3GPP物联网技术：EC-GSM-IoT、LTE-M与NB-IoT标准与性能详解

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The introduction of the smartphone not only changed the usage of the phone but also had a pro-

found impact on the requirements on the underlying communication systems providing the wireless

connectivity. For a classic mobile phone supporting voice and text messages, the most important re-

quirements are acceptable voice quality and reliable delivery of messages. Since the introduction of the

smartphone, expectations go far beyond this and requirements in terms of, e.g., high data rates and low

latency have become more prominent. The requirements set by the ITU on the world’s ﬁrst 4G systems

were also to a signiﬁcant extent shaped by this and focused on the ability of the candidate solutions to

provide mobile broadband services. For base station to device transmission, a peak downlink data rate

of 1.5 Gbit/100 MHz/s was one of the ITU targets. For the uplink direction, i.e., transmission from the

device to the base station, the target was slight ly relaxed to 675 Mbit/100 MHz/s. A latency of less than

10 ms was another important requirement intended to secure an acceptable mobile broadband expe-

rience [5].

With the introduction of Machine-to-Machine (M2M), MTC, and IoT applications and services,

the expectations as well as the set of requirements placed on the mobile communication technologies

changed again. A not too advanced smartphone user may, for example, stream several gigabits of data

every month with high requirements on quality of experience while it may be sufﬁcient for an average

utility meter to access the network once per day to send the latest billing information of a few bytes to a

centralized billing system. The requirements associated with M2M and IoT services are not, however,

only being relaxed, they are becoming more diverse also, as new applications are emerging. Although

the mentioned utility meter displays relaxed requirements in terms of latency and throughput, other

requirements may be far more stringent than what is expected from the smartphone use case. It is not

rare for utility meters located deep indoors, for example, in basements, to plac e high requirements on

the wireless coverage provided by the supporting communications systems. It is furthermore expected

that the number of M2M and IoT devices will, by far, eventually outnumber the smartphone population

and thereby effectively set new requirements on system capacity and network availability.

1.2.2 MASSIVE MACHINE-TYPE COMMUNICATIONS AND ULTRA RELIABLE AND

LOW LATENCY COMMUNICATIONS

From a service, applications, and requirements point of view, the IoT market is often said to be divided

into at least two categories: mMTC and URLLC. The Next Genera tion Mobile Networks Alliance is in

its 5G white paper [6] describing these two categories in terms of typical use cases and their associated

requirements. Smart Wearables and Sensor Networks are two industrial vertical features mentioned as

belonging to the mMTC market category. Smart wearables comprise not only, e.g., smart watches but

also sensors integrated in clothing. A main use case is sensing health-related metrics such as body

temperature and heartbeat. It is clear that if this tren d gains traction, the number of devices per person

will go far beyond what we see today, which will put new requirements on the capacity that must be

supported by cellular networks providing IoT services. It can furthermore be expected that in order for

clothing manufacturers to ﬁnd wearables an appealing concept, the devices must be extremely

compact to support seamless integration in the clothing. The devices must also be of ultra-low cost to

attract clothing manufacturers as well as consumers.

Sensor networks is a family name for various utility meters such as gas, water, and electricity

meters. Potentially, every home is equipped with a multitude of sensors that will put high requirement

on the capacity of the communication system providing them with connectivity. As utility meters are

4 CHAPTER 1 THE CELLULAR INTERNET OF THINGS

associated with stringent requirements on coverage, which is radio resource consuming, the task to

provide sufﬁcient capacity for these becomes even more challenging. Meters may in addition entirely

rely on battery power, which will put high requirements on device energy efﬁciency to facilitate

operation for years on small and low-cost batteries.

URLLC can, on the othe r hand, be exempliﬁed by high-end applications such as automated driving,

industrial automation, and eHealth. The news is ﬁlled with article s about traditional car manufacturers

and giants from the ICT industry competing in the development of autonomous vehicles. If such

applications are to be supported by cellular communication networks, the network needs to offer close

to perfect reliability combined with support for extreme latency requirements. It is also not far-fetched

to imagine remote steering as an attractive alternative to, or perhaps ﬁrst step toward, fully autonomous

vehicles. In this case also requirements on support for high data rates to support high-resolution video

may come into the picture. Similar requirements can obviously also be mapped to the industrial

automation and eHealth verticals.

Figure 1.1 summarizes the just-made observations with a high level illustration of expected re-

quirements for the mMTC category and the URLLC category in terms of coverage, number of

supported connections, latency, throughput, mobility, device complexity, and device battery life.

For comparison also typical mobile broad band requirements discussed in Section 2.1 are depicted.

The center of the radar chart corresponds to relaxed requirements while the outskirts of the chart map

to stringent require ments.

1.2.3 INTRODUCING EC-GSM-IOT, NB-IOT, AND LTE-M

The three technologies EC-GSM-IoT, NB-IoT, and LTE-M, described in Chapters 3e8 in this book,

were to a large extent designed to serve use cases belonging to the category of mMTC. The work on

Latency

Throughput

Coverage

ComplexityBattery

Connections

Mobility

mMTC

URLLC

Mobile Broadband

FIGURE 1.1

mMTC, URLLC, and mobile broadband requirements.

1.2 NEW APPLICATIONS AND REQUIREMENTS 5

LTE-M started in September 2011 with the 3GPP feasibility study named Study on Provision of Low-

Cost MTC UEs Based on LTE [7], referred to as the LTE-M study item in the following. The main

justiﬁcation for this study item was to extend the LTE device capabilities in the low-end MTC domain,

provideanalternativetoGeneral Packet Radio Service (GPRS) and Enhanced General Packet Radio

Service (EGPRS) devices, and facilitate a migration of GSM networks toward LTE. As the aim was to

replace GPRS/EGPRS as a bearer for MTC services, the study naturally used GPRS/EGPRS perfor-

mance as the benchmark when setting its objectives. It was, e.g., required that data rates, spectrum

efﬁciency, and power consumption should be at least as good as EGPRS. The main focus of the study

was, however, to provide a solution with device complexity and cost on par with GPRS. In September

2012, it was decided to add a new objective on study of the feasibility of a coverage improvement of

20 dB beyond normal LTE coverage. LTE devices have typically been considered far more expensive

than GPRS/EGPRS devices, mainly because of the improved capabilities provided by LTE. Therefore

for LTE to become competitive in the low-end mMTC market, a reduction in device cost and complexity

was considered crucial. The coverage enhancement was considered to be needed to facilitate deep indoor

coverage in locations where, for example, utility meters are expected to be located.

The work on EC-GSM-IoT and NB-IoT started one release later in the 3GPP feasibility study

named Cellular System Support for Ultra-low Complexity and Low Throughput Internet of Things [8],

referred to as the Cellular IoT study item in the following. Many aspects of this study can be recog-

nized from the LTE-M study item. The overall objective did, however, change from targeting a solution

comparable to GPRS/EGPRS to ﬁnding a solution competitive in the Low Power Wide Area segment,

which at the time to a large extent was deﬁned by technologies for unlicen sed operation designed for

ultra-low complexity, extreme coverage range, and long device battery life as discussed in more detail

in Section 1.3.

As for the work on LTE-M, an important part of the Cellular IoT study was to meet an objective of

extending coverage with 20 dB. While the LTE-M study item used LTE coverage as reference, the

Cellular IoT study item deﬁned the improvement in relation to GPRS coverage. The GPRS technology

is often seen as one of the most capable technologies in terms of coverage, and today it is still the main

technology providing cellular IoT connectivity. But just as for LTE, its capability was believed to be

insufﬁcient to cater for deep indoor coverage. Part of the reasoning behind this objective was that

modern building materials besides their ability to provide excellent thermal insulation often are

characterized by high attenuation of radio waves. A further aspect that was taken into consideration is

that many IoT devices have a compact form factor where efﬁcient antenna design is not prioritized.

This limits the achievable antenna gain and further increases the need for coverage and increased

Maximum Coupling Loss (MCL).

MCL is deﬁned as the maximum loss in the conducted power level that a system can tolerate and

still be operable (deﬁned by a minimum acceptable received power level). Hence, it can be calculated

as the difference between the conducted power levels measured at the transmitting and receiving

antenna ports, and it is an attractive metric to deﬁne coverage because of its simplicity. Because it is

deﬁned using the antenna connector as the reference point, the directional gain of the antenna is not

considered when calculating MCL. Coverage can also be expressed by the Maximum Path Loss (MPL)

a technology can support. The path loss is deﬁned by the loss in the signal path (e.g., distant-dependent

propagation loss, building penetration loss, etc.) of the radiated power. Hence, it can be calculated by

6 CHAPTER 1 THE CELLULAR INTERNET OF THINGS

the difference in radiated power levels at the transmitting and receiving antennas. To determine the

MPL also the antenna gain at the transmitter and receiver need to be considered. The difference be-

tween MCL and MPL is illustrated in Figure 1.2. MCL has been chosen by 3GPP as the metric to

evaluate coverage enhancements. In the remainder of the book, the focus will therefore be on MCL

with a few exceptions when describing the capabilities of technologies operating in unlicensed

spectrum. The concept of MCL is described in Section 3.2.8.1 in detail.

In addition to coverage enhancement, it was required in the Cellular IoT study to show that device

battery life of at least 10 years were feasible to support, for example, utility meters with no access to a

mains power source. To minimize the maintenance cost of applications and equipment relying on

limited battery capacity, low energy consumption leading to long battery life is of high importance. A

network supporting a large-scale deployment of millions of devices requiring a fresh battery every year

would be difﬁcult to maintain on commercial terms.

Furthermore, the candidat e technologies were require d to present a net work capaci ty sufﬁcient to

support IoT type of services for central London under an assumption of 40 connected devices per

household, resulting in over 60,000 devices/km

. Last but not least, it was requested to achieve all this

with string ent requirements o n keeping the device complexity ultra-low to secure as low device cost

as possible. Table 1.1 summarizes these performance objectives required to be fulﬁlled by the

candidate technolog ies d eveloped withi n the Cellula r IoT stu dy item, inc luding EC-G SM-IoT and

NB-IoT.

Signal power level

Conducted TX power

TX antenna gain

Radiated power (EIRP)

Thermal noise power

RX noise figure

Required SNR

Receiver sensitivity

Transmitter (TX)

Receiver (RX)

RX antenna gain

Coupling Loss (CL)

Path Loss (PL)

FIGURE 1.2

Illustration of coupling loss and path loss.

1.2 NEW APPLICATIONS AND REQUIREMENTS 7

1.3 LOW POWER WIDE AREA NETWORKS

1.3.1 AN INTRODUCTION TO TECHNOLOGIES FOR UNLICENSED OPERATION

As mentioned in Section 1.1, the 3GPP cellular technologies are not the only solutions competing for

IoT trafﬁc. Also well-known technologies such as Bluetooth and Wi-Fi can serve as bearers for MTC

trafﬁc. A distinction between the group of cellular technologies and Bluetooth and Wi-Fi is that the

former is intended for operation in licensed spectrum while the latter two belong to the group of

systems operating in unlicensed spectrum, in so-called license exempt frequency bands.

Licensed spect rum corresponds to a part of the public frequency space that has been licensed by

national or regional authorities to a private company, typically a mobile network operator, under the

condition of providing a certain service to the public such as cel lular connectivity. At its best, a

licensed frequency band is globally available, which is of considerable importance for technologies

aiming for worldwide presence. The huge success of GSM is, for example, to a signiﬁcant extent built

around the availability of the GSM 900 MHz band in large parts of the world. Licensed spectrum is,

however, commonly associated with high costs, and the media frequently give reports of spectrum

auctions bringing in signiﬁcant incomes to national authorities all across the world.

Unlicensed spectrum, on the other hand, corresponds to portion s of the public frequency space that

can be said to remain public and therefore free of licensing costs. Equipment manufacturers using this

public spectrum must, however, meet a set of national or regional technical regulations for

Table 1.1 Overview of the performance objectives in the CIoT study item [8]

Objective Description Requirement

Coverage The MCL of the system was required to surpass GPRS

coverage by 20 dB. The GPRS coverage reference was

estimated to be equal to 144 dB.

164 dB

Throughput A coverage requirement becomes meaningful only when

associated with a throughput target. It was therefore required

that the candidate technologies should support a data rate of at

least 160 bps at the coverage limit.

160 bps

Latency mMTC is, in general, expected to provide delay tolerant

services. But to guarantee high-alert reporting, a latency

requirement of 10 s was set for high-priority reports.

10 s

Capacity Capacity supporting 40 connected devices per household in

downtown London with roughly 1500 households/km

was

required.

60,000 devices/km

Power efﬁciency To secure operation regardless of the access to a mains power

source, and with minimal requirements on battery capacity, it

was expected that a 5-watt-hour (Wh) battery would last for at

least 10 years in the most extreme coverage situations.

10 years/5 Wh

Complexity An ultra-low device complexity was required to support mass

production and deployment of devices of ultra-low cost.

Ultra-low device

complexity

8 CHAPTER 1 THE CELLULAR INTERNET OF THINGS

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