Single Channel With Frequency Mixed Gmsk Signal Demodulation

In the current complex electromagnetic environment of the communication signals reconnaissance, we often receive more signals using only one sensor. We will demodulate the mixed signals if we want to get the initial sequnence information. This issue is mainly studied in this paper.In this paper, we focus on the single channel (cochannel) demodulation for two co-frequncy Gaussion Minimun Shift Keying (GMSK) signals in order to recover the two initial sequences from the received signals by only one sensor.Firstly, brief reviews of GMSK modulate and demodulate theory are introduced in this paper, and then we study the single channel demodulation for GMSK signals from two aspects: joint demodulation and demod-remod.In the considering of joint demodulation of signals, we describe the joint maximum lilelihood sequence estimation (JMLSE) reciver based on the maximum lilelihood sequence estimation (MLSE) and coherent receiver of GMSK signal, give the state trellis of GMSK signals and deduce the closed form abot Euclidean distance in viterbi algorithm.Next, we demodulate the single channel co-frequncy GMSK signals by viterbi algorithm which is used in grid sequence decode. Then, analyze the complexity and design the flow chart of this algorithm.At last, a lot of simulations are done to test and verify the performance of algorithm.On the other hand, we suggest a method which is based on the recovery of one signal to demodulate two signals by turns.In some assumptions, we focus on the demod-remod techniques of the first signal from two different considerations that whether some initial sequence of one signal are known.Except that, we study a method about the estimation of amplitude. At last, we simulate this algorithm, and presented the demodulating performance results of two signals under the two considerations above. We also analyze some parameters on the performance and conclude the advantages and disadvantages of this algorithm.