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Communications, IEEE Transactions on

Issue 4 • Date April 2008

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Displaying Results 1 - 21 of 21
  • Table of contents

    Publication Year: 2008 , Page(s): i - ii
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  • Transactions Letters - Random Redundant Iterative Soft-in Soft-out Decoding

    Publication Year: 2008 , Page(s): 513 - 517
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (227 KB) |  | HTML iconHTML  

    This letter presents an iterative soft-in soft-out (SISO) decoding algorithm based on redundant Tanner graphs that is applicable to arbitrary linear block codes. The proposed algorithm utilizes the permutation group of a code in order to efficiently and randomly generate redundant parity-checks. View full abstract»

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  • Multistage Selective ML Decoding for Multidimensional Multicode DS-CDMA with Precoding

    Publication Year: 2008 , Page(s): 518 - 522
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (290 KB) |  | HTML iconHTML  

    A high-rate, reliable uplink transmission is designed using multistage selective maximum-likelihood (ML) decoding for the multicode (MC) direct-sequence code-division multiple access (DS-CDMA) with precoding. The precoding achieves a constant envelope MC signal by adding some redundancy bits, resulting in rate loss, but multidimensional signaling on top of MC DS-CDMA enables to further increase the date rate. The designed multistage selective ML decoding is shown to be promising for use in uplink high-rate and reliable data transmission. View full abstract»

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  • Effects of Spreading and Training on Capacity in Overloaded CDMA

    Publication Year: 2008 , Page(s): 523 - 526
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    We address the issue of sum-capacity in an overloaded, uplink, synchronous CDMA system in a quasi-static fading environment. Part of each fading block is reserved for channel training and the remainder of the block is used for data transmission. We evaluate bounds on sum-capacity using the estimates from channel estimation, and consider the effects on the lower bound caused by the spreading-coding-training tradeoff. View full abstract»

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  • Asymptotic Error Rate Analysis of Dual-Branch Diversity over Correlated Rician Channels

    Publication Year: 2008 , Page(s): 527 - 530
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    Asymptotic error rate expressions are derived for equal gain combining and selection combining on dual-branch correlated Rician channels. The asymptotic error rate performances of three popular diversity combining techniques are compared and some insights are obtained. The impacts of various channel parameters on the asymptotic performances of these diversity combining techniques are studied comprehensively. Some previous observations on diversity performances on correlated Rician channels are unified and further extended. View full abstract»

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  • Optimum Resource Allocation for Relay Networks with Differential Modulation

    Publication Year: 2008 , Page(s): 531 - 534
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    In this paper, we investigate the resource allocation in a differentially modulated relay network. In addition to the energy optimization, we also consider location optimization to minimize the average symbol error rate (SER). The closed- form solution is derived for the single-relay case, and formulas allowing numerical search are provided for multiple-relay cases. Analytical and simulated comparisons confirm that the optimized systems provide considerable improvement over the unoptimized systems, and that the minimum SER can be achieved via the joint energy-location optimization. View full abstract»

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  • A Framework for the Analysis of UWB Receivers in Sparse Multipath Channels with Intra-Pulse Interference via Pade Expansion

    Publication Year: 2008 , Page(s): 535 - 541
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (445 KB) |  | HTML iconHTML  

    In this letter, we propose a framework for analyzing the performance of ultra wide band (UWB) receiver architectures in sparse multipath channels with overlapped multipath components (MPCs). The proposed methodology is based on approximating the moment generating function (MGF) of the received signal-to-noise ratio (SNR) via Pade expansion. The method can be applied to any fading scenarios and to any UWB receiver architectures, provided that the MGF of the SNR can be characterized in terms of a convergent Pade expansion. By comparing the results obtained from the analysis with those obtained from simulations in selected reference scenarios, it can be observed that the proposed approximation is very accurate. View full abstract»

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  • Performance Improvement of Non-Data-Aided Feedforward Symbol Timing Estimation Using the "Better Than" Raised-Cosine Pulse

    Publication Year: 2008 , Page(s): 542 - 544
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (114 KB) |  | HTML iconHTML  

    It is known that the "better than" raised-cosine pulse has several advantages over the conventional raised-cosine pulse. In addition to the advantages previously reported, this letter reports that the "better than" raised-cosine pulse enables better performance of symbol timing estimation than the raised-cosine pulse. Both Cramer-Rao lower bounds and simulations of practical synchronizers show the superiority of the new pulse. The performance gain can be as much as 3.4 dB for a practical system. View full abstract»

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  • Transactions Papers - Constructions of Nonbinary Quasi-Cyclic LDPC Codes: A Finite Field Approach

    Publication Year: 2008 , Page(s): 545 - 554
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (457 KB) |  | HTML iconHTML  

    This paper is concerned with construction of efficiently encodable nonbinary quasi-cyclic LDPC codes based on finite fields. Four classes of nonbinary quasi-cyclic LDPC codes are constructed. Experimental results show that codes constructed perform well with iterative decoding using a fast Fourier transform based q-ary sum-product algorithm and they achieve significant coding gains over Reed-Solomon codes of the same lengths and rates decoded with either algebraic hard- decision Berlekamp-Massey algorithm or algebraic soft-decision Kotter-Vardy algorithm. View full abstract»

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  • Turbo Coded Modulation for Unequal Error Protection

    Publication Year: 2008 , Page(s): 555 - 564
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (486 KB) |  | HTML iconHTML  

    A major concern in designing communication systems is to maintain quality of service for a wide range of channel conditions. This is an important issue particularly for the applications where precise characterization of the channel is impossible. For such applications, the source data can be classified into several classes and Unequal Error Protection (UEP) can be used to effectively protect the more important classes even in poor receiving conditions. This paper is focused on the study, design, and performance evaluation of unequal error protecting turbo coded modulation schemes. We first propose several schemes for unequal error protecting using turbo coded modulation. All these schemes provide high performance gains for more important classes that can hardly be achieved using conventional coded modulation schemes. We then study unequal error protecting turbo coded modulation schemes by deriving channel capacity and cutoff rates for different protection levels. We show that for more important classes more room is available for improvement. View full abstract»

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  • A Unified Framework for Layered Transmission Over Fading and Packet Erasure Channels

    Publication Year: 2008 , Page(s): 565 - 573
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (363 KB) |  | HTML iconHTML  

    We consider layered transmission of a successively refinable source over a quasi-static fading channel. We establish a duality relationship between this problem and that of packet transmission over erasure channels and use it to share solution techniques in both domains. For a Gaussian source and the fading channel, a low-complexity, optimal algorithm is proposed, and it is shown that the corresponding dual for packet erasure channels has a linear complexity as opposed to the quadratic complexity of the best known optimal algorithms in the literature. For non-Gaussian sources, the optimal rate allocation problem for fading channels is solved using the dual solution for erasure channels. It is also shown that a single-layer system is optimal for fading channels if the goal is to maximize the rate. Numerical results for multiple antenna Rayleigh fading channels are presented for Gaussian sources and practical image coders. It is shown that a few number of layers significantly improves the performance. Finally, we numerically show that for practical operating conditions, optimizing the asymptotic measure of distortion exponent is not enough when there are more than one transmit or receive antennas. View full abstract»

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  • Multiuser Interference Cancellation and Detection for Users with More Than Two Transmit Antennas

    Publication Year: 2008 , Page(s): 574 - 583
    Cited by:  Papers (34)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (427 KB) |  | HTML iconHTML  

    We consider J transmitter units each equipped with N transmit antennas over wireless Rayleigh fading channels. Previously in [1], it was proved that when each transmitter unit has TV transmit antennas, using (J - 1)N + r receive antennas for any r ges 1, the receiver can completely separate the signals of J users. The provided diversity to each user was shown to be Nr if the units employ space-time trellis codes even if the units transmit asynchronously. Here, we consider the case when all units are synchronized and employ quasi-orthogonal space-time block codes (N > 2). It is proved that in this case a receiver with J + r - 1 antennas with r ges 1 can separate the transmitted signals of all units and provide each unit with a diversity order of Nr. Based on our interference cancellation technique, we then offer an array processing scheme which provides trade-off between diversity and spatial multiplexing. It is shown via simulations that this array processing scheme performs better than well-known modulation schemes, e.g. space-time block codes and BLAST, for a moderate number of receive antennas. View full abstract»

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  • Trade-Off Between Diversity and Channel Estimation Errors in Asynchronous MC-DS-CDMA and MC-CDMA

    Publication Year: 2008 , Page(s): 584 - 597
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (461 KB) |  | HTML iconHTML  

    This paper investigates the trade-off between diversity and channel estimation errors for asynchronous multi-carrier CDMA (MC-CDMA) and multicarrier direct-sequence CDMA (MC-DS-CDMA). We construct a side-by-side comparison between the two systems by assuming equal operating and channel conditions. Both systems perform pilot-symbol- aided channel estimation and maximal ratio combining at the receiver, where the weighting coefficients are determined by the channel estimates at each sub-carrier. Closed-form expressions for the probability of error of both systems are derived under two separate channel scenarios. These two scenarios assume a frequency-selective Rayleigh fading channel, where the coherence bandwidth is equal to either the bandwidth of a MC-DS-CDMA sub-band or the bandwidth of a MC-CDMA sub-band. Finally, we compare the bit error rates of the two systems for different information rates, number of users, and number of pilot symbols used in each channel estimate. View full abstract»

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  • Network Coding for Efficient Multicast Routing in Wireless Ad-hoc Networks

    Publication Year: 2008 , Page(s): 598 - 607
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    Network coding is a powerful coding technique that has been proved to be very effective in achieving the maximum multicast capacity. It is especially suited for new emerging networks such as ad-hoc and sensor networks. In this work, we investigate the multicast routing problem based on network coding and put forward a practical algorithm to obtain the maximum flow multicast routes in ad-hoc networks. The "conflict phenomenon" that occurs in undirected graphs will also be discussed. Given the developed routing algorithm, we will present the condition for a node to be an encoding node along with a corresponding capacity allocation scheme. We will also analyze the statistical characteristics of encoding nodes and maximum flow in ad-hoc networks based on random graph theory. View full abstract»

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  • Differentially-Encoded Di-Symbol Time-Division Multiuser Impulse Radio in UWB Channel

    Publication Year: 2008 , Page(s): 608 - 618
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (695 KB) |  | HTML iconHTML  

    Ultra-wideband (UWB) communication systems are expected to operate in a highly frequency-selective multipath fading environment. To exploit multipath diversity gains in a multiuser scenario, we developed a differentially-encoded, di-symbol time-division multiuser impulse radio (d2TD-IR) system with delay-sum autocorrelation receivers. In traditional time-division multiple access systems, each user transmits a single pulse during a symbol duration in a pre-assigned chip which is longer than maximum excess delay of the channel. However, due to the exponential decay property of UWB channel, we proposed the use of much shorter chip duration, which significantly increases the transmission rate. Because dense pulse transmission will induce multiuser interference, two time-hopping access sequences, which alternately encode the odd- and even-index symbols, are employed with delay-sum autocorrelation receivers to maximally suppress the interference. It was shown that when the chip duration is properly chosen, the proposed system outperforms the conventional time-hopping impulse radio system at high signal-to-noise ratio. This paper also proposed a method to estimate the optimal chip duration when only the average power decay profile of the UWB channel is known. View full abstract»

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  • Scattered Pilots and Virtual Carriers Based Frequency Offset Tracking for OFDM Systems: Algorithms, Identifiability, and Performance Analysis

    Publication Year: 2008 , Page(s): 619 - 629
    Cited by:  Papers (8)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (559 KB) |  | HTML iconHTML  

    In this paper, we propose a novel carrier frequency offset (CFO) tracking algorithm for orthogonal frequency division multiplexing (OFDM) systems by exploiting scattered pilot carriers and virtual carriers embedded in the existing OFDM standards. Assuming that the channel remains constant during two consecutive OFDM blocks and perfect timing, a CFO tracking algorithm is proposed using the limited number of pilot carriers in each OFDM block. Identifiability of this pilot based algorithm is fully discussed under the noise free environment, and a constellation rotation strategy is proposed to eliminate the c-ambiguity for arbitrary constellations. A weighted algorithm is then proposed by considering both scattered pilots and virtual carriers. We find that, the pilots increase the performance accuracy of the algorithm, while the virtual carriers reduce the chance of CFO outlier. Therefore, the proposed tracking algorithm is able to achieve full range CFO estimation, can be used before channel estimation, and could provide improved performance compared to existing algorithms. The asymptotic mean square error (MSE) of the proposed algorithm is derived and simulation results agree with the theoretical analysis. View full abstract»

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  • On the Amplify-and-Forward Cooperative Diversity with Time-Hopping Ultra-Wideband Communications

    Publication Year: 2008 , Page(s): 630 - 641
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (637 KB) |  | HTML iconHTML  

    In this paper, we extend the Amplify-and-Forward cooperative diversity scheme to the context of impulse radio ultra wideband (IR-UWB). In particular, we present the construction of three families of minimal-delay and totally-real distributed algebraic space-time (ST) codes suitable for IR-UWB. The first family encodes adjacent symbols and is based on totally-real cyclic division algebras. The second family encodes the pulses used to transmit one information symbol and permits to achieve high performance levels with lower complexity. Both families of codes achieve full rate, full diversity with non-vanishing determinants for various number of relays. These schemes can be associated with pulse position modulation (PPM), pulse amplitude modulation (PAM) and hybrid pulse position and amplitude modulation (PPM-PAM). The third family of codes is information-lossless and does not require any pulse repetitions. It is specific to M-PPM-M'-PAM with M ges 3 and for all values of M'. Simulations performed over realistic indoor UWB channels are provided to verify the theoretical results. View full abstract»

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  • The Impact of Non-Isotropic Scattering and Directional Antennas on MIMO Multicarrier Mobile Communication Channels

    Publication Year: 2008 , Page(s): 642 - 652
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (791 KB) |  | HTML iconHTML  

    In outdoor environments, waves propagate non- isotropically because of non-uniform distribution of scatterers. In addition directional antennas, which are efficient for communication applications, have considerable impact on the response of the communication channel. The impact of non-isotropic propagation and directional antennas is more significant when the system employs multiple antennas. In this paper, we propose a space-time-frequency cross-correlation function (CCF) for multiple-input multiple-output multicarrier channels in a two-dimensional (2D) random scattering medium. The expression of the CCF turns out to be a multiplication of three CCFs. Two of these terms characterize the impact of mobile station and base station, respectively and are linear Bessel expansions, where the coefficients are given by the linear convolution of the Fourier series coefficients (FSC)s of the employed antenna patterns and the FSCs of the probability density function describing 2D non-isotropic environment. The third expression characterizes the impact of the wireless channel. In the stationary case, we derive the expression of the fading channel power spectrum (CPS) in terms of the non-isotropic pdf and antenna patterns. Using the expression of the CCF, we also calculate coherence-bandwidth (CB)/coherence-time (CT) as a function of carrier-frequency/time separations. Our numerical results show a good fit to the available experimental results obtained for the CB/CT of realistic outdoor channels. View full abstract»

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  • On the Performance of Closed-Loop Transmit Diversity with Noisy Channel Estimates and Finite-Depth Interleaved Convolutional Codes

    Publication Year: 2008 , Page(s): 653 - 665
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1572 KB) |  | HTML iconHTML  

    In this paper, closed-form expressions for the uncoded bit error probability of closed-loop transmit diversity (CLTD) algorithms with two transmit and one receive antennas and noisy channel state information (CSI) in time-varying Rayleigh fading channels are derived. Two CLTD algorithms considered are the phase-amplitude CLTD (PA-CLTD), where the transmit antennas may transmit with different signal energy, and the phase-only CLTD (PO-CLTD), where the transmit antennas must transmit with the same signal energy. In addition to the uncoded bit error probability, this paper also derives the pairwise error probability when finite-depth interleaved convolutional codes are used with CLTD algorithms. However, due to the complexity of the coded system, the pairwise error probabilities are not in the closed-form expressions. The results have shown that PA-CLTD performs slightly better than PO-CLTD although PA-CLTD requires significantly more feedback information and that, when the Doppler spread is large, the performance of CLTD algorithms may degrade significantly. Moreover, a comparison between PA-CLTD, the Alamouti space-time code and the SISO system indicates that PA-CLTD outperforms the other two systems when the Doppler spread is small and the pilot SNR is large. Finally, the analytical results are compared with results from Monte Carlo simulation and the comparison shows that the analytical results match well with the simulation results. View full abstract»

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  • Performance Analysis of Multiuser Diversity under Transmit Antenna Correlation

    Publication Year: 2008 , Page(s): 666 - 674
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (434 KB) |  | HTML iconHTML  

    In this paper, we investigate the effect of spatial correlation on throughput performance of downlink multi-antenna transmission schemes exploiting multiuser diversity, in which partial channel information such as signal-to-interference plus noise power ratio (SINR) is available at the transmitter. The asymptotic analysis is performed based on the extreme value theory. From this analysis, we demonstrate that the throughput optimal transmission scheme depends on the degree of the antenna correlation and the operating SNR. Especially, the multiuser spatial multiplexing known as the asymptotically optimal transmission scheme is no longer optimal in highly correlated multiple antenna channels. View full abstract»

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  • Effect of Channel Estimation Error on Bit Error Probability in OFDM Systems over Rayleigh and Ricean Fading Channels

    Publication Year: 2008 , Page(s): 675 - 685
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (415 KB) |  | HTML iconHTML  

    A characteristic function-based method is used to derive closed-form bit error probability (BEP) expressions for orthogonal frequency-division multiplexing (OFDM) systems in the presence of channel estimation error over frequency-selective Rayleigh fading channels and frequency-selective Ricean fading channels. Both single channel reception and diversity reception with maximal ratio combining (MRC) are examined. The BEP expressions are shown to be sums of several conditional probability functions which can be calculated by using proper complex Gaussian random variable theory and a characteristic function method. The closed-form BEP expressions can be used to accurately investigate the bit error rate performance degradation caused by channel estimation error under different wireless channel environment models. The performances of two interpolation methods, a sine interpolator with Hamming windowing and a Wiener interpolator, are compared. 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