What is a BBU?

1. Centrally manages the entire base station system, including operation and maintenance, signaling processing, and system clock.

2. Processes uplink and downlink baseband data and provides CPRI ports for communicating with RF modules.

3. Provides physical interfaces between the base station and the transport network for information exchange.

4. Provides the OM channel to connect to the OMC.

5. Provides a communication interface with the environmental monitoring device to receive and forward signals from the environmental monitoring device.

Three types of BBUs are commonly used in Huawei: BBU3910, BBU3910A, and BBU5900.

Huawei BBU adopts the modular design. Therefore, one BBU has the following modules:

LMPT（UMPT）

LTE main control and transmission unit and the main control and transmission unit of the case-shaped BBU. Manages the operation and maintenance (OM) and signaling processing of the entire eNodeB. Provides clock signals for the case-shaped BBU.

LBBP（UBBP）

The LTE baseband processing unit processes baseband signals and CPRI signals.

FAN

The fan module controls the wind speed, monitors the temperature of the module, and dissipates heat from the boards and modules of the case-shaped BBU.

UPEU

The power module of the case-shaped BBU. Converts the +24 V or –48 V DC voltage to the voltage required by the boards and modules of the case-shaped BBU, and provides ports for transmitting external monitoring signals and eight dry contact signals.

Modules of the BBU3900 and BBU3910

Modules in the BBU5900

The three types of BBUs are different, as shown in the following figure.

BBU Product Difference

Differences Between BBU Boards

Type of the base station corresponding to the BBU

Next, I'd like to introduce RF units.

What Are RRUs, RFUs, and AAUs?

RRU

The RRU is used for macro base stations. It performs modulation, demodulation, data compression, amplification of RF signals and baseband signals, and VSWR detection.

Schematic diagram of the RRU

RFU

RFUs are used for macro base stations. Performs modulation, demodulation, data compression, RF signal and baseband signal amplification, and VSWR detection.

RFU block diagram

AAU

Integrated active antennas. The functions of the AAU are implemented by functional modules.

Because there are many types of RRUs, RFUs, and AAUs, I will not introduce them much. I will mainly talk about their module composition.

AAU block diagram

Both RRUs and RFUs use modular design and have the same functions. The following modules are available:

CPRI interface processing

Receives downlink baseband data from the BBU and sends the uplink baseband data to the BBU to implement communication between the RRU and the BBU.

Power Supply Processing

Converts the -48 V input power to the power voltage required by the RRU modules.

TRX

1. The TRX consists of two uplink RF RX channels, two downlink TX channels, and one feedback channel.

2. The RX channel down-converts the received signals into IF signals, and then performs amplification and digital-to-analog conversion (A/D conversion).

3. The TX channel filters downlink signals, performs digital-to-analog conversion (D/A conversion), and up-converts RF signals to the TX frequency band.

4. The feedback channel assists in downlink power control, digital pre-distortion DPD, and VSWR measurement.

PA(Power Amplifier)

Amplifies low-power TR signals from carriers.

LNA

A low noise amplifier Amplifies the received signal from the antenna.

Duplexer

The duplexer multiplexes the RX and TX signals of the RF channel. The duplexer enables the RX and TX signals to share the same antenna channel and filters the RX and TX signals.

As an integrated RF antenna, the AAU has a different structure from the RRU and RFU. However, their functions are basically the same except that the AAU can transmit and receive radio waves and perform beamforming.

The main difference between RRU, RFU, and AAU is that they apply to different environments. Since they come in a variety of device models, I won't explain the differences here.

That's what I'm sharing today, and you're welcome to comment.