Research On Adaptive Acoustic Echo Cancellation Algorithm And VLSI Design

The ability of an adaptive filter to operate satisfactorily in an unknown environment and track time variations of input statistics makes the adaptive filter widely used in communications, radar, sonar, seismology and biomedical engineering. In the speech communications, acoustic feedback makes bad influence to the quality of voice. The adaptive filter is always used to give solutions to acoustic feedback.The mathematical model of acoustic feedback reduction with adaptive filter is given. And according to the characteristics of long distance acoustic echo cancellation (AEC) and short distance acoustic feedback reduction (AFR), which are the typical application of acoustic feedback, the solution to the problem of their own is proposed. In addition, the very characteristic of AFR is running in real time. To solve the problem, the corresponding circuit implementation is made.The dissertation mainly focuses on the following aspects:Firstly, an AEC algorithm is proposed. During AEC process, the presence of double-talk and under-modeling noise affects the algorithm behavior seriously. At the present time, it's successful to overcome one of the two noises separately. There is only one paper reported which claimed that it can overcome the two noise at the same time. But the double-talk time is limited in two seconds, which can not meet the requirements in practice. Based on the researching for the reference, an AEC algorithm which can overcome both double-talk and under-modeling noise at the same time is proposed by making modification to the algorithm existed, and the algorithm is called VSS-NLMS-UMDT algorithm. The double-talk time is not limited for the algorithm proposed, which makes it practical.Secondly, one of least mean square (LMS) algorithms with high convergence precision and fast convergence speed is proposed. The LMS algorithms reported all adopt instantaneous gradient, and the modification to LMS algorithm is always made to the step size. A target function with obviously physical meaning and zero-minimum is given first, and a theoretical math expression of zero-minimum target function system identification (ZMTFSI) algorithm is derived. The gradient of the algorithm proposed adopts online-averaging-gradient in practical, which can reduce the gradient noise. The algorithm proposed has high convergence precision and fast convergence speed. In addition, the amount of data storage needed is small, and the data flow is regular during calculation. The algorithm proposed has high parallelism, and includes only summation and multiplication, which makes it very convenient to be realized by VLSI. The ZMTFSI algorithm makes good preparation for AFR algorithm in both theory and practice.Lastly, an AFR algorithm is proposed by modifying the ZMTFSI algorithm, the AFR algorithm is realized by VLSI implementation and the layout of the circuit chip is obtained. The AFR algorithm inherits the characteristics of high convergence precision and high convergence speed in the ZMTFSI algorithm, and has much stronger parallelism than the later one. During the VLSI implementation, the parallelism in the algorithm is mined sufficiently, the reusable data is mined and reused, and translates the multiplication with constant factor into shift operation. The results of VLSI implementation demonstrate that the VLSI implementation can meet the throughput in real application very well, and it's practical very much.