Stochastic geometric analysis of cognitive wireless networks

The prime objective of this thesis is to study these interference management mechanisms for quantifying the potential gains of CRs in terms of spectral utility. Interference modeling is the most important aspect of this extensive evaluation. Accurate modeling of the cognitive network interference, accommodating its stochastic nature (triggered by both spatial and propagation dynamics) is therefore a central contribution of this thesis. Since the aggregate interference from CRs is a function of the access strategy, two wellknown access paradigms, namely, spectrum underlay and interweave, are thoroughly analyzed.
For the spectrum underlay access mechanism, a guard-zone based interference control mechanism is examined. Specifically, CRs are obliged to maintain silence in a spatial no-talk zone of a certain radius which is centered on a primary receiver. It is shown that the radius of the guard-zone is strongly coupled with the medium access and routing strategies employed by the CRs. While the guard-zone provides a robust mechanism to protect a single
primary user, it is a challenging task to achieve the same for a large scale primary network. An alternative degree of freedom, i.e., medium access probability (MAP), can easily address this issue. Furthermore, for a large CR network (CRN), significant gains can be harnessed by furnishing
nodes with multiple antennas. Performance evaluation of such a network with MAP adaptation is one of the key contributions of this dissertation. It is shown that the multi-antenna paradigm results in a “win-win” situation
for both primary and secondary users. In order to facilitate multi-hop communication between CRs, a quality-of-service (QoS) aware routing is also devised. We show that there exists an optimal MAP which maximizes the
spectral utility of the secondary network. However, such an optimal point often lies outside the permissible operational regime dictated by the primary user’s co-existence constraint. Another approach can be adopted where we exploit a different degree of freedom, i.e., the transmit power employed by the CRs. Thus CRs can extend their operational regime by adapting one degree of freedom and selecting an optimal value for another. The optimality
of this adapt-and-optimize strategy is shown for a variety of networking paradigms. Finally, the performance of the primary user in the presence of the interference-channel-aware CRs is quantified.
For a CRN employing an interweave configuration, the performance of a legacy user is investigated. The impact of different network parameters is explored. It is shown that the cooperation between the CR transmitter and receiver can significantly improve the performance of the interference avoidance mechanism. Furthermore,we highlight that ignoring the self-coexistence criteria for the secondary network leads to an over-estimation of the aggregate
interference and consequently results in pessimistic design strategies. The analysis is extended to consider the performance of a large primary network. Finally, a novel modification in the analytical approach is proposed so
that performance guarantees can be provided to the existing users.
Another contribution of this dissertation is to evaluate (currently very topical and very important) the energy efficiency of an ad hoc wireless network. The key motivation is to investigate the impact of the co-channel interference on the network-wide energy consumption. Both energy and spectral efficiency problems have a common origin, i.e., growing bandwidth demand. Also the design of both problems require understanding of co-channel interference management strategies.
Finally,we try to put pull together all the analysis and simulation results to look at both open problems and directions for future research in this highly topical, and strategically important research areas of enabling high speed, future wireless networks.