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.

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 telephone 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.