Why first and seventh cyclic prefix is larger in 5G in each slot?

5G NR
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1

Hello Experts.

Why first and seventh cyclic prefix is larger in 5G in each slot?

Why first and seventh cyclic prefix is larger in 5G in each slot

2

My take for this important question wrt various aspects is summarized in following points:

The larger first and seventh symbol cyclic prefix (CP) in each 5G NR subframe for numerology 0 (for other numerologies= 0,7*2^mu) serves following specific purposes:explained for mu=0 and applicable to other ones:

  1. Initial synchronization: The first symbol’s larger CP helps with initial time and frequency synchronization, particularly in scenarios with larger delay spreads or timing uncertainties.
  2. Midpoint resynchronization: The seventh symbol’s larger CP allows for resynchronization at the subframe’s midpoint, helping maintain timing alignment throughout the subframe.
  3. Robustness against multipath: Longer CPs provide better protection against intersymbol interference in challenging channel conditions with long delay spreads.
  4. Flexibility: This structure allows for consistent timing across different numerologies, facilitating multi-numerology operation and carrier aggregation.
  5. Backward compatibility: It maintains similarity with LTE’s extended CP structure, easing migration and coexistence.

This design balances the need for efficient spectral usage with system robustness and flexibility across various deployment scenarios.

3

A cyclic prefix length is calculated based on the cell size and delay spread to overcome ISI.

So, a normal CP (like the CP for all other symbols) is well enough and serves the purpose.

And ideally, that is what we should have done across all the symbols.

But by doing so, our slot/subframe boundaries go unaligned.

We make sure that at every 1 ms timings boundaries are aligned.

In order to do so, we need to add extra time somewhere in between the slots or ofdm symbols so that at the end of every 1 ms, we are well aligned, that means last symbol of last slot ends at 1 ms.

In 5G at every 0.5 ms, we have a longer CP.

4

Since the cp can be same across all symbols (extended cp option) so ,sorry, but all your discussion points are not valid.