Subject: RE: [Fwd: Re: Does 802.11b do multi-hop well?]

From: "Aben, Guido (Guido)" <[email-masked]>
Date: Tue, 13 Nov 2001 16:04:12 -0000

Hollos, all,

a) Are you saying 802.11a will not be allowed to operate in the European
spectrum allocated in the 5 GHz band? I thought these were license free, and
available to anybody who would adhere to the channel rules. When did the
licensing take place (if at all)?

b) OK, there's 19 adjacent 20MHz bands. That doesn't necessarily imply you
can co-locate 19 HL/2 systems there... especially in their 54Mbit/s mode I
expect them to suffer from adjacent channel RF activity.

c) a native multihop scheme, nice! Are the drafts available?

Guido

-----Original Message-----
From: Hollos Daniel [mailto:[email-masked]]
Sent: Tuesday, November 13, 2001 4:43 PM
To: Aben, Guido (Guido)
Cc: MANET Discussion
Subject: RE: [Fwd: Re: Does 802.11b do multi-hop well?]

Guido,

   Good question, how to make the systems in licence-free bands cooperate.
The first question may be: Do you really need to make different MACs
cooperate on the same channel, or it's enough to detect the presence of a
jamming signal, and jump to another, unjammed channel?
Now I don't know any good solutions to cooperate with an uknown MAC in the
same channel.

   Anyway, the Hiperlan 2 uses licenced frequency bands, it has a
licencing group
for this problem, the frequency allocation has been done. In
Europe the available bandwith makes 19 channels for H/2, so
you can operate 19 parallel H/2 systems in the same place, same time. It
seems to be enough for a cell-based system.

However, to increase the spatial reuse, we are working on an extension to
this standard, which makes possible to use two-hop relay in a cell
to reach the destination. It means, one relay station can be used for
a transmission. This makes sense when the target terminal is far
from the AP,
eg. on the edge of the cell. This case, it doesn't have to reach the AP
directly making really ugly interference level in the neighboring cell(s),
just the relaying terminal. So it needs to transmit really less power,
because of the exponential behaviour of the channel gain.

Yours, Daniel Hollos

****************** Daniel Hollos *************************
*                                                        *
* Technical University of Berlin                         *
* Faculty of Electrical Engineering and Computer Science *
* Telecommunication Networks Group                       *
* Phone: +49 30 31479677 (Office)                        *
*        +49 16095401825 (Cell/Mobile)                   *
*                                                        *
**********************************************************

On Tue, 13 Nov 2001, Aben, Guido (Guido) wrote:

> All,
> 
> Most of the wireless last-hop systems seem to operate in license-free
bands
> (which might just account for their popularity :) -- hence my first
> question: how would a scheduled MAC cope with co-existance issues in
> licence-free bands?
> e.g, will two (or more) Hiperlan/2 systems live next to each other and
play
> nice on the same subchannel?
> 
> A second question: with regard to the question of 802.11 performance on
> multihop systems -- when an ad-hoc system scales to a size where not all
> nodes are able to hear each other directly, does anyone have experience
with
> the behaviour of the distributed-beaconing mechanism as defined in 802.11
> IBSS mode? The way I read it, it seems to imply all STAs must be able to
> hear each other...
> 
> just trying to get up to speed in this fascinating arena,
> 
> Guido

---

From: Hollos Daniel <[email-masked]>
Date: Tue, 13 Nov 2001 17:41:44 +0100 (CET)

Guido,

  a) The answer for your first question, yes, of course 802.11 also can
operate in the 5GHz frequency band, it's not uniqe for H/2. What I still
don't understand, why should two H/2 cells operate on the same subchannel
if they disturb each other? For that reason there is the DCF mechanism in
H/2, so it simply jumps to another subchannel in that case.

  b) I really hope, you never need all the 19 subchannels in the same
place and time. But in my previos mail I wanted to point to another thing:
The idea behind is, you may use a cell-based system to build an ad hoc
network without loosing any of its ad hoc behaviours.
So, it can work quite well in the case of some cell-based systems also, if
the cell-interconnection problem is solved, and the system anyway is
capable of handling the general ad hoc problems. And I think, H/2 is
capable of doing this.

  c) Unfortunately I can't publish the protocol description until jan, 
2002. From the beginning of 2002 this will be available, I will notify you
about that.

Yours, Daniel Hollos