Performance Metrics of RAKE Receivers

Abstract

This paper deals with performance evaluation of RAKE receivers. The need to evaluate the performance of RAKE receivers is the necessity of quantitative analysis for the purpose of comparison with other wireless communications based receivers and analysis of market value for deployment in receiver based devices. In CDMA spread spectrum systems, the multipath components of transmitted signals are those signals which are received at the CDMA receiver side after some propagation delay involved during transmission from the transmitter side. Therefore multipath components are referred as morphological forms of transmitted signals in CDMA spread spectrum based systems. It has been said that the propagation delay of multipath components must not exceed the chip rate of CDMA receivers. The RAKE receiver is CDMA spread spectrum system based receiver designed on the basis of triple modular redundant system. The RAKE receiver has three correlators which work as sub modules of triple modular redundant system. The three correlators of RAKE receiver are receivers which receive and process the time shifted multipath signals and propagate the processed signals to summer or integrator if the propagation delay is lesser than chip period after assigning weights to the processed time shifted multipath signals. The outputs of correlators are weighted with waiting coefficients then propagated to the summer for further signal processing. The RAKE receiver is always CDMA spread spectrum system based receiver. Using quantitative modeling techniques I found out that using M decision based correlators in RAKE receivers for receiving time shifted multipath signals improves the overall performance of RAKE receivers by reducing the bit error rate of the time shifted multipath signals and overcoming signal fading effects.