ADAPTIVE DFE FOR GMSK IN INDOOR RADIO CHANNELS

We simulate the performance of an equalized Gaussian minimum shift key ing (GMSK) signal in an indoor radio environment with fading, noise, i mperfect carrier recovery, cochannel interference (CCI), and intersymb ol interference (ISI). We show that data rates of 20 Mb/s at bit error rates (BER) less than or equal to 10(-4) are possible with root mean square (rms) delay spreads up to 25 ns using a simple limiter-discrimi nator-integrator (LDI) receiver and a (6,4) decision feedback equalize r (DFE). In environments with larger rms delay spreads, coherent detec tion is required for the same performance. We show that using a decisi on-directed second-order digital carrier synchronizer with time varyin g loop filters, frequency offsets up to 200 kHz can be corrected with negligible performance degradation. This paper utilizes a DFE structur e which compensates for both modulator and channel ISI, and yet requir es no power-intensive multiplication operations in the feedback sectio n. A DFE(8,8) with two-level snitched (selection) diversity is shown t o allow 20 Mb/s data transfer at BER less than or equal to 10(-4) for rms delay spreads under 150 ns, with CCI. A light BCH(26,31) code allo ws error-free reception of over 90% of packets with rms delay spreads under 150 ns, and up to 70% of packets with rms delays of 150 ns.