Cross-layer design has been shown to offer high spectral efficiency which benefits from the inherent multi-user diversity in wireless fading channels. 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 logK) due to the MuDiv gain. However, with imperfect CSIT, it is still not clear whether we can get the same performance as that of the perfect case....[ Read more ]

Cross-layer design has been shown to offer high spectral efficiency which benefits from the inherent multi-user diversity in wireless fading channels. 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 logK) due to the MuDiv gain. However, with imperfect CSIT, it is still not clear whether we can get the same performance as that of the perfect case.

In the first part of this thesis, we shall consider the cross-layer OFDMA scheduling design under various practical PHY layer and MAC layer constraints for a wireless system with one base station and K mobile users . We study the cross-layer scheduling design with imperfect channel state information (CSI) at the base station for delay-tolerant applications. The imperfectness of CSI is assumed to be the result of feedback or duplexing delay. With imperfect CSI at transmitter (CSIT), there exists a potential packet transmission error when the scheduled data rate exceeds the instantaneous channel capacity referring to packet outage. The OFDMA cross-layer design with delayed CSIT is modeled as an mixed integer and convex optimization problem where the rate adaptation, power adaptation and subcarrier allocation policies are designed to optimize the system goodput (b/s/Hz successfully received by the mobiles). At the time same time, we are interested to know the trade-off between packet outage diversity gain and multi-user diversity gain. Therefore, by using extreme value theorem, we are able to show the trade-off analytically.

In the second part of this thesis, we would like to evaluate the performance of a uplink multiaccess channel with successive interference cancellation receiver equipped in the base-station. We derive analytically the per-user packet outage probability and the total system goodput for multi-access systems using multiuser detector with adaptive successive interference cancellation (MUD-SIC). Slow fading channel is assumed where packet transmission error (outage) is the primary concern even if strong channel coding is applied. To capture the effect of potential packet error, goodput should be used as performance measure. Unlike previous works, our analysis focuses on the error-propagation effects in MUD-SIC detector where the packet outage event for a single user is depending on the other users. Also, we derive the optimal SIC decoding order (to maximize system goodput) and evaluate the closed-form per-user packet outage probabilities for the n users for MUD-SIC. Simulation results are used to verify the analytical expressions.