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To share frequencies without interfering, cognitive radio systems need to constantly monitor for the presence of licensed users and to continuously adjust the spectrum of their transmitted signal.By Jun Ma, Geoffrey Ye Li, Fellow IEEE, and Biing Hwang (Fred) Juang, Fellow IEEE ABSTRACT | Cognitive radio allows for usage of licensed frequency bands by unlicensed users. However, these unlicensed (cognitive) users need to monitor the spectrum continuously to avoid possible interference with the licensed (primary) users. Apart from this, cognitive radio is expected to learn from its surroundings and perform functions that best serve its users. Such an adaptive technology naturally presents unique signal-processing challenges. In this paper, we describe the fundamental signal-processing aspects involved in developing a fully functional cognitive radio network, including spectrum sensing and spectrum sculpting.

Development and tests on an algorithm to enhance the intelligibility of speech degraded by an interfering talker is reported. This paper discusses the formulation of the problem, the techniques developed, and the results of a limitedscale intelligibility test.While the test results indicate that no intelligibility improvement is obtained from the processing, several promising new directions for this problem have been identified.

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