A new adaptive echo canceller used in the ISDN U-interface

A good adaptive echo canceller (EC), in terms of its performance, is an interesting problem for those who are engaged in the ISDN (integrated-services digital network) U-interface subscriber loop design. It is also important to implement an EC with low cost chips. An adaptive EC is proposed that makes its contribution in this respect. The filter combines some advantages possessed by common types of FIR (finite-impulse response) adaptive filters, transversal, and table lookup filters, together. In implementation, the filter design is mainly based on developing DSP (digital-signal-processor) chips, e.g. the Texas Instruments TMS320 family of microprocessors. The proposed architecture not only has a faster convergence speed than that of usual table lookup adaptive filters, but can also compensate the long period of echo tail caused by insufficient filter taps, especially when it is used in the full-duplex two-wire data transmission system with a net rate of 144 kb/s