Capacity and optimal resource allocation for fading broadcast channels - Part II: Outage capacity

In this two-part paper, we study three capacity regions for fading broadcas t channels and obtain their corresponding optimal resource allocation strat egies: the ergodic (Shannon) capacity region, the zero-outage capacity regi on, and the capacity region with outage, In Part I, we obtained the ergodic capacity region of the fading broadcast channel under different spectrum-s haring techniques. In this paper, we derive the outage capacity regions of fading broadcast channels, assuming that both the transmitter and the recei vers have perfect channel side information. These capacity regions and the associate optimal resource allocation policies are obtained for code divisi on (CD) with and without successive decoding, for time division (TD), and f or frequency division (FD), We show that in an M-user broadcast system, the outage capacity region is implicitly obtained by deriving the outage proba bility region for a given rate vector. Given the required rate of each user , we find a strategy which bounds the outage probability region for differe nt spectrum-sharing techniques. The corresponding optimal power allocation scheme is a multiuser generalization of the threshold-decision rule for a s ingle-user fading channel. Also discussed is a simpler minimum common outag e probability problem under the assumption that the broadcast channel is ei ther not used at all when fading is severe or used simultaneously for all u sers, Numerical results for the different outage capacity regions are obtai ned for the Nakagami-m fading model.