CPRI AxC: Antenna Carrier Definition and Container Size

This page defines what a CPRI AxC is and discusses its container size.

AxC is short for Antenna Carrier in the CPRI (Common Public Radio Interface) standard.

Definition: The CPRI standard uses AxCs (antenna carriers) for transmitting and receiving digital I/Q data.

An AxC is essentially a container for a single I/Q sample. The size of this container, measured in bits, depends on the length of the I/Q sample itself. For example, if an I/Q sample is 16 bits long, the AxC will also be 16 bits.

CPRI AxC Examples

Here are a couple of cases illustrating how AxCs are used:

Case 1: Basic Frame Transmission at 3.84 MHz

The basic frames are transmitted over the CPRI link at a fixed clock rate of 3.84 MHz. This means a new basic frame is sent every 0.26 µs. The required data rate dictates how many AxCs are needed per basic frame to carry the I/Q data.

For instance, with a 3GPP signal having a sample rate of 3.84 MHz, only one AxC is needed per basic frame. Every 0.26 µs, a basic frame is transmitted, carrying one AxC, i.e., one I/Q sample. This results in an I/Q data rate of 3.84 MHz over the CPRI link.

Case 2: Signal with Sample Rate of 11.52 MHz

In this case, you’d need three AxCs per basic frame to handle the higher sample rate. Again, a basic frame is transmitted every 0.26 µs, but this time it contains three AxCs, representing three I/Q samples. The resulting I/Q data rate over the CPRI link becomes 3.84 MHz * 3, which equals 11.52 MHz.