Engineering 101

Transceiver Taps into Higher Frequency Bands of 5G Networks

While consumer devices that support 5G benefit from increased speeds and lower latency, some frequency bands allocated for 5G aren’t working efficiently due to tech limitations. Depending on the country, these bands span from 37 GHz to 43.5 GHz, including the New Radio (NR) 39 GHz. The NR band offers notable advantages in performance over other lower frequency bands 5G networks use today, such as enabling ultra-low latency in communication, data rates of over 10 Gb/s, and a massive capacity to accommodate several users.

High-frequency signals attenuate quickly as they travel through space. It is, therefore, crucial that the transmitted power is concentrated in a narrow beam aimed directly at the receiver. This is achieved using phased-array beamformers, transmission devices composed of an array of carefully phase-controlled antennas. High-frequency regions of the NR band decrease the efficiency of power amplifiers as they tend to suffer from nonlinearity issues, which distort the transmitted signal.

Researchers led by Professor Kenichi Okada from Tokyo Institute of Technology (Tokyo Tech), Japan, recently developed a novel phased array beamformer for 5G base stations. Their design adapts two techniques, the Doherty amplifier and digital predistortion (DPD), into a mmWave phased-array transceiver, but with a few twists. The researchers will present their findings in the upcoming 2022 IEEE Symposium on VLSI Technology and Circuits.

The research team modified the conventional Doherty amplifier design and produced a bi-directional amplifier so that the same circuit can both amplify a signal to be transmitted and a received signal with low noise.

Despite its several advantages, however, the amplifier can exacerbate nonlinearity problems that arise from mismatches in the elements of the phased-array antenna. The team addressed this problem by employing the DPD technique, which involves distorting the signal before transmission to cancel out the distortion introduced by the amplifier effectively. Their implementation used a shared look-up table (LUT) for all antennas, minimizing the complexity of the circuit. Second, they introduced inter-element mismatch compensation capabilities to the phased array, improving its overall linearity.

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