隠れ端末問題及びフロー内干渉キャンセルを考慮したワイヤレスアドホックネットワークに関する研究

摘要

Performance of CSMA/CA (carrier sense multiple access/collision avoidance) wireless ad hoc network is severely affected by hidden terminal (HT) problem that results in the failure of carrier sense and causes the packet error due to collision. This thesis proposes a method of improving the performance of multi-hop ad hoc network by 4 steps which can be summarized as follows. First, the thesis analyzes HT effect on CSMA/CA unicast communication taking into account actual radio environments including both fading and capture effect. Based on the analysis results, it is predicted that multi-hop transmission is vulnerable to HT problem because of intra-flow interference (IFI). Regarding to this issue, as the second step, a CINR (carrier to interference and noise ratio) -based analysis method is proposed that can precisely estimate the packet delivery probability for CSMA/CA multi-hop transmission suffering from HT-caused IFI under fading environment. The results prove that conventional CSMA/CA media access control cannot achieve efficient multi-hop transmission. Therefore, as the third step, this thesis further proposes IFI-canceling multi-hop transmission (IFIC-MHT) scheme that enables efficient relaying with the highest traffic load for half-duplex multi-hop networks. The interference cancellation (IC) technique employs adaptive signal processing with a normalized least mean square (NLMS) algorithm for channel estimation and has good BER (bit error rate) and PER (packet error rate) performance under a wide range of SNR (signal to noise ratio) and SIR (signal to interference ratio) conditions. A multi-hop packet transmission frame format dedicated to the IFIC is designed. Finally, this thesis studies the effect of IFIC on large-scale ad hoc network where both intra-flow interference and inter-flow interference take place and together affect the multi-hop transmission.