Subject: Re: [MOBILE-IP] IPv6 handover document

From: "Hesham Soliman (EPA)" <[email-masked]>
Date: Sat, 19 Aug 2000 01:15:22 +1000

Chip,

You stated:
    If the link medium is using different physical channels (different
frequencies,
    not CDMA technology, for instance), then a receiver can usually only
lock onto
    one single of these channels, since (due to cost) it is only equipped
with one
    transceiver. If access point A is on subnet Na and using channel Ca, a
mobile
    node locked onto channel Ca won't be able to hear or measure anything of
a
    possible access point B on subnet Nb on channel Cb. The only way for the
mobile
    node to detect the presence of B would be to start a scan over all
channels
    (and do so occasionally) or to be informed of its existence by the
network over
    channel Ca.

This is not quite true, as it is possible for the receiver to have
only enough circuitry to determine the power level in a band - and
thus detect activity in other frequency bands -- even though it is not
listening to the actual data in these bands (for example DECT
receivers do this).

In addition, it is also possible to use wideband front ends to the
receiver and do the decoding of multiple narrow bands within (for
example using software radio techniques). Again, a useful aspect is
that you might not need to actually decode all the narrowband
contents, but just look for some feaure -- such as a pilot tone or the
freq. spectrum or perhaps only decode it once in a while.

All of the above means that you don't necessary have to have a second
full receiver nor do you have to necessary time multiplex this
receiver (and hence lose the current communication channel) by having
it scan the other channels.

However, I think we are rapidly reaching the point where it will be
the case that we have multiple receivers in many devices and it will
be nature to use one for the current communication and the others
either for additional communication channels or to (occasionally) look
for better communication channels. This is certainly the case with
cellular handsets which have multiple distinct radio receivers (such
as GSM and DECT or the long awaited GSM and Bluetooth).

Further, it does not cost that much to listen to multiple channels --
vs. the cost to both listen and transmit on multiple channels.

I've often thought of having CDMA beacons that annouce what resources
are available -- in analogy with the signs you see on many highways
which tell you want are the local radio stations (for traffic/public
safety information). Such a beacon could be design to have a very low
data rate (and very long spread code) - so that it could be very
readily detected, but minimize its interference.

=> That's an interesting analysis. Are there any products that
you know of and can do this (ie. WLAN, CDMA terminals).
I'm talking about receiving more than one traffic stream
simultaneously on the same receiver.

---

From: Gerald Maguire <[email-masked]>
Date: Fri, 18 Aug 2000 18:07:47 +0200

"Hesham Soliman (EPA)" <[email-masked]> said:

I don't know of hand of any products (for mobiles) which do this,
however, Daniel Kerek had an experimental Direct Sequence Spread
Spectrum receiver here (in ~1992) where all you had to do was
replicate the correlators to receive multiple streams (since then you
can load different spreading codes in the different correlators and
hence have multiple receivers). This should be perfectly feasible with
existing direct sequence receivers -- if they have enough
resources. Note that the amount of resources necessary to do this
correlation is pretty small (especially when you put it all on one
chip as Intersil can easily do). {In fact his and many other RAKE
receivers already use 3 sets of correlators - early, late, and in sync
-- so as to easily track the signal.}

There are at least two papers about his design (and I think it is
also covered in his licentiate thesis):

D. Kerek, H. Tenhunen, G. Maguire, F. Reichert, Direct Sequence CDMA
Technology and its Application to Future Portable Multimedia
Communication Systems, IEEE ISSSTA'94 - Third International Symposium
on Spread Spectrum Techniques & Applications, July 4-6, 1994,
University of Oulu, Finland.

D. Kerek, H. Tenhunen, G. Maguire, F. Reichert, The Walkstation
Transceiver Design, Proceedings of the 44th IEEE Vehicular Technology
Conference `94, Volume 1, pages 462-466, Stockholm, Sweden, June 1994.

There are some chipsets such as the Harris Semiconductor HSP50214
which is designed (~1997) to "to permit a single digital radio to
support a variety of air-interface standards.
The HSP50214 is aimed
at multimode DSP-based software receivers that used in basestations
and test sets. ..." {The price in 1997 in 10K quantities as US$15.}

In fact there are quite a lot of multichannel receivers for commercial
cellular basestations.

One of the changes which needs to occur is that WLAN manufacturers
have to start designing their systems to support mobile clients,
rather than the current model of simply eliminating the wire. If you
really want to support mobility, you gain an enormous amount by having
this second receive channel -- since then you can look for new access
points. We also pointed out in an early paper that this means that you
can also use a dedicated spreading code to send from an access point
to a particular mobile (or group) or mobiles - while still using the
first channel for two way communication. As the access point alone
controls this 2nd channel you can have very highly efficient use of
the channel and thus burst large amounts of data.

The nice things is that Mobile IP readily supports this - since the
different interfaces can have their temporary IP addresses, but the
mobile has its fixed IP address. Hence the access point can send
different traffic via the different interfaces (and channels) but the
traffic can all be combined at the mobile when it detunnels the
packets and then sends them all to the single mobile IP address.

Regards,
Chip