Research On Downlink Rake Receiver Of WCDMA Reconnaissance Receiver

Recently, WCDMA has become a3G standard which is the most widely used in countries and regions in the current world with widest terminals. The purpose of this topic is to design and implementation of WCDMA reconnaissance receiver. The function of WCDMA reconnaissance receiver is acquisition of cell broadcast information and client information. From the client’s point of view, reconnaissance receiver is a pseudo base station; from the cell base station’s point of view, reconnaissance receiver is a common receiver.In mobile communications, the received electromagnetic wave is composed of waves from different directions, which are caused by scattering, reflection and diffraction of trees, buildings and other obstructions. This phenomenon is called multipath transmission. The received signal will suffer from frequency selective fading due to multipath signals having the different time delays. The Rake receiver technology has been introduced to counter the effects of multipath fading.The thesis analyzes the WCDMA downlink Rake receiver technology according to signal characteristics and application scenarios. The thesis includes:(1)Based on mathematical model of multipath transmission, the effects of signal loss, time broadening and spectral broadening caused by multipath transmission are quantitatively analyzed. And the principle and block diagram of Rake receiver are introduced.(2) The modulation method and timing of the downlink physical channel signal are introduced. Based on mathematical expression of received signal, the auto-correlation properties of spread spectrum code are discussed. And the schemes of cell search and multipath search are proposed to achieve coarse synchronization signal and separate distinguished multipath.(3) After introduction of the synchronous tracking technology in spread spectrum communications, a scheme applied to WCDMA downlink synchronization tracking is proposed, which includes tracking loops bases on code tracking loop and carrier tracking loop and secondary controller such as C/N0estimator and out of lock detection. The principle of the maximum ratio combining technique is described. The designed Rake receiver adopting the proposed synchronous tracking scheme is simulated for performance verification, which meets the requirements of the reconnaissance receiver for downlink reception performance.(4)The multiple access interference of DPCH with low spreading ratio caused by P-CPICH is analyzed. A Rake receiver combined with pilot cancellation is designed, and the algorithm of pilot cancellation is proposed in detail. When the code phase, the carrier phase are precisely synchronized, the amplitude estimate is key to pilot suppression performance. Two schemes of amplitude estimate are proposed for signal reconstruction. Simulation results show that performance of the designed Rake receiver design based on the pilot cancellation is better than traditional Rake receiver’s.