By Asish Jain, Application Engineer, Keysight Technologies India Pvt. Ltd.
The “internet of things” (IoT) is currently a buzzword in the technology industry. Depending on the industry’s area of work, this word has variants such as the internet of everything and the internet of medical things. IoT devices and services are slated to bring about the next revolution in the cellular industry.
IoT requirements and 3GPP approach
The key requirements of IoT devices are low device cost, low energy consumption, low deployment cost, ubiquitous connectivity and support for massive scale of connections. To address these requirements, 3GPP Release 12 introduced a new user equipment (UE) category called Category 0.
The following two variations in existing long term evolution (LTE) technology are being discussed for Release 13 to address practical challenges and meet the key requirements of IoT devices:
- NarrowBand IoT (NB-IoT): This is being referred to as a clean slate solution, which will operate in the following modes – “stand-alone operation” utilising, for example, the spectrum currently being used by GSM EDGE radio access network systems as a replacement of one or more GSM carriers; “guard band operation” utilising the unused resource blocks within an LTE carrier’s guard-band; and “in-band operation” utilising resource blocks within a normal LTE carrier. NB-IoT will support the following radio specifications – UE uplink (UL) and downlink (DL) bandwidth of 180 kHz, OFDMA on DL and FDMA with GMSK and SC-FDMA are being considered for UL.
- LTE-M: This new category is being discussed in Release 13 as an improvement over the Cat 0 device introduced in Release 12. It will help meet the enhanced coverage, low complexity and low energy consumption requirements of cellular IoT. The objective of LTE-M is to enable machine-to-machine communication by supporting all LTE-duplex modes with reduced bandwidth of 1.4 MHz, both in UL and DL, and reduced maximum transmit power to 20 dBm.
In addition to the above two proposed standards, GSMA has proposed a complementary standard called extended coverage GSM to be discussed in 3GPP Release 13. The aim of introducing these new standards and definitions is to make cellular IoT a success by developing low power wide area solutions and using licensed spectrum in the most optimised and efficient way, which will help meet the requirement of diverse IoT applications.
3GPP Release 13 and cellular IoT: Simplification, efficiency and ubiquity
Simplification in design: Reduction in cost
The half-duplex frequency division duplex mode of operation eliminates the need for a duplex filter through time multiplexing. Further, Cat 0 devices use a single radio frequency (RF) chain, which means a single receiver path unlike other LTE devices where 2×2 multiple-input and multiple-output paths are mandatory. Moreover, peak data rates of 1 Mbps on the uplink and downlink and buffer of 20 kB further reduce the processing complexity and memory requirements. Together, these factors will bring down the overall cost of cellular IoT devices. 3GPP Release 13 specifications for cellular IoT viz LTE-M and NB-IOT will further bring down device costs. Bandwidth reduction to 1.4 MHz or 180 kHz in the case of NB-IOT will simplify the RF design to narrowband architecture. The maximum transmit power specification of 20 dBm will be met by an integrated power amplifier on a single chip. Some other aspects that could bring down cellular IoT device costs are single radio access technology, single band RF architecture and single chip solutions.
Efficiency in power usage: Lower energy use
A new power saving mode (PSM) was introduced in Release 12 to address the power consumption challenge. This new low power consumption process works by moving the device from idle mode to PSM mode where the device, though registered on the network, does not wake up for checking paging information. Another power saving proposal for Release 13 is to standardise enhanced discontinuous reception (eDRX). As a result, the devices will have flexible DRX cycles higher than 2.56 seconds depending on data delay tolerance.
Ubiquitous coverage: Always connected
To meet network coverage targets, Release 13 specifications will enable LTE-M to provide 15 dB of coverage improvement and NB-IOT with 20 dB of coverage improvement with respect to nominal coverage. The coverage challenges can be overcome either by simplifying PHICH (Physical Hybrid-ARQ Indicator Channel) and PCFICH (Physical Control Format Indicator Channel) functionality or by finding an alternative mechanism to PHICH and PCFICH functionality so that coverage limited UE is not constrained by PHICH and PCFICH physical channels.
Can cellular IoT deliver as promised?
In addition to the technical aspects, the success of cellular IoT depends on efficient business models and services provided by network operators to meet the application-specific demands.
