The Study On V-BLAST System Over MIMO Channels

Multiple Input Multiple Output (MIMO) technique is a great breakthrough in wireless communications, which can greatly increase the capacity and spectrum efficiency of a wireless system without occupying more bandwidth. This paper firstly introduces the basic concept and system model of MIMO, and then derives the formulas of channel capacity for the slow flat Rayleigh fading channels. We also explain current space time code schemes, that is , Bell Laboratory Space Time(BLAST), space time block code(STBC) and space time Trellis code(STTC). Their applications to future wireless communications are also introduced in this paper.Vertical Bell Laboratory Space Time(V-BLAST) can achieve a spectrum efficiency of more than 20 bps/Hz, which has attracted many research interests. Based on in-depth analysis of the origial detection algorithm, this paper proposes an improved iterative detection scheme, which greatly improves the system performance. What's more, the system complexity can be greatly reduced due to the introduction of QR decomposition.Currently, most research interests in V-BLAST are restricted to narrow band system, which is not suited for future 3G and 4G system. In wide band system, generally, Orthogonal Frequency Division Multiplexing (OFDM) and equalizers can be utilized to mitigate the effect of the frequency selective fading. This paper extends the concept of decision feedback equalizers(DFE) for SISO and introduces the DFE suited for MIMO system. What's more, LMS-DFE and decorrelating LMS-DFE adaptive algorithm are also presented to track the channel variations and increase the rate of convergence.We use MATLAB to first build up a flat fading channel and compare the performance of origial V-BLAST system and the proposed V-BLAST system. Then we model a frequency selective channel and simulate the performance of proposed DFE, LMS-DFE adaptive algorithm and decorrelating LMS-DFE adaptive algorithm. The simulation results demonstrate the validity of the proposed equalizer to combat the frequency selective fading with good convergence performance. The work of this paper lays a theory foundation for future practical space time code hardware implement.