Research Of MIMO On Mobile Communication

As wireless Internet and multimedia services are more and more widely used in our life, a lot of data need to be transmitted in wireless environment. But wireless spectrum resource is limited, and single antenna systems cannot meet this requirement. Multiple antenna systems system can potentially meet this requirement.MIMO systems, having multiple antennas at transmit and/or receive ends, can increase channel capacity and provide very high spectral efficiency while using the same total power and bandwidth as SISO systems. In ideal conditions, the capacity of the MIMO channel can be improved linearly with the number of transmit/receive antennas. So MIMO becomes one of the key technologies for high data rate and performance in 3G mobile communication systems and beyond.The performance of detection algorithm for a MIMO system is one of the key criteria to judge whether it can be used in practice. And the research of detection algorithms with high performance and low complexity is important in MIMO field.BLAST simultaneously launches the parallel substreams with multiple transmitter antennas and multiple receiver antennas, which can achieve capacities of MIMO (Multiple-Input-Multiple-Output) system to meet the requirement of high data rate. Space-time coding can improve the reliability of communications over fading channels using multiple transmit antennas with redundancy of multiple antennas.Under flat fading channels there are mainly two classes of detection techniques: optimal and suboptimal ones. Although maximum-likelihood detecting (MLD) is the optimal detecting algorithm, its extremely high complexity excludes its application in practical multi-antennas systems, especially when high order modulation and large number of antennas are employed. So detectors with resemble BER performance and lower complexity are research hotspots, such as sphere decoding (SD) and suboptimal detectors. Then suboptimal detectors are presented, including zero-forcing (ZF) detector, MMSE detector and classical successive interference cancellation (SIC) and ordered successive interference cancellation (OSIC) techniques based on ZF and/or MMSE.This thesis focuses on BLAST and space-time block coding, which is proposed byenhanced 3gpp standard.There are 3 parts in this thesis. The first part provides the introduction of MIMO systems. The second part describes BLAST (Bell-Lab-Layered-Space-Time) in details, and analyzes the detection algorithms such as ZF, MMSE and IC (Interference-Canceller). Finally, the sphere decoding (SD) algorithms are described in this part. Some modifications are proposed from it. Schnorr-Euchner (SE) search strategy and sorting the order of the receiver that can reduce the computational efforts than general CSD algorithm over the range of SNRs. The initial radius is defined as the distance between the receive point and Minimum Mean Squared Error (MMSE) detection point, which can avoid no solution in the sphere. In low SNR, the proposed algorithm can reduce the complexity evidently.