On the BER performance of digital demodulators using fixed point FIR interpolators

Due to their rapid acquisition performance, feedforward symbol timing estimation techniques are advantageous in digital demodulators used for packet based communications systems and communications systems which suffer from fading phenomena. When feedforward symbol timing estimation is used in a demodulator which is implemented using digital techniques, feedforward interpolation is required to re-sample the received signal at the estimated location of the symbol centre. This paper presents results on the effect of the performance of the interpolator, or fractional sample delayer, on the bit error rate (BER) of the digital demodulator. Emphasis is placed on the effect of finite precision arithmetic. Results are presented which describe the effects of the quantiser transfer function and the number of bits used to represent the signal and filter tap values