Order recursive lattice decision feedback equalization for digital cellular radio

Apparatus for demodulating a Time Division Multiple Access (TDMA) signal having a time slot comprised of a plurality of symbols including at least one sequence of synchronizing symbols and a plurality of data symbols, comprising:

• receiver means for receiving the signal over a channel;
• adaptive filter means for adaptively filtering the received signal to minimize inter-symbol interference due to channel multipath propagation, the adaptive filtering means having a first input coupled to an output of the receiving means and comprising multi-stage lattice decision feedback equalizer means having (M=N.sub.1 N.sub.2) scalar stages followed by (N.sub.2 -1) two-dimensional stages, said adaptive filter means including metric forming means coupled to an output of each of said stages for forming a metric in accordance with a predetermined mathematical relationship between respective stage output signal and another stage output signal, said metric forming means including accumulating means for accumulating a plurality of the formed metrics over a plurality of time slots;
• and
• recursive means having an input coupled to outputs of said accumulating means for recursively determining a number of stages for the lattice decision feedback equalizer means for use following said time slot, the recursive means including comparison means for comparing the difference between output signals at two outputs of said accumulating means outputs to a threshold value.