Analog broadcasting in Japan will end in July Terrestrial broadcasting necessitates

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1 The articles describe the technical aspects of our effort to complete the switchover to all digital broadcasting by 2011 as well as new and improved services that will be offered in the future. Preparations for the Full Digitalization of Broadcasting Toru Kuroda, Director, Broadcasting Networks Research Division Analog broadcasting in Japan will end in July Terrestrial broadcasting necessitates nationwide installation of transmitting towers to deliver signals to homes. To prevent interference between signals, neighboring towers transmit analog broadcast signals over different channels. In contrast, digital broadcasting can be transmitted on the same frequencies without interference as long as certain conditions are met. This enables more effective utilization of the nation's limited radio frequency resources. For instance, the frequencies made available by the switchover to digital broadcasting can be allocated to new cellular phone and broadcasting services. Digitalization will also bring about new ways to deliver more information to our viewers, including i-ision (DT) service, which has more than five times the resolution of analog broadcasting, 5.1 surround sound, and data broadcasting to provide users with the information they need at anytime. The Japanese government decided that analog broadcast must end by July 24, 2011, and to meet that deadline, the Science & Technology Research Laboratories (STRL) are working steadily to ensure a smooth transition. In particular, we are developing the means of large-capacity terrestrial broadcasting for home reception and stable broadcasting for mobile reception. We are also resolving the issues such as interference within regions and countermeasures for single frequency networks (SFN) to alleviate interference from distant radio towers. While our long-term goal is to deliver Super i-ision (S) to homes in the future, we are currently improving today's ISDB-T digital terrestrial broadcasting system. By expanding the present One-Seg service, we will enable large-capacity, stable reception for mobile receivers. The goal in this case is to broadcast DT quality video to mobile receivers. The next article in this series will present an overview of our work to improve the current digital terrestrial broadcasting, our recent work on field pickup units (FPU), and our efforts to promote our technologies and systems overseas. F 1~3ch F 4~12ch UF 13~62ch Present Analog T broadcasting Analog T broadcasting Analog T broadcast/digital T broadcast After termination of analog broadcasting Multimedia broadcast for a regional block Nationwide multimedia broadcast Digital T broadcast (UF13~52ch) ITS (10Mz) Cellular phone (40Mz) Exclusive communications for agencies such as police/ fire departments Guard band 5Mz Guard band 5Mz Figure: Frequency-use policy for the post-analog broadcasting 18 Broadcast Technology No.41, Summer 2010 C NK STRL

2 Challenge Series: Technologies That Support Digital Terrestrial Broadcasting Multipath Channel Equalizer for Echoes outside the OFDM Guard Interval and Co-Channel Interference Canceller (CCI) Kazunori Yokohata, Principal Research Engineer, Broadcasting Networks Research Division Delivering digital terrestrial broadcasting radio waves throughout the country requires the installation of a large number of relay broadcasting stations. STRL has been working on technologies that will enable the construction of a low-cost broadcast-wave network of relay stations. Besides its effective use of frequencies, a broadcast-wave relay has cost and maintenance advantages over other methods of signal transmission to relay stations (microwave, optical fiber network, etc.). owever, it is prone to various forms of interference on the radio-wave propagation path, necessitating signal compensation at receivers. This article discusses two types of compensators. The multi-path channel equalizer for echoes outside the OFDM guard interval eliminates (i.e., equalizes) degradation from multipath waves. As shown in Figure 1, it equalizes multipath signals from an SFN station, which Large vessels at sea SFN relay station Mountains, etc. Upstream station Broadcast-wave relay station using multipath channel equalizer for echoes outside the OFDM guard interval share the same modulation content as the desired wave, along with the reflections from geographical formations and large vessels. It handles multipath waves with delays within the guard interval, as well as those outside the GI within a range of 454 sec. It requires a single receiving antenna. A co-channel interference canceller (CCI) receives signals with multiple antennas and controls the antenna directionality on basis of the adaptive array antenna principle. It eliminates interference waves by increasing the sensitivity in the desired wave's direction of arrival and reducing the sensitivity in the arrival directions of waves with different modulation content from that of the desired wave. It also reduces the sensitivity to multipath waves outside the guard interval. As Figure 2 indicates, the employment of four receiving antennas, for example, can create three directions with no sensitivity, which leads to cancellation of Digital relay station broadcasting different programs SFN relay station Multipath waves outside GI Upstream station Radio duct Mountains, etc. Direct-wave (desired wave) Analog interference wave Digital interference wave Sea Multipath waves ome Multiple receiving antennas Broadcast-wave relay station using co-channel interference Analog relay station canceller Figure 2: Co-channel interference waves and broadcast-wave relay example Direct wave (desired wave) Multipath waves outside GI Figure 1: Broadcast-wave relay and multipath waves outside the GI example interference from these directions. STRL has conducted many experiments that have proved the effectiveness of these compensators. Long-term testing at relay stations has also been done to ensure their reliability. Since the compensators used for broadcast-wave relays vary in terms of their number of receiving antennas and conditions needed for effectiveness, thorough research on the reception environment at specific sites is an essential step in selecting an appropriate compensator. Broadcast Technology No.41, Summer 2010 C NK STRL 19

3 OFDM Mobile Transmission Technology Tetsuomi Ikeda, Senior Research Engineer, Broadcasting Networks Research Division Digital terrestrial broadcasting employs a multi-carrier transmission technology called orthogonal frequency division multiplexing (OFDM). To enhance broadcasting services for mobile reception, we are studying a multiple-input multiple-output (MIMO)-OFDM transmission technology that utilizes multiple transmitting/receiving antennas. Besides its use in next-generation digital terrestrial broadcasting, this technology can be incorporated into field pick-up units (FPUs) used in DT mobile relay broadcasts. Transmission signal Transmission side Space-Time coding 1 2 M MIMO propagation path Independent transmission path Reception side 1 Space-Time decoding Figure 1: MIMO transmission principle 2 N Reception signal MIMO-OFDM Mobile Transmission Technology and Its Challenges Figure 1 describes the principle of MIMO transmission. Transmission capacity is increased by encoding signals to be transmitted from different transmitting antennas over the same frequency. Although the signals experience mutual interference, when multiple receiving antennas receive these mixed signals, the individual signals can be separated and decoded through appropriate signal processing. The propagation path is called the MIMO propagation path because it includes multipleinput and multiple-output paths. To attain accurate separation and decoding of the original signals, the reception signal-intensity variation between individual signals should be as wide as possible; i.e, the signal should be only weakly correlated. Correlation is weak when the reception point is not in sight of the transmission point (nonline-of-sight environment); whereas it is strong in a line-of-sight environment. Therefore, MIMO transmission schemes should pay particular attention to the signal separation characteristics in line-ofsight environments. MIMO Transmission Scheme Based on Orthogonally Polarized Waves The MIMO transmission scheme illustrated in Figure 2 utilizes two transmitting antennas and eight receiving antennas, and it can provide higher transmission capacity than the conventional scheme. Signal separation becomes relatively easy because the two transmitting antennas send out orthogonally polarized waves (vertically and horizontally polarized) and the correlation between these waves is weaker at the receiver. That is, the scheme suppresses interference at the receiver and improves signal Signal 1 Signal 2 Improved separation of signals with waves having different polarizations Good reception quality even in line-ofsight environment in which ordinary MIMO transmission does not perform well Signal 1 Signal detection (MMSE filtering) : ertical polarized antenna : orizontal polarized antenna Signal 2 Figure 2: 2x8 MIMO-OFDM transmission scheme based on orthogonal polarized waves separation. Outdoor transmission experiments conducted in the vicinity of STRL confirmed that the use of orthogonally polarized waves dramatically improves the error rate characteristics. 20 Broadcast Technology No.41, Summer 2010 C NK STRL

4 Challenge Series: Technologies That Support Digital Terrestrial Broadcasting Emergency Warning Broadcast/ Earthquake Early Warning for Security and Safety Kenichi Murayama, Principal Research Engineer; Broadcasting Networks Research Division NK provides two types of emergency broadcasts: Emergency Warning Broadcasting (EWB) system and Earthquake Early Warning (EEW) system. In addition to an activation signal for receivers, the EWB system consists of information about the expected major Tokai earthquake and tsunamis. It can also include information from local municipal authorities. The EEW systems contains information from the Japan Meteorological Agency on the estimated scale and seismic center of an earthquake, and it is possible to send this warning before large tremors (S-wave) strikes by measuring small tremors (P-wave) that come immediately before it. Sometimes the broadcast does not reach people near the seismic center in time, and there are technical limitations, such as a seismic scale estimation error of 1. owever, it is believed that the damage from an earthquake can be reduced by using the small window of time available before the large tremors strikes. NK automatically broadcasts EEW sent from the Japan Meteorological Agency during its programming. This means that only people who are watching T at the time can receive emergency information on the earthquake. We are thus developing a way to activate T receivers automatically when an EEW is released. Since it is only a matter of seconds before tremors strike, EEW has to be delivered to the receivers as quickly as possible. The method of delivery that we are working on at STRL automatically activates receivers using One- Seg broadcast-signals. It uses a special transmission path called the Auxiliary Channel (AC)* 1 to quickly reach those carrying One-Seg receivers outdoors. owever, automatic receiver activation requires constant monitoring of the EEW activation signal at the receiver. The battery power consumption associated with constant reception of One-Seg signals limits the method's feasibility on a small portable receiver like a cellular phone. To deal with this issue, we devised a new technology that enables prompt activation of the receiver while suppressing battery use through the intermittent* 2 transmission of the activation signal notification on the AC. * 1 AC: Auxiliary Channel, a transmission path for additional information related to a broadcast. * 2 a 231 msec interval in this case. Emergency Warning Broadcasting Warning of the expected Tokai earthquake. Release of tsunami warning. Upon request to broadcast an evacuation order by a municipal mayor or governor. Earthquake Early Warning Sent when a tremor is expected to occur with an intensity greater than a weak 5 on the Japanese seven-level seismic scale. Ding-dong Automatically turns on the power. seismograph P-wave Japan S-wave Meteorological Agency seismograph P-wave Japan Meteorological S-wave Agency Ding-dong Automatically turns on the power. A earthquake occurs. A earthquake occurs. (1) A seismograph detects a P-wave before an S-wave strikes. (2) The Japan Meteorological Agency releases earthquake information including the scale. Figure 1: Emergency Warning Broadcasting and Earthquake Early Warning Figure 2: Automatic receiver activation Broadcast Technology No.41, Summer 2010 C NK STRL 21

5 The Next Generation of Digital Terrestrial Broadcasting Systems iroyuki amazumi, Senior Research Engineer; Broadcasting Networks Research Division The next generation of advanced digital terrestrial broadcasting systems will have to be capable of high-capacity delivery of content services such as Super i- ision (S). We recently launched a new research project that will build on the current ISDB-T* 1 scheme to achieve a high-capacity delivery capability. The first phase of our study involves an ultra-multilevel OFDM* 2 transmission technology based on the orthogonal frequency division multiplexing (OFDM) scheme of ISDB-T. We also initiated (a) Current ISDB-T (64 signal points) (b) Ultra-multilevel OFDM (1024 signal points) Figure 1: Signal point example research on dual polarized MIMO broadcasting* 3, which simultaneously employs horizontal polarization and vertical polarization. Advanced digital terrestrial broadcasting R&D is progressing towards the four goals described below: - Capability to provide high enough capacity for services such as compressed S programs. - Stable reception characteristics in various reception environments that may be affected by multipath and other forms of interference. - Simple receiver design and manufacture. - Secure, economical system with a minimum impact on the environment. Ultra-multilevel OFDM transmission technology The present ISDB-T scheme transmits data with a maximum of 6 bits in a single carrier symbol for an OFDM signal (64 signal points) as shown in Figure 1 (a). For the advanced high-capacity transmission system, we are exploring the possibility of 10-bit maximum data transmission (1024 signal points) as in Figure 1 (b). The feasibility of such a broadcasting system will be verified once the prototype system has been fabricated and its performance examined. Dual polarized MIMO broadcasting An effective method for dramatically expanding transmission capacity is the use of dual polarized MIMO broadcasting, which simultaneously broadcasts different information on horizontal polarization and vertical polarization. We have begun an examination of a scheme that utilizes two transmitting antennas for broadcasting and more than two receiving antennas for reception (Figure 2). * 1 ISDB-T (Integrated Services Digital Broadcasting-Terrestrial): Japanese digital terrestrial broadcasting system. * 2 OFDM (Orthogonal Frequency Division Multiplexing) orizontal polarization Signal * 3 MIMO (Multiple-Input Multiple- Output) Signal Signal ertical polarization Interference Interference Signal separation Signal Figure 2: Dual polarized MIMO broadcasting outline 22 Broadcast Technology No.41, Summer 2010 C NK STRL