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

[Alexandre Petrescu <[e-mail]>]

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