Introduction

Efficient use of the limited available spectrum is required to cover the increasing demands for wireless services such as internet and media rich applications. By exploiting the spatial domain in rich scattering environment, it is widely acknowledged that spatial multiplexing (SM) multiple input multiple output (MIMO) communications are the key techniques for higher data rates without consuming extra bandwidth and transmit power. Therefore, it is considered as the fundamental enabling technology that can fulfil the high spectral efficiency demand of fourth generation cellular (4G) wireless systems and potentially leading to Gigabits communications.

 In cellular wireless systems, the practical emergence of multiuser MIMO (MU-MIMO) systems such as the IEEE worldwide interoperability for microwave access (WiMAX) and the third generation partnership project long term evolution (3GPP-LTE) has opened up the possibility of allowing multiple users equipped with one antenna or more to access the base station (BS) simultaneously without subdivision in the scarce resources of time, frequency and codes. Since the multiple antennas at the users’ side can be regarded as “virtual” transmit antennas, developments in this field appears as extension of single user MIMO (SU-MIMO) concepts for the multiple access channel (MAC) and able to increase the spectral efficiency by exploiting the rich multipath environment, spatial difference among users and the available number of BS antennas. Therefore, multiple users can be served as in spatial division multiple access (SDMA) with appropriate complexity/performance tradeoff. This leads to substantially increase in the user capacity and hence sum rate capacity with much reduction in latency for each user compared with TDMA systems. However, it is seriously affected by channel correlations due to insufficient antenna separation at the communication terminals and poor scattering environment. As a result, the sum rate capacity and bit error rate (BER) performance are significantly degraded and users with highly correlated channels may not be served which reduces the user capacity. Therefore, efficient and practical techniques are proposed in this project to address these key problems for MU-MIMO systems in different channel conditions.

Project Aims and Objectives

This project aims to improve the channel/user capacity and bit error rate (BER) performance of MU-MIMO systems in different channel conditions.  To achieve our targets, the following objectives are considered: •Investigating the effects of signal design on the performance of MU-MIMO systems under different channel conditions, number of users and modulation levels. •Investigating new efficient methods for the generation of correlated Rayleigh fading channels for capacity and performance evaluations. •Effects of receive antenna selection techniques on the channel capacity of spatial multiplexing MIMO and MU-MIMO systems. •Investigating new design approaches for high user capacity MU-MIMO system with affordable complexity by employing receive antenna selection techniques and layered multiuser detection with interference cancellation.  

 

 

 

 

 

 

 
Fig.1:  Generic  block diagram of MU-MIMO mobile communication system with receive antenna  selection.

Contributions  

Generic block diagram of MU-MIMO mobile communication system with receive antenna selection is shown in Fig.1 and the major contributions are categorized under the following areas:

•Transmission side

To improve the performance of wireless MU-MIMO system under different channel correlations, number of users and modulation levels, two signal constellation designs are proposed (see Fig. 2) to maximize the minimum distance of combined received signals.

•Channel modeling

To consider the problems of channel correlations and multiple access interference (MAI), two novel techniques are proposed to overcome the shortcomings of conventional methods for generating correlated Rayleigh fading channels (see Fig. 3).

•Reception side

1.Novel receive antenna selection technique is proposed to increase the channel capacity of single user SM-MIMO and MU-MIMO systems under different channel correlations. Compared with optimal selection and norm based selection (see Fig. 4). 2.To increase the user capacity of MU-MIMO systems with affordable complexity, a novel MU-MIMO scheme is proposed (see Fig. 5).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
Fig.3:  Correlated  Rayleigh fading envelopes.

 

 

 

 

 

 

 

 

Fig.4:  Channel  capacity of MU-MIMO system over uncorrelated channels.

Fig.5:  BER  performance of MU-MIMO system over correlated channels.