Discrete multitone echo cancelation

Multicarrier transmission methods have long been known to optimize the performance of data transceivers on bandlimited communication channels. One form of multicarrier transmission, known as discrete multitone modulation (DMT), is particularly attractive for its ability to be implemented using efficient digital signal processing techniques. Given a basic DMT system, it is possible to increase the aggregate data rate with full-duplex transmission using echo cancelation. However, DMT echo cancelation at first appears difficult because of the computational complexity required in a straightforward implementation to cancel the cross-echoes produced by each carrier into every carrier. This paper presents high-speed echo cancelation techniques for full-duplex data transmission using DMT systems. The techniques estimate the echo with a method of fast convolution that combines a complex multiply per tone with a short convolution in the time domain. In addition, the frequency-domain update of the echo parameters consists of one complex multiply per tap. As a result, these techniques can achieve much lower complexity than that required by traditional single-carrier technique, such as the least mean square (LMS) algorithm. This approach has been implemented for asymmetric digital subscriber line (ADSL) applications.