Multiple antenna (MIMO) techniques are among the most important technologies for improving capacity and reliability of radio communications links. Currently MIMO is frequently employed in common terrestrial communication networks, such as WiMAX, LTE, and WLAN. Despite the clear advantages, MIMO techniques have not yet, however, been widely deployed for satellite communications.
In a multi-year project supported by the European Space Agency´s ARTES programme, a consortium led by Elektrobit (Finland) explored the challenges of applying MIMO techniques to satellite systems by first carrying out a series of simulations and then undertaking practical lab experiments with a real-time test bed to determine the benefits of MIMO techniques on link performance.
As part of MIMO HW Demonstrator project, Elektrobit developed a sophisticated, software-defined-radio based test environment, which is now being offered to satellite operators and infrastructure vendors. This advanced test environment can be used by the company’s customers to study the RF link performance on their existing or planned satellite networks, as well as ancillary terrestrial links.
What the computer simulations suggested and hardware experiments verified, MIMO techniques, when applied to a mobile satellite link, can indeed provide significant gain over traditional dual-polarized satellite links. While it has now been demonstrated that MIMO can provide significant performance gain to a mobile satellite system with minimal additional cost, further analysis and experiments are required to investigate the applicability of MIMO to fixed satellite service links operating on very high frequencies, such as the Ka- and Ku-bands.
“Based on this study, MIMO techniques provide the most benefits when the channel model of the system is complex, or when the user terminal is in a place where there are shadowing buildings or other obstacles,” explains Elektrobit’s Jarno Majava, Director of Specialized Terminal Products. “MIMO can also help in closing the link at the edges of the coverage area where there is a low elevation angle to the satellite.”
“Currently, the mobile satellite market represents only a fraction of the total satellite communications business; the next step would be to study whether MIMO could be deployed for fixed broadcast and broadband solutions,” Majava says.
Spectral resources are becoming increasingly crowded. Terrestrial operators are in fierce competition for the available spectrum. Hence the importance of current research such as this which focuses on developing new spectrally-efficient techniques, such as MIMO and cognitive radio. Deploying technologies that improve the spectral efficiency, and coverage of the satellite systems will become critical in order to maintain the competitiveness of the satcoms business.