  We study the energy performance of random linear network coding for time
division duplexing channels. We assume a packet erasure channel with nodes that
cannot transmit and receive information simultaneously. The sender transmits
coded data packets back-to-back before stopping to wait for the receiver to
acknowledge the number of degrees of freedom, if any, that are required to
decode correctly the information. Our analysis shows that, in terms of mean
energy consumed, there is an optimal number of coded data packets to send
before stopping to listen. This number depends on the energy needed to transmit
each coded packet and the acknowledgment (ACK), probabilities of packet and ACK
erasure, and the number of degrees of freedom that the receiver requires to
decode the data. We show that its energy performance is superior to that of a
full-duplex system. We also study the performance of our scheme when the number
of coded packets is chosen to minimize the mean time to complete transmission
as in [1]. Energy performance under this optimization criterion is found to be
close to optimal, thus providing a good trade-off between energy and time
required to complete transmissions.
