Research On Distributed Antennas Technology And Its Application In LTE-Advanced System

Distributed antenna (DA) technology has become a hot spot in the research of mobile communication for its large capacity and uniform coverage, which can effectively solve the contradiction between the current increasing mobile users and limited spectrum resources. The LTE-Advanced system, as the smooth evolution of the Long Term Evolution (LTE) system, must be greatly improved in peak rate, average spectral efficiency, cell edge spectral efficiency and more to meet or exceed the ITU's requirement for IMT-Advanced (International Mobile Telecommunications) system. The most meaningful indicator is cell edge spectral efficiency. The thesis aims to increase this indicator to improve the cell edge user performance.Distributed MIMO (D-MIMO) is the combination of DA and MIMO (Multiple Input Multiple Output) technology, which is the basic architecture in this thesis. Firstly, the channel capacity of the D-MIMO is investigated. Considering the composite channel model including fast fading, slow fading and path loss, the ergodic capacity in the downlink and uplink are analyzed. The simulations show that D-MIMO has larger capacity than the co-located MIMO (C-MIMO) system. Secondly, based on the D-MIMO system, the cooperative transmission schemes of the single-user and multi-user are discussed. There are two existing cooperative transmission schemes used for single-user: hybrid SFBC (Space Frenquency Block Code) scheme and hybrid CDD (Cyclic Delay Diversity) scheme, both of which are based on the multi-antennas technology used in the remote antenna unit (RAU) to achieve the diversity gain. PS CDD is proposed for not suffering from frequency selective nulls. Taking the adavantages of the SFBC and PS CDD into consideration, an improved scheme SFBC PS CDD is proposed. The simulation of the throughput illustrates that the improved scheme has better performance. BD (Block Diagonalization) algorithm and the SLNR (Signal-to-Leakage-and-Noise- Ratio) algorithm used for multi-user in cooperative transmission is researched, two of which aim to suppress co-channel interference between the multi-user. The restriction on the number of transmit and receive antennas is removed in the improved BD algorithm. The SLNR precoding algorithms for the single-stream-per-user and multi-stream-per-user are also analyzed and derived. Based on the cooperative transmission of the RAUs, the simulation verifies SLNR algorithm is better than BD algorithm, which is consistent with the theoretical analysis. The reason is that SLNR algorithm considering the influence of noise.At last, the application of the D-MIMO in the LTE-Advanced system, or the CoMP (coordinated multiple point transmission and reception) technology is investigated. An inter-cell cyclic delay based on multi-cell transmit diversity structure is proposed. The performance analysis and simulation results show that the proposed scheme is superior over existing schemes while keeping the back compatibility with the LTE system.