Research On The Non-orthogonal Multiple Access In Hybrid Satellite Terrestrial Networks

By combing the terrestrial network and the satellite network,an important network architecture,referred as hybrid satellite terrestrial networks,has been proposed and expected to provide high quality of service for users and efficient use of spectrum resources of satellites and terrestrial networks.Although the orthogonal multiple access(OMA)scheme used in the hybrid satellite terrestrial networks can effectively reduce interference between users,it does restrict the improvement of resource utilization efficiency and the number of served users since only one user is served at any time/frequency slot.Having the ability to provide higher resource utilization efficiency and user fairing than that of OMA scheme,power-domain non-orthogonal multiple access(NOMA)has recently received significant attentions from research and industry.The key idea of this scheme is to superpose multiple signals in the power domain at the transmitter and use successive interference cancellation(SIC)at the receiver,and thus,the NOMA scheme can serve multiple users simultaneously on the same time/frequency block and provides an improved resource utilization efficiency and user fairing at the cost of reasonable increased complexity.However,compared to terrestrial networks,the channel fading of satellite networks is more complicated,which brings challenges to introduce the NOMA scheme into the hybrid satellite terrestrial networks.In addition,the diversity of scenes and the complex environment of the hybrid satellite terrestrial networks are another difficult problem for accurately evaluating and analyzing the relevant performance of the NOMA based hybrid satellite terrestrial networks.After verifying the feasibility of applying the NOMA scheme in satellite communication networks,this thesis focuses on the resource allocation and performance analysis of the application scenarios.The specific work includes:1.The methods of improving user fairness and resource utilization in the NOMA based downlink and uplink satellite networks are analyzed.Firstly,in the downlink scenario,we obtain the power allocation coefficients by maximizing the sum rate while meeting the predefined target rates of each NOMA user.Then,based on that power allocation factor,the ergodic capacity and energy efficiency of the proposed system,as well as the outage probability and average symbol error rate of each NOMA user are derived.Secondly,in the uplink communication scenario,we analyze the relationship between users' SINRs and antenna pointing error,the location information of the user,and the inaccurate channel estimation.Based on these derivations,we derive the analytical expression for the achievable ergodic capacity of the considered network.The simulation results show that compared with OMA technology,NOMA based downlink satellite communication system can obtain better system throughput and energy efficiency,the NOMA based uplink satellite network has greater capacity advantage in system capacity and key parameters,such as the length of training data,user locations,fading configuration,and transmission power have significant influence on the performance of considered system.2.By applying the NOMA scheme in hybrid satellite terrestrial networks,the methods of improving resource utilization efficiency in the scenario where relay node exists and users' line-of-sight links are unavailable and scenario where relay node does not exist are studied,models of NOMA based hybrid satellite terrestrial network and cooperative NOMA based hybrid satellite terrestrial network are proposed.Firstly,assuming the relay node adopted an amplify and forward strategy,we investigate and derive the closed-form expressions for the outage performance of the considered NOMA users in the NOMA based hybrid satellite terrestrial network.Secondly,since that a user with better channel condition in the NOMA scheme can decode the information for user with worse channel condition,we pair users with different direct link qualities as a NOMA group and provide the model of the cooperative NOMA based hybrid satellite terrestrial network,the relationships between the outage probability and the ergodic capacity of the considered system and the power allocation factor are analyzed.Simulation results show that if selecting an appropriate power allocation factor,the communication reliabilities of NOMA users in the NOMA based hybrid satellite terrestrial network are better than that with the OMA technology,which reveals that the introduction of NOMA technology can further improve the resource utilization.Moreover,we also can find from the simulation results that,in the cooperative NOMA based hybrid satellite terrestrial network,under the low transmit power configuration,the proposed solution can achieve the dual purpose of increasing the number of users accessing the network and improving the user performance of the link condition.3.By applying the NOMA scheme in hybrid satellite terrestrial networks,the methods of enhancing resource utilization efficiency for cognitive network and quality of communication for deep fading user are investigated,models of NOMA based hybrid satellite terrestrial cognitive networks and NOMA based cognitive satellite terrestrial cooperative networks are proposed.Firstly,by jointly considering the constricts of limited transmission power of cognitive network and limited interference can suffered at the primary network,we analyze the relationship between the performance of the considered network and power allocation coefficient.Secondly,in the NOMA based cognitive satellite terrestrial cooperative network,a cooperative relay transmission scheme based on NOMA technology is proposed.Specially,on one hand,the source node with the proposed strategy can utilize NOMA technology to broadcast information and adaptively adjust power allocation factor according to the channel characteristics to maximize the transmission rate of the deep fading cognitive user.On the other hand,the transmission power of relay node with decode-and-forward is reasonably set by relay-source power ratio parameter.Simulation results show that compared with OMA technology,with appropriate power allocation factor,the proposed NOMA based hybrid satellite terrestrial cognitive network can achieve higher system capacity,the transmission rate of the NOMA based cognitive satellite terrestrial cooperative network will improve about 13.7% within a certain limit of relay-source power ratio.Moreover,the total power of the NOMA based cognitive satellite terrestrial cooperative network will reduce 30% in the same transmission rate,thus minimize the power consumption.