Research On Key Technologies Of Multi-h CPM Reception Under Low SNR

With the development of remote tracking telemetry and command(TT&C),such as space-based TT&C and deep spaceTT&C,the rate of transmitting information is increasing and modulations with high spectral efficiency arepaid more attention to.Continuous phase modulation with multiple indexes(Multi-h CPM)is a constant envelope modulation with highspectral efficiencyand high power efficiency,which is suitable for the remote TT&Cwhose channelis bandwidth limited,power limited and nonlinear.However,in the communications ofremoteTT&C,the transmission loss is large due to the remote distance.Therefore the signal to noise ratio(SNR)of the received signal is very low,which brings severe challenges to the receiver of Multi-h CPM.These challenges in the low SNR are mainly include the demodulation difficulties,the high complexity of receiver andthe difficult synchronization.This paper focuses on the key technologies of Multi-h CPM receiving under low SNR,and the main results are as follows:1.Two reduced complexitydetection methods are proposed for Multi-h CPM:singular value decomposition based on frequency pulse truncation(FPT-SVD)and simplified detection based on virtual modulation index set(VhD).In addition,combinations of several simplified detection algorithms are studied to solve the biggest obstacle of Multi-h CPM in low SNR.2.An efficient coding and modulation system consist ofserially concatenated convolutional codes(including interleaver)andMulti-h CPM is presented.The maximum a posteriori(MAP)detectionand iterative detection with lowcomplexity are developed for Multi-h CPM.The system performances and iterative detection are improved by simulationsand convergenceanalysing.The simulation results show that the serially concatenated a convolutional codeand Multi-h CPM is better than the LDPC-coded(with the same code length and the same bit rate)Multi-h CPM in terms of coding gain and decoding complexity.3.Two code-aided timing synchronizers are proposed for Multi-h CPM under low SNR:one is based on code-aided early-late loop(ELL)algorithm and the other is based on thereduced-complexity ofexpectation maximization(Re-EM)algorithm.First of all,the simplified timing synchronization based on ELL and sequence detection is put forward to solve the problems of traditional timing for uncoded multi-h CPM.Then the ELL timing is extended to the iterative detection for the serially concatenated system,which constructs the code-aided ELL(CA-ELL)timing.On the other hand,by simplifying the original EM algorithm,a novel timing synchronizer based on reduced EM algorithmis proposedfor Multi-h CPM.Both of these two code-aided timing synchronization can improve the timingaccuracy of Multi-h CPM under low SNR.Compared with the other,the CA-ELL has better performance under quitelow SNR.4.Two code-aided carrier phase synchronizers are proposed for Multi-h CPM under low SNR,including Re-EM algorithm and code-aided decision-directed(CA-DD)algorithm.The former is similar to the principle of timing synchronization based on the Re-EM algorithm,and the latter is constructed by addinga backtracking module in the symbol-by-symbolMAP detection.Both of them can effectively solve the problems of traditional carrier phase synchronizerfor Multi-h CPM under low SNR.And their performance isequivalent,but in terms of complexity,carrier phase synchronizerbased on CA-DDis better.5.Noncoherent iterative detections with low complexity are proposed for Multi-h CPM in low SNR.Firstly,the low-complexity of noncoherent sequence detection based on the minimum error probability(MEP)criterion is studied,and then extended to the noncoherent iterative detection for the serially concatenated Multi-h CPMsystem.The simulation results show that the noncoherent iterative detection based on MEP criterioncan perform better than the coherent iterative detection in the channel with residual frequency offset or phase noise.