| Summary: | 碩士 === 國立中興大學 === 電機工程學系 === 87 === This thesis can be divided into two parts. In the first part, we consider an antenna array based mobile cellular system and its scattering channel models. In the second part, we will study the efficiency of beam-forming optimization algorithms and discuss system performance with various RAKE receivers in CDMA cellular mobile communication system.
Taking into account channel characteristics of a mobile cellular environment, we introduce entire scattering circular channel model (using geometrically based circular model) and propose forward scattering semi-circular and backward scattering semi-circular channel model. In these channel models, we assume that scatterers are uniformly distributed within a certain range. Then, we analyze the variation of three principal parameter distributions (i.e., AOA, delay spread and Doppler spread) in diverse channel model when a base-station uses both omni-directional antenna and directional antenna. We derive the probability density function for the AOA distribution and use the circumference of ellipse approximation method to compute the delay spread and utilize geometrically accumulation method to calculate the Doppler spread. Because of the space filtering characteristics of antenna array communication systems, the results show that it is indeed helpful to improve the capacity and the performance of systems. Therefore, we propose a beam-forming optimization algorithm to increase the system capacity at a reasonable hardware cost. We also have compared the performance of equal gain combining, maximum ratio combining and mean square maximum ratio combining RAKE receivers.
The obtained results show that the circumference of ellipse approximation method and geometrically accumulation method are very effective and accurate to compute parameter distributions of the channel model in varying environments, such as in entire scattering circular, forward scattering semi-circular and backward scattering semi-circular channel models. Also, the beam-forming optimization can greatly reduce multiple user interference and increase the system capacity in a mobile cellular communication system.
|
|---|
