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Control Resource Set (CORESET)

CORESET is the Resource Allocation unit in 5G.

• CORESET (Control Resource Set) : a grid of subcarriers x symbols, organized in REGs, REG-bundles and CCEs.

A Coreset is a set of Resource Blocks and symbols for carrying PDCCH.

Definitions

Picture this: You are now zoomed in at the Subframe level. You are trying to

5G NR Numerology | 5G NR Terminology (rfwireless-world.com)

Resource Grid (RG) A combination of subcarriers and OFDM symbols. Defined for each numerology, carrier and antenna port. • The resource grid which consists of number of subcarriers in frequency axis and number of OFDM symbols in time axis is known as resource grid.

• 5G supports $(N_{grid,x}{)}^{size,\mu }\times (N_{SC}{)}^{RB}$ subcarriers and $(N_{symb}{)}^{subframe,\mu }$ OFDM symbols.

Resource Block (RB) Resource Block (RB): Consists of 12 consecutive subcarriers in the frequency domain. It’s not defined for the time domain. (PRB).

• $(N_{SC}{)}^{RB}=12$ 
• There are more than one RBs in a resource grid.
•  Resource elements are grouped into PRB (Physical Resource Blocks). Each PRB consists of 12 subcarriers as mentioned.

Resource Element (RE) The smallest unit of resource grid.

• 1 subcarrier x 1 OFDM symbol
• Each element in resource grid for antenna port (“p”) and SCS configuration (i.e. Numerology) (“μ”) is known as Resource Element.
  - It is uniquely identified by $(k,l{)}_{p,\mu }$ where
  - $k$ = index in the frequency domain.
  - $l$ = symbol position in time domain.

Resource Element Group (REG) Made of 1 RB (Resource Block), i.e. 12 REs x 1 OFDM symbol.

REG Bundles 1 REG bundle is made of multiple REGs, Bundle size is specified by parameter “L”. valid sizes: 2,3, or 6 REGs

• REG (Resource Element Group) : 12 subcarriers x 1 symbol
• REGs are numbered time first and increasing frequency

Control Channel Element (CCE) One CCE is made of multiple REGs.

Aggregation level It indicates number of allocated CCEs for PDCCH. It can be 1/2/4/8/16.

NB: REG and REG-bundles are the physical resources and CCEs are logical resources (CCEs map to specific physical resources).