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Constant Modulus Algorithms And The Applications In Blind Beamforming

Posted on:2002-09-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y GuoFull Text:PDF
GTID:1118360062975186Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
Smart antenna has been widely researched in communication and signal processing, The adaptive beamforming algorithm is the key technique of smart antenna. It could adaptively steer the array directional pattern to form the main narrow beams with high gain in the direction of the users' signals while deeply nulling the interference signals. It is an effective way to realize the optimal receiving of the interesting signals. However, the additional adaptive beamforming algorithms need some kind of reference signal. And transferring the reference signal would occupy some frequency which is valuable and in short. Therefore, the blind beamforming that does not need reference signal have enjoys widespread popularity as soon as emergence. It has been developed as a research hotspot these years. As an important kind of blind beamforming algorithm, the constant modulus algorithm (CMA) is straightforward to implement, robust, fast to convergence and computationally of modest complexity. This dissertation is a special study on CMA.The author's main contributions are as follows:1 The convergence property of the CMA,.2 and CMA2., is analyzed. Special stepsizes to remove different signals with different power are given. The direction-of-arrival (DO A) of the strongest signal are derived from the weight vector of the CMA.2 To overcome the shortcoming of the interference capture caused by the least square CMA (LS-CMA) under severe environment, we provide the preprocessing LS-CMA which combine the advantage of the stochastic gradient descent CMA and the LS-CMA. The simulation results confirm its effectiveness and feasibility. With the preprocessing controlled by the stochastic gradient descent CMA, the LS-CMA rejects the interference capture and converges to the user signal with weak power. Furthermore, satisfactory output signal-to-interference-and-noise-ratio (SINK) is achieved.3 When there exits several constant modulus signals, the CMA could not adaptively distinguished different users. To meet this demand, firstly, we transform the input data of the array into the signal subspace. The necessary condition of separating several signals in the signal subspace is derived. And then the orthogonalization CMA in the signal subspace is presented. This new algorithm could effectively forced different weight vectors of the multi LS-CMA to recover distinct constant modulus (CM) signals. Therefore, the blind beamforming for several CM signals could be implemented at the same time.4 A new blind beamforming algorithm for multi CM signals is presented. After the LS-CMA captures a CM signal, the relationship between the weight vector and the DO A of the other signals is derived. Initial weight vectors are set hi the directions of the other CM signals by LCMV algorithm. Thereafter, the blind beamforming for the other CM signals can also be realized. The parallel and serial implements are given. Compared with the original multistage CMA, this new method does not need the signal canceller. Therefore, it is easier to be actualized.5 Recursive adaptive beamforming algorithm to fast track several moving targets ispresented. Instead of the continuous beamforming independently of the traditional beamfonning algorithms, we make full use of the information on the DOA of the users from the previous beamforming, which could greatly speed up the following beamforming. Therefore, the blind beamforming algorithm could keep up with the moving targets more quickly, Which is important in practical communication systems. Furthermore, the recursive CMA to fast track several CM targets is provided. The simulation results show that it takes about one seventh of the time for the recursive algorithm to track the targets than that of the traditional algorithm.Finally, it is worth pointing out that our emphasis was only laid on the CMA in this dissertation, hi fact, the idea of the above 3, 4 and 5 could also be used in other beamforming algorithms.
Keywords/Search Tags:smart antenna, adaptive beamforming, blind adaptive beamforming, constant modulus algorithm, direction-of-arrival, weight vector
PDF Full Text Request
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