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Communications, IEEE Transactions on

Issue 5 • Date May 2007

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Displaying Results 1 - 25 of 40
  • Table of contents

    Publication Year: 2007 , Page(s): C1 - C4
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    Freely Available from IEEE
  • IEEE Transactions on Communications publication information

    Publication Year: 2007 , Page(s): C2
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  • Convergence Speed and Throughput of Analog Decoders

    Publication Year: 2007 , Page(s): 833 - 836
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB) |  | HTML iconHTML  

    This letter is concerned with the implementation of iterative decoding algorithms in analog integrated circuits. We study the convergence speed and the throughput of analog decoders for low-density parity-check codes, and show that they depend on the code, the decoding algorithm, the signal-to-noise ratio, and the average time constant of the analog circuit interconnections. However, they are not a function of the variance of the time constants. The analysis presented here can be used for selecting suitable codes and decoding algorithms for analog decoding. Furthermore, it can be used to estimate the throughput of an analog decoder, if the average time constant of the analog circuit is known View full abstract»

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  • Structured IRA Codes: Performance Analysis and Construction

    Publication Year: 2007 , Page(s): 837 - 844
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB) |  | HTML iconHTML  

    In this letter, we present design techniques for structured irregular repeat-accumulate (S-IRA) codes with low error-rate floors. These S-IRA codes need not be quasi-cyclic, permitting flexibility in code dimension, length, and rate. We present a simple ensemble estimate of the level of the error-rate floor of finite-length IRA codes on the additive white Gaussian noise channel. This performance estimate provides guidance on the choice of IRA code column weights which yield low floors. We also present two design algorithms for S-IRA codes accompanied by software- and hardware-based performance results which demonstrate their low floors. Lastly, we present two design algorithms for multirate S-IRA code families implementable by a single encoder/decoder View full abstract»

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  • Performance Analysis for OFDMA in the Presence of Tone Interference

    Publication Year: 2007 , Page(s): 845 - 849
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (238 KB) |  | HTML iconHTML  

    Space-frequency coded (SFC) orthogonal frequency-division multiple access (OFDMA) is considered in the presence of multitone (MT) interference. Analytical expressions for the bit-error probability (BEP) are derived for OFDMA with SFC in a frequency-selective fading environment. It is shown that SFC increases the resistance of OFDMA against the MT interference and reduces BEP considerably View full abstract»

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  • Source-Matched Spreading Codes for Optical CDMA

    Publication Year: 2007 , Page(s): 850 - 853
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (419 KB) |  | HTML iconHTML  

    Puncturing is studied as a physical layer mechanism for efficiently transmitting datastreams containing bits of unequal priority via wavelength-time optical code-division multiple access. Puncturing increases system capacity, while ensuring that important bits are received with low bit-error rate View full abstract»

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  • Genetic-Algorithm-Assisted Maximum-Likelihood Detection of OFDM Symbols in the Presence of Nonlinear Distortions

    Publication Year: 2007 , Page(s): 854 - 859
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1031 KB) |  | HTML iconHTML  

    This letter aims at proposing the use of evolutionary computation methodologies (i.e., genetic algorithms) in order to solve the problem of the maximum-likelihood estimation of orthogonal frequency-division multiplexing symbols in the presence of nonlinear distortions. Experimental results can prove the effectiveness of the proposed detection algorithm achieved with a reasonable computational load View full abstract»

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  • A Near-Optimal Linear Crosstalk Precoder for Downstream VDSL

    Publication Year: 2007 , Page(s): 860 - 863
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    This letter presents a linear crosstalk precoder for very-high-speed digital subscriber lines (VDSL) that has a low run-time complexity. A lower bound on the data rate of the precoder is developed, and guarantees that the precoder achieves near-optimal performance in 99% of VDSL channels View full abstract»

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  • Pilot Designs for Consistent Frequency-Offset Estimation in OFDM Systems

    Publication Year: 2007 , Page(s): 864 - 877
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1833 KB) |  | HTML iconHTML  

    This paper presents pilot designs for consistent frequency-offset estimation of orthogonal frequency-division multiplexing systems in frequency-selective fading channels. We describe two design approaches, namely, consistency in the probabilistic sense and absolute consistency. Existing preambles and pilot designs in the literature do not guarantee the absolute consistency. We derive general criteria for both approaches, present sufficient conditions on the pilot structures over the maximum carrier frequency offset (CFO) estimation range (half of the sampling rate), and derive simple pilot designs satisfying these conditions. We also extend the sufficient conditions to any arbitrary but fixed CFO estimation range, and present some generalized design patterns. Furthermore, the CFO estimation performances of distinct consistent pilot designs can be quite different at moderate or low signal-to-noise ratio (SNR) due to different statistics of outliers which also yields a link failure. We develop efficient pilot-design criteria that provide both consistency and robustness against outliers at moderate-to-low SNR. Our consistent pilot designs facilitate flexible and economical implementation, while our robust pilot designs enable wireless links with less outage and better resilience View full abstract»

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  • A Stochastic Approximation Approach to the Power-Control Problem

    Publication Year: 2007 , Page(s): 878 - 886
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (617 KB) |  | HTML iconHTML  

    This paper proposes and analyzes a new distributed power-control algorithm based on the theory of stochastic approximation. The power-control problem is first converted into a stochastic approximation problem in which the zero point of a specific function is determined. A distributed power-control algorithm is then derived and its convergence properties are analyzed using standard techniques. In the distributed algorithm, each user iteratively updates its power level by using estimates of the inverse of the signal-to-interference ratio (SIR) of its channel. No knowledge of the channel gains or state information of other users is required. Moreover, the algorithm is robust in the sense that it can handle errors in the bit-error rate estimates, and hence, can be used in practical scenarios. Convergence of the algorithm is analyzed in the almost-sure sense View full abstract»

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  • Performance of Optimum and Suboptimum Combining Diversity Reception for Binary and Quadrature DPSK Over Independent, Nonidentical Rayleigh Fading Channels

    Publication Year: 2007 , Page(s): 887 - 894
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    This paper is concerned with the error-performance analysis of binary and quadrature differential phase-shift keying with differential detection over the nonselective, Rayleigh fading channel with combining diversity reception. The diversity channels are independent, but have nonidentical statistics. The fading process in each channel is assumed to have an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. Both optimum diversity reception and suboptimum diversity reception are considered. Results available previously apply only to the case of second-order diversity, and require numerical integration for their actual evaluation. Our results are more general, in that the order of diversity is arbitrary. Moreover, the bit-error probability (BEP) result is obtained in an exact, closed-form expression which shows the behavior of the BEP as an explicit function of the one-symbol-interval fading correlation coefficient at the matched-filter output, the mean received signal-to-noise ratio per symbol per channel, and the order of diversity View full abstract»

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  • Slow Adaptive M -QAM With Diversity in Fast Fading and Shadowing

    Publication Year: 2007 , Page(s): 895 - 905
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB) |  | HTML iconHTML  

    This paper investigates the performance of adaptive M-ary quadrature amplitude modulation (QAM) with antenna subset diversity. We consider a slow adaptive modulation (SAM) technique that adapts the constellation size to the slow variation of the channel due, for example, to shadowing. The proposed SAM technique is more practical than conventional fast adaptive modulation (FAM) techniques that require adaptation to fast-fading variations. Our results show that the SAM technique can provide a substantial increase in throughput with respect to fixed schemes while maintaining an acceptable low bit-error outage. We also compare SAM and FAM techniques, showing that the throughput of SAM can be, in many practical cases, close to that of FAM, despite the fact that SAM is less complex and requires a lower feedback rate. For example, using a set of possible modulations {4,16,64}-QAM with dual-branch maximal ratio combining reception, 5% outage at a bit-error probability of 10-2 and a median signal-to-noise ratio of 22 dB, SAM is capable of improving the mean spectral efficiency of fixed schemes from about 1.9 to 4.7 b/s/Hz, which is close to the 5.5 b/s/Hz achieved by FAM View full abstract»

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  • Blind Receiver Design for OFDM Systems Over Doubly Selective Channels

    Publication Year: 2007 , Page(s): 906 - 917
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB) |  | HTML iconHTML  

    We develop blind data detectors for orthogonal frequency-division multiplexing (OFDM) systems over doubly selective channels by exploiting both frequency-domain and time-domain correlations of the received signal. We thus derive two blind data detectors: a time-domain data detector and a frequency-domain data detector. We also contribute a reduced complexity, suboptimal version of a time-domain data detector that performs robustly when the normalized Doppler rate is less than 3%. Our frequency-domain data detector and suboptimal time-domain data detector both result in integer least-squares (LS) problems. We propose the use of the V-BLAST detector and the sphere decoder. The time-domain data detector is not limited to the Doppler rates less than 3%, but cannot be posed as an integer LS problem. Our solution is to develop an iterative algorithm that starts from the suboptimal time-domain data detector output. We also propose channel estimation and prediction algorithms using a polynomial expansion model, and these estimators work with data detectors (decision-directed mode) to reduce the complexity. The estimators for the channel statistics and the noise variance are derived using the likelihood function for the data. Our blind data detectors are fairly robust against the parameter mismatch View full abstract»

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  • The List-Sequential (LISS) Algorithm and Its Application

    Publication Year: 2007 , Page(s): 918 - 928
    Cited by:  Papers (36)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (996 KB) |  | HTML iconHTML  

    For iterative detection/decoding (turbo) schemes, we modify sequential decoding, which contrary to a posteriori probability (APP) Bahl-Cocke-Jelinek-Raviv (BCJR) decoding, enjoys a complexity almost independent of the number of states. This novel list-sequential (LISS) decoder avoids most of the drawbacks of the classical sequential decoders, such as variable workload and erased frames when working within a turbo scheme. It uses a metric containing a priori and channel values, a metric length bias term for speeding up the tree search, a soft extension of paths without increasing the stack size, and soft weighting to obtain a soft output. We present several turbo applications using the LISS including equalization, single-antenna interference cancellation, multiuser and multiple-input multiple-output detection. It is shown that the LISS achieves the optimal (genie) or APP performance at a bit-error rate after the outer decoder of less than 10-4, but it also works with channels which have a high number of taps, constellation points, antennas, and states where the APP (BCJR) algorithm becomes infeasible View full abstract»

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  • Performance Evaluation of UWB Systems Exploiting Orthonormal Pulses

    Publication Year: 2007 , Page(s): 929 - 935
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (507 KB) |  | HTML iconHTML  

    The novel pulses, which not only meet the power spectral mask of the Federal Communications Commission (FCC) but also preserve orthonormality at the correlation receiver, have been proposed by Kim for high data rate communications in indoor ultra-wideband (UWB) systems. The proposed multiple orthonormal pulses comply with the FCC spectral mask without additional frequency shifting or bandpass filters, and furthermore, provide enhanced bit-error rate (BER) performance, compared with a well-known Gaussian monocycle and modified Hermite pulses. This paper analyzes the impact of the proposed pulses' properties, such as their auto- and cross-correlations, on the correlation receiver of the UWB system based on the pulse position modulation. The performance of the proposed pulses are compared with different waveforms under various conditions, such as multipath fading, timing mismatch, and multiuser interference. We also discuss a modulation scheme using the multiple orthogonal pulses to achieve the enhancement of data rate and the impact of the correlation characteristics of the proposed waveforms on the BER performance. Simulation results demonstrate the effectiveness of the proposed orthonormal pulses in various conditions, comparing with different waveforms View full abstract»

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  • Signal Sets From Functions With Optimum Nonlinearity

    Publication Year: 2007 , Page(s): 936 - 940
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    Signal sets with the best correlation property are desirable in code-division multiple-access (CDMA) systems. In this paper, the construction of Wootters and Fields for mutually unbiased bases is extended into a generic construction of signal sets using planar functions. Then, specific classes of planar functions and almost bent functions are employed to obtain (q2+q,q) signal sets. The signal sets derived from planar functions are optimal with respect to the Levenstein bound, and those obtained from almost bent functions nearly meet the Levenstein bound. The signal sets constructed in this paper could have a very small alphabet size, and have applications in synchronous DS-CDMA systems, where the number of users is greater than the signal space dimension or the spreading factor View full abstract»

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  • Opportunistic Beamforming and Scheduling for OFDMA Systems

    Publication Year: 2007 , Page(s): 941 - 952
    Cited by:  Papers (50)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (715 KB) |  | HTML iconHTML  

    Orthogonal frequency-division multiple access (OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses three problems in multiuser diversity for OFDMA systems. First, we propose a way to significantly reduce the amount of channel state information (CSI) feedback without sacrificing performance too much, by selective and adaptive feedback. Second, we propose a way to increase the cell throughput and fairness by applying an opportunistic beamforming scheme to orthogonal frequency-division multiplexing. This beamforming scheme increases the frequency fading rate, which increases the multiuser diversity effect. Thirdly, we deal with the issue of fairness and quality-of-service (QoS) in opportunistic systems by proposing a modified proportional fair (PF) scheduler for OFDMA. Key features in the scheduler are that it incorporates QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate the performance of the proposed schemes. The opportunistic beamforming scheme performed well in comparison with several other schemes. The modified PF scheduler was able to give users different QoS, based on their requirements, while still exploiting multiuser diversity View full abstract»

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  • Channel-Aware ALOHA-Based OFDM Subcarrier Assignment in Single-Cell Wireless Communications

    Publication Year: 2007 , Page(s): 953 - 962
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (777 KB) |  | HTML iconHTML  

    Usually, centralized channel state information (CSI) is assumed to exploit the multiuser diversity with a smart transmission scheduler. However, such centralized CSI can be impractical for a broadband wireless communication system with a large number of mobile users (MUs). In this paper, we propose a decentralized method to exploit the multiuser diversity in a single cell scenario with orthogonal frequency-division multiplexing (OFDM) based downlink. The central part of our approach is the channel-aware ALOHA-based OFDM subcarrier assignment. According to it, each MU measures the channel at all OFDM subcarriers and tries to obtain proper ones by sending a service-request packet through the corresponding orthogonal uplink subchannel. This packet is sent when the measured channel-fading level exceeds a predetermined threshold xi. The base station processes these request packets with a collision-reception model, and assigns the corresponding subcarrier(s) to the MU whose request packet has been successfully received. Two implementation algorithms are developed, by solving the problem of optimization of xi under different system configurations. Computer simulations show that in comparison with the standard round-robin method, the proposed algorithms offer a substantial data-rate improvement, especially when the correlation property of the OFDM subcarriers is properly exploited View full abstract»

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  • Utility Max-Min Flow Control Using Slope-Restricted Utility Functions

    Publication Year: 2007 , Page(s): 963 - 972
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1285 KB) |  | HTML iconHTML  

    We present a network architecture for the distributed utility max-min flow control of elastic and nonelastic flows where utility values of users (rather than data rates of users) are enforced to achieve max-min fairness. The proposed link algorithm converges to utility max-min fair bandwidth allocation in the presence of round-trip delays without using the information of users' utility functions. To show that the proposed algorithm can be stabilized not locally but globally, we found that the use of nonlinear control theory is inevitable. Even though we use a distributed flow-control algorithm, it is shown that any kind of utility function can be used as long as the minimum slopes of the functions are greater than a certain positive value. Though our analysis is limited to the single-bottleneck and homogeneous-delay case, we believe that the proposed algorithm is the first to achieve utility max-min fairness with guaranteed stability in a distributed manner View full abstract»

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  • Preservation of Conditionally Nonblocking Switches Under Two-Stage Interconnection

    Publication Year: 2007 , Page(s): 973 - 980
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2469 KB) |  | HTML iconHTML  

    The two-stage interconnection network is conceivably the most compact design for interconnecting small switches into a large switch. Switches so constructed typically can be controlled in the self-routing manner, because the route from an input to an output is unique. Different orderings of network input/output result in different versions of the two-stage interconnection network, two of which are known to preserve various classes of conditionally nonblocking switches. This paper adds Latin-square switches, rotators, reflectors, twisters, and untwisters to this set of classes with applications in load balancing, crosstalk-free optical switching, full connectivity among multiple users, etc. Knowledge of switch preservation under a certain style of multistage interconnection not only allows recursive construction of indefinitely large switches, but also provides insight, generality, and algorithmic flexibility in the construction View full abstract»

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  • Strictly Nonblocking f-Cast Logd(N,m,p) Networks

    Publication Year: 2007 , Page(s): 981 - 986
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (770 KB) |  | HTML iconHTML  

    Necessary and sufficient conditions for Logd(N,m,p) network to be point-to-point strictly nonblocking are known. Recently, Kabacinski and Danilewicz obtained necessary and sufficient conditions for the Log2(N,0,p) network to be broadcast strictly nonblocking. In this paper, we give necessary and sufficient conditions for Logd(N,m,p) to be f-cast strictly nonblocking for every f, thus covering the point-to-point case (f=1) and the broadcast case (f=N) as special cases View full abstract»

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  • A Complete 8-GHz QPSK-MODEM Featuring Novel Subcarrier and Data Synchronization for Optical Communications

    Publication Year: 2007 , Page(s): 987 - 995
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2072 KB) |  | HTML iconHTML  

    We describe the application of subcarrier multiplexing (SCM) to enable broadband transmission beyond the modal bandwidth of multimode fiber (MMF) optical links. The application of a quadrature phase-shift keying modem featuring novel carrier and symbol-timing recovery circuits, demonstrates significant enhancement in channel capacity. By using a 2.7-GHz pilot-tone-injected phase-locked loop (PLL) and referencing subscriber data to a prescaled version of the subcarrier, zero-latency carrier and data synchronization has been achieved exhibiting 675 Mb/s bit-oriented clock extraction in network terminal equipments. The novel scheme is scalable to higher aggregate rates and upgrades to existing installed-base 50 mum MMF infrastructure to provide low-cost, high-capacity interconnects for storage area and campus network applications View full abstract»

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  • Optimal Transmission Power for Single- and Multi-Hop Links in Wireless Packet Networks With ARQ Capability

    Publication Year: 2007 , Page(s): 996 - 1006
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    In this paper, we rigorously investigate the energy minimization problem for wireless packet networks with automatic repeat request (ARQ) capability. We first formulate the problem for the single-hop case under constrained packet delay and reliability and derive the necessary and sufficient condition for the optimal transmission power at each ARQ stage. We formulate a global rule of optimal transmission power control that achieves optimality regardless of the delay and reliability constraints. Then we extend it to encompass the multi-hop case by dividing the overall problem into two subproblems-energy determination for each ARQ stage and energy distribution among the constituent nodes. We show that the optimality condition established for the single-hop case is also applicable to solve the energy determination problem in the multi-hop case, rendering an optimal solution to the energy distribution problem. Numerical examples reveal that a significant amount of energy is saved by adopting the optimal transmission power and the performance gain is strongly correlated with the decreasing property of the frame error rate View full abstract»

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  • Performance of Two Dual-Branch Postdetection Switch-and-Stay Combining Schemes in Correlated Rayleigh and Rician Fading

    Publication Year: 2007 , Page(s): 1007 - 1019
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (761 KB) |  | HTML iconHTML  

    The performance of binary frequency-shift keying (BFSK) and M-ary frequency shift keying (MFSK) with dual-branch postdetection switch-and-stay combining (SSC) in correlated Rayleigh and Rician fading is studied. Two postdetection SSC receivers are considered and the performances of noncoherent BFSK and MFSK are analyzed. Closed-form expressions are derived for the average bit-error rate (BER) of BFSK and MFSK with postdetection SSC in correlated Rayleigh and Rician fading. Optimum switching thresholds that minimize the average BER are obtained. Extensive Monte Carlo simulations are presented to test the validity of the analytical results. The performance of dual-branch postdetection SSC is compared with the performance of dual-branch predetection SSC. The effects of correlation, fading parameter, average fading power imbalance, and switching threshold on the performances of postdetection SSC receivers are examined View full abstract»

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  • Opportunistic Feedback for Multiuser MIMO Systems With Linear Receivers

    Publication Year: 2007 , Page(s): 1020 - 1032
    Cited by:  Papers (27)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1402 KB) |  | HTML iconHTML  

    A novel multiuser scheduling and feedback strategy for the multiple-input multiple-output (MIMO) downlink is proposed in this paper. It achieves multiuser diversity gain without substantial feedback requirements. The proposed strategy uses per-antenna scheduling at the base station, which maps each transmit antenna at the base station (equivalently, a spatial channel) to a user. Each user has a number of receive antennas that is greater than or equal to the number of transmit antennas at the base station. Zero-forcing receivers are deployed by each user to decode the transmitted data streams. In this system, the base station requires users' channel quality on each spatial channel for scheduling. An opportunistic feedback protocol is proposed to reduce the feedback requirements. The proposed protocol uses a contention channel that consists of a fixed number of feedback minislots to convey channel state information. Feedback control parameters including the channel quality threshold and the random access feedback probability are jointly adjusted to maximize the average throughput performance of this system. Multiple receive antennas at the base station are used on the feedback channel to allow decoding multiple feedback messages sent simultaneously by different users. This further reduces the bandwidth of the feedback channel. Iterative search algorithms are proposed to solve the optimization for selection of these parameters under both scenarios that the cumulative distribution functions of users are known or unknown to the base station View full abstract»

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Aims & Scope

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

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia