What is Rate Matching?

Hi all.
I am trying to understand Rate Matching with respect to 4G/5G.
Could somebody give a brief idea on what exactly is Rate Matching?

LTE CRS rate matching: When 5G-NR physical downlink shared channel (PDSCH) is using 15 kHz subcarrier spacing, the subcarrier of LTE and 5G-NR are also orthogonal.
To avoid the LTE CRS subcarriers, a 5G-NR user is configured with the LTE CRS frequency information so that the 5G-NR user can calculate the LTE CRS positions as reserved resources, and the 5G-NR PDSCH will rate match around those reserved resources.
By rate.

Thanks @xsdenied07. But this is specific to DSS.
I wanted to understand in the most basic way what is Rate Matching and why we need it.
We need it for even single RAT cases also, like LTE only or NR only.

In very simple words, you rate match the incoming bits to available resources.

You have some resources available for data transmission over the resource grid including all the antennas, time and subcarriers.

Now you also have the encoded bits in you hand which you need to transmit over those available resources after modulation.

You rate match these encoded bits to those available resources either by repeating few of them if they are less, or discarding few of them if they are more.


The rate-matching is to extract the exact set of bits to be transmitted within a given TTI.
The rate-matching for Turbo coded transport channels is defined for each code block: there are three basic steps composing a rate-matching.
Namely, sub-block interleaver, bit collection, and bit selection. Finally, after the rate-matching, each individually processed code block has to be concatenated and transferred to a modulation block.

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Rate matching is required around LTE CRS pattern and if 5G subframes collide with those frames.