Research On Transmission Technology And Fading Performance Of Hardware-constrained Cooperative Communication Systems

Cooperative communication systems can not only improve the transmission performance of the system effectively,but also obtain extra diversity gain without increasing the hardware costs.However,in practice,radio frequency front-ends suffer from several types of impairments,such as the high-power amplifier nonlinearity,in-phase/quadrature-phase imbalance,phase noise and quantization error.This can be explained by the fact that relays are prone to low-cost and lower power efficiency nodes.Although the performance loss caused by these effects can be partly mitigated by means of compensation and calibration algorithms,the residual hardware impairments are always existing.In this thesis,the fading performance of hardware constrained cooperative communication systems is investigated,and the impact of hardware impairments on cooperative communication systems under different scenarios is also analyzed.Additionally,to improve the performance of hardware constrained cooperative communication systems,we focus on NOMA,SWIPT and relay selection.The main contributions of this thesis are summarized as follows:First,the outage performance of cooperative relay NOMA systems under the condition of ideal hardware is analyzed,where the locations of randomly distributed users are modeled by stochastic geometry.Then,the wireless channel model between the users and relay is established.The performance of uplink and downlink NOMA communication links and whole communication systems is evaluated under the conditions of perfect SIC and imperfect SIC,and the corresponding expressions of outage probability are derived.Then,considering the statistical characteristics of different types of hardware impairments,a mathematical characteristic model is established.Aiming at the problem of hardware impairments,a generalized channel model is established.The system performance under two scenarios of direct communication path and non-direct communication path between the source node and the destination node is studied,and the influence of system parameters on the system performance is analyzed.The results show that hardware impairments have a deleterious impact on system performance.Moreover,NOMA technology is introduced into the hardware constrained cooperative relay systems in order to further improve user fairness,network capacity and reliability.The performance of cooperative NOMA communication systems with both hardware impairments and channel estimation error is investigated,the outage probability and ergodic capacity expressions are derived under the cooperative NOMA and non-cooperative NOMA scenarios.In the cooperative NOMA scenario,the destination node selects and combines the received signals from each branch,and then brings the array gain of the spatial diversity of the received signals.The results show that the performance of cooperative NOMA systems is better than that of non-cooperative NOMA systems.Finally,the single-relay system is extended to multi-relay system,and a partial relay selection algorithm based on hardware impairments and imperfect CSI is proposed.A cooperative NOMA SWIPT system,consisting of a base station,multiple energy harvest relays and two NOMA paired users,is studied,in which the relays harvest energy from the received RF signals.In this thesis,the performance of a non-ideal cooperative SWIPT NOMA system is analyzed in terms of outage probability,diversity gain,ergodic capacity and energy efficiency.