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Wireless Communications, IEEE Transactions on

Issue 1 • Date Jan. 2004

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Displaying Results 1 - 25 of 39
  • Table of contents

    Publication Year: 2004 , Page(s): 1
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    Freely Available from IEEE
  • IEEE Transactions on Wireless Communications

    Publication Year: 2004 , Page(s): 0_2
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  • Two-dimensional code acquisition in environments with a spatially nonuniform distribution of interference: algorithms and performance

    Publication Year: 2004 , Page(s): 1 - 7
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    In this paper, we investigate code acquisition in the delay and angular domain in environments where interference and noise are nonuniformly distributed in the spatial (angular) domain. It is seen that performance is clearly degraded by the presence of nonuniform spatial distributions of interference. The degree of impairment is related to the actual shape of the distribution and becomes more significant when large amounts of interfering power are concentrated in one or more angular directions. As compared to a reference case with a uniform distribution of equivalent interfering power, the mean acquisition time could increase by factors of up to four. Some effective approaches to compensate for the loss of performance due to the uneven nature of interference are also studied. First, the effect of search strategies in the delay and angular domains on acquisition performance is assessed. A searching algorithm up-ranking angular cells according to the amount of associated interference is proposed as one solution to reduce the performance gap. It is shown that applying this search strategy can considerably reduce the mean acquisition time. Finally, two adaptive schemes based on setting integration times or threshold values according to the level of interference prevailing in each angular cell, are discussed. The former approach returns performance figures similar to those obtained with the uniform equivalent interference distribution while the latter provide moderate performance gains. View full abstract»

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  • The application of nonlinear programming for multiuser detection in CDMA

    Publication Year: 2004 , Page(s): 8 - 11
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    In this paper, a heuristic algorithm based on a nonlinear nonconvex programming relaxation of the CDMA maximum likelihood (ML) problem is presented. Simulation results have shown that the BER performances of a detection strategy based on the heuristic algorithm are similar to that of the detection strategy based on the semidefinite relaxation. Furthermore, average CPU time of the heuristic algorithm is significantly lower than that of the randomized rounding algorithm based on a semidefinite relaxation. This approach provides good approximations to the ML performance. View full abstract»

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  • A Laguerre polynomial-based bound on the symbol error probability for adaptive antennas with optimum combining

    Publication Year: 2004 , Page(s): 12 - 16
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    We derive a simple closed-form upper bound on the symbol error probability for coherent detection of M-ary phase-shift keying using antenna arrays with optimum combining, in the presence of multiple uncorrelated equal-power cochannel interferers and thermal noise in a Rayleigh fading environment. The new bound, based on Laguerre polynomials, is valid for an arbitrary number of antenna elements as well as arbitrary number of interferers, and it is proven to be asymptotically tight. Comparisons with Monte Carlo simulation are also provided, showing that our bound is useful in many cases of interest. View full abstract»

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  • Estimating signal strengths in the design of an indoor wireless network

    Publication Year: 2004 , Page(s): 17 - 19
    Cited by:  Papers (6)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    One issue in the design and implementation of a wireless local area network is the selection of access point (AP) locations. Proper AP placement is necessary to provide adequate signal coverage and also to minimize cochannel coverage overlap. The impact of incorrect placement of APs is significant. Placing APs too far apart can lead to gaps in coverage. On the other hand, placing the units too close together leads to excessive cochannel coverage overlap, degrading system performance. Currently, AP placement involves a "trial and error" technique. When a technician tests the effect of moving an AP from one location to another, it is necessary to spend considerable time manually measuring signal strengths in order to determine how this move affects the AP's coverage area. In this letter, we describe a procedure for estimating the coverage areas of relocated APs. The procedure can be used as part of a manual design process or as part of an automated design tool. View full abstract»

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  • A transmit preprocessing technique for multiuser MIMO systems using a decomposition approach

    Publication Year: 2004 , Page(s): 20 - 24
    Cited by:  Papers (333)  |  Patents (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    We introduce a transmit preprocessing technique for the downlink of multiuser multiple-input multiple-output (MIMO) systems. It decomposes the multiuser MIMO downlink channel into multiple parallel independent single-user MIMO downlink channels. Some key properties are that each equivalent single-user MIMO channel has the same properties as a conventional single-user MIMO channel, and that increasing the number of transmit antennas of the multiuser system by one increases the number of spatial channels to each user by one. Simulation results are also provided and these results demonstrate the potential of our technique in terms of performance and capacity. View full abstract»

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  • On the average output SNR in selection combining with three correlated branches over Nakagami-m fading channels

    Publication Year: 2004 , Page(s): 25 - 28
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    An exact and rapidly converging infinite series for the average output signal-to-noise ratio in a triple selection diversity system, over correlated Nakagami-m fading channels, is presented. Numerical results are presented to illustrate the proposed approach and to point out the effect of the fading correlation to the performance of the combiner, as well as the improvement achieved by the triple selection combining compared to the dual diversity case. View full abstract»

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  • Efficient performance evaluation for generalized selection combining on generalized fading channels

    Publication Year: 2004 , Page(s): 29 - 34
    Cited by:  Papers (59)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    The authors propose an efficient moment generating function (MGF)-based method to evaluate the performance of generalized selection combining (GSC) over different fading channels. Employing a recently proposed method which is, however, only applicable to GSC diversity with independent and identically distributed branches, they derive a general MGF expression for the GSC output signal-to-noise ratio (SNR) for generalized fading channels, where the channel statistics in different diversity branches may be nonidentical or even distributed according to different distribution families. The resulting MGF expression is applicable to the analysis of the error probability, the outage probability, and the SNR statistics for GSC in a number of wireless communications scenarios with generalized fading. Numerical examples are presented to illustrate the application of the new analysis. View full abstract»

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  • Dynamic rate adaptation and integrated rate and error control in cellular WCDMA networks

    Publication Year: 2004 , Page(s): 35 - 49
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    Optimal dynamic rate allocation among mobile stations for variable rate packet data transmission in a cellular wireless network is an NP-complete problem; therefore, suboptimal solutions to this problem are sought for. In this paper, three novel suboptimal dynamic rate adaptation schemes, namely, peak-interference-based rate allocation, sum-interference-based rate allocation, and mean-sense approximation-based rate allocation, are proposed for uplink packet data transmission in cellular variable spreading factor wide-band code division multiple access (WCDMA) networks. The performances of these schemes are compared to the performance of the optimal dynamic link adaptation for which the rate allocation is found by an exhaustive search. The optimality criterion is the maximization of the average number of radio link level frames transmitted per frame time under constrained signal-to-interference-plus-noise ratio (SINR) at the base station receiver. Two different error control alternatives for variable rate packet transmission environment are presented. We demonstrate that the dynamic rate adaptation problem under constrained SINR can be mapped into the radio link level throughput maximization problem with integrated rate and error control. Performance evaluation is carried out under random and directional micromobility models with uncorrelated and correlated long-term fading, respectively, in a cellular WCDMA environment for both the homogeneous (or uniform) and the nonhomogeneous (or nonuniform) traffic load scenarios. View full abstract»

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  • Turbo space-time equalization of TCM for broadband wireless channels

    Publication Year: 2004 , Page(s): 50 - 59
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    This paper presents a space-time turbo (iterative) equalization method for trellis-coded modulation (TCM) signals over broadband wireless channels. For fixed wireless systems operating at high data rates, the multipath delay spread becomes large, making it impossible to apply trellis-based equalization methods. The equalizer proposed here consists of a broadband beamformer which processes antenna array measurements to shorten the observed channel impulse response, followed by a conventional scalar turbo equalizer. Since the applicability of trellis-based equalizers is limited to additive white noise channels, the beamformer is required to preserve the whiteness of the noise at its output. This constraint is equivalent to requiring that the finite-impulse response (FIR) beamforming filters must have a power complementarity property. The power complementarity property imposes nonnegative definite quadratic constraints on the beamforming filters, so the beamformer design is expressed as a constrained quadratic optimization problem. The composite channel impulse response at the beamformer output is shortened significantly, making it possible to use a turbo equalizer for the joint equalization and decoding of trellis modulated signals. The proposed receiver structure is simulated for two-dimensional TCM signals such as 8-PSK and 16-QAM and the results indicate that the use of antenna arrays with only two or three elements allows a large decrease in the channel signal-to-noise ratio needed to achieve a 10-4 bit-error rate. View full abstract»

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  • Dynamic fair scheduling with QoS constraints in multimedia wideband CDMA cellular networks

    Publication Year: 2004 , Page(s): 60 - 73
    Cited by:  Papers (42)  |  Patents (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    A class of dynamic fair scheduling schemes based on the generalized processor sharing (GPS) fair service discipline, under the generic name code-division GPS (CDGPS), is proposed for a wideband direct-sequence code-division multiple-access (CDMA) cellular network to support multimedia traffic. The CDGPS scheduler makes use of both the traffic characteristics in the link layer and the adaptivity of the wideband CDMA physical layer to perform fair scheduling on a time-slot by time-slot basis, by using a dynamic rate-scheduling approach rather than the conventional time-scheduling approach. Soft uplink capacity is characterized for designing an efficient CDGPS resource allocation procedure. A credit-based CDGPS (C-CDGPS) scheme is proposed to further improve the utilization of the soft capacity by trading off the short-term fairness. Theoretical analysis shows that, with the C-CDGPS scheme, tight delay bounds can be provided to delay-sensitive traffic, and short-term unfairness can be bounded so that long-term weighted fairness for all users can still be satisfied. Simulation results show that bounded delays, increased throughput, and long-term fairness can be achieved for both homogeneous and heterogeneous traffic. View full abstract»

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  • Joint scheduling and power control for wireless ad hoc networks

    Publication Year: 2004 , Page(s): 74 - 85
    Cited by:  Papers (191)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB) |  | HTML iconHTML  

    In this paper, we introduce a cross-layer design framework to the multiple access problem in contention-based wireless ad hoc networks. The motivation for this study is twofold, limiting multiuser interference to increase single-hop throughput and reducing power consumption to prolong battery life. We focus on next neighbor transmissions where nodes are required to send information packets to their respective receivers subject to a constraint on the signal-to-interference-and-noise ratio. The multiple access problem is solved via two alternating phases, namely scheduling and power control. The scheduling algorithm is essential to coordinate the transmissions of independent users in order to eliminate strong levels of interference (e.g., self-interference) that cannot be overcome by power control. On the other hand, power control is executed in a distributed fashion to determine the admissible power vector, if one exists, that can be used by the scheduled users to satisfy their single-hop transmission requirements. This is done for two types of networks, namely time-division multiple-access (TDMA) and TDMA/code-division multiple-access wireless ad hoc networks. View full abstract»

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  • The optimality of beamforming in uplink multiuser wireless systems

    Publication Year: 2004 , Page(s): 86 - 96
    Cited by:  Papers (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB) |  | HTML iconHTML  

    This paper considers the optimal uplink transmission strategy that achieves the sum-capacity in a multiuser multi-antenna wireless system. Assuming an independent identically distributed block-fading model with transmitter channel side information, beamforming for each remote user is shown to be necessary for achieving sum-capacity when there is a large number of users in the system. This result stands even in the case where each user is equipped with a large number of transmit antennas, and it can be readily extended to channels with intersymbol interference if an orthogonal frequency division multiplexing modulation is assumed. This result is obtained by deriving a rank bound on the transmit covariance matrices, and it suggests that all users should cooperate by each user using only a small portion of available dimensions. Based on the result, a suboptimal transmit scheme is proposed for the situation where only partial channel side information is available at each transmitter. Simulations show that the suboptimal scheme is not only able to achieve a sum rate very close to the capacity, but also insensitive to channel estimation error. View full abstract»

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  • Antenna diversity combining schemes for WCDMA systems in fading multipath channels

    Publication Year: 2004 , Page(s): 97 - 106
    Cited by:  Papers (14)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    In this paper, we analyze the performance of various receive antenna diversity schemes for use in combination with transmit diversity on the downlink of wideband code-division multiple-access third-generation systems. We consider open loop and closed loop versions of both maximal ratio combining and selection diversity, and study the impact of channel correlation on the performance of these schemes. We also present an analysis of the asymptotic performance of coded systems. The analytical results are compared with simulation results obtained in typical channels. View full abstract»

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  • Adaptation of the code rate and transmitter power in frequency-hop communications

    Publication Year: 2004 , Page(s): 107 - 116
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    An adaptive transmission technique for frequency-hop packet transmission is described and its performance is evaluated for certain channels with unknown or time-varying parameters. The power in the transmitted signal and the rate of the error-control code are adapted in a way that provides energy-efficient communications. The slow-frequency-hop packet transmissions have several bits per hop and several hops per packet. Feedback is limited to a few bits in each acknowledgment packet, and the feedback for our adaptive transmission consists of only the counts of errors and erasures from the previous packet transmission. The performance of the adaptive transmission system is evaluated for channels with unknown but fixed partial-band interference and propagation loss and for certain channels with time-varying partial-band interference and propagation loss. View full abstract»

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  • Symbol-based space diversity for coded OFDM systems

    Publication Year: 2004 , Page(s): 117 - 127
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    The authors present a coded orthogonal frequency division multiplexing (COFDM) system with multiple-input/multiple-output (multiple transmit and/or multiple receive) antennas for high-rate wireless data transmission. A symbol-based space diversity technique, which can take advantage of the inherent space diversity, is proposed. In contrast to conventional subcarrier-based space diversity, it is shown that the proposed technique can be implemented using only one discrete Fourier transform block and the same weighting coefficients for the whole OFDM symbol. This significantly reduces the system complexity while achieving almost the same diversity order as that of the traditional space diversity approach. They also propose an iterative algorithm to obtain the antenna weighting coefficients. Simulation results show that the proposed algorithm converges fast and approaches the global optimal solution for most channel realizations. It is also shown that, when the proposed technique is employed in a time division duplex scenario, where the uplink and downlink channels are reciprocal, the system complexity can be further reduced. View full abstract»

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  • Range and antenna beamwidth dependencies in multidimensional fixed wireless channels

    Publication Year: 2004 , Page(s): 128 - 137
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    This paper describes a multidimensional model of the fixed wireless propagation channel, which is well suited to system-level simulations. The proposed method yields realistic predictions of various channel characteristic parameters as a function of the range and antenna beamwidths, in agreement with experimentally observed results. The originality of the approach is that the power-delay profile for omnidirectional antennas at the edge of the cell is used to predict the time-varying channel over the whole cell for any antenna beamwidth. The method is based on a set of spatially distributed scatterers, which can be scaled to any range within the cell. The time-varying channel impulse response is then calculated as the combination of all scattered contributions by means of a ray approximation. The multidimensionality of the channel model is explored through predictions of signal statistics, level-crossing rate, delay-spread and angle-spread. In contrast to most existing models, the impact of range and antenna beamwidth is clearly addressed and found to be close to experimentally observed behaviors. View full abstract»

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  • Analysis of multipath Routing-Part I: the effect on the packet delivery ratio

    Publication Year: 2004 , Page(s): 138 - 146
    Cited by:  Papers (70)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    In this paper, we develop an analytical framework for evaluating multipath routing in mobile ad hoc networks. The instability of the topology (e.g., failure of links) in this type of network due to nodal mobility and changes in wireless propagation conditions makes transmission of time-sensitive information a challenging problem. To combat the inherent unreliability of these networks, we propose a routing scheme that uses multiple paths simultaneously by splitting the information between a multitude of paths, so as to increase the probability that the essential portion of the information is received at the destination without incurring excessive delay. Our scheme works by adding an overhead to each packet, which is calculated as a linear function of the original packet bits. The resulting packet (information and overhead) is fragmented into smaller blocks and distributed over the available paths. The probability of reconstructing the original information at the destination is derived in an analytical form and its behavior is studied for some special cases. It is shown that, under certain constraints, the packet dropping probability decreases as the number of used paths is increased. View full abstract»

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  • Packet-length adaptive CLSP/DS-CDMA: performance in burst-error correlated fading channels

    Publication Year: 2004 , Page(s): 147 - 158
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    The authors analyze throughput-delay performance of an unslotted channel load sensing protocol (CLSP)/direct sequence (DS)-code division multiple access (CDMA) packet radio network (PRN) with adaptive packet length over burst-error correlated fading channels. CLSP controls the packet access in uplink of unslotted ALOHA/DS-CDMA systems so that contention is avoided and throughput is maximized. However, due to high uncertainty of radio channels, the performance of CLSP/DS-CDMA PRN may suffer from notable degradations. Using theoretical analysis and simulation, the authors show that in highly correlated fading environments adapting the length of radio packets to fading conditions significantly improves system performance and energy efficiency of mobile terminals. In their modeling, they study the relation between the fade statistics and the packet length in correlated Rayleigh fading channels. The effects of reception diversity, imperfect transmit power control (TPC), and user mobility are considered. The results are used to develop simple, energy-efficient, and robust adaptation mechanisms. View full abstract»

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  • A flexible dynamic traffic model for reverse link CDMA cellular networks

    Publication Year: 2004 , Page(s): 159 - 164
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    In this paper, we focus on the reverse link traffic analysis of a code-division multiple-access (CDMA) cellular network in dynamic environments. In this respect, we propose a new and flexible traffic model, which takes into account the interference-limitedness attribute of CDMA capacity as well as its soft-handoff feature. This new traffic model is developed according to an interference-based call admission control (ICAC) method and a geographical structure with three regions. The main advantage of this traffic model is in its flexibility when we consider different traffic conditions including time-varying status of traffic in the neighboring cells. View full abstract»

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  • Optimum packet data transmission in cellular multirate CDMA systems with rate-based slot allocation

    Publication Year: 2004 , Page(s): 165 - 175
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    High-rate packet transmission is realized for the downlink in cellular multirate code-division multiple-access systems using multicode concatenated signaling, combined with iterative detection and self-interference cancellation. Since an optimum packet transmission is to allocate the maximum allowable rate to the user with the best received signal-to-interference-plus-noise ratio (SINR), a problem with fairness arises, in the sense that only a very small number of users receive at or near the maximum allowable rate, and the rest of the users do not receive at all. To overcome this, a new soft multimodal fairness control is proposed to adjust the latency (or waiting time) between two extreme values. Throughput is analyzed by deriving the probability distribution of the rate allocation, which is based on the maximum received SINR in a slot. For this, statistics on the SINRs are jointly characterized under three-sector cell structure because of their mutual correlation. Traffic variations are also taken into account to formulate the statistics under two algorithms for adaptive base station selection. It is shown that high-rate transmission can be achieved by a substantial reduction in in-cell interference, and the tradeoff between throughput and fairness can be met by the fairness control. View full abstract»

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  • Chip-interleaved block-spread CDMA versus DS-CDMA for cellular downlink: a comparative study

    Publication Year: 2004 , Page(s): 176 - 190
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB) |  | HTML iconHTML  

    A so-termed chip-interleaved block-spread (CIBS) code division multiple access (CDMA) system has been introduced for cellular applications in the presence of frequency selective multipath channels. In both uplink and downlink operation, CIBS-CDMA achieves multiuser-interference (MUI) free reception within each cell. This paper focuses on the cellular downlink configuration and compares CIBS-CDMA against the conventional direct-sequence (DS) CDMA system, which relies on a chip equalizer to restore code orthogonality and, subsequently, suppresses MUI by despreading. We provide a unifying framework for both systems and investigate their performance in the presence of intercell interference and soft-handoff operation. Extensive comparisons from load, performance, complexity, and flexibility perspectives illustrate the merits, along with the disadvantages, of CIBS-CDMA over DS-CDMA, and reveal its potential for future wireless systems. View full abstract»

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  • Direction-of-arrival tracking scheme for DS/CDMA systems: direction lock loop

    Publication Year: 2004 , Page(s): 191 - 202
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    In this paper, a new direction-of-arrival (DOA) tracking algorithm, direction lock loop (DiLL), is proposed for wireless direct-sequence code-division multiple-access systems. It has a similar concept to the delay lock loop that is used for timing synchronization. It may track the DOA of sources by iterations. Its computational requirements are NK+O(K) for coherent DiLL and 2NK+O(K) for noncoherent DiLL, where N is the number of antenna elements and K is the number of signal sources, which is less than that of the projection approximation subspace tracking with deflation algorithm. The DOA tracking accuracy is demonstrated by analysis and computer simulations. View full abstract»

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  • Multilevel coding for multiple-antenna transmission

    Publication Year: 2004 , Page(s): 203 - 208
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    The application of powerful coding for transmission over multiple-input/multiple-output channels is discussed. The authors emphasize that as an immediate consequence of the mutual information chain rule, multilevel coding (MLC) constitutes the optimum coded modulation scheme. On the other hand, simple bit-interleaved coded modulation (BICM) is only a convenient alternative for the case of two transmit and one receive antennas when combined with orthogonal space-time block codes. Starting from MLC, the authors further propose a hybrid coded modulation scheme, which favorably combines the advantages of MLC and BICM. View full abstract»

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The IEEE Transactions on Wireless Communications publishes high-quality manuscripts on advances in the state-of-the-art of wireless communications.

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Editor-in-Chief
Jeff Andrews
Cullen Trust for Higher Education Endowed Professor of Engineering