A wide dynamic range four-port spectrum sensor for cognitive radio

This paper presents a compact, low-cost spectrum sensor with very large dynamic range, to detect arbitrarily modulated input signals with respect to identifying the spectrum holes available for cognitive radio applications. The sensing technique is based on the combination of a tunable pre-selector filter with a four-port circuit consisting of logarithmic detectors. Since the four-port is a passive circuit, the sensed signal is processed without requiring additional power consuming nonlinear circuits (like mixers and their necessary local oscillator driver circuits). Additionally, the four-port circuit consumes less schematic area as compared to other delay line based spectrum sensors e.g., six-port circuits. Also, the use of logarithmic detectors enables the detection of signals over a wide dynamic range exceeding 80 dB, making it almost comparable to that of commercially available heterodyne receivers. Such a technique provides a fast, low-cost and low-power sensing strategy, therefore making it an extremely interesting alternative to present heterodyne receivers used for rapid wide-band sensing, which is a key pre-requisite for cognitive radio applications.