LoRaWAN Range Part 2: Range and Coverage of LoRaWAN in Practice (Updated)

April 1, 2019

In Part 1, “The Key Factors for a Good LoRaWAN Radio Range” in our range of coverage, we looked at the theoretical factors that affect the range of a LoRaWAN. In this second piece, the isolated consideration of radio links between two points will be followed by practical examples. Specific examples from actual cases will be presented and evaluated.


 

The specific properties of LoRa, especially the low susceptibility to interference, the low path loss and the very good building penetration, make very high ranges possible , even in the urban environment . Even with modern, software-based simulation methods, the actual range and coverage of a wireless network can only be calculated to a limited extent – which applies to any wireless technology, not only to LoRa, For this reason, especially in the first phase reach and penetration tests, It is an important tool for better understanding the behavior of radio waves in reality in various environments.

In this article, we refer to three documented tests in different scenarios:

  • Urban environment: 5 different test cases
  • LoRaWAN in a suburban area
  • Penetration of cellars for reading meter data

In general, only a few experimental range tests have been well documented in the literature so far.

This is complemented by three calculation models for network coverage:

  • LoRa signals in forest areas
  • indoors and
  • under water – admittedly very special, but nevertheless interesting, as we found out.

In addition, we incorporated our own experience from previous range and penetration tests into different customer scenarios and evaluated the documented tests and calculation models. In a separate article, we will discuss these results in more detail (planned release Q1 2018).

 

Scenario 1: LoRaWAN in the center of a European city

Most of the cities that we have data for have a classical development pattern for Europe: Roughly speaking, there are only a few very tall buildings, some tall buildings and many buildings of only a few floors high. These are not megacities, and high-rise development is limited almost exclusively to the city center.

In more than 20 range tests in the urban environment, we were able to cover more than 10 km with exposed gateway locations. Individual measurements will be discussed later.

In a publication of the hardware provider Libelium, the experimental set-up and the resulting ranges were well documented in Zaragoza [see Source 1 and Source 2]

Description of the experimental setup:

  • These were so-called non-visual links (NLOS, non-line-of sight) in urban environments
  • Spreading Factor 12 (maximum range)
  • maximum output power: 14 dBm
  • Frequency channel: 868 MHz band
  • the receiving gateway Rx was mounted on the roof at about 12 meters height.
  • The transmitting unit (Tx) changed position between 5 control points.
  • At each point, 50 transmission attempts were made.

 

The properties of the control points and the results of the measurement series are summarized in a list:

  • Checkpoint 1: The signal passes through four buildings. Three skyscrapers and a low-rise building do not allow any line of sight on this path. In addition, there is a free space on the way to the recipient. The range is 830 m. 96% of the sent data packets were received.
  • Checkpoint 2: The signal passes through 14 buildings. In this case, there is a large group of low-rise homes near checkpoint 2. There also is an apartment block on the way to the receiver. The range is 960 m. 92% of the sent data packets were received.
  • Checkpoint 3: The signal passes through six buildings. This point is located on the side of a large square in the area. The path goes through a large residential building and then some industrial buildings. The range is 1070 m. 98% of the sent data packets were received.
  • Checkpoint 4: The signal passes through 14 buildings. This is the biggest path. This point comes up against four tall residential buildings. Then there is an open space without obstacles before it reaches another group of skyscrapers. Finally, several industrial buildings are found before the way to the receiver is terminated. The range is 1530 m. 98% of the sent data packets were received.
  • Checkpoint 5: The signal passes through six buildings. This checkpoint is separated from the receiver by several industrial buildings that have no clearances between them. The range is 863 m. 100% of the sent data packets were received.

 

Control point Distance to the gateway (Rx) Number of buildings between Tx und Rx Success rate
1 830 m 4 96 %
2 960 m 14 92 %
3 1070 m 6 98 %
4 1530 m 14 98 %
5 863 m 6 100 %

 

Evaluation of the result and practical optimization suggestions.

The fact that not always 100% of the packets are transmitted is countered with the LoRaWAN standard by the usual methods: If necessary, the communication can be configured so that messages must be confirmed by the recipient (so-called confirmed uplinks and downlinks). the sender waits for an acknowledgment of receipt and sends the data again after a defined period of time if this confirmation does not occur. The values obtained here can all be considered as uncritical.

There are three key strategies to maximize reach and coverage:

  1. With regular LoRaWAN applications, the acceptance of lower success rates can also provide greater coverage and increased range, i.e. the ranges in the test could have been increased by accepting single failed transmissions and then retransmissions.
  2. Network topologies with redundant gateways from different directions lead to higher network coverage with a constant or improved success rate.
  3. The illumination in the area could be significantly improved with a higher positioning of the gateway. The gateway in this test was only attached at 12m height. The so-called Hata Propagation Model, a simple radio propagation model for calculating the path loss of radio waves in the open air, describes the relationship between range and altitude in a very clear way: When the gateway location is increased from eg. 2 to 30 meters, the original range almost doubles (see chart below, Source: Kerlink, Kerlink Manual LoRa IoT Station v2.17).

In one of our customer projects, three gateways (5, 10 and 45 meters in height) were installed in a major German city with more than 150,000 inhabitants and a wide variety of coverage and penetration tests were carried out. A summary of the results can be found in the table.

Height Number of data points Max. Reach Reach average
Gateway 1 5 m 444 5,53 km 1,43 km
Gateway 2 10 m 762 16,27 km 3,3 km
Gateway 3 45 m 1619 20,99 km 2.92 km

 

The results obtained there outweigh the results of the construction cited above, especially by the location with the very high-altitude gateway. The detailed results of this and other tests will be published in early 2018. (Please register at the bottom of the article to receive a message as soon as the results are published)

Scenario 2: LoRaWAN in a suburban area

 

In “A Study of LoRa: Long Range & Low Power Networks for the Internet of Things” by Aloÿs Augustin, Jiazi Yi, Thomas Clausen and William Mark Townsley, a range test carried out in a Parisian suburb was well-documented.

Experimental setup

The gateway was on the second floor of a house, right in front of the window. On the test day, the humidity was 55% with an outside temperature of 15 ° C. Five different test points were chosen, with the distance to the gateway being 650 m to 3,400 m.

The terminal was in a car during the tests. The transmission power of the terminal was set to 14 dBm, which is the default value.

In order to test the performance of different spreading factors, the package confirmation and the retransmission were switched off. The connection check was also disabled, so the distribution factor did not change even if there was a packet loss. – By default, the LoRaWAN network adjusts the spreading factor to the connection quality.

The spreading factors 7, 9 and 12 were chosen for these tests. For each test, about 100 packets with a sequence number were transmitted to the network server.

Result

The higher spreading factors have better coverage than previously described – with an SF value of 12, more than 80% of the packets were received at 2,800 m, whereas with an SF of 7 no packet was received. The gateway was located on the second floor at about 5 m above the ground. The checkpoint was located at 2,800 meters directly behind a building with seven floors. At 3,400 meters, the cover was supplied only by SF12. The price for the high transmission rate using the high spreading factor is a much lower bit rate. On the other hand, network coverage with low spreading factors is much lower.

For a permanent installation, the positioning of the gateway at a more favorable location would have to be considered. Positioning in a building on the 2nd floor is certainly less than optimal for the widest possible coverage.

Scenario 3: LoRaWAN for reading water meters, gas meters and electricity meters in a cellar

In the previously mentioned source of Libelium a scenario is also mentioned in which the basement needs to be covered. Unfortunately, the general conditions are only roughly outlined: In this case, the transmitter was located outside the first floor of an office building at a height of about 3 meters. The receiver was located under the ground floor, at a garage entrance. There was no line of sight between the points and the LoRaWAN range reached 206 m. Not much more was documented.

Much more revealing are the results we achieved with our customers in penetrating tests. Again, we would like to briefly outline three examples (further details will follow in the coming weeks).

In the first test, networking of a water meter was transmitted over a distance of 998 meters from a shaft embedded in the street to a gateway at a height of 35 meters. The connection could be made despite the metallic cover of the shaft. In order to test real conditions, a delivery van was also parked on the shaft, but signals could still be received with satisfactory quality.

Another customer tested penetration in five different basements within a radius of 4 km,

 

1 2 3 4 5
Distance Success rate Distance Success rate Distance Success rate Distance Success rate Distance Success rate
Gateway 1: 5 m 3 600 m 0% 2 700 m 0% 1 600 m 0% 5 100 m 0% 1 100 m 0%
Gateway 2: 10 m 4 000 m 0% 3 400 m 0% 3 800 m 1% 2 800 m 0% 4 100 m 25%
Gateway 3: 45 m 800 m 82% 1 800 m 4% 2 100 m 86% 2 600 m 77% 3 900 m 55%

 

The table shows the distance to the gateway and the associated success rate. The individual locations were tested over several hours or days with several thousand transmission attempts. Basement rooms with their respective adversities (reinforced concrete, 2nd basement, steel cellar doors, etc.) can also be networked over long distances. Here, the height of the gateway plays a significant role.
In addition, it is assumed that use cases require a new transfer of values if the success rate cannot always guarantee a direct transfer.

In a further installation in a neighborhood, data from basements with good connection quality are transferred into an energy management system with 2 redundantly installed gateways. Read more in our blog post “LoRaWAN – a practical example”.

These examples show that LoRaWAN offers great potential for utilities and billing companies when used to transfer data from water, gas, heat and electricity meters from cellars to billing and monitoring systems.

Model calculation 1: The cover of LoRaWAN indoors.

 

Planning for wireless network coverage typically involves both indoor and outdoor planning requirements. Accordingly, statistical propagation models have been developed to support area planning. Here the model of Davide Magrin is idiscussed (see Network level performances of a LoRa system). LPWAN communications networks such as LoRaWAN are essentially PMP, with sensors installed on various floors, including basements. These requirements force network planners to develop digital 3D maps and apply path-specific, deterministic propagation models.

To model the losses caused by the outer and inner walls of buildings, there are several solution approaches. For example, in one of the available models, the influence of buildings on the path loss of LoRaWAN networks is determined by the following units:

  1. Losses through the external walls of buildings hereinafter referred to as EWL.
  2. Losses through the inner walls of buildings;
  3. Increased power consumption due to the fact that a device is above the first floor.

This model can be used as an approach to determining path losses through buildings as follows:

a) Losses through the external walls of buildings:

The EWL for a device is modeled as a uniform random variable that adopts values in a particular range. Due to the fact that two devices do not necessarily experience the same path loss through outer walls, the diversity of materials and thickness of the outer walls should be modeled in a variety of different buildings. Three possible ranges of values and the probability of a node experiencing this type of loss are given in Table 2.

Probability Range r
0,25 [4, 11] dB
0,65 [11, 19] dB
0,1 [19, 23] dB

Table 2:

b) Losses through the inner walls of buildings:

The influence of the inner walls is expressed as the maximum value between two values. The first value represents the loss due to the number of interior walls:

Tor1 = Wi · p, (5)

in which

Wi = evenly distributed in the [4, 10] dB range and
p = number of interior walls separating the transmitter from the receiver.

It is assumed that p = 3 for 15% of the devices and that the rest of the devices are evenly distributed to the values of p = {0, 1, 2}.

The second value needed to model path loss through interior walls is:

Tor3 = αd, (6)

in which

α = 0.6 dB / m – the coefficient of penetration depth and
d value evenly distributed in the range [0, 15] m.

c) The increase of received power:

Finally, the GFH contribution describes the better reception achieved by antenna height. This parameter is determined by the following expression:

GFH = n * Gn, (7)

in which

Gn = 1.5 dB/floor – the profit due to the increase in height by one floor
n = number of floors, is evenly distributed to the values ​​of n = {0, 1, 2, 3, 4}.

These three parameters define the total building loss for an indoor unit as follows:

L Building (dB) = EWL + max (Tor1, Tor3) – GFH (8)

 

In the real world, some tests with different scenarios indicate that installing a gateway on the same roof of a multi-level building with the basement room or basement to be networked can make sense – even if, according to total loss calculation, the direct route is through several floors and walls theoretically no penetration could be guaranteed.

Here, the direct route through the building is rarely decisive, but rather the reflection on neighboring buildings. The path is longer, but also limited by the damping on 1-2 walls and the reflection factor of the building envelope.

Model calculation 2: LoRaWAN range in the forest

 

In rural and semi-rural regions, trees, in particular, can lead to considerable path loss. In addition, a variety of variables must be considered: For example, the tree species, whether the tree is wet or dry, and, in the case of deciduous trees, if leaves are present or not.

Isolated trees are usually not a big problem, but a dense forest is quite a challenge. The attenuation depends on the distance the signal has to travel through the forest and increases with the frequency.

A brief analysis of the impact of forests on the range of a wireless network is provided in CCIR Report 1145 “Propagation over Irregular Terrain with and without vegetation” (International Telecommunication Union, Geneva, 1990) and recommended in ITU-R P.833-4. I n Figure 1, this is summarized as the ITU-R P.833-4 recommendation, which examines the impact of forest land on attenuation.

The attenuation is in the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz, 0.3 dB/m at 2 GHz, and 0.4 dB/m at 3 GHz. Even at lower frequencies, the attenuation is slightly lower for horizontal polarization than for vertical. This difference does not apply to frequencies above 1 GHz. This means that this criterion affects path loss if the signal has to penetrate several hundred meters of forest.

Fortunately, there is also a significant amount of propagation over the treetops due to diffraction, especially if one can fix the antennas almost at treetop height or maintain a distance from the forest.

So it’s not all lost if your network is used near or above a forest. In some cases, this may even be essential (for example, in water level measurements in a wooded area). With a link budget of 150dB (see blog post 1), ranges of 750-1500 meters can theoretically be expected directly through dense forest. In a customer scenario for level measurement, a gateway was installed at treetop height (about 10 meters) and tested a total of 8 locations within a radius of 500-2500 meters. The transmitters were mounted at a height of 30 cm. All locations had good to very good success rates, so quite long ranges can be achieved by diffraction as described also without visual contact (NLOS).

A LoRaWAN network in rural and semi-rural areas that are partially covered by vegetation, has a range of more than 20 km on LOS (Line Of Sight) connections.

Model calculation 3: attenuation in water

 

The attenuation for radio waves is very high in water. Water increases both the mean conductivity and the signal frequency. This can be calculated by the following formula:

α=0.0173 (fσ) (9)

where:

α = attenuation (in dB / meter)
f = frequency in hertz and
σ = conductivity in mhos/meter

The conductivity of seawater is between 2 and 8 mhos/meter, depending on the salinity. In order to be able to communicate at all, it is necessary to use VLFs (very low frequencies, longwaves of 10 to 30 kHz), the attenuation being in the order of 3.5 to 5 dB per meter.

So how would the described relationships affect the LoRaWAN network? For example, if you have a node that can send 5 km through the air with line of sight at 868 MHz frequency, how far would it go underwater?

α = 0.0173 (fσ) = 0.0173 (868000000*2) = 720dB/m.

The power transfer balance of the LoRaWAN network depends on the environment, but for this example, we assume that it is 150 dB. Underwater you could communicate with it about 20 cm wide.

 


If you have specific questions on this topic you can always contact us.

With this admittedly rather theoretical consideration ends the second part on the scope of LoRaWAN. The first part of the article, which describes the key factors that affect the reach of wireless networks, can be found elsewhere on our blog.

 

If you would like to be informed about this topic at the next publication, please leave us your e-mail address.

 

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