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Communications Letters, IEEE

Issue 9 • Date Sept. 2002

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Displaying Results 1 - 17 of 17
  • Improved upper bounds on error-probability for biorthogonal trellis-coded CDMA systems

    Publication Year: 2002 , Page(s): 361 - 363
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB) |  | HTML iconHTML  

    We employ the transfer function approach to obtain error-probability upper bounds for asynchronous trellis-coded CDMA systems based on biorthogonal signature sequences. The technique provides uniformly tight bounds for the biorthogonal sequence based trellis codes, both with and without parallel transitions, in contrast to previously published results. View full abstract»

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  • Effects of multipath diversity on adaptive QAM in frequency selective Rayleigh fading channels

    Publication Year: 2002 , Page(s): 364 - 366
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    We derive the average bit error rate (BER) and the average throughput for adaptive quadrature amplitude modulation (AQAM) with constant transmit power over frequency selective Rayleigh fading channels. Based on these derived BER and throughput expressions, we go on to investigate the effect of multipath diversity on AQAM using two BER constraints. View full abstract»

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  • Analysis of non-uniform cell destination distribution in virtual output queueing systems

    Publication Year: 2002 , Page(s): 367 - 369
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB) |  | HTML iconHTML  

    We develop a discrete-time analytical queueing model for studying the performance of input-queued switches with non-uniform cell destination distribution. Virtual output queues are assumed at the ingress ports where cell arrivals are geometrically distributed and the service process is based on a work conserving random selection scheme. We consider the conditions for stability as basis for deriving closed-form expressions for the stationary queue size distributions from which the mean queue sizes and mean cell latencies are derived. We show that a very good agreement is obtained between simulation and analytical results. View full abstract»

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  • Space-time-frequency (STF) coding for MIMO-OFDM systems

    Publication Year: 2002 , Page(s): 370 - 372
    Cited by:  Papers (68)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    We consider the capacity of multiple-input-multiple-output (MIMO) systems that use OFDM as the modulation format. We point out a basic equivalence between antennas and OFDM-tones. This similarity immediately allows us to essentially reuse all space-time codes designed for flat-fading channels in MIMO-OFDM systems operating in frequency-selective channels. An optimum code would thus code across all antennas and tones (as well as time) simultaneously. Since this can become very complex, we propose a method for grouping antennas and codes in such a way that the inherent diversity is retained, while the complexity is greatly reduced. Capacity computations between the full-complexity and the reduced-complexity systems illustrate this tradeoff. View full abstract»

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  • Capacity estimation of a SIR-based power-controlled cellular CDMA system with base station diversity in a multipath fading environment

    Publication Year: 2002 , Page(s): 373 - 375
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    This article estimates the reverse link capacity of an SIR-based power-controlled code-division multiple access system in a multiple cells environment. The effect of multipath fading on the interference statistics is explicitly accounted for and mobiles are assumed to connect to a base station based on minimum attenuation criterion. View full abstract»

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  • Multislot estimation of fast-varying space-time channels in TD-CDMA systems

    Publication Year: 2002 , Page(s): 376 - 378
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB) |  | HTML iconHTML  

    We propose a subspace method to estimate the time-varying space-time channel by taking into account the different rates of variation between delays/directions of arrival (slowly-varying) and faded amplitudes (fast-varying) of the multipath propagation. The stationarity of angles and delays across several time-slots is exploited to perform an unstructured estimation that avoids the explicit computation of the path parameters. Numerical analysis for a TD-CDMA system shows that the asymptotic performance is reached with a reasonable number of slots. View full abstract»

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  • A distributed source coding technique for correlated images using turbo-codes

    Publication Year: 2002 , Page(s): 379 - 381
    Cited by:  Papers (26)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    The Slepian-Wolf (1973) theorem states that the output of two correlated sources can be compressed to the same extent without loss, whether they communicate with each other or not, provided that decompression takes place at a joint decoder. We present a distributed source coding scheme for correlated images which uses modulo encoding of pixel values and encoding (compression) of the resulting symbols with binary and nonbinary turbo-codes, so that larger rate savings than using modulo encoding. alone are achieved, practically without loss. View full abstract»

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  • Cryptanalysis of fast encryption algorithm for multimedia FEA-M

    Publication Year: 2002 , Page(s): 382 - 384
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (198 KB) |  | HTML iconHTML  

    Certain weaknesses in the algebraic structure of the previously proposed fast encryption algorithm for multimedia FEA-M are pointed out. It is shown that, when the secret key consists of k bits, under realistic chosen and known plaintext attacks, the secret key recovery has complexity proportional to 2k/sup 2/ and k/sup 4/, respectively, implying that FEA-M is an insecure algorithm even if the secret keys of 4096 bits are employed. View full abstract»

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  • Application of efficient Chase algorithm in decoding of generalized low-density parity-check codes

    Publication Year: 2002 , Page(s): 385 - 387
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    We consider the iterative decoding of generalized low-density (GLD) parity-check codes where, rather than employ an optimal subcode decoder, a Chase (1972) algorithm decoder more commonly associated with "turbo product codes" is used. GLD codes are low-density graph codes in which the constraint nodes are other than single parity-checks. For extended Hamming-based GLD codes, we use bit error rates derived by simulation to demonstrate this new strategy to be successful at higher code rates. For long block lengths, good performance close to capacity is possible with decoding costs reduced further since the Chase decoder employed is an efficient implementation. View full abstract»

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  • Pairwise error probability evaluation of multiple symbol trellis-coded continuous phase frequency shift keying in a slow fading channel

    Publication Year: 2002 , Page(s): 388 - 390
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (213 KB) |  | HTML iconHTML  

    This article evaluates the pairwise error probability (PEP) of multiple symbol trellis-coded modulation applied to continuous phase frequency shift keying (MTCM/CPFSK) in a slow fading environment with and without channel state information (CSI). The fading amplitude is assumed to be constant during an error event and distributed as Rician. For the case with CSI, the PEP is approximated using the Gauss-Chebysev formula and a tight upper bound is presented. For the case without CSI, a simplified upper bound is derived by using the improved Chernoff bound technique. Simulation results are also presented. View full abstract»

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  • Bootstrap decoding of low-density parity-check codes

    Publication Year: 2002 , Page(s): 391 - 393
    Cited by:  Papers (18)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    An initial bootstrap step for the decoding of low-density parity-check (LDPC) codes is proposed. Decoding is initiated by first erasing a number of less reliable bits. New values and reliabilities are then assigned to erasure bits by passing messages from nonerasure bits through the reliable check equations. The bootstrap step is applied to the weighted bit-flipping algorithm to decode a number of LDPC codes. Large improvements in both performance and complexity are observed. View full abstract»

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  • Compression of binary memoryless sources using punctured turbo codes

    Publication Year: 2002 , Page(s): 394 - 396
    Cited by:  Papers (47)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (198 KB) |  | HTML iconHTML  

    In this letter, we propose the use of punctured turbo codes to perform near-lossless compression and joint source-channel coding of binary memoryless sources. Compression is achieved by puncturing the turbo code to the desired rate. No information about the source distribution is required in the encoding process. Moreover, the source parameters do not need to be known in the decoder, since they can be estimated jointly with the iterative decoding process. View full abstract»

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  • Non-full rank space-time trellis codes for serially concatenated system

    Publication Year: 2002 , Page(s): 397 - 399
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (210 KB) |  | HTML iconHTML  

    The feasibility of the non-full rank space-time trellis codes (NFR-STTCs) for the serially concatenated system is described carefully in this letter and a QPSK-based NFR-STTC suitable for the system is proposed. As the simulation results show, over the flat block Rayleigh fading channels, a concatenated system with the proposed NFR-STTC inner code can achieve full diversity, and improve the coding gains compared with other concatenated systems adopting full-rank space-time trellis codes (FR-STTCs) of the same complexity. The introduction of the NFR-STTC to serial concatenation space-time (SCST) system provides a new research community of SCST. View full abstract»

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  • A new reliability measure for telecommunication networks

    Publication Year: 2002 , Page(s): 400 - 402
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    A new reliability measure is introduced. The measure takes into account service degradations once the network is disconnected. A network retailer can use this measure to choose an optimal set of paths such that the desired compromise between cost and reliability is achieved. View full abstract»

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  • Measurement-based admission control using maximum burstiness

    Publication Year: 2002 , Page(s): 403 - 405
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (201 KB) |  | HTML iconHTML  

    We introduce a new measurement-based admission control using the maximum burstiness (MB) of the aggregate traffic. In the MB algorithm, admission control is performed by testing the schedulability of a new flow request using the target loss probability to get a feasible value of a performance tuning parameter. The MB algorithm obtains robustness by applying the quality-of-service requirements to the admission control test and achieves high bandwidth utilization by adopting statistical multiplexing. View full abstract»

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  • A disjoint path selection scheme with shared risk link groups in GMPLS networks

    Publication Year: 2002 , Page(s): 406 - 408
    Cited by:  Papers (44)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (209 KB) |  | HTML iconHTML  

    This letter proposes a disjoint path selection scheme for generalized multi-protocol label switching (GMPLS) networks with shared risk link group (SRLG) constraints. It is called the weighted-SRLG (WSRLG) scheme. It treats the number of SRLG members related to a link as part of the link cost when the k-shortest path algorithm is executed. In WSRLG, a link that has many SRLG members is rarely selected as the shortest path. Simulation results show that WSRLG finds more disjoint paths than the conventional k-shortest path algorithm. View full abstract»

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  • System performance comparison of optical CDMA and WDMA in a broadcast local area network

    Publication Year: 2002 , Page(s): 409 - 411
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    The performance of optical code-division multiple-access (CDMA) systems with wavelength-hopping/time-spreading codes is compared to that of a wavelength-division multiple-access (WDMA) system. The multiple-access techniques are applied in a time-slotted broadcast local area network. The utilization, defined as the throughput per unit of time-domain bandwidth expansion, and packet delay are used as metrics of performance. When more than seven wavelengths are available, optical CDMA systems using asymmetric prime-hop codes and all-optical signal processing are shown to have higher peak utilization and lower corresponding delay than a WDMA system with the same number of wavelengths. When the encoders/decoders operate at the chip rate, the utilization of optical CDMA exceeds that of WDMA at high offered loads; however, the peak utilization of the WDMA system is still superior. 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