Abstract

Sensors enabled Internet of things (IoT) has become an integral part of the modern, digital and connected ecosystem. Narrowband IoT (NB-IoT) technology is one of its economical versions preferable when low power and resource limited sensors based applications are considered. One of the major characteristics of NB-IoT technology is its offer of reliable coverage enhancement (CE) which is achieved by repeating the transmission of signals. This repeated transmission of the same signal challenges power saving in low complexity NB-IoT devices. Additionally, the NB-IoT devices are expected to suffer from congestion due to simultaneous random access procedures (RAPs) from an enormous number of devices. Multiple RAP reattempts would further reduce the power saving in NB-IoT devices. We propose a novel power efficient RAP (PE-RAP) for reducing power consumption of NB-IoT devices in a highly congested environment. The existing RAP do not differentiate the failures due to poor channel conditions or due to collision. After the RAP failure either due to collision or poor channel, the devices can apply power ramping or can transit to a higher CE level with higher repetition configuration. In the proposed PE-RAP, the NB-IoT devices can re-ascertain the channel conditions after an RAP attempt failure such that the impediments due to poor channel are reduced. The power increments and repetition enhancements are applied only when necessary. We probabilistically obtain the chances of RAP reattempts. Subsequently, we evaluate the average power consumption by devices in different CE levels for different repetition configurations. We validate our analysis by simulation studies.

Highlights

  • The Internet of things (IoT) has been gaining popularity for its smart decision making capabilities using data acquired through several sensors

  • We focus on manifesting power saving in the random access procedure (RAP)

  • A particular device that fails an RAP attempt checks the channel status for a reattempt and selects the coverage enhancement (CE) level state based on channel condition

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Summary

Introduction

The Internet of things (IoT) has been gaining popularity for its smart decision making capabilities using data acquired through several sensors. The narrowband Internet-of things (NB-IoT) is the standardized form of the IoT that is compatible with the legacy Long Term Evolution(LTE) mobile networks It is especially attractive for low energy sensor based applications that require wireless data transmission using the backbone network. The spectral resources, but the power consumption of the NB-IoT devices would be affected by the increase in the number of repetitions. We believe that it is important to address the power saving challenge when a congested RAP is considered together with the transmission repetition characteristics of NB-IoT devices. In a massively connected NB-IoT environment where collisions are umpteen, the power ramping and sequential CE level upgradations would sharply degrade the performance of RAP in terms of power consumption.

Literature Survey Random Access in NB-IOT
NPRACH Fundamentals
12 Subcarriers
Related Work
Average Power Consumption in PE-RAP
ACB Factor and Collision Probability
Average Power Consumption in Existing NB-IoT RAP
If the Device Starts RAP in CE0
If the Device Starts RAP in CE1
Performance Evaluations
Simulation Results
Conclusions

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