| There are two technique problems for Terrestrial digital TV transmitter: one is the channel coding modulation technique whch is dependent of TV system; the other is the HPA adaptive predistortion technique independenting of TV system. Because of the independence of the two problems, before determining the Terrestrial digital TV criterion, we must study the adaptive predistortion technology.At present, the amplifier's nonlinear compensation, that is linearisation technique has become a very hot topic at home and abroad. This paper analysis the basic theory of the amplifier linearisation in COFDM system, the factors that influence the amplifier reliability in detail. On the other hand, this paper introduces systematically the main linearisation techniques of the amplifier at home and abroad. Based on those researches, this paper researches digital baseband signal predistorting technique. The author thinks, the main obstacles of the development of predistortion technique in COFDM system are:1. Predistorting technique was implemented with analogue mode early, which used for the micrawave communication transmission system, which circuit is complexity and adjust inconveniently. Predistorter operating at a radio frequency is easy implemened, but can't adjust adaptively. In the recently decades, with the development of the DSP technology, predistorting technique is realized with digital mode, due to baseband signal is easily dispose and temperature and aging, variations of operating point etc. The paper gives a particular description of the realm. Until now, there are lots of works that have been done in the realm of predistorting technique, in which most of them are limitted to theoretical research. And the higher compensation is at the cost of higher complex,which isn't practical in real world. So, the research and design of simple and practical adaptive predistorting algorithm is one of the most important topics of power amplifier solving.The construction and implementation of real-time adaptive predistortor increase the complexity of the system in most degrees. The predistortor and adaptive algorithm in the single-carrier Software can't satisfy the requirement with multicarrier system application.Because CDMA, OFDM signal is made up of the hundreds and thousands signals, the signal has nonconstant envelope, the amplifier results in intermodulation distortion products. So, it need to design a new predistortor and adaptive algorithm to make the lower amplifier backoff , high power efficiency, and at the same time, adaptive predistortor, while keeping system satisfy with the requrements,. The realization in2. application level will make the burden on the application designers heavily, and make the control of the quality of software harder. So, how to keep the system level to be simple, common, and high efficiency, and at the same time, convergence reduce the burden of application designer is another important research realm of adaptive predistorting system.Based on the analysis of the main obstacle of adaptive predistorting system, this paper focus on the views of the adaptive algorithm and architecture of real-time predistortor.And the main contributions are shown below:1. Presenting a digital adaptive compensation method based on estimator. Predistortion achieved by the method is by estimating HPA nonlinear characteristic by piecewise linear function and adjusting HPA estimator parameters via performing inverse transform section by section. The computer simulation shows that the method algorithm converges fast and RAM requires less and compensates effect well. The HPA input backoff decrease 6dB at a BER of 10-4.2. Presenting an novel digital adaptive predistorting design method based on HPA nonlinear fitting. The method design HPA estimator based on the characteristic and it is easy to obtain the inverse of the reasonal bilinear function. The reasonal bilinear function nonlinear preserve HPA nonlinear characteristic, while the characteristic of easily obtaining the inverse of the reasonal...
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