Broadcast Packet Erasure Channels with Alternating Single-User Feedback

Delayed channel state information (CSI) feedback was shown to be very helpful in enlarging the capacity region of the two-user broadcast packet erasure channel (PEC), even with single-user feedback. However, feedback link itself requires additional resources and may also cause additional delay to data transmission. In this work, we aim to study how to optimally tradeoff the number of feedback bits and the reliable forward communication rate. In our model, one receiver does not provide its CSI while the other one can alternate between delayed CSI feedback and no feedback. This model includes the intermittent single-user feedback as a special case. Our achievability is an extension of previous opportunistic network coding such that the network coding gain can still be enjoyed even when the single-user feedback is not always available. Interestingly, when two users have the same link erasure probabilities, boundaries of the capacity regions are identified since they can be achieved by the proposed schemes. Our results also reveal that even when the single-user feedback is alternating, strictly positive capacity benefits can be attained over the no-feedback capacity.