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Optimal deployment of mobile gateways in LoRaWAN environments
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Authors
Advisor(s)
Abstract(s)
The recent growth of the Internet of Things (IoT) has given rise to new applications
and technologies. Of these technologies, LoRa is the one that has stood out
recently due to its ability to transmit packets over long distances at low energy
costs. In addition to this, this technology also uses unlicensed frequency bands,
and all these factors make it possible to build low energy cost networks with large
coverage areas at low monetary cost. This makes LoRa very appealing for environments
where multiple square kilometers need to be covered for monitoring,
such as agriculture. This thesis focuses primarily on positioning gateways in a Lo-
RaWAN in order to achieve energy fairness in the network.The target in question is
an environmental sensor network that monitors conditions inside tree canopies in
an orange orchard in the Algarve, south of Portugal.The peculiar characteristics of
these orange trees, with heights up to 3.5 m and very dense foliage, makes it a very
challenging environment for radio waves propagation and causes a rapid drop in
signal quality. The power consumption of the end-nodes of the network is defined
by 7 combinations of spreading factor and bandwidth (0 to 6) where 0 represents
the slowest and most reliable transmission at the cost of higher power consumption
while 6 represents the opposite. The combination of bandwidth and spreading
factor is denominated data rate. Environmental factors can negatively impact the
quality of LoRa packets and the necessary power adjustments of the end-node to
overcome this, and increase signal reliability, can easily define whether a device
is able to transmit for 1 year or 10! The main factors that can affect signal quality
are obstruction, distance and meteorology. In the case study, of these 3 factors,
obstruction affects transmission quality the most. Most of the literature suggests
solutions within the framework of optimizing the datarate optimization algorithm
(ADR). ADR aims to minimize energy consumption while ensuring the best possible
packet transmission rate and achieves this by changing the data rate based
on the quality of the last 20 packets received.However, this optimization is done
directly to individual end-nodes and does not solve the problem of energy fairness over the whole network because, regardless of how optimized this algorithm is,
the algorithm cannot transcend the physical constraints imposed by the devices
and the technology itself. Distance and obstruction will always be obstacles to
signal quality. Since these physical constraints will always be present in a network
and the solutions proposed by the literature only improve performance at
the level of individual devices, this ends up creating a large lifetime discrepancy
between devices depending on their placement. In the case of LHT65s, the discrepancy
in device life expectancy is high. For example the difference between
using a data rate of 0 or 5 is about 10 years.
The solution proposed in this thesis to overcome this problem is to precompute
the optimal position for the gateways in order to guarantee the highest life
expectancy for the network. Given a number of available positions for the gateways
and having a certain number of gateways less than the number of positions,
the goal is to compute the optimal positioning of the gateways in order to maximize
the overall network life expectancy by ensuring a fair energy consumption
among different end-nodes.
The first step in this process was to collect information about signal quality
from a real case LoRaWAN deployment. This allowed to better understand the
constraints and problems associated with its implementation. This was done using
25 LTH65 devices, 1 RAK 7244 gateway and Chirpstack as the framework
to manage the network. Regarding the study of the algorithm before applying it
to the practical case, a simulator was used to collect data. The simulator chosen
for the development of the application was OMNet++, which besides being easier
to use is also better documented than the other options considered. This simulator
also offers a graphical interface with great detail that allows you to easily
observe the behavior of the network. Using the Flora module it was simulated a
LoRaWAN network with the structure suggested by the LoRa Alliance® with 25
devices using Oulu’s path loss model. The information obtained from this simulation
was used as input and test for the algorithm that was compiled by CPLEX. In
each simulation about 10,000 packets were sent per device and each experiment was repeated 30 times.
The results show that the optimization model has the ability to identify the best
placement for the gateway given a predefined locations and network geometry.
This is due to the fact that the algorithm identifies the lowest value in the highest
energy consumption per packet, and minimizing this value creates a balance of
consumption among the devices and consequently extends the life expectancy of
the network. It can then be concluded that this methodology is indeed efficient
for deployments where changing network devices cannot be done frequently. Although
it is not easy to relocate gateways in already implemented networks, but in
new environments where monitoring and optimization are requirements, and these
new environments are built considering the network structure, we can use this
methodology since it has proven to be able to improve network life expectancy.
O recente crescimento da Internet das Coisas (IoT) deu origem a novas aplicac¸ ˜oes e tecnologias. Destas tecnologias, a LoRa ´e a que se tem destacado recentemente devido `a sua capacidade de transmitir pacotes a longas distˆancias a baixos custos energ´eticos. Al´em disso, esta tecnologia tamb´em utiliza bandas de frequˆencia n˜ao licenciadas, e todos estes factores tornam poss´ıvel a construc¸ ˜ao de redes de baixo custo energ´etico com grandes ´areas de cobertura a baixo custo monet´ario. Isto torna LoRa muito apelativo para ambientes onde v´arios quil´ometros quadrados precisam de ser cobertos para monitorizac¸ ˜ao, tais como a agricultura. Esta tese centra-se principalmente no posicionamento de gateways numa rede LoRaWAN, a fim de alcançar a energy fairness na rede.(...)
O recente crescimento da Internet das Coisas (IoT) deu origem a novas aplicac¸ ˜oes e tecnologias. Destas tecnologias, a LoRa ´e a que se tem destacado recentemente devido `a sua capacidade de transmitir pacotes a longas distˆancias a baixos custos energ´eticos. Al´em disso, esta tecnologia tamb´em utiliza bandas de frequˆencia n˜ao licenciadas, e todos estes factores tornam poss´ıvel a construc¸ ˜ao de redes de baixo custo energ´etico com grandes ´areas de cobertura a baixo custo monet´ario. Isto torna LoRa muito apelativo para ambientes onde v´arios quil´ometros quadrados precisam de ser cobertos para monitorizac¸ ˜ao, tais como a agricultura. Esta tese centra-se principalmente no posicionamento de gateways numa rede LoRaWAN, a fim de alcançar a energy fairness na rede.(...)
Description
Keywords
IoT LoRaWAN LPWAN Chirpstack OMNet++