Research On MIMO Precoding Technique Of LTE System

With the rapid development of multimedia service and mobile internet, it requires a wireless communication systems with higher data-transmission rate. However, due to limited radio spectrum resource, improving spectrum efficiency becomes a key problem for LTE and LTE-A system. Multiple-Input Multiple-Output (MIMO) technique, which is a multi-antenna transmission technique, can improve the capacity, spectral efficiency and the reliability of the communication system significantly without occupying more bandwidth or increasing the transmission power because of extra freedom in spatial domain. So it is listed as one of the mandatory techniques in the LTE system. In MIMO system, precoding technique is one of the key techniques which help realize its high performance. The error propagation can be avoided and the complexity of the user equipment can be greatly reduced by MIMO precoding technique. Therefore, how to design the MIMO precoding algorithms to improve the data-transmission rate and bit error rate performance becomes a research hotspot in communication field.The main content of this thesis includes studying on the codebook-based precoding technique of LTE system, analyzing the performance of this technique by simulation, and trying to propose a optimal scheme. In chapter one, I begin with the brief introduction to the MIMO techniques. Aftert that, in chapter two, I introduce the codebook-based MIMO precoding technique and its simulation performance. Based on the analysis of simulation result, it’s easy to find that, in codebook-based MIMO system, since each user needs to calculate its channel gain when adopting each code in the codebook and feedback, the uplink feedback load is heavy. Therefore, limited resource of uplink feedback channel may become the bottleneck of codebook-based MIMO system, especially when the number of users served by the base-station is large.The main content and contribution of this thesis are as follows:1. Studying on the precoding technique of LTE system, analyzing the performance of ideal precoding technique and codebook-based precoding technique by simulation.2. Proposing new precoding schemes for three different scenarios (single user single beam, single user multiple beam and MU-MIMO scenario), which use pseudo-random precoding vectors and applying some thresholds for the feedback process.3. Giving the theoretical performance of this new scheme under single user single beam, single user multiple beam and MU-MIMO circumstances, including theoretical system throughput and theoretical feedback load.4. Giving the performance simulation result of this new scheme under single user single beam, single user multiple beam and MU-MIMO circumstances, and making a comparison with the performance of codebook-based scheme. It shows that, assuming the base-station serves certain amount of users, adopting this scheme can largely reduce feedback bits with little channel capacity loss in comparison with the codebook-based scheme. And when the sum feedback rate of uplink channel is upper bounded by a constant, this scheme can have a better performance.