October 13, 2021

How to Solve RF Interference & Signal Propagation Challenges in a RTLS

14 minute read

Radio frequencies (RF) play a key role in locational awareness due to their ability to pinpoint the location, speed and distance of an object. Often described as the GPS of the indoors, different RF frequencies like Ultra-Wideband (UWB), Bluetooth Low Energy (BLE) and Chirp, provide valuable data on the movement of people, assets and vehicles, helping to inform and optimize various operations of a business across multiple industries. In contrast to wired communications, wireless RF systems are agile, particularly in offering the blue dot location experience with reliability and visibility within different physical conditions and devices.  

However, this doesn’t mean that RF is not subject to interference – in fact, there are multiple ways for RF signals to be disrupted. We’ll go over the three most common ways your RF signals are scrambled and more importantly, how to overcome these issues.  

How Does RF Encounter Interference to Begin With?  

Since RF signals are invisible, it can be difficult to explain each type of interference without a strong analogy. Luckily, there’s one that is easy to explain and is accessible to us – sound. Sound waves operate much in the same way as radio waves - vibrating at higher and lower frequencies to produce different results. In order to better explain how each type of signal propagation challenge occurs and can be fixed, let’s move forward with using sound as a metaphor.

What are the Three Major Types of Signal Propagation Challenges? 

There are three main types of RF signal propagation challenges – packet collisions,  attenuation and multi-path propagation. Each lead to a disruption of RF signals which means the sensors emitting and receiving these signals are unable to communicate and detect the location of the objects they are tracking as planned.  

What are Packet Collisions? 

Packet collisions occur when two, or more sensors are transmitting signals at the same time and frequency to a receiver. Because the receiver is getting signals from both, it’s unable to properly interpret and understand the signals being emitted from either one of them. This is akin to two people speaking to one person standing in-between them, at the same time. Since they’re trying to communicate simultaneously, in the same language (frequency), they end up talking over each other. 

Likewise, when devices aren’t configured or set up properly, they can talk over each other when sending signals to a receiver. Imagine two tagged assets aiming to reach the same receiver – because they’re both emitting signals of the same frequency, the receiver cannot properly receive and process their signals.  

The solution? Ensure your devices “listen” before they “talk” so that they start to send signals to a receiver only when no other asset is already transmitting. This is in most cases the best solution to prevent the sensors “talking” over each other. In computer networking, this is known as carrier-sense multiple access with collision avoidance (CSMA/CA). 

What is Attenuation?

Attenuation is the loss of energy of a signal due to its need to pass through a medium. It’s like talking through a pillow or a thick wall – you know that something is being said, but certain materials are blocking the way, making it impossible to hear what a person could be trying to say to you. Cables, air, and water between a RF signal and receiver all count as potential attenuation barriers.  

For example, tagged assets in a warehouse may be stacked closer to the ceiling while receivers may be placed at ground-level, making the air, objects and cables between them immediate barriers to the RF signals emitted by assets. Also, if an asset moves too far from the area’s receivers, its signal may become too weak to be detected due to new barriers between itself and the receiver it’s trying to reach, leading to signal loss. 

While this may sound like a daunting issue, solving this challenge is simply a matter of proper planning and awareness on how to mount and place assets and receivers within a particular facility. When deployed intelligently within an indoor location, asset tags will have no issue reaching their receivers, despite potential attenuation barriers. And here’s an extra consideration to keep in mind – each RF signal has its own capabilities when it comes to which materials it can easily pass through. If you choose the right type of RF signal based on the types of barriers that are present in your facility, you can significantly reduce the chance of signal loss due to attenuation. 

What is Multipath Propagation? 

Multipath propagation is a type of interference which occurs when the original signal being emitted from a transmitter is directed to the receiving antenna via two or more paths. To go back to our analogy of sound, it works just like an echo. Take for example, how sound echoes in a big hallway – if you clap, the sound will come back to you through multiple reflective surfaces (wall, floor, smooth objects), resulting in an echo. Multipath propagation is the RF version of an echo, except instead of sound, it’s the RF signal that’s being reflected and received by the same antenna multiple times.  

While multipath propagation doesn’t necessarily block the RF signal of an asset from reaching a receiver within a facility, it can lead to inaccuracies in where the receiver pinpoints the asset to be since it’s getting a reflected signal instead of a direct one. That’s why it’s very important to keep the potential for multipath propagation in mind when deploying your RF solution.  

Furthermore, based on the scenario, multipath propagation might even help instead of hinder your RF set-up. However, if multipath propagation is preventing your receivers from getting the accuracy they need, it’s important to place receiver antennas in direct line of sight (LOS) of tagged assets and ensure that anything that could reflect the RF signal is either blocked from doing so or moved out of the way.   

In a Nutshell - Solutions for RF Interference Caused by Packet Collisions, Attenuation and Multipath Propagation

Problem 

Solution 

Packet Collisions

  • Devices that listen before they talk, also known as CSMA/CA, that can automatically stop themselves from talking over each other 
  • Switch devices that might fire simultaneously to a different RF technology to avoid frequency interference when trying to reach the same antenna

Attenuation 

  • Add more receivers in your facility so moving assets will transmit to not just one but multiple receiver antennas.  
  • Tailor deployments based on your environment to specifically avoid signal attenuation 

Multipath Propagation 

  • Optimize the signal detection logic and signal selection of a scenario to keep multipath propagation in mind 
  • Increase the quantity of transmitters and receivers deployed as so to increase the chance of at least one getting a direct Line of Sight (LOS) RF signal 
  • Selecting the shortest distance possible between transmitters and receivers tailored signal detection logic 

The right RTLS technology should consider the different types of RF interferences, including the above, preventing any disruption in RF signals and reception.

Avoid RF Signal Interference with Inpixon’s Real-Time Location Solution (RTLS)

Inpixon's RTLS solutions offer leaders instant real-time visibility into their operations, allowing them to track and gather data on their assets, equipment or personnel that help them make smarter, more informed decisions about their business. Explore in-depth RF deployment solutions for your facilities or get in touch with our team of RTLS experts by messaging us directly! 

Topic(s): IoT , Positioning
Author

Norman Dziengel

Norman is the Product Manager at Inpixon, with over 5 years of experience at the company. Norman holds a PHD in Computer Science with a focus on wireless sensor networks. With experience in product marketing, product management, and design of ranging and RTLS products, he is a core member in refining and innovating Inpixon’s RTLS product portfolio.

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