We have progressed with our research on Hybridcast^®, which makes possible new services that meet the needs of viewers by combining broadcasting and communications.

■ Hybridcast platform

　Hybridcast makes broadcasting more advanced, flexible and extensible by taking advantage of the complementary characteristics of broadcasting and communications. The NHK three-year administrative plan beginning in FY2012 sets a priority target of developing new services suited to the era of integrated broadcasting and communications (Figure 1). In line with this plan, we aim to make Hybridcast a reality within two years.

Figure 1. Hybridcast overview

　At the STRL Open House, we introduced prototype television and set-top-box (STB) receivers developed by television manufacturers and a STB with highly accurate synchronization technology to present multi-view or stereo 3D television. Various services for prototype mobile devices that communicate with TVs were also introduced. These efforts demonstrated that it will be possible to provide such Hybridcast services very soon (Figure 2). We also exhibited a screen display control technology that can reliably give priority to emergency information from broadcasts such as earthquake early warnings.

Figure 2. Hybridcast prototype receivers exhibited at the STRL Open House

　We widely promoted the possibilities of these services, domestically and internationally by exhibiting Hybridcast and making presentations at CEATEC2011, IMC2011, IBC2011, and others. In particular, our Hybridcast presentation won the Best Paper Award at NAB2011⁽¹⁾.
　We continued work on prototype test receivers in cooperation with television manufacturers toward the early launch of Hybridcast.
　We published technical descriptions summarizing the overall architecture, service models, and technical requirements of Hybridcast at the time of the Open House. After that, we continued to study the detailed specifications. Since these specifications are for a browser-based system, NHK is participating in W3C, which is a community standardizing web-related technologies including HTML5. In particular, NHK proposed a set of requirements for services combining broadcasting with communications which should be satisfied by a browser in a TV and HTML5 language. We are also participating in the HTML5 working group at the IPTV Forum, which is developing technical specifications for combining broadcasting and communications in Japan.
　In the future, we will complete these specifications by testing prototype receivers equipped with HTML5 browsers developed by television manufacturers and conduct field trials using these receivers. Part of this research was conducted in cooperation with Sony Corporation and NTT Corporation.

■ Security for receivers combining broadcasting and communications functions

　We are researching and developing security technology for Hybridcast, to provide services that link broadcasting and communications safely and securely. In FY2011, we developed control schemes for presenting communications applications on television screens and for accessing broadcast resources and receiver functions.
　Hybridcast enables new services that cannot be realized with broadcasting alone and that are to be implemented through use of communications applications; a problem is that there is a possibility that important information about the broadcast content could be obscured by these applications. Thus, it is important to have a mechanism that ensures that priority information is conveyed while also considering the needs of viewers. Accordingly, we developed a screen display control scheme⁽²⁾ for when broadcast content and communication applications are combined on the screen. It sends a presentation policy reflecting the broadcaster's intentions to the receiver so that important information such as Earthquake Early Warnings can be given higher display priority (Figure 3). Tests of Hybridcast prototype receivers confirmed that this scheme is effective and that receivers so equipped can quickly and appropriately control the display of applications according to the broadcast information such as Earthquake Early Warnings.
　Hybridcast assumes that receivers will provide a specialized application programming interface (API) that will allow communications applications to use receiver functions and broadcast resources. The API will allow applications to easily reference and control receiver functions and broadcast resources such as channel tuning, program specific information and service information (PSI/SI). However, allowing all communications applications to use these APIs unconditionally presents security risks, so we have developed a scheme for API access control to be used in Hybridcast receivers, to protect viewer information and broadcast content according to application authentication and the viewer’s intentions.

Figure 3. Screen presentation control

■ Multiplexing schemes for hybrid delivery

　Hybridcast realizes varied and versatile services by combining video, audio, and data components on various delivery channels, such as broadcast and communication networks. Components can be reliably delivered with a fixed delay on broadcast channels, but there is a delay variation on communication networks and a portion of components sent may be lost. This means the multiplexing technology must reliably transport these components on the various delivery channels with the appropriate timing.
　To achieve this, we are developing an advanced multiplexing scheme based on MPEG-2 Transport Stream (TS), which combines components on the current digital broadcast system with components on Internet Protocol (IP) based communication networks. We are also developing an IP-based multiplexing scheme for when broadcasting and communications become based on IP in the future.
　With the MPEG-2 TS based multiplexing scheme, both components from broadcast channel and communication networks are synchronized with the system-clock delivered on the broadcast channel. However, when a broadcast station (Station B in Figure 4) receiving a TV program from the original broadcast station (Station A in Figure 4) and retransmits it, the system-clocks on the both stations are not the same. In this case, because of the difference in the system clocks, a receiver receiving the components from Station B cannot synchronize components in the same way as a receiver receiving the components from Station A does. To deal with this problem, we developed a system that calculates and corrects the difference between the system clocks. Our system enables every receiver to synchronize any set of components.

Figure 4. Synchronization using time adjustment data

　In the future, when broadcasting and communications are based on IP, much more flexible and integrated services will be possible. However, in the case of IP, neither transmission delay nor delivery quality is fixed, so reliability cannot be maintained by simply transmitting MPEG-2 TS in IP packets. Because of this, MPEG-2 TS has been extended many times in various ways. As a result of the extensions, MPEG-2 TS has become too complicated.
　Recognizing the necessity of an IP-friendly media transport mechanism, we have developed the Advanced Transport Scheme (ATS), which is an IP-based multiplexing scheme on heterogeneous networks⁽³⁾. We proposed it to MPEG as a candidate technology for the next-generation MPEG Media Transport (MMT) and are actively promoting standardization of the scheme. MMT will be a system technology that will enable media transport over heterogeneous networks and will be a system part of the new MPEG multimedia standard, MPEG-H.

■ Future directions

　Going forward, we will contribute to standardization of technologies that integrate broadcasting and communications in Japan, based on specifications proposed by NHK and through discussions with other broadcasters and manufacturers. We will work toward early field trials at events such as the London Olympics.
　We will also pursue standardization of our new multiplexing scheme, using IP for both broadcasting and communications, at MPEG.

Hybridcast^® and its logotype are registered trademarks of the NHK Engineering Service Inc.

[References]
(1) A. Baba, K. Matsumura, S. Mitsuya, M. Takechi, Y. Kanatsugu, H. Hamada and H. Katoh: “Advanced Hybrid Broadcast and Broadband System for Enhanced Broadcasting Services,” NAB Broadcast Engineering Conference, pp. 343-350 (2011)
(2) K. Otsuki, H. Ohmata, A. Fujii, K. Majima and T. Inoue: “A Presentation Control Method of Applications in Hybridcast,” ITE Annual Convention, 11-11 (2011) (in Japanese)
(3) S. Aoki, K. Aoki, H. Hamada, Y. Kanatsugu, M. Yamamoto and K. Aizawa: “A New Transport Scheme for Hybrid Delivery of Content over Broadcast and Broadband,” IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, mm11-11 (2011)