טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentReuven Gal
SubjectDual Transfer Function Generalized Sidelobe Canceller and
Application to Joint Noise Reduction and
Echo Cancellation
DepartmentDepartment of Electrical Engineering
Supervisors Dr. Sharon Gannot
Professor Israel Cohen


Abstract

Full duplex hands-free man/machine interface often suffers from directional nonstationary interference, such as a competing speaker, as well as stationary interferences which may comprise both directional and non-directional signals. The transfer-function generalized sidelobe canceller (TF-GSC) exploits the nonstationarity of the speech signal to enhance it when the undesired interfering signals are stationary. Unfortunately, the TF-GSC is rendered useless when  a nonstationary interference is present.

In this thesis, we propose an adaptive beamformer, based on the TF-GSC, that is suitable for cancelling nonstationary interferences in noisy reverberant environments. We modify two of the TF-GSC components to enable suppression of the nonstationary undesired signal. A modified fixed beamformer is designed to block the nonstationary interfering signal while maintaining the desired speech signal. A modified blocking matrix is designed to block both the desired signal and the nonstationary interference. We introduce a novel method  for updating the blocking matrix in double talk situations, which exploits the nonstationarity of both the desired and interfering speech signals.


A performance analysis of the DTF-GSC performance is presented as well. A general expression of the enhancer output is first derived. Three figures of merit are evaluated, the amount of deviation of the desired signal from its nominal value, the noise reduction and the interference cancellation abilities.


In many cases the competing signal is due to the coupling of the loudspeaker and microphone in hands-free communication, i.e., an echo signal. In that case, a reference signal to a direct measurement of the echo signal can be exploited. Hence, a TF-GSC based scheme is suggested to jointly reduce noise and cancel echoes.