Maan A. Kousa

Bit error rate performance of a generalized diversity selection combining scheme in Nakagami fading channels

The severity of fading on mobile communication channels calls for the combining of multiple diversity sources to achieve acceptable error rate performance. Traditional approaches perform the combining of the different diversity sources using either: the conventional selective diversity combining (CSC), equal-gain combining (EGC), or maximal-ratio combining (MRC) schemes. CSC and MRC are the two extremes of compromise between performance quality and complexity. This paper presents a generalized diversity selection combining (GSC) scheme in which only those diversity branches whose energy levels are above a specified threshold are combined. Doing so, the proposed scheme will have a bit error (BER) performance that is upper- and lower-bounded by those of the CSC and MRC schemes respectively. Simulation results for the performances of this scheme over Nakagami (1960) fading channels are shown.

An adaptive error control system using hybrid ARQ schemes

A simple and efficient system utilizing the class of Hamming codes in a cascaded manner is proposed to provide high throughput over a wide range of channel bit error probability. Comparisons with other adaptive schemes indicate that the proposed system is superior from the point of view of throughput, while still providing the same order of reliability as an ARQ (automatic repeat request) system. The main feature of this system is that the receiver uses the same decoder for decoding the received information after each transmission while the error-correcting capability of the code increases. As a result, the system is kept to the minimum complexity and the system performance is improved. >

A novel approach for evaluating the performance of SPC product codes under erasure decoding

Product codes are powerful codes that can be used to correct errors or recover erasures. The simplest form of a product code is that where every row and every column is terminated by a single parity bit, referred to as single parity check (SPC) product code. This code has a minimum distance of four and is thus guaranteed to recover all single, double, and triple erasure patterns. Judging the code performance based on its minimum distance is very pessimistic because the code is actually capable of recovering many higher erasure patterns. This paper develops a novel approach for deriving an upper bound on the post-decoding erasure rate for the SPC product code with iterative decoding. Simulation shows that the derived bound is very tight.

Multi-hop capacity of MIMO-multiplexing relaying systems

This paper derives the multi-hop capacity of OFDM-based MIMO-multiplexing relaying systems. MIMO-multiplexing relaying presents a spectrally efficient means of realizing mesh supports in wireless networks operating over licensed bands by providing separate links for access and mesh relaying services on the same broadband radio channel. We show that for an NtimesN MIMO-multiplexing relaying system with amplification factor alpha at relay nodes, R-hops relaying degrade the capacity by at most -Nlog2(alpha2R/ (1 + Sigma r=1 R alpha2rNr)) + RNlog2(N) bits/sec/Hz. Therefore, greater capacity loss is experienced in MIMO-multiplexing relaying involving high order MIMO systems. We also illustrate that the capacity loss is independent of the OFDM configurations employed; thus network operators could employ higher OFDM configurations to compensate for data rate loss in access services when some of the MIMO-multiplexing links are dedicated to mesh relay. This pioneering analysis provides useful guidelines for network operators planning to employ MIMO-multiplexing option for mesh relay supports.

Performance of ATM networks under hybrid ARQ/FEC error control scheme

In ATM networks, fixed-length cells are transmitted. A cell may be discarded during the transmission due to buffer overflow or detection of errors. Cell discarding seriously degrades transmission quality. This paper analyzes a hybrid automatic repeat request/forward error control (ARQ/FEC) cell-loss recovery scheme that is applied to virtual circuits (VCs) of ATM networks. FEC is performed based on a simple single-parity code, while a Go-Back-N ARQ is employed on top of that. Both throughput efficiency and reliability analysis of the hybrid scheme are presented. In the process we investigate the interactive effects of the network parameters (number of transit nodes, traffic intensity, ARQ packet length, ...) on the performance. The analysis provides a method for optimizing the FEC code size for a given network specification.

Bit error rate performance analysis of a threshold-based generalized selection combining scheme in Nakagami fading channels

The severity of fading on mobile communication channels calls for the combining of multiple diversity sources to achieve acceptable error rate performance. Traditional approaches perform the combining of the different diversity sources using either the conventional selective diversity combining (CSC), equal-gain combining (EGC), or maximal-ratio combining (MRC) schemes. CSC and MRC are the two extremes of compromise between performance quality and complexity. Some researches have proposed a generalized selection combining scheme (GSC) that combines the best branches out of the available diversity resources (). In this paper, we analyze a generalized selection combining scheme based on a threshold criterion rather than a fixed-size subset of the best channels. In this scheme, only those diversity branches whose energy levels are above a specified threshold are combined. Closed-form analytical solutions for the BER performances of this scheme over Nakagami fading channels are derived. We also discuss the merits of this scheme over GSC.

Improved regular and semi-random rate-compatible low-density parity-check codes with short block lengths

Powerful rate-compatible codes are essential for achieving high throughput in hybrid automatic repeat request (ARQ) systems for networks utilising packet data transmission. The paper focuses on the construction of efficient rate-compatible low-density parity-check (RC-LDPC) codes over a wide range of rates. Two LDPC code families are considered; namely, regular LDPC codes which are known for good performance and low error floor, and semi-random LDPC codes which offer performance similar to regular LDPC codes with the additional property of linear-time encoding. An algorithm for the design of punctured regular RC-LDPC codes that have low error floor is presented. Furthermore, systematic algorithms for the construction of semi-random RC-LDPC codes are proposed based on puncturing and extending. The performance of a type-II hybrid ARQ system employing the proposed RC-LDPC codes is investigated. Compared with existing hybrid ARQ systems based on regular LDPC codes, the proposed ARQ system based on semi-random LDPC codes offers the advantages of linear-time encoding and higher throughput.

Modified algorithm for hard decision decoding of product codes

Product coding produces powerful long codes from short constituent codes. The conventional row-column decoding algorithm of the product code does not exploit its full power of correcting random errors and proposes a modification to the conventional decoding algorithm, which makes it capable of reaching the theoretical error correction capability of the code. In addition to its theoretical significance, the modified algorithm is shown to provide a gain of 0.5 dB over the conventional algorithm for AWGN channels.

Jigsaw cooperative learning in engineering classrooms

Jigsaw is a cooperative style of learning that has been around for more than four decades. Started as a technique for bridging ethnic boundaries and including minorities gently within the crowd, Jigsaw is now seen as one of the very effective techniques of student-centered learning, team-based learning, and project-based learning. Most of the successful stories on Jigsaw come from the fields of social and humanitarian sciences and K-12 education. Only recently there have been some pilot studies on the application of Jigsaw to university level engineering courses. For the application of Jigsaw in engineering to gain more momentum, the engineering education community has to share their experiences and success, as well as challenging stories in this regard. This paper presents the authors experience with the application of Jigsaw in two formats, subject-based and problem-based. Some preliminary surveys and statistics are presented.

Extended low-density parity-check codes for feedback-based cooperative diversity schemes

Cooperative diversity or user cooperation achieves the diversity gain without adding physical antennas to the users or mobile stations. The users work in a cooperative fashion by using their single antennas to create a virtual transmit diversity, called relay diversity or cooperative diversity. The diversity gain achieved by cooperative diversity can be further improved using error correction codes. Low-density parity-check (LDPC) codes are linear block codes with good error correction capabilities. The authors present a novel approach using extended LDPC codes to increase the diversity gain in cooperative diversity. The authors also compare the extended LDPC codes with the punctured LDPC codes in a cooperative diversity and show that there is a performance–complexity tradeoff between the punctured and the extended LDPC codes in the cooperative diversity. Furthermore, the authors will propose two feedback-based protocols for cooperative diversity and compare their throughput with non-feedback-based cooperative diversity using extended LDPC codes.