[USRP-users] USRP captured data information

alok ranjan alokranjan007 at hotmail.com
Wed Apr 15 08:05:29 EDT 2015


Dear Marcus,

Thank you for sharing useful resource with me .

I will spend time to understand the channel modeling concepts and how to deal with the necessary parameters for channel modeling.

Thank you so much for your time and support.

Regards,

Alok Ranjan


Date: Wed, 15 Apr 2015 13:57:51 +0200
From: marcus.mueller at ettus.com
To: alokranjan007 at hotmail.com; USRP-users at lists.ettus.com
Subject: Re: [USRP-users] USRP captured data information


  
    
  
  
    Hi, 

    I'm not familiar with optical models myself, so this is only a
    guess:

    *Geometrical* optical model sounds like it would ignore all effects
    that happen due to interference, meaning that you wouldn't see any
    multipath fading; I'm pretty sure that would not be the model of
    choice for radio waves inside a subway, since they definitely will
    de- and constructively interfere.

    

    When I was proofreading a few pages of a thesis, I skimmed through
    [1] to get a understanding for the topic; maybe that will give you
    some inspiration for what to measure; it sadly is already more than
    20 years old, so there might be "cooler" existing models that I
    don't know of. Anyway, it really nicely covers the three main
    aspects that you probably also will need to cover:

    

    1. it describes how the channel is modelled (as a discrete impulse
    response)

    2. it describes why considering the channel as something that varies
    randomly is necessary and thus explains the need for statistical
    description

    3. it is kind of a lengthy tutorial on how to actually characterize
    the channel. I didn't read that part completely, because it was "a
    bit too long", but then again, I was not in the business of
    modelling a channel myself.

    

    I must admit that I think what you're doing might be a bit hard for
    someone completely new to radio communications and if that actually
    is the case for you, you might find it hard to understand all the
    technical terms in the first three chapters of [1], but you only
    said you were new to SDR, so my hope is that you already know most
    of this stuff, or will have fun catching up on a bit of channel
    theory.

    

    Greetings,

    Marcus

    

    [1] http://wsl.stanford.edu/~ee359/hashemi_indoor.pdf

    On 04/15/2015 01:33 PM, alok ranjan
      wrote:

    
    
      
      Dear Marcus,

        

        Thank you for your all valuable suggestions and assistance to my
        issues.

        

        Yes! you are very true that the subway scenario suffers from
        multi path effects and shadowing phenomena. 

        

        I have just completed my Graduation and working as project
        assistant. 

        

        As such i dont have exact idea that which channel model will
        work fine. I am reading literatures on wireless communication
        possibilities  and found that Geometrical Optical model may work
        fine and there are literatures available.

        

        What you have  suggested, I will keep in mind for sure about the
        antenna and the filters. 

        

        

        If you have any other suggestions then I will feel happy to hear
        from you.

        

        

        

        

        

        Thank you, Regards,

        

        Alok Ranjan

        

        

        
          Date: Wed, 15 Apr 2015 11:49:17 +0200

          To: usrp-users at lists.ettus.com

          Subject: Re: [USRP-users] USRP captured data information

          From: usrp-users at lists.ettus.com

          

          Hi Alok,

          

          we'll, Matlab is a math tool, and thus, you'll have to find a
          real-valued mathematical representation of the entities you
          want to plot.

          Power of a digital signal is commonly defined as the square
          magnitude of the samples, that is , so this might be
          what you want to plot.

          

          However, you might find yourself in a situation where you'll
          first want to define more closely what you're measuring. Do
          you want to measure the RX power of a single sine wave? In
          that case, it would be advisable to use a very narrowband
          digital filter, just to get as little power as possible into
          your measurement. If you transmit digital data (most probably
          what you do when using benchmark_tx), you might now your TX
          pulse shape, and thus you can use a matched filter on the RX
          side, giving you the maximum SNR any filter could offer.

          

          Also, the frequency range from 300MHz to 5GHz is quite large
          -- unless you have an extremely broadband antenna, you will
          need to use different antennas. And: every antenna has a
          frequency-dependent behaviour as well, making both the
          geometrical properties and the maximum achievable field
          strength extraction a function of the carrier frequency. You
          will be fine if you use "simple" geometries like monopole
          antennas and for small frequency deviations, and if you try to
          keep RX and TX in each others main direction, but that's
          another factor to consider; so I'd recommend doing one center
          frequency first, shifting your signal in smaller steps around
          that, and then trying out other frequencies.

          

          Your application really sounds exciting; subway channels
          really sound like they'd actually have impressive multipath
          propagation, small scale fading etc, due to being in a metal
          cage; this together with the doppler of signals leaving the
          cabin, bouncing of the tunnel seems really interesting! Do you
          have a reference channel model you're building on? Maybe the
          Matlab IEEE802.11n indoor channels?

          

          Greetings,

          Marcus

          

          On 04/15/2015 07:17 AM, alok
            ranjan via USRP-users wrote:

          
          
            
            Dear Marcus and Raj,

              

              Thank you for your assistance so far. 

              

              I am trying to do some channel modeling for wireless
              communication in subway.  To accomplish this I am using
              two USRP1 having DB WBX connected to my pc over USB 2.0. 

              

              As I am new to both SDR and USRP , I initially used the
              two scripts i.e. benchmark_tx.py and benchmark_rx.py for
              transmission and reception.  I am sending baseband samples
              at different frequencies and modulation scheme at varying
              amplitude of TX. (The distance between the TX and RX was 5
              mtr)

              

              I have captured the transmitted data at different
              frequencies at receiver using uhd_rx_cfile.  As, the
              Marcus has mentioned that these captured data is in terms
              of I/Q complex format, 16 bit for each.  

               

              I am trying to simply measure the power in the signal i
              have recorded at receiver using uhd_rx_cfile. I want to do
              this analysis at different frequencies say 300 MHz to 5
              GHz.  

              

              Another things i would like to do is capture the data with
              the moving receiver while the transmitter is fixed.

              

              Now, I want to do some curve fitting (best fit, polynomial
              or linear regression) on the captured data therefore I
              converted the captured data into .mat format using octave.
              When i load the data in workspace in MATLAB, I am not
              getting how to start with the plot and do curve fitting
              for Recorded reception power level VS distance to further
              proceed for channel modeling

              

              

              Any help in this regard is appreciated.

              

              Thank you all for your time and endeavour  pain.

              

              Best Regards,

              

              Alok Ranjan

              Graduate student 

              NIT, Rourkela

              

              

              
                Date: Tue, 14 Apr 2015 15:32:57
                -0400

                To: usrp-users at lists.ettus.com

                Subject: Re: [USRP-users] USRP captured data information

                From: usrp-users at lists.ettus.com

                

                Alok,
                  

                  
                  If you tell us a bit more about what you are
                    trying to accomplish with your curve fitting and
                    plotting, maybe we can be of more assistance. What
                    kind of curve fit or plot do you wish to generate?
                    Are you trying to demodulate a signal? Analog or
                    digital? Are you trying to simply measure the power
                    in the signal you recorded? What center frequency
                    and bandwidth are you interested in recording? What
                    kinds of signals are being transmitted in that band?
                    Are you going to move your receiver around and take
                    measurements from fixed transmitters?
                    

                    
                    -- 

                    
                      
                        Raj Bhattacharjea
                        Georgia Institute of Technology
                        School of Electrical and Computer
                          Engineering
                        http://www.prism.gatech.edu/~gtg037s/
                        404.894.7516
                      
                    
                  
                
                

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