  Device-to-device (D2D) communications as an underlay of a LTE-A (4G) network
can reduce the traffic load as well as power consumption in cellular networks
by way of utilizing peer-to-peer links for users in proximity of each other.
This would enable other cellular users to increment their traffic, and the
aggregate traffic for all users can be significantly increased without
requiring additional spectrum. However, D2D communications may increase
interference to cellular users (CUs) and force CUs to increase their transmit
power levels in order to maintain their required quality-of-service (QoS). This
paper proposes an energy-efficient resource allocation scheme for D2D
communications as an underlay of a fully loaded LTE-A (4G) cellular network.
Simulations show that the proposed scheme allocates cellular uplink resources
(transmit power and channel) to D2D pairs while maintaining the required QoS
for D2D and cellular users and minimizing the total uplink transmit power for
all users.
