Experimental Study Of Efficient Reliable Transmission For IEEE 802.11n Long-Distance Wireless Links

LDmesh(Long Distance Wireless mesh) Networks feature with low cost,, and easy to deploy, so it could provide Internet access for rural areas and developing countries. However previous research are all based on 802.11b/g which suffer from many inherent defects such as high loss rate, low throughput comparing with IEEE 802.11 n protocol proposed in 2002. Meanwhile, propagation delay and ACK timeout is much longer than that in wireless local area networks, which make CSMA-based MAC protocol cannot work well in long-distance links.In our outdoor testbed, the long-distance is 22 Km long. All experiments were carried out on this link. Network nodes work on channel 36 of 5GHz. There is only one external WiFi node working on channel 161, so it did not interfere with our nodes at all.Based on practical measurement experiments in wireless long-distance links, we studied theoretical fundamentals and implementations of channel bonding in physical layer and frame aggregation, block ACK in MAC layer. We carried out experiments and demonstrated how FA impacts throughput of links and analyzed the results in theory. We proposed and implemented a modified ARQ(Automatic Repeat-reQuest) protocol by enlarging size of aggregated fames to increase link utilization. By collecting and analyzing error pattern of frames from long-distance links, we proposed an FEC(Forward Error Correction) mechanism to recover the error frames thus to improve the link throughput. The FEC mechanism deployed Turbo codes. The modified ARQ was verified in our testbed, and the FEC mechanism was evaluated by simulation with real trace.