Energy and bandwidth efficiency in wireless networks

In this paper, we consider the bandwidth efficiency and energy efficiency of wireless ad hoc networks in which the energy supply of nodes and bandwidth are the primary resource constraints. Energy consumption of the receiver in order to process each coded bit is considered as well as the wasted energy of a nonideal transmit amplifier. A simplified network consisting of a large number of nodes between the source and destination is considered. We consider the case where multiple simultaneous transmission can take place provided they sufficiently far apart (spatial reuse). The parameters we, vary are the input power to the amplifier, the error control code rate and the transmission distance for each hop, or equivalently the number of hops between the source and destination. The result is a tradeoff between the energy efficiency and bandwidth efficiency of the network similar in nature to that found by Shannon for a single link. While Shannon's results indicate that arbitrarily low code rates minimize the energy required for reliable communication, when receiver processing energy strictly larger than 0 is included, then optimum code rate is much closer to 1. We also consider the transport efficiency defined as the number of bits per second per Hz per Joule of energy to transport information reliably between a source and a destination node as a single network performance metric. The transport efficiency combines the bandwidth efficiency and energy efficiency into a single metric. The transport efficiency for the case of no spatial reuse decreases linearly with distance but if we allow large number of hops, with spatial reuse the transport efficiency approaches a floor that is independent of the path loss exponent. The minimum energy consumption as a function of distance increases linearly as a function of distance.