# Why to add trailing zeros to allow channel delay, and how many to add?

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Giti Dimrov el 28 de Jul. de 2022
Respondida: Bhanu Prakash Reddy el 9 de Oct. de 2023
Hi all,
I am trying to use the 802.11ac simulation example given in https://de.mathworks.com/help/wlan/ug/802-11ac-packet-error-rate-simulation-for-8x8-tgac-channel.html, but I have a question regarding adding trailing zeros to allow channel delay. Does anyone know how to estimate the number of zeros to add. How do the trailing zeros really help?
In my simulations I am using a frequency selective rayleigh channel with different path delays, and I don't know how to define the number of zeros to add, for different path delays
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### Respuestas (1)

Bhanu Prakash Reddy el 9 de Oct. de 2023
Hi Giti,
I understand that you want to know the purpose of using trailing zeros for channel delay and the procedure for the estimation of the same.
In a communication system, signals may experience delays during propagation through a medium. These delays lead to alignment issues during the processing of signal and can also lead to data loss. To avoid these issues, trailing zeros are added to the delayed signal to synchronize it with the original signal for further processing.
To estimate the number of zeros to be added, the maximum delay (in seconds) and the sampling rate (in samples per second (Hz)) are to be determined. In case if the channel has different path delays, the largest delay among all the path delays is considered as the maximum delay.
To calculate the number of zeros, multiple the maximum delay with the sampling rate.
For example, if the maximum delay is 1 millisecond (0.001 second) and the sampling rate is 10KHz (10000 Hz), then the number of zeros to be added is 0.001 * 10000 = 10 zeros.
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