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Flexible multibeam satellite communications system using beam forming technology and frequency assignment of reducing intermodulation interference

Ｗe propose a multibeam payload system with a beam-forming network (MSSBF) and a carrier assignment method that is effective in improving the C/IM3 ratio in an MSSBF system.

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Multibeam satellite communications systems that cover their service area with a large number of spot beams can obtain high antenna gain and can consequently improve EIRP and G/T.

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Thanks to their reduced transmitting power and increased receiving power, such systems are very effective for mobile communications or for multimedia access networks in which small, economical terminals are indispensable. Frequency reuse is also available to save limited resources.

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The use of a multiport amplifier (MPA) system has been previously proposed as the power amplifier system for mobile multibeam communications. This system is a special configuration composed of a power divider, a power combiner, and an array of high power amplifiers (HPAs), as shown in Fig.1 and it can overcome the problems of traffic imbalance among satellite beams, traffic variation over time, and environmental changes with maximum flexibility and minimum hardware.

Several commercial satellite mobile communications services have been employing an MPA, and further developments are being made toward delivering higher output power and utilizing higher frequency bands.

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However, the circuit loss of the power combiner following the HPAs degrades the transmitting power. The larger the number of beams used and the higher the frequency used, the larger this loss becomes. Therefore, employing the MPA for a multibeam system with a large number of beams may be difficult.

 

We propose a multibeam payload system with a beam-forming network (MSSBF) for a multibeam system (Fig. 2).

The system incorporates a digital signal processed beam-forming network, up-converters, an array of power amplifiers, and a phased array antenna.

 

We study the characteristics of the system and also discuss nonlinear distortion generated in an array of power amplifiers.

 

An MSSBF in which power amplifiers (PAs) are directly connected to a phased array antenna and are shared among multiple beams can solve the problems of traffic imbalance among beams, traffic changes due to access distribution, and environmental changes, and it can efficiently use the total transmitting power.

 

In addition, an MSSBF can control and shape the multibeam patterns by changing the weight values in the beam-forming network.

However, the PAs' nonlinear characteristics degrade the system's linearity. Intermodulation (IM) products generated by this nonlinearity can interfere with signals and degrade their transmission quality.

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To develop an effective power amplifier system that achieves high efficiency, we analyzed the third-order IM (IM3) products produced in an MSSBF, and we found that controlling the beam directions of IM3 products to be different from those of signals can lessen the IM3 interference as shown in Fig. 5.

 

Based on these results, we propose a carrier assignment method that is effective in improving the C/IM3 ratio in an MSSBF system. The analysis and our proposed system will help make possible construction of power-efficient satellite systems for multi-beam mobile communications and other uses.

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Figure 5 shows an example of controlling the communication wave and IM3 to radiate in different directions. IM3, F1 + F3 - F2 (= F2) is radiated in the direction different from the beam of communication wave F2 and no interference occurs.

The studied multi-beam arrangement is shown in Fig. 6. This system covers the service area with 10 beams, assigns 10 channels (ch) to each beam, and accommodates 100 channels (ch) as a whole. 

Figure 7 shows the interference distribution and frequency assignment when carrier frequencies are assigned sequentially.The maximum number of interferences is 2,245 waves/channel.

Figure 8 shows the interference distribution and frequency assignment when the frequency allocation assigned to each beam is controlled so that the interference generation is reduced. Compared with Fig. 7, the maximum number of interferences is reduced to 872 waves/channel.

Published Papers:

  1. Masayoshi TANAKA, Frequency Allocation Method for Intermodulation Interference Reduction in Multibeam Wireless Communication, Proceeding of Academic Conference of Nihon University, College of Industrial Technology, 2-44, pp261-264, 2019, ISSN 2186-5647. Ref.pdf

  2. Masayoshi.Tanaka & Hideaki Masaki, Multibeam Mobile Satellite Communication Payload with Beam-forming Network, 25th AIAA International Communications Satellite Systems, AIAA ICSSC, AIAA-2007-3179, 2007.  Ref.　  Ref(pdf).

  3. Zhi Dong Liu, Masayoshi TANAKA， Multibeam Direction Control in Beam-Forming-Network System Considering Setting Errors， IEICE National Conf.， B-3-16,2009

  4. Zhi Dong Liu, Masayoshi TANAKA， A Study on Intermodulation Interference in Digital Multibeamforming System with Setting Errors, IEICE National Conf., B-3-7,2008

  5. Hideaki Masaki, and Masayoshi Tanaka, Intermodulation Interference Reduction of Frequency-reused Multibeam Satellite System Employing Digital Beamforming， IEICE, Nationa Conf., B-3-13，2007

  6. Hideaki Masaki, and Masayoshi Tanaka, Intermodulation Interference Reduction of Multibeam Satellite System Employing Digital Beamforming， IEICE, Comm Society Conf., B-3-8，2006

  7. Hideaki Masaki, and Masayoshi Tanaka, Intermodulation Analysis of Multibeam Satellite System Employing Digital Beamforming， IEICE, Nationa Conf., B-3-8，2006

  8. Kiminori SATOH, and Masayoshi TANAKA， Inter-beam Interference Reduction in Multibeam Satellite System Employing Digital Beamforming Technology， IEICE, National Conf., B-3-1, 2006

  9. Kiminori SATOH, and Masayoshi TANAKA， Influence of RF element failure and its compensation in digital beamforming，IEICE, Comm Society, B-3-18，2005

  10. Kiminori SATOH, and Masayoshi TANAKA， A Study on Multi-Beam Satellite System using DSP Technology - Variable Beam Pattern and Variable Transmitting Power IEICE, National Conf., B-3-20，2005


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