Streaming OFDM Transmitter and Receiver

[ErikL]

This example provides a continuous streaming implementation of OFDM.  This example provides easy to read and easy to modify OFDM reference design based on LTE-like parameters (with regards to sub-carriers, reference symbols, and null subcarriers.

It includes both a simulated and USRP based implementation to aid in offline work with impairments. In the future I hope the community will add synchronization that will allow a BER calculation when using two USRP devices.

I wish to thank Douglas Kim, Miro Tomaska, Anthony Fuller and the many other contributors.

For more information about the sources of error in IQ based RF signal generation, reference http://www.ni.com/tutorial/5657/en/

[ktilina6]

hi.

I have a question, in the Tx file, the array division in 125, the 125 is the number of subcarriers to do a OFDM quadrature?

thanks in advance

[ErikL]

It’s the number of data subcarriers before reference symbols are interleaved and zeroes added.

[RaviSingh]

Hi Erik,

I have managed to stream the OFDM signal over FlexRIO kit. I have a question regarding expansion of bandwidth. The code is currently set to work with 5 MS/s. I tried to use 10 MS/s sampling rate with the FlexRIO transmitter and receiver and the system does not work anymore. The constellation is corrupt even after the channel equalisation.

Is it that we must increase the number of subcarriers and the CP lenght, if we are to increase the system bandwidth?

I look forward to hear from you soon.

BR

Ravi

[OsamaS]

hello Erikl,

I have modefied the code to be suti for optical communication channel (such as removing the complex and nigave values ). it seems such it is work fine . But when i do off line process and mesure BER. Sometimes the system work perfict (have 0 BER but other time i got 100% BER). I am doing the same process for same the same indoor channel ..Is thisbehaveur related to the USRP itself (sometimes doesnt work good) or is that because the MIMO cable is needed to make my system always syncronised. Hopefully i will got unswer for this prbem,  i been facing this issue for long time ..Thanks for the code and thanks for opening the descusiion.

[ErikL]

Hello Osama -

Its likely related to the energy detector.  You really need an adaptive energy detector and automatic gain control.  We did not implment either of these.

[Waseem90]

Hi LiYi,

How can I use the same OFDM system with using USRP RIO??  Is there any example for that??

Many thanks,

Waseem

[OsamaS]

Hi Erik,

For my scheme  zero padding process should be removed. However after i remove  zero padding my spectrum is not stable any more and have number of errors in constellation points. May i ask why zero padding is so important and is there any alternative process that can fix the problem.

Many thanks in advance for your help and regards

[Imdadinho]

Can you please tell me whether this example code is supposed to work on two USRPs (2921) i.e 1 separate USRP for transmission and a separate USRP as a receiver.

Thanks

[OsamaS]

Hi,

is the IQ rate equal to the sampling frequency.. is there away to change the sampling rate of the reciever to make it twice or more of the 1Q rate

Regards

[brunoFdezGV]

Hi, I have one question... when I load the VI project, LabView ask to me where it can find complex data waveform and more things like this, what does it mean? Sorry for the question, I'm a beginner in this area and I am sure that this is a stupid question...

[Gan_Zheng]

Dear Erik,

May I know which version of LabVIEW Comms is needed to run the code? I have ver 1.1 and got many errors like below

Is it because a higher version is needed? Thanks. 

[mcan06]

Hi ErikL and other community members, thanks ErikL and everyone the infrastructure and commnets respectively.ErikL I want to ask a question, I want to calculate BER by using MT BER Calculate .gvi, can I directly calculate without using any extra .gvi block for single NI USRP-2922 or two NI USRP-2922 whic are connected by using MIMO expansion cable.Thanks...

[ashwini11]

Hello sir,

I tried executing this code. we can decode the bits properly but bit loss is there at the receiver side. For different mapping techniques (ex QAM, PSK) the bit loss is different. but when i executed the code with only mapping and de-mapping of bits i am able to recover all the bits. can anybody help me to know where and why the bits are lost. 

[lucky_patna]

Hi Erik ! In the provided example. One SubVI "Ramp Pattern by Samples" is missing in CFO Correction dependency at RX.VI. Can you please help me ? 

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Lucky Kumar

[Sylvia__]

Hello，ErikL！Thank you very much for sharing. I downloaded your program from here, but opening it on my computer will display the error in the picture above. My computer's software environment is：windows 7，labview2017 ，NI-RFSG17.0, NI-RFSA17.0, Spectral Measurements Toolkit17 and Modulation Toolkit 17.0 . so how can I run these programs?

Best regards,

Sylvia

[ardisns]

hi erik, 

I have been using your gvi for my project to measure a wide band channel. the challenge that i am facing right now is the way to change subcarriers from 125 ( that you have used right now) to 101. because i want to compare the result of it with VNA. i'm sorry if i'm bothering you, thank you in advance

[ayanzav]

Hi Erik, thanks for you work. I have a doubt about the block of crop signal, anyone knows how work?, any paper or on what is based? I don't understand cuzz use the values for this block. Thanks.