A Robust Joint Model-Based Demodulator for Continuous Phase Modulation Signals in an Unknown Environment

Cellular communications systems often suffer from co-channel interference, due to signals from adjacent cells interfering with each other. Previous demodulation techniques have relied on interference rejection to extract only the highest power signal; cancellation techniques are required to extract weaker ones. In this paper, we describe a joint model-based demodulator (J-MBD) that extracts two or more co-channel signals using continuous phase modulation (CPM) simultaneously. The technique is based upon a root selection algorithm using forward-backward linear prediction (FBLP), whereby multiple unequal powered signals are extracted by choosing the highest powered roots. The algorithm is compared to the conventional quadrature demodulator (QD) and the previously introduced single user model-based demodulator (MBD), which extracts only the highest powered user. We show that the new technique outperforms all of the conventional techniques when two co-channel signals are present, by as much as 5 dB, and can more reliably demodulate both strong and weak signals, with few samples, even when the signals have near equal power.