Research On Blind Demodulation Of PCMA Signals

Paired Carrier Multiple Access technology (PCMA) is a multiple access multi-plexing of satellite communications proposed in recent years. In the PCMA satellitecommunication systems, both of the two-way communication earth stations use thesame radio resources to send satellite uplink signal; the satellite will transmit the mix-ture of the two signals directly; the earth stations will demodulate the mixed signalusing local information. Since the satellite downlink signal is the two mixed signals,the non-cooperative third party is difcult to demodulate it without knowing any infor-mation sequences. For military reconnaissance, how to demodulate the PCMA signalsblindly without knowing the channel parameters and any information sequences is im-portant.For the asymmetric PCMA signals with great power diference between the twosignals can be demodulated by interference cancellation algorithms, research is moremature, so this article focuses on blind demodulation of power symmetry PCMA sig-nals. The main work of this paper includes the following two parts:(1) for the channelwith parameters changing slowly approximating constant, this article presents a PC-MAblindchanneldemodulationalgorithmbasedonoversamplingandcoding-assisted;(2) for the complex channel with rapid changes in the frequency and frequency shift,this article presents a self-tuning of frequency and self-tuning of the survivor-path-number algorithm.For the channel with parameters changing slowly approximating constant, this ar-ticle presents a PCMA blind channel demodulation algorithm based on oversamplingand coding-assisted. Increase the sampling rate can take advantage of the receivedanalog signals to improve the blind demodulation performance, so this article propos-es the Per-Survivor Processing (PSP) algorithm based on oversampling. This articlederives the channel parameter estimation model based on oversampling, and uses the exponentially weighted recursive least squares (EWRLS) algorithm who has a fasterconvergence rate to estimate channel parameters, So PSP algorithm can be used in lowSNR (SNR=3dB). Due to the use of channel coding information can reduce the num-ber of search paths, this papaer proposes the use of coding assistance, to reduce thetotal number of surviving state, bit error rate and computation in PSP algorithm. Sim-ulation shows that the proposed algorithm has a lower threshold than the traditionaldemodulation PSP algorithm, and coding assistance can be more substantial improvethe separation performance of PCMA signals blind demodulation.Inthecomplexchannelwithparameterschangingrapidlyandfrequencydrift, fre-quency ofset accumulation can be increased over time, so channel parameters changeaccelerates and EWRLS algorithm can not track the channel variations. This articleproposes the use of short-time changes in the channel parameters to estimate frequen-cy ofset error and correct it. If the channel parameter estimation is not very accuracy,PSP algorithm needs to increase the number of surviving path, leading to increase incomputational complexity. So this paper proposes the use of short-time changes inthe channel parameters to calculate channel estimation accuracy, to adjust the numberof surviving paths. Simulation shows that frequency self-tuning algorithm can trackchannel frequency ofset changes; survivor-path-number self-tuning algorithm can re-duce the amount of computation required when channel parameters estimation is notvery accuracy. This two algorithms make the former algorithm, PSP algorithm basedon oversampling, apply to the complex chanel with rapid changes in the channel pa-rameters and frequency drift.