| Multi-target telemetry system is a typical wireless multi-access communicationsystem, which combines direct sequence spread spectrum with digital beamformingtechnology. It fulfills multi-access communication by using code division multi accessand space division multi access. Furthermore, the abilities of interference reduction ofspread spectrum communication and the advantages of spatial filtering of smart antennacan both be taken to enhance the interference resistance in the combined application.But being different from the cell phone communication systems, the telemetry systemalways has a simpler architecture for the same function as mobile communicationsystem, especially when the power of amplifier must be fully used to extend thedistance to the ultimate edge. Thus, the redundancy of the link is limited, the lowersignal-to-noise rate caused by the long distance and high spread spectrum gain must beconsidered for the detection and acquisition in signal processing. In such applications,the code acquisition and antenna beamforming can not be achieved without each other,so the spatial beamforming and tempotal code acquisition should be consideredsimultaneously, instead of being done separately. Thus, the two-dimention acquisition isthe focus of the thesis. Three kinds of algorithms are further researched, includingcorrelator-based joint acquisition, spatial and temporal serial search acquisition andadaptive spatial and temporal acquisition, several novel method and conclusion areachieved.The main achievement and innovations include:1. Aiming at interference suppression, the adaptive spatial and temporal acquisitionalgorithm is proved theoretically and by simulation to have more than one solution withpresence of interference. Thus, the iteration diverges instead of converging. To avoid theproblem, two novel algorithms are proposed, of which, one is based on a twodimentiaonal adaptive wiener filter model and subsequently a new suggested costfunction, which has only one solution being same as the original algorithm. The other isbased on one more constraint on the original cost function to avoid the undesired trivialsolution. The two novel algorithms have better iteration convergence and only one solution in low signal to interference and noise rate scenarios.2. Of joint acquisition algorithm based on correlators, the normalized least meansquare algorithm has more than one solution and probably diverges during iterration inlow signal to interference and noise rate scenarios, which is proved in simulation. Anovel algorithm is proposed and theoretically analysed to eliminate these defects, whichis based on the additional constraints on the weight vector. Simulations are presented toprove it has better performance of interference resistance.3. A novel joint acquisition algorithm based on correlators is proposed, whichadheres to maximum signal-to-interference-plus-noise rate criterion. Theoreticalanalysis and simulation results prove that the better performances of acquisition andinterference suppression can be achieved.4. In the serial search method, a direction of arrival estimation algorithm usingdifferential covariance matrix is studied. By forward/backward smoothing of covariancematrix, the noise is reduced and the direction estimation performance is improved,which is presented with theoretical analysis and simulaton. Angular spread is consideredfor code acquisition with antenna array. Analysis and simulation lead to the conclutionthat with diversity effects, the presence of angular can improve the code acquisition.5. A intermedium frequency digital receiver with eight channels is designed andfabricated. In addition, an experimental system with two targets is constructed,including a static model in which the source terminal is placed on a fixed spot and adynamic model in which the source terminal is palced on a flying helicopter. Theexperiment results verify the algorithm and the signal acquisition are effectivelyachieved. |
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