Study On Blind Receiving Technologies Of Shortwave Burst Signals

In recent years burst communications, due to its obvious advantages, have become more and more popular in modern shortwave communications, especially in military communications. Whereas the corresponding technologies of blind (non-cooperative) receiving for burst signals, especially for very short burst signals, are still not so mature as that for conventional signals. Just on above background, this paper is focusing on a study and implementation of the key technologies of shortwave burst signal blind receiving while laying emphasis on the development of high-efficient algorithms with lower computational complexity. The work finished in this paper is a part of a large scale army project of research undertaken by the lab the author works with.The existence detection of burst signal, which is the first thing to begin with, can be considered to consist of decision statistic selection, adaptive shrehold setting and decision algorithm development. Two practical algorithms for threshold setting and decision making respectively are proposed which can considerably reduce the false-alarm probability and false-dismissal probability by appropriate design of the threshold and the corresponding decision making mechanism.Blind symbol synchronization is one of key technologies of the blind receiving of the shortwave burst signals. Severl important NDA(nondata-aided) feedforward symbol timing estimation algorithms are analyzed and compared with each other in terms of their performances. Based on above discussion a novel NDA feedforward symbol timing estimator employing two samples per symbol is proposed. The new estimator can eliminate the spectrum overlap by the use of anti-aliasing filter, which can make the conventional non-linear algorithms, such as squared processing etc., safely be used in cases of two samples per symbol. Simulations have proved the performance improvement of the proposed estimator over the former one.Blind equalization is another one of key technologies of the blind receiving of the shortwave burst signals, and successful design of the blind equalizer is also a challenging issue in the field, especially for very short burst with only several hundreds or even decades of symbols. A variety of typical blind equalization algorithms are discussed and summarized with the emphasis laid on the Bussgang blind equalization algorithms. And then, the Bussgang blind equalization algorithms based on data-reusing are analyzed, which can generally be classified into three categories, and two of them are discussed in depth. A novel CM algorithm based on affine projection and data-reusing is proposed which, compared with CMA without data reusing, can converge much faster, however the steady-state error is increased. To solve this problem another novel CM Algorithm based on set-membership filtering and data-reusing is proposed. Besides, a blind equalization algorithm based on repeated data-reusing is proposed, which is of lower computational complexity. Simulation results have shown that the algorithm can converge even within dozens of symbols, thus very suitable for shortwave burst signals.Carrier synchronization is also critical and indispensable for blind receiving. Conventional algorithms for estimations of carrier and phase offset are summarized, simulated and compared to each other. Based on the discussion a new algorithm with wide estimation range, high accuracy and low-complexity for carrier offset estimation is proposed. Firstly, the capturing-range is widened by using the phase difference between consecutive symbols, and then higher estimation accuracy is obtained based on correlation function with longer delay while the phase folding and low SNR problems are overcomed. To solve the equivocal phase problem in phase offset estimation caused by residual frequency offset and noise, a modified and a novel algorithms are proposed, which can greatly reduce the phase hopping probability and improve the anti-noise performance.Finally, two blind receiving platforms based on Software Defined Radio (SDR) for shortwave narrowband multi-channel signals are developed. All of the blind receiving algorithms proposed in this dissertation are applied to the two platforms, and test results have proved the validity of the whole systems.