1/2017

Super-efficient next generation base stations

Together with Nokia Bell Labs, researchers from Tampere University of Technology and Aalto University have developed a new type of 5G transmitter that is 20 times more efficient than its predecessors. The 5G radio transmitter is designed for small fifth generation base stations.

Mikko Valkama

 

"AATU project combined the expertise of researchers from two universities and Nokia Bell Labs," says professor Mikko Valkama from TUT.

 

Adaptive Antenna Transceiver Unit (AATU)

  • In cooperation between Tampere University of Technology, Aalto University and Nokia Bell Labs
  • Funding providers: Nokia Bell Labs, Nokia Networks and Tekes.
  • Duration: approximately three years, 2014–2016
  • The developed radio transmitter technology will be introduced in 2 to 3 years.
 

The number of mobile devices in use is growing rapidly, which is why the coverage area of a single base station for mobile communication systems must be reduced in the future. New base stations are smaller than their predecessors but located more densely. Together with Nokia Bell Labs, researchers from Tampere University of Technology (TUT) and Aalto University have developed a new type of 5G radio transmitter for use in future base stations.

The operating principle of the new radio transmitter is as digital as possible: the signal is not converted into analogue format until in the transmitter’s final amplifier stage.

“Other similar technology will definitely be introduced over the next 2 to 3 years,” says Mikko Valkama, Professor of Communications Engineering at TUT.

The development of semiconductor processes has enabled the signal to be processed in digital format in the radio transmitter until it nearly reaches the antenna, where it is converted into electromagnetic radiation. The researchers developed a new type of integrated electronic circuit for the transmitter that can be used to significantly increase both the instantaneous bandwidth as well as the range of center frequencies at which the base station is operating. The data transmission capacity of base stations can increase up to 20-fold.

“The newly developed 5G base station transmitter prototype will introduce new opportunities for modifying and programming the transmitted radio signals. The quality of the signal will improve, as well,” says Valkama.

“In addition to 5G networks, this type of technology can also be used to simultaneously generate and process signals from different mobile network operators and radio networks thanks to the transmitter’s very large instantaneous bandwidth of 400 megahertz and because it can be quite freely adjusted between 700 megahertz and 4 gigahertz. Until now, we have been using separate parallel narrowband transmitters.”

Cutting edge of signal processing

Processor

 

Prototype of the integrated base station transmitter.

 

The multidisciplinary study – which incorporated electromagnetics, expertise in analogue and digital electronic circuits, signal processing algorithms, digital radio communication methods, and communication theory – combined the expertise of researchers from two universities. The researchers at Aalto University focused on integrated circuit design aspects, while the researchers at TUT concentrated on developing signal processing algorithms. The overall transmitter architecture was a product of joint innovations. A variety of digital signal processing methods were developed and studied at TUT in order to correct the non-ideal characteristics of the involved circuit structures and particularly to linearise its amplifier stages with the help of digital pre-distortion.

“TUT has some of the world’s best expertise in signal processing for wideband radio transmitters and radio receivers,” says Mikko Valkama.

The study also served as a good example of effective cooperation with the corporate world.

“In addition to strong commercial and industrial interests, many high-quality scientific publications were also prepared on the subject with great support from Nokia,” emphasises Valkama.

The research project was funded by Tekes and Nokia. Among other venues, the results were published at the IEEE International Solid-State Circuits Conference held in the United States at the beginning of February. The conference is a forum where the semiconductor industry and the academic research community present their best results in the field of integrated electronic circuits.

Text: Sanna Schildt
Photos: Marjaana Malkamäki and Aalto University

 
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