The FCC will address exactly what TCBs can review for SAR and simultaneous transmitters in future updates to the TCB exclusion list.
David A. Case, Cisco Richfield, Ohio, USA
For those involved with product approval for Federal Communications Commission (FCC) certification, the use of the Telecommunication Certified Body (TCB) for approval helps speed the process for product review. Still, as we know, one of the stipulations the FCC has placed on the process is that TCBs can neither evaluate nor certify products in instances where the test procedures are unclear or not yet fully documented.
For those developing converged devices this stipulation generally meant that a mobile handheld system with multiple transmitters that could operate simultaneously could not be reviewed by a TCB but would be required to go through the FCC review process. In fact, the current version of the published standards does not address simultaneous transmitters. Further, the current published SAR test standards—specifically IEEE 1528 and IEC-62209*—do not address body-worn or laptop devices, and the versions that will address these devices are still being developed by the standards committees. Though the FCC allowed TCBs to approve modules, there was no clear guidance on specific or recommended methodology for testing SAR in these types of devices.
The FCC laboratory has prepared some specific guidance documents to address questions on these test methods. In addition to these guides, the FCC also addresses some of the requirements for the different devices in their Knowledge Data Base guideline #447498l.
The SAR (specific absorption rate) evaluations of mobile handsets is becoming more complex as various additional technologies are being incorporated into the devices. The procedures for single transmitters in a handset or device are no longer adequate to perform testing for systems where multiple transmitters are operating. Though simultaneous transmitters pose unique challenges, some issues remain unchanged. First, each individual transmitter in the mobile phone must each be assessed as a stand-alone device in accordance with the requirements as set forth in FCC regulations. Second, even if multiple transmitters are included in the system, if they cannot transmit simultaneously, then there is no need for the evaluation. Further, in some cases if the total level of the SAR of the transmitters (even if transmitting simultaneously) is well below the 1-g SAR limit, it is not required to be evaluated under simultaneous operation.
BASIC GUIDELINES FOR SIMULTANEOUS TRANSMITTERS
First and foremost, one needs to determine if the system requires simultaneous transmission evaluations. Whether or not the transmitter requires evaluation vis-à-vis simultaneous requirements, , the first step is the independent evaluation of each individual transmitter. Upon completion of this evaluation, the issue of simultaneous transmission must then be addressed.
If the device has multiple transmitters, but they do not operate simultaneously, then no further evaluation is needed. If they do operate simultaneously, the next issue to address is the proximity of the various antennas. In cases where a stand-alone SAR evaluation is not required for one antenna and the antennas are located at distances greater than 5cm apart, no simultaneous SAR evaluation is required.
By taking into account the 1-g SAR limit and an antenna separation distance of 5 cm, one can determine a ratio for antenna-to-SAR separation that will help minimize SAR overlap. When the antenna-to-SAR separation ratio to antenna pair separation is greater than 3, then it must be evaluated for simultaneous transmissions.
When the testing is required, the setup must be configured to produce the highest SAR as recorded in the stand-alone configuration. If the system is transmitting in the same frequency band for simultaneous transmission, then it must be tested in the same configuration and SAR test set up.
If the system is being evaluated for different bands, it must be evaluated with different tissue simulating liquids and SAR probe calibrations are required for each band. In addition the antennas must be measured separately using volume scans. The handsets must remain in the same position for all tests. Additional constraints and requirements for different set ups may be applicable and our discussed in the standard..
The procedural focus differs for systems where the antenna is imbedded in the display of the host device in contrast to systems that have a card and built-in antenna placed within a PCMCIA or card bus port. As with previous SAR tests, each transmitter and antenna combination must be evaluated as a stand-alone device. One can expect the SAR to vary depending on the antenna displacement, transmitter power, and frequency band of operation. In some cases, different test setups may be required. In those systems where the antenna position is clearly defined, it may be possible to reduce the number of test configurations.
For simultaneous procedures involving laptop devices additional guidance is provided. Specifically, when measuring the SAR from simultaneous transmitters installed in the laptop with the antenna imbedded in the display, additional considerations come into play.
After determining the location of the peak SAR measurement, the main objective is to keep the device in the same position as the various the various transmitter frequencies are measured. As with the other TCB procedures, 60/f is the magic threshold number for determining if and what type of testing will required.
The establishment of guidelines to address some of the issues of simultaneous transmitters and devices not held to the head will provide additional guidance that should help facilitate the ability of TCBs to start reviewing additional products that they have been precluded from evaluating in the past. Note, however, that the FCC will address exactly what TCBs can review for SAR and simultaneous transmitters in future updates to the TCB exclusion list. Manufacturers should check with the TCB to verify with the TCB that it to review and certify the particular product in question.
The procedures can be considered complimentary to the FCC SAR procedures for 802.11, 3G and 3- to 6-GHz test procedures that were developed to address specific issues that were— or are still not addressed—in the current published version of the standards.
Additionally, these guidance notes are being reviewed by the members of the IEEE TC34 committee developing the next version of the IEEE 1528 standard. Once these issues are addressed in the IEEE and IEC SAR test procedures, these guidelines may be withdrawn, or they may be updated. Only time will tell.
*Currently IEC 62209.2, which addresses body-worn devices, is being readied to be sent out for a CDV (Committee Draft for Vote) for approval.
1. 47 CFR Part 2.1093
2. FCC Bulletin OET 65C 01-01
3. IEEE 1528
4. FCC KDB #447498
ABOUT THE AUTHOR
David A. Case, NCE, is a technical leader for Cisco Systems Compliance and Certification Group. He was a member of the U.S. working group that developed the DFS test procedure and is a member of a number of technical standards working groups. He currently serves on the Board of Directors for the Mobile Manufacturers Forum.