What is 5G NR CORESET | Function of CORESET in 5G NR

This page mentions 5G NR CORESET basics including function of CORESET (Control Resource Set). It describes CORESET for PDCCH including various fields used in Control Resource Set (CORESET) information element.

Introduction:
• Resource allocation unit in 5G NR is CORESET.
• In LTE, control channels are allocated across entire system bandwidth. This makes it difficult to control the inter-cell interference.
• To address above, in 5G NR system, PDCCHs transmit in specifically designed CORESET.
• Here CORESET is analogous to LTE control region but it is generalized in 5G NR with set of RBs and OFDM symbols.
• Frequency allocation in CORESET configuration can be contiguous or non-contiguous.
• In time domain, CORESET configuration spans 1 to 3 consecutive OFDM symbols.
• REs in CORESET are organized in REGs (RE Groups).
• Each REG consists of 12 REs of one OFDM symbol in one RB.

Parameters of CORESET are as follows.
{RE, REG, REG bundles, CCE, Agggegation level}

Time domain and frequency domain parameters of CORESET are defined in TS 38.211 document. RRC signaling message consists of following fields.
• N_RB^CORESET: The number of RBs in frequency domain in CORESET.
• N_Symb^CORESET: The number of symbols in time domain in CORESET. This can be 1/2/3.
• N_REG^CORESET: The number of REGs in CORESET.
• L: REG bundle size

Use of CORESET in 5G NR PDCCH channel

• A PDCCH channel is confined to one CORESET and transmitted with its own DMRS (Demodulation Reference Signal). Hence UE specific beamforming of control channel is possible.
• PDCCH channel is carried by 1/2/4/8/16 CCEs (Control Channel Elements) to carry various DCI payload sizes or coding rates.
• Each CCE consists of 6 REGs.
• The CCE to REG mapping for CORESET can be interleaved (to support frequency diversity) or non-interleaved (for localized beamforming).

Control Resource Set (CORESET) information element

Following are the fields used to configure CORESET. It is defined in TS 38.331 document published by 3GPP.

Following table describes fields of CORESET information element.

References

• 3GPP TS 38.211, V15.2.0 (Physical Channels and Modulation)
• 3GPP TS 38.331, V15.2.0 (Radio Resource Control (RRC) protocol specification)

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