FEATURE Development of Microwave Link for 8K Super Hi-Vision Program Contribution Hirokazu Kamoda, Kenji Murase, Naohiko Iai, Hiroyuki Hamazumi and Kazuhiko Shibuya*1 *1 NHK Engineering System, Inc. As the satellite broadcasting of 4K/8K Super Hi-Vision is band is not strongly affected by rain and can be transmitted scheduled to start in 2018, the portable wireless contribution over distances up to 50 km, making efficient FPU operation links for program production, which are used for electronic possible. To maintain the same efficient operability with news gathering, outside broadcasting, etc., must be adapted FPUs used for 4K/8K reporting and production (4K/8K to the 4K/8K format. We upgraded a HD (2K) microwave FPUs), the FPUs must be upgraded to 4K/8K while still us- contribution link system particularly used for fixed and ing microwave band frequencies. line-of-sight transmissions to adapt it to 4K/8K operations There is also a need to introduce 4K/8K FPUs smoothly by increasing the transmission capacity. A 200-Mbps-class while maintaining the existing microwave band channel transmission capacity was achieved by enhancing the spec- allocations so that the operation of current HD FPUs can tral efficiency while keeping the conventional channel band- continue. Thus, technology is needed to increase spectral width (18 MHz). efficiency and dramatically increase transmission capacity To enhance the spectral efficiency, we employed dual- without changing allocated channel bandwidths. polarized MIMO (Multiple-Input Multiple-Output) using In earlier research on technologies to increase spectral both horizontal and vertical polarizations and OFDM (Or- efficiency for next-generation digital terrestrial broad- thogonal Frequency Division Multiplexing) with higher-order casting1)-3), dual-polarized multiple-input multiple-output modulation. We conducted outdoor experiments using a (MIMO) and orthogonal frequency division multiplex- preliminary prototype built halfway through the develop- ing (OFDM) with higher-order modulation were found to ment and proved the feasibility of the technologies by suc- be able to dramatically increase the transmission capacity cessful transmission of 8K video and audio signals over 50 while maintaining digital terrestrial television broadcasting km. bandwidths (6 MHz). From the perspective of increasing capacity, the application of this technology in FPUs is a promising option. 1. Introduction The authors have studied increasing the transmission ca- NHK has been conducting R&D on 4K/8K Super Hi- pacity by applying dual-polarized MIMO and OFDM with Vision, a television broadcasting service that will provide higher-order modulation to upgrade microwave-band FPUs highly realistic, ultrahigh-definition images. Test satellite to 4K/8K. This article discusses a microwave band 4K/8K broadcasting of 4K/8K Super Hi-Vision began in 2016, and FPU system that we have developed and reports on field preparation to begin regular service in 2018 is in progress. transmission tests performed to confirm its feasibility. This also generates a need to upgrade field pick-up units (FPUs) to 4K/8K. These are portable radio transmission devices that can quickly transmit live coverage or program 2. Microwave band 4K/8K FPU system materials for reporting or program production from venues around the country to the broadcast studio. Upgrading FPUs 2.1 Technical requirements for transmission capacity, to 4K/8K involves increasing their transmission capacity so frequency, and power that they can transmit 4K and 8K video and audio signals To transmit 4K/8K signals using limited frequency re- (4K/8K signals), which require more capacity than HD sig- sources, as with current HD systems, the compression cod- nals. ing of video and audio signals is unavoidable. Using H.265/ Microwave band (6-7 GHz) FPUs are used for most cur- HEVC (High Efficiency Video Coding), the latest video rent HD reporting and program production. This microwave compression encoding, a bit rate of between 100 and 300 2 FEATURE Mbps would be needed to transmit a 4K/8K signal4). Cur- orthogonally polarized signal components can be canceled rent HD FPUs have a transmission capacity of approximate- using MIMO detection*1. ly 60 Mbps, so the transmission capacity must be increased OFDM with higher-order modulation increases the num- by a factor of 2 to 5. ber of modulation levels used for the quadrature amplitude To maintain the same operability of current FPUs, the modulation (QAM) of subcarriers from 64QAM, as used same channel bandwidth of 18 MHz in the C (6.425-6.570 by current FPUs (Fig. 1 (a)), to 1024QAM (Fig. 1 (b)) or GHz) and D (6.870-7.125 GHz) bands is preserved. Also, 4096QAM. This increases the number of bits transmitted to prevent new interference with existing radio systems, with each carrier symbol from 6 bits to 10 bits or 12 bits, including current FPUs, the maximum transmission power increasing the transmission capacity by a factor of 1.7 to 2. is set at 5 W, the same as for current FPUs (although it is The transmission capacity was further increased by in- set to 0.2 W if an analog FPU is operating in an adjacent creasing the number of points used for fast Fourier Trans- channel). The proposed system described below will use forms (FFTs) from the current 2,048 to 8,192, increasing the horizontal and vertical polarizations simultaneously, so the effective symbol length relative to the guard interval (GI) transmission power refers to the total power of both polar- length (Fig. 2), and by reducing the number of pilot signals. ized signals. The transmission capacity can be increased by a factor To summarize, the transmission capacity must be in- of 2 to 5 by combining the above technologies. Note that to creased by a factor of 2 to 5 while maintaining current regu- minimize the increase in the required carrier-to-noise ratio lations of bandwidth and transmission power. (C/N) as a result of increasing the number of modulation levels, instead of convolutional and Reed-Solomon concat- 2.2 Overview of technologies to increase spectral enated coding used in current FPUs, a low-density parity efficiency check (LDPC) and Bose-Chaudhuri-Hocquenghem (BCH) Technologies to increase spectral efficiency, including concatenated coding is used as the forward error correction dual-polarized MIMO and OFDM with higher-order modu- (FEC). lation, had already been developed for next-generation ter- restrial broadcasting research and were employed for the *1 With MIMO, the multiple transmitted signals arrive at the 4K/8K FPU. receiver having interfered with each other along the propaga- tion path. The process of reconstructing the originally trans- Dual-polarized MIMO is a technology that uses two mitted signals from multiple received signals is called MIMO orthogonally polarized waves to provide double the trans- detection. Generally, known signals are used to estimate the mission capacity of current FPUs, which use a single po- propagation path and the results are used to estimate the larization. Interference between the polarizations of the transmitted signals. Carrier orthogonal component amplitude Carrier in-phase component amplitude 64 (26) constellation points 1024 (210 ) constellation points 64QAM (Current HD FPU) 1024QAM (a) (b) Figure 1: Increasing number of constellation points for subcarrier modulation 3 FEATURE Guard interval Effective symbol interval Number of FFT points: 2,048 100.14 µs 12.5 µs Number of FFT 400.57 µs points: 8,192 12.5 µs 8.3% improvement Time axis Figure 2: Increased transmission efficiency by increasing number of FFT points 2.3 4K/8K upgraded microwave band FPU system in Fig. 3. Block diagrams for this system are shown in Fig. 4 A photograph of the microwave band 4K/8K FPU intro- and the transmission parameters and the realized transmis- ducing the advanced technologies discussed above is shown sion bit rates are given in Tables 1 and 2, respectively. This system is based on the standards used for current OFDM Table 1: Microwave band 4K/8K FPU transmission parameters FPUs, ARIB STD-B335) and STD-B576). The system is de- Item Specification scribed in this section in order of the signal flow. FFT size 2,048 8,192 Occupied bandwidth (MHz) 17.21 17.20 (1) Converting input signals to FEC blocks Carrier interval (kHz) 9.99 2.50 In Fig. 4 (a), the input signal is an MPEG-2 transport stream (TS), with video and audio compression encoding Total 1,723 6,889 Data carriers 1,428 6,426 Table 2: Microwave band 4K/8K FPU transmission rates Number of Pilot (CP/SP)*1 216/217 216/217 carriers Transmission rate (Mbps) *2 Subcarrier TMCC 16 64 Code rate modulation 2,048 FFT 8,192 FFT AC*3 62/61 182/181 points points 64QAM, 256QAM, Subcarrier modulation 1/2 76.5 93.8 1024QAM, 4096QAM 2/3 101.9 125.1 FFT sampling clock (MHz) 20.450743 64QAM 3/4 112.1 137.6 Effective symbol length (µs) 100.14 400.57 5/6 127.4 156.4 Guard interval length (µs) 12.52 12.52 1/2 101.9 125.1 Symbol length (µs) 112.66 413.09 2/3 135.9 166.8 Number of symbols/OFDM frame 440 440 256QAM 3/4 149.5 183.5 OFDM frame length (ms) 49.57 181.76 LDPC code 5/6 169.9 208.5 Inner code (Approx. code rates R 1/2 127.4 156.4 =1/2, 2/3, 3/4, 5/6) 2/3 169.9 208.5 Outer code BCH code 1024QAM 3/4 186.9 229.4 MIMO-supporting CP/SP SP: Horiz. (1,0), Vert. (0,1) carrier multiplication CP: Horiz. (1,1), Vert. (1,-1) 5/6 212.4 260.7 coefficient*4 1/2 152.9 187.7 *1 CP: Continual Pilot, SP: Scattered Pilot *2 Transmission Multiplexing Configuration and Control 2/3 203.9 250.2 4096QAM *3 Auxiliary Channel 3/4 224.3 275.2 *4 In parenthesis: (even-symbol multiplier, odd-symbol multiplier) 5/6 254.9 312.8 4 FEATURE using H.256/HEVC (or other) and multiplexing, so this Dual-polarized antennas TS is first converted to FEC blocks.