Detection and Jammer-to-Noise Ratio Estimation of Interferers Using the Automatic Gain Control

In this work two issues concerning the use of the Automatic-Gain-Control (AGC) gain level for detecting and estimating the Jammer-to-Noise (J/N) ratio of Radio-Frequency Interference (RFI) are investigated. In the presence of RFI the AGC will reduce the gain level to keep the rms noise level at the input to the Analogue-to-Digital Converter (ADC) at a set level. As this level has to be estimated using quantized samples it was found that there is an error in the J/N estimate if the RFI is not a wideband signal. At J/N = 20 dB, this estimation error is equal to 0.82 dB for a Continuous-Wave (CW) RFI. By changing the specified histogram bin percentages this error can be minimised, allowing better J/N estimation with only a slight increase in the quantization loss when no interferer is present. Another issue that this paper analyses is the effect of temperature perturbations on the AGC gain level. To study the influence of this the AGC gain level along with the receiver temperature was monitored over a number of days utilising a receiver with a temperature sensor attached. The relationship between temperature and the AGC gain was found to be linear. Hence, by utilising this information and compensating for the AGC gain level changes due to temperature, interference detection performance using the AGC could be improved by 10 dB. This results in capability of detecting RFI down to a J/N of -8 dB.