Environment aware spectrum shaping for cognitive radio systems

The coexistence of OFDM-based cognitive radios (CRs) with licensed wireless systems puts strong attention on protection of primary links. In this paper, we have shown how environment-aware CR can calculate protection requirements for Out-of-Band (OOB) radiation attenuation on the basis of licensed users´ receivers characteristic. In dynamically changing environment this approach can provide significant advantage over classical static spectrum masks. In the second part of this paper we have investigated how the calculated OOB attenuation requirement can be obeyed by OFDM system employing combination of windowing and cancellation carriers (CCs) shaping methods. We have shown how the transmitter can estimate a spectrum shape before any OFDM symbol being sent. On this basis the CR will not operate until spectrum shaping mechanisms fulfil the requirements. The calculations and simulations were carried for a wireless microphone being licensed system as the application of the CR in the UHF band is the most probable.