Coded Slotted ALOHA Based Access And Congestion Control Schemes

With the development of the communication technologies in recent years,the communication services have been diversified,and it has been an urge requirement to keep in touch with others at any time and any place in daily life and routine work.Since the terrestrial cellular mobile network has shortcomings of short communication distances and high construction costs,it cannot be an optimal solution to truly accomplish global seamless connection.Therefore,the satellite communication system can be a better option to satisfy the requirement of global communication.Satellite is an effective relay to provide a long distance and a large range data transmission,furthermore,it is pretty easy to construct a communication network,which is hardly affected by the geographical characteristic.Making satellite communication a key research direction in the field of wireless communications.In the national “One Belt and One Road” strategic layout and the blueprint of air and space integrated networks,the satellite communication system plays an irreplaceable role.As the first step of communication,one user has to access the system before transmitting,uplink access is a key technology in satellite communication system,the access performance will directly influence the service quality of the whole system.Due to the limited communication resources of satellites,when massive access occurs simultaneously in the satellite internet of things,a heavy collision would happen because of packets overlapping,which will result in data loss and a waste of system resources.The satellite random access scheme is the starting point of research in this thesis,and a deep study on M2 M massive access technology in satellite internet of things is conducted,especially on the high-throughput,high-energyefficiency access schemes and congestion control methods,the main tasks are as follows: 1.This thesis proposes two new random access schemes,dubbed polarized multiple input multiple output-coded slotted aloha(polarized MIMO-CSA)and adaptive code rate CSA based on CSA scheme.Firstly,several improved random access schemes based on slotted aloha(SA)and framed slotted aloha(FSA)are introduced.In order to find the key problems in previous schemes,some computer simulations are performed to analyze the throughput,packet loss rate and energy efficiency performance.After that,the polarized MIMO-CSA based on MIMO and multiuser detection,and adaptive code rate CSA based on the traffic load estimation are proposed.In adaptive code rate CSA scheme,the satellite transponder obtains the estimation of the system traffic load,and then adjusts the code rate of each user in the system,which can reduce the number of packets transmitted by a single user,while maintaining the system throughput.As a result,the energy efficiency can be promoted.At last,some simulations are performed to verify the performance of the proposed schemes.2.A modified congestion control method is proposed,with the expectation to resolve the collision problem of massive access in satellite internet of things.Firstly,several congestion control schemes are analyzed combing the characteristic of satellite internet of things,and the scheme based on access class barring(ACB)is selected as the optimal option.Then,a new traffic load estimation method is proposed to achieve an optimal control performance.Since the methods presented in previous literatures cannot meet the requirements of massive access congestion control,this thesis proposes a new method based on Multipacket Reception(MPR),which achieves a lager range and a higher accuracy,and aides the control method to decide an optimal parameter.Finally,the performance of the proposed method is verified by simulations.