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Comparative Study of LPWAN Technologies on Unlicensed Bands for M2M Communication in the IoT: beyond LoRa and LoRaWAN

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Low power wide area networks (LPWAN) are widely used in IoT applications as they offer low power consumption and long-range communication. LoRaWAN and SigFox have taken the top positions in the unlicensed ISM bands, while LTE-M and NB-IoT have emerged within cellular networks. We focus on unlicensed bands operation because of their availability for both private and public use with one's own infrastructure. New technologies have since been developed to overcome limitations of LoRaWAN and SigFox, based on LoRa or other modulation techniques, and are finding their way mainly into the industrial IoT. These include Symphony Link or Ingenu RPMA. To the best of our knowledge, previous works have not been focused on comparing LPWAN technologies in-depth including alternatives to the link and network layers over LoRa other than LoRaWAN. This paper provides a detailed comparative study of these technologies and potential application scenarios. We defend that LoRaWAN is the most suitable for small-scale or public deployments, while Symphony Link provides a robust solution for industrial environments. SigFox is one the most widely deployed networks; and RPMA has the advantage of using the 2.4GHz band, equally regulated in most countries.
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Procedia Computer Science 00 (2018) 000–000
www.elsevier.com/locate/procedia
The 14th International Conference on Future Networks and Communications (FNC)
August 19-21, 2019, Halifax, Canada
Comparative Study of LPWAN Technologies on Unlicensed Bands
for M2M Communication in the IoT: beyond LoRa and LoRaWAN
J. Pe˜
na Queraltaa,, T. N. Giaa, Z. Zoub, H. Tenhunenc, T. Westerlunda
aDepartment of Future Technologies, University of Turku, Finland
bSchool of Information Science and Technology, Fudan Universtiy, China
cDeptarment of Electronics, KTH Royal Institute of Technology, Sweden
Abstract
Low power wide area networks (LPWAN) are widely used in IoT applications as they oer low power consumption and long-
range communication. LoRaWAN and SigFox have taken the top positions in the unlicensed ISM bands, while LTE-M and NB-IoT
have emerged within cellular networks. We focus on unlicensed bands operation because of their availability for both private and
public use with one’s own infrastructure. New technologies have since been developed to overcome limitations of LoRaWAN and
SigFox, based on LoRa or other modulation techniques, and are finding their way mainly into the industrial IoT. These include
Symphony Link or Ingenu RPMA. To the best of our knowledge, previous works have not been focused on comparing LPWAN
technologies in-depth including alternatives to the link and network layers over LoRa other than LoRaWAN. This paper provides a
detailed comparative study of these technologies and potential application scenarios. We defend that LoRaWAN is the most suitable
for small-scale or public deployments, while Symphony Link provides a robust solution for industrial environments. SigFox is one
the most widely deployed networks; and RPMA has the advantage of using the 2.4GHz band, equally regulated in most countries.
©2018 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the Conference Program Chairs.
Keywords: IoT; IIoT; M2M Communication; LoRa; SigFox; LoRaWAN; LPWAN; Symphony Link; Ingenu; RPMA; Smart City; Industry 4.0;
1. Introduction
With the rapidly growing number of devices being deployed as part of the Internet of Things (IoT), power con-
sumption and battery life are becoming increasingly important in multiple application scenarios. In cases where data
acquisition is sparse in time, transmitting data easily becomes the most power consuming factor in passive sensor
nodes. Low power wide area networks (LPWAN) not only enable very low power but also long-range and low-cost
machine-to-machine (M2M) communication. This permits the deployment of end-devices with battery lives spanning
years or decades [1]. The development of new LPWAN technologies has brought new IoT application scenarios.
E-mail address: {jopequ, tunggi, tovewe}@utu.fi, zhuo@fudan.edu.cn, hannu@kth.se
1877-0509 ©2018 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the Conference Program Chairs.
2J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000
Low power and long-range communication have evident applications in rural areas where cell network coverage is
poor and deploying infrastructure for Wi-Fi or similar networks might be costly due to challenging terrain or scattering
of sensor nodes over large areas. However, while LPWANs have been leveraged for a variety of industrial applications
related to farming and agriculture, most of the public LoRaWAN gateways are in urban areas [2]. Applications in a
metropolitan context include diverse use cases such as smart parking, flood monitoring, weather stations, infrastructure
monitoring, smart metering, and lightning or waste management [3,4,5]. LoRaWAN and SigFox are the two most
popular LPWAN solutions at the moment. LoRaWAN is an open standard for the link and network layers which
operates on top of LoRa as the physical layer [6]. SigFox was the first LPWAN to be introduced for the IoT (2009).
More recently, new LPWAN technologies have emerged that overcome some of these limitations. Symphony Link,
developed by Link Labs in 2016, is a proprietary solution that uses the LoRa modulation with frequency hopping
to avoid any duty cycle limitations [7]. Weightless and Ingenu RPMA LPWAN technologies also take advantage of
unlicensed radio bands for long-range and low power transmission.
LPWAN technologies have been widely studied in recent years [8,9,10,11]. Previous work has been mostly
focused on LoRaWAN and Sigfox. To the extent of our knowledge, there is no technical comparison of Symphony
Link with LoRaWAN and Sigfox. Though mentioned by some researchers [12], it has not been widely used for
research purposes. Patel et al. have performed an experimental study to analyze the performance of Symphony Link
in a mobile end-device [13]. However, the authors do not explain the technology behind the application, nor do they
compare the performance to other LPWAN solutions. While we do not carry out comparative experimental studies in
this paper, we have put an emphasis on summarizing the best LPWAN solution for dierent applications in the IoT.
Mekki et al. performed a technical comparative study of LoRa, Sigfox, and NB-IoT, concluding that one advantage of
LoRa over Sigfox was the option to deploy local networks [14]. In our work, we compare these with Symphony Link
as an alternative for the link and network layers over LoRa. Ismail et al. discussed the opportunities and challenges
of LoRa, Sigfox, IQRF, RPMA, Telensa, Dash7, Weightless-N, Weightless-P and SNOW [15]. The authors provide a
clear overview of the dierent technologies and potential applications. However, we put more focus on the technical
details of the most predominant cases and provide consistent arguments on which are the benefits and drawbacks of
each technology for dierent applications. Raza et al. provided an exhaustive description of several LPWA networks,
including cellular standards and technologies for unlicensed ISM bands [1]. In this paper, we focus on a more reduced
number of technologies that represent LPWAN technology. LoRaWAN as an open network standard and Symphony
Link as an advanced proprietary standard over LoRa. Sigfox because of its wide availability in many countries, and
ease of use via a subscription payment, and Ingenu RPMA because its technology is radically dierent from most
LPWANs, and operates in a dierent radio band.
2. LoRa Modulation at the Physical Layer
LoRa (long-range) is a patented modulation technology for wireless communications acquired by Semtech Corpo-
ration in 2012 [16]. LoRa was designed to allow low-power, low-rate, long-range transmissions with very-long-range
in rural areas or line-of-sight situations up to 10 or 20km. LoRa is designed to work on unlicensed frequency bands
such as 433MHz, 868MHz or 915MHz, depending on the geographical location and the corresponding regulations.
LoRa refers to the physical layer, does not include any form of encryption, and defines a spread spectrum modulation
technique based on chirp spread spectrum (CSS) technology [17]. CSS, or linear frequency sweeping (LFS), modula-
tion has theoretical superior characteristics to more traditional modulation techniques such as frequency or phase-shift
keying (FSK/PSK) in the cases of a partially coherent and fading channel [18].
Semtech’s LoRa modulation gives a bit rate Rbproportional to the bandwidth and inversely proportional to 2S F ,
where S F is the spreading factor taking values from 7 to 12. A single LoRa chirp codes a number of bits equal to the
spreading factor. Thus, even if the data rate is halved when the spreading factor increases one unit, the number of bits
encoded in each symbol is also increased by one[19]. This is achieved by coding each possible bit value into a shifted
chirp, creating a sharp change in the frequency trajectory. The actual transmission bit rate changes when taking into
account that LoRa applies forward error correction by increasing the redundancy in the transmitted payload. The final
bit rate is multiplied by a factor 4/(4 +CR), where CR is the coding rate taking values from 1 to 4. The coding rate
represents the number of bits that actually contain data, as compared to the total number of transmitted bits.
J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000 3
ClassA ClassB ClassC
LoRaWAN
TX
RX1
RX2
PING
BC
DEV GTW DEV GTW DEV GTW
BC
RX1
Delay
RX2
Delay
?
?
RX1
RX2
RX2Extendsto
nextuplink
RX2
TX
?
?
RX
RX
RX
RX
RX
RX
RX
TX
Fig. 1: Tx/Rx Windows for LoRaWAN Classes A,
B and C. Packets with (?) are optional downlinks.
LoRa DBPSK
+GFSK
LoRaWAN SymphonyLink
RPMA
ISMSubGigahertz 2.4GHz
FDMA
+TDMA
SIGFOX INGENU
WEIGHT
LESSP
GMSK
+QPSK
TVBands
WEIGHT
LESSN
BPSK
WEIGHT
LESSW
Frequency Band
Modulation
(Physical Layer)
Network Layer
Link Layer
Fig. 2: Dierent LPWAN solutions and their modulation schemes. From top to bottom, the rows
reference to network and link layers, physical layer and frequency bands.
Table 1: LoRaWAN vs. Symphony Link
LoRaWAN Symphony Link
Acknowledgement Limited Always
Bidirectional Link Mostly uplink (Class A) Yes
Built-in Adaptive Data Rate No Yes
Duty Cycle Limitations Yes (1%) No
Encryption Scheme AES128 PK (needs setup)
Repeaters Not integrated Yes
Over-the-air updates Limited (one-by-one) Yes, multi-cast
Protocol Aloha (Class A) Synchronous
Licensed No - Open standard Yes - Proprietary
One of the main advantages of LoRa is the high receiver sensitivity and, therefore, a large communication link
budget. This enables very long-range transmissions. Typical SNR levels for spreading factors 10 and 12 when using
LoRa modulation are -20dB and -15dB, obtaining receiver sensitivities of -134dBm and -129dBm, respectively. These
values are barely comparable to the typical sensitivity of Wi-Fi or Bluetooth receivers, which often is in the range of
-40dBm to -80dBm [20]. However, we should note that the data rates that are achievable with LoRa modulation
are several orders of magnitude lower. Time on air is also significantly larger. Chirps are transmitted at a frequency
equivalent to the signal bandwidth. A symbol is encoded in 2S F chirps, with time on air Tsym =2S F /BW.
The key properties of LoRa modulation are (1) its scalable bandwidth and frequency, easily changing from nar-
rowband hoping to wideband; (2) resistance to Doppler shift; (3) relatively high immunity to fading or multi-path,
especially in dense urban scenarios, and (4) robustness to interference. This is on top of the very-long-range, low
transmission power required with constant envelope, and increased capacity because of the orthogonality of signals
with dierent spreading factors. The parameters that have the most impact on the transmission reliability and com-
munication range are the bandwidth (BW), spreading factor (SF), and coding rate (CR) [21,22,23,24]. LoRa is
particularly resilient to interference and packet collision with low packet loss rate in nominal link conditions.
Taking all the above into account, we can outline the advantages of LoRa for the IoT as enablers of (1) long-
range transmissions over 10km in line-of-sight; (2) low cost deployment of nodes and gateways due to the low cost
of LoRa transceivers and a reduced number of gateways compared to Wi-Fi or Bluetooth solutions; (3) adaptable
bandwidth, coding rate and spreading factor to increase reliability in dierent channel conditions and allow multi-
channel transceivers to operate in parallel, enabling a single gateway to receive data from a very large number of nodes,
even in the order of thousands; (4) very low energy consumption for battery-powered devices; and (5) orthogonal
packet transmission using dierent spreading factors without compromising transmission reliability.
3. Link and Network Layers over LoRa
The LoRa specification just provides the physical layer for radio communication. LoRaWAN is the most popular
media access control (MAC) protocol for wide area networks, mainly used on top of LoRa but also suitable for FSK
modulation [6]. In this section, we introduce the LoRaWAN protocol and discuss its alternatives.
LoRaWAN
LoRaWAN is, fundamentally, a network protocol that has been designed keeping in mind that in most use cases of
LoRa devices are battery-powered and therefore energy consumption must be kept as low as possible. Moreover, these
devices can be either fixed or mobile, and therefore would not build a connection with a specific gateway. The network
4J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000
topology of LoRaWAN is a star network, where several end-devices transmit to a given gateway. In fact, devices
broadcast their transmissions and might be received by several gateways. Then, back-end servers where all gateways
are connected to make an automatic decision on which gateway handles the received packets. Uplink transmissions
are considered predominant in LoRaWAN, and therefore have preference over downlink. Because LoRa focuses on
battery-powered end-devices, a large number of transmissions being received at the node would rapidly increase the
power consumption, due to long listening times waiting for a package to arrive. LoRaWAN takes this into account
by defining dierent classes of communication depending on the energy consumption constraints of dierent end-
devices. The protocol tackles this by defining three dierent classes of connected end-devices with an incremental
number of features: (1) Class A devices, with the basic set of features that all devices must implement; (2) Class B
devices, with scheduled listening windows; and (3) Class C devices, for bi-directional communication at any time.
The transmitting and receiving windows for each of the three LoRaWAN end-device classes are illustrated in
Figure 1. Class 1 devices are those with more strict requirements in terms of power consumption. To minimize the
opening time for receiving windows, the LoRaWAN specification defines two short windows, each of them starting at
a predefined time from the end of the transmission. The first receiving window, RX1, is configured with frequency and
data rate parameters that depend on those used for the uplink based on a given, predefined function. By default, these
are parameters are simply the same than in the last uplink transmission. The second receiving window is configurable
with parameters that can be set through dierent LoRaWAN MAC commands. The default values are region specific
and fixed, independent of the parameters used during the uplink. This is similar to the Aloha method, in which
acknowledgement is not expected for every transmitted message [25]. As such, Class A devices do not automatically
receive receipt acknowledgement unless specifically requested. Moreover, these devices must not start a new uplink
transmission until the second receiving window has been closed. An application that needs to transmit data back to
the end-device can do so only in the fixed windows after an uplink message. This means that the application needs
to wait for the end-device to transmit in the first place, and limits the amount of data that can be sent back. Class
B devices address this problem by scheduling receiving windows with a given period of time. These windows are
defined by beacons being transmitted by all gateways in the network, which must be accordingly synchronized to
transmit at the same time. End-devices always register to a LoRaWAN network as Class A and then request, through
MAC commands, to change their status to Class B. If the end-device does not receive a beacon during a given period,
then it must switch back to Class A automatically. In Figure 1, ping messages from gateways can be sent at any time
corresponding to the scheduled RX windows. RX windows close shortly after being opened if no preamble is detected,
and remain open until the full message has been decoded otherwise. Ping messages are meant to track the location of
the end-device and switch the assigned gateway if necessary for any incoming downlink transmission. Class B devices
send a short reply after a ping message. For less power-constrained devices, the LoRaWAN specification defines the
Class C. Also known as continuously listening end-devices, Class C devices that have sucient power shall listen
with RX2 window parameters (as defined for Class A) as often as possible, with RX1 windows still opening after
each uplink transmission. Gateways can, therefore, send any downlink transmission at any time, taking into account
the last uplink time so that modulation parameters are chosen correspondingly to those of window RX1 or RX2.
Due to the relatively limited number of channels in the frequencies at which LoRa operates and the local regulations
that apply in dierent countries or geographic areas, LoRaWAN defines three basic rules for all connected devices
to comply with: (1) Devices must change the LoRa modulation parameters in order to use dierent channels for
dierent transmissions, therefore increasing robustness towards interference; (2) individual transmission time on air
must respect the limits set by corresponding local regulations; and (3) total duty cycle of consecutive transmissions
must respect limits set either by LoRaWAN or local regulations, whichever is more restrictive. Through these rules,
LoRaWAN allows a more uniform usage of the available spectrum while ensuring that all connected devices will have
enough open time and frequency for transmitting, reducing the packet error rate. This becomes particularly important
for Class A devices that do not necessarily receive acknowledgement for the transmitted data.
Symphony Link
LoRaWAN is the most popular network protocol that operates on top of LoRa. However, other open source and
proprietary solutions have been designed to tackle the limitations of LoRaWAN. Symphony Link, developed by Link
Labs, overcomes some of the limitations of LoRaWAN [26,7]. Symphony Link puts a stronger focus on industrial
applications and provides a solution to eliminate the duty cycle limits by using frequency hopping and dierent
available frequencies. It also provides built-in support for repeaters to increase the range of a single gateway without
J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000 5
trading ototal bandwidth. Another strong point of Symphony Link is that it allows one-to-many communication
from a gateway to end nodes. This simplifies and increases the speed of over-the-air updates or broadcast messages.
The Symphony Link protocol varies significantly with respect to LoRaWAN. There are no device classes. Instead
all devices operate under the same conditions. Both gateways and end-devices perform interference scans to select
the transmission channels. Gateways select a 500 KHz channel (or 125 KHz in Europe) and transmit beacons with
a 0.5 Hz frequency. The beacons are encrypted by a network id, which needs to be configured in the end devices
before connecting. Gateways broadcast information about the numbers of channels being used during transmission
for the frequency hopping scheme. These can be configured as 1, 8 or 64 channel gateways, and repeaters and end-
nodes adapt to this setup. Gateways also transmit information about the quality of service (QOS). This is useful for
choosing which packets are transmitted by end-devices if the network is congested and more priority is given to
some information. With Symphony Link, nodes can save power by adapting the transmit power and LoRa modulation
through the spreading factor based on the received signal power. While this can be done in LoRaWAN, the lack of
frequent downlink messages for standard Class A devices makes the estimation harder.
The advantages of Symphony Link over LoRaWAN can be summarized as (1) guaranteed message receipt, (2)
firmware updates with multicasting, (3) duty cycle limit removal, (4) built-in support for repeaters, (5) adaptive data
rate with dynamic modulation and power adjusted with transmit power and spreading factor calculated based on
reverse link, (6) public-key based encryption, (7) higher capacity and less collisions in multiple gateway environments.
The sensitivity of Symphony Link is basically the same than LoRaWAN, as well as the frequencies in which it
operates. In terms of open access, the LoRaWAN is an open standard while Symphony Link is proprietary. Deploying
private networks is possible with both protocols but operating a public LoRaWAN network requires a network ID
given by the LoRa Alliance, which are available to contributor members or above.
MoT: MAC on Time
Hassan et al. have developed a MAC protocol that is based on LoRa for the physical layer, with a focus on reducing
energy consumption, enabling scalable networks with fair usage and maximize capacity [27]. The authors have de-
signed a protocol called MoT (MAC on Time), with guaranteed package delivery and improved bandwidth utilization.
One key dierence is that the time that a node will stay idle or in sleep mode will be decided by the network and
communicated from the gateway via the packet acknowledgement. With this approach, MoT overcomes clock drifts
with a centralized scheduling. The performance of the protocol has been tested through multiple simulations. MoT
has proved to be able to provide 4 to 15 times more network capacity and better latency than LoRaWAN.
4. Low-power, long-range modulation alternatives to LoRa
LoRaWAN and Symphony Link are the most widely used network layers that operate with LoRa modulation.
However, other LPWAN technologies rely on dierent frequency bands or use a distinct modulation scheme.
SigFox
Sigfox provides both a modulation technology for the physical layer and a media access control protocol on top of
it [28]. Moreover, Sigfox partners with operators to build its network infrastructure and provide it as a service. At the
physical layer, and compared to LoRa’s use of CSS, Sigfox is based on dierential binary phase-shift keying (DBPSK)
and Gaussian frequency shift keying (GFSK). The data is transmitted in channels of only 100 Hz of bandwidth (ultra-
narrowband, UNB) in order to minimize noise, and a total 192 KHz of the spectrum is used. Because device and
network are not synchronized, in pursuance of higher quality of service (QOS), data transmission is done using
frequency hopping and replicating the message twice, for a total of three random frequencies. As in LoRaWAN,
end-devices are not registered to a single gateway. An average of 3 base stations or gateways receive each message,
further increasing the QOS with spatial diversity on top of time and frequency diversity. Sigfox restricts the length
of payloads to 12 bytes and transmission speed is of 100 bps. The number of daily messages is limited to 140, in
order to comply with the 1% duty cycle limitation set by European regulations. Sigfox works on the 902 MHz band in
North America and 868MHz in Europe. In the US, FCC regulations limit the time-on-air of UNB signals, so Sigfox
uses a dierent implementation with frequency hopping [29]. All data goes through the Sigfox Cloud servers and is
available to end-users via their web-interface and a REST API. The power consumption, communication range, and
data exchange process is overall similar to the case of LoRaWAN Class A devices. Data encryption is based on AES,
6J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000
without impact on the size of the payload, and without key exchange over-the-air. Instead, each device is provided
with a symmetrical authentication key when it is manufactured. This can be used both for authenticating a sender and
message integrity.
In summary, the advantages of Sigfox over other LPWAN solutions are the wide coverage of its network, the
broad range of compatible hardware from dierent vendors and their power eciency. It is most suitable for metering
applications with very time sparse sampling. Sigfox’s main limitation is the maximum number of daily messages,
especially downlink transmissions. Therefore, it is not recommended for applications that need to access online data.
Furthermore, Sigfox is not an open protocol and its built-in security is minimal. Private network deployment is not
possible and Sigfox operators charge a fee per device, so its usage is more similar to a cellular network. In terms of
availability and coverage, SigFox has strong business traction and nearly countrywide coverage in central Europe.
Ingenu RPMA
Ingenu RPMA is a technology built from scratch with advanced modulation techniques that was designed with a
focus on minimizing the total cost of ownership while increasing the range of a base station and link capacity of LoRa
and Sigfox. Random Phase Multiple Access (RPMA) is a technology patented in 2010 by Ingenu [30]. On top of it,
Ingenu has developed LPWAN technology that allows much higher link capacity than LoRa or Sigfox. It works on the
2.4 GHz ISM band, in contrast with most LPWAN technologies using sub-gigahertz frequencies. This has the benefit
of being equivalently regulated over the world. However, the 2.4 GHz is widely used by many other technologies,
including Wi-Fi and Bluetooth, and therefore interference is more probable as the spectrum is more congested.
RPMA is based on the direct-sequence spread spectrum (DSSS) modulation technique. Communication is two-
way, and devices perform scanning in the background with handover so that the best access point is chosen for each
transmission. Gold codes in base stations or gateways are configurable to eliminate ambiguity. Its downlink capacity
is much larger than in the case of Symphony Link due to an adaptive spreading factor methodology. One of the key
advantages of RPMA over LoRa and Sigfox is the network capacity. Ingenu claims that a single gateway can handle
up to 2 million devices per access point [31]. While LoRa receivers can demodulate signals with dierent bandwidths
or dierent spreading factors simultaneously, RPMA supports parallel demodulation of up to 1200 signals on the
same frequency. As with Symphony Link, Ingenu requires all gateways in the same network to be synchronized, so
that end-devices are aligned in time with them. Another similarity is the adaptive spreading factor of the transmission
to reduce the power consumption based on channel conditions at each transmission time. While this could be done
with LoRaWAN or Sigfox, the functionality is not built-in in their modules. In general, Ingenu RPMA oers similar
features to Symphony Link. The main dierences are its increased capacity per access point and the ISM band used for
transmission. RPMA has a higher link budget, longer range in open space, and the 2.4GHz band is regulated consisted
through the globe, as compared to sub-gigahertz bands. However, a higher frequency also means that penetration
through most materials is less eective. This translates into less range in dense urban areas or large indoors facilities.
Other Alternatives
There are many LPWAN technologies that have been developed for the IoT. Sigfox and Ingenu RPMA are the
most popular solutions that do not use LoRa modulation, and we have put a focus on them. However, Weightless
technologies are also well known and are summarized here. Weightless, formerly known as Weightless-P, is an open
standard developed by the Weightless Special Interest Group. The group initially developed three LPWAN technolo-
gies, namely Weightless-W, Weightless-N, and Weightless-P [1]. The N and P versions both use sub-gigahertz bands,
with Weightless-N aimed a lower power use with one-way communication and based on narrowband with DPSK
modulation. Weightless-P, as with Symphony Link or RPMA, provides packet acknowledgement and two-way com-
munication, with FDMA+TDMA modulation. Weightless-W uses TV bands white spaces.
Considerations
When comparing wireless communication technologies, a common benchmark used as a reference is the maxi-
mum data rate. However, in the case of LPWANs, because of the wide range of modulation possibilities for a single
technology, this is not an immediate comparison. Moreover, if the amount of data that can be transmitted is limited,
then the speed at which it is transmitted remains in the background. LoRaWAN’s data rate ranges from 0.3 to 27 kbps
depending on the spreading factor and bandwidth. Sigfox’s is fixed to 100bps, but this figure is not so important when
taking into account the maximum of 140 messages per day. Ingenu RPMA oers the highest data rate when compared
to most LPWAN technologies, though the real transmission speed will adapt according to channel conditions.
J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000 7
5. Application Scenarios
LPWANs are being applied in an increasing number of scenarios in the IoT, from smart cities to the industrial IoT
[9,32,33]. In this section, we discuss the most appropriate LPWAN technology for dierent applications.
Urban Areas and Smart Cities
In urban areas, power eciency, ease of deployment and scalability are perhaps the most significant factors when
selecting an LPWAN technology. While a minimum range is required in order to keep the number of gateways or base
stations reduced. For a smart city, having an open and public network has the benefit of allowing more people and
organizations to use it. This can increase the level of technology penetration in the city. With an open network open for
local businesses, educational institutions and all citizens, the number of applications can rapidly grow and serve as an
economic boost. Therefore, not only does it serve the purpose of providing connectivity through the metropolitan area,
but it also increases the interaction with local businesses and citizens. Deploying a private network such as Symphony
Link or Ingenu with less widely available hardware and a smaller community of users would be beneficial for cities
only for specific applications where more control over the network might be required. Taking these considerations
into account, we propose LoRaWAN as the first LPWAN network solution to be considered for a Smart City. This
has already been done in Amsterdam or Bristol [2]. The economic and social benefits can rapidly overcome the small
investment in infrastructure required. Sigfox is an option to consider if a lower cost is required. However, recurrent
payments over a long usage of Sigfox might sum more than the investment needed to deploy a LoRaWAN network.
Industrial Internet of Things
In industrial applications, it is often preferable to deploy a private network. An open network does not meet the
requirements for a reliable connection and higher levels of security. Moreover, for applications that may be critical in
terms of business performance or safety, it is essential to have full control over the network. Therefore, Sigfox and
public LoRaWAN networks would have the disadvantage of being used by multiple users, which increases the prob-
ability of packet collision, interference and bandwidth saturation. Moreover, Sigfox and LoRaWAN do not provide
acknowledgement and limit the number of transmissions. In an industrial environment, a more flexible solution can
be better adapted to the intrinsic dynamic environment. Both Symphony Link and Ingenu allow higher data rates, do
not have limitations in the number of messages and provide acknowledgement. Acknowledgements are not critical in
metering or similar common urban applications. Nonetheless, a series of undelivered messages in relation to critical
processes in a production line might severely aect performance. Additional features such as one-to-many transmis-
sions from gateways in Symphony Link eases the process of updating firmware. While this is not significant in public
networks with a large number of dierent connected devices, in industrial applications there is more homogeneity. In
conclusion, we would advise private companies to use Symphony Link or Ingenu RPMA for industrial environments.
Both of these technologies have been designed after LoRa and Sigfox were introduced in the market, and therefore
have been able to tackle the main problems that they presented while improving the overall network performance.
Farming and Agriculture
In farming and agriculture, LPWANs have a more clear advantage over other technologies such as Wi-Fi or Blue-
tooth. While the range in urban areas is already much better, it is in rural and open areas where the range of a single
gateway can be extended beyond 10km with LoRa and over 30km with Sigfox. Ingenu claims some of its customers
reported coverage of 400 square miles per tower in Texas, and they have deployed their Machine Network in the
greater Phoenix area (1900 square miles) with 9 access points. Because of low interference in rural areas, any of the
technologies presented in this paper can be used eectively for farming or agricultural applications, depending on the
requirements. For time sparse data such as measurements of soil moisture and temperature, water levels, gate access
control or hourly rain volumes, LoRaWAN and Sigfox can be both used depending on whether Sigfox is available in
the area or a new network infrastructure based on LoRaWAN is preferred. In these scenarios, as compared to industrial
places that could be situated near urban areas, the probability of interference and packet collision is much lower. For
applications that require more frequent data exchanges or downlink capabilities, Symphony Link and Ingenu RPMA
could be deployed instead. This includes monitoring of machinery or vehicle tracking. In particular, because of the
built-in support for repeaters in Symphony Link, and the relatively low number of devices that would be deployed in
farming or agriculture applications, it is a technology that can decrease the overall infrastructure cost. A single base
station and a set of repeaters could be used to extend the range to tens of kilometers if the network capacity allows.
8J. Pe ˜na Queralta et al. /Procedia Computer Science 00 (2018) 000–000
6. Conclusion
In this paper, we have presented a comprehensive review of low power wide area network technologies. We have
focused on technologies that use unlicensed radio bands. From the technical point of view, at the physical layer,
Sigfox and Ingenu RPMA use narrowband modulation, while LoRa uses spread spectrum. In urban environments, all
of them have a similar range, while uplink capacity of Ingenu RPMA might be larger. However, in the cases of Ingenu
and Symphony Link, the downlink activity aects the network capacity. This eect is less noticeable in LoRaWAN
Class A and Sigfox due to the limited downlink possibilities. Because of the more recent development of Ingenu and
Symphony Link, they have been developed taking into account the drawbacks and main limitations of LoRaWAN and
Sigfox. The main advantages can be summarized as full acknowledgement of all messages, support for repeaters and
one-to-many downlinks for over-the-air updates, increased data rates and elimination of transmission limitations.
We have defended that LoRaWAN can be the best option for deployment in a smart city or urban areas by public
parties. Deploying a LoRaWAN network can enrich the diversity of applications and allow economic growth be-
yond the initially planned applications. For industrial environments, control over the network is more important and
therefore having a private network deployment is preferable. For low volumes of data and low-frequency acquisition,
LoRaWAN or Sigfox may be sucient. For real-time data acquisition Symphony Link and Ingenu are better options.
In conclusion, there is a large number of LPWAN technologies and new ones are being actively developed. The
number of applications that these technologies enable grow by the day together with their penetration in society. In this
paper, we have covered a small representative subset, with an emphasis on the unlicensed spectrum and introducing a
set of technologies that can be of interest for dierent fields in the IoT. In particular, Symphony Link has been barely
mentioned as an alternative to LoRaWAN in previous work, and we have put a focus on its benefits and drawbacks.
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