Research On Channel State Information Acquisition Technology Of Distributed Antenna System

With the advancement of social development and wireless communication technology,the demand for data transmission has increased exponentially,which poses a challenge to existing mobile communication systems.In order to make the data rate higher and faster,many technical solutions have been proposed.,including millimeter wave communication,Multiple Input Multiple Output(MIMO),and Distributed Antennas System(DAS).Among them,DAS technology has received extensive attention.On the one hand,the DAS system shortens the distance between the user and the access node(AP,Access Points),thereby reducing path loss and reducing transmit power.On the other hand,multi-AP deployment provides opportunities for diversity and spatial multiplexing.Therefore,due to its potential advantages in terms of capacity,power consumption,coverage and outage probability,DAS has become an important candidate for future mobile communications.However,while the DAS system brings many advantages,there are still many problems to be studied,such as network planning,performance analysis,and resource allocation.This paper focuses on the DAS limited feedback system in FDD(Frequency Division Duplex)mode,and proposes a limited feedback resource allocation method based on the minimum criterion of quantitative capacity loss;and in the multi-cell DAS system,The user is subject to strong inter-cell interference.Based on the idea of suppressing phase ambiguity and saving feedback overhead,a channel training method based on pilot frequency combination is proposed.The main research work of this paper is as follows:Firstly,this paper introduces the basic structure and research background of the DAS system,and briefly analyzes the research status and main research directions of the DAS system.And a finite feedback bit allocation method is proposed in the DAS system.In the FDD mode multi-user DAS system,due to different channel conditions between different access nodes and users,optimizing the allocation of limited feedback resources can effectively improve the overall performance of the system.The method in this article adopts the AP selection method based on the distance threshold to cancel the limitation on the number of APs accessed by the user,and minimizes the quantization capacity loss as an objective function,combined with the quantization characteristic of the random vector quantization codebook(RVQ)and the Taylor expansion method.Compared with other allocation methods,the method of the proposed method is more universal without limiting the number of access APs of users.The simulation results show that the proposed method is better than the traditional equal bit allocation scheme when the feedback resources are limited,and the better gain can be obtained.Then the paper extends the scope of the DAS system to multiple cells.In this case,the inter-cell interference experienced by the multi-cell edge users is more serious.In this paper,a multi-cell edge is considered as a virtual cluster.Since the APs in the cluster cannot directly cooperate,a channel training method based on pilot reuse is proposed.In this method,when the AP is configured with more access antennas,multiple access nodes serving the same user can reuse the same pilot sequence.This method reduces the computational complexity while saving pilot resources and reducing feedback overhead.It is verified by simulation that the proposed method can obtain better performance after weighting.