非频率选择性衰落信道下捕获性能的分析

Analysis of Acquisition Performance over Frequency-nonselective Fading Channels

对基于数字匹配滤波器(DMF)捕获系统在非频率选择性衰落信道下的捕获性能进行了深入讨论,利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式。对平坦慢衰落信道和快衰落信道下的平均捕获时间进行了数字分析,得出的主要结论是:无论信道是否存在衰落,基于DMF的捕获系统都具有很快的捕获速度;基于DMF的捕获系统在衰落信道下的捕获性能明显要比非衰落信道差;衰落速度越快,平均捕获时间就越长,系统的捕获性能就越差。因此当信道存在非频率选择性衰落时,可以在接收端采用分集接收(比如空间分集)来改善系统的捕获性能。

The receiver based on digital matched filter (DMF) is investigated extensively in order to study the performance of the PN code acquisition over frequency-nonselective fading channel. By using the state transition diagram, the authors derive the analytic expressions of the mean acquisition time for a non-fading channel, a slowly fading channel and a fast fading channel. Numerical analysis is also given. It is shown that the proposed receiver based on DMF can accelerate the process of PN code acquisition whether the channel is fading or not. The acquisition performance of the system over the fading channel is worse than that over the non-fading channel. If the channel fades faster, the mean acquisition time is longer and the performance is worse. So the advantage of selection diversity (such as space diversity) is therefore obtained in a frequency-nonselective fading channel.