Re: [ipwave] draft-ietf-ipwave-ipv6-over-80211ocb-00 FYI quarter-, half- and full-rate comments

[Alexandre Petrescu <[e-mail]>]

Le 11/02/2017 à 05:35, Dick Roy a écrit :
> This text is flawed.  OCB has NOTHING to say about the PHY!  OCB can be used
> with any of the 802.11 PHYs and is NOT restricted to 5.9GHz PHYs.  In
> discussing data rates and channel bandwidths, OCB is irrelevant other than
> to say in the US, in the 5.9GHz band, OCB is (or soon will be :^)) mandatory
> (see 802.11-2016 and SAE J2945/1).
>
> Secondly, half-rate refers to the fundamental system clock in an 80211
> chipset.  10MHz channels are achieved by simply downsampling the system
> clock (40MHz usually) by a factor of 2 (then 2 again to get 5MHz channels).
> As a consequence, all the data rates get halved (the halved again).  It's
> really quite simple. There is NOTHING about 802.11p that changes any of
> this.  The ONLY PHY related changes are to the Rx sensitivity and the Tx
> masks, but this is WAY OUTSIDE the scope of IETFs effort.
>
> All this stuff is much ado 'bout nothin'.  Simply note the default data
> rates that must be supported in 5.9GHz operations (and the optional others
> if you care) in the 10 MHz and 20MHz channels in the 5.9GHz band and charge
> ahead.

Noted.  Version -01 will talk much less about PHY.  Maybe in the 
appendices, or maybe not at all.

Alex

>
> Cheers,
>
> RR
>
> -----Original Message-----
> From: Alexandre Petrescu [mailto:[e-mail]]
> Sent: Friday, February 10, 2017 2:03 AM
> To: [e-mail]
> Subject: [ipwave] draft-ietf-ipwave-ipv6-over-80211ocb-00 FYI quarter-,
> half- and full-rate comments
>
> draft-ietf-ipwave-ipv6-over-80211ocb-00
> FYI quarter-, half- and full-rate comments
>
> Hello IPWAVErs,
>
> We received an FYI commenting the quarter-, half- and full- data
> rates of 802.11 OFDM.
>
> The old text being commented is the following:
>> 4.  Aspects introduced by the OCB mode to 802.11
> [...]
>> o 'half-rate' encoding
> [...]
>> o  It is worth mentioning that more precise interpretations of the
>> 'half-rate' term suggest that a maximum throughput be 27Mbit/s (which
>> is half of 802.11g's 54Mbit/s), whereas 6Mbit/s or 12Mbit/s
>> throughputs represent effects of further 802.11p-specific PHY
>> reductions in the throughput necessary to better accommodate
>> vehicle-class speeds and distance ranges.
>
> I will replace the above bullet points with this new text:
>> o 'quarter-rate' encoding: whereas 802.11 affords multiple
>> combinations of distinct x-rate encodings, widths of spacing between
>>  channels and modulation techniques, the 802.11 operating outside the
>>  context of a Basic Service Set for Intelligent Transport Systems
>> (ITS) mobile and non-mobile operations informally promotes the use of
>> quarter-rate, 5 MHz channel spacing, modulation '64 QAM' with r ==
>> 3/4, leading to a maximum data rate of 13.5 Mbit/s.  See details in
>> section "x-rate encodings for 802.11".
>
> The new appendix section titled "x-rate encoding for 802.11":
>> Quick summary of 802.11 OFDM data rates:
>>
>> o	Half-rate (10 MHz channel spacing) maximum data rate is 27 Mb/s -
>> Modulation 64-QAM; r == 3/4;
>>
>> o	Half-rate minimum data rate is 3 Mb/s - Modulation BPSK; r == 1/2 -
>>  Note this is a default and is mandatory by ALL 802.11 STAs.
>>
>> o	Full-rate (20 MHz channel spacing) the maximum data rate is 54
>> Mb/s; 64-QAM; r == 3/4;
>>
>> o	Full-rate minimum data rate is 6 Mb/s - Modulation BPSK; r == 1/2;
>>
>> o	Quarter-rate (5 MHz channel spacing) maximum data rate is 13.5 Mb/s
>> - Modulation 64-QAM;   r == 3/4;
>>
>> o	Quarter-rate minimum data rate is 1.5 Mb/s - Modulation BPSK; r ==
>>  1/2.
>>
>> Note: Per IEEE 802.11, the operating class 16 (5 MHz channel spacing)
>> is defined for ITS_nonmobile_operations, ITS_mobile_operations.
>>
>> o  'Half-rate' encoding: as the frequency range, this parameter is
>> related to PHY, and thus has not much impact on the interface between
>> the IP layer and the MAC layer.  The standard IEEE 802.11p uses OFDM
>> encoding at PHY, as other non-b 802.11 variants do. This considers
>> 20MHz encoding to be 'full-rate' encoding, as the earlier 20MHz
>> encoding which is used extensively by 802.11b. In addition to the
>> full-rate encoding, the OFDM rates also involve 5MHz and 10MHz. The
>> 10MHz encoding is named 'half-rate'.  The encoding dictates the
>> bandwidth and latency characteristics that can be afforded by the
>> higher-layer applications of IP communications.  The half-rate means
>>  that each symbol takes twice the time to be transmitted; for this to
>>  work, all 802.11 software timer values are doubled.  With this, in
>> certain channels of the "5.9GHz" band, a maximum bandwidth of
>> 12Mbit/s is possible, whereas in other "5.9GHz" channels a minimal
>> bandwidth of 1Mbit/s may be used.  It is worth mentioning the
>> half-rate encoding is an optional feature characteristic of OFDM PHY
>>  (compared to 802.11b's full-rate 20MHz), used by 802.11a before
>> 802.11p used it.  In addition to the half-rate (10MHz) used by
>> 802.11p in some channels, some other 802.11p channels may use
>> full-rate (20MHz) or quarter-rate (5MHz) encoding instead.
>>
>> o  It is worth mentioning that more precise interpretations of the
>> 'half-rate' term suggest that a maximum throughput be 27Mbit/s
>> (which is half of 802.11g's 54Mbit/s), whereas 6Mbit/s or 12Mbit/s
>> throughputs represent effects of further 802.11p-specific PHY
>> reductions in the throughput necessary to better accommodate
>> vehicle-class speeds and distance ranges.
>
>
> Alex
>
>
>
>