802.11 was the first WLAN standard and was created in 1997 by the Institute of Electrical & Electronics Engineers (IEEE). As this only supported a maximum network bandwidth of 2Mbps, the IEEE developed the 802.11b specification in 1999, which supported an increased bandwidth of up to 11 Mbps. Of course, both of these standards use the same unlicensed radio signalling frequency of 2.4 GHz, which can incur interference with other appliances also using that range.
However, as the 2.4 GHz spectrum has become further popular, wireless device and mobile phone manufacturers are increasingly developing products for the less populated 5GHz range, using the 802.11a standard. However, the 5GHz range is part of the wireless spectrum that is strictly regulated in many countries as it is already allocated to many radar applications, including those for military, meteorological and maritime use.
The opening up of this spectrum for unlicensed use has created a requirement for Dynamic Frequency Selection (DFS), a usage protocol designed to stop such devices affecting radar systems as it continuously monitors for potential interference, ceasing transmission and switching to an alternative channel if it detects radar presence.
Manufacturers of many of the devices utilising the 5GHz bands must therefore prove that their products comply with DFS requirements, so that the operation of radar systems will not be compromised. TÜV SÜD’s DFS test & certification service will test against regulatory requirements for major regions of the world, including the European Union’s harmonised standard EN 301 893 (version 1.7.1), which affects 31 countries in Europe, CFR47 Part 15E (USA) and RSS-210 (Canada).
European Union overview
The European harmonised standard that covers unlicensed devices operating in the 5GHz band, and which also contains the DFS requirements, is ETSI EN 301 893 V1.7.1.
The standard states that a Radio Local Area Network (RLAN) must employ a DFS function to:
- Detect interference from radar systems (radar detection) and to avoid co-channel operation with these systems
- Provide on aggregate a near-uniform loading of the spectrum (Uniform Spreading)
Radar detection is required when operating on channels whose nominal bandwidth falls partly or completely within the frequency ranges 5 250 MHz to 5 350 MHz or 5 470 MHz to 5 725 MHz. This requirement applies to all types of RLAN devices regardless of the type of communication between these devices. Uniform Spreading is only required across the frequency ranges 5 150 MHz to 5 350 MHz and 5 470 MHz to 5 725 MHz. Uniform Spreading is not applicable for equipment that only operates in the band 5 150 MHz to 5 250 MHz.
EN 301 893 does not require this feature for client devices provided that they:
- Operate below a power level of 200mW
- Are not capable of initiating communication on a channel
- Only operate on a channel under control of a master device
- Respond to the commands to move to another channel from the master device
- Meet the channel move time and channel closing transmission time.
The Standard defines how master and slave devices are required to operate in conjunction with each other, including how a master device must perform a Channel Availability Check to ensure that there are no radars operating on any selected channel before the RLAN starts operations on an available channel. The Standard also defines the Channel Shutdown process that must be followed if a radar signal has been detected.
Importantly, the Standard also outlines user access restrictions which ensure that the user cannot access and change the DFS controls (hardware or software) that are related to radar detection.
North America overview
The FCC’s test procedure and radar parameters procedures were released in January 2006. However, interference problems between unlicensed devices and radar systems were reported, and the FCC therefore introduced interim measures. These allow new grants and permissive changes to be issued for master devices, provided that they meet all of the following requirements:
- Devices must not operate in the 5600 – 5650 MHz band
- Test data must not include measurements of, or references to, operating channels that fall into the 5600 – 5650 MHz sub-band
- Applications for FCC approval must include a full explanation as to how operation in the 5600 – 5650 MHz band has been prevented.
The FCC has recently amended its rules to allow devices operating in the 5150-5250 MHz band to operate outdoors at increased power levels.
Certification applications for master devices i.e. those that have radar detection capabilities, and operate in the DFS bands, can be approved by a TCB however the FCC also requires a sample of the device in order to perform its own pre-approval tests against DFS requirements, including a review of the device’s Graphical User Interface to check conformance to the FCC Software Configuration Control policies of KDB publication 594280. Products will not be certified until this has been successfully completed. Any devices being tested by the FCC must also contain special test software to facilitate a quick test.
In Canada the original FCC requirements for DFS are followed for both the 5250 – 5350 MHz and 5470 – 5725 MHz bands, but operation in the 5600 – 5650 MHz sub-band is allowed, with certifications based on the FCC’s test methods for evaluating DFS.
Stretching across the globe
In Japan the DFS requirements are similar to those for the FCC in terms of radar parameter and apply to the 5250 – 5350 MHz and 5470 – 5725 MHz bands. If radar-type signals are detected, then, as with Europe and North America, the wireless network needs to move to another channel.
Taiwan’s Low-power Radio-frequency Devices Technical Regulations LP0002 requires DFS for devices operating only in the 5470-5725 MHz band, with certification test requirements following those of the FCC.
Why choose TÜV SÜD?
TÜV SÜD supports its customers to comply with test standards for many types of radio equipment, including Short Range Devices (SRD), Bluetooth and WLAN (802.11a/b/g/n), base stations, repeaters, 2G/3G/LTE mobile phones and PMR radio, as well as marine equipment including DSC, ATIS, AIS, EPIRB & VHF/HF radio.
TÜV SÜD also performs compliance testing for RF, EMC, Safety and SAR. Pre-compliance investigation and testing is also an area of our expertise.
TÜV SÜD BABT, is the world’s leading radio and telecommunications certification body, and is authorised by the FCC to issue grants for a wide range of equipment. TÜV SÜD BABT can also issue Industry Canada Type Acceptance Certificates, R&TTE Directive Notified Body Opinions and was the UK’s first Registered Foreign Conformity Assessment Body for radio products under the EU – Japan MRA.