobile systems: slow random
frequency hopping between co-channel cells and interference cancellation
of the dominant interferer by joint detection. The former technique is
based on the averaging the interference between all users leading to the
so-called interference diversity gain. The latter technique can enhance
the receiver performance by performing joint demodulation for the
desired and interfering signals. We study the combination of the two
techniques by radio link and network simulations to quantify the total
capacity gain
This article presents the FRAMES multiple access (FMA) concept
designed for third-generation mobile radio systems. The concept consists
of two modes, TDMA-based FMA1 and CDMA-based FMA2, which have
contributed to the standardization processes of third-generation
systems. FMA1 uses the TDMA slot structure where spreading can be
applied inside the slot or, alternatively, plain TDMA-type transmission
can be used. FMA2 is a single-carrier wideband CDMA solution using a
4.096 Mchips/s basic chip rate. The FMA concept facilitates common
upper-layer protocol structure as well as GSM backwards compatibility
for evolution from second-generation systems to third-generation mobile
radio systems. The defined concept fulfils the UMTS/IMT-2000
requirements in providing the services needed for the next millennium
Data estimation in the uplink of a synchronous mobile radio system
applying code-division multiple access (CDMA) is considered. In mobile
radio systems applying CDMA, multipath propagation leads to intersymbol
interference (ISI) and together with time variance, to cross
interference between the signals of different users regardless of
whether the user codes are chosen orthogonal or not. A linear unbiased
data estimation algorithm is presented that eliminates both ISI and
cross interference perfectly by jointly detecting the different user
signals, leading to unbiased estimates of the transmitted data symbols.
By theoretical analysis and simulation, the performance of the linear
unbiased data estimation algorithm is examined under the assumption that
the radio channel impulse responses are known at the receiver. The price
to be paid for the interference elimination are SNR degradations, which
are calculated for typical mobile radio situations in urban areas. The
resulting average uncoded bit error probabilities lead to the conclusion
that systems applying the linear unbiased data estimation algorithm are
well suited for mobile radio applications
Consider a Gaussian multiple-access channel shared by K users who transmit asynchronously independent data streams by modulating a set of assigned signal waveforms. The uncoded probability of error achievable by optimum multiuser detectors is investigated. It is shown that the K -user maximum-likelihood sequence detector consists of a bank of single-user matched filters followed by a Viterbi algorithm whose complexity per binary decision is O(2^{K}) . The upper bound analysis of this detector follows an approach based on the decomposition of error sequences. The issues of convergence and tightness of the bounds are examined, and it is shown that the minimum multiuser error probability is equivalent in the Iow-noise region to that of a single-user system with reduced power. These results show that the proposed multiuser detectors afford important performance gains over conventional single-user systems, in which the signal constellation carries the entire burden of complexity required to achieve a given performance level.
Special Issue on IMT-2000: Standards Efforts of the ITU
- I€€€
111 I€€€ Pers. Commun., Special Issue on IMT-2000: Standards Efforts of the ITU. vol. 4, no. 4, Aug. 1997.
Recent Study on Candidate Radio Transmission Technology for IMT-2000
- Y Ishida
Y. Ishida, "Recent Study on Candidate Radio Transmission Technology for IMT-2000," 1st Annual CDMA Euro. Cong., London, U.K., Oct. 1997.
Wideband CDMA technology for FPLMTS
- J M Koo
- E K Hong
- J I Lee
BDMA Band Division Multiple Access - A New Air-Interface for 3rd Generation Mobile System in Europe
- H Alikhani
- R Bohnke
- M Suzuki
Will cdma One be the third choice
- S Chia
Performance of Wideband CDMA System for IMT-2000
- Y Hang
- S C Bang
- H-R Park
- B-J Kang