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# Transmit and Receive WLAN packets on a two separate Radios platform problem:

I have developed an algorithm using Matlab for the Zynq SDR using two zedboards and AD9361. I have one Radio set on IP 192.168.3.2 and the other radio is set on IP 192.168.3.5. I transmit from one IP and receive on another IP Radio.

I have developed the algorithm using Schmidl-cox method as described in the book “SDR4Engineers” written by Travis et.al. Now the problem is as follows:
I can not send one single transmit wave and try to receive from another radio to demodulate and decode the data. The error rate is very high.

I have managed to send the picture into 171 frames where each frame contains about 1152 bytes long. Each frame is sent from one radio and received on another Radio. The antennas are just 10cm apart. It is really a time consuming process. However, after receiving all the frames and decoding the data and assembling for final display of the figure shows 2% to 3% error rate. The schmidl-cox method does not achieve 0% error rate. In some frames “wlanpacketdetect” library do not detect the correct offset and hence there are some error in the received bits.

Now, if the buffer rate is about 284 bytes long, the number of frames send from one Radio and received on another radio, the error rate may come 0%. However, it is very unpredictable. I have realized that the schmidl-cox algorithm can not achieve 0% error rate. It is very unpredictable for the transmit and receive from two separate radios. Yes! As suggested by Travis, I use WLAN method in the matlab program. Not LTE method of transmission reception of the waveforms.

Here are my questions:

1. Is there any other way or other methods that we can achieve 0% error rate of transmission and receiver with two different Radios. If any other scholars have proposed a method and I can use in a real environment, I can try to write the matlab code. Kindly advise me on this!

2. Can we use LTE technology to accomplish the outcome of 0% error rate?

3. Is it possible to successfully achieve 0% error rate of transmission and reception in a Multi-SDR environment?

4. Is there any other method proposed by other scholars to successfully transmit and receive a picture as shown for a single radio code using LTE or WLAN transmission and reception?

5. I have read the book written by Travis et.al. After understanding the book and mastering matlab, I have a doubt that we can achieve this solution at all. Am I correct on this?

Anybody can respond to me with your valuable input and I would very much appreciate. I hope that Travis can make some comments about my inquiry.  Thanks in anticipation.

• Hi,

This is moved to Design Support AD9361 community. Someone here should be able to assist you.

• Yes providing LTE as an input signal will reduce the error as it has in built internal synchronization.

For synchronizing the receive and transmit boards, you should use an external GPS REF_CLK . Refer to the below link:

I need more input as to how to use GPS REF_CLK in matlab while I transmit and receive signals.

• Have you tried using LTE signal? Has the error reduced with LTE signals?

• LTE Signals error rate is about 43%. I was also advised by the experts to use WLAN instead of LTE.

Hence, I used WLAN as well as Schmidl-cox algorithm as advised by Travis et.al who wrote the book called SDR4Engineers.

Thanks

•  Are you still facing the issue?

Can you comment on this?

• If you have undesirable performance you will need to dig into the recovery algorithm to understand where the source of error comes from. These synchronization algorithms are generally tunable to select between different tradeoffs. For example, Schmidl & Cox will have a threshold to select. How you set this will either favor false positives in the form of incorrect packets or you will miss packets.

The algorithms need to be tuned for your hardware and implementation. I would recommend manually going through the data to understand how and why mistakes were made by the specific implementation. Generally, all receiver designs will have some tweaks based on their characteristics compared to the journal papers.

-Travis