We are conducting R&D on a 1.2-GHz/2.3-GHz-band field pick-up unit (FPU) for transmitting video and sound materials and a millimeter-wave-band wireless camera with the goal of using them for program production in 4K/8K live broadcasting of emergency reports and sports coverage.

■1.2-GHz/2.3-GHz-band 4K/8K mobile relay FPU

  To enable the mobile relay broadcasting of 4K/8K signals by using the 1.2-GHz/2.3-GHz-band, we conducted R&D on a multiple-input multiple-output (MIMO) system with adaptive transmission control using the time division duplex (TDD) scheme and contributed to the standardization⁽¹⁾⁽²⁾.
  In FY 2018, we improved the functions of the MIMO system with adaptive transmission control to enhance transmission performance. To overcome a problem of transmission performance degradation caused by long-delay multipath reflected waves in urban areas with many obstacles, we designed a transmission parameter to expand the guard interval length of orthogonal frequency-division multiplexing (OFDM) signals from the conventional value of 6 μs to 18 μs. Also for a further increase in the transmission capacity, we prototyped experimental equipment that increases the amount of information that can be transmitted per OFDM carrier symbol from the conventional value of 16 bits to 20 bits (Figure 2-22). We achieved a maximum transmission capacity of about 180 Mbps by using a rate-matching technology⁽³⁾, which controls the coding rate of error correction codes adaptively to prevent transmission errors even in a channel environment with instantaneous variations such as during mobile transmission.
  We also contributed to the establishment of a national standard on advanced 1.2-GHz/2.3-GHz-band FPUs at the Information and Communications Council of the Ministry of Internal Affairs and Communications and the preparation of a standard at the Association of Radio Industries and Businesses (ARIB) so that these FPUs can be put into practical use in 2020.

■Millimeter-wave-band 4K/8K wireless camera

  We made progress in our research on wireless cameras that can transmit video for 4K/8K program production by using 42-GHz-band radio waves.
  As a transmission system, we are studying a single-carrier-frequency domain equalization (SC-FDE) scheme, which is generally robust to the distortion of a power amplifier and has high power efficiency. In FY 2018, we developed a compact transmitter using the SC-FDE scheme (Figure 2-23)⁽⁴⁾ and conducted wireless transmission experiments. The prototype compact transmitter, which supports a transmission frequency of 42 GHz, a channel bandwidth of 125 MHz and a transmission power of 200 mW, achieved a transmission capacity of 185 Mbps when using the 32APSK (Amplitude Phase Shift Keying) modulation scheme and an error correction coding rate of 1/2 using convolutional codes. We also studied ways to improve the transmission performance of the SC-FDE scheme. We identified an optimum power ratio of pilot signals used for channel estimation during demodulation and data signals ⁽⁵⁾, and we also improved the performance of frequency domain equalization⁽⁶⁾.

■Radio over Ethernet System

  We are researching a Radio over Ethernet system to transmit video and audio signals transmitted by radio waves over Ethernet. In FY 2018, we developed Ethernet intermediate-frequency (IF) transmission equipment that would allow the easy connection of reception base stations for millimeter-wave-band 4K/8K wireless cameras (Figure 2-24).
  An effective way to ensure stable reception from a moving wireless camera is to perform demodulation using signals received by multiple reception base stations. Conventional analog optical transmission equipment required the installation of optical fibers to each reception base station and the level adjustment of signals. Meanwhile, the Radio over Ethernet system can digitize received signals and transmit them over a local area network (LAN), which enables the easy installation just by connecting a cable to the hub without the need for signal level adjustment.
  To digitize and transmit radio signals, it is necessary to accurately synchronize the sampling clock between the transmitting device and the receiving device. This equipment can modify errors of the sampling clock with high precision in a short time by using the departure and arrival timings of each packet that transmits digitized radio signals. This way, it can start transmission immediately after the transmitting side and the receiving side are connected with a cable.
  To verify the effectiveness of the Ethernet IF transmission equipment, we conducted an experiment in which we constructed a wireless camera system using three reception base stations in a circuit-type underground parking lot with a circumference of about 100 m. The results demonstrated that camera images were successfully transmitted without interruption even when the wireless camera circled the underground parking lot.

 

[References]
(1)	F. Ito, F. Uzawa, K. Mitsuyama and N. Iai: "Field Trial of 4×4 TDD-SVD-MIMO System with Rank Adaptation," IEEE Global Communications Conference 2018 (IEEE GLOBECOM 2018), Technical Session: WCS-I5-Wireless communication-5 (2018)
(2)	F. Ito, F. Uzawa, K. Mitsuyama and N. Iai: "Mobile Transmission Trial of 8K Video using 4x4 TDD-SVD-MIMO System with Adaptive Transmission Control," ITE Technical Report, Vol.42, No.36, BCT2018-85, pp.73-76 (2018) (in Japanese)
(3)	F. Uzawa, F. Ito, K. Mitsuyama and N. Iai: "Implementation of Rate-matching Function for Next Generation Mobile Relay FPU," IEICE Multiple Innovative Kenkyu-kai Association for wireless communications 2018 (MIKA 2018), P2-2 (2018) (in Japanese)
(4)	Y. Matsusaki, F. Yamagishi, A. Yamasato, S. Okabe and N. Iai: "Development of Compact Transmitter for Millimeter-wave SHV Wireless Camera," ITE Technical Report, Vol. 43, No. 10, BCT2019-42, pp. 25-28 (2019) (in Japanese)
(5)	F. Yamagishi, Y. Matsusaki, A. Yamasato, S. Okabe and N. Iai: "A Study on Boost Ratio for SC-FDE Millimeter-wave SHV Wireless Camera under Mobile Transmission Circumstances," ITE Technical Report, Vol. 43, No. 10, BCT2019-43, pp.29-32 (2019) (in Japanese)
(6)	Y. Matsusaki, F. Yamagishi, A. Yamasato, S. Okabe and N. Iai: "A Study on Improving Transmission Performance for SC-FDE," Proceedings of the 2019 IEICE General Conference, B-5-68 (2019) (in Japanese)
(7)	K. Aoki, K. Murase and K. Imamura: "A Study on Radio over Ethernet System for Mobile Wireless Camera," ITE Technical Report, Vol.42, No.23, pp.13-16 (2018) (in Japanese)