Cross-Layer Resource Allocation and Scheduling

The aim of this chapter is to justify the need for reduced-complexity, reduced-overhead and cross-layer approaches to resource allocation, scheduling and channel estimation and to present some possible approaches. A resource allocation algorithm is first examined that employs chunks of subcarriers instead of individual subcarriers, thus resulting in reduced complexity and overhead. It is shown that, by appropriately choosing the chunk size as a function of the coherence bandwidth of the channel, the algorithm can be employed in Distributed Broadband Wireless systems without significant penalty. A cross-layer user scheduling and resource allocation is then presented. The algorithm modifies previous approaches that had focused on the sum rate, in order to also provide Quality-of-Service guarantees. It is demonstrated that the algorithm can improve fairness and accommodate MAC layer requests at the cost of some additional control overhead. Finally, the problem of channel estimation is considered, which is of crucial importance for the operation of scheduling and resource allocation algorithms. A scheme that relies on careful placement of pilots and superposition of pilots to data symbols is proposed. It is shown that the scheme can reduce the overhead that is required for channel estimation. Moreover, the complexity for the hardware implementation of the scheme is considered