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Selected Areas in Communications, IEEE Journal on

Issue 7 • Date July 2000

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Displaying Results 1 - 19 of 19
  • Soft-output detection of CPM signals in frequency flat, Rayleigh fading channels

    Page(s): 1145 - 1152
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    Symbol-by-symbol detection algorithms are useful in systems in which soft-decision metrics are important, e.g., systems with interleaved coded modulation. A soft-output algorithm for the detection of continuous phase modulated (CPM) signals transmitted over frequency flat, Rayleigh fading channels is developed. Since the optimum detector is computationally too complex for any practical implementation, some suboptimal detectors which give near optimal performance are proposed. Some theoretical approximations for the performance of the interleaved coded system are given. The performance of the soft-output algorithms is also extensively characterized by means of Monte-Carlo simulations. View full abstract»

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  • Adaptive multidimensional coded modulation over flat fading channels

    Page(s): 1153 - 1158
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    We introduce a general adaptive coding scheme for Nakagami multipath fading channels. An instance of the coding scheme utilizes a set of 2L-dimensional (2L-D) trellis codes originally designed for additive white Gaussian noise (AWGN) channels. Any set of 2L-D trellis codes for AWGN channels can be used, Sets for which all codes can be generated by the same encoder and decoded by the same decoder are of particular interest. A feedback channel between the transmitter and receiver makes it possible to transmit at high spectral efficiencies under favorable channel conditions and respond to channel degradation through a smooth reduction of the spectral efficiency. We develop a general technique to determine the average spectral efficiency of the coding scheme for any set of 2L-D trellis codes. As an illustrative example, we calculate the average spectral efficiency of an adaptive codec utilizing eight 4-D trellis codes. The example codec is based on the International Telecommunications Union's ITU-T V.34 modem standard. View full abstract»

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  • Analytic forward link performance of pilot-aided coherent DS-CDMA under correlated Rician fading

    Page(s): 1159 - 1168
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    This paper presents a methodology for analyzing the forward link performance of a pilot-aided coherent DS-CDMA system under correlated Rician fading. In the forward link of a CDMA system, orthogonal modulation is usually used to minimize the self-interference. To maintain the orthogonality and reduce the receiver complexity, a common pilot channel (shared by all users) is employed to provide the reference for coherent demodulation. A tradeoff shows that a higher pilot ratio yields good channel estimates but takes away some capacity from traffic users, while a lower pilot ratio results in poorer channel estimates and leads to higher traffic power per user. This paper derives the analytical error performance, which includes (1) imperfect channel estimation by the pilot channel, (2) a very general channel model where correlations between paths as well as Rician fading are considered, and (3) interference patterns due to multiple paths and the surrounding base stations' transmissions. This paper also considers self-interference due to the loss of orthogonality caused by pulse shaping. View full abstract»

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  • A differential detection scheme for transmit diversity

    Page(s): 1169 - 1174
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    We present a transmission scheme for exploiting diversity given by two transmit antennas when neither the transmitter nor the receiver has access to channel state information. The new detection scheme can use equal energy constellations and encoding is simple. At the receiver, decoding is achieved with low decoding complexity. The transmission provides full spatial diversity and requires no channel state side information at the receiver. The scheme can be considered as the extension of differential detection schemes to two transmit antennas. View full abstract»

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  • A space-time model for frequency nonselective Rayleigh fading channels with applications to space-time modems

    Page(s): 1175 - 1190
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    This paper extends the traditional Clarke/Jakes (1968, 1974) model for a frequency flat fading process in a land mobile radio system to facilitate the examination of coherent space-time demodulation systems. The work develops a space-time correlation function using a ring of scatterers model around the mobile unit. The resulting correlation function permits the investigation of a variety of issues concerning base station configurations in space-time systems. The interrelationship of the fading process between the space and the time domain is explored. A detailed example regarding the effects of antenna separation in a receiver diversity system is considered. A set of design rules for interleaving depth and antenna separation in a space-time modem is presented and quantified. View full abstract»

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  • SINR maximizing space-time filtering for asynchronous DS-CDMA

    Page(s): 1191 - 1202
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    Direct sequence code division multiple access (DS-CDMA) is a core technology for wireless access that is proposed for future generation (3G) mobile and personal communication systems. The use of a base-station antenna array is strongly endorsed in these systems, because of its capabilities of filtering out the interference in the space domain. This paper considers space-time one shot single user receivers for DS-CDMA, based on a multiple input single output time invariant linear filter. The optimization of the filter response is performed jointly in the space and time domains yielding maximal signal-to-interference-plus-noise ratio. Using this framework, a space-time noise whitening matched filter (ST-NWMF) for DS-CDMA demodulation is introduced. It is shown that combined spatio-temporal filtering, taking advantage of the fact that the multiple access interference is colored in the space as well as time domains, can reduce the effects of strong interference components and improves the performance. Simpler suboptimal space-time linear receivers, consisting of a single temporal LT filter following the antenna array, are also considered. It is shown that such a filter approaches the ST-NWMF in the limit, when the M chip waveform has a flat spectrum with no excess bandwidth and N the observation interval is infinite. These schemes, optimal as well as suboptimal, for large observation intervals are suitable also for DS-CDMA systems employing long sequence spreading. View full abstract»

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  • Multiple-access interference-resistant acquisition for band-limited CDMA systems with random sequences

    Page(s): 1203 - 1213
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    The problem of estimating the propagation delay of a new user in a coded band-limited DS/CDMA system in the presence of multiple access interference (MAI) is considered. MAI-resistant acquisition schemes are developed for a general CDMA system without the constraint that the spreading sequences of the users repeat every symbol period. It is assumed that the spreading sequences and delays of the interfering users are known. However, knowledge of their amplitudes, which would need estimation, is not assumed, and their unreliable code-symbol estimates are not used. Under this scenario, acquisition schemes are derived based on the maximum-likelihood (ML) criterion. The performance of an approximation to the ML scheme is analyzed using Gaussian approximations and by assuming that the chip boundaries of the new user are known a priori. Simulations show that the analysis is reasonably accurate for parameters in the realm of practical interest. View full abstract»

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  • Joint equalization and interference suppression for high data rate wireless systems

    Page(s): 1214 - 1220
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    Enhanced Data Rates for Global Evolution (EDGE) is currently being standardized as an evolution of GSM in Europe and of IS-136 in the United States as an air interface for high speed data services for third generation mobile systems. In this paper, we study space-time processing for EDGE to provide interference suppression. We consider the use of two receive antennas and propose a joint equalization and diversity receiver. This receiver uses feedforward filters on each diversity branch to perform minimum mean-square error cochannel interference suppression, while leaving the intersymbol interference to be mitigated by the subsequent equalizer. The equalizer is a delayed decision feedback sequence estimator, consisting of a reduced-state Viterbi processor and a feedback filter. The equalizer provides soft output to the channel decoder after deinterleaving. We describe a novel weight generation algorithm and present simulation results on the link performance of EDGE with interference suppression. These results show a significant improvement in the signal-to-interference ratio (SIR) performance due to both diversity (against fading) and interference suppression. At a 10% block error rate, the proposed receiver provides a 20 dB improvement in SIR for both the typical urban and hilly terrain profiles. View full abstract»

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  • Performance analysis of linear multisensor multiuser receivers for CDMA in fading channels

    Page(s): 1221 - 1229
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    Bit-error probability (BEP) analysis for linear multiuser receivers with multiple sensors in frequency selective Rayleigh fading channels is presented. The analysis is applied to evaluate the BEP in antenna diversity reception and in a cellular CDMA system. Diversity and multiuser receivers are compared based on the examples. It is observed that adding new diversity antenna elements improves performance even if the correlation between the antenna elements is relatively large (up to 0.7). However, the large correlation values pose a significant reduction in the diversity gain in comparison to the zero correlation. It is also seen that the macroscopic diversity improves the performance of receivers significantly in cellular CDMA networks. When comparing diversity and multiuser receivers it is concluded that multiuser receivers are necessary to provide low BEPs. It is also highly beneficial to have at least two diversity antennas available, in particular, if there is no multipath diversity provided by the channel. The results also show that the reduction of intercell multiple-access interference yields a significant performance advantage in cellular networks. It is also demonstrated that the combination of spatial diversity and a multiuser receiver provides a significant receiver performance or system capacity gain in comparison to implementing only one of them. View full abstract»

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  • On antenna design and capacity analysis for the forward link of a multibeam power controlled satellite CDMA network

    Page(s): 1230 - 1244
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    This paper deals with the problem of rigorously analyzing the forward link behavior of a power controlled CDMA-based satellite multibeam communication system. For the first time, the complete system links equations are expressed in a compact matrix form so that they can be solved simultaneously, thus leading to an exact problem solution. In particular the effect of actual antenna beam patterns, overlapping satellites interference, users location, conventional and linear blind minimum output energy (MOE) CDMA detectors are accounted for by comprehensive system analysis. Under simplified yet realistic system assumptions, the proposed technique allows us to derive the key satellite antenna parameters. It is shown that for power controlled CDMA satellite networks, the key antenna figure of merit is the average gain and the so-called antenna inverse average interference-to-carrier ratio rather than the more intuitive average carrier-to-interference ratio. It is shown that under simplified system assumptions, these parameters can be used to compute simple yet accurate one-dimensional system link budget. Also, by means of a simplified system analysis, the antenna beam overlapping point capacity impact is determined. Furthermore, results about system capacity and outage probability for a practical personal communication satellite network are presented with and without adopting an advanced CDMA MOE single-user detector. The MOE advantages in terms of capacity increase for a given outage probability are shown to be substantial when the system loading is appreciable, even assuming perfect power control. View full abstract»

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  • Output and delay process analysis for slotted CDMA wireless communication networks with integrated voice/data transmission

    Page(s): 1245 - 1253
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    This paper presents the output and delay process analysis of integrated voice/data slotted code division multiple access (CDMA) network systems with random access protocol for packet radio communications. The system model consists of a finite number of users, and each user can be a source of both voice traffic and data traffic. The allocation of codes to voice calls is given priority over that to data packets, while an admission control, which restricts the maximum number of codes available to voice sources, is considered for voice traffic so as not to monopolize the resource. Such codes allocated exclusively to voice calls are called voice codes. In addition, the system monitoring can distinguish between silent and talkspurt periods of voice sources, so that users with data packets can use the voice codes for transmission if the voice sources are silent. A discrete-time Markov process is used to model the system operation, and an exact analysis is presented to derive the moment generating functions of the probability distributions for packet departures of both voice and data traffic and for the data packet delay. For some cases with different numbers of voice codes, numerical results display the correlation coefficient of the voice and data packet departures and the coefficient of variation of the data packet delay as well as average performance measures, such as the throughput, the average delay of data packets, and the average blocking probability of voice calls. View full abstract»

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  • A new random walk model for PCS networks

    Page(s): 1254 - 1260
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    This paper proposes a new approach to simplify the two-dimensional random walk models capturing the movement of mobile users in personal communications services (PCS) networks. Analytical models are proposed for the new random walks. For a PCS network with hexagonal configuration, our approach reduces the states of the two-dimensional random walk from (3n/sup 2/+3n-5) to n(n+1)/2, where n is the layers of a cluster. For a mesh configuration, our approach reduces the states from (2n2-2n+1) to (n/sup 2/+2n+4)/4 if n is even and to (n/sup 2/+2n+5)/4 if n is odd. Simulation experiments are conducted to validate the analytical models. The results indicate that the errors between the analytical and simulation models are within 1%. Three applications (i.e., microcell/macrocell configuration, distance-based location update, and GPRS mobility management for data routing) are used to show how our new model can be used to investigate the performance of PCS networks. View full abstract»

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  • Performance evaluation of candidate MAC protocols for LMCS/LMDS networks

    Page(s): 1261 - 1270
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    Broadband wireless access (BWA) offers attractive features such as ease and speed of deployment, fast realization of revenues, and low infrastructure cost. This paper focuses on medium access control (MAC) alternatives that can find application in an LMDS/LMCS network capable of supporting multimedia traffic. Multifrequency demand assignment TDMA-based schemes appear (at the moment) to be a suitable choice in this context. The selected protocol should be dynamically capable of providing multirate capabilities and quality-of-service guarantees. An obvious candidate for the aforementioned purpose is the LMDS-specific MAC proposal in the DAVIC 1.2 recommendation. For purposes of comparison, we also examine the evolving IEEE 802.14 MAC convergence protocol and MCNS (multimedia cable network system) DOCSIS (ITU J-112) MAC standard that are intended to support similar applications and services in an HFC (hybrid fiber coax) environment. The three protocols are examined under noiseless and noisy channel conditions. Previous results on LMDS channel characteristics are summarized and used for modeling noisy channel conditions. The candidate protocols are compared in terms of mean access delay, throughput, and collision multiplicity statistics, when contention of users is involved. The effect of dynamic slot allocation on the performance of the candidate protocols is also examined. View full abstract»

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  • Comparison of time slot allocation strategies for CDMA/TDD systems

    Page(s): 1271 - 1278
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    The traffic (load) asymmetry between uplink and downlink is a remarkable traffic characteristic in cellular mobile multimedia communications. The code division multiple access system with time division duplex mode (CDMA/TDD system), adopting unbalanced slot allocation between uplink and downlink, is a good solution for this traffic asymmetry. However, the level of traffic asymmetry may be significantly different from cell to cell. In this paper, we investigate a slot allocation strategy (DA strategy), by which each cell has its own slot allocation according to the level of traffic asymmetry. We compute the system capacity with DA strategy and find out the optimal slot allocation for the system. We also compare the maximum capacity to that with another strategy (SA strategy), by which all cells have the same slot allocation. As a result, this paper shows that the system with DA strategy outperforms the system with SA strategy in the aspect of capacity. View full abstract»

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  • An efficient algorithm for the link allocation problem on ATM-based personal communication networks

    Page(s): 1279 - 1288
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    The personal communication network (PCN) is an emerging wireless network that promises many new services for the telecommunication industry. The proliferation of demands for extending wireless services to integrated services which supports the transmission of data and multimedia information has resulted in the need for broadband wireless systems that are able to provide service capabilities similar to those of wireline networks. The ATM cell-relay paradigm is one possible approach to provide broadband wireless transmission with PCNs using the ATM switching networks for interconnection of PCN cells. In an ATM-based PCN, the communication path between a pair of mobile terminals might be elongated due to the mobility of the terminals. The link allocation problem is that of allocating backbone links among ATM switches to reduce the effects of terminal mobility on the performance of ATM-based PCNs. Huang and Wang (1997) have shown that this problem is NP-complete. In this paper, we propose a new efficient heuristic algorithm for the link allocation problem. One novel feature of our algorithm is that we are able to derive sufficient conditions under which our algorithm is able to guarantee optimal solutions. Our empirical study shows that the average lengths of communication paths obtained by our algorithm are shorter than those obtained by Huang and Wang's algorithm. In addition, the number of successfully established paths obtained by our algorithm is significantly more than that obtained by the aforementioned. View full abstract»

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  • Throughput analysis of TCP on channels with memory

    Page(s): 1289 - 1300
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    The focus of this paper is to analyze the relative sensitivity of the bulk throughput performance of different versions of TCP, viz., OldTahoe, Tahoe, Reno, and New Reno, to channel errors that are correlated. We investigate the performance of a single wireless TCP connection in a local environment by modeling the correlated packet loss/error process (e.g., as induced by a multipath fading channel) as a first-order Markov chain. A major contribution of the paper is a unified analytical approach which allows the evaluation of the throughput performance of various versions of TCP. The main findings of this study are that 1) error correlations significantly affect the performance of TCP, and in particular may result in considerably better performance for Tahoe and NewReno; and 2) over slowly fading channels which are characterized by significant channel memory, Tahoe performs as well as NewReno. This leads us to conclude that a clever design of the lower layers that preserve error correlations, naturally present on wireless links because of the fading behavior, could be an attractive alternative to the development or the use of more complex versions of TCP. View full abstract»

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  • A pattern recognition system for handoff algorithms

    Page(s): 1301 - 1312
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    In wireless cellular systems, handoff algorithms decide when and to which base station to handoff. Traditional handoff algorithms generally cannot keep both the average number of unnecessary handoffs and the handoff decision delay low. They do not exploit the relative constancy of path loss and shadow fading effects at any given location around a base station. This information can in fact be used to improve the efficiency of handoff algorithms, as we do in our new handoff algorithms using statistical pattern recognition. Handoff algorithms with both a negligible number of unnecessary handoffs and a negligible decision delay can therefore be realized. View full abstract»

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  • A general methodology based on the handover rate for network planning of cellular radio networks based on ATM

    Page(s): 1313 - 1325
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    Mobile radio networks based on ATM (asynchronous transfer mode) technology, such as wireless ATM, are considered. More precisely, the topology of connections between the ATM nodes and the base stations is investigated, taking the limited capacity of ATM nodes into account. This requires the partitioning of cells, that is, the set of cells has to be subdivided into subsets so that base stations of cells belonging to the same subset are connected to the same ATM switch. Among the possible partitions, the optimum solution is that giving the minimum number of handovers requiring a change of ATM switch: in this case, a path rerouting procedure must be carried out, causing additional delays in executing the handover. The optimum partition could be found by exhaustively considering all possibilities once the handover rates between cells is known; however, this would lead to an incredible complexity for the planning of large networks. We define a general methodology based on the concept, of "handover rate" between cells, which allows the choice of the best partition by taking mobility, radio, and fixed network aspects into account. Moreover, some new low-complexity partitioning algorithms determining suboptimum solutions are proposed. Finally, we show that the suboptimum partition slightly depends on some radio interface choices, such as the handover algorithm, thus allowing separate design of the two aspects. View full abstract»

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  • Distributed fault-tolerant channel allocation for cellular networks

    Page(s): 1326 - 1337
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    A channel allocation algorithm includes channel acquisition and channel selection algorithms. Most of the previous work concentrates on the channel selection algorithm since early channel acquisition algorithms are centralized and rely on a mobile switching center (MSC) to accomplish channel acquisition. Distributed channel acquisition algorithms have received considerable attention due to their high reliability and scalability. However, in these algorithms, a borrower needs to consult with its interference neighbors in order to borrow a channel. Thus, the borrower fails to borrow channels when it cannot communicate with any interference neighbor. In real-life networks, under heavy traffic load, a cell has a large probability to experience an intermittent network congestion or even a communication link failure. In existing distributed algorithms, since a cell has to consult with a large number of interference neighbors to borrow a channel, the failure rate will be much higher under heavy traffic load. Therefore, previous distributed channel allocation algorithms are not suitable for real-life networks. We first propose a fault-tolerant channel acquisition algorithm which tolerates communication link failures and node (MH or MSS) failures. Then, we present a channel selection algorithm and integrate it into the distributed acquisition algorithm. Detailed simulation experiments are carried out in order to evaluate our proposed methodology. Simulation results show that our algorithm significantly reduces the failure rate under network congestion, communication link failures, and node failures compared to nonfault-tolerant channel allocation algorithms. Moreover, our algorithm has low message overhead compared to known distributed channel allocation algorithms, and outperforms them in terms of failure rate under uniform as well as nonuniform traffic distribution. View full abstract»

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Aims & Scope

IEEE Journal on Selected Areas in Communications focuses on all telecommunications, including telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation.

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Editor-in-Chief
Muriel Médard
MIT