Real-life experiments of Multi-Radio Multi-Channel wireless mesh networks: 802.11n is not any better than 802.11a!

Wireless Mesh Network (WMN) has become a popular access network architecture in the community due to its low cost and readily deployable nature. However, it is well known that multi-hop transmission in WMN is vulnerable to bandwidth degradation, primarily due to contention and radio interference. A straightforward solution to this problem is to use mesh nodes with multiple radios and channels. In this paper, we demonstrate through real-world experiments that the use of multiple radios and channels solely cannot solve the multi-hop TCP throughput degradation problem in IEEE 802.11n mesh networks. We verify that it is because the round trip time (RTT) for wireless communication path increases significantly with the number of hops, and the TCP throughput is limited inversely by the RTT. Due to this TCP throughput limitation, we also found interestingly that the multi-hop TCP throughput (up to five hops) of 802.11a is comparable to that of 802.11n. Our results give a key message that a new generation of TCP needs to be proposed and adopted so as to support the ever advancing wireless technologies and growing demand of multi-hop communications in wireless mesh networks.