Channel and Multiuser Diversities in Wireless Systems: Delay-Energy Tradeoff

We consider a communication system with multi-access fading channel. Each user in the system requires certain rate guarantee. Our main contribution is to devise a scheduling scheme called "Opportunistic Super-position Coding" that satisfies the users' rate requirements. Using mean-field analysis, i.e., when the number of users go to infinity, we analytically show that the energy required to guarantee the required user rate can be made as small as required at the cost of a higher delay ("delay-energy tradeoff"). We explicitly compute the delay under the proposed scheduling policy and discuss how delay differentiation can be achieved. We extend the results to multi-band multi-access channel. Finally, all the results can be generalized in a straightforward fashion to broadcast channel due to the AWGN multiaccess-broadcast duality.