Research Area

1.8  Satellite broadcasting technology

  We are researching 12-GHz-band satellite broadcasting system to improve the transmission performance for 8K UHDTV broadcasting, and researching next-generation satellite broadcasting systems such as 21-GHz-band satellite broadcasting for future broadcasting services.


Advanced transmission system for satellite broadcasting

  We are researching 64APSK (Amplitude Phase Shift Keying) coded modulation using set partitioning in order to further increase the capacity of satellite transmission. As a way of improving the transmission performance through a channel with nonlinear distortion caused by the satellite transponder, we designed 64APSK coded modulation that considered the characteristics of the nonlinear distortion on the satellite and the performance of an adaptive equalizer using the LMS (Least Mean Squares) algorithm on the receiver side. Using the number of constellation points on the circles of 64APSK modulation as parameters, we designed the number of the points, bit allocation to signal points and LDPC(Low Density Parity Check) coding that obtain the best required carrier-to-noise ratio (C/N) after error correction under the condition of an output back-off of 5 dB, which is the optimum operation point of a 12-GHz-band satellite transponder during 64APSK transmission. Computer simulations showed that the designed 64APSK coded modulation (our proposed method)(1) improved the required C/N by approximately 0.4 dB compared with the conventional method optimized by considering only AWGN (Additive White Gaussian Noise), when the output back-off was 5 dB (Figure 1-10).
  We prototyped a cross-polarization interference cancellation device equipped with a negative-phase synthesized algorithm that reduced the deterioration in transmission performance caused by the simultaneous reception of right- and left-hand circularly polarized waves. We demonstrated that this interference cancellation function improved the required C/N by 0.2 dB when the cross-polarization discrimination was 25 dB and the modulation scheme of the desired waves was 32APSK (3/4).



Figure 1-10. Transmission performance of 64APSK coded modulation

Advanced satellite broadcasting systems

  With the aim of increasing the capacity of 12-GHz-band satellite broadcasting by using multilevel coded modulation, we are investigating a way of increasing the output power of the broadcasting satellite transmission. If the output power is increased, the side lobes of an on-board antenna need to be suppressed to keep radio wave interference to other countries below the level agreed by international adjustment. To develop an on-board 12-GHz dual-polarized reflector antenna with low side lobes, which is capable of separately receiving right- and left-hand circularly polarized waves, we selected and prototyped a corrugated horn antenna to be used as the feeder. The radiation patterns of our prototype feeder agreed with the designed values and a cross-polarization discrimination of 30 dB or more was obtained in the 300-MHz bandwidth. We plan to design a dual reflector antenna using two noncircular aperture reflectors based on the designed feeder to further reduce the side lobes of an on-board antenna.
  We designed a 12/21-GHz-band dual-polarized feeder that allows a single antenna to receive both 12-GHz-band and 21-GHz-band satellite broadcasting by right- and left-hand circular polarization. The feeder has a multilayer structure of four-element microstrip array antennas, which enables the simultaneous arrangement of the focal point of the reflector (Figure 1-11). The feeder obtained a VSWR (Voltage Standing Wave Ratio) of 1.1 or less for both frequency bands. An evaluation using the feeder design values showed that an offset parabolic reflector antenna with 50 cm aperture diameter achieves gains more than 34 dBi for the 12-GHz band and 38 dBi for the 21-GHz band as well as a cross-polarization discrimination more than 25 dB.
  Weak signals in the intermediate-frequency range (2.2 GHz to 3.2 GHz) for left-hand circular polarization leak from a reception system for 12-GHz-band 4K/8K satellite broadcasting. To measure these signals, we devised a method for improving the C/N of the measured signals (leaked signals) by correlation processing of the leaked signals and received signals, and we prototyped and evaluated a measurement tool capable of the high-precision measurement of the leaked power. We confirmed by the prototype that the C/N can be improved by 40 dB or more by limiting the band of correlation output signals with a narrow-band pass filter.
  As a feeder that increases the output satellite transmission power by spatial synthesis using a 21-GHz-band array-fed reflector antenna, we prototyped a three-element partial model using a sequential array structure in which horn antennas are arranged with rotational symmetry. We confirmed that a cross-polarization discrimination 30 dB or more is obtained by reducing radio waves reflected inside the neighboring elements.
  To conduct a wide-band transmission experiment using a 21-GHz-band experimental transponder of the BSAT-4a broadcasting satellite and evaluate rain attenuation characteristics in the 21GHz band, we set up 21-GHz-band reception equipment that combines a parabolic antenna with 1.5 m aperture diameter (48 dBi gain) and an automatic satellite-tracking system.



Figure 1-11. Structure of 12/21-GHz-band dual-polarized feed antenna

[References]
(1) Y. Koizumi, Y. Suzuki, M. Kojima, H. Sujikai and S. Tanaka: “Study on the optimization of 64APSK coded modulation design under the nonlinear transmission path simulating the satellite transponder characteristics,” Proceedings of the 2018 IEICE General Conference, B-3-10 (2018) (in Japanese)