Research On Pattern Division Multiple Access Technology In Satellite Internet Of Things

As a typical application scenario in massive machine-type communication,Internet of Things provide network connection and data exchange service between a large number of machine-type terminals.In a variety of Internet of Things application scenarios,the ternimals of Internet of Things need to be set in remote areas.Under these circumstances,the construction of terrestrial network is limited by geographical and economical factors.Thus,it's difficult to provide access service to terminals in remote areas.In these scenarios,satellite communication technology become an effective supplement to the terrestrial Internet of Things for its seamless global coverage.Compared with the traditional terrestrial Internet of Things,the satellite Internet of Things technology needs to provide access services for more Io T terminals.Thus,the access scheme for satellite Io T need to be designed.Compared with the traditional orthogonal multiple access technologies,non-orthogonal multiple access technologies have higher resource effiency and could provide access service for more terminals at the same time.In this thesis,a high overload non-orthogonal grant-free pattern division multiple access technology is applied to satellite Io T system,which can effectively improve the access ability for the system.MCMC algorithm is applied to reduce the decoding complexity and it is flexible to be adjusted according to the state of users.Pattern division multiple access technology is mainly introduced and the improvement of throughout capacity by this technology is analyzed in this thesis.And the system structure and code book allocation strategy are proposed based on the various business requirement of satellite Internet of Things system.The message passing algorithm is introduced in this thesis,which is commonly used and could provide approximate optimal decoding result for PDMA systems.Aiming at the high complexity of this algorithm,a decoding algorithm based on Marcov Chain Monte Carlo is applied on PDMA systems.The results show that this algorithm could provide satisfactory decoding results with low computational cost and low complexity.But under the high signal-noise-ratio condition,the decoding performance of this algorithm reach a plateau.The cause of the performance plateau is analyzed in this paper.Based on the analyzation,two improved MCMC algorithm is proposed from the aspect of initial state of sampling point sequence and the aspect of probability of state transition for sampling points respectively.The simulations show that the proposed improved MCMC algorithm could decrease the possibility of falling in deadlock state for sampling points sequence,alleviate the decoding plateau problem and improve the decoding performance without extra sampling points.In order to reduce the signal overhead of Io T and save terminal resources,the grant-free transmission technology is combained with PDMA.Due to the lack of scheduling between terminals and satellite base station,codebook idleness and codebook collision will occur when uplink grant-free technology is applied in satellite Internet of Things system.In this paper,the advanced decoding algorithms with and without active user information are proposed respectively.According to the results,the MCMC decoding algorithm is more flexible and easier to be adapted with the state changes of active users.