Delay issue from Buffer/Unbuffer block

Question

Fumihiko Sato 2024-10-10

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2158835-delay-issue-from-buffer-unbuffer-block

回答： vidyesh 2024-10-28，8:46

Hello Community Experts,

I'm seeking assistance with my E2E wireless communication simulation, which consists of three components: Baseband Tx (DBPSK modulation), RF Receiver, and Baseband Rx (Direct Conversion method). Here are the details:

Baseband Tx:

Original bits: 208, padded with 10 zeros → Total Tx bits: 218
Modulation: DBPSK
Filter: RRX Tx filter, filter span = 10, output samples per symbol = 2

RF Receiver:

Input: Use Unbuffer block to convert 436 samples (218*2) to 1 sample per frame.
Output: Use Buffer block to convert 1 sample back to 436 samples (Output Buffer size = 436).
Other configuration as below screenshot

Baseband Rx:

AGC desired output: 0.5 W
Filter: RRX Rx filter, filter span = 10, input samples per symbol = 2, Decimation Factor = 2
Tail padding removal: 208 bits before demodulation
Demodulation: DBPSK and convert bit stream back to string.

The issue is that the first frame (first 208 bits or possbily 218 bits) consistently outputs '0'. It seems there's an unintended delay in the model, but I can't pinpoint where.

Could anyone please suggest how to eliminate this delay? or is it possbile that is come from other cause?

Thank you!

Best Regards,

Fumihiko Sato

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Fumihiko Sato 2024-10-11

Hello all,

I'd like to update on this.

I recreated a simple version to identify the source of the delay, as shown in the attached screenshot. The total source bit is 60 (50+10) with a sample time of 10.

It appears that the delay is being introduced by the "Buffer" block, as evidenced by the captured signal in the Scope block. The signal after the Buffer block shows an exact delay of 10 seconds, which corresponds to a 1-frame delay.