A Two-Dimension Opportunistic CSMA/CA Protocol for OFDMA-Based In-Home PLC Networks

Multichannel systems can benefit from multiuser diversity by assigning channels to users with best channel conditions in different time instants. In this paper, a two-dimension opportunistic scheme for OFDMA-based in-home PLC systems with random access is presented in order to exploit multiuser diversity over different subchannels and time diversity across different time slots. The proposed scheme adjusts the backoff time for each user based on the knowledge of instantaneous channel information in both frequency and time domains, and thus assigns users with better channel quality higher priority to channel accessing. Moreover, users are scheduled to transmit over their favorable subchannels in order to further improve the system throughput. The analysis shows that the collision probability of the proposed scheme is extremely small. Additionally, simulation results demonstrate that the saturated throughput is significantly augmented even in the case that the number of users is highly exceeds that of subchannels.