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.
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