Co-channel interference measurement for TDMA radio mobile communication systems

In cellular radio systems, the signal is affected by co-channel interference due to frequency reuse. Power control is a technique for minimizing this co-channel interference. Recent algorithms, based on a minimum signal-to-interference ratio (SIR) requirement, need an accurate SIR measurement. A method of measuring co-channel interference for analogue mobile communication systems has previously been proposed but was restricted to pilot signals. In this paper, we extend this method by applying it directly to the received modulated signal and, therein, we improve spectral efficiency. The envelope of the received signal is affected by fluctuations which can be separated into two terms: slow fluctuations resulting of fading and fast fluctuations (at a frequency related to the bit rate) due to co-channel interference. The method exploits the possibility of separating these terms in the frequency domain in order to evaluate the signal-to-interference ratio. Extensive simulations have been carried out to analyse the measurement errors. Used modulations are 2PSK, 4PSK, GMSK and GMSK preceeded by Miller precoding that leads to the best performances. These good performances (less than 1dB error for SIR greater than 10 dB) for the estimation of signal-to-interference ratio can significantly enhance the efficiency of power control algorithms in cellular mobile radio systems.