| IntroductionWith the development of wireless communication technology, high-quality transmission becomes the focus of modern communication. Channel estimation, as a technology which can extract the characteristic parameter of wireless mobile channel in real-time, is the key to ensure high-quality transmission. It is also the basic of receive technology such as multi-user detection and joint detection.Due to the lack of frequency resource and the demand for more services, 2G couldn't meet people's requirement more and more. As a result, the research and development of 3G or other mobile communication networks with higher bandwidth is a definitely trend. 3G is a self-interference because of its spread-spectrum technology, which result its more complicated channel characteristics. From this point of view, channel estimation is one of the key technologies for 3G.Channel estimation techniques can be divided into two major categories: blind channel estimation and non-blind channel estimation. Blind channel estimation only used the structure characteristics of channel and the signal, not know the specific of received signal at all. The algorithm of Blind channel estimation depends on the various characteristics of unknown parameters for different applications. The blind channel estimation receiver is very complicated. However, it doesn't plot the symbol, in which way can save the channel resources and increase the system capacities. Non-blind channel estimation extracts the useful channel characteristic parameter by receiving and judging the already known pilot sequence. It is relatively easy to realize and has better receive performance. In the WCDMA system, both of uplink and downlink use channel estimation mechanism which is under the assistant of the pilot signal. The difference is that the downlink has the common pilot channel, this is because the transmit station is not restricted by complexity and power consumption. For the uplink, it is restricted by the UE, so it has to use the pilot-part estimation mechanism by inserting the fixed pilot symbol to dedicated control channel.This paper mainly research the channel estimation algorithm of WCDMA system. For this part, the paper proposes a novel adaptive algorithm by researchingMMSE algorithm, Adaptive LMS algorithm, Iterative algorithm. According to the analyses of Rayleigh fading channel, an improved LMS estimation algorithm for channel estimation in 3G (WCDMA) mobile communication system is presented; and simulation shows the improvement of algorithm. But the improved LMS estimation algorithm has its shortcomings. After that the algorithm combines the traditional algorithms closely which makes itself more robust, smaller amount and more widely application scope.1. An improved algorithm for the adaptive LMSWCDMA system is used pilot symbols for downlink and uplink, thus, Coherent receive can used for both downlink and uplink. However, the Pilot is TDM, This makes the data slot of the channel parameters can only be based on the estimated value estimated by some part of the guidance algorithm is to be achieved. WCDMA system, the mobile station can be as high as 500km/h speed and This access to the data of the estimated more difficult. WCDMA system, as time-varying signal reception through multi-path fading channel, it will result in distortion; factor in the decline of the need for channel estimation. Adaptive estimation algorithm for the calculation is usually larger and more difficult to achieve. Based on the analysis of the characteristics of the multi-path fading channel, we advanced a novel algorithm. First make sure the order of LMS filter through the characteristics of channel. Then get the real-time characteristics of channel from the LMS filter.2. WCDMA system's channel estimation algorithm based on pilotIn DS-CDMA system employing Rake reception, the interference power is reduced considerably at the base station by performing temporal correlation of the signal received. There are some major differences between WCDMA and narrowband CDMA. Especially, pilot channel is added into the uplink and downlink of WCDMA. We utilize pilot symbols to estimate channel parameters. and then fulfill the correlated RAKE receiver to improve the receiver performance. Linear interpolation, adaptive filter, wiener filter and interpolation based on least squares are used to estimate channel parameters of data symbols with pilot symbols. Linear interpolation in cannot track channel quickly, and their performances get worse under high mobile speed. Adaptive filter in needs lots of train sequences and cannot hack quickly, which limits its application. Wiener filter method in requiresfading channel statistic characteristic, which is hard to estimate. Wiener filter method need to inverse matrix, its calculation is complex. Channel estimation method of interpolation on a second order curse using the instantaneous channel estimation of two neighboring slots based on least squares method is presented, but this method does not work well at low speed. The channel estimation methods mentioned above are only suitable for high speed mentioned above are only suitable for high speed or low speed. So it is necessary to develop an adaptive channel estimation method, which can meet simultaneously high speed, low speed, medium speed and varying-speed. A novel adaptive channel estimation method based on least squares (ALS) is presented in this paper to meet simultaneously the needs of high speed, low speed, medium speed and varying-speed, and the weighed combination function is introduced to solve this problem, and this method is required. |
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