Interference measurements in an 802.11n Wireless Mesh Network testbed

Interference measurements in an infrastructure 802.11n Wireless Mesh Network (WMN) testbed are described. Each wireless router consists of a Linux processor with multiple dual-band 802.11a/b/g/n transceivers. The 5 GHz band can be used for backhauling, and the 2.4 GHz band can be used for end-user service. The backhaul links use sectorized 3×3 MIMO directional antenna, to support directional parallel transmission over orthogonal channels. A Linux-based device driver has been modified to adjust the physical layer parameters. Each 802.11n transceiver can be programmed to transmit over a 20 MHz spectrum without channel bonding, or a 40 MHz spectrum with channel bonding. The 802.11n standard supports up to three orthogonal channels, 1, 6, and 11. The routers can be programmed to implement any static mesh binary tree topology by assigning Orthogonal Frequency Division Multiplexing (OFDM) channels to network edges. The routers can be programmed to implement any general mesh communication topology by using a Time Division Multiple Access (TDMA) frame schedule, and assigning OFDM channels to network edges within each TDMA time-slot. Measurements of co-channel interference, the Signal to Interference and Noise (SINR) ratio and TCP/UDP throughput for the 802.11n network testbed are presented. It is shown that maximizing TCP/UDP throughput in 802.11n networks can be challenging, even with very high SINR (30-40 dB) links, MIMO directional antenna, and frame aggregation with block acknowledgements. In order to maximize bandwidth efficiency, the highest quality (and cost) MIMO directional antenna appear to be necessary, and it is unlikely that mobile users can use such antennas. Our interference measurements can be used to optimize the performance of large WMNs using 802.11n technology.