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:marcus.muel...@ettus.com] Sent: 22 February 2015 23:26 To: Sajeev Manikkoth; discuss-gnuradio@gnu.org 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 _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
