A radio base station forms an area (cell) in which user terminals such as mobile phones are allowed to wirelessly communicate with the base station.
A radio base station is configured to have a radio equipment control (REC) that performs baseband signal processing in a digital domain, control/management, and the like, and radio equipment (RE) that performs radio signal processing (modulation, amplification, and the like) in an analog domain.
There is a radio base station in which a remote radio head (RRH) having RE is located in a position distant from a base station main body having an REC. In this case, the REC and the RE are connected by an optical fiber, for example.
Common Public Radio Interface (CPRI) has been known as an interface for communication between the REC and the RE (refer to Non-Patent Literature 1). The CPRI defines a CPRI link that connects the REC to the RE. Further, the CPRI supports a layer 1 (physical layer) and a layer 2 (data link layer).
In the CPRI, as a layer 1 frame for communication between the REC and the RE, a frame defined as a basic frame is adopted.
The basic frame adopted in the CPRI consists of 16 words (1 word consists of 8 bits, for example).
The basic frame includes one control word at the beginning, and an IQ data block consisting of 15 words, which follows the control word. Note that IQ (Inphase/Quadrature) data is user data. That is, the user data is transmitted by a radio signal from a radio base station to user equipment, or from the user equipment to the radio base station.
In the CPRI, one “hyperframe” consists of 256 basic frames. One “CPRI 10 ms frame” consists of 150 hyperframes.
The CPRI uses two types of control and management (C&M) channels, a slow C&M channel and a fast C&M channel, as control channels between the REC and the RE. A part of the 256 control words included in one hyperframe constitutes the slow C&M channel, while another part of the 256 control words constitutes the fast C&M channel.
The CPRI supports, as the layer 2, ETHERNET® network technology, High-level Data Link Control (HDLC) procedure, and the like.
In the CPRI, the layer 2 (data link layer) frame structure for the slow C&M channel is based on the HDLC, and the layer 2 frame structure for the fast C&M channel is based on the ETHERNET® network technology.