| Massive Machine-Type Communication(mMTC)is one of the three ma-jor application scenarios in the fifth generation mobile communication system.As the important part to support the Internet of Things and ubiquitous net-work,mMTC will make human to human,human to machine and machine to machine widely connected.mMTC is applied into many vertical-industries,such as smart industry,smart medical,smart environment,smart transport and smart home,promoting the explosive growth of ubiquitous intelligent IoT.Fur-thennore,it drives the real economy toward digital,networked and intelligent.However,the services of mMTC have different traffic patterns and character-istics,such as uplink-dominated,energy-efficient,long life-time,short packet,low complexity,precise timing,discontinuous data transmission,multi-level delay tolerance,a large amount of overhead and control signalling,which make the traditional communication system hard to support various Quality of Ser-vice in mMTC.mMTC devices' accessing the network makes the network load increasing and produce massive data.It aggressives the challenge of radio re-source allocation,compels mMTC devices with low-cost and limited capabili-ties to face the dilemma of big data processing and makes the communication security of IoT more important than ever.It not only has important scientific and theoretical significance but also has great practical application value to pro-vide energy-efficient and secure transmission for mMTC devices with limited capabilities in the uplink Non-orthogonal Multiple Access(NOMA)system.This dissertation studies on secure and energy-efficient transmission tech-nologies for mMTC devices to solve the challenges of massive connected,up-link transmission dominated,limited energy powering,finite transmission packet blocklength,constrained security capabilities and computing capabilities.The studied technologies include uplink cooperative NOMA-based low-power tech-nology,energy-efficient short packet transmission technology,security enhance-ment technology and energy-efficient secure computation offloading technol-ogy.The main contributions include:(1)Focusing on the problem of mMTC devices with limited energy,this dissertation proposed a joint time and power optimization scheme to minimize the total energy consumption of uplink transmission in mMTC,with consider-ation of requirements in transmission time,energy,massive connectivity and uplink-dominated.The clustering scheme for mMTC devices was designed,where the group-head was dynamically selected according to the residual en-ergy and distance of MTC devices.The uplink cooperative NOMA scheme was proposed.In the transmission phase,the MTC devices in one cluster will share the same resource block and transmit their data to the group-head.In a coop-erative phase,the selected group-head transmit the received data and their data to BS by sharing the same resource block.Furthermore,the fractional trans-mit time allocation algorithm was formulated and the transmission power was obtained.Compared with the TDMA-based power allocation scheme,the pro-posed scheme reduces the average energy consumption of mMTC devices with 16.7%.(2)Focusing on the problem of mMTC devices with limited packet block-length,this dissertation proposed a joint subchannel and power resource al-location scheme to maximize the achievable effective energy efficiency(EE)of uplink transmission in mMTC,with consideration of requirements in lim-ited subchannel number and transmission power,massive connectivity,uplink-dominated and short packet transmission.First,based on the theory of finite blocklength coding,the residual interference model of imperfect successive in-terference cancellation was proposed and the achievable effective energy effi-ciency was defined.Then,the optimization problem for uplink short packet communication was modelled with constraints of the minimum transmission rate,subchannel and maximal transmission power.To solve the subchannel al-location problem,an efficient Q-learning algorithm was proposed based on the multi-agent Markov decision process.Furthermore,the optimal transmission power policy was obtained by approximating the achievable effective rate of uplink NOMA-based short packet communications.Compared with the joint subchannel and power allocation scheme adopted in OFDMA system,the pro-posed scheme improves the achievable effective EE of mMTC networks with 5.93%.(3)Focusing on the problem of mMTC devices with limited security ca-pabilities,this dissertation proposed a joint power and subchannel allocation scheme to maximize the secrecy capacity of uplink transmission in mMTC,with consideration of factors in limited subchannels,constrained transmission power and more vulnerabilities.Based on the physical layer security,the definition of secrecy capacity in uplink NOMA was given and the joint maximization prob-lem of uplink secrecy capacity with constraints of subchannel and transmission power was modelled.Particularly,the power allocation problem was modelled as a non-cooperative game with a distributed perspective,where each mMTC device selfishly optimizes its power allocation over multi-channels to maximize its own secrecy capacity.The existence of Nash Equilibrium(NE)was proved and a sufficient condition to ensure the uniqueness of NE is given.Moreover,the distributed power allocation and preference secrecy capacity maximum al-gorithms were proposed for power allocation and sub-channel allocation prob-lem,respectively.Simulation results show that the proposed scheme converges quickly.Compared with the scheme maximizing the secrecy capacity in up-link OFDMA system,the proposed scheme improves the secrecy capacity with 71%.(4)Focusing on the problem of mMTC devices with limited computing capabilities,this dissertation proposed a joint computation and communication resource allocation scheme to maximize the EE of secure computation offload-ing under constraints of limited radio and computation resources and require-ments in energy-efficient and secure computation offloading.Based on the physical layer security,the computation task secure offloading rate and energy efficiency were defined and the relay equipped with a Mobile Edge Comput-ing server assisting computing model was given.The optimization problem of computation task secure offloading energy efficiency was modelled with con-straints of delay,computation resource and radio resources.The corresponding computing resource allocation problem was modelled as the Knapsack problem with limited computation resource.Furthermore,the subchannels allocation problem was modelled as mMTC device-to-Subchannel matching.Exploiting difference of convex programming and successive convex approximation,the Dinkelbach-based EE optimization algorithm was formulated and the closed-form expression of power allocation for mMTC devices' on each subchannel was obtained.Simulation results show that the proposed scheme converges quickly.Compared with the scheme maximizing secure computation offload-ing rate in NOMA system,the proposed scheme improves the secure computa-tion offloading energy efficiency with 193.3%. |
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