Chapter 8 - Power Allocation Games and Learning in MIMO Multiuser Channels

Abstract

This chapter explores a multiple access channel (MAC) consisting of several transmitter nodes and a common destination. The receiver node decodes the incoming messages from all the transmitters. The transmitters are assumed to use good codes. Also, coherent communications are assumed, like the receiver has perfect channel state information and decodes all its intended messages perfectly. There are two different decoding techniques: single user decoding (SUD) and, successive interference cancellation (SIC). The SIC decoding technique involves the existence of a coordination signal representing the decoding order at the receiver. The coordination signal is assumed to be perfectly known at the transmitter side. If it is generated by the receiver; its distribution can be optimized, but this induces a certain cost in terms of downlink signaling. On the other hand, if the coordination signal comes from an external source, like an FM transmitter, the transmitter nodes can acquire the coordination signal for free in terms of downlink signaling. This generally involves a certain sub-optimality in terms of uplink rate. In a real wireless system, the frequency with which the realizations would be drawn would be roughly proportional to the reciprocal of the channel coherence time. The proposed coordination mechanism is suboptimal because it does not depend on the realizations of the channel matrices. The corresponding performance loss is in fact very small.