In this paper, we present ROSALNet, a low-cost TDM mesh network which is designed to opportunistically exploit TV white spaces (TVWS) to provide broadband Internet connectivity to remote rural areas. Recent research has proposed WiFi-based wireless networks as cost-effective solutions to bridge the last-mile problem. However, WiFi normally operates in the 2.4 GHz band and above, where signal propagation is not as good as in sub-GHz bands such as terrestrial TV bands. Exploiting TV white spaces for broadband connectivity can potentially further bring down the cost of such wireless networks to a more affordable level. ROSALNet is implemented on commodity hardware using the open-source OpenWrt operating system. A single mesh node currently costs US$330, which is significantly cheaper than competing TVWS commercial solutions. ROSALNet can opportunistically use spectrum by looking up a white space database and by performing spectrum sensing. Our experiments with ROSALNet on a university campus demonstrates the superior coverage possible with TVWS compared to 2.4GHz. ROSALNet exploits an existing TDM mesh implementation originally designed to use WiFi bands, called FRACTEL, thereby inheriting its attractive features of low-latency and low jitter. Results from a lab testbed consisting of 4 nodes show that ROSALNet can provide an aggregate throughput of 11Mbps, which is sufficient to support triple play services.
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