IEEE Communications Letters

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»

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»

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 derivin... View full abstract»

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... View full abstract»

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»

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 computa... View full abstract»

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 symb... View full abstract»

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 sec... View full abstract»

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... View full abstract»

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 ... View full abstract»

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... View full abstract»

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 ca... View full abstract»

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... View full abstract»

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»

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 t... View full abstract»

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 selec... View full abstract»

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... View full abstract»