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

[John Kenney <[e-mail]>]

FWIW, I find DSRC people don't often use this quarter-rate/half-rate
terminology. We just refer to the bandwidth of the channel in absolute
terms.  What is called half rate is a 10 MHz channel.   What is called
quarter rate is a 5 MHz channel.  Full rate is a 20 MHz channel.  I find it
less confusing to use 20/10/5 explicitly than full/half/quarter.  It also
makes sense give that 99% of the time we're only interested in the 10 MHz
case.

John


On Fri, Feb 10, 2017 at 2:02 AM, Alexandre Petrescu <
[e-mail]> wrote:

> 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
>
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-- 
John Kenney
Director and Principal Researcher
Toyota InfoTechnology Center, USA
465 Bernardo Avenue
Mountain View, CA 94043
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