Simultaneous Transmission: Some comments from FCC

1. Simultaneous Transmission:Some comments from FCC Jim Lansford Jim.Lansford@mobilian.com (405) 377-6170 Jim Lansford, Mobilian Corporation

2. Motivation • Simultaneous Tx is a different view of coexistence • Normally think of Tx-Rx coexistence • Tx-Tx raises approval issues • Some companies claim simultaneous Tx is not allowed • This is meant to clarify Jim Lansford, Mobilian Corporation

3. Presentation overview • Dialog with Tim Harrington • FCC Labs • Equipment Authorization Branch • Addresses approval issues for simultaneous Tx • Dialog format is: • My question • My assumed answer • The FCC’s response Jim Lansford, Mobilian Corporation

4. Q1: Simultaneous Tx • Lq1) Can 802.11b and Bluetooth transmit at the same time in the same device? • La1) Yes, with restrictions. They must have separate power amplifiers. If coupled to the same antenna, the PA outputs can only be passively combined (PA sharing is not allowed). • FCCa1) Yes for 802.11b and Bluetooth (BT). Probably yes for 802.11b or BT with 802.11a. Compliance with 15.31(k) for composite devices must be addressed. La1 mentions use with same antenna. In that case must address RF exposure (RFx) and intermod from simultaneous Tx as needed. Jim Lansford, Mobilian Corporation

5. Q2: Authorization requirements • Lq2) If so, are there special requirements for equipment authorization for such devices? (SAR, etc.) • La2) A device that does simultaneous transmission must be tested to make sure it falls within SAR limits for its intended usage. Thus, a TCB cannot be used for equipment authorization. Test results must be submitted to the FCC for review before an FCCID will be granted. • FCCa2) Some considerations were listed in FCCa1. Based on mobile or portable exposure conditions, compliance should be evaluated to either MPE or SAR limits. See attached notes for other comments. At the present time, TCBs are cleared to review SAR only for single-Tx Part 22, 24 handsets. Jim Lansford, Mobilian Corporation

6. Q3: What is “same device”? • Lq3) What is the definition of "same device?" (For example, are radio modules on opposite ends of a PC laptop considered to be in the same device, even though they are 25 cm apart?) • La3) Same device isn't the issue - it's exposure to RF energy from two or more sources. If a laptop has two transmitters, overall exposure from both combined at a pre-determined distance (20cm?) is what matters. • FCCa3) Depending on powers and frequencies (near-field effects), two Tx’s 20 cm apart on a laptop computer can possibly be considered separately, as long as mutual interactions are negligible with respect to EMC and RFx. Mobile phones with 1mW BT have been certified, as well as laptops with 802.11b and BT. We have not seen many 802.11a devices. For any Tx device, if persons can approach closer than 20 cm, compliance with SAR limits is required. Depending on relative powers (levels TBD by FCC; we will consider industry suggestions), special considerations are needed for RFx evaluation of multi-Tx devices, including multi-band and probe calibrations for simultaneous frequency-band tests, and possible alternate on/off and on/on testing for each Tx with summation of all RFx responses in each applicable operating and intermod frequency bands. Jim Lansford, Mobilian Corporation

7. Q4: Antenna Spacing • Lq4) If two transmitters are located on the same IC or PCB, but have separate antennae, are they considered to be the same device? Is this dependent on antenna spacing? • La4) See La3. Two or more transmitters in the same chip are allowed, but the device must still meet the requirements of 15.247, 15.209, and other relevant rules in all modes...especially the SAR limits. • FCCa4) See also FCCa3. Per 15.31(k), each separate Tx must meet its applicable rule parts. For EMC and RFx testing, the devices should transmit simultaneously, and emissions due to simultaneous operation must not exceed limits for the applicable rule parts of each separate Tx. Depending on frequencies, aggregate power levels, and exposure conditions, routine evaluation for compliance with SAR limits is required when used in portable configurations (2.1093). Two Tx on one board can have one FCC ID, but for example a 15.247 device with a 15.407 device may require application filing under two equipment classes with two fees. Jim Lansford, Mobilian Corporation

8. Q5:Frequency band • Lq5) Does it matter if the devices are in the same frequency band (for example, Bluetooth and GSM1900 are in different bands, while 802.11b and Bluetooth share the 2.4GHz ISM band) • La5) Different band or same band doesn't matter - again it's an issue of meeting harmonic and spurious specifications as well as SAR limits. • FCCa5) No. Different bands may wind up having different power thresholds. We agree with La5. Jim Lansford, Mobilian Corporation

9. Summary • FCC doesn’t care if devices interfere • But each needs to follow Part 15.247 restrictions • Simultaneous Tx poses special approval issues • Can potentially exceed SAR limits • Can’t use TCB program at present BUT • FCC does allow simultaneous transmission Jim Lansford, Mobilian Corporation