| With the development of technology,Internet of Things(IoT)has achieved a rapid progress in recent ten years.Massive IoT,which is an important part of IoT,involving many applications such as remote meter reading,intelligent city,and remote sensing,is more and more popular and still in fast development.As an important foundation to realize massive IoT,how to connect the ever growing IoT devices to the core network becomes a big challenge.Cellular communications technology with a central control structure,utilizing licensed spectrum,has advantages in interference management,spectral efficiency,quality of service(QoS),which makes it a candidate of the massive IoT wireless access technology.Cellular network aims on human-type communications(HTC),whose devices are high cost as well as high power consumption whereas machine-type communications(MTC)used for massive IoT has some requirements such as low cost,wide coverage,high system capacity,and low power consumption.It is thus not appropriate to make traditional cellular system for HTC as the massive IoT wireless access system directly.When implement the massive IoT wireless access system in cellular,the corresponding improvement and design on account of the above requirements for massive IoT are necessary.This dissertation focuses on the design and implementation of the massive IoT wireless access technology.The main content and contributions are as follows.(1)Taking LTE network as an example,the techniques for the extension from the existing cellular system to MTC are studied.These techniques can meet the requirements of coverage extension with transmission time as short as possible under the premise of cost reduction for MTC device.First,this thesis researches the reduction in devices’ complexity due to the MTC low cost requirement and the deficit in link-budget due to the coverage extension requirement along with corresponding influence to performance and design.After a comprehensive comparison of all the formats of control channel,distribution enhanced physical downlink control channel(EPDCCH)is selected as the base format of the MTC control channel.These techniques listed following are then adopted to close the deficit of link-budget due to the coverage extension:1)repeating the base signal across the time,which increases total signal energy and time diversity;2)acquiring frequency diversity through frequency hopping,which compensates for the lost in frequency diversity due to the narrowband transmission;3)implementing joint channel estimation by the reference signals of the neighboring resource blocks in frequency and time domain,which increases the accuracy of the channel estimation so as to improve the combination efficiency of the repetition.4)Utilizing orthogonal precoding to acquire spatial diversity,which compensates for the spatial diversity loss due to the single-antenna receiver.The developed techniques are extended to other LTE physical channels(e.g.,uplink control channel and random access channel),which can also achieve the requirement of coverage extension and low power consumption at the same time.The effectiveness of the proposed techniques is verified through simulations.(2)The transmission bandwidth decision for massive IoT wireless access technology is studied.First,the main massive IoT wireless access technologies,involving the technologies in unlicensed band(e.g.,SIGFOX UNB and LoRa)and licensed band(e.g.,LTE-M and NB-IoT)are widely researched.These technologies all utilize the narrow-band transmission mechanism as a leverage to achieve three fundamental goals,i.e.,high system capacity,deep coverage,as well as long battery life.The thesis gives an analysis for capacity extension and coverage extension and then introduces an "effective bandwidth" concept that ties these three goals.In system design,the effective bandwidth is determined for a given target coverage.The device transmission bandwidth should be configured in the neighbor of the effective bandwidth such that the bandwidth saved can be used to accommodate other devices without significantly increasing the transmission duration.Effective bandwidth concept provides important reference for the bandwidth selection in system design,which has theoretical significance and practical value.(3)Taking NB-IoT as an example,two primary synchronization signal detection techniques,i.e.,correlation detection and differential detection,are analyzed.The thesis then introduces two important factors,Rx SNR factor and frequency offset factor.It can be shown that when the Rx SNR factor prevails,the correlation detector outperforms the differential detector and vice versa.Based on these two factors,the operating region can be divided into two parts.The receiver can choose the proper detector according to its location in the operating region determined by its receive SNR and frequency offset and then the detection performance is improved.Finally,the thesis derives a new frequency offset resilient synchronization signal.It can be shown that this form of signal has the capability of converting the frequency offset uncertainty into a timing uncertainty so as to avoid a tremendous loss in detection energy due to the large frequency offset.Because of this admirable property,it is feasible to perform correlation detection,which is free from a considerable noise amplify effect caused by the differential detector in low SNR scenario.Through simulation,this thesis verifies the favorable detection performance via comparison with the synchronization signal in NB-IoT.(4)The device discovery techniques in cellular network are studied,which provides the foundation to solve the communication issues between base station and massive IoT devices in deep coverage through device-to-device(D2D)communications in cellular network.This thesis researches D2D device discovery techniques in traditional ad hoc network,which includes IrDA,Bluetooth,WiFi Direct,WiFi ad hoc and FlashlinQ.B’ased on this,the challenge and design criterion of device discovery in cellular network are then discussed.Finally,a detailed device discovery scheme in cellular network which combines a signature-based scheme and a packet-based scheme is proposed.This proposed device discovery scheme is superior in reducing implementation complexity,improving energy efficiency and minimizing dependence on the network.This scheme shows a good coexistence with cellular network architecture and has commendably implementation value.(5)First,the dominating applications in wireless energy IoT is analyzed and the licensed spectrum allocated specifically for power industry in 230 MHz is researched.This thesis then proposes a concrete design of system architecture,frame structure,and the primary physical channels for wireless energy IoT with corresponding simulation results.This design is an application example for massive IoT wireless access system design,which meets the requirement of wireless energy IoT such as high reliability,wide coverage,and low power consumption. |
