November 29, 2021

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When to Use LTE Cat M for IoT Devices

Illustration: © IoT For All

What is Cat M?

LTE Cat M (also regarded as LTE-M) is a reduced ability huge location (LPWA) technology made to assist “Massive IoT,” i.e., hundreds of billions (!) of IoT gadgets, with cellular systems. Cat M largely refers to Cat M1, as Cat M2 adoption will take a number of more several years. 

LTE radio technology works by using “categories” to differentiate the capacity of every unit that attaches to an LTE community. For illustration, Cat 1 refers to equipment that can assistance download speeds up to 10 Mbps, while Cat 4 refers to devices that can use provider aggregation and assist download speeds up to 150 Mbps. Cat M1 refers to a class of units that work on a narrow 1.4 MHz channel with noticed obtain speeds in the 589 Kbps vary and 1.1 Mbps on the uplink (3GPP launch 14). The more mature Cat M modules have even lessen speeds (300 Kbps downlink / 375 Kbps uplink). 

Essential Added benefits of Cat M

There are critical advantages of Cat M for both the Cellular Community Operators (MNOs) and IoT builders. 

The main benefit to MNOs is that Cat M products function on a great deal scaled-down frequency bands (1.4 MHz). This allows them to pack more devices into the readily available spectrum at each mobile web site. A typical LTE cell internet site can assistance 10x the active Cat M equipment as opposed to lively standard LTE units.

The main profit to IoT builders is that Cat M modems use less electric power, enabling electric power-constrained equipment to run for months or yrs on a small battery with superior electricity-saving attributes. Cat M modems also boot up a lot quicker than Cat 1 modems from cold boot up, resulting in more quickly relationship times. Another important benefit is that Cat M modems tend to price considerably less than regular LTE modems, which will help in lessening the hardware price tag.   

Cat M Power-Preserving Features

Cat M delivers a few of power-conserving characteristics that enable IoT devices to work in lower power manner and reach extended battery life. 

Energy Conserving Method (PSM)

The PSM feature lets an IoT gadget to snooze for extended durations of time with no becoming woken up by network paging. Regular mobile devices actively transition amongst two modes – IDLE and Lively. When the system is not sending/acquiring site visitors, it goes IDLE, which positively has an effect on battery daily life. Suppose there are IP packets that have to have to be delivered to the system and the device’s community webpages. The machine have to reply to the web site and changeover to Lively mode to obtain the site visitors. This has an impression on IoT devices that are electricity-constrained. PSM allows these IoT equipment to negotiate an extended sleep period (hours or times) with the network and keep away from currently being paged during that rest cycle. If any website traffic arrives for the product all through the rest period, the traffic is buffered in the network (at minimum the very last 100 bytes) and shipped when the product turns into Energetic. 

Prolonged Discontinuous Reception (eDRX)

eDRX is a Cat M attribute that makes it possible for gadgets to sleep for lengthier durations of time and wake up at set intervals (also known as the eDRX cycle) to send out and receive site visitors. An eDRX-enabled gadget desires to negotiate the eDRX cycle with the network to avoid becoming paged by the community throughout these snooze durations. eDRX enables gadgets to use, e.g., a 10.24-next paging cycle alternatively of the 1.28-2nd paging cycle applied by standard LTE devices.

PSM and eDRX are complementary and can the two be employed by a Cat M unit. eDRX aids the device slumber a bit for a longer period, wake up at set intervals, and typically cuts down “chattiness” involving the system and the network. PSM will help the system sleep for substantially longer – hours or days.

Dependent on the use scenario, you may possibly have to have to use just eDRX, PSM, or both equally. Observe that not all Cat M networks guidance eDRX and PSM, yet most do these days. We expect the scenario to preserve increasing, with extra networks turning on these two vital characteristics to help ability-constrained equipment. 

Cat M Network Constraints

Whilst Cat M provides a large chance for electric power-constrained IoT products, there are some negatives as well. 

  • Cat M supplies very low bandwidth. Even nevertheless Cat M supports peak upstream speeds of all around 1 Mbps, our checks present that normal speeds are close to 300 Kbps.
  • Cat M support is not greatly accessible yet all around the earth. There are still numerous nations around the world where Cat M networks have not been released yet. Cat M protection is a subset of frequent LTE protection for the foreseeable long run. 
  • Gadgets utilizing Cat M may well get pushed off the community (preempted) in case of congestion. When a mobile internet site is congested, the community might pressure people Cat M products that have been related for a very long time to disconnect and re-attach at a later on time.

Cat M Use Instances

As ought to have turn out to be obvious by now, Cat M is greatest suited for IoT devices that are ability-constrained and trade reduced volume of targeted visitors with your software cloud. Use Situations contain asset tracking (e.g. squander administration), sensible meters (commonly any sensors that periodically report readings these kinds of as temperature, air high quality, and so forth.), and intelligent irrigation.

In standard, any product that operates on small batteries, which can not be changed or recharged quickly, reward drastically from making use of Cat M. 

LTE Cat 1 vs Cat M

If your IoT use situation involves keeping an “always-on” connection amongst your products and your application cloud, then an LTE Cat 1 (or Cat 3/4) modem is greater suited for your product. In an “always-on” manner, which prevents your devices from at any time sleeping, you are not getting advantage of any of the ability preserving functions supplied by Cat M, but at the similar time struggling with the constraints of getting on a small bandwidth connection and receiving pressured to disconnect when there is congestion at the nearby cell site to which you are related.

Typical LTE protection is much top-quality to Cat M protection. There are nations around the world where Cat M is not accessible, and even if offered, not all cell community functions in that place guidance Cat M. So, when you use Cat M for your IoT products, it routinely translates into less possibilities concerning out there connectivity companies.

If your device routinely transfers substantial quantities of facts to/from the community, a common LTE modem may well be a better alternative than a Cat M modem. The very low bandwidth presented by a Cat M connection means the unit has to remain on the web for a for a longer period interval of time to transfer the huge information.

If you are utilizing PPP (stage to stage protocol), some of the Cat M reduced electrical power modes are not supported. These modems avert coming into into the lower electrical power modes when PPP is applied. 

Vijay Devarapalli is a Principal Products Supervisor for Twilio IoT, accountable for the Twilio Dispersed IoT Cellular Core that drives Super SIM and other IoT cellular connectivity merchandise. Vijay is a telecom field veteran, owning intended and built 3G and LTE packet main and edge computing solutions, as well as systems for increasing radio network performance. He has also built significant contributions in the standards space, having authored 17 RFCs in the IETF and many contributions to 3GPP LTE specifications.