  Energy efficiency is an important design criterion for wireless
communications. When parallel frequency channels are used for multiuser
transmission, the channel bandwidths and user power are adjusted to maximize
the sum information rate with the bandwidth budget, the transmit power budget,
and the user-specific rate requirements. The maximum sum rate is used in
measuring the energy efficiency. With fixed or flexible bandwidths of the
frequency channels, practical methods are developed to find the total transmit
power with the unique optimal resource (bandwidth and power) allocation for
maximum energy efficiency. This resource allocation ensures that, while each
user's minimum rate requirement is satisfied, all the excess resource of the
spectrum and transmit power is dedicated to the one user with the best channel
quality. Simulation results validate the optimal solutions of total transmit
power and resource allocation that support the energy-efficient multiuser
transmission.
