Comparing to wired networks, wireless networks have some special features in the physical layer, medium access control (MAC) layer, and the network layer. This work discusses several research topics in the physical layer, and studies the cross-layer design of wireless networks.

First, we consider a Code-division multiple-access (CDMA) system with multiuser detection when the presence of a subset of the users is unknown to the receiver. The performance of the system in terms of Signal-to-Interference and noise-Ratio (SIR) and user capacity is given, by assuming symmetric signals. Then, we study the power control problem with multiple flow types. Each node has multiple flow types requiring different QoS, (for example in a multimedia system,) and has the constraint of using the same power level for all of the flow types. The conditions for solution to exist are given; and the characteristics of the solution are provided. Next, we propose a passive rate adaptation, in which some bits are dropped at the receiver end of a link, for the ad hoc network to use in the temporary channel fluctuation. We study the performance of this passive rate control scheme in terms of both symbol error probability and mean square distortion.

Finally, we study the coupling between layers of the network structure, and the cross-layer design. We explore the coupling between the physical layer and the MAC sublayer first, and propose the scheduling algorithm with power control. Then we consider the coupling between MAC sublayer and the network layer, and propose the joint scheduling and routing algorithm. The simulation results demonstrate that the joint algorithm improves the performance significantly.