Fractionally spaced equalization for analog cellular data modems

The authors consider a simple add-on system to analog cellular radios to offer 9600 b/s data services. The feasibility of using a fractionally spaced equalizer with a burst noise detector is considered. The authors examine equalization performance for subcarrier-based quadrature amplitude modulation (QAM). The performance of a T/4 and a T/2 spaced equalizer is compared with the performance of a symbol spaced equalizer for low to medium signal-to-noise ratios (SNRs). 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 after 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