Re: [Discuss-gnuradio] Project enquiry/interest

[Sajeev Manikkoth]

Hi Marcus,

Thanks again for the detailed explanation of current access technologies. As
discussed current scheme allows shared access of the channels in time,
frequency, and space. What I am talking is about a full simultaneous
parallel use or access of channel. This is kind of necessity as wireless
bandwidth demands are ever growing and we are hitting spectrum scarcity. The
scheme I am discussing is close to CDMA/MIMO. CDMA base stations already
differentiate handsets using same frequency with signature sequences.
Implementing a similar approach on the handset side also to differentiate
base stations or similar approaches can be in place.

In its simplest form the requirement is to allow 2 FM stations using same
frequency in a location area. And the receivers tune to the station names to
enjoy different music rather than just to the frequency ! Nothing new as a
concept, limitations to achieve this reasons we have all the existing
implementations, but 100s of years of engineering fineness. Now this should
be possible with soft transceivers using today's digital radio techniques
combined with soft techniques...

Thanks and Regards,
Sajeev Manikkoth 

-----Original Message-----
From: Marcus Müller [mailto:address@hidden 
Sent: 22 February 2015 23:26
To: Sajeev Manikkoth; address@hidden
Subject: Re: [Discuss-gnuradio] Project enquiry/interest

Hi Sajeev,

On 02/22/2015 05:37 PM, Sajeev Manikkoth wrote:
> Hi Marcus,
>
> Thanks for your input and as suggested I can check on the GNU radio
> presentations. As far as I know none of the current wireless access
> technologies allow simultaneous transmissions on same channel. 
Um, being access technologies, that's actually exactly what they do, and
why they're existing.

"Simultaneous" is kind of a difficult term, and of course TDMA systems
like GSM allow different people to use the same channel "at the same
time" only from a higher-up point of view; functionally, the same
channel is shared simultaneously. "Same Channel" is yet another
difficult term, but for example in the context of GSM, the same channel
estimate applies to successive access by different users to the same
subchannel, which is, from a information theoretical perspective, what
I'd call "accessing the same channel".

There are various different FDMA schemes, which allow parallel access to
the spectrum (think the OFDM-based LTE, where you as a user are assigned
resource blocks), and of course, CDMA systems share the same
time-frequency ranges without interfering; that's what they use codes for.
> And we do all
> form of frequency planning and interference avoidance schemes offline and
> deploy wireless solutions.
And that is a must, no matter what you'll do technically, because being
absolutely synchronous and knowing the channel exactly would be the only
alternative to that. You might want to read up on stuff like
inter-symbol-interference and why you can't allow unlimited interference
power in any channel, no matter how good your system becomes at handling
that (channel capacity).
> I was looking for research interests on new PHY
> and MAC layer techniques which can allow 2 or more transmitters at the
same
> location to use same frequency, but receivers being capable of turning to
> the desired transmitters.  
What you describe applies to things like CDMA, and basically any form of
MIMO.
These are not new research, though, since CDMA has at least been in
use/development since the mid-1950s (cold war) and is used in many
mobile phone standards (2G: IS-95, 3G: UMTS, CDMA2000 etc), and GPS.
MIMO is a umbrella term for systems that use a single channel with
multiple "observers" and "signal producers" (e.g., antennas): It's
wide-spread in many access technologies (WiFi, WiMax, LTE, but even
stuff like home-network powerline standards) and allows for the
"creation" of multiple let's say "virtual" channels over one medium.


Best regards,
Marcus Müller