Coexistence testing, similar to compatibility testing, measures the ability of multiple devices to interact in a single environment with limited bandwidth. Coexistence tests are usually conducted for wireless devices operating in shared or crowded wireless environments.
Importance of coexistence testing
As interconnected devices over radio frequency (RF) proliferate worldwide, they must coexist, even if they perform different tasks and operate by different rules. Many such devices operate simultaneously but have a limited RF spectrum available to do so, making coexistence more important.
Here, coexistence refers to ensuring that one wireless device does not negatively impact another wireless device. Impacts can range from loss of function to corrupted data to interrupted signals.
Proper coexistence testing ensures safe, effective data transmission in a shared wireless environment. It also ensures that the various functions of the devices in the environment are not impeded, and there are no signal interruptions or losses. These capabilities can be critical in environments where even slight disruptions can have catastrophic consequences. One example is healthcare.
Benefits of coexistence testing
Thorough, systematic wireless coexistence testing ensures that the various wireless devices in a shared environment coexist seamlessly. It provides a proactive way to confirm that the devices will perform their tasks adequately without disrupting or being disrupted by the other devices. Furthermore, it ensures that data and information are transmitted properly with minimal data corruption or loss.
To help verify seamless and disruption-free coexistence with other devices, coexistence testing enables device manufacturers to simulate realistic end-to-end scenarios, such as interference and jamming. They can then implement proactive, appropriate fixes to ensure that devices continue to function well even under adverse conditions.
Coexistence testing also allows manufacturers to quantify performance metrics for their devices. These wireless key performance indicators (KPIs) may include uptime (also known as availability), network jitter, signal strength, bandwidth, throughput, packet loss, and latency/roaming latency.
Measuring and quantifying these KPIs is crucial to establishing relevant baselines for device and network efficiency and stability, speeding up issue detection and resolution, minimizing downtime duration and frequency, and ultimately enhancing wireless performance and the user experience.
Finally, coexistence testing provides a way for manufacturers to demonstrate that their wireless device complies with globally accepted standards like ANSI C63.27-2021. This standard promotes robust and functional wireless performance (FWP). It provides evaluation procedures, supporting test methods, and KPIs to assess and quantify the ability of wireless devices to coexist with other devices. It is also an FDA-recognized “consensus standard” for medical devices, meaning the FDA recognizes it as a complete standard for assessing the RF wireless coexistence of medical devices in their intended operational environments.
Coexistence testing process (how to perform coexistence testing)
The first step of coexistence testing is to create a test plan. In this plan, the test engineer must define the intended environment the device is most likely to operate under, such as a professional, healthcare or home setting. They must also choose the test signal, which is an RF signal used to assess how well the equipment under test (EUT) functions when other devices or signals are also present in the RF environment and potentially sharing the same or adjacent frequency bands.
Next, the engineer compiles the FWP requirements and KPIs for the device’s intended environment. They will define “optimum” performance and document “acceptable” tolerable failure, and establish baseline FWP and signals (e.g., ambient noise). The primary functions, associated wireless protocols and necessary RF bands (that the device will use) also need to be determined.
Testing begins by modeling the intended environment and introducing interferences to see how the device and signals react using a spectrum analyzer. Basically, testing is first done for the intended environment without any signals. Then, interference is introduced to see how the device, signals, and interference interact. During testing, the tester tests the FWP against the previously determined acceptance criteria and KPIs.
After testing — which can take several days or even weeks — devices are categorized into various risk levels. These levels determine the next steps needed to increase coexistence. For example, the tester may implement techniques like frequency allocation or may increase physical separation between the devices. In some cases, a device redesign is required.
During testing, it’s best to use a signal generator. This device generates interference signals that will challenge the device being tested against real-world scenarios. Additionally, the test environment should include a signal analyzer that monitors the signals in the RF spectrum. It is also recommended that dedicated, customizable software be used to accommodate specific test cases and KPIs and to automate (thus simplifying and accelerating) the coexistence tests.
Uses of coexistence testing
Coexistence testing can be applied to a wide range of use cases, such as:
- Ensuring that medical devices peacefully interact with other medical devices in a clinical or commercial environment.
- Testing website functionality across a range of browsers and devices.
- Running applications on a range of OSes and versions.
- Analyzing compatibility or the integration of various software.
- Examining whether IoT devices or smart home configurations perform independently over one network.
Coexistence testing is particularly important in the medical field. In healthcare environments, the number of wireless devices that interact with each other and share data is growing rapidly. These include wireless electrocardiogram (ECG) monitors, glucose meters, cardiac monitoring systems, wearable health monitors, pulse oximeters, and insulin pumps. Many of these devices are critical for human health and safety, so it’s important that their critical functionality stays intact. It’s also essential to ensure that they interact safely and reliably and perform at expected levels.
There have been recorded instances of cell phones causing infusion pumps to stop or pacemakers to be controlled by unauthorized sources. Manufacturers must test that devices can perform when introduced to external devices or interferences to address safety, reliability and mortality concerns. This is where coexistence testing is vital.
Coexistence testing is also relevant in many other sectors that use radio technologies and wireless devices:
Device risk categorization in coexistence testing
Device risk categorization is an important aspect of coexistence testing. Devices are usually categorized into one of four risk-based tiers:
- Major risks associated with the failure of coexistence.
- Moderate risks such as delayed or disrupted service are associated with device coexistence.
- Minor risk, such as inconvenience, is associated with device coexistence.
- Negligible risk where no further testing is needed.
Depending on the device and risk tier, product redesign may be needed prior to release. Risk management standards require wireless technology to be assessed in relation to external, potentially hazardous factors. Multiple techniques, such as physical separation, frequency allocation, improved security mechanisms and transmission variation, can improve device coexistence.
Coexistence testing methods and best practices
Types of setup for coexistence testing include mimicking a realistic wireless open environment or conducting radio frequency over a direct coaxial cable connection. During testing, testers should evaluate cases where multiple devices of the same type are operating simultaneously and cases where a device is operating simultaneously alongside other systems.
Ideally, testers should evaluate all the potential or expected sources of electromagnetic disturbance (EMD) in a known environment. They should also check for channel interference (co-channel and adjacent) from other systems. Finally, they should evaluate the EUT against multiple signal types, including Bluetooth Low Energy, Wi-Fi and LTE.
Coexistence testing offerings
Coexistence testing products can bundle signal generators, companion devices for radio signals, and automated software. Reliable offerings include multiple RF ports, with each port supporting multiple virtual signal emulations. This multi-port/multi-emulation combination provides for multiple interference signals to test the device for numerous real-world scenarios.
Besides generating signals, coexistence testing products can also monitor signals in the RF spectrum and characterize system-level path loss. Path loss indicates the level of signal attenuation (loss) as it travels from the transmitter to the receiver and is an important determinant of wireless network coverage, reliability, and performance.
Most include a companion device for radio signals (Wi-Fi or LTE) and software that automates coexistence tests. The software ensures that the tests comply with relevant standards. It provides pre-configured interference scenarios that simplify testing for a wide range of possible issues. Testers can also easily select the required frequencies and make power level adjustments to interfering signals.
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