Cellular IoT Fundamentals

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LTE-M and NB-IoT

Important

When progressing through the lessons, make sure to complete all the topics, before taking a quiz. The quiz is considered to be the last step in lesson completion. If the lesson is completed in a different order, make sure to re-take the quiz to mark the lesson as completed.

Cellular network architecture

Before we can discuss the cellular network technologies used in this course, it is important to understand how a cellular network is formed. Note that this section only contains a simplified explanation, but the terms introduced here are very relevant in further reading about cellular technology.

The first part of the cellular network is the device (called UE) communicating with the cellular tower (called eNB). The UE sends uplink (UL) signals to the eNB and receives downlink (DL) signals from the eNB.

Definition

UE (User equipment): This is the device used by an end-user to communicate over the cellular network.

eNB (Evolved Node B): The hardware connected to the cellular network that communicates directly with the UE’s. These are commonly referred to as “base stations” or “cell towers”.

UL (Uplink): Signal sent from the UE to the eNB.

DL (Downlink): Signal coming from the eNB to the UE.

This part of the network is referred to as E-UTRAN (Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network). Beyond the connection between the UE and the eNB, the E-UTRAN communicates with the Evolved Packet Core (EPC), which then enables communication with the internet. The EPC is composed of several functional entities, most notably the Mobility Management Entity (MME), which manages the connections with the UE’s, and the PDN Gateway (P-GW), which is a gateway to the internet.

Definition

EPC (Evolved Packet Core): The framework that provides the connection to the rest of the internet in cellular networks. It is composed of several functional entities.

E-UTRAN (Evolved UMTS Terrestrial Radio Access Network): The wireless communication technology used in cellular networks.

The need for new cellular technologies

Until recently, things like better quality phone calls and faster internet connections has been the main driver behind the advance of cellular technologies. But with the rise of IoT, a new profile of applications has emerged, giving cellular technologies a new direction for growth. This new applications category is called Machine-type Communications (MTC).

MTC differs from human-generated traffic in both nature and requirements. Consider two people having a phone call: data packets are sent very frequently and in long bursts, requiring very low latency, and traffic is usually symmetric between uplink and downlink. On the other hand, for MTC, data packets are shorter, some delays might be acceptable, traffic is mostly uplink, meaning most signals are sent from the UE, and the number of connected devices per eNB is massive. It is clear that MTC requires different technology than what standard LTE can offer.

3GPP Release 13

To meet these new MTC requirements, 3GPP Release 13 introduced the two cellular technologies: LTE Cat M1 and LTE Cat NB1, also known as LTE-M and Narrowband IoT (NB-IoT), respectively.

The 3GPP (3rd Generation Partnership Project) is the body responsible for developing cellular technologies, and their standards are structured as Releases. This is similar to how the Bluetooth Special Interest Group (SIG) releases versions of the Bluetooth standard, where Bluetooth 4.0 includes the first specification of Bluetooth Low Energy.

Although both technologies were developed with the MTC use-case in mind, there are some key differences that need to be understood before selecting which one to use in your application.

Technical comparison

Choosing the most appropriate cellular IoT technology is key to creating a stable, future-proof, and cost-effective solution. LTE-M and NB-IoT, despite both being LTE-based IoT enablers, have some differences which when understood correctly and taken into account can save resources and time. Let’s discuss some key parameters and see how LTE-M and NB-IoT compare.

Note

NB-IoT encompasses two technologies LTE Cat-NB1 in 3GPP release 13, and LTE Cat-NB2 in release 14. Nordic’s nRF91x1 Series SiP’s all support LTE Cat-NB2, while the nRF9160 does not.

The comparison table shows both NB-IoT technologies, LTE Cat-NB1 is shown in parentheses where they differ.

The table below shows a comparison between the key features of both technologies.

LTE-MNB-IoT
3GPPRelease 14Release 14 (Release 13)
Also known as“eMTC”, “LTE Cat-M1”“LTE Cat-NB2” (“LTE Cat-NB1”)
Bandwidth1.4 MHz180 kHz
Maximum data rate (DL/UL)300/375 kbps
159/127 kbps (30/60 kbps)
Typical range estimate11 km15 km
Latency50-100 ms1.5-10 s
Mobility/
cell reselection		SupportedSupported
RoamingSupportedLimited
Deployment density estimateUp to 50,000 devices per eNBUp to 50,000 devices per eNB
Battery lifetime estimateUp to 10 yearsUp to 10 years
LTE-M and NB-IoT Comparison Table

Data rate

Due to the narrowband nature of NB-IoT, it only uses 180 kHz of channel bandwidth. Despite giving a number of advantages, this limits the system data rate to a maximum of 159 kbps. On the other hand, LTE-M uses 1.4 MHz as system bandwidth which can provide downlink data rates of up to 300 kbps. This is among the highest in Low-Power Wide-Area Networks (LPWAN) in general and allows LTE-M to enable downlink-heavy applications, meaning most signals are being sent to the UE.

Definition

LPWAN (Low-power wide-area network): A type of wireless wide area network (WAN) technology designed for long-range communication at a low bit rate among “things”.

Coverage

NB-IoT focuses its power in a narrower band and accepts the decrease in data rate, which gives it an edge over LTE-M when it comes to coverage. Therefore, NB-IoT is more suitable for applications requiring deep penetration where devices can be installed behind concrete walls or in basements as well as applications requiring wide coverage areas. In most normal use cases, there are enough eNB’s available so even though NB-IoT has better range, LTE-M can just reconnect to the next eNB.

Latency

Since LTE-M supports higher data rates, an LTE-M device can send more data in less time, which directly reflects on latency. Therefore, LTE-M provides significantly lower latency than NB-IoT. This makes it more appropriate for applications that require real-time communications.

Power consumption

Power consumption comparisons between the two technologies are not as one-dimensional as the previously discussed parameters. On a purely numerical level, we know that LTE-M supports higher data rates. This means that an LTE-M device requires less time having the radio on to transmit a certain packet, while an NB-IoT device requires more time to transmit this same packet. NB-IoT also uses more time during the attach procedure to the eNB. For the total power consumption of an application, LTE-M is generally more power efficient.

That said, it’s uncommon that LTE-M and NB-IoT receive the same network parameters. This means that in certain areas, NB-IoT might perform better, power-wise.

Definition

Attach procedure: The attach procedure is the procedure in which the UE registers with the network. It is initiated by an attach request from the UE followed by a number of exchanges back and forth between the UE and eNB.

For more information, the blog post: LTE-M vs NB-IoT Field Test: How Distance Affects Power Consumption explores how moving away from the eNB affects the power consumption on the device and compares the two protocols.

More on this

The Online Power Profiler for LTE is a tool that estimates the current consumption values for both LTE-M and NB-IoT based on various network and device parameters, and can be used to estimate which protocol will be best suited for your use case when it comes to power consumption.

Mobility

Mobility in this case means two things. It refers to the support for handovers, and it also means maintaining a connection when the device is moving at relatively high speeds. In both cases, LTE-M has the edge.

Handovers refer to the process of transferring the connection from one eNB to another as the device moves between coverage areas. Handovers are an inherent feature of LTE-M, as a device moves from one coverage area to another it will seamlessly start communication with the eNB covering the new area, without any connection drops.

When the NB-IoT device eventually loses connection with the initial eNB, it will have to attach to the new eNB, also consuming power and time. However, this was significantly improved with the introduction of Cat-NB2, which allows the device to transfer the connection when moving between eNBs, improving the technologies mobility as compared with Cat-NB1.

Despite this improvement, LTE-M is more suitable for applications that require support for mobility, where latency and power consumption are important.

More on this

For more information on what things to consider when selecting which technology to use in your cellular application: nWP044 – Best practices for cellular IoT developmentThis white paper introduces the main aspects and decisions you need to consider before and during your development phase of a low-power cellular IoT product.

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