1. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 1 IEEE 802.11a In Outdoor Mobile Environments 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, 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 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.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2006-09-15 Authors:

2. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 2 Abstract This submission demonstrates that the IEEE 802.11a waveform can be used in outdoor, mobile environments without modification. This is achieved with receive side PHY processing improvements only. The channel experienced under outdoor, mobile conditions is reviewed and a baseband receive processor is presented that can cope with these conditions. This is followed by results from a recent field trial incorporating such a receiver.

3. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 3 Channel Model : Delay Spread & Mobility Degree of Non-LOS (RMS Delay Spread) Mobility LOS with no reflections LOS with mild reflections LOS with strong reflections No LOSNo LOS with long delay spread Pedestrian Highway Vehicle Fast Train City Vehicular

4. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 4 Indoor vs. Outdoor Mobile IEEE 802.11a is designed with a standard radio in mind A standard radio uses cyclic prefix to combat delay spread, and preamble and pilot symbols to tackle time varying channels This results in a simple, robust receiver for indoor channels with little mobility However, when outdoors and mobile the delay spread becomes longer and the channel changes more rapidly Despite the self-interference induced by these effects, the energy is still there, so why not use it? This can be done by simply modifying the receiver.

5. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 5 Standard Radios: Mobility Problem:Channel estimated during preamble ages and becomes redundant by the end of the packet (magnitude & phase evolve differently by sub-carrier). Solution 1:Use short packets to avoid the problem. Cost: reduced network throughput. Solution 2:Deploy networks in Line-Of-Sight conditions where Mobility manifests as a frequency offset rather than a Doppler Spread. Cost: Elevated node density

6. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 6 Standard Radios: Delay Spread Problem 1:For delay spread components > 200ns Channel estimated during preamble cannot be improved using pilots, leading to performance degradation at range. Problem 2:For delay spread components > 800ns Inter Symbol and Inter Carrier Interference result leading to self interference limited performance. Solution 1:Deploy networks in Line of Sight conditions. Cost: Elevated node density Solution 2:Time Domain Filtering. Mild improvement. Solution 3:MIMO. Diversity gain delivers mild protection from excessive delay spread. Solution 4:Half OFDM symbol rate (e.g. 10 MHz BW, 2x CP length) Cost: Throughput

7. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 7 Alternate Receiver Technologies Although a received signal may be changing rapidly in frequency and time, it may have high SNR allowing the possibility of effective reception. What can be done at the physical layer receiver to combat the simultaneously problems of High Mobility and Long Delay Spread?

8. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 8 Alternate Receiver Technologies: Design Preferred approach is Frequency Domain equalisation and Time Domain Channel estimation since these domains are the natural fits to the problem domains. –ISI (and ICI) Frequency Domain Equalisation using Decoder outcomes Not simply cancellation since this ignores useful energy in other symbols –Time Domain Channel Estimation using Decoder outcomes Uses energy received in CP interval to improve channel estimate quality Estimate small number of fundamental parameters instead of 52 Tracking updates channel estimate every 4us (Up to 10KHz Doppler) Time domain equalisation is not convenient since DFE symbols not easily defined. Non DFE based performance is limited. Frequency domain channel estimation results in high order estimation of a small number of time domain parameters. Frequency domain smoothing of channel estimate is not allowed since coherence frequency drops to the order of the Sub Carrier Spacing

9. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 9 Alternate Receiver Technologies: Baseband Receiver Block Diagram Key technical features 1.collect all energy pertaining to each OFDM symbol 2.remove interference arising within and between OFDM symbols 3.track variations in the radio environment throughout the packet 4.zero additional latency

10. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 10 Alternate Receiver Technologies: Performance Alternate is Robust to Twin Evils of Outdoor Multipath & Mobility 12 Mbps, 1000 Byte, Indoor: ETSI B, Outdoor: 800ns RMS delay spread

11. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 11 Alternate Receiver Technologies: Performance (cont) Doppler Frequency up to about 10% OFDM symbol frequency (25 kHz) and RMS Delay spreads up to about 2us can be simultaneously tolerated with minimal performance loss –100 mph = 850 Hz Doppler @ 5.7 GHz –2us corresponds to 600m reflected/diffracted path length difference

12. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 12 Alternate Receiver Technologies: Indicative Outdoor Coverage CoveredEnough Rx Power but too much Delay Spread Single AP 6 Mbps coverage No mobility impairments Standard CoverageAlternate Coverage

13. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 13 Alternate Receiver Technologies: Indicative Outdoor Coverage (cont) * Performance data from Standard 802.11a/b/g Wireless PCI Adapter data sheet 10 Nodes on roof tops, 43% Power & RMS Delay Limited Coverage 89% Power Limited Coverage 10 Nodes on roof tops, 95% Power & RMS Delay Limited Coverage 95% Power Limited Coverage

14. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 14 Trial Network Specification Trial network deployed in the Norwood suburb of Adelaide, Australia –Over one square mile coverage with just 6 fixed nodes –typical urban environment with tree lined streets, narrow laneways, 1-2 story dense housing, and 2-3 story office buildings Fixed nodes –IEEE 802.11a/j compliant APs –Dual radios: 4.9 GHz (fixed-mobile) and 5.8 GHz (infrastructure-mesh backhaul) –Supports full motion video and VoIP from multiple vehicles –Single gateway Mobile nodes –IEEE 802.11a/j compliant STAs –Single 4.9 GHz radios –Connectivity at vehicular speeds permitted by local speed limits –Seamless, fast handover between fixed nodes –95% in-street coverage

15. doc.: IEEE 802.11-06/1339r0 Submission September 2006 Paul Alexander, Cohda WirelessSlide 15 Trial Network Norwood, South Australia 1 mile