Maximizing bits-per-Joule capacity over parallel channels

Bits-per-Joule capacity is measured in [bit/Joule] and denotes the maximum number of bits that can be reliably transmitted on a noisy channel for each Joule of energy used for transmission. In this paper properties of the bits-per-Joule capacity of the bandlimited additive white Gaussian noise (AWGN) channel are discussed. Then, for the case of independent parallel Gaussian channels, the problem of optimal power allocation maximizing the energy efficiency is considered, and comparisons with the classical rate-maximizing waterfilling strategy are given.