Asymptotic tradeoff between cross-layer goodput gain and outage diversity in OFDMA systems with slow fading and delayed CSIT

There are two important aspects of cross-layer gains in multiuser OFDMA systems with slow fading channels. They are the system goodput gain as well as the packet diversity gain. The former aspect of cross-layer designs has been well- studied under perfect CSIT conditions and is known as the multi-user diversity gain (MuDiv). In cross-layer OFDMA systems with perfect CSIT, it is well known that the system throughput (ergodic capacity) scales in the order of O(log log Kldquo) due to the MuDiv gain, where K is the number users. However, in slow fading channels with delayed CSIT, there will always be potential packet errors (due to channel outage if the scheduled data rate exceeds the instantaneous mutual information) even if very strong channel coding is applied at the base station. In this case, the cross-layer packet outage diversity is important to protect the packet errors due to channel outage and there is a natural tradeoff between the goodput gain and packet diversity. In this paper, we shall focus on the asymptotic tradeoff analysis between the system goodput gain and the packet outage diversity gain in cross-layer OFDMA systems with delayed CSIT.