DIGITAL COMMUNICATION SYSTEM (PCM) DESIGN AND IMPLEMENTATION USING LABVIEW WITH USRP

[msacikgoz]

Hi,

I'm trying to find out digital communication system's (Pulse Code Modulation) transmitter and receiver using labview with usrp.I learned usrp's transmitter and receiver template but i have problems with pcm modulation and demodulation parts.I didn't understand Modulation Toolkit's vi so i designed quantization and encoder with mathscript.Please help me!

[smoores]

msacikgoz,

Pulse code modulation is a scheme for turning an analog signal into a digital signal, much like what is done in an ADC.  Could you clarify what you are trying to do?  Your signal, in this case a sound file (.wav most likely?), is already stored on your computer in a digital format.  Why are you trying to pulse code modulate a signal that is already in a digital state?

[msacikgoz]

smoores,

Thanks for answering me. I want to  transmit and receive audio  so I took the audio from computer.If I succes to do this, I will use a microphone .I designed quantizer and encoder for transmitter part because sound was already sampled and sampling rate is 44,1k Hz.

[smoores]

This is how I imagine your application working.  Why not do it something like this?

[msacikgoz]

I'm very grateful for your answer.I have a few more questions.Which block diagrams can I use to prevent Intersymbol Interference (ISI) and channel noise?

[smoores]

One solution you could do is to implement a pulse-shape filter.  See the heading in this white paper for reducing ISI:

http://www.ni.com/white-paper/3876/en/

If you have the modulation toolkit, a pulse-shape filter can be easily implemented with the MT Pulse Shaping Filter VI.

[msacikgoz]

Thanks for your reply.I set up block diagram as you say and it gave error like this.I couldn't figure it out this error.

[smoores]

You need to modulate your digital data into complex I and Q data before writing it to the USRP.  You have the digital waveform already, now you just need to take that waveform and convert it into a bit stream for modulation.  Check out the examples in a directory similar to:

C:\Program Files (x86)\National Instruments\LabVIEW 2014\examples\instr\niUSRP

There you will be able to find examples that use various digital modulation schemas.  Try experimenting with those.  The DWDT Digital to Binary U8 VI may come in handy.

[msacikgoz]

I ran niUSRP EX PAM Tx and niUSRP EX PAM Rx examples and I didn't understant where I should enter the bits of audio signal.

[smoores]

You are going to need to do some additional data manipulation in order to accomplish what you are trying to do.  The examples are built to be foundation in which you expand upon.  I would recommend looking at what others have done to transmit digital data, then adapt their methods to your application.  I found a community example that does some packet based digital communication using the USRP.  I'm sure there are some ideas you will be able to take away from it:

https://decibel.ni.com/content/docs/DOC-18801