Research On Key Technologies Of Uplink Transmission For 5G Internet Of Things

The fifth-generation(5G)mobile communication system is expected to enter the commercial phase by 2020,and millions of devices will connect to the network,which is called the“Internet of Everything(IoT)".Massive Machine-Type Communications(mMTC)is one of the three generic 5G services.Its features include massive uplink access,small data packets,strict device energy requirements and high latency tolerance.Ensuring efficient uplink access is a prerequisite for realizing IoT.However,when traditional communication technologies are applied in mMTC scenario,there are key problems:First,the frequency domain resource capacity for mMTC is limited,so it cannot meet the demand for bursting and synchronous uplink comm unications.Secondly,the uplink access technologies have consistently adhered to orthogonal multiple access(OMA)and grant-based transmission,which lead to problems such as insufficient connection resources and large proportion of scheduling signaling overhead in the face of bursty mMTC services.Therefore,this thesis designs effective uplink access and data transmission schemes,key technologies related to non-orthogonal multiple access(NOMA)are designed.The detailed research results are summarized as follows.· Aiming at the problem that the machine-type communication resources are unadequate for massive uplink synchronous access of 5G IoT,this thesis gives an energy-efficient and spectral-efficient uplink cooperative transmission scheme based on narrow-band NOMA.Firstly,a multi-subchannel NOMA-based uplink maximization problem is given.Then the mixed integer nonlinear programming(MINLP)problem is transformed into a convex optimization problem on a compact convex set.Finally,an uplink dynamic power allocation algorithm based on the branch and bound(BNB)principle is given,which finds the global optimal solution of the optimization problem.Compared with the traditional OMA solution and general 2-users NOMA scheme,the scheme has a double gain in system connection performance.· Traditional scheduling-based access schemes have large signaling overheads and high device energy consumption,which are not suitable for 5G bursty communications.This thesis gives a non-cooperative distributed NOMA-based grant-free transmission scheme.Firstly,a new distributed hierarchical NOMA virtual network fiamework is designed,then the closed expression of the system throughput is derived.To optimize the throughput,a simple and effective joint access control and NOMA layer selection algorithm is given.The numerical analysis and simulation results show that,compared with the random scheme,the scheme has grant gain in terms of expected connection throughput;compared with the scheduling-based OMA scheme,the connection has a gain of 3 1.25%,and the signaling overhead is only 0.0189%of OMA.·Aiming at solving the problem of system instability due to random access mechanism of distributed NOMA transmission,this thesis designs a stable transmission scheme based on distributed NOMA.Firstly,based on the Foster-Lyapunov criterion,the system instability of the distributed scheme based on fast retransmission mechanism is comprehensively analyzed.Then,a controlled transmission probability is given to ensure a stable system.Numerical analysis and simulation results show that when the system is overloaded,compared with the non-scheduled NOMA scheme without transmission probability control and OMA scheme considering transmission probability control,the expected system throughput is increased by 45.2%and 87.5%,respectively.