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What is CORESET?

The set of physical resources that is time frequency resource in which device tries to decode candidate control channels using one or more search spaces is called as the control resource set (CORESET).

Coreset is the concept of central to downlink control signaling in 5G NR.

Need to introduce CORESET:

The downlink control signaling in LTE uses the full carrier bandwidth in the first 1-3 OFDM symbols (four for the most narrowband case). This is known as the control region in LTE.

The desire for frequency diversity and the fact that all LTE devices support the full 20 MHz carrier bandwidth motivated the need of having control channels covering the full carrier bandwidth.

However this was one of the cons as this lead to complications when introducing support for device not supporting the full carrier bandwidth in later LTE release. (EG. eMTC devices in release 12)

The inability to handle frequency domain interference coordination between cells for the downlink control channels is another disadvantage of LTE.

But to some extent all these disadvantages with the LTE control channel were overcome with the introduction of EPDCCH in release 11.

However the EPDCCH feature is not brought into practice as LTE network still needs to provide PDCCH support for initial access and to handle non EPDCCH capable devices.

All this lead to the introduction of more flexible structure in NR called CORESET.

Difference between CORESET and LTE control region:

The Control Region in LTE in equivalent to CORESET in NR.
The main difference between CORESET and LTE Control Region is that, the control region in LTE is spread across the whole channel band width  (CBW) and NR CORESET is localized within each BWP.

Frequency Domain parameter of CORESET VS LTE control region:

A CORESET can be found at any point within a slot and anywhere in the frequency range of the carrier.

However, a device should not handle CORESETs outside its active bandwidth part. The reason behind configuring corsets on cell level and not as per bandwidth part is to avail the facility of reusing of corset between band width parts.

On the other hand as Control Region in LTE is always spread across the whole channel band width, there are no parameters defining the frequency domain region for LTE control region.

Time Domain parameter of CORESET VS LTE control region:

In time domain length both NR CORESET and LTE Control Region can vary.

CORESET can be up to three OFDM symbols in duration and located anywhere within a slot in time domain, although a common scenario, suitable for traffic scenarios when a scheduling decision is taken once per slot, is to locate the CORESET at the beginning of the slot. This is similar to the LTE control region with control channels at the start of each LTE subframe.

The time domain length of control region is defined by the physical channel known as PCFICH in LTE.

CORESET is defined from a device point of view and only indicates where a device may receive PDCCH transmissions.

Stay tune for more update on CORESET..........................

3gpp TS 38.331
3gpp TS 38.331



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