Research And Implementation Of Medium Access Control In 5G System For The Super Base Station

Traditional cellular network balances the limited spectrum resources with the infinite user access requirements by increasing the number of base stations.However,with the explosive growth of wireless data,large-scale deployment of base stations can cause huge waste of resources.In this regard,the Institute of Computing Technology of the Chinese Academy of Sciences proposed a centralized cellular network architecture based on resource pooling—super base station.To meet the needs of 5G system,super base station improves system resource utilization by multiplexing statistically base station pool resource,modularizing hardware and software,etc.However,in order to meet the performance requirements of super base station communication software platform and business processing,a completely new design of the entire protocol software architecture is required.In the 5G protocol stack,the medium access control layer(MAC)is an important part of the protocol stack,which is mainly responsible for random access,hybrid adaptive retransmission,resource scheduling,multiplexing and demultiplexing,etc.In this paper,the research and implementation of 5G MAC layer is carried out under the super base station architecture,including the research of random access procedure,hybrid automatic repeat request(HARQ)process,and the design and implementation of key submodules of MAC layer.The main work of this paper is as follows:1.This paper first studies the random access procedure of the super base station system.In the 5G machine-like communication scenario,there is a serious preamble conflict when a large number of devices access the wireless network,resulting in access failure.So,this paper proposes a multi-priority-based random access congestion control strategy,and adds the accession-free priority factor to access control parameters based on the Access Class Barring(ACB)in the base station.Then according to different priorities,the access load of the devices is dynamically configured by the ACB control parameters,which can effectively alleviate network congestion and ensure that delay sensitive devices access preferentially.The UE compares the access control delay with the delay tolerance,and then dynamically update the priority according to the comparison result.Finally,whether to initiate the random access procedure according to the access control parameters can ensure the delay requirement of devices with low priority.The simulation results show that the strategy of this paper can guarantee the access delay of devices with different priority while alleviating network congestion.2.This paper further studies the HARQ process.It is noted that when transmitting a large data packet,a transmission block(TB)makes errors may only because an error in the individual code block(CB).But traditional single-bit HARQ feedback mechanism will retransmit the entire transmission block,resulting in waste of resources.This paper proposes an improved HARQ feedback mechanism based on Code Block Group(CBG),which provides flexible multi-bit feedback based on erroneous CB blocks.The simulation results show that the HARQ feedback mechanism in this paper can effectively reduce the retransmission of CB blocks and improve resource utilization.3.In this paper,the software architecture of 5G MAC layer based on super base station is designed.Besides,the random access module,HARQ module and memory management module are designed and implemented in detail.Finally,based on the hardware and software platform,the random access module and the HARQ module were tested in various ways to verify the functional integrity and correctness.