With any successful wireless system, you want to have some theoretical basis that your transmitted information can reach its intended receiver with enough power to be deciphered correctly. This is the basic idea behind a link budget where you compile information about your radio hardware and setup such as transmitter power, receiver sensitivity, antenna gain, frequency of operation, feed line loss, and other environmental factors and use a basic free space path loss equation to determine how far you would be able to send a message successfully.
On the Helium network, this translates to the best place to put your hotspot so you can provide the best coverage and mine the most HNT. Thankfully a new SAAS will allow you to create an easy RF simulation for your potential hotspot placement. The HotspotRF software considers the basic path loss variables, as well as more complex ones such as ground topography and elevation to provide a visual of signal propagation and an estimate on potential earnings.
The service will give you 10 free simulation credits when you sign up. Each credit corresponds to one full simulation in the simulation portal. The simulation credits you have left show up in the right corner of the settings panel. Once in the portal, there are a few things that you will need to set up before your first simulation.
The left panel shows the settings for your simulation environment. This includes the frequency of operation, antenna gain, feed line loss, elevation above ground level, and terrain properties. You will also need to set the simulation latitude and longitude by placing the black dot on the map at your future hotspot location.
Once these are all configured you can run a simulation by clicking the “Simulate Location” button.
Current Hotspot Setup Analysis
Since I already had a hotspot set up, I decided to test the results against my known set of Helium witnesses.
Based on the simulation run above I should have a wide range of potential hotspots to witness and beacon to. Let’s see how that compares with an overlay of my witness list and the heat map.
The overlapping image was just created by overlapping two screenshots with the HotspotRF results at a lower opacity. From this simple analysis, the witnesses in yellow almost perfectly overlap with the RF propagation results! This provides a high level of confidence in the ability to translate the simulation to the real world.
Simulating a New Hotspot Location
Once I was able to acquire a second hotspot I started to look for a new location to set it up. Now I could have tried to optimize the location but the benefits of a place that I have access to that has power, internet, and antenna mounting options is pretty limited. So I decided to optimize for the type of antenna and elevation.
I simulated three elevation heights for a medium gain antenna.
The real takeaway from these is the importance of elevation. You essentially want to get the antenna as high as physically possible so that you can maximize the coverage area.
Simulation vs Actual Setup
Once I was able to get my antenna and hotspot setup I was only able to achieve ~4m of elevation and need a taller ladder to get the antenna higher in the future. but with that caveat let’s check the witness and heatmap overlap.
The Math Behind RF Propagation
The math behind creating a simulation like this is not that complicated. It is essentially a combination of a path loss equation with a line of sight calculator. The most basic path loss equation is the Free Space Path Loss or FSPL equation.
This is derived from the Friis transmission equation by simplifying the antenna directivity and splitting the wavelength into its components of frequency and the speed of light constant.
This allows us to calculate an estimate of the power at the receiver but does not help us determine if a location can be seen by the transmitter and not blocked by terrain.
This is the Line of Sight problem and has been explored by more than a few researchers especially for viewpoint depiction in first-person video games. To learn more about the issue check out the link below.
Matlab RF Topographic Propagation Simulation
This type of RF analysis is not new and has been used for other wireless communication systems to plan their provided coverage maps. This is very important in cellular networks to determine tower placement and forms a strong corollary to the Helium network. One key difference is that cell coverage in LTE is planned from the top down, where Helium requires individuals to determine the best placement for their personal hotspot.
So we can use other tools to perform the same analysis as HotspotRF but requires more involvement from the user to pull in the various data sources needed.
To find your desired Latitude and Longitude on a map you can use the Latlong.net website to find your exact position.
Download Digital Terrain Maps from EarthExplorer. You will need to sign up to download the map files but the process is free.
Just enter the center point of your location and a search distance, select SRTM 1 Arc-Second and download one of the files in the results tab.
Now that we have all the data we can use Matlab to import it for us using the addcustomterrain function of the RF Propagation portion of the Antenna Toolbox.
Matlab Documentation: addcustomterrain
The documentation gives a pretty solid example which I extended with my own terrain file that I downloaded.
With just a simple visual inspection we can see that the RF propagation of my Matlab simulation roughly matches the HotspotRF propagation heatmap. The main differences are due to mismatches in power, gain, and frequency but the topographic landscape and elevation have much more influence on potential reach.
Conclusion
The HotspotRF software is a quick and easy way to check how a potential Helium hotspot location could perform or could be a great tool to optimize a currently set up hotspot location. But it has its limitations true RF propagation is by no means a simple problem and you could encounter real-world issues that the simulation cannot predict like noise or interference sources, building obstructions, dense vegetation as well as atmospheric effects. The deeper you go the more complex the channel models become which could take hours or days to complete. The other issue is incomplete or out-of-date data in the model which could have disastrous effects on the results.
RF propagation by nature is a chaotic system that is difficult to model, it is best to understand that simulations like these are best-case scenarios where none of the other problems are present. It is just one other tool that can help you find the best hotspot placement but that does not mean it guarantees the results.
Extras
Once you do get your hotspot up and running consider checking out Hotspots Health which combines a dashboard interface with a performance analyzer to help you get the most out of your hotspot.
1 thought on “Simulating Helium with HotspotRF”
Comments are closed.