Discrete-time RAKE receivers with applications

Wireless channels are often multipath channels. In a multipath channel, a path can be defined as a copy of the transmitted signal arriving at the receiver with a particular delay and amplitude. If the multipaths are resolvable, RAKE receivers can collect the energy of distinct paths. DS-CDMA systems, with their low auto-correlation spreading sequences, enable resolving of the multipaths and therefore the use of RAKE reception. Each RAKE finger, the elementary receiver in RAKE reception, is associated with one of the strongest incoming paths. The outputs of those fingers are combined together to detect the transmitted symbols. The conventional RAKE receivers have several weaknesses. This thesis focuses on the major weaknesses of sensitivity to interference and channel estimation error. It introduces a receiver model to cope with both of them for both single and multi antenna (MIMO) systems. We propose a new RAKE reception method, which is called the generalized decorrelating RAKE receiver (GD-RAKE). GD-RAKE is obtained by the combination of two advanced RAKE receivers: the decorrelating discrete time RAKE receiver (D-DTR) and the generalized RAKE receiver (G-RAKE). The method enables robust performance in the presence of channel estimation errors and colored noise plus interference with the help of statistics on the channel, noise and interference. Additionally the performance of the new receiver is tested in MIMO channels. Soon to be commercialized ultra wideband (UWB) systems use more than 500 MHz bandwidth. Such a high bandwidth results in many resolvable multipaths and as such the employment of RAKE receivers is very suitable. We tested the performance of a G-RAKE receiver with decision feedback equalizers and showed that it can be used to improve overall performance of the system