Baseband Unit | Glossary

Baseband refers to the original frequency range of a transmission signal before it is modulated. Baseband can also refer to a type of data transmission in which digital or analog data is sent over a single non-multiplexed channel.

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A baseband unit (BBU) is a unit that processes baseband in telecomm systems. A typical wireless telecom station consists of the baseband processing unit and the RF processing unit (remote radio unit - RRU). The baseband unit is placed in the equipment room and connected with RRU via optical fiber. The BBU is responsible for communication through the physical interface. A BBU has the following characteristics: modular design, small size, low power consumption and can be easily deployed.

A BBU in a cellular cell site is comprised of a digital signal processor to process forward voice signals for transmission to a mobile unit and to process reverse voice signals received from the mobile unit. The digital signal processor also serves to produce a first supervisory audio tone (SAT) for transmission to the mobile unit by generating successive digital SAT samples which are decoded into a continuous tone. Finally, the digital signal processor detects the presence of a second SAT generated by the mobile unit by sampling and processing successive samples of the second SAT and measuring the power.

Read our blost post to learn all about the importance of BBU emulation in the overall test process for tunring up cell sites.

The baseband unit (BBU) is another important component of the telecommunication infrastructure. Unlike the RRU which is located at the top of the tower, the BBU is located at the foot of the tower. In this article, we discuss, what BBU is, its functions, as well as its components.

Image: BBU

What Is a Baseband Unit?

The baseband is the original frequency spectrum of a transmission signal before it is modulated. Additionally, it can also be referred to as a method of data transmission where both analog and digital data are transferred through a single, non-multiplexed channel.

Image: Baseband Transmission

In a telecom system, a BBU processes baseband. The BBU and the RF processing unit (or RRU) are both components of a typical telecom station. Positioned within the equipment room, the BBU is connected to the RRU through optical fiber links. This facilitates a physical communication interface.

Components of the BBU

The BBU is made up of the following components which are all inserted into dedicated slots:

Image: Components of the BBU

LBBP

The acronym LBBP stands for LTE Baseband Processing Unit. LBBP can be found in different variations including LBBPa, LBBPb, and LBBPc in some series. In series like the Huawei BBU , the LBBP module is denoted as UBBP.

For more information, please visit HUAXUN.

The difference between LBBP and UBBP is that LBBP is designed for LTE or 4G communication, while UBBP is designed for 2G and 3G communication. Nevertheless, they both have similar functions such as:

• Provides CPRI interfaces for RF module communication.
• Processing of baseband signals for both uplink and downlink.

UMPT

UMPT, an abbreviation for Universal Main Processing and Transmission Unit, performs the following key functions:

• Execution of OM (Operation and Maintenance) tasks, which often include signal processing, performance monitoring, configuration management, equipment management, and active/standby switchover.
• Provision of clock synchronization references, transmission interfaces, and the maintenance link that establishes connectivity with the Operation and Maintenance Center (OMC). The OMC can be the Local Maintenance Terminal (LMT) or the M client.

UPEU

UPEU, an acronym for Universal Power and Environment Interface Unit, performs the following essential functions:

• Converts the -48V input power into +12V. This provides the required power capacities of 300 watts and 650 watts for the operation and processing of the BBU.
• The UPEU connects with EMUB units by receiving EMUB signals via RS485 serial communication and translating them into Boolean signals. In this way, it serves as an important link between the BBU and the Environment Monitoring Unit (EMUB), which is responsible for sensor alarm monitoring

FAN

The Fan unit serves the dual purpose of heat dissipation from the BBU and the monitoring of inlet temperature. Furthermore, it regulates the rotational speed of the fans and communicates fan status information to the Universal Main Processing and Transmission Unit (UMPT) within the BBU.

Functions of BBU

Below are the functions of the BBU:

1. Provides CPRI ports or optical links for establishing communication with Remote Radio Units (RRUs) and undertakes the processing of baseband signals in both the uplink and downlink.
2. Provides S1 ports to facilitate communication between an Evolved NodeB (eNodeB) and a Mobility Management Entity/ Serving Gateway (MME/S-GW), as well as X2 ports for inter-eNodeB communication.
3. Offers clock ports for synchronization, ports for monitoring environmental alarms, and a Universal Serial Bus (USB) port for commissioning using a USB flash drive.
4. Manages the eNodeB through the execution of operation and maintenance (OM) tasks and the processing of signaling messages.

NOTE: A GPS sensor is built into the BBU to track its installation location. The GPS coordinates are routinely tracked and then sent to the control center of the telecommunications provider in the event that the BBU is removed without authorization.