Spectrum Sensing in Wideband OFDM Cognitive Radios

In this paper, spectrum sensing of an orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) is addressed. The goal is to identify the portions of the spectrum that are unused by primary user systems and other CR systems, called existing user (EU) systems altogether, with the emphasis on conquering the challenge imposed by multipath fading channel. The sensing of EU systems consists of two steps. In the first step, the maximum likelihood (ML) estimates of the frequency bands of EU systems are calculated; in the second step, detection is performed at each suspected band to decide whether an EU system is truly in operation. The idea is that an EU system appears at a segment of continuous subcarriers. This fact can be exploited by employing measurements at a continual subcarriers and executing the sensing along the frequency domain. An autoregressive (AR) model is adopted to track the variation of the received EU signal strength along frequencies. It is shown by simulations that the proposed spectrum sensing algorithm is robust in a severe frequency-selective fading channel.