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Wireless Communications, IEEE Transactions on

Issue 6 • Date June 2008

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  • Table of contents

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  • Precoder Design for Space-Time Coded MIMO Systems with Imperfect Channel State Information

    Page(s): 1977 - 1981
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    We address the problem of designing a linear precoder for space-time coded multiple-input multiple-output (MIMO) system with imperfect knowledge of channel state information at the transmitter (CSIT), subject to a total transmit power constraint. Assuming an uncorrelated flat-fading channel and using a maximum likelihood decoder at the receiver, we analytically reveal that the derived precoder is a function of the noise variance, the eigenvalues of the estimated channel matrix and the eigenvalues of the codeword distance matrix. Furthermore, the power allocation on the eigenvalues of the precoder is shown to follow the water-pouring policy and hence the proposed precoder allocates more power to the stronger channels. View full abstract»

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  • A New Full-band Feedback Scheme Using the Adaptive Grouping Method in OFDMA Systems

    Page(s): 1982 - 1986
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    Opportunistic scheduling algorithms with link adaptation can increase system throughput, but have the drawback of requiring the channel quality information (CQI) to be transmitted from all the candidate users. In order to alleviate this problem, we propose a new feedback reduction scheme that preserves CQIs over all channels. The proposed scheme binds similar CQIs in groups to represent them more effectively, and uses a simple method for fast grouping. Simulation results show that the proposed scheme with this simple grouping achieves close to perfect feedback performance with respect to the original CQIs under reasonable feedback loads. View full abstract»

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  • MIMO Block Spread CDMA Systems for Broadband Wireless Communications

    Page(s): 1987 - 1992
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    This paper studies two MIMO architectures for single-carrier CDMA system employing block spreading, namely Layered Space-Time Block Spread CDMA (LST BS-CDMA) and Space-Time Coded Block Spread CDMA (STC BS-CDMA). It is shown that under low mobility conditions, the proposed systems are virtually free from Multiple User Interference (MUI) and the block processing technique used leads to considerable reduction in the overall processing complexity. Extensive simulation was performed to study the impact of the spreading factor and Doppler frequency on the proposed systems. A new parameter called channel coherence ratio (CCR) is introduced as a key parameter in determining the performance of MIMO BS-CDMA. View full abstract»

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  • Improving TCP Throughput over HSDPA Networks

    Page(s): 1993 - 1998
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    The various link adaptation techniques employed by High Speed Downlink Packet Access (HSDPA) in the third generation (3G) networks augment the bandwidth oscillation, which is identified as one of the most important factors resulting in the throughput deterioration of Transmission Control Protocol (TCP). In this paper, we firstly explain why the bandwidth oscillation degrades the TCP performance through a special simulation experiment. Subsequently, a split connection Window Adaptation TCP Proxy is proposed to improve the TCP throughput over HSDPA networks. In this solution, the built-in attributes of HSDAP system are sufficiently utilized. In order to effectively use the precious cellular link resources, the length of the queue connected with it is intentionally kept around the reference value through adjusting the sending window size of TCP proxy based on the dynamic values of varying bandwidth. A discrete-time stochastic state space model is formulated to analyze the system stability. The validity of enhanced scheme is verified through simulation experiments. The performance of TCP proxy is compared with the standard TCP protocol. The numerical results show that our TCP proxy is able to keep the cellular link utilization over 90%, and to improve TCP throughput by 100% under most conditions. View full abstract»

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  • A Dynamic Channel Assignment Scheme for TDMA-based Multihop Cellular Networks

    Page(s): 1999 - 2003
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    In this paper, we propose a multihop dynamic channel assignment (MDCA) scheme for time division multiple access (TDMA)-based multihop cellular networks. The proposed MDCA assigns channels to calls based on interference information in surrounding cells, provided by the interference information table (IIT) in the network. Two different channel searching strategies, Sequential channel searching (SCS) and packing-based channel searching (PCS), for use in MDCA are proposed and studied. A channel reassignment procedure to further enhance the performance is also investigated. Simulation results show that MDCA significantly improves the system capacity. Furthermore, the MDCA can efficiently alleviate the call blocking in hot-spot cells. View full abstract»

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  • A New DFT-Based Channel Estimation Approach for OFDM with Virtual Subcarriers by Leakage Estimation

    Page(s): 2004 - 2008
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    Equidistance in pilot spacing is an essential condition for discrete Fourier transform (DFT)-based channel estimation in OFDM systems. However, virtual subcarriers break this condition, degrade the estimation performance, and cause the interference (called ''leakage') because the orthogonality of Fourier matrix is broken. To solve this problem, we first analyze the leakage using the DFT-inverse DFT process. The pilot subcarriers inside virtual subcarriers area are estimated by the inverse of the estimated leakage. Thus, the equidistance condition is satisfied. The proposed estimator operates well in realistic environment such as IEEE 802.16, and it is robust to an increase of virtual subcarriers. View full abstract»

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  • On Accelerating the Computation of Weight Enumerators for Convolutional Codes

    Page(s): 2009 - 2014
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (263 KB) |  | HTML iconHTML  

    The input-output weight enumerator of a convolutional code characterizes the distance spectrum and allows error probability bounds to be conveniently evaluated. To efficiently compute the weight enumerator, Pimentel recently introduced the so-called state reduction algorithm which has a convenient implementation using existing symbolic mathematical software. In this paper, we propose a dynamic state elimination ordering heuristic to further accelerate the algorithm. As demonstrated by our empirical results, the accelerated state reduction algorithm can achieve impressive complexity savings relative to the original algorithm when applied to compute the weight enumerators and its various truncated versions of convolutional codes with moderate-to-large constraint lengths. View full abstract»

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  • Outage Probabilities of a MIMO Scheme in Shadowed Fading Channels with Micro- and Macrodiversity Reception

    Page(s): 2015 - 2019
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    A compound probability density function (pdf) model is used for the outage analysis of a multiple input multiple output (MIMO) scheme operating in shadowed fading channels. Instead of the lognormal pdf, the compound pdf uses a gamma distribution to account for shadowing, leading to a closed form expression for the pdf of the signal-to-noise ratio in a shadowed fading channel. While the mitigation of short term fading is achieved through the use of multiple transmitters and multiple receivers, the shadowing is mitigated with macrodiversity using two base stations. Taking into account the fact that shadowing has a larger correlation distance, the two base stations are treated to have nonzero correlation. It is shown that the expression for the outage probability in a MIMO scheme operating in shadowed fading channels can be written in a simple form eliminating the need for numerical evaluation of double integrals. Results demonstrate the usefulness of the approach for the analysis of MIMO schemes. View full abstract»

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  • Application of Nonbinary LDPC Cycle Codes to MIMO Channels

    Page(s): 2020 - 2026
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (217 KB) |  | HTML iconHTML  

    In this paper, we investigate the application of nonbinary low-density parity-check (LDPC) cycle codes over Galois field GF(q) to multiple-input multiple-output (MIMO) channels. Two types of LDPC coded systems that employ either joint or separate MIMO detection and channel decoding are considered, depending on the size of the Galois field and the modulation choice. We construct a special class of nonbinary LDPC cycle codes called the parallel sparse encodable (PSE) codes. The PSE code, consisting of a quasi-cyclic (QC) LDPC cycle code and a simple tree code, has the attractive feature that it is not only linearly encodable, but also allows parallel encoding which can reduce the encoding time significantly. We provide a systematic comparison between nonbinary coded systems and binary coded systems in both performance and complexity. Our results show that the proposed nonbinary system employing the PSE code outperforms not only the binary LDPC code specified in the 802.16e standard, but also the optimized binary LDPC code obtained using the EXIT chart methods. Through a detailed complexity analysis, we conclude that for the MIMO channel considered, the nonbinary coded systems achieve a superior performance at a receiver complexity that is comparable to that of the binary systems. View full abstract»

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  • Systematic Expansion of Full Diversity Space-Time Multiple TCM Codes for Two Transmit Antennas

    Page(s): 2027 - 2032
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    This paper proposes improved space-time multiple TCM (ST-MTCM) codes via a systematic expansion of space- time block code (STBC) for two transmit antennas. Starting from the orthogonal STBC, the STBC set is expanded into super- orthogonal STBC, and further expanded up to spatial multiplexing in the case of BPSK and QPSK constellations. Exploiting the expanded set of STBCs as the number of states increase, improved full diversity ST-MTCM codes can be designed by increasing the coding gain and Euclidean distance of the pairwise errors. View full abstract»

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  • Energy Efficiency Analysis of Channel Aware Geographic-Informed Forwarding (CAGIF) for Wireless Sensor Networks

    Page(s): 2033 - 2038
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    This letter analytically examines the achievable energy efficiency of channel aware geographic-informed forwarding (CAGIF) algorithm, which chooses the next hop relay node by taking into consideration the underlying channel conditions, rather than purely maximizing the forwarding progress. The theoretical analysis in terms of the average forward distance is developed and the upper bound and lower bound of the average energy consumption are provided by referring to the retransmission techniques. Numerical results show that CAGIF significantly improves the energy efficiency over the previous geographic information based routing algorithms that ignore the channel conditions. View full abstract»

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  • EXIT Chart Analysis Aided Turbo MUD Designs for the Rank-Deficient Multiple Antenna Assisted OFDM Uplink

    Page(s): 2039 - 2044
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (349 KB) |  | HTML iconHTML  

    In this paper, the mutual information transfer characteristics of several novel turbo multiuser detectors (MUD) employed in space division multiple access (SDMA) aided orthogonal frequency division multiplexing (OFDM) systems are investigated with extrinsic information transfer (EXIT) charts. These novel schemes are the Bayesian, the Soft Interference cancellation aided minimum bit error rate (SIC-MBER) and the reduced-complexity minimum Bit Error Rate (RMBER) turbo MUDs. In order to increase the effective throughput of the system, a powerful MUD has to be employed in the so- called "rank-deficient" scenario, namely when the number of transmit antennas exceeds that of the receiver antennas. The classic minimum mean square error (MMSE) solutions exhibit a low complexity. However, they are overwhelmed in rank-deficient scenarios. In these situations powerful non-linear MUDs are required, which are designed in this treatise. View full abstract»

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  • User Set Estimation for Adaptive Resource Allocation in a Multiuser-OFDM System

    Page(s): 2045 - 2049
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    In the multiuser OFDM system, various adaptive subcarrier-bit-and-power allocation algorithms have been investigated based on the assumption that the number of supportable users is given. This paper proposes a supportable user set estimation in order to adopt those allocation algorithms in the multiuser-OFDM system. The number of supportable users is estimated in an iterative way by calculating the required power approximately and comparing it with an available power after determining the number of subcarriers to be allocated. Simulation results show that the proposed user set estimation provides a significant complexity reduction for the adaptive subcarrier-bit-and-power allocation in the multiuser-OFDM system. View full abstract»

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  • Low Complexity Adaptive Turbo Space-Frequency Equalization for Single-Carrier Multiple-Input Multiple-Output Systems

    Page(s): 2050 - 2056
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB) |  | HTML iconHTML  

    By combining single-carrier (SC) frequency domain equalization (FDE) and Turbo equalization, we propose a minimum mean square error (MMSE) based block-wise low complexity Turbo space-frequency equalization (TSFE) structure, which offers a tremendous complexity reduction over the symbol-wise TSFE and Turbo time-domain equalization (TTDE) structures. With a moderate code rate, the proposed SC TSFE significantly outperforms its Turbo OFDM (TOFDM) counterpart, at a comparable complexity. Besides, TSFE based on the least-mean-square structured channel estimation (LMS-SCE) provides a performance close to the case with perfect channel state information (CSI), at a high convergence rate. View full abstract»

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  • A New Time of Arrival Estimation Method Using UWB Dual Pulse Signals

    Page(s): 2057 - 2062
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    Ultra-wideband (UWB) signals can be used for accurate time of arrival (TOA) based ranging because of their high time resolution. In this paper, a novel data-aided TOA estimation method is presented using dual pulse (DP) signal structure. It employs received signal autocorrelation and threshold crossing to detect the direct path. The effects of different threshold values and training sequence lengths on the estimation accuracy of the proposed method are studied. The performance improvement of this approach over the conventional energy detection based method is also demonstrated via simulation. View full abstract»

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  • Scheduling Algorithms for Time-Varying Downlink Channels

    Page(s): 2063 - 2068
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (542 KB) |  | HTML iconHTML  

    To maximize the spectral efficiency for a time- varying downlink channel with multiple users, the scheduling order of the users needs to be optimized. The scheduling problem naturally is a combinatorial optimization problem with high complexity, which exponentially increases with the number of users. This paper proposes several low-complexity scheduling algorithms. Computer simulation results show that the proposed algorithms approach optimal performance. View full abstract»

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  • MRC Analysis of Cooperative Diversity with Fixed-Gain Relays in Nakagami-m Fading Channels

    Page(s): 2069 - 2074
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (471 KB) |  | HTML iconHTML  

    We derive the exact maximal-ratio combining (MRC) performance of dual-hop cooperative diversity systems with L-antenna destination reception in Nakagami-m fading channels, where a single-antenna relay operates in fixed-gain (semi-blind) amplify-and-forward (AF) mode. We also show that if m0, m1, and m2 are the respective Nakagami parameters for the source-to-destination, source-to-relay, and relay-to-destination links, the fixed-gain AF cooperation with MRC achieves the diversity order of m0L + min {m1, m2L}. View full abstract»

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  • Optimization of CDMA Systems with Respect to Transmission Probability, Part I: Mutual Information Rate Optimization

    Page(s): 2075 - 2083
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    Direct sequence code division multiple access (CDMA) systems that use non-continuous transmission were considered throughout the history of spread spectrum systems, but gained renewed interest with the emergence of impulse radio (IR) technology. Recently, several works had shown that in non- continuous CDMA, the transmission duty cycle (or transmission probability) has a significant effect on system performance. In this work we address the optimization of the performance of CDMA systems with adjustable transmission probabilities. We consider CDMA systems that implement non-continuous transmission by random puncturing, and study the system optimization with respect to both transmission powers (termed power control) and transmission probabilities (termed probability control). We show that the joint optimization has a significant performance advantage over the optimization with respect to transmissions powers only. For some cases we even show that the optimization with respect to transmission probabilities alone is sufficient to achieve optimal performance. In this part, we demonstrate the importance of probability control, by studying the case of frequency-flat slow-fading multiple access channel (MAC) and no spreading. We prove, for this special case, that mutual information rate optimization is achieved by probability control only, while power control is redundant. The theory is supported by simulation results, which show that the achievable rates of all users are better in a system that uses probability control instead of power control. View full abstract»

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  • Optimization of CDMA Systems with Respect to Transmission Probability, Part II: Signal to Noise Plus Interference Ratio Optimization

    Page(s): 2084 - 2093
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    Code division multiple access (CDMA) systems commonly use power control mechanism to reduce the amount of interference between the users. In part I of this paper, we introduced the concept of probability control that optimizes system performance with respect to the users' transmission probabilities. The importance of probability control was demonstrated by proving that probability control alone optimizes the mutual information rates over a frequency-flat slow-fading multiple access channel. In this part we extend this result to the optimization of the average signal-to-noise plus interference ratio (SIR) in a CDMA system over a frequency-selective slow- fading channel model and any network topology. We prove that there is a group of CDMA receivers, in which the average SIR (ASIR) of all users is maximized using probability control (while all users transmit their maximal allowed power). This receivers group includes, among others, the common matched filter (MF) RAKE receiver, as well as the sophisticated minimal mean square error (MMSE) RAKE receiver. Simulations demonstrate for a 2- users scenario that both users achieve significantly higher ASIR using probability-control instead of power-control. Results are applicable both for CDMA and impulse radio (IR) systems. View full abstract»

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  • Bandwidth-Guaranteed Fair Scheduling with Effective Excess Bandwidth Allocation for Wireless Networks

    Page(s): 2094 - 2105
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB) |  | HTML iconHTML  

    Traffic scheduling is key to the provision of quality of service (QoS) differentiation and guarantees in wireless networks. Unlike its wireline counterpart, wireless communications pose special channel-specific problems such as time-varying link capacities and location-dependent errors. These problems make designing efficient and effective traffic scheduling algorithms for wireless networks very challenging. Although many wireless packet scheduling algorithms have been proposed in recent years, issues such as how to improve bandwidth efficiency and maintain goodput fairness with various link qualities for power-constrained mobile hosts remain unresolved. In this paper, we devise a simple wireless packet scheduling algorithm called bandwidth-guaranteed fair scheduling with effective excess bandwidth allocation (BGFS-EBA), which addresses these issues. Our studies reveal that BGFS-EBA effectively distributes excess bandwidth, strikes a balance between effort-fair and outcome- fair, and provides a delay bound for error-free flows and transmission effort guarantees for error-prone flows. View full abstract»

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  • Optimal Diversity Performance of Space Time Block Codes in Correlated Distributed MIMO Channels

    Page(s): 2106 - 2118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (654 KB) |  | HTML iconHTML  

    This paper investigates optimal transmission of space-time block codes (STBCs) in distributed multiple-input multiple-output (D-MIMO) Rayleigh fading channels. The optimal diversity performance is achieved through transmit power allocation implemented at the receiver based on transmit and receive correlations to minimize the average symbol error rate (SER). Evaluation of SER performance of uncoded STBCs over a generalized distributed antenna (DA) topology is first presented, with exact analytical SER expressions derived for MQAM and MPSK symbols. SER upper bounds are also derived, based on which two criteria for complexity reduced antenna subset selection with sub-optimal power allocation are further proposed, whose performance approaches optimal over correlated D-MIMO channels. Moreover, a novel simplified but close SER approximation scheme is devised to significantly facilitate optimal SER calculation. We continue to thoroughly analyze how the optimal diversity is affected by large scale fading, targeted data rate, antenna correlations and transmit power. Finally, we develop a surprisingly close and useful analogy between open loop STBCs in co-located MIMO and optimal STBCs in D-MIMO with minimum feedback (i.e., n bits for n DAs in Criterion 2 with power allocation scheme 2 which equally allocates power to the selected DAs). Extensive simulation results have been presented to demonstrate the effectiveness of our analysis. View full abstract»

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  • Enhanced QoS Multicast Routing in Wireless Mesh Networks

    Page(s): 2119 - 2130
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    Wireless mesh network (WMN) has recently emerged as a promising technology for next-generation wireless networking. In WMNs, many important applications, such as mobile TV and video/audio conferencing, require the support of multicast communication with quality-of-service (QoS) guarantee. In this paper, we address the QoS multicast routing issue in WMNs. Specifically, we propose a novel network graph preprocessing approach to enable traffic engineering and enhance the performance of QoS multicast routing algorithms. In this approach, we employ prioritized admission control scheme and develop a utility-constrained optimal priority gain policy. Extensive simulation results show that our approach can significantly improve the performance of QoS multicast routing in WMNs. View full abstract»

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  • Fixing the Complexity of the Sphere Decoder for MIMO Detection

    Page(s): 2131 - 2142
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    A new detection algorithm for uncoded multiple input-multiple output (MIMO) systems based on the complex version of the sphere decoder (SD) is presented in this paper. It performs a fixed number of operations during the detection process, overcoming the two main problems of the SD from an implementation point of view: its variable complexity and its sequential nature. The algorithm combines a novel channel matrix ordering with a search through a very small subset of the complete transmit constellation. A geometrically-based method is used to study the effect the proposed ordering has on the statistics of the MIMO channel. Using those results, a generalization is given for the structure this subset needs to follow in order to achieve quasi-maximum likelihood (ML) performance. Simulation results show that it has only a very small bit error rate (BER) degradation compared to the original SD while being suited for a fully-pipelined hardware implementation due to its low and fixed complexity. View full abstract»

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  • Spectral Efficiency Enhancement in Multi-Channel Systems Using Redundant Transmission and Diversity Reception

    Page(s): 2143 - 2153
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (487 KB) |  | HTML iconHTML  

    We first consider conventional multi-channel systems with fixed-power variable-rate transmission of independent data streams as a function of channel variations. In these conventional systems, no data is transmitted through the sub-channels whose received signal strength is below a certain cutoff threshold. We then propose new hybrid adaptive modulation and diversity schemes for multi-channel transmission systems. The proposed hybrid schemes attempt to increase the overall spectral efficiency by (i) transmitting redundant information symbols through the deeply faded sub-channels that are not to be used in conventional multi-channel systems and then (ii) diversity combining these replicas at the receiver end. We evaluate the performance of the newly proposed hybrid schemes and compare their spectral efficiency with that of (i) the conventional scheme and (ii) a benchmark scheme which maximizes the overall spectral efficiency but is too complex for practical implementation. We show using some selected numerical examples that the proposed hybrid schemes offer spectral efficiency very close to that of the optimal scheme with much reduced complexity. View full abstract»

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Aims & Scope

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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Meet Our Editors

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