Lte-tdd Downlink Beam Forming Technology

Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplex (OFDM) are the key technologies of 3rd Generation Partnership Project Long Term Evolution (3GPP-LTE). The key MIMO techniques used in LTE includes beamforming, transmission diversity and spatial multiplexing. The application of transmit diversity and beamforming can effectively increase the signal to noise ratio (SNR) of received signal, thereby enhance the transmission rate or coverage.It has been shown by MIMO theory that with the Channel State Information at Transmitter (CSIT), the application of beamforming or precoding can further improve the link quality and system capacity. In the 3GPP-LTE Time Division Duplex (TDD) system the signal of uplink and downlink use the same frequency with different timeslot, it make the base station get CSIT easily because of channel reciprocity. Therefore, in the 3GPP LTE-TDD system the application of beamforming has certain advantages than Frequency Division Duplex (FDD) mode.How to estimate the Direction of Arrival (DOA), and how to design low-complexity beamforming algorithm is two key issues in the 3GPP-LTE broadband MIMO-OFDM system. However, when it comes to multi-user system, how to coordinate and eliminate interference between users and then enhance performance of system is the core issue. Therefore, this paper focuses on beamforming techniques with the framework of 3GPP LTE-TDD system and is organized as follows:The first chapter is the introduction, describes the research status and structure of this paper.The second chapter introduces the MIMO-OFDM system model, and then according to the needs of this paper, Spatial Channel Model (SCM) recommended by 3GPP-LTE specifications is analyzed, together with a brief description of two classical beamforming algorithms, that is Eigenvalue Based Beamforming (EBB) and DOA Based Beamforing (DBB).Single user beamforming is studied in the third chapter. The EBB and DBB is introduced. Based on the traditional DOA estimation, this paper proposes a new DOA estimation algorithm in OFDM system using frequency domain channel fading matrix, and further proposed DOA based beamforming in frequency domain of OFDM systems. Proposed beamforming algorithm is simulated and comparied with EBB over SCM channel. It is shown by simulation that proposed beamforming algorithm performs 0.5dB better than EBB when the precoding unit is 5 resource block at the Bit Error Ratio (BER) of 10-3.In the foruth chapter, Block Diagonalization Eigenvalue Based Beamforming (BD-EBB) algorithm is proposed based the Block Dianonlaization (BD) algorithm, togetther with the interference sorting algorithm to reduce the computational complexity of BD-EBB. It is shown by simulation results that, BD-EBB algorithm can enhance system capacity greatly than BD algorithm with slight complexity increasingThe last chapter summarizes the previous research work and points out the possible research direction of future.