Reliable Multicast Mac Protocol for Spatial Reuse Efficiency Assisted by Multicarrier Ds-cdma in Wlan Systems

We propose a reliable multicast MAC protocol based on the multicarrier direct-sequence code-division multiple access (MC DS-CDMA) scheme to enhance spatial reuse efficiency in wireless local area networks (WLANs). Conventional multicast MAC protocols using RTS-CTS handshake exchange CTS and ACK packets consecutively for reliable transmission. Although this protocol guarantees transmission reliability by avoiding the hidden node (HN) problem, multiple CTSs and ACKs degrade network efficiency and cause the well-known exposed node (EN) problem, rather than the HN problem. The multicast sender must receive multiple CTSs and ACKs from all multicast receivers in its own multicast group for reliable multicast. The range of the EN problem is greater than that of the unicast, and spatial reuse efficiency decreases. In the proposed protocol, CTS/ACK messages of multiple receivers can be transmitted concurrently through the MC DS-CDMA mechanism to alleviate the EN problem and enhance spatial reuse efficiency. This can reduce the transmission and carrier sensing range of multiple receivers, since the protocol spreads the CTS/ACK transmission power by the spreading gain. The proposed protocol also reduces the total transmission delay due to the reduction of the overhead of consecutive CTSs and ACKs. The proposed protocol is thoroughly examined by simulation and theoretical methods. Results show that the proposed protocol significantly reduces the aforementioned overhead, and thus improves the performance of WLAN systems.