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5G NR CORESET Explained: Function and Parameters

5g nr coreset pdcch resource allocation

This document explains the basics of 5G NR CORESET (Control Resource Set) including its function. It describes the CORESET for PDCCH (Physical Downlink Control Channel) and the various fields used in the Control Resource Set (CORESET) information element.

Introduction

  • In 5G NR, the basic resource allocation unit is the CORESET.
  • In LTE, control channels are allocated across the entire system bandwidth, which can make inter-cell interference management difficult.
  • To address this, 5G NR uses specifically designed CORESETs for PDCCH transmission.
  • Think of CORESET as analogous to the LTE control region, but generalized in 5G NR as a set of Resource Blocks (RBs) and OFDM symbols.
  • Frequency allocation within a CORESET can be either contiguous or non-contiguous.
  • In the time domain, a CORESET configuration spans 1 to 3 consecutive OFDM symbols.
  • Resource Elements (REs) within a CORESET are organized into Resource Element Groups (REGs).
  • Each REG consists of 12 REs of one OFDM symbol in one RB.

CORESET Parameters

The key parameters of a CORESET are:

  • RE (Resource Element)
  • REG (Resource Element Group)
  • REG Bundles
  • CCE (Control Channel Element)
  • Aggregation level

Here’s a breakdown in table format:

TerminologyDescription
RE (Resource Element)The smallest unit of the resource grid, defined as 1 subcarrier x 1 OFDM symbol.
REG (Resource Element Group)Made up of 1 RB (Resource Block), which is 12 REs x 1 OFDM symbol.
REG BundlesOne REG bundle consists of multiple REGs. The bundle size is determined by the parameter “L”.
CCE (Control Channel Element)One CCE is composed of multiple REGs.
Aggregation levelThis indicates the number of allocated CCEs for a PDCCH. It can be 1, 2, 4, 8, or 16.

The time and frequency domain parameters of CORESET are defined in the 3GPP TS 38.211 document.

RRC Signaling Fields

The Radio Resource Control (RRC) signaling message includes the following fields related to CORESET:

  • N RB CORESET: The number of RBs in the frequency domain within the CORESET.
  • N Symb CORESET: The number of symbols in the time domain within the CORESET. This can be 1, 2, or 3.
  • N REG CORESET: The number of REGs within the CORESET.
  • L: REG bundle size.

Use of CORESET in 5G NR PDCCH channel

  • A PDCCH channel is restricted to a single CORESET and is transmitted with its own DMRS (Demodulation Reference Signal). This enables UE-specific beamforming for the control channel.
  • The PDCCH channel is carried by 1, 2, 4, 8, or 16 CCEs (Control Channel Elements) to accommodate different DCI (Downlink Control Information) payload sizes or coding rates.
  • Each CCE consists of 6 REGs.
  • The mapping of CCEs to REGs for a CORESET can be interleaved (to support frequency diversity) or non-interleaved (for localized beamforming).

Control Resource Set (CORESET) information element

The following fields are used to configure CORESET, as defined in 3GPP TS 38.331.

CORESET IE fields

The table below describes the fields within the CORESET information element.

CORESET Information Element Fields

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)