FW: stds-802-16-tg3: support for AAS (C802.16a-02/49)
Hi All
The work that we are doing here is to enable and to have easy support for
all the modes (SC and OFDM/OFDMA) with the optional adaptive array.
The support of converging the optional OFDMA2 to the OFDMA/OFDM spec. came
by product of that work. I don't see an Interoperable problem.
I don't agree with the statement about the different permutations, the
cluster approach especially the one proposed at ETSI BRAN is not a good one
for frequency selective channels or Narrow Band Interferences.
All the best
Zion
-----Original Message-----
From: owner-stds-802-16-tg3@majordomo.ieee.org
[mailto:owner-stds-802-16-tg3@majordomo.ieee.org]On Behalf Of
nico.Vanwaes@nokia.com
Sent: Monday, May 13, 2002 2:38 AM
To: stds-802-16-tg3@ieee.org
Subject: stds-802-16-tg3: support for AAS (C802.16a-02/49)
Colleagues,
Reading through C802.16a-02/49, I find that an excellent effort has been
made to rewrite and improve the AAS support in a concise manner. It's an
effort I hope will find widespread support.
There is however in my opinion one major exception to which I'd like to draw
some early attention, so that the interested people have some remaining time
to reconsider the matter.
This one exception is the text discussed as:
The substantial difference between OFDMA modes is how logical carriers are
mapped to physical carriers.
OFDMA2 uses sub-channels that are composed of adjacent sub-carriers. A
separate permutation mapping can represent this. Using this permutation in
conjunction with adaptive array makes the array implementation simpler, and
is therefore justified.
which finds its suggested implementation on page 212, line 55 in the 23rd
suggested modification.
Imho, the main problem with this language is that it once again introduces
two entirely incompatible OFDMA modes. Yet instead of clearly indicating the
failure to compromise on one harmonized carrier allocation by having an
OFDMA and OFDMA2 PHY, the proposal is yet again to stuff this principle
incompatibility into an "optional" subclause; a situation similar to what we
started out with way too many meetings ago.
There is currently, to my understanding, a single major technical argument
for either carrier allocation. The fully distributed carrier allocation is
claimed to be preferable for optimum frequency diversity, the contiguous
carrier allocation is claimed to be preferable for minimum array processing
overhead, as only one weight per contiguous allocation is needed.
In my mind, as somebody who isn't hung up on either implementation, it seems
to be, entirely from a technical perspective, worth it to ponder
compromising alternatives to either, such as for example a scheme in which 4
clusters of 13 contiguous carriers are distributed with a modified version
of the current mandatory permutation algorithm, in order to retain
significant frequency diversity and drastically reduce the AAS
implementation complexity.
This may be painful for the proponents of both current carrier allocation
schemes, but imho, this is the only alternative to voting one scheme off the
table.
Regards,
/Nico