Performance of binary CPM schemes in frequency selective fading channels with pilot symbol assisted detection

Abstract

We present a coherent detector for binary continuous phase modulation (CPM) schemes operating in a frequency selective fading environment. The technique uses embedded pilot symbols for the purpose of channel impulse response estimation. Unlike pilot symbol assisted linear modulation, the pilot symbols in our CPM system are divided into two groups. The first group of pilot symbols is data dependent and is used to force the modulator to return periodically to a known system state. On the other hand, the second group is not data dependent and is used to specify a known waveform emanating from the periodic known state, for the purpose of channel estimation. The proper pilot symbol encoding rules, as well as the structure of the companion channel estimator, are presented. It is shown that CPM schemes employing this detection technique exhibit no irreducible error floor even in the presence of fast fading and large delay spread. To the contrary, the modem actually performs better in a heavily frequency selective fading environment, due to the implicit diversity effect provided by the channel. The difference in energy efficiency between frequency selective and flat fading can be as large as 5 dB at a 10/sup -3/ bit error rate and 8 dB at a 10/sup -4/ error rate.