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Communications Letters, IEEE

Issue 6 • Date June 2005

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Displaying Results 1 - 25 of 35
  • Table of contents

    Publication Year: 2005 , Page(s): 01 - 04
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    Freely Available from IEEE
  • IEEE Communications Society

    Publication Year: 2005 , Page(s): 02
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  • An adaptive code position modulation scheme for wireless sensor networks

    Publication Year: 2005 , Page(s): 481 - 483
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (914 KB) |  | HTML iconHTML  

    In this letter, an energy-efficient adaptive code position modulation scheme is proposed for wireless sensor networks to provide the relatively stable bit error ratio (BER) performance expected by the upper layers. The system is designed with focus on the adaptive control of transmission power, which is adjusted based on the measured power density of background noise. Interfaces among the modulation module, packet scheduling module and upper layer are provided for flexible adjustments to adapt to the background noise and deliver expected application quality. Simulations with signal processing worksystem (SPW) validate the effectiveness of the scheme. View full abstract»

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  • Unequal error protection by modulation with unequal power allocation

    Publication Year: 2005 , Page(s): 484 - 486
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB) |  | HTML iconHTML  

    In digital communication systems for speech, audio or video signals the individual bits of the transmitted parameters u exhibit different bit error sensitivities. Usually channel coding with unequal error protection (UEP) is applied. However, some transmission systems do not include channel coding for several reasons. For this situation, a novel concept is proposed which achieves UEP by allocating different transmission power to individual bits according to their bit error sensitivities. The optimization criterion for unequal power allocation is the mean square of the error between the original parameter-u and the decoded parameter u which has a strong correlation with subjective perception. View full abstract»

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  • GLRT receivers for UWB systems

    Publication Year: 2005 , Page(s): 487 - 489
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (830 KB) |  | HTML iconHTML  

    This letter investigates generalized-likelihood-ratio-test (GLRT) detectors for ultra-wideband (UWB) impulse radio systems employing two alternative signaling schemes. One is the so-called transmitted reference method where, in each time frame, a reference pulse is transmitted prior to the data pulse. The other is the differential transmitted reference scheme, wherein the data pulse received in the previous frame is used as a template waveform in the current frame. The two detectors are compared in terms of bit error rate performance. View full abstract»

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  • On the impact of SNR estimation error on adaptive modulation

    Publication Year: 2005 , Page(s): 490 - 492
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (911 KB) |  | HTML iconHTML  

    In this letter we investigate the impact of signal-to-noise ratio (SNR) estimation on the performance of adaptive modulation. The adaptive modulation technique uses an estimate of the SNR at the receiver to choose a modulation scheme so that a given performance target is met. By adapting the modulation scheme, the link is able to improve the spectral efficiency as compared to static modulation. An analytic expression for the impact of SNR estimation error is derived and it is shown that SNR estimation has minimal impact on the performance. View full abstract»

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  • A subspace detection method of analog space-time codes for multiantenna ultra-wideband transmissions

    Publication Year: 2005 , Page(s): 493 - 495
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (918 KB) |  | HTML iconHTML  

    In this letter, we propose a subspace based detection method for space-time block codes (STBC) wedded with ultra-wideband (UWB) transmissions. Without the need of channel information, the proposed algorithm yields the estimation of transmitted symbols by minimizing some quadratic form built on the orthogonality between signal and noise subspaces. Simulations in flat-faded application scenarios show that the subspace method can achieve the same diversity and a loss of about 2 dB at the 10-3 level with more than four successive space-time codes being decoded jointly, compared to the coherent decoding algorithm. View full abstract»

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  • A family of ISI-free polynomial pulses

    Publication Year: 2005 , Page(s): 496 - 498
    Cited by:  Papers (28)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (897 KB) |  | HTML iconHTML  

    A family of ISI free polynomial pulses that can have an asymptotic decay rate of t-k for any integer value of k has been proposed. The proposed family provides flexibility in designing bandlimited pulses in accordance with the desired application, even after the roll-off factor α has been chosen. Pulses obtained from this family have been found to be better than the currently known good pulses. View full abstract»

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  • Second-order statistics of maximal-ratio and equal-gain combining in Weibull fading

    Publication Year: 2005 , Page(s): 499 - 501
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (997 KB) |  | HTML iconHTML  

    Exact expressions for the level crossing rate and average fade duration of M-branch equal-gain and maximal-ratio combining systems in a Weibull fading environment are presented. The expressions apply to unbalanced, nonidentical, independent diversity channels. In addition, new closed-form solutions for some special cases are obtained. View full abstract»

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  • Rake-MMSE-equalizer performance for UWB

    Publication Year: 2005 , Page(s): 502 - 504
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB) |  | HTML iconHTML  

    The performance of a joint rake and minimum mean square error (MMSE) equalizer receiver for high data rate ultra-wideband communications is studied in this paper. The proposed receiver combats inter-symbol interference by taking advantage of the rake and equalizer structure. The receiver performance is investigated using a semianalytical approach and Monte-Carlo simulation. The effects of the number of rake fingers and equalizer taps on the error performance are examined. View full abstract»

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  • An iterative singular vectors estimation scheme for beamforming transmission and detection in MIMO systems

    Publication Year: 2005 , Page(s): 505 - 507
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (956 KB) |  | HTML iconHTML  

    A novel iterative singular vector estimation scheme has been proposed for a beamforming transmission and detection in wireless multiple input multiple output (MIMO) systems. Two singular channel matrix vectors, which correspond to the largest singular value, are iteratively obtained at the transmitter and the receiver without estimating the channel coefficients. The proposed singular vectors estimation strategy has advantages over the conventional MIMO channel estimation schemes in terms of both frame-error-rate performance, bandwidth efficiency and computation complexity. View full abstract»

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  • A delay model for IEEE 802.11e EDCA

    Publication Year: 2005 , Page(s): 508 - 510
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (953 KB) |  | HTML iconHTML  

    In this paper, we present a model to analyze the delay behavior of the enhanced distributed channel access (EDCA) mechanism of IEEE 802.11e. Simulation results validate the accuracy of the analysis. View full abstract»

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  • Collaborative transmit diversity with adaptive radio resource and power allocation

    Publication Year: 2005 , Page(s): 511 - 513
    Cited by:  Papers (38)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB) |  | HTML iconHTML  

    We consider optimized collaborative transmit diversity schemes for the situation when the source and the relay know the magnitudes of all channel gains in the system. We demonstrate how one can optimally allocate not only transmit power but also the time and bandwidth used by the different nodes. Numerical examples illustrate the possible performance gain over nonadaptive collaboration. View full abstract»

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  • Performance analysis of downlink smart antenna system with auxiliary pilot in CDMA2000 IX

    Publication Year: 2005 , Page(s): 514 - 516
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (911 KB) |  | HTML iconHTML  

    The auxiliary pilot has been defined in the CDMA2000 IX standard for the purpose of providing an accurate channel estimation to each of mobile terminals during the downlink beamforming. In this letter, we first analyze the multipath signal environment to verify under exactly what conditions the auxiliary pilot becomes inevitable and what happens if the auxiliary pilot is not assigned to each of the subscribers. Then, we present a systematic procedure of applying the auxiliary pilot together with a proper call processing method to handle the auxiliary pilot. Performance analysis is also given through the computer simulations and the experimental data obtained from the smart antenna base transceiver station (SA BTS) that has been implemented for the CDMA2000 IX standard. View full abstract»

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  • An approximate maximum likelihood estimator for SNR jointly using pilot and data symbols

    Publication Year: 2005 , Page(s): 517 - 519
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (979 KB) |  | HTML iconHTML  

    A novel maximum likelihood-based estimator for signal-to-noise ratio (SNR) is derived. Previous SNR estimators are mainly based on using either the pilot symbols or the data symbols. However, in a practical communication system, a frame usually consists of both pilot and data symbols. In this work, a new SNR estimator that uses all available symbols (pilot and data) in a frame is developed for binary phase shift keying signals. The performance of this estimator is examined. Numerical results are presented to show the potential improvement obtained by using this new estimator. View full abstract»

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  • Enhanced power-saving mechanism for broadcast and multicast service in WLAN

    Publication Year: 2005 , Page(s): 520 - 522
    Cited by:  Papers (2)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB) |  | HTML iconHTML  

    When a WLAN station has low battery-power, a normal power-saving mechanism is not desirable and sparse wake-up should be used. In that case, the station cannot remain awake throughout every delivery-traffic-indication-message (DTIM) interval, which results in the loss of broadcast and multicast packets. In this letter, we propose a double-buffering power-saving mechanism for stations with low battery power. Broadcast and multicast packets can be delivered to stations with low battery power more reliably with the new scheme. View full abstract»

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  • On the capacity of UWB over multipath channels

    Publication Year: 2005 , Page(s): 523 - 525
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (970 KB) |  | HTML iconHTML  

    In this work we compute the information theoretic capacity C of binary orthogonal pulse position modulated (PPM) signals for ultra wideband (UWB) communications over multipath channels. We consider binary PPM signals with random energy and correlation values. Numerical examples are given to illustrate the capacity results. View full abstract»

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  • Joint subcarrier and power allocation in uplink OFDMA systems

    Publication Year: 2005 , Page(s): 526 - 528
    Cited by:  Papers (126)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (885 KB) |  | HTML iconHTML  

    In this letter, we focus on joint subcarrier and power allocation in the uplink of an OFDMA system. Our goal is to maximize the rate-sum capacity in the uplink. For the purpose, we formulate an optimization problem subject to subcarrier and power constraints and draw necessary conditions for optimality, from which we derive joint subcarrier and power allocation algorithms. Simulation results show that our proposed scheme enhances the system capacity, providing almost near optimal solutions with low computational burden. View full abstract»

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  • An interference suppression scheme for UWB Signals using multiple receive antennas

    Publication Year: 2005 , Page(s): 529 - 531
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (969 KB) |  | HTML iconHTML  

    In this letter a simple narrow band interference (NBI) mitigation scheme for ultra-wide bandwidth (UWB) signals using multiple receive antennas is examined. The low spatial fading characteristic of UWB signals is exploited to provide "interference diversity" by selecting the signal with the lowest received power among multiple antennas. The resulting distribution of the signal-to-interference ratio (SIR) at the receiver is derived and compared with results based on measurement data. The performance improvement of the scheme in mitigating NBI is also examined through BER simulations. View full abstract»

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  • Representations of finite fields and the Naini-Seberry partitioning problem

    Publication Year: 2005 , Page(s): 532 - 533
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (838 KB) |  | HTML iconHTML  

    Safavi-Naini and Seberry suggested a subliminal channel based on partitioning a set Γ of the generator matrices of error-correcting codes. We give a systematic procedure to partition Γ into Ei's with |Ei|=2m for any m, which is more efficient than the method in Yang, C-N et al., (1997). View full abstract»

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  • Flexible construction of irregular partitioned permutation LDPC codes with low, error floors

    Publication Year: 2005 , Page(s): 534 - 536
    Cited by:  Papers (9)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (883 KB) |  | HTML iconHTML  

    Irregular partitioned permutation (IPP) low-density parity-check (LDPC) codes have been recently introduced to facilitate hardware implementation of belief propagation (BP) decoders. In this letter, we present a new method to construct IPP LDPC codes with great flexibility in the selection of code parameters. Meanwhile, small stopping sets are avoided in the code construction, thus good error floor performance can be achieved. View full abstract»

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  • Low-frequency performance of guided scrambling DC-free codes

    Publication Year: 2005 , Page(s): 537 - 539
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (979 KB) |  | HTML iconHTML  

    We analyze the effect of coding parameters on low-frequency suppression in guided scrambling (GS) dc-free codes based on computer simulation. Simple expressions to accurately estimate the sum variance and low-frequency spectrum-weight of these codes are developed. Systematic design of GS dc-free codes is discussed. View full abstract»

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  • The EXIT-characteristic of softbit-source decoders

    Publication Year: 2005 , Page(s): 540 - 542
    Cited by:  Papers (3)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1026 KB) |  | HTML iconHTML  

    We outline a new technique to compute the EXIT-characteristic of softbit-source decoders analytically without extensive histogram measurements. Based on the analytic considerations it is straightforward to derive a compact determination rule for the maximum value of attainable extrinsic information. We also show that the area under the EXIT-characteristic grows almost logarithmically with the prediction gain which is utilizable due to the residual redundancy in the source data. View full abstract»

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  • Convergence rates comparison of sum-product decoding of RA codes under different message-passing schedules

    Publication Year: 2005 , Page(s): 543 - 545
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (945 KB) |  | HTML iconHTML  

    In iterative decoding of turbo-like codes, serial schedule generally provides a much faster convergence rate compared with parallel schedule. With the aid of extrinsic information transfer (EXIT) charts, sum-product decoding of repeat accumulate (RA) codes under both message passing schedules is investigated as an example for verifying the above statement. View full abstract»

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  • Optimal regular LDPC codes for the binary erasure channel

    Publication Year: 2005 , Page(s): 546 - 548
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (854 KB) |  | HTML iconHTML  

    We prove that for any given R between 0 and 1 the best threshold value for a regular LDPC code of rate R with common variable degree v and common check degree c occurs when v is at least 3 and is minimal subject to the condition R=1-v/c. View full abstract»

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Aristotle University of Thessaloniki
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