Research On System Moding Based On 3gpp Scm

With the rapid development of mobile communications, the communication system capacity can not meet the increasing demand of the users, which makes more and more attention be payed on how to make efficient use of the wireless spectrum day by day. On the other hand, the wireless communications environment is multipath and time varying, so the signals are affected by various declines, and how to solve all these problems to get good communication performance is another target of the wireless communications.Multiple-input multiple-output (MIMO) technology makes it possible to transmit multiple data streams in separate parallel channels in space, which effectively increasing the system's capacity. That is to say the spectrum utilization is improved without additional bandwidth by spatial diversity provided by MIMO technology. Orthogonal frequency division multiplexing (OFDM) converts a frequency-selective channel into parallel collection of frequency flat subchannels, which can meet the requirement of MIMO technology for narrowband. In OFDM, the entire channel is divided into many narrow parallel subchannels, thereby lengthening the symbol duration and reducing or eliminating the inter symbol interference (ISI) caused by the multipath. For all these reasons, MIMO technology combined with OFDM technology not only can increase the system transmission rate, but also improve the reliability of the system.Spatial Channel Model (SCM) is a standard model proposed by the Third Generation Partnership Project (3GPP), which adds multiple fading, MIMO antennae, antenna polarization and so on. It is very suitable to do research on MIMO technology. And it has more practical significance to study MIMO-OFDM based on a standard model, there has been few people do research based on SCM by now. Space-time coding is one of the critical techniques in MIMO-OFDM system, which is an important way to realize MIMO system capacity. Decoding of Space time block coding (STBC) is easier to implement compared with other coding methods, which makes it more attractive to small mobile devices.This paper first describes the characteristics of SCM and analyzes its parameters. The relationships of the channels correlation and space of the antennae as well as the antenna polarization are studied by simulation. Some processes are done to make SCM channel matrix able to be applied in the simulations as the channel matrix can be used directly. Then, the principles of MIMO-OFDM design are discussed in this paper, and the system block diagram is given. We also put forward the two implement ways of STBC combined with OFDM—encoding between two OFDM subcarriers and encodeing between two OFDM symbols, analyze their advantages and disadvantages, and analyse system performances in tyoical channel environments. Finally, we discuss the influence of channel correlation, spatial diversity and polarization diversity on system BER performance by simulations.