Power Consumption Modeling And Optimization For NB-IoT Extended Discontinuous Reception Mechanism

Narrowband Internet of Things(NB-IoT)is a Low Power Wide Area(LPWA)technology proposed by 3GPP for low-rate of Internet of Things application scenario such as smart meters and environment monitoring,facing with challenges as massive connectivity,ultra-low power consumption and wide-area coverage.One of the most important requirements for NB-IoT system is to improve power efficiency of NB-IoT terminals to up to ten years battery life with battery capacity of 5 W?h(Watt-hours).Compared with other existing LPWA technologies(such as LoRa),NB-IoT uses authorized frequency bands to coexist with existing networks,providing better communication service quality in deep coverage and high-density connection scenarios,but battery life is sacrificed accordingly.In order to extend the service life of NB-IoT terminal battery,3GPP proposes extended Discontinuous Reception(eDRX)mechanism,and increases the PSM(Power Saving Mode)state with lower power consumption.According to characteristics of NB-IoT services and eDRX mechanism,the following research work is carried out on the low power consumption problem of NB-IoT:(1)According to the application scenario characteristics and service transmission interval of the NB-IoT services,NB-IoT services can be classified into three categories: the Mobile Autonomous Reporting Periodic Reports(MAR-P),the Mobile Autonomous Reporting Exception Reports(MAR-E)and Software Upgrade/Reconfiguration(SUR)services.And this paper establishes Markov models of the state variable with eDRX and PSM mechanisms for MAR-P,MAR-E and SUR services respectively and the corresponding power consumption and delay analyze.Besides,the “connected state” is divided into “random access state” and “data transceiving state” to assess the additional energy consumption casued by the collision of massive concurrent users in the network.(2)In view of the highest occurrence frequency of MAR-P service,this paper focuses on the battery life and service delay when terminal carries MAR-P service.To ensure the success probability of the transmission of services in the NB-IoT terminal synchronously entering the network and in the harsh communication environment,this paper proposes a optimization model to maximaize the battery life by limiting the minium probability of success of random access and data transmission.The success probability of single service transmission is defined as a communication performance indicator to observe the impact of eDRX and PSM mechanism on MAR-P service.The simulation results show that the battery life can be extended by reducing the maximum number of random access requests and the maximum number of data retransmissions,which can reduce the service transmission success probability and cause the increase of delay.The optimization design proposed in this paper to maximize battery life can maintain the service success rate at a high level in different PSM periods(ie different service transmission intervals)and different communication environments to meet communication requirements.(3)In the environment monitoring application scenario,the energy harvesting mechanism can be introduced to the NB-IoT terminals to extend battery life.Based on the characteristics of periodic reception and transmission of eDRX,the energy queue and data queue are established for the NB-IoT terminal with energy harvesting mechanism.And the energy supply probability and average delay are defined to analyze the constraints of energy harvesting performance and data transceiving performance of the terminal.NB-IoT terminals in the environmental monitoring application scenario is facing with MAR-E and MAR-P services coexistence and 3GPP have proposed a limitaion of delay of 10 seconds for MAR-E service.Therefore,an optimized design model with maximum energy supply rate and minimized average delay is proposed for the NB-IoT terminal with energy harvesting mechanism to make the optimized energy supply rate and average time delay respectively satisfy the system of energy acquisition and data transceiver mechanism performance requirements.The simulation results show that the average delay can reduce by reducing the eDRX cycle,which can reduce energy supply rate.In this paper,the optimization design of eDRX cycle proposed for NB-IoT energy harvesting terminals can make the optimized energy supply rate and average delay meet the performance requirements of the system for energy harvesting mechanism and data transmission and reception mechanism.