Channel-aware ALOHA with SINR capture: When is the knowledge of channel not helpful?

We consider an ALOHA network in which users have the knowledge of their own channel state information (CSI). In each time slot, each user transmits its packet to the base station (BS) according to a CSI-dependent transmission scheme. A packet is successfully received if its signal to interference plus noise ratio (SINR) is larger than the capture ratio. We analyze the throughput of this network under a threshold-based transmission scheme in which a user transmits only when its channel gain is higher than a threshold. It is shown that in some cases the conventional ALOHA transmission scheme without CSI may outperform the threshold-based transmission scheme in terms of the maximum possible throughput. We give the condition for this phenomenon and find that this phenomenon will not occur if the BS is capable of receiving three or more packets simultaneously. Besides, we present a transmission scheme in which a user only transmits when its channel gain lies in an interval. This scheme includes the threshold-based one as a special case.