International Journal of Communication Systems

In this paper, we propose an analytical cross-layer model for a TCP connection running over a covariance-stationary wireless channel with completely reliable ARQ/FEC. The model allows to evaluate the effect of many parameters of wireless channels on TCP performance making it suitable for performance optimization studies. These parameters include stochastic properties of the wireless channel characteristics, the strength of the FEC code, the use of ARQ, the raw data rate of the wireless channel, and the bottleneck link buffer size. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents an analysis of asynchronous MCCDMA systems over frequency-selective multipath fading channels when the carrier frequency offsets (CFOs) of all users are random variables and the frequency offset for the desired user is compensated. The effect of residual CFO on the average bit error rate (BER) is evaluated by the semi-analytical method, and then the approximated BER performance is obtained as a closed-form expression. Moreover, the signal-to-noise ratio (SNR) loss caused by residual CFO is evaluated. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, we propose to design a Distributed Multichannel Assignment with Congestion control (DMAC) routing protocol. In this protocol, a traffic-aware metric provides solution for multichannel assignment and congestion control. Hence, the proposed protocol can improve the throughput and channel utilization to a very high extent. The proposed algorithm avoids self-interference by not assigning a channel to any link whose incident links have already been assigned channels. By our simulation results, we show that our proposed protocol attains high throughput and delivery ratio along with reduced delay. Copyright © 2011 John Wiley & Sons, Ltd.

Minimum-shift-keying (MSK)-based M-ary cyclic-hift keying (MCSK) transceiver has been proposed for spread spectrum (SS) communications under multipath channel. Moreover, the low complexity structure of the MSK-based MCSK SS system with combating inter-block interference and preserving constant-envelope property has been designed to provide the high rate and quality performance. Simulation results show that the proposed system significantly outperforms the conventional direct-sequence SS system under the additive white Gaussian noise channel, and attains a more robust performance under the multipath fading channel. Copyright © 2011 John Wiley & Sons, Ltd.

The ‘counter starvation’ problem about unfairness induced by different hops and unfairness induced by MAC protocol is analysed in detail, especially illustrating how cross-layer process of TCP layer and MAC layer introduces ‘counter starvation’ problem. The Cross-layer ECN method is described using pseudocode. To solve the ‘counter starvation’ problem, Cross-layer ECN is analysed through the closed loop of TCP, as well as the probability model of the cross-layer ECN method. CCLE (Counter Cross-layer ECN) is processed by weight derivation, which is most innovative in recent researches. At the same time, other MAC metrics except RTS counter is applied into CCLE method. Copyright © 2011 John Wiley & Sons, Ltd.

This paper details the downlink performance analysis of a IEEE 802.16e based OFDMA system that combines adaptive beamforming and MIMO. Performance analysis is based on the results of experiments and simulations obtained from a prototype system implementation and fixed-point simulator. Both experiments and simulations demonstrate that the proposed system improves the required SNR over the conventional MIMO OFDMA system by 3 dB (QPSK)/ 2.5 dB (16-QAM) for the frame error rate (FER) of 1% in the WiBro signal environments. Copyright © 2011 John Wiley & Sons, Ltd.