Research On Mimo Precoding Techniques For LTE-A System

As one of the4th Generation mobile communication standards, LTE (Long Term Evolution) project has obvious advantages in the aspects of peak rate, spectral efficiency, Qos, bandwidth deployment and network latency over existing3G (3rd Generation) technology. LTE is the premise and foundation of studying LTE-A (LTE-Advanced). And it has been selected by the world’s major operators.LTE systems use OFDM (Orthogonal Frequeney Division Multiplexing) and MIMO (Multiple input multiple output) as the key techniques of physical layer tramsimission. OFDM can effectively resist frequency selective fading and the processing complexity can be simplified by transforming the channel equalization into frequency domain from the time domain.MIMO can provide spatial diversity gain and multiplexing gain. Spatial diversity gain can ensure the reliability of the system through mergering the copies of signal in domains of frequency and sapce. Multiplexing gain can ensure the high spectral efficiency through shooting out the different parallel data streams from the different antennas under the constraints of maintaining bandwidth and transmit power of system.Meanwhile, MIMO causes interference between multiple parallel data streams and multi-users, and it is not practical to recover datas only relying on the MIMO detection techniques at the receivers, so MIMO precoding technique is propodes to solve such problems. MIMO precoding can effectively reduce the interference between the parallel data streams and multi-user to improve the channel capacity by enabling the transmitter to adjust the launch strategies according to the channel state information at the time, meaningwhile the complexity of the receiver can be greatly simplify.This thesis mainly discusses the precoding techniques for LTE-A, and the key factors that affect MIMO precoding performance are also been analyzed. MIMO precoding techniques for LTE-A mainly include linear and non-linear precoding techniques according to the standard whether the transmitter is linear operations. Linear precoding techniques include the codebook-based and non-codebook-based precoding techniques. The codebook-based linear precoding techniques include spatial multiplexing and transmit diversity precoding techniques. The codebook-based non-linear precoding techniques include ZF(Zero-Forcing), MMSE (Minimum-Mean-Square-Error), SVD(Singular Value Decomposition) and GMD (Ggeometric Mean Decomposition) precoding techniques. Nonlinear precoding techniques include dirty paper precoding, TH precoding and improved TH precoding algorithm. Finally, the key factors of influnce of MIMO precoding performance, such as the doppler shift, delay spread of the channel, the spatial correlation of the channel and different channel types are also analyzed. In addition, the thesis also discusses the performance of various precoding schemes in the imperfect CSI conditions on the basis of perfect CSI conditions.