An Accurate Self-synchronising Technique for Measuring Transmitter Phase and Frequency Error in Digitally Encoded Cellular Systems

Modulation quality in most of digitally encoded cellular systems is examined by measuring the phase error and the frequency error of the transmitted signal. Phase error is an indication of how accurately the individual bits modulate the radio-frequency carrier; frequency error is the difference between the specified carrier frequency and the actual carrier frequency. The paper proposes a new technique for phase and frequency error measurement. The technique is based on a suitable digital signal-processing algorithm, capable also of gaining burst synchronisation on TDMA signals; downconversion and digitisation of the incoming signal are preliminary executed. Exploiting the instantaneous frequency trace related to the analysed burst and performing a nice interpolation of sampled data, the technique assures reliable demodulation along with low uncertainty. Paying attention to GSM cellular system, the fundamental stages of the digital signal-processing algorithm are first described in detail. Then, the metrological characterisation of the proposed technique is carried out by means of experiments on GSM signals with known characteristics; the obtained results are finally compared to those obtainable by similar techniques already available in literature.