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Communications, IEEE Transactions on

Issue 2 • Date Feb 1997

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Displaying Results 1 - 18 of 18
  • Adaptive symbol and parameter estimation in asynchronous multiuser CDMA detectors

    Publication Year: 1997 , Page(s): 213 - 220
    Cited by:  Papers (29)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    Existing multiuser code-division multiple-access (CDMA) detectors either have to rely on strict power control or near-perfect parameter estimation for reliable operation. A novel adaptive multiuser CDMA detector structure is introduced. Using either an extended Kalman filter (EKF) or a recursive least squares (RLS) formulation, adaptive algorithms which jointly estimate the transmitted bits of each user and individual amplitudes and time delays may be derived. The proposed detectors work in a tracking mode after initial delay acquisition is accomplished using other techniques not discussed here. Through computer simulations, we show that the algorithms perform better than a bank of single-user (SU) receivers in terms of near-far resistance. Practical issues such as the selection of adaptation parameters are also discussed View full abstract»

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  • Optimal PN sequence design for quasisynchronous CDMA communication systems

    Publication Year: 1997 , Page(s): 221 - 226
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    Direct sequence (DS) code-division multiple-access (CDMA) is a modulation and multiple access technique currently being implemented in digital cellular mobile radio communication systems. The conventional quasisynchronous (QS) DS-CDMA communication system is generalized, and the problem of optimal spreading pseudonoise (PN) sequence design for new QS DS-CDMA communication systems is formulated. The classes of optimal PN sequences which have good pseudo-randomness and very small cross-correlation values for some range of offsets are designed by using a matrix-based approach. In contrast to the case of the other sequences, the optimal PN sequences produce small multiple-access interference (MAI) which is not affected by the number of users if there are sufficiently large number of users in the link. The new results are compared with the commonly used PN sequences to prove the superiority of our designed sequences, and the system performance of the QS-CDMA systems using different PN sequences are also evaluated View full abstract»

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  • On the capture probability for a large number of stations

    Publication Year: 1997 , Page(s): 254 - 260
    Cited by:  Papers (52)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    The probability of capture under a model (for a land mobile radio direct sequence spread spectrum system) based on the ratio of the largest received power to the sum of interference powers is examined in the limit of a large number of transmitting stations. It is shown in great generality that the limit depends only on the capture ratio threshold and the roll-off exponent of the distribution of power received from a typical station. This exponent is insensitive to many typical channel effects such as Rician or Rayleigh fading and log-normal shadowing. The model is suitable for large systems with noncoherently combined interference View full abstract»

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  • Multiamplitude and multidimensional digital communication system in a Gaussian channel

    Publication Year: 1997 , Page(s): 159 - 163
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    We analyze the performance of a multiamplitude and multidimensional digital communication system with a simple detector in the presence of additive white Gaussian noise (AWGN). We compute the power and spectral efficiency of this scheme and compare them with those of conventional schemes with three different pulses View full abstract»

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  • Joint maximum-likelihood parameter estimation for burst DS spread-spectrum transmission

    Publication Year: 1997 , Page(s): 227 - 238
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    We first derive the joint optimal maximum-likelihood (ML) estimator of the carrier phase, both Doppler shift and Doppler rate, and the spreading code delay for a short burst direct sequence/spread spectrum (DS/SS) transmission in the absence of the data modulation. The typical burst duration is three data bit periods (60 ms). The performance of the joint estimator is analytically derived separately for high and low carrier-to-noise ratio (CNR) values. A suboptimal ML estimator based on the method of averaged periodogram is proposed for the data modulation present case, allowing the joint estimation of the data bit values. Then the above parameters are assumed correctly estimated and a segmentation approach is adopted, deriving the optimal joint ML estimator for the bit synchronization epoch and data. Simulations show the joint estimators perform reliable down to a CNR of approximately 30 dB·Hz View full abstract»

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  • On the probability of symbol error in Viterbi decoders

    Publication Year: 1997 , Page(s): 152 - 155
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    An upper bound is derived on the probability that at least one of a sequence of B consecutive bits at the output of a Viterbi (1979) decoder is in error. Such a bound is useful for the analysis of concatenated coding schemes employing an outer block code over GF(2B) (typically a Reed-Solomon (RS) code), an inner convolutional code, and a symbol (GF(2B)) interleaver separating the two codes. The bound demonstrates that in such coding schemes a symbol interleaver is preferable to a bit interleaver. It also suggests a new criterion for good inner convolutional codes View full abstract»

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  • Time signal distribution in communication networks based on synchronous digital hierarchy

    Publication Year: 1997 , Page(s): 247 - 253
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    A new method that uses round-trip paths to accurately measure transmission delay for submicrosecond time synchronization in synchronous digital hierarchy (SDH) networks is proposed. Since the proposed system uses virtual container-3 (VC-3) signal as the time reference signals, existing SDH equipment can be used without any changes. The feature of this method is that it separately measures the initial round-trip path delay and subsequent variations in round-trip path delay. The initial uncertain delay due to the administrative unit-3 (AU-3) pointer operations in SDH equipment is determined by controlling the reference clock of the equipment. The characteristics of the equipment delay caused by the pointer operations are also described. In an experiment with actual SDH equipment, the error in initial delay determination was suppressed to 30 ns. The delay variation measurement of the round-trip path is not affected by the pointer operation in the proposed method. The precision of delay variation measurement can be better than 10 ns View full abstract»

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  • Multidimensional trellis coded phase modulation using a multilevel concatenation approach .II. Codes for the AWGN and fading channels

    Publication Year: 1997 , Page(s): 177 - 186
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    For pt.I see ibid., vol.45, no.1, p.64-72, 1997. We use the construction technique proposed in part I to construct multidimensional trellis coded modulation (TCM) codes for both the additive white Gaussian noise (AWGN) and the fading channels. Analytical performance bounds and simulation results show that these codes perform very well and achieve significant coding gains over uncoded reference modulation systems. In addition, the proposed technique can be used to construct codes which have a performance/decoding complexity advantage over the codes listed in literature View full abstract»

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  • On the equivalence of the simultaneous and separate MMSE optimizations of a DFE FFF and FBF

    Publication Year: 1997 , Page(s): 156 - 158
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    There is great interest in the use of decision feedback equalization (DFE) to mitigate the effects of intersymbol interference (ISI) on wireless multipath fading channels. The coefficients of a DFE feedforward filter (FFF) and feedback filter (FBF) are usually adjusted based on the minimum mean square error (MMSE) criterion. The equalizer coefficients can be calculated by recursive adaptation or by direct computation based on a channel estimate. The equivalence of the simultaneous and separate MMSE optimization of the FFF and FBF of a finite-length DFE is established View full abstract»

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  • High-performance VLSI architecture for the Viterbi algorithm

    Publication Year: 1997 , Page(s): 168 - 176
    Cited by:  Papers (24)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    The Viterbi (1967) algorithm (VA) is known to be an efficient method for the realization of maximum-likelihood (ML) decoding of convolutional codes. The VA is characterized by a graph, called a trellis, which defines the transitions between states. To define an area efficient architecture for the VA is equivalent to obtaining an efficient mapping of the trellis. We present a methodology that permits the efficient hardware mapping of the VA onto a processor network of arbitrary size. This formal model is employed for the partitioning of the computations among an arbitrary number of processors in such a way that the data are recirculated, optimizing the use of the PEs and the communications. Therefore, the algorithm is mapped onto a column of processing elements and an optimal design solution is obtained for a particular set of area and/or speed constraints. Furthermore, the management of the surviving path memory for its mapping and distribution among the processors was studied. As a result, we obtain a regular and modular design appropriate for its VLSI implementation in which the only necessary communications between processors are the data recirculations between stages View full abstract»

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  • Capacity of synchronous coded DS SFH and FFH spread-spectrum multiple-access for wireless local communications

    Publication Year: 1997 , Page(s): 200 - 212
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    The performance of synchronous spread-spectrum multiple-access (SSMA) communications based on direct-sequence (DS), slow frequency-hopped (SFH), and fast frequency-hopped (FFH) systems for wireless local communications of micro-cellular personal communications is analyzed. Using an indoor multipath fading channel model with clusters of arriving rays, we investigate multiuser DS systems with RAKE and diversity reception by selection combining (SC), multiuser SFH systems with equal-gain (EG) diversity reception, and multiuser FFH systems with correlated EG and self-normalization (SN) combining techniques. Reed-Solomon codes are considered to further improve the system performance. Given a fixed available bandwidth with narrow band interference (NBI), capacities and packet error rates are determined under various system configurations. Total capacities of hybrid frequency-division multiple-access (FDMA)/SSMA (DS and SFH) systems are compared with those of wide-band SSMA systems. For high data rate communications, wide-band DS-SSMA systems have larger capacities than hybrid FDMA/DS-SSMA systems. For low data rate communications, a capacity comparison between wide-band DS-SSMA and hybrid FDMA/DS-SSMA systems depends on fading statistics. Hybrid FDMA/SFH-SSMA systems have larger capacities than wide-band DS-SSMA systems, FFH-SSMA systems could not provide satisfactory performance due to correlation among hopping bands View full abstract»

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  • Channel coding for narrow-band Rayleigh fading with robustness against changes in Doppler spread

    Publication Year: 1997 , Page(s): 148 - 151
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    For digital transmission over frequency-nonselective fading channels, data security can be obtained by error correction coding, but the coding scheme has to be adapted to the channel properties. For many vehicular applications, the range of possible vehicle speeds is large and in the UHF band the resulting Doppler frequency may not be small relative to the symbol rate-suggesting a differential detection scheme. Therefore, the channel coding should be robust against changes in Doppler spread. A combination of a convolutional code (soft-decision decoding) and a Reed-Solomon (RS) code is considered, and the performance in a narrow-band Rayleigh-fading channel with differential quaternary phase shift keying (DQPSK) modulation without interleaving is evaluated as a function of signal-to-noise ratio (SNR) and Doppler spread by computer simulations. This transmission scheme is proved to have good performance over a large variety of vehicle speeds View full abstract»

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  • Efficient evaluation of the error probabilities of spread-spectrum multiple-access communications

    Publication Year: 1997 , Page(s): 239 - 246
    Cited by:  Papers (34)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    We consider the performance of code-division multiple-access (CDMA) communications. In particular, we illustrate the use of a semianalytical approach which is combined with importance sampling for the efficient evaluation of the average bit-error rates (BERs) of asynchronous direct-sequence (DS) based CDMA systems employing binary phase shift keying (BPSK) modulation along with specific signature sequences for a variety of system parameters View full abstract»

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  • Packet radio performance of inhibit sense multiple access with capture

    Publication Year: 1997 , Page(s): 164 - 167
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    Current portable and land-mobile radio systems employ frequency modulation which exhibits a distinct capture effect. Furthermore, multipath propagation, shadowing, and the spatial distribution of the terminal units create data packets with varying signal strength. We investigate the performance of nonpersistent inhibit sense multiple access (ISMA) applied to the forward channel of packet radio communication networks. We show that the aggregate capacity of ISMA substantially increases compared to the noncapture case for small capture ratios. The mean packet delay of ISMA is also reduced with capture. The effect of different signal strength distribution is explored, and the capacity and delay improvements discussed View full abstract»

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  • Smart antennas in wireless systems: uplink multiuser blind channel and sequence detection

    Publication Year: 1997 , Page(s): 187 - 199
    Cited by:  Papers (21)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Space-division multiple-access (SDMA) schemes have been proposed to increase the capacity of wireless communication systems by simultaneously transmitting and receiving multiple co-channel signals through different spatial channels. We address the uplink (remote users to the base station antenna array) blind channel and sequence identification problem for an SDMA system. We show that multiuser blind identification can be accomplished by exploiting the spatial and temporal diversities of an antenna array system. In particular, a recursive estimation algorithm is developed to recover multiple signals from intersymbol interference (ISI) and co-channel interference (CCI) by taking advantage of a special structure of the array output and the finite-alphabet property of digital communication signals. The implementation of the proposed approach in practical applications is discussed, and field experiments have been conducted to demonstrate the effectiveness of the proposed algorithm View full abstract»

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  • On systematic punctured convolutional codes

    Publication Year: 1997 , Page(s): 133 - 139
    Cited by:  Papers (10)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    This paper investigates high rate systematic punctured convolutional codes based on Forney's (1970) results. High rate systematic punctured convolutional codes of rate-2/3 with constraint length 3⩽K⩽7 and rate-3/4 through 15/16 with K=7 are derived using the rate-1/2 best known nonsystematic convolutional codes. Weight spectra of newly discovered systematic punctured convolutional codes are provided and compared with the best known nonsystematic punctured codes. Simulation results on bit-error probabilities (BEPs) are also given View full abstract»

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  • Interleaving and decoding scheme for a product code for a mobile data communication

    Publication Year: 1997 , Page(s): 144 - 147
    Cited by:  Papers (1)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    We propose a new ordered decoding scheme for a product code for mobile data communications. The ordered decoding scheme determines the order of decoding for both row and column component codewords according to the probability of decoding the component codeword correctly. Component codewords are decoded independently. To randomize burst errors in both row and column codewords, a diagonal interleaving scheme is used for code symbols in the codeword. It is shown that the ordered decoding scheme combined with diagonal interleaving improves the performance of a product code with reasonably long code length for mobile data communications View full abstract»

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  • Performance evaluation of a finite buffer generalized selective repeat ARQ scheme for satellite communications

    Publication Year: 1997 , Page(s): 140 - 143
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB)  

    This article presents a new generalized selective repeat automatic repeat request (ARQ) scheme for error control in broadcast and point-to-point satellite communication systems. In the proposed scheme, each bit in a packet is repeated m times consecutively to increase the transmission reliability. Finite capacity buffers have been assumed at the earth stations. The throughput, theoretically derived for the proposed scheme, is optimized with respect to the number of copies transmitted per bit. A suitable algorithm to adaptively choose this number in relation to the transmission channel propagation conditions can also be used. In comparison with classical and modified versions of the selective repeat ARQ scheme as described in the literature, the proposed scheme provides enhanced throughput, especially with poor channel conditions and a high number of receiving earth stations 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