A Novel Receiver and a Related Performance Bound for Combined Equalization and Decoding of Tcm- Data in Tdma-based Cellular Mobile-radio Systems

This contribution describes a new fast adaptive coherent receiver for the detection of Trellis-Coded-Modulated (TCM) signals transmitted over Time-Division-Multiple-Access (TDMA) based cellular mobile radio links affected by fast-fading multipaths and cochannel interference. The equalization and decoding tasks are jointly accomplished by a Symbol-by-Symbol (SbS)-MAP [8,Sect.6.6] combined equalizer-decoder which outputs both hard-decisions and soft-statistics in form of suitably defined A Posteriori Probabilities (APPs). These APPs (and not the usual harddecided data) feed an “ad hoc” developed nonlinear Kalman-like channel estimator, which accomplishes fast convergence through a full exploitation of the redundancy introduced by the TCM-code. A related analytical performance bound is also presented together with a criterion for the design of good TCM codes. I. THE TCM-CODED TDMA CELLULAR RADIO LINK TCM signaling is very attractive for data transmissions on TDMA land mobile cellular radio systems [2,Chap.1]. However, TDMA systems with net bit rates over 100 Kb/s and linking high speed mobile units (like, for example, the European GSM) are affected by multipath phenomena introducing severe randomly time-varying ISI into the received signal [2,Sect.8.7]. So, powerful adaptive coherent equalization and decoding strategies are generally requested to mitigate these impairments. Now, referring to the link between a MobileStation (MS) and a Base-Station (BS) sketched in Fig.1, the baud-rate sampled (complex) signal {y(k)} received at the output of the equivalent low-pass randomly time-variant ISI channel can be modeled as follows [8,Sect.6.3]: y k h( k l c k l i k H k c k i k k L l Lc