With the rapid increase of IoT, the world around us now has billions of devices connected to the internet, and many more are coming online every second. IoT consists of devices for the consumer marketplace, agriculture or mission-critical industries such as healthcare or automotive electronics. Device designers are adding more wireless functionalities into devices. However, they may not be aware of the regulatory compliance tests and certifications required in the countries where they plan to sell the product. This article chronicles the framework of regulatory compliance tests and the evolution to meet the rapid growth of wireless devices on the industrial, scientific and medical (ISM) bands.
Regulatory compliance tests
ISM bands are available for unlicensed use, which makes them convenient for consumer applications without the complications of licensing each installation. These bands are located at frequencies from hundreds of kilohertz to hundreds of gigahertz in about two dozen frequency allocations. The initial ISM specifications were intended for noncommunication purposes, such as industrial heating for metal furnaces and microwave or induction heating for consumer appliances. Over the past few years, with the increase of IoT applications, services such as near-field communication, Wi-Fi, Zigbee standard, Bluetooth and wireless telephones dominated these ISM bands with various types of modulations and protocols.
Since the proliferation of devices on ISM bands, interference has become a serious problem. Regulatory agencies such as the Federal Communications Commission (FCC) in the U.S. and European Telecommunications Standards Institute (ETSI) in the European Union set out to facilitate effective and efficient use of the radio spectrum. These agencies established standards to enforce cooperative behaviors between devices in the same frequency spectrum to avoid mutual interference and inefficiency resulting from the interference.
Tests such as receiver blocking and spurious emissions focus on receiver performance to ensure devices can operate in the busy radio spectrum without radiating unnecessary signals. Protocols such as the 802.11 family of Wi-Fi signals can demodulate signals from similar nearby networks. The process allows them to use the spectrum cooperatively to avoid collisions and interference. However, there are many types of modulation on the ISM bands. Devices cannot decode extrinsic modulations and protocols, therefore, cannot intelligently share the channels. This results in collisions. Wireless regulatory compliance tests now include checks to reduce interference between radio frequency (RF) signals, regardless of their modulation and protocol.
One example is the ETSI adaptivity test of the channel access mechanism in the wireless subsystem. New wireless communication chips and subsystems must contain a channel access engine mechanism to sense, avoid other signals and share the spectrum over time. This mechanism will sense RF energy in the active channel prior to the start of transmission. If the detected RF energy is above a certain level, it delays the device's transmission until after the sensed energy is no longer present. The delay, or idle period, must also extend for a semi-random duration beyond the end of the sensed signal. This random delay is needed especially if multiple devices are waiting to transmit. Only one device will initiate the next "conversation" on the air, and other devices will detect that signal and pause.
This step is critical to avoid the collisions that would happen if all the devices were to transmit simultaneously after the delay period. The channel access engine includes calculations based on priority class and pause duration to allow fair sharing of the spectrum over time.
The ETSI EN 301 893 adaptivity test measures the behavior of the channel access mechanism. It should reduce the likelihood of collisions between different signal types and increase the tolerance of extrinsic signals. The adaptivity test simulates three different signal types using standard RF test waveforms of orthogonal frequency-division multiplexing, additive white Gaussian noise and LTE.
Complex challenges using new bands
As the radio LAN band expands to include nearby frequencies, the existing services in the band require protection from the new unlicensed users. For example, radar services that operate at the 5 GHz range might experience interference when the ISM band expands to allow operation in these radar frequencies. Regulatory agencies defined the dynamic frequency selection (DFS) test to sense common radar signals. The channel associated with the radar signal is vacated or flagged as unavailable for use by the transmitter if it detects a signal.
The use of radar varies by geography. In some locations, there could be only a few radars with which the radio LANs would interfere. Based on its operating frequency, the device must show a certain probability to detect a radar signal. The device needs to cease operation or rapidly move its network to another channel to keep off the radar frequency for 30 minutes.
The regulatory tests for DFS are challenging because they require significant behavior sequences and timing in the radio LAN device. Many types of radar signals are in use, and each signal type must undergo testing. Furthermore, radar signals may be present on different channels. Automated test systems can significantly reduce the overall time needed for engineers to complete tedious and repetitive DFS testing tasks.
New regulatory test requirements for Wi-Fi 6E
Wi-Fi 6E is another expansion of the 5 GHz ISM band, up to 7.2 GHz in the U.S. and less in some other countries, which is 1.2 GHz of additional spectrum above the present allocation with services active in the additional spectrum. The FCC has defined a new set of tests for devices used in the Wi-Fi 6E bands. The primary intent of these tests is to protect the incumbent services, such as terrestrial microwave links and satellite services. The new test requirements address antenna patterns to avoid radiating signals more than 30 degrees above the horizon. Another new operation requirement uses a database to identify available channels based on the geographical location of the Wi-Fi 6E device. In locations of known incumbent users, unoccupied frequencies will be available, but occupied frequencies will not.
The Wi-Fi 6E test requirements also include a function named contention-based protocol. This protocol is very similar to the ETSI adaptivity test and will detect a device's activity on the active channels and cause it to delay transmissions until after the detected signal is gone. A semi-random delay will help to time transmissions, avoid collisions and increase the likelihood of success on the first transmission.
Prepare for complex regulatory compliance tests
These new regulatory compliance tests have significantly increased the complexity of the test process. Gone are the days when simple tests for power, bandwidth and frequency were all that was necessary to attain regulatory compliance. New tests such as DFS, adaptivity and contention-based protocol now require collecting large volumes of data at high speed, with precise timing of the device under test's (DUT) behavior. To prepare for the future of regulatory compliance tests, it is crucial to:
- invest in an automated test system that can perform these complex tests with speed and accuracy;
- ensure the test system can collect test data and process and analyze the data sets;
- maximize test system utilization through reconfiguration of subsystems for parallel tests; and
- protect an investment through a frequent software upgrade as wireless standards and regulatory test requirements continue to evolve.
Early preparation will help to reduce the overall test time and help to achieve time-to-market goals, even with the complex new tests required for regulatory compliance certifications.
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About the author
Janet Ooi is a lead in Keysight IoT Industry and Solutions Marketing. She graduated from Multimedia University in 2003 with Business Engineering Electronics with honors majoring in telecommunications. She worked at Intel as a process and equipment engineer for five years before joining Agilent Technologies -- now known as Keysight Technologies -- in 2008 as a product marketing engineer. Since then, Janet has also taken on product management, business development and market analyst roles.