  In this paper, we study the effect of channel output feedback on the sum
capacity in a two-user symmetric deterministic interference channel. We find
that having a single feedback link from one of the receivers to its own
transmitter results in the same sum capacity as having a total of 4 feedback
links from both the receivers to both the transmitters. Hence, from the sum
capacity point of view, the three additional feedback links are not helpful. We
also consider a half-duplex feedback model where the forward and the feedback
resources are symmetric and timeshared. Surprisingly, we find that there is no
gain in sum-capacity with feedback in a half-duplex feedback model when
interference links have more capacity than direct links.
