Study On The Symbol Error Rate Performance Of The Hybrid Satellite-terrestrial Relay Network Based On Fading Channel

The Hybrid Satellite-Terrestrial Relay Network(HSTRN)can effectively improve the signal transmission quality of satellite communications,expand the coverage of satellite signals,improve the stability of communication links,and achieve the integration of satellite networks and ground networks.It will play an important role in the future global Internet construction.However,the signal sent by satellite to the relay is still affected by shadow fading,and the signal transmitted from the relay to the destination is also subject to multipath fading due to factors such as obstacle occlusion and refraction,which reduce the signal quality received by the destination.Therefore,it is necessary to pre-evaluate the performance of HSTRN based on the fading channel.The existing researches mainly focus on the impact of fading channels on the performance indicators of HSTRN system,such as outage probability and ergodic capacity,while pay less attention to the symbol error rate and mostly considers the single user scenario.With the rapid growth of the number of Internet terminals,HSTRN system will face the access needs of a large number of users in the future.At present,it is urgent to analyze the symbol error rate for the scenario of multi-user access to the HSTRN system,so that the performance of the HSTRN system can be more comprehensively evaluated.In this paper,the symbol error rate performance of multi-user HSTRN system is theoretically analyzed,and the closed-form expressiones of the average SER are derived.The influence of the number of users,the severity of channel fading,channel noise,relaying protocol,signal modulation mode,hardware impairments and other factors on the SER are taken into account.The system performance is optimized through opportunistic scheduling scheme,maximum ratio combining,and non-orthogonal multiple access.It provides reference for future HSTRN system engineering practice.The main contributions of this paper includes:1.A multi-user HSTRN employing amplify-and-forward relay is constructed,and opportunistic scheduling is used to select users with the best channel quality to establish communication.Considering the shadow effect and multipath effect of the relay system,it is assumed that the satellite relay link follows the shadow Rician distribution,and the relayuser links experience Nakagami-m fading.The closed-form expressions of the average SER for fixed gain relay and variable gain relay is derived by using moment generating function,and the asymptotic expressions of the average SER and the diversity order under the condition of high signal-to-noise ratio are derived.Finally,the derived expressions are simulated by computer.The simulation results show the difference of SER performance between HSTRN using two types of AF protocols,and analyze the impact of the number of users,relay gain and the severity of shadow fading on the average SER of the system.2.A multi-user multi-relay HSTRN with fixed gain amplify-and-forward relay is constructed,and the relay and user with the best channel quality are selected to establish communication.Based on the double opportunistic scheduling scheme,the closed-form expressions of the average SER in multi-relay multi-user HSTRN and the asymptotic expression under high SNR are derived.The simulation results show that the SER performance of multi-user multi relay HSTRN with double opportunistic scheduling scheme is significantly improved,compared with single relay and single user HSTRN systems.3.Based on non-orthogonal multiple access(NOMA)technology,a HSTRN system model considering the hardware impairments of nodes is constructed.The system adopts the relay opportunity scheduling scheme to select the optimal relay with the maximum instantaneous SNR,and adopts the maximum ratio combining technique at the users to achieve the combination of LOS signals from satellites and forwarding signals from relays.According to this model,the closed-form expressions of average SER for near user and far user are derived,and the correctness of the expressions are verified by computer simulation.The simulation results show that the average SER of the far user always reaches a saturation value independent of the channel conditions with the increase of the average SNR,and the average SER of the near user is more sensitive to hardware impairments than the average SER of the far user.