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An analysis for simultaneous sensing of multiple primary user activity in cognitive radios has been presented here from a signal-processing perspective. First, the drawbacks of using simple harmonic power detection in wideband cognitive radios is demonstrated. Then, the impact of preprocessing the received signal to improve detection performance is highlighted along with its tradeoff involving complexity and corresponding delays in cognitive radio networks. It has been shown that a polyphase DFT filter bank with an optimal window as prototype filter can lead to reliable as well as efficient sensing and detection architecture in cognitive radios with minimal overhead. A detailed account of challenges, performance limits and computational complexity comparisons for various spectrum-sensing solutions is also provided. The study is supported through simulations with parameters corresponding to the IEEE 802.22 standard.