Efficient channel monitoring using running Lank-Reed-Pollon frequency estimates

A sequence of Lank-Reed-Pollon (1973) frequency estimates provides a kind of frequency history of a signal. Each LRP frequency estimate represents the "composite frequency" of the signal during the time interval over which it was computed. Sequences of LRP frequency estimates (computed over signal segments that may be non-overlapping and separated in time) can be useful for detection of "narrowband sinusoidal events" (such as line and register signals in voice channels, or FSK T.30 facsimile preambles) and for "coarse classification" of "wideband" sinusoidally modulated signals (e.g., QAM signals). Such detections can be regarded as "tipoffs" to processors that perform more computationally intensive, signal-specific functions. At low signal-to-noise ratios, LRP frequency estimates for narrow band signals are superior to those obtained from a conventional frequency discriminator, since the LRP averaging process improves the signal-to-noise ratio prior to computing phase. Also, detections of events at different frequencies are more efficient using LRP frequency estimates, since only a single LRP estimate is required during each selected interval, rather than a bank of filters, one for each frequency.