Low vs high spectral efficiency communications with SIC and random access

The interplay of physical layer enhancement due to Successive Interference Cancellation (SIC) and classic random access protocols used in most multi-access communication chan- nels is the object of this paper. Considering the classic representatives of random access pro- tocols, Slotted ALOHA and Channel Sensing Multiple Access (CSMA), we show that two operation regimes can be identified as a function of the communication link spectral efficiency. In case of high levels of spectral efficiency, multi packet reception as granted by SIC is of limited usefulness. The obtained overall sum- rate performance are dominated by the MAC protocol algorithm. On the contrary, for low spectral efficiency levels, sum-rate performance are essentially dependent on physical layer SIC capability, while the MAC protocol is of marginal. Limitations due to limited transmission power level dynamic range are shown to induce unfairness among nodes, i.e., nodes closer to the sink achieve better sum-rate and success probability performance. However, the unfairness issues fades away when the system is driven to work around the sum-rate peak achieved for low spectral efficiency communications. This is a major finding of this work: apparently, SIC can boost performance while still maintaining a fair sharing of the achieved sum-rate performance among nodes, irrespective of the quality of their respective communication channels.