Wireless nodes in a wastewater sewer - Project 2

In this issue of IoT M2M Times, we describe the solution of wireless IoT with the deepest indoor using the example of a wastewater sewer. We hope you enjoy reading this.

The marketing guys from the LoRaWAN Alliance, Semtech and 3GPP often don't have a degree in electronics and physics and want to teach us that LPWAN enables long ranges. The guys from TTN take it to the extreme and fly like Icarus high into the sky and show us a 700 km range. Let's do it better with SubGHz mesh net called Neomesh by NeoCor

Table of content

• Unlicensed like Icarus flying to the sun or licensed like Charon in the underground
• Wireless sensors for Charon's underground waters
• Which components and services should be used

Unlicensed like Icarus flying to the sun or licensed like Charon in the underground

Icarus wanted to go high up unlicensed. If you don’t follow the rules like Icarus, then the fall comes after the flight. Icarus melted the wings. Why do the unlicensed LPWA companies of all firms repeatedly report hot-air balloons or weather balloons with extreme ranges and fly towards the sky and the sun? Up there towards the earth’s atmosphere, there are not so many customers and projects. Life takes place on the ground. A proverb says “The streets are paved with gold”. Let’s get back to the ground of facts.

The electricity, water, and gas meters are in Germany in the basement and thus in the underground. Wastewater channels are in the deepest underground. Dogs and cats do not fly around and canaries are rarely located. Our ageing society moves on foot or in a wheelchair and so far wheelchairs have no jet propulsion. Plants grow with roots in the soil. Vehicles move on roads and railways in cities often travel underground.

In realistic IoT applications you do not fly to the sun like Icarus, but climb down into the underworld. In the modern world, access to the underworld is via manholes. Such manholes are often monitored for water levels. The Styx River does not flow there, but the wastewater of our society does.

As soon as the radio wave is out of the manhole, it only has to overcome the walls of the buildings to arrive at the finish of an LPWA antenna mast. Icarus could see far over the country. The ferryman Charon in the underground can’t see the sun and even if he comes to the edge of the manhole, in a big city like Berlin he will only see the walls of buildings. The direct view to the sun or to the LPWA tower is impossible for Charon.

The same will happen to the LPWA radio wave in our state capital Berlin. Berlin has an area of 892 km2. With only 36 promised LPWA masts each antenna must supply approx. 25 km2. That means approx. 2.9 km radius per cell. The pictures illustrate how 25 km2? (big circle) in the unlicensed band in Berlin look compared to the cellular base stations. Each blue triangle represents one cellular base station. We have three network operators in Germany. The dots in three colors (red, blue, green) around the triangles symbolize the three network operators. Probably the two large operators have more antenna towers than the smaller operator. In the diagram, we divide them into equal parts. The result shows the clear majority of licensed network operators. Each of the licensed NB-IoT / LTEM operators owns at least 50 sites in the marked half-circle area in Berlin. It is in summary estimated to have 300 cellular base stations. If 30 % will run on NB-IoT and LTEM then we talk about an estimated 100 NB-IoT / LTE-M base stations against just one gateway in the unlicensed band.

The Olympic LPWA championship in Berlin was won by NB-IoT. The map of Vodafone clearly shows that NB-IoT was ahead in Berlin in September 2018. In the meantime, Deutsche Telekom and Telefónica did their homework and launched their NB-IoT as well. On top we got LTE-M and the peak of the 3GPP iceberg is national roaming on NB-IoT and LTE-M worldwide. In the best case, one sensor can access 6 networks.?

We did the analysis of the base stations and the gateway in parallel to the Sigfox Congress in Berlin in September 2018. 36 base stations should be sufficient. At that time, we only had 2 NB-IoT networks in Germany. In the meantime, we have 3 NB-IoT and 3 LTE-M networks. The cellular LPWANs have densified their network. The French Icarus fell from the sky on the 26th of January 2022.

Wireless sensors for Charon's underground waters

If you want to find gold you may have to dig deep. Deep under the ground of our cities, we don't find gold but the wastewater channels. If we dig even deeper we might find Charon.

Wireless IoT for water and wastewater is worth its weight in gold. Water is a limited resource worldwide. Too much water in too short a time is a problem. Corrosion and ageing of sewers is also a problem. There is much to measure in the underground of our cities. The high link budget of LPWAN techniques is usually not enough to get underground.

The GIF video shows the problem with LPWAN and the solution with a Sub-GHz mesh net from NeoCortec. The graphic is not in scale. The sewers in Germany are laid deeper to avoid freezing of the water during frost. If the LPWAN mast is close to the manhole, then reading the sensor is possible. If the mast is further away it is impossible. With an LPWAN to NeoMesh gateway reading is always possible. The gateway establishes the connection to the LPWAN mast. Since NB-IoT, LTEM and NeoMesh use a TDMA and have been optimised for minimal energy from the start, the gateway, router and nodes can operate on battery power. In NeoMesh, every node is also a router. Node, router and gateway go to sleep at the same time. A node can operate on 2 AA cells for 7 years. Network planning is not necessary. The network builds itself. There are 65000 nodes allowed in a NeoMesh. The number of hops is infinite. For example, with a range of 50 metres and 65000 nodes in a row, you can bridge 1300 metres. Due to the many hops, the message is delayed. All messages are acknowledged. The connection from end to end is therefore secured. How is it solved now?

Which components and services should be used?

Sub-GHz mesh net by NeoCortec?

A sub-GHz mesh net from NeoCortec called NeoMesh was used to complement the low-power mobile technology and NB-IoT/LTE-M. NeoCortec drastically reduces energy consumption per node through extremely precise timing. Instead of transmitting 1 to 3 km to the mobile phone mast, NeoMesh transmits up to approximately 100 metres indoors. Outdoors, 500 metres are possible. In the wastewater channel, tunnel or mine the range is related to the diameter of the tube. A message hops from the radio node to the next radio node in the NeoMesh. Each node in the NeoMesh is also a router. In addition, each message is acknowledged to the next node. In the event of a fault, the message is transmitted again in the next cycle on another of the 15 channels. If a node fails, the module in the NeoMesh automatically searches for a new path. All nodes synchronise every 1 to 30 seconds. With a pulse of 30 seconds, a node can operate for up to 7 years from 2 alkaline AA cells. NeoCortec drastically reduces energy consumption per node through extremely precise timing. Instead of transmitting 1 to 3 km to the mobile phone mast and passing the ground surface, NeoMesh transmits up to approximately 50 metres deep underground with standard antennas.

NB-IoT, LTEM, GSM module

NB-IoT and LTE-M, unlike GSM, were specified from the start for data communication with low energy consumption. However, we use a fallback to GSM, because wastewater monitoring is a worldwide business. NB-IoT and LTE-M use various timers that enable an IoT device to be connected bidirectionally. For example, the NeoMesh gateway listens to the cellular channel every minute to 175 minutes to check if a message arrives. The NeoMesh gateway can go to sleep, receive nothing and still remain registered. In the event of a fault, the cellular radio module is woken up. There is no need to register again in the cellular network, thus saving energy. Furthermore, NB-IoT and LTE-M offer up to 20 dB more link budget than the previously used GPRS. 8 dB corresponds approximately to doubling the range or roughly the attenuation in a wall in a building. With 20 dB, the user can penetrate 2 more walls or reach devices in the basement better. However, this is not enough for wastewater channels.?

MCU STM32L496

The MCU STM32L496 with 256 KB flash memory is woken up every 30 seconds by the NeoCortec module, writes the measured value to the memory and makes a target/actual comparison. If a limit value is exceeded, the cellular module is woken up and the message is transmitted to the server within 2 to 10 seconds. Since the fault message is the exception, the gateway usually sleeps and transmits the data to the cloud once or twice a day if desired.

SIM card

SIM cards from Crout are used. SIM cards from Crout can receive profiles remotely, just like an iPhone. When it is switched on, the drone checks the country and then receives the right profiles from the local network operators. You can safely reach any of the country's 3 NB-IoT / LTE-M networks. In the profiles, we can specify the sequence of the networks. The SIM card is not roaming in Germany but is basically three SIM cards in the form of one SIM card. In total, there can be up to 7 SIM cards on one SIM card. The settings for the default can vary from region to region.?

LwM2M server

We have chosen LwM2M from Crout for the protocol. Crout thus supplies not only the SIM card but also the test server for LwM2M. Unlike MQTT and CoAP, LwM2M is much more than just a transmission protocol for data. One of the remarkable features of LwM2M is device management. Since LwM2M was co-influenced by mobile network operators at the OMA, their experience in managing wireless phones has been incorporated. Logging on to the LwM2M server is possible in various very secure ways. The bootstrap start-up of a device is also standardised under LwM2M. Necessary firmware updates are also managed by the LwM2M server. The communication of a device is standardised with profiles and resources. Through the mandatory profiles Device (/3), Connectivity monitoring (/4), Firmware update (/5), Location (/6), any LwM2M device from any manufacturer can communicate worldwide with any LwM2M server on the beautiful blue planet. After successful registration, the LwM2M server asks which profiles are supported and then knows whether it is a water meter, presence detector, level meter or tracking device, for example. An LwM2M device can also support several profiles in parallel. For the LwM2M server, the wastewater monitoring is a kind of router or also a kind of I/O device. Most functions required by the monitoring device are already specified via the LwM2M protocol. The project team can therefore immediately focus on programming the application. Everything else is already specified through LwM2M. LwM2M is a very open protocol and allows users to create their own profiles. There are profiles for I/O channels but we have up to 65000 nodes in the network. Practically, there are 500 to 1000. No one reached 65000 right now. But there is no suitable profile for 500 - 1000 I/O channels. That's why we have to develop our own profiles.

Antennas

A cellular PCB antenna is used in the gateway. This reduces the cost of the components. At the same time, the antenna can be easily adapted to the enclosure.

In the tunnel/wastewater channel, a PCB antenna with approximately 0 dBi antenna gain can be used. Such antennas can be found in the study "Do it yourself PCB antennas for the wireless IoT" by NeoCortec. When selecting antennas, a test setup is recommended. The radio waves will propagate in the wastewater channel not only directly, but also by refection. Depending on the water level, the reflection and phase will change. The radio waves are added up and the signal increases or decreases depending on the phase position. As NeoMesh hops over 15 channels across the whole band, the phase will also change a little. An antenna that is good for a sensor network on the surface of the earth does not necessarily have to be good in a wastewater channel.

Sources:

• Article about LPWAN in the underground: https://www.gsm-modem.de/M2M/iot-university/unlicensed-ikarus-licensed-charonn-the-underground/
• Low cost do it yourself PCB antennas for the wireless IoT: https://www.akoriot.com/white-papers/

Your wireless IoT projects:

If you have a need for a custom antenna or are just starting a new innovative wireless IoT project, I would love to hear from you. Wireless IoT and antennas are my mission. Thank you in advance for your request to harald.naumann (at) lte-modem.com

Imprint

• Harald Naumann, Ludwig-Kaufholz-Weg 4, 31535 Neustadt, Germany
• Contact: harald.naumann (at) lte-modem.com, Phone: +49-5032 801 9985, Mobile:+49-152-33877687