Summary

Due to the fixed spectrum assignment policy, a large portion of the assigned spectrum in today’s wireless networks is not fully utilized. This necessitates a new communication paradigm to exploit the existing wireless spectrum opportunistically called Dynamic Spectrum Access (DSA) for next generation network (NGN). The key enabling technology to NGN is the cognitive radio. The Cognitive Radio (CR) enables spectrum aware communication protocols to sense the spectral environment and use this information to opportunistically provide wireless links that meet the user communications requirements optimally. Ultra wideband (UWB) technology offers underlay and overlay modes where the signal typically overlaps many existing and potentially future services. CR techniques can be applied to Multi-band OFDM based UWB systems in order to continuously detect the presence of primary users, and accordingly shape the transmitted signal spectrum to allow peaceful coexistence between the primary and cognitive systems. In this paper, cognitive radio technology and its ’ main functionalities are discussed. Spectrum sensing as the key element of CR awareness is described. Spectrum shaping in cognitive UWB MB-OFDM for an efficient spectrum usage are investigated. Existing research efforts in cross layer design in cognitive radio is also highlighted. Interaction of spectrum sensing and spectrum shaping at the PHY layer with the MAC layer spectrum scheduling, as well as application layer are addressed in our proposed cross layer design framework.