Cognitive Technology for Ultra-Wideband/WiMax Coexistence

Cognitive radios have been advanced as a technology for the opportunistic use of under-utilized spectrum wherein secondary devices sense the presence of the primary user and use the spectrum only if it is deemed empty. The distinguishing aspect of cognitive radios is the ability to sense the primary user and modify their transmission parameters to avoid interference to the primary. In this paper we explore the use of cognitive technology to enable the operation of ultra-wideband (UWB) devices in WiMax bands. In this particular example UWB devices must incorporate cognitive technology to detect and avoid (DAA) WiMax devices in certain regulatory domains. We start by discussing various options for detection and avoidance. We then describe the obstacles faced in achieving robust detection and avoidance with an on-chip implementation of basic DAA functionality. This implementation is based on the energy detector and can reliably detect WiMax uplink transmissions. Finally, we present empirical results for the operation of a single cognitive technology enabled UWB device with a WiMax system. This interaction also highlights the problem of dealing with listen before speak primaries where secondary transmission could interfere by denying the primary access to the medium.