Capacity bounds for cooperative relay and cognitive radio channels in wireless networks

Abstract

There are two distinctive channel models in modern wireless communication networks. One of them is a cognitive radio channel which allows unlicensed secondary users to access licensed primary users` spectrum that is either unused or lightly used in most of the time. The other is a cooperative relay channel which exploits multiple relays to help communication between the source and the destination nodes such that they cooperatively forward the messages received from the source node to the destination node. In this thesis, we especially focus on capacity bounds for cooperative relay and cognitive radio channels. Expanding the concept of the cognitive radio, we first propose a cognitive radio system with opportunistically permitting excessive secondary-to-primary (S-P) interference by performing multiuser decoding at the primary receiver whenever excessive S-P interference is allowed. Assuming a slowly-varying fading interference channel with two-senders and two-receivers, the primary sender adjusts its rate and power depending on its own channel, while ignoring the secondary user. Through an optimization process, the secondary sender`s rate and power are determined and the decision is made on whether the secondary sender violates the S-P interference power limit. Remarkably, the proposed system can provide a considerably high data rate for the secondary user even without sacrificing the data rate for the primary user over a wide range of signal-to-noise ratios. We next consider a cooperative relay channel with two half-duplex relays that alternately forward their received messages such that one of the relays transmits data to the destination while the other receives data from the source.For the Gaussian alternating two-path relay channels, we propose a decode-and-forward (DF) strategy to combine two distinctive schemes which differently treat codewords that each relay receives from the other relay.We show that combining both schemes can be better than simply ...