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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 1 Regarding NAV Setting with L-SIG TXOP Protection Notice: This document has been prepared to assist IEEE 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// Date: Authors: NameCompanyAddressPhone Tom KenneyIntel JF NE 25th Ave Hillsboro, OR thomas.j.kenne Eldad PerahiaIntel JF NE 25th Ave Hillsboro, OR

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 2 Abstract Several comments address issues with NAV Setting with L-SIG TXOP Protection in the presence of errors in L-SIG or HT-SIG in Clause 9.15: –Jim Petranovich; cid 7177 –Gal Basson; cid –Menzo Wentink; cid 8277 –Menzo Wentink; cid 8278 –Yuichi Morioka; cid 6788 This presentation provides simulation analysis to address these comments

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 3 Introduction L-SIG length and rate field are used for spoofing and L-SIG TXOP Protection The following analysis was conducted to provide statistics related to the following questions: –Should an HT device respect the Legacy length field for NAV setting if during a MM packet the HT-SIG CRC fails and the L-SIG parity passes? –What are the false positive statistics of L-SIG given the HT-SIG CRC passes? The specific intent of this analysis is to provide statistics of the various HT-SIG and L-SIG error event combinations The events were attained by simulating a HT Mixed Mode transmission and gathering the receiver statistics

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 4 Classification Cases For the Legacy Length study, four classification cases were identified. –case 1) probability that L-SIG will have no errors, and parity passes –case 2) probability that L-SIG parity passes, rate decoded correctly as 6Mbps, length decoded incorrectly –case 3) probability that L-SIG parity passes, rate decoded incorrectly –case 4) probability that L-SIG parity fails

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 5 Simulation Results – HT-SIG CRC Fail HT-SIGNo L-SIGL-LengthL-RateL-Parity Tx/RxCh.SNRCRC FailErrors*Error* Fail* Model(dB)(%)( Case 1 )( Case 2 )( Case 3 )( Case 4 ) 1x1D x1B x2B x2D *Percent of HT-SIG CRC fail As an example, for a 1x1 system, channel model B, 3 dB SNR, the probability of a HT-SIG CRC failure is 33.7%. Given the occurrence of a HT-SIG CRC failure: 33.2% of the events will have no L-SIG errors (case 1). 34% of the events will have an L-SIG parity bit failure (case 4). 23.7% of the events will have an L-SIG rate failure with L-SIG parity passing (case 3). 9.1% of the events will have an L-SIG length error with L-SIG parity passing (case 2).

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 6 Implications of Simulation Results Given a HT-SIG CRC failure, the L-SIG has no errors % of the time An L-SIG Parity bit failure (detectable by an HT device) occurs 16 – 34% of the time when the HT-SIG CRC fails The remaining cases are the situations where the L-SIG parity passes, yet the length or rate field is in error –This occurs 5 – 33% of the time when the HT-SIG CRC fails Since the rate in the L-SIG is defined in a MM packet as 6Mbps, the rate field could be ignored when computing the duration resulting in a small error percentage –An incorrect (random) length would be used to determine the amount of back off –The impact of an incorrectly decoded L-SIG length field is given in the following slide

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 7 Simulation Results – Distribution of L-SIG Length Field –For Case 2, the L-SIG length field is fairly uniformly distributed from , with some slight clustering around 1000 bytes (the simulated packet length).

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 8 Simulation Results – HT-SIG CRC Pass *Percent of HT-SIG CRC pass As an example, for a 1x1 system, channel model B, 3 dB SNR, the probability of a HT-SIG CRC Pass is 66.3%. Given the occurrence of a HT-SIG CRC Pass: 98.8% of the events will have no L-SIG errors (case 1). 0.60% of the events will have an L-SIG parity bit failure (case 4). 0.29% of the events will have an L-SIG rate failure with L-SIG parity passing (case 3). 0.29% of the events will have an L-SIG length error with L-SIG parity passing (case 2). HT-SIGNo L-SIGL-LengthL-RateL-Parity Tx/Rx/NssCh.SNRCRC PassErrors*Error Only*Error*Fail* Model(dB)(%)( Case 1 )( Case 2 )( Case 3 )( Case 4 ) 1x1D x1B x2B x2D

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doc.: IEEE /0865r0 Submission July 2006 Tom Kenney (Intel), Eldad Perahia (Intel)Slide 9 Summary Should an HT device honor the L-SIG during a MM transmission if the HT-SIG CRC fails? –An error in the length or rate field of the L-SIG will lead to a random NAV setting up to 33% of the time –Therefore, the NAV should not be set based on the L-SIG when the HT-SIG CRC fails In the case when the HT-SIG CRC passes, undetectable length errors in the L-SIG only occur 0.2% - 0.4% of the time Therefore, the NAV can be reasonably set based on the L-SIG length when both the HT-SIG CRC passes and the L-SIG parity passes.

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