CPRI protocol stack | RRH protocol stack
This article section on CPRI basics covers following sub topics:
Remote Radio Head
CPRI protocol stack
CPRI frame structure
As mentioned in the article on CPRI frame structure, CPRI interface lies between REC and REs in RRH system architecture. CPRI interface covers two layers layer-1 (physical layer) and layer-2(data link layer). The figure below depicts CPRI protocol stack mentioning this layers.
The CPRI interface supports following information types:
• IQ Data which is user plane information in the form of in-phase and quadrature phase
modulation data (i.e. digital baseband signals).
• Synchronization data used for frame and time alignment.
• L1 Inband Protocol: Signalling information that is related to the link and is directly
transported by the physical layer. This information is required, e.g. for
system start-up, layer-1 link maintenance and the transfer of time
critical information that has a direct time relationship to layer-1 user
data.
• C&M data:Control and management information exchanged between the control
and management entities within the REC and the RE. This information flow is given to the higher protocol layers.
• Protocol Extensions: This information flow is reserved for future protocol extensions. It may
be used to support, e.g., more complex interconnection topologies or other radio standards.
• Vendor Specific Information: This information flow is reserved for vendor specific information.
Layer-1 and Layer-2 functions
In RRH, CPRI protocol stack consists of layer-1(physical layer) and layer-2(data link layer).
RRH protocol stack Layer-1 defines following:
• Electrical characteristics
• Optical characteristics
• Time division multiplexing of the different data flows
• Low level signalling
RRH protocol stack Layer-2 defines following:
• Media access control
• Flow control
• Data protection of the control and management information flow
Following are the functions of various protocol data planes:
The following data flows can be discerned:
Control Plane: Control data flow used for call processing.
Management Plane: Management information for the operation, administration and maintenance of the
CPRI link and the RE.
User Plane: Data that has to be transferred from the radio base station to the mobile station and
vice versa. These data are transferred in the form of IQ data.
Synchronization: Data flow which transfers synchronization and timing information between REC and
RE.
The control and management plane will be mapped to a single information flow over the CPRI link.
User plane data:
The user plane data are transported in the form of IQ data. Several IQ data flows will be sent via one
physical CPRI link.
Here each I/Q data represents per carrier and it is for one antenna.
It is referred as antenna carrier.
Antenna-carrier (AxC):
One antenna-carrier is the amount of digital baseband (IQ) U-plane data necessary for either reception or
transmission of one UTRA-FDD carrier at one independent antenna element.
AxC Container:
It contains the IQ samples of one AxC for one UMTS chip duration.
Service Access Points:
For all protocol data planes layer 2 services access points are defined that will be used as reference points
for performance measurements. These service access points will be denoted as SAPCM, SAPS and SAPIQ.
Downlink:
Direction from REC to RE.
Uplink:
Direction from RE to REC.
The table below describes the functions of REs and REC entities in a RRH (Remote Radio Head).
| Functions of REC | Functions of RE | ||
|---|---|---|---|
| Downlink | Uplink | Downlink | Uplink |
| Radio Base Station Control and Management | |||
| lub Transport | RRC Channel Filtering | ||
| lub Frame protocols | D/A conversion | A/D conversion | |
| Channel Coding | Channel Decoding | Up Conversion | Down Conversion |
| Interleaving | Deinterleaving | ON/OFF control of each carrier | AGC |
| Spreading | Despreading | Carrier Multiplexing | Carrier De-multiplexing |
| Scrambling | Descrambling | Power amplification and limiting | LNA |
| Adding of physical channels | signal distribution to signal processing units | Antenna supervision | |
| Transmit power control of each physical channel | Transmit power control & feedback information detection | RF filtering | RF filtering |
| Frame and slot signal generation(including clock stabilization) | |||
| Measurements | Measurements | ||
RRH, CPRI and eCPRI Related Links
5G NR Numerology | 5G NR Terminology
5G NR Control channels | 5G NR Traffic Channels | 5G NR Reference Signals and sequences
5G TECHNOLOGY RELATED LINKS
This 5G tutorial also covers following sub topics on the 5G technology:
5G basic tutorial
5G Frequency Bands
5G millimeter wave tutorial
5G mm wave frame
5G millimeter wave channel sounding
Difference between 4G and 5G
5G testing and test equipments
5G network architecture
5G NR Physical layer
5G NR MAC layer
5G NR RLC layer
5G NR PDCP layer