Research On Uncoordinated Non-orthogonal Multiple Access For Space-air-ground Internet Of Things Networks

The space-air-ground internet of things networks(SAG-IoTNs)is the development trend of Internet of Things technology.In the future,it can effectively support major application services such as navigation and positioning,ocean navigation,emergency rescue,space transportation,and so on.To realize the data transmission of massive machine type communication(mMTC)in SAG-IoTNs,in this paper,we study the uncoordinated non-orthogonal multiple access(NOMA)for SAG-IoTNs,and analyze the system outage probability and achievable throughput under the use of successive interference cancellation(SIC)and successive joint decoding(SJD).Then utilize superimposing pilot scheme to further enhance the ability of SAG-IoTNs in supporting mMTC services.Firstly,the typical communication system model of mMTC is established in SAG-IoTNs,and we study the transmission mechanism of uncoordinated NOMA protocol.On this basis,the expressions of the total number of colliding users and the total interference power in a single slot are analyzed,which lays a foundation for the derivation of subsequent performance.The derived total interference power expression can be extended to other fading model.The generalized form of Rayleigh fading is given and compared with the performance under the shadowed-Rician fading.Then,the system performance of the uncoordinated NOMA system using orthogonal pilot scheme is studied.The decoding process of SIC and SJD decoding methods and the performance calculation formulas of outage probability and achievable throughput are given.Under the condition of the shadowed-Rician fading,the expression of the outage probability and achievable throughput of the system under orthogonal pilot is derived.Monte Carlo simulation is used to verify the accuracy of the derived expression,and the performance of the two decoding methods in different device numbers,different device collision probabilities and different code rates are compared and simulated.The system performance under SJD is better than SIC when the number of access devices is high.Finally,superimposed pilot mechanism is employed to further increase the achievable throughput of the uncoordinated NOMA system.The signal model under superimposed pilot is designed,and the estimation error caused by the system using the superimposed pilot for channel estimation is quantized.On this basis,the system performance under the two decoding methods is re-derived and simulated.The simulation compares the performance of the system usingsuperimposed pilot and orthogonal pilot,and analyzes the selection of the system decoding method under the condition of different access devices and different code rates.It is verified that the superimposed pilot can be used in high access requirement which can significantly increases the system achievable throughput.