Presentation is loading. Please wait.

Presentation is loading. Please wait.

Doc.:IEEE 802.11-10/1281r0 Submission Nov. 2010 Brian Hart, Cisco SystemsSlide 1 Bandwidth Indication and Static/Dynamic Indication within Legacy Date:

Similar presentations


Presentation on theme: "Doc.:IEEE 802.11-10/1281r0 Submission Nov. 2010 Brian Hart, Cisco SystemsSlide 1 Bandwidth Indication and Static/Dynamic Indication within Legacy Date:"— Presentation transcript:

1 doc.:IEEE /1281r0 Submission Nov Brian Hart, Cisco SystemsSlide 1 Bandwidth Indication and Static/Dynamic Indication within Legacy Date:

2 doc.:IEEE /1281r0 Submission Nov Outline Bandwidth and Static/Dynamic Indications are needed in non-HT PPDUs Inserting a new indication in a non-HT PPDU is complicated How to insert Bandwidth and Static/Dynamic Indications into the First 7 Bits in Scrambling Sequence How to indicate that the First 7 Bits in Scrambling Sequence are modified Pre-Motion Slide 2

3 doc.:IEEE /1281r0 Submission Nov Bandwidth and Static/Dynamic Indications are Needed in non-HT PPDUs E.g. Send RTS/CTS duplicated across 80 MHz Sending RTS/CTS in a non-HT PPDU ensures that all nearby STAs can set their NAV Using an RTS rather than a new control frame preserves the NAV cancellation feature unique to RTS RTS + no CTS + no Data => clear NAV In 11n, the duplication of a frame (e.g. RTS) is not explicitly signaled Receivers should perform extra, error-prone processing This gets still more unreliable and expensive with 20/40/80/160/80+80 MHz operation Static/Dynamic indication in an RTS is needed since it affects CTS behavior. See 10/1289 RTS/CTS Operation for Wider Bandwidth for a description of Static/Dynamic Slide 3

4 doc.:IEEE /1281r0 Submission Nov Inserting a New Indication in a non-HT PPDU is Complicated Three bits (2 bits of Bandwidth Indication and 1 bit of Static/Dynamic Indication) need to be inserted Plus an indication that these bits have actually been inserted (i.e. this is not a pre-VHT non-HT PPDU) The selected method should have the broadest compatibility with the range of devices already deployed at 5 GHz Deployed receivers may require that Reserved fields have particular values, else a frame is discarded Diminishes the purpose of sending an RTS/CTS A range of options was considered and rejected. For instance: There is little opportunity to change bits within a) the RTS/CTS MPDU, b) the one Reserved bit in the L-SIG field or c) the nine Reserved bits of the Service field without a reduction in legacy-compatibility Some important control frames have only 2 Pad bits, and these Pad bits would lack a Tail Slide 4

5 doc.:IEEE /1281r0 Submission Nov Properties of the OFDM Scrambler Crucially, the mapping between Scrambler Seed and First 7 Bits in Scrambling Sequence is one-to-one So, defining the First 7 Bits in Scrambling Sequence is equivalent to defining the Scrambler Seed In the following, we define the scrambler via the First 7 Bits in Scrambling Sequence, instead of via the Scrambler Seed Slide 5 SERVICE 9 Reserved Zeros PSDU, Tail, Pad L-STF, L-LTF, L-SIG Scrambler Init ( ) Scrambling Sequence XOR = Scrambled DATA DATA Scrambler Seed = 7 random bits (1-127) First 7 Bits in Scrambling Seq

6 doc.:IEEE /1281r0 Submission Nov How to Insert Bandwidth & S/D Indications into First 7 Bits in Scrambling Sequence (1/2) scramblingSequenceStart4 is randomly chosen from 1-15 scramblingSequenceStart5 is randomly chosen from 1-31 Ensures First 7 Bits in Scrambling Sequence is non-zero (and so the Scrambler Seed is non-zero) Provides reduced yet still good protection against sequences with pathologically poor PAPRs IsDynamic: 0 (Static), 1 (Dynamic) Bandwidth: 0 (20 MHz), 1 (40 MHz), 2 (80 MHz), 3 (160 or MHz) Very high compatibility since this First 7 Bits in Scrambling Sequence can arise from a valid Scrambler Seed Slide 6 Bits RTSscramblingSequenceStart4IsDynamicBandwidth CTS etcscramblingSequenceStart5

7 doc.:IEEE /1281r0 Submission Nov How to Insert Bandwidth and S/D Indications into First 7 Bits in Scrambling Sequence (2/2) Slide 7 Since the first 7 bits of Data In are all-zeros, therefore the shift register input is the same as Scrambled Data Out, and therefore the state of the shift register after 7 bits equals the first 7 Scrambled Data Out bits Thus the Scrambler Sequence for the remainder of the DATA field is generated by setting the Scrambler State to First 7 Scrambled Bits after 7 bits, and then continuing to run the scrambler as shown above

8 doc.:IEEE /1281r0 Submission Nov How To Indicate that the First 7 Bits in Scrambling Sequence are modified by VHT A MAC Address comprises 48 bits with a Unicast/Multicast bit and 47 other bits The Unicast/Multicast bit in the TA has heretofore been set to Unicast To indicate that the First 7 Scrambled Bits are modified by VHT, a VHT Initiator sets the Unicast/Multicast bit to Multicast in the TA of a TBD non-response (e.g. RTS) frame carried in a non-HT PPDU sent to a VHT recipient The VHT Responder doesn’t signal anything explicitly in the response (e.g. CTS) frame – the signaling behavior is inherited from the frame that solicited the response frame When a VHT Recipient receives a TBD (e.g. RTS) frame with the Unicast/Multicast bit of the TA set to Multicast, the recipient needs to copy the TA and change the Unicast/Multicast bit to Unicast before inserting it as the RA of the response (e.g. CTS) frame This should have high legacy compatibility Unchanged response (e.g. CTS) frame Slightly modified TA in the soliciting frame (e.g. RTS frame), but the RA never matches a pre-VHT STA’s MAC address No known devices that use the Multicast/Unicast bit of a TA at 5 GHz Slide 8 VHT InitiatorVHT Responder RTS(TA with M/U=M, RA=Responder) CTS (no TA) Third Party

9 doc.:IEEE /1281r0 Submission Nov Pre-Motion Slide 9 Do you support adding to the Specification Frame Work document, the insertion of the Bandwidth and Static/Dynamic indications into the First 7 Bits in Scrambling Sequence as per Slides 6 and 7, with the insertion signaled by the Multicast/Unicast bit of the TA as per Slide 8 Y/N/A

10 doc.:IEEE /1281r0 Submission Nov Backup Slides Slide 10

11 doc.:IEEE /1281r0 Submission Nov Existing Scrambler Slide 11


Download ppt "Doc.:IEEE 802.11-10/1281r0 Submission Nov. 2010 Brian Hart, Cisco SystemsSlide 1 Bandwidth Indication and Static/Dynamic Indication within Legacy Date:"

Similar presentations


Ads by Google