In this work, we describe our experiences in building a low cost and low power wireless mesh network using IEEE 802.15.4 technology to provide telephony services in rural regions of the developing world. 802.15.4 was originally designed for a completely different application space of non-real-time, low data rate embedded wireless sensing. We use it to design and prototype a telephony system, which we term as Lo 3 (Low cost, Low power, Local voice). Lo 3 primarily provides two use cases; (1) local and broadcast voice within the wireless mesh network, and (2) remote voice to a phone in the outside world. A Lo 3 network can cost as less as $2K, and can last for several days without power "off the grid", thus making it an ideal choice to meet cost and power constraints of rural regions. We test deployed a full-fledged Lo 3 system in a village near Mumbai, India for 18 hours over 3 days. We established voice calls with an end-to-end latency of less than 120ms, with an average packet loss of less than 2%, and a MOS of 3.6 which is considered as good in practice. The users too gave a positive response to our system. We also tested Lo 3 within our department where it can be used as a wireless intercom service. To our knowledge, Lo 3 is the first system to enable such a voice communication system using 802.15.4 technology, and show its effectiveness in operational settings.

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In India, the rural teledensity is just 37% and there are a large number of villages which do not have cellular coverage to this day but many such villages are only a few km away from the cellular coverage. Exploiting these cellular points near villages, we present a low cost and low power gateway system to extend the cellular coverage into the rural areas. Specifically, we develop and demonstrate a low cost, low power 802.15.4 gateway which can connect a number of villages in its vicinity to the cellular backhaul. In prior work, we designed a low cost, low power, local voice (called as Lo 3 ) system using 802.15.4 technology. Lo 3 system enabled villagers inside a village to communicate with each other. In this demo, we show that, using the gateway node, the 802.15.4 handsets of Lo 3 system enable villagers to establish real-time voice calls from/to the village to/from the outside world. We test deployed our system in Ahupe village near Mumbai, India for 18 hours over 3 days, and received positive response from the villagers.