Dynamic spectral shaping in cognitive radios with quality of service constraints

In this paper we consider cognitive radios (CR) that employ orthogonal frequency division multiplexing (OFDM) modulation at the physical layer and present an algorithm for transmitter adaptation subject to specified quality of service (QoS) constraints. The proposed algorithm explicitly considers multipath channels between the CR transmitter and its intended receiver, and performs joint spectral shaping and transmitter power control in order to avoid spectral bands used by licensed users of the spectrum while maintaining specified target signal-to-interference+noise-ratios (SINR) at the CR receiver. The algorithm is illustrated with numerical examples obtained from simulations in which dynamic scenarios are considered with licensed transmitters getting in and out of the system.