| With the rapid development of Cellular Internet of Things(C-IoT),intelligence and automation have become the critical feature of 5G mobile communication systems.In CIoT,billions of devices can connect to the cellular network through a BS(Base Station).The most widely used of these mass devices are MTCDs(Machine Type Communication Devices).In fact,many recent predictions have predicted that:(1)over 50 billion MTC(Machine Type Communication)devices will be deployed in the network by 2020;(2)MTC traffic in the network will increase by 24 times by 2020 compared to 2012;(3)Compared with the current mobile communication network,the volume of future network traffic will be 1000 times.MTC plays a decisive role In C-IoT.In fact,MTC is not a completely new concept.MTC is just an extension of their existing research for people working on WSN(Wireless Sensor Network)research.On the one hand,MTC has similar features as WSN,such as device power consumption in both MTC and WSN,which are the focuses of both.On the other hand,there are some differences between MTC and WSN.For example,in remote smart medical scenarios and smart home scenarios,there are many downlink data transmission in the network.Downlink data transmission in these scenarios has high demands on data rates and network system throughput,and the C-IoT must be able to meet these requirements.Of course,there still exists HTC(Human Type Communication)in C-IoT,a scenario we call this a hybrid business scenario.In hybrid business scenario,the massive MTC business will inevitably have a serious impact on the traditional HTC business,especially in the random access process.Therefore,optimizing the random access is a significant issue.In order to solve the above practical problems in C-IoT,we take C-IoT as the main research object and take MTC communication as an entry point to extract three different aspects of the scientific issues and conduct a series of research on MTC communication performance optimization.The research results obtained are as follows:1)Different from the previous classification of service types(MTC service / HTC service),in C-IoT,this paper takes the sensitivity of the service to the delay as a criterion,and divides the priority of the service.In order to guarantee the access performance of the high priority service,we focus on the static preamble allocation strategy for random access and propose a scalable preamble allocation strategy with reservation.Based on our proposed strategy,we propose a preamble reuse-based random access optimization scheme.The scheme considers the priority differences at the initial time and distinguishes the priority of the services by reused preamble.It does not need to introduce extra signaling,which is very reasonable and feasible.The simulation results show that the proposed scheme also ensures a successful access of high-priority services and avoids redundant collision retransmission and random back off.2)In C-IoT,there exists a large amount of downlink data distribution for massive MTCDs.We design a D2D-aided C-IoT architecture using D2D(Device to Device)communication technology in combination with the current C-IoT architecture.Based on this architecture,we design a “D2D-aided data distribution flow” and build an optimization model aimed at maximizing system throughput based on the data distribution flow.Through analyzing the problem,we propose a greedy algorithm based on the minimum distance by using distance as a measure.On this basis,we introduce the MTCD degree of intimacy and propose a greedy algorithm based on the maximum degree of intimacy.The simulation results show that the proposed algorithm can minimize the BS load and improve the overall network capacity with ensuring the fairness of the system.3)Third Generation Partnership Project(3GPP)proposed a DRX(Discontinuous Reception)mechanism to allow the device to receive data in a specific time slot and to turn off the wireless module in the remaining time slots to save energy.Based on the DRX mechanism,we design a power-saving mechanism with a coercive sleep mode.In the proposed mechanism,a metric,,was introduced to measure the number of packets and to control the transfer of state in conjunction with the inactivity timer in the DRX mechanism.We use the semi-Markov process to model the proposed mechanism and design the power saving factor and wake-up latency in the model.Through theoretical simulation and system simulation,we obtain a series of numerical results.Numerical results show that the proposed mechanism can achieve better power saving efficiency,which is undoubtedly a good research result for MTC that has higher requirements on power consumption. |
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