Estimation and compensation of radiated feedback coupling in a high gain repeater using gain dithering

On-frequency repeaters, whose input and output signals are the same frequency, often experience radiated coupling between the input and output antennas which causes echoes to be transmitted. In addition, the repeater will oscillate if the forward gain of the repeater is higher than the isolation between antennas. This paper proposes a method of estimating and compensating for the effects of the radiated coupling using digital processing. The real and imaginary components of the forward gain are dithered. The change in the power spectrum of the signal in response to the dithering is used to estimate the residual feedback coupling and reduce the echo magnitude. The dithering based echo measurements are unaffected by the auto-correlation of the input signal making it suitable for repeaters with low insertion delay. Results based on computer simulation models are provided.