Physical layer aspects
OFDM with CP is utilized for DL and in NR UL direction. Carrier spacing of 15 KHz , 30 KHz and 60 KHz can be used for network deployments operating in frequency bands below 6 GHz. Network distribution above 24 GHz, 60 KHz and 120 GHz subcarrier spacing can be used. NR assists both FDD & TDD working with the same frame structure. Such very short transmissions mainly target usage cases requiring low latency , such as some URLLC services.
Channel coding & modulation
In NR, LDPC coding is used for data for L1 control signalling. Polar coding is utilized in case of more than 11 information bits. QPSK, 16 QAM , 64 QAM and 256 QAM are supported for DL and UL.
Radio physical layer aspects
Initial access & mobility
NR synchronization signals i.e PSS & SSS are transmitted over 127 sub carriers and are designed to carry the PCID selected from 1008 candidates.
PSS & SSS are transmitted together with PBCH and DMRS for PBCH as an SS/PBCH block for a carrier within four OFDM symbols in time domain and 240 subcarriers , corresponding to 20 resource blocks , in frequency domain.
SIB 1 & other SIB 2 are carried by PDSCH which is scheduled for PDCCH.
Paging message is carried by PDSCH which is scheduled by PDCCH.
For random access in NR, a four step procedure ( Msg 1, Msg 2, Msg 3 and Msg 4) similar to LTE is defined.
NR supports multi-layer transmission with a maximum of 8 to 4 transmission layers for DL & UL transmission directions respectively.
RSs are specified assuming multi-antenna transmission.
CSI-RS can also be used for fine frequency/time tracking i.e Tracking RS, mobility measurements and beam management measurements.
Beamforming / precoding is an important technique for achieving higher throughput and sufficient coverage.
Phase tracking RS can be used in both DL & UL to compensate for the increased phase noise for the higher frequency ranges.
The basic way of controlling data transmission in NR is scheduling in a similar way as in LTE.
Each device monitors a no. of PDCCHs , typically once per slot.
The PDCCHs are transmitted in one or more control resource sets, each of length one to three OFDM symbols.
General description of NR PDCCH
In NR, PUCCH delivers UCI which consists of HARQ-ACK , SR or CSI.
NR PUCCH supports durations of 1 to 2 symbols or 4 to 14 symbols.
Long PUCCH is used to improve coverage.
Short PUCCH is used to reduce coverage.
For a UE, TDM between long-PUCCH and short-PUCCH is also supported.
Scheduling / HARQ
DCI formats0_0/0_1 and 1_0/1_1 schedule PUSCH and PDSCH respectively.
For each DCI format, frequency-domain and time-domain resource allocation fields are included.
Radio physical layer aspects
CA, BW parts & LTE/NR dual connectivity
In NR, the maximum BW of a NR carrier is 100 MHZ for carrier frequencies below 6 GHz and 400 MHZ for carrier frequencies above 24 GHZ respectively.
Both intra-band CA & inter-band CA are supported.
Both self-carrier scheduling & cross-carrier scheduling are supported.
NR well defines the concept of the bandwidth part.
Up to four BWP can be configured for a UE per NR carrier for DL and UL respectively.
Higher - layer signalling can be used to configure reserved resources and LTE CRS - related information to be rate - matched around.
The corresponding backhaul signalling between eNodeB and gNodeB is also specified.
PDSCH resource mapping in NR allows LTE, NB-IOT and LTE-M to operate on the same frequency as NR.
In this , an SDL carrier can be aggregated with CA together with another DL & UL carrier .
In SUL, the UE is configured with 2 ULs for one DL of the same cell and UL transmissions on those two ULs are controlled by the network to avoid overlapping PUSCH/PUCCH transmissions in time.
NR UL power control is designed to allow dynamic power adjustment and multiple power control processes e.g for switching.
When UE supports dynamic power sharing, power allocations are dynamically adjusted on condition that the total transmission power never exceeds allowed value.
Higher layer aspects
Layer 2 related aspects
- Mapping between logical channels and transport channels.
- Multiplexing / demultiplexing of MAC SDUs.
- Scheduling information reporting
- Error correction through HARQ
- Priority handling between UE’s by means of dynamic scheduling.
Transfer of upper layer PDUs
Sequence numbering independent of the one in PDCP ( UM & AM)
Error correction through ARQ ( AM only)
Reassembly of SDU ( AM and UM)
Protocol error detection.
Transfer of user data
Reordering and duplicate detection
PDCP PDU routing
- Mapping between a QoS flow and a data radio bearer.
- Marking QoS flow ID in DL and UL packets
Higher layer aspects
RRC related aspects
- Broadcast of system information related to AS & NAS.
- Safety functions
- Initialization, configuration , maintenance and release of signalling radio bearers and data radio bearers.
- Mobility functions
Network interface related aspects
X2 AP functions :
- EUTRA - NR dual connectivity function
- Secondary RAT data usage report function
S1 AP functions :
- Report of secondary RAT data volumes function
Xn AP functions :
- Xn setup function
- Error indication function
- Xn reset function
- Xn configuration data update function
- Handover preparation function
- RAN paging function’
- Energy savings function
NG AP functions :
- Paging function
- UE context management function
- Mobility management function
- PDU session management function
- NAS node selection function
- AMF management function
F1 AP functions :
- F1 interface management function
- System information management function
- F1 UE context management function
- RRC message transfer function
- FR 1 : sub 6 GHz : 450-6000 MHz
- FR 2 : mm wave : 24250 - 52600 MHz
Both conducted and over the air (OTA) techniques can be used in FR1 , but only OTA can be used in FR2. Ranges ( 65-256) and (257-512) are reserved as band number for NR new bands in FR1 and FR2.
5G NR bands
LTE connectivity to 5G-CN
LTE connectivity to 5G-CN does not only permit RAN level interworking but gives a migration path where the core network is 5G-CN whereas the radio remains LTE. The attribute “ LTE connectivity to 5G-CN” or the E-UTRA connected to 5GC.
LTE connectivity to 5G-CN functionality
- 5G NAS message transport
- Flow based QoS
- Network slicing
- NR PDCP