Signal Processing in Random Access: A Cross Layer Perspective†

The design of medium access control (MAC) protocols has traditionally been separated from that of the physical layer. To a MAC protocol designer, the physical layer is a black box satisfying the so-called collision model: when only one user transmits, the packet arrives at the receiving node error-free. But when transmissions are simultaneous, packets are lost due to collision. Until recently, the theory of random access was based on such an idealized model, and random access protocols were viewed as collision resolution or collision avoidance techniques.