1. White Space Regulatory Issues
Month Year
doc.: IEEE yy/xxxxr0
April 2011
White Space Regulatory Issues
Date:
Authors:
Slide 1
Ron Porat, Broadcom
John Doe, Some Company

2. FCC PSD Issue April 2011 Current FCC rule in document FCC-10-174 is:
Month Year
doc.: IEEE yy/xxxxr0
April 2011
FCC PSD Issue
Current FCC rule in document FCC is:
“The power spectral density conducted from the TVBD to the antenna shall not be greater than the following values when measured in any 100 kHz band during any time interval of continuous transmission:
(ii) Personal/portable devices operating adjacent to occupied TV channels: dBm”
It is our understanding that measurement of PSD at a resolution of 100KHz is used to prevent multiple narrowband users sharing a TVWS channel each transmitting at full power.
Slide 2
Ron Porat, Broadcom
John Doe, Some Company

3. Problems With Current 802.11 Systems
April 2011
Problems With Current Systems
We see three potential problems caused by the rules:
Current OFDM based systems use a short training field that concentrates power in one out of every four consecutive subcarriers while maintaining same total average power across the transmission bandwidth. Since the resolution measurement is 100KHz in any time interval it will require devices to lower their average transmit power below the maximum level allowed in order for the increased power in those subcarriers to remain below the required threshold of dBm/100KHz
Current OFDM systems use up to 256QAM modulation that cause significant fluctuation of energy from symbol to symbol. The average energy across a long packet and across the entire transmission bandwidth is the same as with constant power modulations such as BPSK
Current OFDM systems use per-subcarrier beamforming techniques that will increase the transmit power on some subcarriers and some antennas while reducing on others (while still maintaining a total output power constraint across all antennas and all subcarriers).
Note that beamforming coefficient do not change over time in a given packet and even across packets if the channel multipath remains the same.
Note: the problems described above will also occur with usage of WiMAX/LTE in this band
Slide 3
Ron Porat, Broadcom

4. Proposed Clarifications - Tentative
Month Year
doc.: IEEE yy/xxxxr0
April 2011
Proposed Clarifications - Tentative
We seek clarifications on the following issues related to PSD measurement:
Can the assumed time interval be several mS to allow averaging?
Long averaging will reduce the effect of the first two problems in slide 3
We are considering proposing a number to the FCC
Can BPSK modulation be assumed for measurements (to completely remove problem 2) ?
What are the rules regarding multiple antenna transmission using beamforming techniques on a per-subcarrier basis (this is not similar to antenna gain applied equally to all OFDM subcarriers)?
We are considering developing rules for beamforming testing and proposing them to the FCC
Slide 4
Ron Porat, Broadcom
John Doe, Some Company

5. Proposed Solutions - Tentative
April 2011
Proposed Solutions - Tentative
We would like to further propose one of these options to help mitigate the effect of in-band power fluctuations from one 100KHz slice to another:
Increase frequency resolution to 500KHz
Alternatively for devices occupying at least 4MHz transmission 3dB bandwidth, base the rules for PSD calculation on using the entire transmission bandwidth
Slide 5
Ron Porat, Broadcom