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Communications Letters, IEEE

Issue 11 • Date Nov. 2002

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Displaying Results 1 - 16 of 16
  • A low bias algorithm to estimate negative SNRs in an AWGN channel

    Page(s): 469 - 471
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (267 KB) |  | HTML iconHTML  

    Signal-to-noise ratio (SNR) is an important parameter in many receivers. In this letter, we derive a maximum-likelihood estimate of the amplitude of a binary phase-shift keying modulated signal and develop an iterative SNR search algorithm. Low bias is achieved for low SNR. View full abstract»

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  • Comments on "On the Doppler spectrum at the mobile unit employing a directional antenna"

    Page(s): 472 - 474
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    In the letter by Xu et al. (see ibid., vol.5, p.13-15, Jan. 2001), the Doppler PSD when using directional antenna at the mobile station was derived. However, the ranges in some equations in this letter were not correctly stated. In this letter, we point out the discrepancies and give correct range of values. View full abstract»

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  • A PDA-Kalman approach to multiuser detection in asynchronous CDMA

    Page(s): 475 - 477
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (293 KB) |  | HTML iconHTML  

    The probabilistic data association (PDA) method for multiuser detection in synchronous code-division multiple-access (CDMA) communication channels is extended to asynchronous CDMA, where a Kalman filter or smoother is employed to track the correlated noise arising from the outputs of a decorrelator. The estimates from the tracker, coupled with an iterative PDA, result in impressively low bit error rates. Computer simulations show that the new scheme significantly outperforms the best decision feedback detector. The algorithm has O(K/sup 3/) complexity per time frame, where K is the number of users. View full abstract»

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  • Performance of TCP protocols in deep space communication networks

    Page(s): 478 - 480
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    The communication requirements for space missions necessitate to address the problems due to deep space communication networks. In this letter, the effects of slow start algorithm, propagation delay and the link errors on the throughput performance of transport layer protocols are investigated in deep space communication networks. The objective of this letter is to demonstrate through experimental results that existing TCP protocols are far from satisfying the deep space communication requirements and point out the urgent need for new TCP solutions. View full abstract»

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  • A simple capacity formula for correlated diversity Rician fading channels

    Page(s): 481 - 483
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (287 KB) |  | HTML iconHTML  

    Appropriate exploitation of the randomness of multipath propagation in wireless communications can considerably increase the system. capacity. The average capacity of correlated diversity Rician channels, however, is not available in the literature due to the nonlinear log function involved in the conditional channel capacity and to the complicated distribution of correlated Rician channels. Rather than using brute force, we tackle this issue by combining a widely adopted statistical technique with an elegant lemma by Porteous, ending up with a simple and accurate formula for average channel capacity on correlated diversity Rician channels. Numerical results are also presented for illustration. View full abstract»

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  • A memetic algorithm for assigning cells to switches in cellular mobile networks

    Page(s): 484 - 486
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (199 KB) |  | HTML iconHTML  

    Assigning cells to switches in cellular mobile networks is an NP-hard problem which, for real size mobile networks, could not be solved using exact methods. In this context, heuristic approaches like memetic algorithms can be used. This paper proposes a memetic algorithm (MA) to solve this problem. The implementation of this algorithms has been subject to extensive tests. The results obtained confirm the efficiency and the effectiveness of MA to provide good solutions for moderate- and large-sized cellular mobile networks, in comparison with tabu search and Merchant and Sengupta's heuristics. This heuristic can be used to solve NP-hard problems, like designing and planning, in the next-generation mobile networks. View full abstract»

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  • On the performance of orthogonal space-time block coding with quantized feedback

    Page(s): 487 - 489
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (283 KB) |  | HTML iconHTML  

    Orthogonal space-time block coding (OSTBC) is a recent technique that provides maximal diversity gains on a space-time channel at a very modest computational cost. Recently, several authors have suggested to improve the performance of an OSTBC system by using a feedback of channel state information from the receiver to the transmitter. In this letter, we study the performance of an OSTBC system with quantized low-rate feedback. We establish conditions under which the system achieves full diversity and we also analyze the performance of a method that employs a feedback consisting of only one information bit. View full abstract»

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  • Comments on "MRC performance for M-ary modulation in arbitrarily correlated Nakagami fading channels"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (198 KB)  

    Using the results in the article by Win et al. (see ibid., vol.4, no.10, p.301-3, Oct. 2000) regarding the maximal ratio combiner for correlated Nakagami-m fading channels, we provide a simple analytic proof, applicable to a general class of modulation schemes, that uncorrelated branches result in a lower symbol error probability than do correlated branches. View full abstract»

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  • Transmit selection in spatial multiplexing systems

    Page(s): 491 - 493
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    In this letter we solve the transmit antenna selection problem for a zero forcing spatial multiplexing system with knowledge of the channel statistics at the transmitter. We show through Wishart matrix analysis that the signal-to-noise ratio on the kth stream is a weighted Chi-squared variable with the weight equal to-the kth diagonal entry of the inverted transmit correlation matrix. We use this result to develop selection algorithms for two cases-maximizing ergodic capacity and minimizing the average probability of error. Monte Carlo simulations illustrate potential performance improvements. View full abstract»

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  • Statistical model of downlink interference for the performance evaluation of CDMA systems

    Page(s): 494 - 496
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    A statistical model of the downlink interference for the analytical performance evaluation of code-division multiple-access (CDMA) systems is proposed. Based on Wilkinson's approximation, the statistical model of the relative other cell interference is developed in closed form. The best base station (BS) selection in the shadowed environment with a correlation is taken into consideration. We show that interference statistics obtained by the proposed analytical model agree with simulation results. It is also shown that the proposed analytical model can replace Monte Carlo simulation in outage analysis. View full abstract»

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  • Spectral efficiency of the feedback receiver for two sets of orthogonal sequences

    Page(s): 497 - 499
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (286 KB) |  | HTML iconHTML  

    We present the spectral efficiency analysis of the recently proposed feedback receiver for two sets of orthogonal sequences (TSOS) scheme which is capable of supporting higher number of users than the spreading gain of the DS/CDMA system. The added complexity is minimal compared to the conventional matched filter. We show that in the case of coded system, spectral efficiency of this scheme is close to that of a Gaussian multiple access channel if the incomplete group of orthogonal sequences is detected first. We also discuss the choice of orthogonal sequences that maximizes the spectral efficiency. This analysis is extended for the case of flat fading channels. View full abstract»

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  • A structure for fast synchronizing variable-length codes

    Page(s): 500 - 502
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    A new approach for transforming variable-length codes, optimal in the minimum average codeword length sense, into fast synchronizing codes with the same length distribution is proposed in this letter. Based on the adaptation of an intrinsically fast synchronizing structure whose properties are demonstrated, this approach provides good synchronization recovery for a very low computational complexity. Finally, numerical results are presented and compared with reference ones. View full abstract»

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  • Channel reliability estimation for turbo decoding in rayleigh fading channels with imperfect channel estimates

    Page(s): 503 - 505
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB) |  | HTML iconHTML  

    In this letter we propose a simple estimation scheme of the channel reliability factor for turbo decoding in Rayleigh fading channels with imperfect channel estimates. The channel reliability factor is required for iterative MAP decoding of turbo codes and depends on the error variance of the channel estimate as well as the signal-to-noise ratio (SNR) when the channel estimation is imperfect. The proposed estimator is based on the statistical computations on the block observation of samples obtained by processing the received signal and provides an accurate estimate of the channel reliability factor for even a short block observation. Simulation results show that the use of this estimate in turbo decoding does not yield perceptible degradation against performance of the turbo decoder using the exact one. View full abstract»

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  • An approximation for the loss probability in a multiserver queue fed by a shifting level process

    Page(s): 506 - 508
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (353 KB) |  | HTML iconHTML  

    A shifting level (SL) process is useful to traffic modeling because it is very easy to match the stationary distribution and autocorrelation function of the SL process with those of measured real traffics. Especially, SL processes have been used to traffic modeling for VBR video traffics reflecting the long range dependence and the scene structure. We give an approximation for the loss probability in a multiserver queue fed by a SL process. Numerical examples show that our approximation is very accurate. View full abstract»

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  • On the scope of end-to-end probing methods

    Page(s): 509 - 511
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    A generic sample path based analysis of a multiple hop model of a network route carrying probe traffic and cross traffic is given. It provides a unifying context for active and passive end-to-end measurement techniques, and a framework to enhance existing and to generate new estimation methods. Novel aspects include focusing on delay variation and allowing general probe stream definitions. All multihop queueing effects acting on probes are identified and four canonical measurable signatures are defined and illustrated using simulation and real measurements. View full abstract»

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  • MaxNet: a congestion control architecture

    Page(s): 512 - 514
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (262 KB) |  | HTML iconHTML  

    On the Internet all the bottlenecked links of a source to destination path contribute to the aggregate congestion signal that controls the source rate. We introduce an architecture, MaxNet, in which only one link, the most severely bottlenecked link on the end-to-end path, controls the source rate. We prove that MaxNet results in MaxMin fairness for sources with general homogenous utility functions and the current architecture may not. MaxNet is distributed and requires no global information or per-flow state in the link. View full abstract»

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IEEE Communications Letters  is aimed at satisfying the need for rapid dissemination of information, offering a vehicle for authors to expose their results to be used in future developments. This ensures early recognition of work. 

 

 

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Editor-in-Chief
George K. Karagiannidis
Aristotle University of Thessaloniki
Greece