The effect of carnier frequency offset on the perfomance of BLAST-OFDM systems is presented. Analysis shows that system performance degrades as frequency offiset and channel state information estimation interval increase. Numerical simulations confim this conclusion A pilot channel is recommended for synchronisation and phase-shift adjustment.

因特网具有复杂的网络拓扑结构，已有的研究发现这种拓扑结构非常有利于病毒的传播。本文采用理论分析和计算机模拟相结合的手段分析了有限规模网络上病毒传播模型的动力学性质。研究表明SIS病毒传播模型在有限规模网络上传播是一个有限状态的马尔科夫过程，病毒传播存在一个瞬时稳态，并分析了瞬时稳态下感染节点密度和存活概率的变化规律。这些结果有助于理解计算机病毒在因特网上传播的现象，并可以为免疫策略的研究提供了一定理论上的帮助

This paper investigates the driving synchronization of spatiotemporal chaos. Using this method, synchronization could be achieved e ciently. By improving the driving sequence generation method, the spatial periodicity in the original system is overcome. Large quantities of chaotic sequences are available, which possess the excellent properties expected in Code Division Multiple Access (CDMA) communications. These chaotic sequences can be used as the spreading sequences in place of the traditional pseudo-noise sequences. We also evaluate the performance of the chaotic CDMA communication systems and compute the average bit error rate caused by the multi-user interference and the noise in the channel. The theoretical and simulation results show the excellent performance of the scheme.

As an effective mechamism acting on the intermediate nodes to support end to end congestion control, active queue management (AQM) takes a trade off between link utilization and delay experienced by data packets. From the point of view of the control theory, it is rational to regard AQM as a typical regulating system. Although proportional integral (PI) controller for AQM outperforms traditional RED algoritlnn, the mismatches in simplified TCP flow modal inevitably degrades the perfomance because the design of PI controller is heavily dependent of the accuracy of the plant, such as, for small buffer the system tends to perform poorly, in this paper, the fuzzy logic controller (FLC) for AQM is designed based on the fuzzy logical control, its superiority is independent of the modal of the plant, which is very suitable to the high variability and uncertainty networks. We present the guidelines and highlights to design the parameters of the FLC. We then compare its performance with the PI controller through sinulations, and investigate the impact of the network configuration and operating parameters on the stability and responsibility. The results show that the FLC is rather robust against the noise and disturbace caused by the round trip time, the llink capacity, the number of the active flows and the non responsive UDP flows, etc., which badly degrade the performance of the PI controller. The transient response and tracldng capability of the FLC is superior to that of the PI controller, which is beneficial to achieve the goals of AQM scheme.

TCP performance in the IEEE 802.1-based multihop ad hoc networks is extremely poor, because the congestion conrtol mechanism of TCP cannot effectively deal with te problem of packet drops caused by mobility and shared channel contention among wireless nodes. In this paper, we present a cross-layer method, which adaptively adjusts the TCP maximum window size according to the number of RTS (Request To Send) retry counts of the MAC layer at the TCP sender, to control the number of TCP packets in the network and thus decrease the channel contention. Our simulation results show that this mehod can remarkably improve TCP throughput and its stability.