5G Channel structure
PBCH : used for MIB distribution System information can be distributed via PDSCH or via PDCH , depending on the UE state.
The MIB is periodically broadcasted in PBCH.
A PDCCH spans only a fraction of the system bandwidth and has its own demodulation reference signals enabling user-specific beamforming. PDCCH is transmitted preferably in the first OFDM symbol in an NR DL slot. Frequency resources unused for PDCCH transmission may be utilized for PDSCH transmission.
DL reference & sync signals
- DMRS for PDCCH
- DMRS for PDSCH
UL reference & sync signals
- PRACH preamble
- DMRS for PUCCH
- DMRS for PUSCH
Layer 2 functions
Radio interface structure - using EPC
The protocols performing the functions in the radio interface for the UP are :
PDCP, RLC , MAC & Physical layer
For control signaling the RRC is used to convey the NAS information over the radio interface as well as the AS signaling. The physical layer maps the transport channel onto a physical channel & performs channel coding , modulation etc.
Services & functions of AS sublayer
- Mapping between a QoS flow and a data radio bearer.
- Marking QoS flow ID in both DL and UL packets.
5G QoS Indicator Parameters
The 5GI is the standardized value range that has one - to- one mapping to a standardized combination of 5G QoS characteristics. The QoS parameter ARP contains information about priority level.
Variable DM-RS patterns for data demodulation are assisted. Front - loaded DM-RS is mapped over 1 or 2 adjacent OFDM symbols. DM-RS configuration can be upto maximum number of DM-RS ports.
- These are transmitted in DL and are primarily intended to be used by UE’s to acquire CSI but could also serve other purposes.
- Effective channel estimation at the UE.
- Discovery signal
MIMO - beamforming , diversity , SMUX , precoding , SU-MIMO, MU-MIMO.
Analog & digital beamforming.
Massive MIMO/beamforming for 5G
A predefined set of fixed beams seems to be the preferred solution for massive MIMO.
The link beam can typically have rank 1-8.
Repository is when an estimate of the UL channel can be used when designing the DL transmission. Different levels are coherent , stationary and directional. It is the strongest form of reciprocity and it is only possible to achieve in TDD.