Coexistence testing: helping multi-technology devices work together with thorough testing

Author : Martin Varga | Wireless & Custom Engineering Team Leader | Anritsu

01 December 2022

WLAN channelization of 2.4 GHZ band, only 3(4) non overlapping channels
WLAN channelization of 2.4 GHZ band, only 3(4) non overlapping channels

Today, as Martin Varga, Wireless & Custom Engineering Team leader at wireless communications T&M specialist, Anritsu tells us here, there are more wirelessly connected devices than ever before. Found everywhere, they range from consumer electronic devices such as laptops, smartphones & wireless headsets, to household appliances such as fridges & washing machines...

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They can also be found in industrial plants, where robots and smart tools communicate with servers. Even cars today can be considered “smart devices on wheels”, where wireless connectivity is provided by a Telematic Control Unit (TCU).

Wirelessly connected devices are a great convenience, with the biggest benefit being that no cables are needed. This is most often seen in the world of consumer electronics, with wireless headphones and earbuds being a common application. Bluetooth technology has revolutionised their use, offering a mobility, convenience and visual simplicity that users find compelling.

However, nothing is perfect, and the convenience of wireless technology comes at a cost. Wirelessly connected devices transmit information over a medium such as the air. This leads to the biggest threat in wireless communication – interference, which degrades the wireless performance of electronic devices, resulting in lower throughput rates, as well as a risk of losing connectivity.  This is not the case with wire connected devices, where information is sent and received via shielded metallic or optical cables.

Wireless technologies use different frequency bands for communication. These frequency bands can be further divided into many communication channels, which act as independent routes for the exchange of information. They can be characterized by the centre frequency and the channel width – also commonly referred to as bandwidth.

In cellular networks, frequency channels are divided between Mobile Network Operators (MNOs), who pay telecommunications regulatory bodies for a license that gives them access and usage rights. This system is designed to distribute frequency resources fairly between competing mobile operators. Telecommunications regulatory bodies impose heavy fines on operators who use different frequencies for their services than the ones allocated. This makes it vital to ensure that no extra unauthorised radio emission is present in the allocated frequencies, in every link of the communication chain. These regulations mean that licensed spectrum is designed to decrease the chance of possible interference.

SRW portfolio suitable for coexistence testing
SRW portfolio suitable for coexistence testing

The threat of interference is much higher in Short Range Wireless (SRW) networks. The most well-known technologies in this category are Wireless Local Area Network (WLAN) and Bluetooth. They both operate in so called Industrial, Scientific & Medical (ISM) frequency bands, sharing some of the frequency resource. These are unlike cellular networks’ frequencies, as they are unlicensed, but still regulated. As the name suggests, the ISM bands were originally meant for industrial, scientific & medical purposes. However, today it is clear the ISM bands also provide a way to connect wireless devices in homes, offices, cars and elsewhere.

The most notable ISM bands are 2.4 GHz and 5.0 GHz. The first band is used by both the above mentioned SRW technologies, while the latter is used by WLAN only. ISM band 5.0 GHz provides many more channels and in general is much less occupied. This makes it the recommended channel for densely populated places, where many connected devices are expected to be active. The only drawback is the smaller reach of networks operating in the 5.0 GHz band, as opposed to 2.4 GHz, as the shorter signal wavelength results in poorer distance coverage. WLAN used in the ISM 2.4 GHz band has only three non-overlapping channels, further increasing the chance of interference. A possible solution in these bands is to use mechanisms such as Listen Before Talk (LBF), Adaptive Frequency Hopping (AFH) or Dynamic Frequency Selection (DFS).

There are many devices which use different wireless technologies in parallel. The best example is a smartphone. It can be connected to a WLAN network for internet connection and in parallel exchange information with a Bluetooth enabled smartwatch, while still being reachable via a cellular network for voice calls. It is important to conduct thorough testing to guarantee a decent level of user experience for all the wireless technologies. However, it is important to bear in mind that the different technologies’ standards and versions will add to the overall complexity of any testing.

So far, the discussion has focused on the interference which exists due to limited availability of frequency resources. Interference can also result from a bad radio front end design. This can lead to unwanted emissions in frequency spectra, producing interference in other channels. The root of such issues is often a bad choice of materials, or bad placement of components, or simply through using defective parts. To mitigate these problems, regulatory limits for signal transmission and reception have been put in place.

In Europe, these limits are defined in European Norms (EN) created by the European Telecommunications Standards Institutes (ETSI) organisation. As well as defining limits, the ETSI ENs also specify testing procedures and many other requirements. Complying to the standards will ensure the product can meet the requirements for safety, health, electromagnetic compatibility and the efficient use of the radio spectrum. A product can be placed on the European market once all the required tests are performed satisfactorily.

The equivalent regulatory organisation in the United States is the Federal Communication Commission (FCC), and radio communication products sold in the USA must comply with its requirements. There are other similar telecommunication bodies around the world.

Cellular network portfolio suitable for coexistence testing
Cellular network portfolio suitable for coexistence testing

To sum up, there are two main reasons for interference: many devices which use the same radio channels where there is a higher chance of interference happening; and a bad design of a final wireless product, which may leak power in other than the intended radio channel. It is important to ensure devices work as they are supposed to, with radio technologies able to work alongside each other harmoniously. Failing to achieve this could greatly increase the overall cost of developing a product.

Anritsu, as a T&M (test & measurement) company, offers solutions to test and measure the quality and performance of a wireless capable device in all phases of development. The offer ranges from spectrum analyzers and signal generators up to network simulators, also known as call boxes.

For SRW validation, Anritsu can offer a WLAN tester, the MT8862A and a Bluetooth tester, the MT8852B. The WLAN tester supports all legacy standards, including the newest, IEEE 802.11ax (aka Wi-Fi 6), with support for the latest extension to 6GHz band Wi-Fi 6E. It is packed with many features, and is built to meet any future WLAN testing challenges. The Bluetooth tester is a robust, well proven testing instrument which supports the testing of both main Bluetooth types – Bluetooth Classic and Bluetooth Low Energy.

For testing cellular technologies, Anritsu offers numerous instruments. The MT8821C Radio Communication Analyzer supports legacy cellular technologies up to 4G, including cellular IoT (internet of things) technologies Cat. M and NB-IoT.

There is also the MD8475B Signaling Tester, also known as a base station simulator. Like the Anritsu MT8821C, it also supports legacy cellular technologies up to 4G, but places more emphasis on testing the application layer instead of RF (radio frequency) performance.

For 5G technology, there is the MT8000A Radio Communication Test Station. This can operate in Stand Alone (SA) and Non-Stand Alone (NSA) mode as well as support both RF and protocol testing in both FR1 (Sub-7 GHz) and FR2 (mmWave) frequency ranges. The modularity of this platform ensures high scalability, from simple network simulation and testing, up to high order MIMO (multiple-input & multiple-output) and high Carrier Aggregation schemes to achieve extremely high throughput rates.

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