Concept and Analysis of Capacity Entropy for Uplink Multi-User Media Access Control for the Next-Generation WLANs

IEEE 802.11ax, an emerging standard for the next-generation wireless local area networks (WLANs), pursues to improve network throughput in high-density deployment scenarios by introducing high-efficiency mechanisms into both media access control (MAC) layer and physical (PHY) layer. In IEEE 802.11ax, high-efficiency multi-user media access control (MU-MAC) is adopted for both uplink and downlink access mechanisms. As for the uplink MU-MAC, it can be further subdivided into two categories, uplink orthogonal frequency division multiple access (OFDMA) scheduling access (UOSA) and uplink OFDMA random access (UORA). How to effectively measure and optimize the joint carrying capacity (JCC) of the networks where both scheduling access mode and random access mode are supported is a key problem for the design of the uplink access mechanism of the 802.11ax. Firstly, in this paper, the concept of capacity entropy for multi-user access (CEM) is proposed to quantitatively measure the JCC of the networks. Secondly, the UORA is modeled and analyzed and we get the access probability of UORA (P_UORA) by using an enhanced Markov chain, then we can calculate the capacity entropy of UORA. Based on it, the CEM of the 802.11ax is further analyzed. Finally, based on the adopted MU-MAC framework in 802.11ax standard draft, an efficient hybrid access strategy (HAS) is proposed, which combines a greedy scheduling strategy based on capacity constraints and a method based on channel quality perception of stations (STAs) in UORA. Simulation results show that HAS achieves higher CEM. In summary, it is believed that the proposed concept of CEM will pave a new technical way to investigate problems of how to optimize the JCC for the next-generation WLANs.