OFDM符号特性对DCF性能影响研究

Research on the impact of OFDM symbol characteristics on DCF performance

认知无线网络由于使用信道频段的长时延特性,OFDM符号时间及Slottime均较大,使得CSMA/CA协议中的SIFS等参数值增大。另外,随着无线局域网络物理层速率的提高,每个OFDM符号携带的数据比特数加大。为评估物理层长时延及高速环境下的DCF性能,基于二维Markov模型得出了CSMA/CA系统吞吐量表达式,数学分析表明系统吞吐量主要由网络节点数、数据包长度、OFDM携带信息比特数、Slottime及OFDM符号时间长度决定。理论计算及仿真测试结果显示,OFDM携带信息比特数越多,Slottime越大,OFDM符号时间长度越长,CSMA/CA的吞吐量性能越低。

For cognitive wireless networks,due to the long time delay characteristics of channel frequency,both OFDM symbol time and slot time are big,which makes the SIFS increase in the CSMA/CA.In addition,with the improvement of the data rate on physical layer in wireless local area network,the number of data bits carried by each OFDM symbol increase.To assess the physical long extension performance of DCF under the environment of high speed model,we obtain the CSMA/CA system throughput expression based on the two-dimensional Markov model.Mathematical analysis shows that the throughput is mainly determined by the node number of the network,packet length,the number bits carried by OFDM,the slot time and OFDM symbol time.Theoretical calculation and simulation results show that as the data bits of OFDM increase,the slot time and the OFDM symbols are longer.And the throughput performance of CSMA/CA is also degraded.