Abstract
Channel and/or sensing aware transmission policies for distributed wireless networks are proposed in this dissertation. In the proposed policies, users are allowed to make transmission decisions based on local channel state information (CSI) and/or spectrum occupancy information (SOI) to maximize the sum throughput of the system. These policies are able to overcome limitations due to fading and interference by allowing users to exploit multiuser diversity, request cooperative relaying from each other, and opportunistically access vacant spectrum. These techniques have been considered in the past but mostly from a centralized perspective, where a central controller is used to coordinate transmissions. This dissertation instead exploits the advantages of channel-aware, spectrum-aware, and cooperative transmissions in a decentralized fashion, allowing users to make independent transmission decisions based only on local information. Specifically, we first consider a slotted ALOHA network where each user determines whether to transmit or not according to a local coin toss. With the goal of maximizing the sum throughput of the network, we derive the optimal channel access policy which determines the transmission probability, rate, and power, by exploiting the uplink CSI. By assuming that the CSI is imperfect, the proposed policy is derived by taking into consideration the statistics of the channel estimation error. The throughput can be increased substantially compared to the case with no CSI or the case where error statistics are not taken into consideration. By allowing users to help by relaying each other's packets, channel-aware transmission control and partner selection policies are also derived for slotted ALOHA networks with cooperative users. In contrast to the policies derived for non-cooperative systems, the transmission control and partner selection are determined based on both the uplink and the inter-user CSI. These concepts can also be applied to cognitive radio environments where transmission decisions should not only be made based on the channel quality but also on the spectrum occupancy. Following similar concepts, a channel and sensing aware channel access policy is proposed to maximize the throughput of secondary users in cognitive radio systems. However, instead of allowing users to transmit their packets directly, a reservation period is employed at the beginning of each time slot for users to compete for transmission. In the reservation period, a channel-aware splitting algorithm is employed to resolve the collision among users and to schedule the user with the best channel quality to transmit if collision is resolved. The efficacy of the proposed transmission policies are demonstrated through extensive computer simulations.