PSEUDO NO-DELAY HDTV TRANSMISSION SYSTEM USING A 60GHZ BAND FOR THE TORINO OLYMPIC GAMES

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1 PSEUDO NO-DELAY HDTV TRANSMISSION SYSTEM USING A 60GHZ BAND FOR THE TORINO OLYMPIC GAMES Takahiro IZUMOTO, Shinya UMEDA, Satoshi OKABE, Hirokazu KAMODA, and Toru IWASAKI JAPAN BROADCASTING CORPORATION (NHK), JAPAN ABSTRACT NHK was appointed to produce the international broadcast signals including the speed skating event at the XX Winter Olympic Games hosted on Torino, Italy on February A rail camera played an important role in the speed skating coverage by running parallel to the athletes and providing dynamic shots of their movement. This could only be achieved by a wireless system because cables could not be pulled at such speed. Conventional rail cameras, however, transmit compressed signals with considerable time delay and live switching with other cable cameras would have been difficult. In the field of transmitting uncompressed HDTV signals, NHK has been developing a 60GHz-band transmission system from the summer of We applied this system to the rail camera for speed skating in Torino and transmitted HDTV signals without delay along more than half of the race track. The pseudo no-delay system permitted live switching between the rail camera and other cable cameras and helped us to produce very high quality and rich international program. INTRODUCTION NHK has been conducting research and development on HDTV (High Definition TV) for about 40 years. HDTV programs have become increasingly popular especially in Japan since the launch of digital satellite and digital terrestrial broadcasting in 2000 and 2003, respectively. On-site HDTV production has become very common and the amount of HDTV equipment is growing steadily. The digital HDTV signal (HD-SDI signal) is a 1.5 Gbps data stream that generally has to be compressed in order to reduce the data rate for wireless transmission or broadcast. In the cases of microwave links or SNG systems, the HD-SDI signal is usually compressed by means of MPEG-2 codecs so far. NHK developed a compact HDTV wireless camera using the MPEG-2 codecs in Wireless cameras are often used in the coverage of various sports, such as golf and athletic tournaments, because of their flexibility and the convenience of not having cables. The conventional systems that use MPEG-2 codecs have a considerable delay due to the compression and decompression processes. This sometimes causes difficulty for switching between wireless and cable camera images. A runner who has crossed the finish line on the cable camera image may not yet have finished on the wireless camera image. Apart from the standard MPEG-2 codec, there are other types of codecs that could be applied to wireless codec HD CAM DVC PRO HD Bit-Rate (Mbps) Delay (frames) Table 1: Low-delay HDTV codecs (as of 2003) IBC2006 Conference Publication 89

2 transmission, as shown in Table 1. Those codecs have a relatively short processing delay but still have delays of several frames. On the other hand, looking at the communication industry in Japan, wireless fixed transmission systems using the 60GHz band have been intensively developed in a wide range of markets. Because the 60GHz band is an unlicensed band, radio stations satisfying certain technical regulations, such as low transmitter power, can be operated without a license. A feature of this band is that it has a broad occupied bandwidth of up to 2.5 GHz, which allows transmission of a very high speed data stream. We focused on commercially available 60GHz band devices that can transmit HD-SDI signals without compression, although the device is not designed for mobile transmission, where multi-path effect and the narrow beamwidth of antennas in the 60GHz band could fatally degrade the transmission quality, resulting in link disconnection. We have developed a system that realizes HDTV mobile transmission without delay, called pseudo no-delay 60GHz-band HDTV transmission system, adopting the existing 60GHz-band devices and the diversity reception techniques [1]. In this paper, we present the system overview and its application to the rail camera used at the speed skating venue in the Torino Olympic Games. SYSTEM OVERVIEW The pseudo no-delay 60GHz-band HDTV transmission system is comprised of a 60GHz transmitter and receiver, and an HD-SDI diversity processor that employs a majority decision algorithm. The existing 60GHz-band devices were used as the 60GHz transmitter and receiver, and were modified to make a compact, practical and highly durable transmitter and receiver that were easy to operate in the field. Table 2 gives the specifications. Bearing in mind that the ASK format requires a high C/N ratio, a high gain lens antenna was also manufactured (Photo 1). Tx Frequency Tx Output Modulation Occupied bandwidth Tx Bit-rate Input/Output 60 GHz Up to 10 mw ASK Up to 2.5 GHz 1.5 Gbps HD-SDI 1080/50i, 1080/59.94i Weight 1.2 kg (both Tx and Rx) Photo 1: 60GHz Transmitter Power Up to 10W (both Tx and Rx) Consumption We introduced the idea of diversity reception and installed multiple receivers at each Table 2: Specification of 60GHz system reception point to mitigate the multipath effect and picked up transmission signals seamlessly by one or more receivers and achieved stable transmission. The diversity processor firstly synchronizes the timing of each receiver s HD-SDI output, as each has a different transmission delay, and then implements the bitbasis majority decision algorithm for bit error correction. Every HD-SDI signal with and 90 IBC2006 Conference Publication

3 without bit error correction is ed for (Cyclic Redundancy Check) error so that the diversity processor can output an error-free signal. With a processing time of about 1 TV line, stable HD-SDI transmission is accomplished with only a minimal delay. Figure 1 is a block diagram of the diversity processor. Input A Input B Input C HD-SDI Majority decision error correction (bit basis) HD-SDI with error correction Application to the Rail Camera System for Speed Skating in Torino The rail camera for speed skating had to have a wireless system to transmit the camera image; a wired system has the physical difficulty of pulling the cables at such a high speed. NHK proposed this transmission system to TOBO (the Torino Olympic Broadcasting Organization), a host Switching diversity HD-SDI output Check result Diversity processor Fig. 1: Configuration of HD-SDI Diversity Processor broadcaster of the Games. The rail camera runs around about half of the oval skating rink. The camera s track was divided into the three areas: the Back Straight, the Second Turn and the Home Straight. The reception points were specified for each. Two transmitters were installed in the rail camera. One was installed in aiming at the travelling direction of the rail camera, and the other installed at 90 degrees to the travelling direction (facing the inside direction of the curve). Multiple receivers were installed at one place on the Back Straight, and their outputs were sent to the diversity processor for seamless reception throughout that area. In addition, on the Home Straight, multiple receivers were installed on an extension beyond the Home Straight to secure stable transmission over a distance of about 150 meters. The curve of the skating rink corresponds to half of a true circle. A dedicated transmitter for the Second Turn, mounted on the camera, radiated millimetre waves to the inner side of the curve perpendicularly to the travelling direction of the camera. The reception point, Base Station 2, was installed on the ceiling above the center of the semicircle. The reception antenna at Base Station 2 was a dielectric leaky-wave antenna [2] developed for the Torino Olympic Games (Photo 2). Figure 2 shows the structure of the dielectric leaky-wave antenna. It consists of a dielectric strip on a ground plane, above which a Photo 2: Leaky-Wave Antenna periodic metal plate is placed. The beam elevation angle ( ) of the antenna can be adjusted easily by modifying spacing (d) of the periodic metal plate. IBC2006 Conference Publication 91

field operations where the system may be used for various purposes. In addition, the combination of broad horizontal and sharp vertical beam pattern was an optimal solution for our requirements.

4 Fig. 2: Structure of Leaky-Wave Antenna Fig. 3: Two-dimensional Radiation Pattern of Leaky-Wave Antenna The fact that the beam elevation angle can be changed by replacing the periodic metal plate provides the antenna with high versatility in field operations where the system may be used for various purposes. In addition, the combination of broad horizontal and sharp vertical beam pattern was an optimal solution for our requirements. Figure 3 shows the measured two-dimensional radiation pattern of the antenna. A dielectric leaky-wave antenna can cover the range of 60 degrees in horizontal direction. The range of 180 degrees in the total angle of the second turn was covered with multiple antennas. This way, we could transmit HDTV signals without making any mechanical adjustment to the antennas at either the transmission or the reception side. Base Station 1 (Back Straight) Back Straight (Area 1) 60 o Base Station 2 (Second turn) on the ceiling Second turn (Area 2) Home Straight (Area 3) Base Station 3 (Home Straight) Base Station 1: Multiple receivers installed on extension beyond the Back Straight. Base Station 2: Reception for Second Turn. Multiple receivers with leaky-wave antenna installed on the ceiling above semicircle center. Base Station 3: Multiple receivers installed on extension beyond the Home Straight. HD-SDI diversity processor 60GHz RX with leaky-wave antenna 60GHz RX with lens antenna To OB VAN Fig. 4: Operational Imagery of 60GHz Uncompressed HDTV Transmission System 92 IBC2006 Conference Publication

To achieve steady transmission over the total range, the diversity processors were introduced into all the reception points like Figure 4.

The master diversity processor outputs an error-free HD-SDI signal to the OB (Outside Broadcasting) van. OPERATION ON SITE Photo 3 shows a transmitter covered the straight area.

A lens antenna with gain of 35dBi was also used for the transmitter over the curved area, because the gain of the dielectric leaky-wave antenna is low.

Station 3 which received the millimetre wave from the straight area of more than 150 meters.

5 To achieve steady transmission over the total range, the diversity processors were introduced into all the reception points like Figure 4. The output signal from the diversity processor of each reception point is input to the master diversity processor. The master diversity processor outputs an error-free HD-SDI signal to the OB (Outside Broadcasting) van. OPERATION ON SITE Photo 3 shows a transmitter covered the straight area. A lens antenna with gain of 25dBi was used for the transmitter over the straight areas. Photo 4 shows a transmitter for the curved area. A lens antenna with gain of 35dBi was also used for the transmitter over the curved area, because the gain of the dielectric leaky-wave antenna is low. Photo 3: Transmitter for Straight Area Photo 4: Transmitter for Curved Area Photo 5: Base Station 3 Photo 6: Base Station 2 Photo 5 shows how the receivers were installed at Base Station 3 which received the millimetre wave from the straight area of more than 150 meters. As the reception condition was not good at the end of the area, a parabolic antenna with gain 40dBi was used for one of four receivers installed on an extension beyond the course. As for Base Station 2, given its location on the ceiling, it was clear that adjustment and maintenance of the receivers would be difficult once the competition had started. In addition, there was no backup receiver there. Therefore, six receivers were installed on the ceiling IBC2006 Conference Publication 93

6 (Photo 6). The output of each receiver was converted to optical signals (E-to-O) and transmitted to Base Station 3 as HD-SDI signals by optical fiber. At Base Station 3, these optical signals were converted back to electrical signals (O-to-E) to be fed to the diversity processors. Figure 5 gives an overall view of our transmission system. The system demonstrated very stable transmission along the entire camera track, successfully transmitting the uncompressed HDTV image of the athletes performance without time delay throughout the two-week Torino Winter Olympic Games. Base Station 1 (Back Straight) Base Station 2 (Second Turn) at the ceiling Master diversity processor Base Station 3 (Home Straight) To OB VAN Fig. 5: Overall Diagram of Uncompressed 60GHz HDTV Transmission System for the Torino Olympics CONCLUSION A 60GHz-band transmission system is not easy to operate on production sites due to the sharp directivity and short transmission range of the millimetre wave. We developed this system, nevertheless, by focusing on three features of broadband transmission, which were stable transmission within a limited propagation range, the low cost, and compactness of the ASK modulation. We applied this system to the rail camera system for speed skating in Torino and transmitted HDTV signals without time delay along more than half of the race track. The pseudo no-delay system permitted live switching between the rail camera and other cable cameras and helped us to produce very high quality and rich international program. REFERENCES [1] H. Nakano, T. Izumoto, S. Okabe and H. Kamoda Live broadcasting of Japan Championships in Athletics, -Use of HDTV Wireless Aerial-wire-camera-system-, Hohsoh Gijyutsu, pp , September.2005, Kenrokukan Publishing Corporation. [2] T. Iwasaki and T. Ikeda, A Study on Beam-Switching Dielectric-Rod Antenna using Periodic Metal Plate, Technical Report of IEICE of Japan, AP , pp.55-60, IBC2006 Conference Publication

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