Ka-band transceiver for satellite communications
Scientists at the Tokyo Institute of Technology and Socionext have developed a transceiver for enabling seamless communication between earth ground platforms and satellites in the low, middle, and geostationary earth orbits.
According to the scientists involved in the project this transceiver could help to bring the Internet to people in remote rural areas and at sea.
Despite communications technologies having advanced rapidly there are still issues when it comes to bringing connectivity to remote locations, such as rural areas or the open sea. Satellite communication (SATCOM) is an attractive option for providing data links to such places; but for effective SATCOM, the right equipment must exist both in space and on Earth.
At the forefront of research into SATCOM technologies are scientists from the Prof Kenichi Okada’s lab at Tokyo Institute of Technology (Tokyo Tech), who have developed a transceiver for SATCOM using standard CMOS technology. The transceiver, which operates in the ‘Ka band’, means a 27–31 GHz frequency range for uplink (ground to satellite) and 17–21 GHz range for downlink (satellite to ground).
The design carries a variety of features. On the transmitter (TX) side, a high-quality-factor transformer is employed to achieve efficient power use and high linearity in transmission, which results in lower distortion during transmission. The receiver (RX) side features a dual-channel architecture that unlocks several capabilities.
By having two RX channels it allows for receiving signals from two satellites simultaneously. These signals are received in parallel using either two independent polarization modes or two different frequencies. In addition, the proposed design can perform adjacent-channel interference cancellation; that is, the ‘contamination’ on a signal received in one channel by another signal on an adjacent frequency band is eliminated using information received at the other channel. This strategy increases the dynamic range of the system, thus allowing it to operate correctly even in less-than-ideal scenarios with stronger noise and interference.
Both the TX and RX perform direct conversion of a signal; that is, the TX directly converts a baseband signal into a modulated signal and the RX performs the inverse process without additional intermediate frequency conversions, unlike the more commonly used superheterodyne receivers. This helps to reduce the overall complexity, size, and power consumption of the transceiver.
The scientists have created a prototype chip to test the actual performance of their design when using all the modulation schemes regulated by the SATCOM DVB-S2X standard. This includes high-order modulation techniques like 64 APSK and 256 APSK, which provide fast data rates.
The performance test results are said to be very promising, especially when compared with other existing SATCOM transceivers.
Commenting Prof Okada said, “Our paper presents the first Ka-band SATCOM transceiver implemented using standard CMOS technology and designed for an earth ground platform communication with geostationary and low Earth orbit satellites.” These orbits are at 35,786 km and 200–2,000 km, respectively.
“Satellite communication has become a key technology for providing interactive TV and broadband internet services in low-density rural areas. Implementing Ka-band communications using silicon – CMOS technology in particular – is a promising solution owing to the potential for global coverage at low cost and using the wide available bandwidth,” said Prof Okada.
