Noise detected, fractionally spaced equalization for analog cellular data modems

The results of an investigation into the feasibility of using a fractionally spaced equalizer with a burst noise detector to achieve a faster, more robust data modem. The equalizer input is a discriminator detected radio signal whose output is the quadrature amplitude modulated (QAM) baseband signal plus noise that has been further distorted by a telephone circuit. The performances of T/4- and T/2-spaced equalizers are compared with the performance of a symbol-spaced equalizer for low to medium signal to noise ratios (SNRs) commonly encountered in the analog cellular regime. Performance criteria are minimum mean square error, timing sensitivity, SNR after equalization, signal to interference ratio (SIR) after equalization and peak distortion (PD) after equalization. By means of simulation the convergence aspects of the T/2-spaced equalizer were investigated under differing burst and correlated noise scenarios. A noise detection plus equalizer control scheme is proposed and evaluated to maintain operation of the equalizer under burst noise conditions