CDMA Detection Guided RAKE Receiver

Student: Siang Pin Gan

Supervisor: John Homer

Category: Engineering Thesis Project - Communications

In the radio environment, transmitted signals arrive at the receiver via a direct, unobstructed path, or via multiple paths from the reflection, diffraction and scattering of surrounding objects such as buildings and trees. This multipath propagation causes the signal at the receiver to distort and fade significantly, leading to inter-symbol interference (ISI).

Spread spectrum mobile communication systems use RAKE receivers to minimize these communication errors resulting from multipath effects. Ideally, the number of correlators in the RAKE receiver should match the number of multipath signals. In general, however the number of multipath signals is unknown and consequently RAKE receivers either contain an excessive number of correlators or the receiver performs sub optimally.

The aim of this thesis is to incorporate a new signal detection technique within the RAKE receiver of the Code Division Multiple Access (CDMA) system, which is able to identify every ‘important’ multipath in the unknown channel using the least mean square (LMS) algorithm. This detection technique involves an activity measure and an activity threshold. A multipath signal whose activity measure exceeds the threshold is deemed as an ‘important’ tap. The threshold has a theoretical basis, but may be increased to reduce the number of detected active multipath components resulting in a lower computational cost. Simulations demonstrate that the CDMA Detection Guided RAKE Receiver has a significant improvement in the signal-to-noise ratio (SNR), subsequently leading to a lower bit error rate than the current RAKE receiver with three correlators.

Index Terms – Activity measure, activity threshold, asymptotic error, CDMA system, least mean square (LMS) algorithm, multipath effects, RAKE receiver.

Thesis Document (PDF)

Other Related Files

Poster Presentation (PDF)