However, there are also sidelink channels that enable direct device-to-device communications. We commonly talk about downlink (base station to UE) and uplink ( UE to base station) channels.
Downlink uplink mac#
MAC structure showing sidelink logical and transport channels. This combats path delay spread and Doppler spread via fine time and frequency tracking.įor beam management to a connected UE, Channel State Information Reference Signal ( CSI- RS) is used in the downlink. Uplink positioning is based on SRS.įor phase tracking and phase noise compensation for PDSCH and PUSCH, Phase Tracking Reference Signal ( PT-RS) is used. In the uplink, Sounding Reference Signal ( SRS) is used for channel estimation when PUCCH and PUSCH are not scheduled.įor downlink positioning, Positioning Reference Signal ( PRS) is used. It's applicable for PBCH, PDCCH, PDSCH, PUCCH and PUSCH. These are transmitted along with PBCH.įor acquisition and channel estimation, Demodulation Reference Signal (DM- RS) is used in both downlink and uplink. For downlink synchronization, there are Primary Synchronization Signal ( PSS) and Secondary Synchronization Signal ( SSS). There are a few physical signals closely associated with the operation of physical channels. UCI carries channel reports, HARQ-ACK and scheduling request. In the uplink, PUCCH carries Uplink Control Information ( UCI), although UCI can also go on PUSCH. DCI comes in many formats and one of them carries SFI to inform the UE which slot format is to be used. It carries Transmit Power Control ( TPC) commands. In the downlink, PDCCH carries Slot Format Indicator ( SFI) and Downlink Control Information ( DCI). These help in gathering feedback and quickly adjusting configuration or resource allocation to respond to varying conditions on the air interface. Information on these channels are only for exchanging control information at the physical layer. Which are the standalone physical channels?īy standalone physical channels, we mean channels that don't map to any transport channel.As an example, we note that RRC signalling messages and NAS messages (that also go through RRC) use DCCH. CCCH, DCCH and DTCH are also present in the downlink.PUCCH carries uplink control information although these could be sent on PUSCH as well.Like, PDSCH in downlink, PUSCH has flexible configuration that can be adapted to link conditions. PUSCH carries UL-SCH, which carries CCCH, DCCH and DTCH logical channels.Random access preambles carried on RACH help overcome message collisions due to multiple UEs transmitting at the same time. PRACH is used by UE for initial access to the network. PRACH carries RACH, which has no mapped logical channel.Uplink physical channels include Physical Random Access Channel (PRACH), Physical Uplink Control Channel (PUCCH), and Physical Uplink Shared Channel (PUSCH). Uplink transport channels include Random Access Channel (RACH) and Uplink Shared Channel ( UL-SCH). Uplink logical channels include Common Control Channel (CCCH), Dedicated Control Channel (DCCH) and Dedicated Traffic Channel (DTCH). In 5G NR uplink, what's the channel mapping?ĥG NR uplink channel mapping.PDCCH is used to schedule transmissions on PDSCH and PUSCH.It can be adapted to current link conditions. PDSCH carries a variety of transport channels.Once a connection is established, DCCH and DTCH become available to the UE. CCCH is used by a UE during initial access when there's no RRC connection yet.This is used to page a UE whose cell location is unknown. PCCH goes on PCH, which goes on PDSCH.PBCH is used by UE for cell acquisition, selection and re-selection.
BCCH for System Information Blocks ( SIBs) goes on DL-SCH, which goes on PDSCH.
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