Low power error control for wireless links

Energy efficiency, which directly affects battery life and portability, is perhaps the single most important design metric in hand-held computing devices capable of mobile networking over wireless radio links. By virtue of their being relatively thin clients, a high fraction of the power consumption in portable wireless computing devices is accounted for by the transport of packet data over the wireless link [Stemm96]. In particular, the error con-. trol strategy (e.g. convolutional and block channel coding for forward error correction (FBC), ARQ protocols, hybrids) used for wireless link data transport has a direct impact on battery power consumption. Error control has traditionally been studied by channel coding researchers from the perspective of selecting an error control scheme to achieve a desired level of radio channel performance. We instead study the problem of error control from a perspective more relevant to battery operated devices: the amount of battery energy consumed to transmit bits across a wireless link. This includes both the physical transmission of useful and redundancy data, as well as the computation of the error control redundancy. We first describe a novel error control where the most battery energy efficient hybrid combination of an appropriate FBC code and ABQ protocol is chosen, and adapted over time, for each stream (ATM virtual circuit or IP/RSVP flow). Next, we present analysis and simulation results to guide the selection and adaptation of the most energy efficient error control scheme as a function of quality of service, packet size, and channel state.