Channel interleaving in narrowband FM mobile communication systems

Techniques for achieving 12.5 kHz channel separation with 6.25 kHz interleaving without degrading speech quality and spectrum efficiency are discussed. These techniques were developed for a high-capacity land mobile telephone system. A high-frequency stability technique, REFRESH, can achieve a frequency stability of better than 0.1 p.p.m. for a mobile subscriber set. Consequently, the required short-term carrier to adjacent channel interference ratio (short-term CIR) can be improved by about 3 dB compared with the case of a frequency drift of 1 kHz. An adjacent channel interference reduction technique, muting, can improve the required short-term CIR by about 3dB. Also, IZCR (intrazone channel reassignment) can improve the CIR margin by about 6 dB. As a result, required long-term CIR can be greatly improved