While study on the radio system during my working hour, found that the system here are using normal Ethernet cable to connect the main system  to the Base Station. Normally an Ethernet cable maximum transmission distance are not recommended to be more the  100 Meter.

According to the senior engineer over there, if the base station located far away from the main system, they normally using fiber optic or some other medium such as wireless, antenna in special frequencies or E1 line from ISP.

An E1 carrier is a telecommunications facility designed to carry digital information at a bit rate of 2.048 Mbps. In conventional telecommunications, the most common use for an E1 carrier is to connect central offices within an individual telephone company. Telephone companies also lease E1 carriers to their customers for their own private purposes. Most systems use E1 circuits to transmit digitized voice, management, and control traffic between zones. The Frame Relay and Cell Relay protocols provide the means for exchanging information over the E1 communication facilities that connect remote zones.

E1 carrier system

Various types of transmission media can be used in implementing a private E1 facility, such as various types of privately installed cabling or point-to-point microwave circuits.

An E1 circuit is divided into 32 time slots, each of which implements a separate communication channel that can support a bit rate of 64,000 bps. Each of these individual channels is referred to as a Digital Signal Level zero (DS0) channel.

The term framing refers to the order in which user bits and other information is transmitted over a physical transmission medium. An E1 frame comprises a total of 256 bits. Each of the 32 inputs is assigned a fixed time slot; the E1 uses a time-division multiplexing technique to divide the capacity of the carrier into 32 channels. The framing bit is used to create a pattern to help synchronize the equipment. Picture above illustrates the format of the E1 transmission frame.