When it comes to selecting a frequency, there are three main factors to consider:
• Type of system
• Country of operation
• Non-licensed or licensed band
Type of System
The type of system and its application will be instrumental in determining the frequency you choose. Broadly speaking, the lower the frequency band, the farther signals can propagate. As such, long-range applications like a reconnaissance drone would stand to benefit from the strength of the 900 MHz band. On the other hand, a higher frequency band like the 5.8 GHz has a smaller and tighter Fresnel zone, allowing it to stay closer to the ground. As a result, it may be an ideal frequency for mobile ground applications. To sum up, each band has its own strengths and weaknesses, making it advantageous for particular applications, so pick wisely.
Country of operation
Radio regulations vary from country to country. So, it is crucial to understand the regulations of the country where your system will be deployed. For example, the U.S. allows the use of the ISM 900 MHz band, while many countries in Europe limit the use of this band. You can refer to our Smart Radio Index for a quick reference. Apart from usage restrictions on certain frequency bands, the level of power output can also be regulated. All in all, it is important to do some research beforehand.
Non-licensed or licensed bands
The non-licensed bands are also commonly known as ISM bands. ISM stands for Industrial, Scientific and Medical. These frequency bands have been designated as open for use by anyone. Therefore, they will experience more noise and interference.
The second group of frequencies is the licensed or federal bands. These bands are reserved exclusively for government organizations and companies that have won government contracts that give them clearance to use specified federal bands for their projects. Regardless of the frequency assigned, all federal bands offer superior reliability and performance. Due to regulated usage of the federal bands, they are much less saturated. Therefore, they have lower noise and interference levels, making these bands the best choice for mission-critical applications for the government and military.
2. Network Topology
Deciding on a network topology is fundamental to the development of any network. There are many network topologies to choose from, such as point-to-point, star, mesh and hybrid, to name a few. Each has its own pros and cons, with some better suited to specific applications than others. So choosing the right one for your application is key to the efficiency, reliability and effectiveness of the system being served.
To-mesh or not-to-mesh
As tempting as it is to choose a mesh topology because of its considerable advancement and popularity in recent years, it is paramount to weigh its pros and cons. We have written an introductory guide to the mesh topology, which you can read here (link to future Mesh article). In short, the network topology that you choose should serve the application for which it has been built.
3. Throughput and Data Load
In every network, it is important to calculate the load. For instance, the build of a network that only carries command and control data would be vastly different from one that requires HD video. Video resolutions range from low-end SD to crystal clear 4K. But more is not always better. Choosing the right video resolution is a balancing act. Enabling 4K resolution can be taxing on the data link, which may make it unstable or even impossible to use. On the other hand, a resolution that is too low may not provide you with adequate video quality.
Another data requirement to consider is lidar – the technology that has been fueling the drone surveying industry. For lidar to accurately acquire and process terrain data, the network must be able to support the data load for imaging, which can be an immense amount of data depending on the imaging software. In recent years, lidar has been used in conjunction with AI software to enable autonomous vehicles to detect obstacles and safely navigate in an open environment. All in all, lidar would add a substantial load to any network.
When designing a wireless system, an important factor to consider is how the RF signals propagate between the transmitter and receiver. This is commonly known as line-of-sight (LOS). The single biggest bane of any wireless network is the lack of line-of-sight.
Not having LOS can cripple or even shut down an entire wireless network. It seems obvious that there should be an unobstructed line-of-sight, but in real-world deployments, things are not so simple or ideal. In fact, an obstructed line-of-sight is usually the norm. Obstructions can come in many forms, including vegetation, buildings and hills. It’s the one problem that RF engineers regularly struggle with.
That’s why Doodle Labs’ Smart Radio features state-of-the-art COFDM and MIMO technology for exceptional multipath performance that thrives in non-line-of-sight, harsh and noisy environments.
Nonetheless, it would be wise to plan ahead and consider the many factors (which we have covered) that contribute to the optimization link. As daunting as it may sound, it is doable.
Two tips to improve non-line-of-sight situation.
- Optimize the antennas’ mounting locations.
Ideally, the antennas should be deployed at a vantage point with minimal obstruction for an optimized Fresnel zone – the line-of-sight area between the transmitter and receiver. The less the Fresnel zone is obstructed, the stronger the signal. Hence, a higher elevation tends to provide better connectivity. In the case of a UGV and other ground-based applications, having one end of the link lower than the other helps to mitigate impact. Compared to a link where the elevation is the same at both ends, a diagonally shaped Fresnel zone has been proven to achieve stronger signal strength for ground-based applications.
- Deploy a multipath network topology.
A star or mesh topology are common recommendations. In the event where a path is met with an obstruction, it will reroute and find another path.
Aristotle’s famous quote “the whole is greater than the sum of its parts” holds true here. All your meticulous planning would come to nothing or, at best, be poorly executed if the network is supported by subpar equipment. The quality of the equipment will make or break the performance of the wireless link. Therefore, it is crucial to dedicate a substantial amount of time to research, procure and evaluate the required equipment.
A good radio is more than just a transceiver. It must be able to do much more.
Firstly, a good radio must have excellent RF capabilities, such as robust data connectivity, secure encryption, signal interference management and low latency.
Secondly, it must be durable, able to withstand extreme temperatures and vibrations, yet be lightweight and compact.
Thirdly, it must be easy to integrate. The easier and faster it is to become familiar with a radio and integrate it into a system, the more time is freed up for other aspects of the project. Time is money.
Lastly, all of the above traits must come in a cost-effective package. There are many options out there on the market, both radios with the highest specs and ones with run-of-the-mill performance. But it’s extremely rare to find radios that offer high performance in a cost-effective package.
We have written an extensive article on antennas previously. So we will keep things brief here.
There are two main points to consider when choosing an antenna: gain and directional orientation.
Gain is one of the most influential factors of a connection as it determines the strength of the signal. Without an adequate level of gain, the data link will not operate. But too much gain leads to oversaturation, which is counterproductive.
Another downside of high-gain antennas is their larger form factor. 900 MHz antennas are notorious for being bulkier than antennas for other frequencies. In addition, a larger form factor usually means additional weight, which is not favorable for applications with constrained space and weight, notably drones.
Once again (pun intended), use a link budget calculator to determine the gain required for your system.
Next up is directional orientation. All antennas can be broadly categorized into two groups based on the direction in which they transmit and receive radiofrequency waves. Omni antennas transmit and receive radiofrequency waves evenly in a 360-degree radiating pattern. A directional antenna focuses radiofrequency energy in a particular direction, enhancing connectivity in that direction but limiting it in others.
Thus, the type of antenna you choose is highly dependent on the application.
For mobile mesh applications (e.g., drones), mobile robotics and unmanned ground systems, we recommend omni antennas because they are more forgiving and suitable for mobile applications where the nodes are constantly changing position and orientation relative to one another. Furthermore, certain omni antennas are multi-polarized to further aid this capability for mobile applications, such as our Doodle Labs antennas (link to DL antennas).
For fixed wireless system applications with little to no mobile nodes, directional antennas may be a better choice. Another reason to deploy directional antennas is their capability to focus radiofrequency energy in a particular direction to achieve longer link distances.
To summarize, when developing a wireless link, the top 5 considerations are:
- Network topology
- Data load
We hope we have given you a basic understanding of how to develop a wireless link. That said, there are many more considerations not covered above.
But the good news is at Doodle Labs, we have developed the Smart Radio with these five main areas in mind. The Smart Radio is optimized for every possible wireless connection and is available in multiple frequencies. It functions well in a myriad of network topologies, especially mesh due to its Mesh Rider OS. And the data load management of the Smart Radio is super-efficient thanks to its built-in intelligence. Find out more about our Smart Radio.