  Cognitive radio that supports a secondary and opportunistic access to
licensed spectrum shows great potential to dramatically improve spectrum
utilization. Spectrum sensing performed by secondary users to detect unoccupied
spectrum bands, is a key enabling technique for cognitive radio. This paper
proposes a truncated sequential spectrum sensing scheme, namely the sequential
shifted chi-square test (SSCT). The SSCT has a simple test statistic and does
not rely on any deterministic knowledge about primary signals. As figures of
merit, the exact false-alarm probability is derived, and the miss-detection
probability as well as the average sample number (ASN) are evaluated by using a
numerical integration algorithm. Corroborating numerical examples show that, in
comparison with fixed-sample size detection schemes such as energy detection,
the SSCT delivers considerable reduction on the ASN while maintaining a
comparable detection performance.
