LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks

Multiuser Diversity and Scheduling

In general, wireless channels are prone to random fluctuations caused by the underlying scattering, diffraction, and reflection phenomena. While a passive approach of dealing with these problems would be trying to mitigate their effects, a more fruitful approach involves exploiting these phenomena to enhance system communication. Such exploitation can be achieved by granting access, that is, allocating resources, to the users with good channel quality. Continuous acquisition of Channel State Information (CSI) for all users, however, would be required - a nontrivial process but with substantial gains.

Taking advantage of multiuser diversity in carefully scheduling the users is a way of achieving efficient resource allocation. However, when the scheduling method solely depends on the CSI, it becomes an unfair scheduler since some users may experience bad channel conditions for prolonged periods of time. On the other hand, a scheduling strategy that ignores the CSI of the different users and simply grants them equal access to the shared resources is a fair strategy. However, this fairness is only in the resource allocation and not in the quality of the delivered services. Consequently, a balance should be struck between exploiting the multiuser diversity, fairness in resource allocation, and fairness in service provisioning.