Echo cancellation on communication circuits (1979)
Type of ContentTheses / Dissertations
Thesis DisciplineElectrical Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury. Electrical Engineering
AuthorsKelly, Mervyn Williamshow all
Echoes present on telephone circuits are a significant problem on long circuits where the round trip delay is greater than 100 mS. This is particularly so on satellite circuits where the round trip delay is in the order of 500 mS for each satellite hop. An echo canceller has been designed for New Zealand conditions which is less complex and, therefore, should be less expensive to produce than current overseas models. Although particularly applicable to New Zealand conditions, the techniques used have wider application. The general problems of echo canceller design are considered with some specific proposals being made. The two cancellers described here are non-adaptive and are based on a digital transversal filter. The later canceller employs Random Access Memory (RAM), uses pseudo random noise for system identification and compands the speech samples and filter coefficients in a true logarithmic format using multiplexing techniques for bulky and costly components.