In this thesis work, we propose a receiver structure which can extract data signals from digitally modulated unknown signals in voice band and implement it in real time using a TMS320C31 digital signal processor. The modulation types covered in this study include BPSK, QPSK, 8-PSK, 8-QAM, 16-QAM1, 16-QAM2 and 32-QAM. We assume the same symbol rate and carrier frequency as 2400 baud and 1800 Hz, respectively, for all these modulation types.
The proposed receiver structure consists of an energy detector, a timing recovery block, an interpolator, a phase splitter, a constellation gain control logic, a blind equalizer, a constellation classifier, a carrier recovery logic, and a slicer. In order to improve the performance of blind equalization, the tricepstrum-based algorithm(TEA) and the constant modulus algorithm(CMA) are sequentially applied to input signal before the normal decision-directed adaptive equalization algorithm.
Performance of the proposed receiver algorithm is obtained for a typical telephone voice channel. The proposed receiver algorithm reveals good convergence property and is able to classify the constellation type of input signals in clean as well as noisy channel environments.
