Wavelet Packet Division Multipex Transmission Technologies For Broadband Satellite Mobile Communication

In 21 century, as unprecedented development of the world aviation communications technology and the wireless network technology, air-space-ground of integrated information communication network become very fast growing field of research and a powerful modern means of information exchange. As a significant component of the air-space-ground integrated information network, the broadband satellite communication system, which is a repeater, will play an important role in providing services to various users anytime, anywhere. For the broadband satellite mobile communication confronting with a series of intractable problems, including channel problem, bandwidth efficiency issue and interference sensitivity etc, the special physical technique which is efficient solution for the problem is needed.Wavelet packet division multiplexing (WPDM) technology is a multi-carrier transmission technology. WPDM with high bandwidth efficiency has the capability of anti-multipath and anti-narrowband interference. The WPDM has better power band limitation and capability of non-uniform capacity divide than OFDM, and therefore the use of WPDM in broadband satellite mobile communication to increase system performance is an important research topic.In this dissertation, broadband satellite mobile communication system using WPDM technique is in-depth researched. The dissertation mainly focuses in the following aspects.First, the applicability research of WPDM based broadband mobile satellite transmission system. For broadband mobile satellite transmission channel characteristics and the specific technical requirements, this dissertation utilize WPDM technology to improve the transmission performance. Analysis shows improvements of the system bandwidth utilization, power spectral density, anti-satellite channel fading and interference, proves that the WPDM is suitable for broadband satellite communication transmission, which are the key points for the following researches.Second, the wavelet packet pruning optimization algorithm based on least cost function. Wavelet packet pruning optimization is the typical optimizing method of WPDM system, in which defining the cost function is the key point. A typical wavelet packet selection algorithm in multipath fading applies only to bipolar code. Typical anti-jamming algorithm using wavelet packet selection needs the location information of the interference in time and frequency domain, which increases the complexity of the algorithms. According to the inadequacies of the typical algorithms, this dissertation proposes a minimum mean square error cost function based wavelet packet pruning optimization, simplifies the optimization algorithm and excessive application of the algorithmThird, Improved Kalman filter based WPDM time-domain channel estimation algorithm. As wavelet packet selection method is not suitable for fast fading channel environment, the channel estimation techniques purposed to improve the system performance is proposed. As typical Wiener filter channel estimation algorithm and the LMS adaptive filter channel estimation algorithm are considered, they both have shortcomings. To overcome those shortcomings, an improved Kalman filter channel estimation method is proposed. In the method, the received signal is modeled with AR model, the channel coefficient estimation is based on the prediction step state. Theoretical analysis and simulation results show that the improved Kalman filter channel estimation algorithm performance nearly the same as the Wiener filter based channel estimation algorithm, and the algorithm does not require a large number of training sequences, so bandwidth utilization is better than adaptive filtered LMS channel estimation algorithm.Lastly, WPDM combines suppressing and filtering to improve anti-jamming algorithm. As the long transmission delay of the satellite channel, the wavelet packet selection method can applie only to interference immunity for a long time constant or slowly changing situation. Based on the characteristics that wavelet packet decomposition will expand the scope of impulse interference and reduce the narrow-band interference, a suppressing and filtering combined anti-jamming algorithm is proposed. Firstly, the received signal is in suppressing treatment to achieve the purpose of impulse interference suppression, then LMS adaptive filtering method is used after WPDM demodulation to achieve the effect of inhibition of narrow band interference, the entire operation process is simple and do not need feedback.