Volume 3, No. 3, July 2007        ISSN: 1744-2400

A SPECIAL ISSUE ON COMMUNICATION SYSTEMS, NETWORKS AND DIGITAL SIGNAL PROCESSING

Guest Editors:

Dr. Michael Logothetis

Associate Professor,  Wire Communications Laboratory, Department of Electrical & Computer Engineering, University of Patras, Greece

Professor. Rolando Carrasco

 School of Electrical, Electronic and Computer Engineering, University of Newcastle-upon-Tyne, Newcastle, United Kingdom

Title: PERCEPTUALLY-OPTIMIZED ERROR CONCEALMENT FOR AUDIO OVER WLANS
Authors: N. Tatlas, A. Floros , T. Zarouchas , J. Mourjopoulos,..............................pp. 77-88
Abstract: Digital audio delivery over Wireless Local Area Networks (WLANs) represents an attractive framework for realizing high quality, multichannel audio applications in home and small office enclosures, offering increased setup flexibility and cable-free, low cost audio system interconnections. However, real-time digital audio streaming over unreliable wireless IP networks, such as WLANs, may encounter significant playback quality degradation, due to the unpredictable and variable link quality that causes delayed audio delivery or even permanent loss of the transmitted packets. In this paper, we present a perceptually efficient error concealment technique which combined with playback synchronization correction schemes, and a high-rate wireless transmission protocol with Quality-of-Service (QoS) support that can significantly enhance the overall audio playback quality of typical multichannel home-theater wireless applications.
Keywords: Audio Over WLANs, Quality-of-Service, Packet Recovery, Error Concealment.

Title: EXACT ANALYSIS OF LCR AND AFD FOR DUAL MRC AND SC DIVERSITY IN CORRELATED SMALL-SCALE FADING ENVIRONMENTS
Authors: J. I. Z. Chen,............................................................................................pp. 87-92
Abstract: In this paper, the performance evaluation with average level crossing rate (LCR), average fade duration (AFD) of the output signal for the maximum ratio combining (MRC), and the selection combining (SC) with a dual-branch receiver has been analyzed. Some of the expressions with average LCR and AFD for both MRC and SC schemes operating in the correlated fading channel are derived with the joint probability density function (jpdf) of the intensity at the diversity receiver output. The channel model of the diversity branches are assumed characterized as Nakagami-m statistics with the features of correlation. The obtained formulas are validated through the numerical analysis, and the results indicate that the average LCR and AFD of dual MRC and SC schemes are significantly affected by the correlation phenomena between the diversity branches when they are working in the correlated fading environments.
Keywords: Average Fade Duration (AFD), Correlated Small-scale Fading, Level Crossing Rate (LCR), MRC, SC.

Title: FRACTIONAL FOURIER TRANSFORM BASED BLIND CROSS-TERM DETECTION AND SIGNAL SYNTHESIS IN WIGNER DISTRIBUTIONS
Authors: S. A. Qazi, L. K. Stergioulas,...................................................................pp. 93-99
Abstract: The paper presents an easily implementable technique to detect and eliminate cross-terms from Wigner distributions using fractional Fourier transforms. The main benefit of this method arises from the fact that no prior knowledge of the signal is required, so the cross-term detection is ‘blind’. Depending on the technicalities of processing, different implementation schemes are discussed and compared with the help of suitably chosen examples. The cross-term detection is also shown to be effective for signal separation problem using binomial expansion.
Keywords: Wigner Distributions, Signal Processing ,Cross-Term.

Title: THE ADAPTIVE POTENTIAL OF SPACE DIVERSITY TECHNIQUES
Authors: L. Cremene, T. Palade,.........................................................................pp.100-109
Abstract: Our analysis is performed in the context of a study of adaptive radio techniques, in the attempt to improve link availability and transmission quality of broadband wireless systems, and especially to achieve an efficient use of radio resources. We have established our focus on spatial diversity techniques, and this paper presents a performance analysis of transmitter and receiver combining techniques for indoor multipath scenarios, in the particular case of an 802.11a PHY. Transmitter diversity based on Alamouti space-time coding schemes have been tested in the following configurations: 2Tx-1Rx, 2Tx-2Rx, 4Tx-1Rx, 4Tx-2Rx. Considerable improvements of packet error rates (PER), signal-to-noise ratio (SNR) and bit rate have been noticed, compared to those obtained with no diversity or receiver diversity techniques. Spatial diversity schemes in the transmitter proved to be especially efficient in keeping the PER values down, thus distinguishing themselves as a solution for multipath scenarios. Regarding receiver combing, even if a performance hierarchy of these techniques is already established – based on diversity gain improvement – we wanted to see which combining technique is better for a particular scenario. The detailed observations will enable us to set the premises for new adaptive techniques or adaptive combinations.
Keywords: Adaptive Techniques, Transmitter and Receiver Diversity, 802.11a PHY.

Title: STBC BASED STTC CODES OPTIMIZED DESIGNS FOR THREE TRANSMIT ANTENNAS: APPLICATION TO LAYERED COMMUNICATION SYSTEMS
Authors: G. Ferre, J. P. Cances, V. Meghdadi,....................................................pp.110-118
Abstract: This paper introduces new variations about the codes recently introduced by Jafarkhani et al. named Super Orthogonal Space Time Trellis Codes (SOSTTC). Using powerful set partitioning rules, these codes are able to combine the coding advantage of Space Time Trellis Codes (STTC) together with the advantage diversity of Space Time Block Codes (STBC). This partitioning is based mainly on the determinant criterion introduced first by Tarokh. In this paper we propose a new application field of these codes in the difficult context of a three transmit antenna system, and then we present a new architecture of layered space-time codes as a combination of Bell Labs Layered Space-Time (BLAST) architecture and the special STTC codes that we design for three transmit antenna. The new obtained STTC codes enables to improve significantly the performances of the best existing STTC codes. The layered system we propose is named Super Quasi Orthogonal Horizontal Layered Space Time Trellis Code (SQOHLSTTC). It consists of a powerful STBC based STTC originally derived in the second part, together with an original block based decoding algorithm which enables to use a higher number of transmit antennas. The decoding of SQOHLSTTC combines group interference suppression and group interference cancellation techniques. To implement the system, we propose a low complexity hard decision iterative decoding method. System performances are presented and proves the usefulness of the proposed transmission scheme.
Keywords: Space-time Codes, Set Partitioning, Space Time Block Code, Space Time Trellis Code, Layered Codes, Super Orthogonal Space Time Trellis Code, Diversity and Coding Gain.