David A. Case, Cisco Systems, Richfield, OH
In July of 2003, the International Telecommunications Union – Radio adopted Recommendation 229, allocating the 5150-5350 MHz and 5470-5725 MHz bands to mobile service, including RLAN systems.*
The following year the FCC updated its Part 15.407 regulations to include the 5470-5725 MHz band, as well as require changes for devices that operate in the 5250-5350 MHz band. As part of sharing the bands with other services on a non-interference basis, the RLAN systems are required to use TPC (Transmitter Power Control) and DFS (Dynamic Frequency Selection), both Cognitive Radio Techniques.
REPORTED PROBLEMS IN THE FIELD
During discussions on CRS /SDR issues at WP5a in late 2008, there was some discussion on RLAN possibly interfering with radar systems despite DFS. However, nothing concrete was presented at these meetings. In April of 2009, it was reported that the FCC was holding up applications for new grants for 5GHz systems specifically in the DFS bands.
In discussions with the FCC lab, the problem told to industry was that there were a number of FAA Terminal Doppler Weather Radars that were being interfered with by RLAN systems and that until the investigation was complete and a possible solution found, no further approvals would be granted for these systems.
Interference was to the TDWRs from RLAN operating in the 5600-5650 MHz band specifically, as well as some interference from systems operating on the channels adjacent to this band.
It was discovered that, in some cases, the users could select different country settings and actually turn off DFS; in other cases, the device could only detect the very specific waveforms of the test procedure.
An ad-hoc industry workgroup was formed by interested parties and after a series of discussions with member companies. Since the systems causing the interference were outdoor systems, based on discussions with members of the industry, the FCC released in October 2009 an interim procedure for approving master devices operating in these bands indoors.
The requirements for the indoor systems operating in the 5470-5725 MHz are as follows per FCC KDB 443999:
1) The device must not be able to operate on the 5600–5650 MHz band
2) The device must be marketed and sold for indoor use only
3) The information on indoor use only in the 5470-5725 MHz needs to be in the manual or on a label on the device
4) The end user cannot have access to controls set to other regulatory domains or country settings nor be able to turn off DFS
The above FCC KDB allowed the process for indoor-only devices to be turned on and then the focus was on outdoor devices. This issue was addressed in a several tier approach.
The first was that the FAA and FCC were investigating the interference and tracking down these systems. In some cases where either the products were non compliant or that the operator made unauthorized changes, fines were assessed. In cases where the systems were compliant, the systems were set to other frequencies to avoid causing problems.
Second, the FCC issued a Public Notice from OET and Enforcement Bureau asking all manufacturers to reach out to their customers and inform them of this issue. As part of this effort, a voluntary database has been developed that allows operators and installers to register the location information of the UNII devices operating outdoors in the 5470–5725 MHz band when they are installed within 35 km of any TDWR location. The manufacturers are conducting an outreach to their customers as part of this effort to help resolve the interference issues. (See http://www.spectrumbridge.com/udia/home.aspx).
The third solution is to work towards a goal to allow the approvals of outdoor RLAN operating in the 5470-5725 MHz band to go forward. This is being done in a multi-step solution. The first is the interim procedure which is the next revision of KDB 443999. This document was sent out for comments and the comments are now being reviewed by the FCC. The proposal is as follows as extracted from FCC KDB:
1. Devices will not permit operation on channels which overlap the 5600 – 5650 MHz band.
2. Devices intended for outdoor use will be further restricted, as follows:
• Devices must be professionally installed when operating in the 5470 – 5725 MHz band,
• Grantees must provide owners, operators and all such installers with specific instructions in their user’s manual on requirements to avoid interference TDWR and information that meet the following instructions:
• Any installation within 35 km of a TDWR location shall be separated by at least 30 MHz (center-to-center) from TDWR operating frequency (as shown in the table below), and
• Procedures must be provided for the installers and the operators on how to register the devices in the industry-sponsored database with the appropriate information regarding the location and operation of the device and installer information in that database.
• Devices must meet all of the other requirements specified in Section 15.407, and no configuration controls (e.g. country code settings or other options to modify DFS functions) may be provided to change the frequency of operations to any frequency other than those specified on the grant of certification for US operation.
• All applications must clearly show compliance with all of the technical requirements under worse case parameters under user or operator control based on frame rates, listen/talk ratios and user data transfer conditions.
• The next phase will be to develop new radar waveforms for the DFS testing which would test the ability of the systems to detect these TDWR systems. To this effort the industry, the FCC and NTIA are meeting to discuss and review requirements. Further NTIA will be doing some additional testing of the WLAN systems against the new radar wave forms.
As the issues progresses it is best to check with the FCC lab on status of approvals of outdoor systems and also to keep up to date on changes via possibly new FCC KDB’s.
DAVID A. CASE, NCE, NCT, is senior regulatory engineer, corporate compliance EMC standards and operations, for Cisco Systems Inc. in Richfield, Ohio. He can be reached at [email protected].
* As of October 15, the FCC has turned on the certification process for systems that operate in the 5GHz DFS bands and operate outdoors. Additional information can be found in the FCC KDB 443999.