12 - Overview

Summary

Wireless is a shared medium and communication performance is affected not only by individual communication links but also by the interaction among the links that reuse the same frequency in the entire network. Interference is one of the major factors limiting system spectral efficiency, especially as wireless networks move toward more aggressive frequency-reuse scenarios in future wireless networks. For users that interfere with each other heavily, advanced medium access control (MAC) schemes can be used to allocate orthogonal network resources. The design of distributed medium access is essential in avoiding signaling overhead, ensuring network scalability, and determining overall network performance. Furthermore, the quality of a wireless channel varies both in time and for the user. To fully exploit network diversity, channel-aware medium access schemes should be used to adapt data transmission and resource assignment based on the states of wireless channels. The difference of channel-aware medium access schemes from traditional MAC protocols is that channel-aware MACs schedule users with favorable channel conditions to transmit with optimized link adaptation based on channel state information (CSI). By exploiting the channel variations across users, channel-aware MAC substantially improves network performance through exploiting multi-user diversity, whose gain increases with the number of users.

Design objective

As discussed in Section 5.1, the goal of distributed MAC protocols is to remove as many idle and collision states as possible. The ideal MAC protocol is able to remove all idle and collision states.