Range in 802.11y and Ramifications on OFDM Symbol Format January 2006 doc.: IEEE 802.11-06/xxxxr0 January 2006 Range in 802.11y and Ramifications on OFDM Symbol Format Date: 2006-01-16 Authors: Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Steve Shellhammer, Qulacomm Steve Shellhammer, Qualcomm

January 2006 doc.: IEEE 802.11-06/xxxxr0 January 2006 Abstract The transmit power in the 3560 MHz band is higher than that allowed in the 2.4 GHz and 5 GHz band. This results in longer range than in those two bands. Estimates of range are given in this presentation The longer range will lead to larger multipath delay spread which will require larger guard interval (GI) than is used in 802.11a/g Suggestions on methods of modifying the OFDM symbol format with larger GI are given Steve Shellhammer, Qulacomm Steve Shellhammer, Qualcomm

Power Allowed in 3650 MHz Band January 2006 Power Allowed in 3650 MHz Band Fixed Devices 25 watts (44 dBm) Maximum 1 watt per 1 MHz (PSD limit) Mobile Devices 1 watt (30 dBm) Maximum 40 mwatts per 1 MHz (PSD limit) Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a This section estimates the range of 802.11y relative to 802.11a Approach Estimate difference in Link Budget between 802.11y and 802.11a For a typical path loss formula translate increase in path loss to the increase in range Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a Difference in path loss due to lower frequency Difference in TX power for Fixed Devices as a function of bandwidth (BW in MHz) Difference in link budget for Fixed Devices Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a Difference in TX power for Mobile Devices as a function of bandwidth (BW in MHz) Difference in link budget for Fixed Devices Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a Assume the BW is a power-of-two fraction of 20 MHz ΔLB (Fixed Device) ΔLB (Mobile Device) 5 MHz 20 dB 6 dB 10 MHz 23 dB 9 dB 20 MHz 26 dB 12 dB The actual bandwidth is not yet specified Estimate range assuming full 20 MHz bandwidth based on increased in link budget Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a Use a simple exponential path loss formula with an exponent of α=3 Ratio of range of 11y and 11a Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a Ratio in Range of 11y and 11a d11y/d11a 20 MHz 7.3 2.5 10 MHz 5.8 2.0 5 MHz 4.6 1.6 2.5 MHz 3.7 1.3 Fixed devices have a range of up to approximately 7 times that of 802.11a Mobile devices have a range of up to approximately 2.5 times that of 802.11a Steve Shellhammer, Qulacomm

Estimates of 802.11y Range Relative to 802.11a January 2006 Estimates of 802.11y Range Relative to 802.11a Two class of applications Long-range WLAN Both Fixed and Mobile devices Estimated range approximately 2.5 times the range of 802.11a Mesh 802.11y AP All fixed devices Estimated range approximately 7 times the range of 802.11a Steve Shellhammer, Qulacomm

Ramifications on OFDM Symbol Format January 2006 Ramifications on OFDM Symbol Format Longer range leads to larger multipath delay spread The OFDM Guard Interval (GI) will need to be increased Currently there are no specific delay spread requirements Once specific delay spread requirements we can be more precise in our statements regarding GI requirements Will consider several methods of obtaining the OFDM symbol format Scaled version of 802.11a Scaled version of 40 MHz mode of 802.11y New OFDM format Steve Shellhammer, Qulacomm

January 2006 Scaled Version of 802.11a Scale the 802.11a OFDM symbol by scaling the clock BW GI 10 MHz 1.6 s 5 MHz 3.2 s 2.5 MHz 6.4 s Scaling the GI to 6.4 s the bandwidth becomes only 2.5 MHz, resulting in lower permitted TX power The practical limit on this approach is scaling by a factor of 4, resulting in a 5 MHz bandwidth Steve Shellhammer, Qulacomm

Scaled Version of 40 MHz Mode of 802.11n January 2006 Scaled Version of 40 MHz Mode of 802.11n Scale the 40 MHz 802.11n OFDM symbol by scaling the clock BW GI 20 MHz 1.6 s 10 MHz 3.2 s 5 MHz 6.4 s Scaling the clock by 4 is a reasonable choice and results 10 MHz bandwidth This results in 3 dB more power permitted TX power than scaling 802.11a Scaling clock by 8 is probably impractical in this case, since the resulting 5 MHz bandwidth does not permit enough TX power to justify such a large GI Steve Shellhammer, Qulacomm

January 2006 New OFDM Symbol Format To obtain full range increase we would need larger BW Use a larger FFT Say that we target a 6.4 s GI FFT duration 25.6 s FFT BW 256 10 MHz 512 20 MHz 256 size FFT gives approximately 5.8 times the range of 11a 512 size FFT gives approximately 7.3 times the range of 11a Steve Shellhammer, Qulacomm

Trade-off between GI size and TX Power January 2006 Trade-off between GI size and TX Power For a fixed FFT size there is an inverse relationship between GI size and BW This assumes a fixed GI overhead Based on PSD regulatory limit maximum permitted TX power scales with BW There are two conflicting factors that limit range TX power GI The following figure illustrated this trade-off Steve Shellhammer, Qulacomm

Trade-off between GI size and TX Power January 2006 Trade-off between GI size and TX Power GI Limits on Range 512 Point FFT 256 Point FFT Range 128 Point FFT 64 Point FFT TX Power Limits on Range Guard Interval (GI) Size (s) Steve Shellhammer, Qulacomm

January 2006 Summary of Options To get a range increase of approximately a factor of four Scale either 802.11a or 40 MHz mode of 802.11n, by scaling the clock down by a factor of four To get a range increase of approximately a factor of eight New OFDM symbol format with larger FFT size Larger GI Larger permitted TX power All these calculations are based on link budget with an assumed path loss model More detailed requirements are needed to decide between the approaches Clearly, reusing available silicon is a Very Useful approach Steve Shellhammer, Qulacomm