# Project enquiry/interest **URL:** \ **Category:** GNU Radio\ **Created:** [February 21, 2015, 5:23am UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285 "2015-02-21T05:23:53Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [February 21, 2015, 5:23am UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/1 "2015-02-21T05:23:53Z")
Hi, I am looking for some references on the following subject. Simultaneous transmissions, multiple users transmitting and receiving on the same channel frequency simultaneously, Multi user detection, etc. Is there any one here involved or aware of any research project or interested in the above subject. Any pointers will be highly appreciated. Thanks and Regards, Sajeev Manikkoth ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 22, 2015, 5:38pm UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/2 "2015-02-22T17:38:55Z")
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. And we do all form of frequency planning and interference avoidance schemes offline and deploy wireless solutions. 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. Thanks and regards, Sajeev ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 22, 2015, 5:00pm UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/3 "2015-02-22T17:00:41Z")
Hello Sajeev, > Simultaneous transmissions, multiple users transmitting and receiving > on the same channel frequency simultaneously, Multi user detection, etc. > that is a bit wide – every multi-user transmission system has > considered these aspects, so you’re basically asking us to list all > communication systems that have been implemented. Maybe have a look at the presentations given at the GNU Radio conferences the last couple of years, search for GNU Radio and any of these key words on IEEExplore, or look at specific communication standards and look for GNU Radio implementations of these. Best regards, Marcus ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 22, 2015, 6:56pm UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/4 "2015-02-22T18:56:50Z")
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 M. ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 23, 2015, 10:57am UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/5 "2015-02-23T10:57:34Z")
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 ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 23, 2015, 3:26pm UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/6 "2015-02-23T15:26:43Z")
Hi Sajeev, On 02/23/2015 10:56 AM, Sajeev Manikkoth wrote: > 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. > Yes, that’s how I understood this discussion. > What I am talking is about a full simultaneous > parallel use or access of channel. > I really really don’t understand what you mean with that – what other > dimensions than time, frequency, space (incl. polarization) and code can > you imagine, that would distinguish one electromagnetic wave from > another? > This is kind of necessity as wireless > bandwidth demands are ever growing and we are hitting spectrum scarcity. > Spectrum scarcity has been a reality ever since Marconi! > 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. > CDMA handsets of course already do CDMA – otherwise, they wouldn’t be > able to communicate with the base station (which would be > disadvantageous, I reckon). > LTE handsets (at least from what I remember about LTE Release 8, which > is the original LTE release) can make use of MIMO. Probably they already > do. > > 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 ! > Well, that would then necessarily be some kind of diversification by > coding – be it CDMA, or be it multiple lower-rate streams embedded in a > broadcast transport stream, which is what DVB does. That doesn’t > inherently increase spectrum efficiency – instead of 100 channels with > bandwidth b, you get 1 channel with bandwidth 100\*b, because you can’t > cheat channel capacity, and as long as you can’t change SNR, the only > thing you can increase to get more information from transmitter to > receiver is to increase bandwidth. > 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… > What kind of soft techniques? Soft decision decoders? > I still don’t really understand where you think that current technology > falls short and what’s to improve, but I think I’m getting closer to > understanding exactly what kind of research is of interest to you; > please do elaborate! Greetings, Marcus ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 25, 2015, 7:51am UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/7 "2015-02-25T07:51:25Z")
Hi Sajeev, the problem is that there are so many projects that you’ll find when you use google with ’ “GNU Radio”’, that it’s very hard to know what you’re looking for – notice how you still say “my references on this topic” whilst I’m still totally confused what your topic actually is. I’ve talked to some other people and they don’t think you’ve made it clear what your talking about, either. You should really, really find the technical terms, the jargon, that describes what you’re looking for, and then it will be easy for us to recommend something. Up until now, I feel you’ve been extremely vague – and yet you make it all sound so interesting 🙂 Greetings, Marcus ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 25, 2015, 11:19am UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/8 "2015-02-25T11:19:23Z")
Hi Marcus, Sorry that I did not made my point clear. To conclude this thread, I was looking for projects and people who think and work following topic is a realizable goal. Radios which transmit and receive without interference worries (co-channel, adjacent channel, etc) by overcoming the hardware and radiator limitations with software algorithms. Perhaps with new hardware techniques too. Regards, Sajeev ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 23, 2015, 6:04pm UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/9 "2015-02-23T18:04:36Z")
Thanks Marcus, and adding some more details. Current signal detection mechanisms for years totally rely on signal attributes (frequency, timing, amplitude) for differentiation of signals. Cognitive detection mechanisms and new PHY layer techniques which emulate human eye like detection and differentiation need to be developed. One simple scheme I can think of is: Human eye can differentiate 2 similar items or let us say identical twins. And when we find it difficult, we add different identification marks on those twins to differentiate and identify. In a similar fashion may be a transmitter can add a unique identification while modulating/transmitting, and the receivers can look for those. Receivers shall first tune to the channel frequency, and then to the unique transmission id to latch to the desired transmitter. In general my interest was to see interest and projects which develops cognitive detection mechanisms and associated new PHY and MAC layer techniques. Hope I am making some sense now… Best regards, Sajeev ---
**Author:** ![Sajeev\_Manikkoth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Sajeev\_Manikkoth](https://www.ruby-forum.com/u/Sajeev_Manikkoth)\ **Post date:** [February 24, 2015, 9:22am UTC](https://www.ruby-forum.com/t/project-enquiry-interest/234285/10 "2015-02-24T09:22:39Z")
Hi Sajeev, thanks for adding more information! There’s two things I’d like to mention at this point; after that, I think it might be a good idea to let this discussion thread die. I feel I’m digressing too much, and it’ll be easier for you to come up with a new email that says “Hey, do you know research on XY, possibly related to GNU Radio”, now that we have mentioned so many concepts with names, and you can pick one or a few XYs from these. Bombarding you with more terms really won’t help either of us, I guess 🙂 So these two things are 1. quantifying your ideas, and 2. cognitive communications: 1. telecommunication with electromagnetic waves is not very much like looking at objects with the human eye, I agree. But that’s basically because the sensory apparati involved are so different: The eye is a focussable matrix detector for photons, which means you kind of get a whole set of per-frequency-bin intensities at once, whereas digital communication usually needs to rely on a single (or a few) antennas receiving a signal, which only has a single quality – voltage over time. Thus, your comparison kind of needs to take a step back: First of all, you’d need to make some kind of “image” out of the temporal signal, before you can do anything cognitive on it. In fact, projecting a received signal into a vector space is a method very common to almost all digital transmission systems: RF engineers of think of signals as combination of points in a N-dimensional room, constructed by base vectors of independent vectors, just like a 2D image might be constructed by mapping colors to points in the plane. The art of finding appropriate signal representations has led to a whole lot of different transmission schemes, some of which are constellation/pulse shape based (think of a PSK with a matched filter), some employ orthogonality of specific frequency components to first map a set of symbols to a time signal (OFDM), some simply represent different symbols/users by different sequences of chips (CDMA); detectors for these different representations use the characteristics of the signal model to optimize correct decoding. “Optimize” is a hard word, here: It demands that the signal model is somewhat mathematical, which allows the engineer to find an _optimal_ decoder, in many cases. After that, there’s the art of channel coding (as opposed to source coding, and largely unrelated to CDMA), which approaches the actual information to be sent from a information theoretical point of view; it adds redundancy at the transmitter to make it easier for the receiver to correctly decode what has been sent, and it gives the receiver appropriate methods to maximize probability of correct decoding. Network Coding is somewhat related to this, and is yet another discipline of communications engineering you should have a look at. Again, there’s a _large_ mathematical background to this, and a lot of things have upper bounds for how well things can possibly work, there are solutions to specific cases that are proven mathematically to be the optimum, and there are lots of research to be done – most of the codes we know today are rather bad compared to what we know must exist, but science has not been able to find better ones, so far[1]. Somewhere in between the mapping of physical quantities to code words, and finding good codes to encode information, to maximize speed/reliability/spectrum efficiency of transmission [2], or somewhere across, sits equalizing. Now, equalizers have a lot of properties that people consider “smart”, “adaptive”, and thus somewhat “cognitive”, but that brings me to my second issue 1. “cognition” is one of the buzzwords of RF communication of the last 15 years, thanks to Mitola '98, who coined the term “cognitive radio”, to describe systems that are aware of their RF environment and act based on this awareness. This comes with a whole lot of theory on what a radio must/can/could know, how to exchange that kind of info etc. Network coding once again comes into play – you should definitely have a look at that. Now, I’m not totally sure you’re going after cognitive radio – from what you describe, designing a good channel code that reaches the channel capacity[3], maybe combined with an equalizer, fits what you’re looking for, which is recognizing advanced patterns in a more-than-1-dimensional representation of the signal. There’s a lot of approaches that do this – chose the one you want to dig deeper into 🙂 Computer vision is a fairly mature field of research, and it has led to a lot of signal models for 2D images; all the things I said about mathematical optimization above apply to these models, too, and the point here is that it’s always crucial to find a good representation (ie. a well-fitting model) that explains the signal to your detection algorithm. There are a lot of decoder classes that are what one could call learning – iterative methods that use the information gathered in the last processing step to aid and improve the next step – be it a definite decision about the (N-1)th bit employed to calculate the likelihoods of the Nth bit, or be it a soft decision state used in a iterative decoder arbitrary times. Have a look at Turbo Decoders – they interleave decoding and equalizing, and thus learn from symbols of the past to interpret the coming symbols more accurately. So, to conclude: 1. you say you want to see things being done better, but you’ll need to mathematically define “better”; in many cases, the structures employed are mathematically proven to be optimal, and 2. you’re comparison to recognition of things by the human eye needs to first find a mathematical model that makes an image from the signal, and for which you can be smarter than the solutions that are already known. Best regards, Marcus [1] which, to me, was one of the core things I took away from my channel coding course. [2] Note that I use these three different goals as one thing here – you can often do this, because the common problem is “for this given channel, how can we get a maximum of bits across”, and a good solution solves all the three problems. [3] Wow, my footnotes are getting channel coding centered these days. Reaching channel capacity means: No matter what you do, for the SNR in this channel you can’t get more bits across (with arbitrarily little error) than possible with this code.