PERFORMANCE ANALYSIS OF SYMBOL/CHIP BASED MINIMUM VARIANCE BEAMFORMER CONFIGURATION FOR SYN

The symbol-based configuration can lead to a significant improvement in Signal-to-interference-plus-

Current direct sequence code division multiple access (DS-CDMA) system suffer from Multiple access interference (MAI) and Inter symbol interference (ISI) due to the frequency selective channel. This interference can be avoided by use of Adaptive Beamforming. There are two different minimum variance Beamformer configurations for the base station receiver in direct sequence code division access (DS-CDMA) systems, namely a chip- based and a symbol-based configuration. In this paper chip- based and symbol- based configurations are studied. In symbol-based configuration, spatial diversity is exploited after despreading and interfering components are rejected, based on both their power and code correlation with the Signal of interest (SOI). The symbol-based configuration is very efficient method to reject higher interfering strength components. Detailed performance analysis and simulation shows that in presence of multiple access interference, the symbol-based configuration can lead to a significant improvement in Signal-to-interference-plus-noise ratio (SINR) relative to that achieved with chip-based configuration for synchronous DS-CDMA systems.
It is expected that the 3rd generation systems can provide a variety of wireless communications to high bit rate video communication including Internet access, which will be a major demand in the future mobile communication. The technology of direct sequence (CDMA) has been chosen for the 3rd generation system because of numerous advantages. A major advantage of the DS-CDMA is that it can provide a better capacity compared to the other possible technologies of multiple access. Interference suppression techniques such as smart antenna and multi-user detection have widely been investigated for applying them in the DS-CDMA. The structure of two dimensional Rake (2D-Rake) combiner has been proposed to detect spread signals at base stations equipped with the smart antenna. For the 2D-Rake combiner, the criterion of maximizing the SINR has been utilized.

The Minimum Variance Beamformer is an important and popular adaptive beamforming technique. Adaptive minimum variance Beamforming can be easily implemented to improve the system capacity by suppressing the co-channel interference and also used to enhance the system immunity to multipath fading. Adaptive minimum variance Beamforming can increase the cell coverage range substantially through antenna gain and interference rejection. It optimally combines the components in such a way as to maximize antenna array gain in the desired direction simultaneously minimize it in the direction of the interference. The use of an antenna array adds an extra dimension and makes the utilization of spatial diversity possible. This is due to the fact that interferers rarely have the same geographical location as the user, and therefore, they are spatially separated. Different from omni-directional antenna systems and sectored antenna systems, adaptive antenna array systems, combine an antenna array and a digital signal processor to receive and transmit signals in a directional manner. Thus, the beam pattern at the base station can be adaptively changed. An improvement of system performance in a multipath environment can be achieved by combining a set of Beam formers and a RAKE combiner. It consists of a Beamformer and one or multiple symbol rate matched filters. The Beamformer is adapted to the antenna array response and the symbol rate matched filter is matched to the path delay.
In this project, the performance of CB and SB configurations in rejecting interference is investigated through theoretical analysis and simulations on the basis of Minimum Variance.
Chip based (CB) and Symbol based (SB) beamformer configurations for direct sequence code division multiple access (DS-CDMA) systems were studied through analysis and simulations. Using the chip-based configuration, different interfering components are spatially rejected in terms of the spatial distribution of their power, regardless of their code correlation with the Signal of interest (SOI).

On the other hand, using the symbol-based configuration, they are rejected on the basis of there interference signals, which depends on both the power and the code correlation with the Signal of interest (SOI). Thus, interference that has a more significant impact on system performance can be more efficiently rejected. As a consequence, the symbol-based configuration leads to a better trade off between signal to-noise ratio (SNR) and signal
to ?interference ratio (SIR) and a higher signal to- interference noise ratio SINR can be achieved. In, effect, the symbol-based configuration is superior relative to the chip-based configuration in the presence of multiple access interference (MAI).