Schemes for detection of double talk and abrupt changes in the echo path in fading communication channels
C. Carlemalm, A. Logothetis · 2002
In this paper, we present novel algorithms for the detection and discrimination of double talk and abrupt changes in the echo path in a wireless communication system. We model the communication channel with a finite impulse response (FIR) channel with parameters that are randomly time-varying. Fading and scattering effects are described by using a multichannel autoregressive (AR) model and abrupt echo path changes and double talk by including finite state Markov processes in the dynamics. The proposed optimal iterative off-line scheme computes the joint, in a maximum a posteriori (MAP) sense, state and parameter estimates of the system. The estimates are computed via an expectation maximization (EM) based algorithm, which is implemented by interconnecting a hidden Markov model (HMM) smoother and a Kalman smoother to derive state estimates, while Yule-Walker and Baum-Welch type equations yield the abruptly changing FIR parameter estimates and the Markov chain parameter estimates, respectively. Replacing the HMM and Kalman smoothers by the corresponding filtered versions, an on-line scheme is proposed. The on-line detection scheme is verified experimentally by way of computer simulations.