5G NR PDCCH | contents, function, physical layer processing

This page covers 5G NR PDCCH function, 5G NR PDCCH contents, mapping and physical layer processing of 5G NR PDCCH.

Following channels are supported by 5G NR wireless system.
Downlink channels: PDSCH (DL shared channel), PBCH (Broadcast channel), PDCCH (DL control channel)
Uplink channels: PRACH (Random Access Channel), PUSCH (UL shared channel), PUCCH (UL control channel)

5G NR PDCCH function, contents and mapping

• PDCCH channel is used to carry DCI (Downlink Control Information) e.g. downlink scheduling assignments and uplink scheduling grants.
• The figure-1 depicts 5G NR PDCCH.
• Unlike LTE control channels which occupies entire system BW, 5G NR PDCCH channels occupy certain subcarriers and OFDM symbols. These channels are transmitted in CORESET (configurable control resource set). 5G NR is flexible in time domain and frequency domain. Moreover certain 5G numerologies are also configurable to address various use cases.
• Frequency allocation in CORESET is either contiguous or non-contiguous. In time domain, it occupies about 1 to 3 consecutive OFDM symbols.
• The REs in CORESAT are arranged in REGs (RE groups). Each REG consists of 12 REs of one OFDM symbol in single RB.

5G NR PDCCH physical layer processing

• In 5G NR, PDCCH is confined to single CORESET and it is transmitted with its own DMRS. This enables UE specific beamforming for control channel.
• A PDCCH channel is transported by 1/2/4/8/16 control channel elements (CCEs) in order to accommodate different DCI payload sizes or coding rates.
• Each CCE consists of about 6 REGs. The mapping for CCE to REG may be interleaved or non-interleaved (for local beamforming). Interleaving is used for frequency diversity.
• The number of bits to be transmitted on the physical channel, is scrambled before modulation block.
• After scrambling, QPSK modulation is applied which results into complex modulated symbols.
• Next these complex symbols are mapped to physical resources with appropriate antenna port (p=2000) taking into consideration DMRS mapping.
• The physical layer processing for PDSCH is shown in the figure-1. Refer complete article on 5G NR Physical layer >> for more information. PDCCH channel follows the same modules with modifications as described in the 3GPP TS 38.211, 38.212, 38.213 and 38.214 specifications.

5G NR Numerology | 5G NR Terminology

5G NR Control channels | 5G NR Traffic Channels | 5G NR Reference Signals and sequences

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