The difference between RRU and digital fiber repeater

1. RRU Working Principle and Application

The Remote Radio Unit (RRU) is a new type of distributed network coverage model. It places large-capacity macro cell base stations in an available central machine room. The baseband part is processed centrally, and optical fiber is used to pull the RF module in the base station to the remote radio unit, which is placed at the site determined by the network planning, thus saving a large number of machine rooms required for conventional solutions. At the same time, by using large-capacity macro base stations to support a large number of optical fiber remotes, the conversion between capacity and coverage can be achieved.

The working principle of RRU is: the baseband signal is frequency-converted, filtered, RF-filtered, amplified, and then transmitted to the antenna feed through the linear power amplifier through the transmission filter. The uplink signal received from the mobile terminal is filtered, low-noise amplified, further RF small signal amplified, filtered, and down-converted, and then the analog-to-digital conversion and digital intermediate frequency processing are completed. The system block diagram is shown in Figure 1.

Figure 1 RRU internal block diagram

There are two types of connection interfaces between RRU and base station interface: CPRI (Common Public Radio Interface) and OBASI (Open Base Station Architecture Initiative). CPRI organization members include: Ericsson, Huawei, NEC, Nortel, Siemens. OBSAI organization members include: Nokia, ZTE, LGE, Samsung, Hyundai. The connection diagram between RRU and RNC is shown in Figure 2.

Figure 2 RRU and base station interface

In terms of signal coverage, RRU can be derived from NodeB through the same frequency and different scrambling codes. It can also be derived from RNC through the same frequency and different scrambling codes. These two coverage methods are conventional methods. Here is another coverage method: the base station has 3 sectors, equipped with redundant channel boards and redundant baseband processing equipment. The baseband pool sharing technology can be used to set the redundant baseband processing equipment as the 4th cell, as shown in Figure 3. In the figure, SC is the scrambling code I/Q radio frequency modulation and demodulation, and SCH is the synchronization code.

Figure 3 RRU new coverage mode