IEEE Consumer Electronics Magazine - November/December 2020 - 54

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single-tone UL is used to further enhance the
coverage.
In Release 13, LTE can typically operate to a
maximum coupling loss (MCL) of about 142 dB.
The MCL for LTE-M and NB-IoT with coverage
enhancement is 164 dB.10
In Release 14, a huge amount of network
resources such as repetitions is required to
enhance the coverage up to 164 dB MCL. The
authorization of the coverage enhancements feature allows the network to limit the use of coverage enhancements to a device based on its
subscription data.
In Release 15, the following coverage enhancements have been made for NB-IoT.

Reduced system acquisition time (FDD): In
FDD, when SIB1-NB is being transmitted with
16 repetitions (the maximum supported),
eNB can transmit additional subframes containing SIB1-NB repetitions on anchor carriers and nonanchor carriers to allow faster
decoding of SIB1-NB and reduce the UE's
power consumption during cell access. Compared to Release 13 which supports up to
8 SIB1-NB repetitions, the number of repetition has been increased.
Random access range enhancement (FDD):
NB-IoT is sometimes deployed in cells with
radius of up to around 100 km. Release 13
NB-IoT physical random access channel
(PRAC) supports cell radii up to 40 km with
unambiguous determination of UE range. To
extend the range, a new random access format is proposed with 1.25 kHz subcarrier
spacing, 800 ms cyclic prefix, and frequency
hopping, which is sufficient to allow unambiguous range determination up to 120 km.

Density
Density is the maximum number of IoT devices
(connected or in idle mode) that can be served
simultaneously in an area of 1 km2. Release 13
design target for capacity is almost 60 000 devices/km2. For NB-IoT, design target is increased
with introduction of using one anchor and up to
15 nonanchor carriers for paging and random
access. The extra spectrum of nonanchor carriers
increases the density. Procedures such as random
access and paging only be implemented on anchor

Figure 2. UL data rate versus MCL in Cat-M1.

carriers which restricts the network's capacity.
This restriction is removed in Release 14 where
the procedures can also be performed in nonanchor carriers. The first R14-based commercial NBIoT solution supports 80 000 devices/km2. Release
15 targets massive IoT which includes 1 000 000
devices per km2.

CASE STUDIES

In this section, we discuss the suitability of
LTE-M or NB-IoT technologies and their corresponding 3GPP Release versions for several IoT
use cases. We show how the enhancements in
LTE IoT can lead to new applications and use
cases. Note that in these case studies our focus is
on the technological aspect of the IoT use cases.
For IoT case studies from the security vulnerability perspective please see the work done by
Alladi et al.11 where the common attacks faced by
consumer IoT devices are described and potential mitigation strategies are suggested.

Use Case 1
In the work by Zhu et al.,12 many opportunities of smart IoT health applications including
remote monitoring, detection, and diagnosis
have been surveyed. We consider an elderly person living in a remote area located in the
extended coverage region of the nearest tower
that supports LTE-M (MCL may reach up to
164 dB) who needs to wear a health monitoring
device for medical purposes. Due to the small
size of the sensors (and hence cell-size batteries), the sensors should transmit their data with
minimum power so that the battery life can last
longer. Assume that in this scenario, the UL data
rate is 40 b/s. As it is shown in Figure 2, due to
the low data rate, and the operation of the sensors within the extended coverage region, LTE-M

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