Joint MAC / PHY Scheduling

Who gets to use radio spectrum, and when, where, and how?

Wireless communication poses a challenge to the clean separation of functional layers. This is especially true of the PHY / MAC boundary: The physical layer, broadly speaking, is about how devices communicate over some medium, and the MAC layer is concerned with which devices do so when.

Fundamentally, MAC is about arbitrating conflict1, but the physical layer defines what kind of conflict exists in the first place. Interesting cross-layer problems occur because many physical layer decisions mitigate some conflicts while exacerbating others and the best MAC decisions depend on those conflicts. The essence of MAC / PHY integration is using higher-layer information to help the PHY determine which conflicts are most worth avoiding.

STDMA Scheduling with Directional Antennas

Adaptive MAC Scheduling

  1. It’s probably better to say that MAC is about arbitrating interaction, which is not necessarily conflict. This is especially true for techniques like physical layer network coding, interference alignment, and network MIMO.