Cellular IoT alphabet soup
Internet of Things requires low complexity, low cost devices with long battery life times as well as good coverage for long communication range and penetration to reach the most challenging locations. Cellular networks cover the globe with secure, reliable mobile access based on standards: a good platform for IoT – with some adaptations made to meet the cost and battery life time requirements. This has been the motivation for us to research and develop the necessary tools. We’ve been one of the key drivers of the work in 3GPP where new technologies and device categories are now being standardized. These cellular IoT technologies will also be a key component of 5G.
MTC – Machine-Type Communications is the term used in 3GPP to refer to Machine-to-Machine (M2M) communications, that is, “machine” devices talking to each other through mobile networks or locally.
As you probably know, 3GPP uses the concept of “Releases” to refer to a stable set of specifications which can be used for implementation of features at a given point of time. User Equipment (UE) Category is one important term here. Categories are used to define general UE performance characteristics – for example, maximum supported data rate in uplink and downlink data channels, and to what extent different multi-antenna capabilities and modulation schemes are supported.
The latest stable release is Release 12, where the categories range from Category 0 up to Category 13. Release 13, which is being finalized at the moment, will include further UE Categories including at least the so-called "Cat-M1" intended for IoT devices.
Next we’ll open up a bit on the different categories targeting MTC and cellular IoT use. Some of the following features are already available and all will be supported in our networks.
Cat-1 – Category 1 – was included in the LTE specifications already in the beginning, Release 8. With a Cat-1 UE, it is possible to achieve 10 Mbps downlink and 5 Mbps uplink channel data rates. No MIMO is supported but the UE should still have 2 receiver antennas. Cat-1 has not been a relevant UE category for LTE-based mobile broadband services, as its performance is below the best 3G performance. Now it has become an attractive, early alternative for IoT applications over LTE, because it is already standardized. Cat-1 can also meet requirements of a wider range of MTC applications thus being a complementary solution to Cat-M1 and also to NB-IoT – which are explained further down.
Cat-0 – Category 0 – is one of the newest standardized categories from Release 12. Cat-0 UEs are intended for IoT use cases, and provide 1 Mbps data rates for both up- and downlink. Cat-0 UEs have reduced complexity by up to 50% compared to Cat-1; requirements include only one receiver antenna and support of half-duplex operation, providing ways for the manufacturers to significantly reduce the modem cost compared to more advanced UE categories.
Cat-M1 – Category M1 (which has informally also been referred to as Category M) – refers to the current work for Release 13, where further complexity reduction techniques on top of the ones for Cat-0 are being standardized at the moment. Up to 75-80% complexity reductions compared to Cat-1 have been indicated. The most important additional feature is the possibility to implement the UE transmitter and receiver parts with reduced bandwidth compared to normal LTE UEs operating with 20 MHz bandwidth. Cat-M1 UEs are able to operate anywhere within an LTE carrier with up to 20 MHz system bandwidth, but each Cat-M1 UE will operate with a maximum channel bandwidth limited to 1.4 MHz. A further helpful feature for many IoT use cases is coverage enhancements of more than 15 dB, which can, for example, be enabled to reach the UEs behind the thickest walls in the cell. Letter ‘M’ in the category name could be seen to stand for ‘machine’, if you will. As the 3GPP work on MTC will continue, we may see further ‘machine’ categories in the future (like Cat-M2 and so on).
LTE-M, or LTE MTC, is not as well defined a term as the others in this article. It was originally used in the work which resulted in Cat-0 UEs, but further work conducted in 3GPP on enhancing LTE capabilities for IoT has since been included. In general, LTE-M can be used to refer to all use of LTE for M2M and IoT and the evolution of LTE MTC features. This includes both Cat-0 and Cat-M1 (even Cat-1) UEs, and other features such as Power Saving Mode (PSM) and extended DRX cycles (eDRX).
NB-IoT stands for Narrowband IoT and is a new narrowband radio technology being standardized in 3GPP. It covers all the components sought after: low complexity, low power consumption and long range. Some key characteristics include 180 kHz bandwidth and uplink and downlink data rates of about 200 kbps with half-duplex operation. Although this is a new radio interface, NB-IoT deployments can be made "inband", so that existing resource blocks in the LTE carrier are used. The term is not to be confused with LTE-M, which refers to more direct use of LTE evolution for MTC and IoT use cases. NB-IoT is subject to a lot of standardization activities at the moment. The complexity reduction compared to Cat-1 is up to 90%.
Note that both Cat-M1 and NB-IoT have been designed so that they would be competitive with today’s cheap, GSM-based M2M modules. For example, for NB-IoT the initial module cost is expected to be less than $5.
EC-GSM-IoT, earlier referred to as EC-EGPRS, stands for Extended Coverage GSM for IoT. It includes the latest enhancements to the GSM and EGPRS standards to support better coverage and other IoT enhancements. EC-GSM-IoT supports 20 dB coverage improvements and can be deployed in the existing GSM networks.
LPWA stands for low power wide area, which means radio technologies providing low power consumption and wide area coverage. An extension of this is LPWAN for low power wide area networks. All of the above mentioned technologies fall under this term when coupled with the power saving techniques. Ericsson will bring complete cellular LPWA solutions into market this year.
eDRX and PSM are features that enable very long battery lifetimes, 10 years or more. eDRX means extended DRX cycles and provides UEs with longer sleeping periods between reading paging or control channels. PSM stands for Power Saving Mode, where the UE can save most power when there is no frequent need to communicate with the device. These are two examples of nice features for IoT, which 3GPP has also been working on other in the latest releases. eDRX and PSM are , however, not tied to the different categories or technologies above, but are applicable to them all!
Figure 1. Rough timeline for the cellular IoT features