OFDM系统中基于跨层的TCP性能增强技术

针对高误码率及高中断率对无线TCP(Transport Control Protocol)的影响,提出了OFDM(Orthogonal Frequency Division Multiplexing)系统跨层TCP增强技术CLTCP(Cross-Layer TCP)。CLTCP利用链路级恢复和TCP冻结技术,提高了无线TCP性能;对于出错的无线帧,链路层能给予有限次的重传,以屏蔽TCP层对高误码率的感知;同时,为了保证出错帧在有限重传次数内被正确递交对端,链路层联合物理层采用自适应调制编码技术来提高重传帧的可靠性。对于无线链路长时间断连,CLTCP利用TCP源端冻结技术冻结RTO(Retransmission Time Out)值,以避免数据包连续超时造成的极大RTO,由此保证无线链路恢复连接后,TCP层能及时恢复工作。通过NS2(Network Semulation 2)软件仿真了多种无线TCP增强技术,并对仿真结果进行了比较和分析。仿真结果表明,CLTCP的吞吐量较Snoop技术最多可提升33%,并同时节省约38%的带宽。

Cross-Layer TCP Performance Enhancement Technique in OFDM System

CLTCP(Cross-Layer Transport Control Protocol) enhancement technique in OFDM(Orthogonal Frequency Division Multiplexing) system is proposed to improve the wireless TCP(Transport Control Protocol) performance.The main idea of CLTCP is the link recovery and Freezing-TCP.The link layer will retransmit the error frames for limited times,which can conquer the decrease of throughput caused by congestion control in TCP layer.Simultaneously,AMC(Adaptive Modulation and Coding) is adopted to improve the retransmission reliability,that the error frames can be sent to the receiver correctly in limited times.Freezing-TCP technique is adopted to freeze the RTO(Retransmission Time Out) value in the TCP source side,which can avoid the huge RTO value caused by continuous expiration of retransmission timer when the air link disconnection happens,the TCP layer can work immediately after the air link recovers.Multiple wireless TCP schemes are simulated in NS2(Network Semulation 2),the simulation shows that CLTCP scheme can improve 33% of the maximum throughput compared to the snoop scheme,while reduces 38% of the air bandwidth.