A multi-stage blind clustering algorithm is proposed for equalisation of M-QAM channels. A navel hierarchical decomposition divides the overall task of equalising a highorder QAM channel into much simpler sub-tasks. Each subtask can be accomplished fast and reliably using a blind clustering algorithm derived originally for 4-QAM signals. The well-known constant modulus algorithm (CMA) is used as a benchmark to assess this novel multi-stage blind equaliser and it is demonstrated that the new blind adaptive algorithm achieves much faster convergence. This multi-stage clustering equaliser only quires slightly more computations than the very simple CMA and, like the latter, its computational complexity does not increase as the levels of digital symbols increase.
This paper studies the performance of RLS and LMS adaptive algorithms for tracking a first order Markov tapped delay line model of a communications channel whose output is observed in a white gaussian noise background. The bandwidth parameter a of the random tap variations varies from zero to unity, allowing the taps to change more rapidly than the adaptation processes. The algorithm mis-adjustment errors are evaluated and, for slow learning, shown to be nearly the same for v = pox2 = 1-1 = p (p = LMS step size and h = exponential weighting of RLS). The misadjustment errors are minimized over v = 0. It is shown that the adaptation process is only useful for a > a1 = 1 -l/2(vo,t)2/3.(i.e., the misadjustment is larger using vOpt than using v = 0).
If a speech signal exhibits Quadratic Phase Coupling (QPC) then this is a strong indication that the signal is produced by some nonlinear mechanism. QPC can be detected by testing for certain properties in the signal bicoherence, but previous measures based only on the magnitude of the bicoherence fail if certain phase randomization assumptions cannot be made. To get around this problem, the bicoherence phase can also be utilized. In this paper a QPC detector is described which comprises a magnitude test (based on the Hinich Gaussianity test 1]) and a phase test (based on empirical results of Sebert and Elgar 2]). A new visualisation of the problem is presented, and the properties of the QPC detector are investigated with some simulations.
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