The acute scarcity of radio frequency spectrum has inspired to think of a new communication technology where the devices are expected to be able to sense and adapt to their spectral environment, thereby appearing as cognitive radios (CR) who can share opportunistically the bands assigned to primary users (PUs). At the same time, low cost, increased coverage, enhanced capacity, infrastructure-less configuration, and so forth, become the essence of future wireless networks. Although the two research fields came up independently, in due time it is observed that CR has a promising future and has excellent applications in wireless networks. To this aim, this chapter explores some scope of integration in CR and ad hoc networks (called here CRAHNETs) in some specific design perspective. First, a brief literature review on CR power allocation and energy aware routing in wireless ad hoc networks (WANETs) is done that highlights the importance for the scope of their integration. Then, power allocation in CRAHNETs with extended network lifetime is considered as an example problem. More specifically, the design problem is: given a set of paths (routes) between a pair of source (S) and destination (D) nodes in CRAHNETs, how to allocate optimal power to the source and relay nodes such that outage probability for data transmission is minimized and network lifetime is enhanced, while meeting the limits of total transmit power of CRs and interference threshold to PU simultaneously. A solution for the stated problem is proposed along with performance evaluation. A few related research problems are mentioned as future research directions.
Precoding Design and Power Allocation in Two-User MU-MIMO Wireless Ad Hoc Networks