On the Feedback Transfer Effort for Rate-Adaptive Multiuser Systems

The benefits of multiuser diversity for fading chanels are well established in the literature. What is not well documented is the effort required to obtain this CSI information at the scheduler for a frequency division duplex (FDD) system. This paper investigates the practical aspects of the feedback transfer process for a discrete rate-adaptive multiuser system including multi-access, feedback delay and feedback channel imperfections due to fading and additive noise. We compute the optimal power and bandwidth allocated for channel estimation and show that tradeoffs exist between these resources and the number of users depending on the feedback delay. It is also shown that quantization and feedback errors may increase the outage region as the number of users increases. This in effect reduces the multiuser diversity gain expected in ideal feedback channels.