1.1 An Overview of wireless Technology
In the past few decades, wireless communication has grown with very rapid speed. Wireless communication becomes popular in field of research since 1897, when Guglielmo Marconi first demonstrates radio ability to provide communication through English Channel . During past two decade the mobile communication industry has grown in such a fast speed that it is fuelded by the digital and RF circuit fabrication, very large scale integration (VLSI) circuit. Digital communication technique facilities a new large scale deployment of the communication network. This trend will continue at an even greater pace during the next decades. With the passage of the time communication trends changes from early radio paging, cordless telephone and cellular telephony to today’s personal communication and other computing devices. The tremendous growth and demand for wireless services increased the internet services and evolution to change wired network into wireless network system. Three different problem faced in the wireless communication system are fading, Inter-symbol interference (ISI) and co-channel interference. Fading and ISI result from the multipath propagation in wireless channel, while the co-channel interference resulted from the same frequency used . To mitigate these problem different diversity schemes such as spatial diversity and transmit diversity are used. To remove the ISI different algorithms are used such a zero forcing algorithm, minimum mean square error.
1.2 INTRODUCTION TO MIMO SYSTEM
Multiple Input Multiple Output (MIMO) technology has concerned attention in current wireless cellular mobile communication system. By using the MIMO technology in cellular network the channel capacity is increased without any additional bandwidth required and transmitted power. By deploying the multiple antennas both at the transmitter and receiver side we can achieve the array gain, spatial diversity gain, spatial multiplexing gain and interference reduction. Thus the spectral efficiency and reliability can be extensively improved .
1.2.1 Array gain [Received SNR]
Array gain can be made available by processing at the transmitter and the receiver which result in an overall increase in an average received SNR, due to coherent combining effect. Transmit/receive array gain require channel state information which is very difficult in practical scenario. Hence various estimation techniques are used to improve overall array gain.
1.2.2 Diversity gain [Improved BER]
Diversity gain signal powers in wireless channels generally fluctuate randomly know as fading. Diversity is the only powerful technique to reduce the effect of fading in wireless link. In addition to time and frequency diversity MIMO system provides spatial diversity to help and reduce the effect of multipath fading.
1.2.3 Spatial Multiplexing gain [Transmission rate]
Spatial Multiplexing gain MIMO channel offers a linear increased in the capacity [Data rate] for no additional power or bandwidth expenditure. Multiplexing gain refers as spatial multiplexing gain is realized by transmitting independent data signal from the individual antennas. At a time minimum of (Mt, Mr) different streams of bits can be accommodate in the communication system to improve overall capacity.