Joint Random Pilot and Multi-Slot Access in Massive MIMO for Space Information Networks

Space information networks (SINs) is viewed as an effective solution to provide broadband access in a seamless and cost-effective manner for future machine-to-machine communications. Moreover, massive multiple-input multiple-output (MIMO) technology over satellites has received a great deal of interests. To solve the problem of pilot collision in the crowded massive MIMO system for SIN, a joint random pilot and multi-slot access (JRPMSA) protocol is proposed. Our JRPMSA protocol allows the failed user equipments (UEs) to reselect a pilot from the remaining pilots in multi-slots, i.e., the pilots that are not selected by any UE or selected by more than one UE in the initial step. The random access satellite estimates and buffers the channel response on each pilot of each UE in multi-slots. By utilizing the and-or tree theory, we analyzed the performance of the JRPMSA protocol, mainly focus on the access failure probability and uplink throughput. Simulation results shows that the proposed JRPMSA protocol can obviously decrease the access failure probability and increase the peak throughput.