1. Overview of mobile TV related standards
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Mobile TV is another kind of independent signal receiving mode other than IP TV, cable TV, satellite TV and terrestrial broadcast TV. It is a new video adapting to mobile phone consumers. At present, there are two main ways to implement mobile TV services: 1) using cellular mobile networks, and 2) using broadcast (both satellite and terrestrial). At present, most mobile operators launch mobile TV services rely on existing cellular networks. China Mobile's mobile TV service (currently renamed as mobile video) is based on GPRS and TD-SCDMA networks, while China Telecom relies on its CDMA1X and CDMA2000 networks. This mobile TV service actually uses streaming media technology to launch mobile TV as a data service. Regardless of whether it is a GPRS mobile phone or a CDMA1X mobile phone, the corresponding playing software needs to be installed on the mobile terminal equipped with the operating system, and the corresponding television program is organized and provided by the operator or the related SP.
It is well known that 3G international standards include WCDMA, CDMA2000 and TD-SCDMA. The mobile TV standard of WCDMA has been determined as MBMS (Multimedia Broadcast/Multicast Service). The TD-MBMS technical solution was submitted to 3GPP in May 2007 and has been accepted as an international standard. This solution was first proposed by Spreadtrum and other vendors, and was supported and improved by TD industry chain manufacturers such as ZTE, which means TD-SCDMA standard. The adoption of MBMS is a foregone conclusion. CDMA2000 adopts MCBCS (Multicast Broadcast Services) defined by 3GPP2 as its mobile TV standard.
At present, the mobile digital TV standards based on the broadcasting method mainly include DVB-H in Europe, DMB (Digital Multimedia Broadcasting in Korea, including terrestrial T-DMB and satellite S-DMB), MediaFLO in the United States, and ISDB-T in Japan. DVB-H (Digital Video Broadcasting Handheld) is a transmission standard established by the European Digital Television Standards Organization (DVB) for providing multimedia services to portable/handheld terminals via terrestrial digital broadcasting networks. This standard is an extended application of the European Digital Television Standard (DVB-T). Compared with DVB-T, DVB-H terminal has the characteristics of lower power consumption, stronger mobile reception and anti-interference performance. Therefore, the standard is suitable for small portable devices such as mobile phones and handheld computers to receive signals through terrestrial digital TV broadcasting networks. . It can also be said that the DVB-H standard relies on the current DVB-T transmission system to enable a portable device such as a mobile phone to stably receive broadcast television signals by adding certain additional functions and improved technologies. Japan has developed a single-band playback specification under its ISDB-T standard for microwave digital TV broadcasting. Although the functions of the two technical specifications are equivalent, there is still a big difference between them. Single-band broadcasting divides the frequency and reduces the bandwidth, while DVB-H uses the bandwidth of time-division digital multimedia broadcasting to transmit the data of each channel in a pulsed manner. In general, the tuner circuit is turned off at other times in addition to receiving the data of the desired channel, thereby effectively reducing power consumption.
DMB (Digital Multimedia Broadcasting) is a technology developed on the basis of Digital Audio Broadcasting (DAB). There are two types of DMB technology: one is T-DMB (terrestrial digital multimedia broadcasting), and the other is S-DMB (satellite digital multimedia broadcasting). In a strict sense, this standard is still an international standard in Europe. This technology is based on the Eureka 147 Digital Audio Broadcasting (DAB) system developed by European manufacturers. It can be modified to broadcast aerial digital video and audio programs to handheld devices such as mobile phones, PDAs and portable TVs. S-DMB broadcasts digital video or audio information through DMB satellites, and mobile reception by mobile phones or other specialized terminals. It is a kind of personalization that can fully satisfy audiovisual broadcast TV in a mobile environment in a wide area. A highly competitive solution. The successful commercial use of DMB mobile TV in South Korea has greatly encouraged South Korea to start promoting the T-DMB standard overseas by the government, in preparation for driving technology and hardware exports. Some areas in China have adopted T-DMB technology for trial commercial use of mobile TV. The DMB standards (including S-DMB and T-DMB) were commercialized in Korea in May and November 2005, respectively, and have now accumulated millions of users.
MediaFLO (Forward Link Only) is an end-to-end solution developed by Qualcomm for high-quality audio and video experiences on wireless terminals. With MediaFLO, operators can leverage existing networks to deliver high-quality audio and video multimedia services to mobile users in a secure and efficient manner. For the user, the MediaFLO program guide, which is similar to the traditional TV program guide created by MediaFLO, can be used to customize the program he wants to watch.
There are many mobile TV standards in China, including CMMB issued by the State Administration of Radio, Film and Television, CDMB issued by China Standardization Association, T-MMB of New Shoreline Company and DMB-TH of Tsinghua University, CMB of Huawei and MBMS proposed by China Mobile. The latter two are technical solutions for providing mobile TV programs by increasing the MBMS multicast function in the telecommunication network. CMMB has been designated by the State Administration of Radio, Film and Television as the industry standard for mobile multimedia broadcasting, and the T-MMB of the new shoreline company has been identified as the national standard for mobile TV due to the support of the National Standards Committee. It can be said that the domestic mobile TV market will be the world of CMMB and T-MMB in the future. Compared with CMMB, the industrialization process of T-MMB is relatively lagging behind, and the market operation is weak. Before the Olympic Games, CMMB successfully deployed the mobile TV business of the 2008 Beijing Olympic Games in 35 cities across the country. It has covered all first-tier cities and most provincial capital cities. Now there are a number of chip companies that can provide mass production chips. More than 10 terminal companies represented by national enterprises can provide different types of CMMB receiving terminals.
The way to install digital TV receiver modules in mobile phones is currently the most promising mobile TV technology. In this way, a digital television signal demodulation module needs to be installed on the mobile terminal, and the digital television signal can be directly obtained without the link of the mobile communication network. In early May, China Broadcasting Satellite Broadcasting Corporation, a subsidiary of the State Administration of Radio, Film and Television, and China Mobile signed an exclusive agreement to jointly promote the development of TD-SCDMA mobile phones with CMMB functions. China Mobile will be responsible for the management of CMMB's fee-based operations. This win-win initiative will be a good attempt for triple play.
2. Introduction to CMMB standard
On October 24, 2006, the State Administration of Radio, Film and Television officially promulgated the China Mobile Multimedia Broadcasting System (CMMB) broadcast channel industry standard "GY/T 220.1-2006 Mobile Multimedia Broadcasting Part 1: Broadcast Channel Frame Structure, Channel Coding and Modulation, determined the adoption of China's self-developed mobile multimedia broadcast transmission technology standards (referred to as STiMi, Satellite-Terrestrial Interactive Multi-service Infrastructure).
2.1CMMB architecture
The CMMB technology system utilizes high-power S-band satellite signals to cover the whole country, and uses the ground-added transponders to transmit the satellite signal to cover the satellite signal blind zone simultaneously with the content forwarding satellite signal. The wireless mobile communication network is used to construct the return channel to form a one-way broadcast and A two-way interactive mobile multimedia broadcast network.
After the ground transmitting center sends the signal to the S-band synchronous satellite, the synchronous satellite forwards the received signal, and the forwarded S-band signal is directly received by the receiving terminal on the ground, and can also be received by the ground after being supplemented by the transponder. The terminal receives it. The satellite also sends the signal to the supplemental repeater through the distribution channel, and then transfers it through the supplemental repeater to supplement the shaded area covered by the satellite.
CMMB is aimed at China's vast territory, complex transmission environment, dense urban areas in the eastern region, sparse population in the western region, and a large number of users and diversified business needs. Based on China's national conditions, it is designed to integrate the world with advanced technology. The technology system of "Star Network" has the advantages of low cost and fast coverage of mobile multimedia broadcast signals nationwide. The STiMi transmission technology adopted by the CMMB system fully considers the needs and characteristics of mobile multimedia broadcasting services in China, and is an independent technology with advanced, practical and economical.
2.2 STiMi signal processing flow
STiMi technology is a wireless channel transmission technology specially designed for the business needs of mobile multimedia broadcasting, and constitutes the core technology in the CMMB architecture independently developed by China. STiMi technology fully considers the characteristics of mobile multimedia broadcasting services, and adopts the most advanced channel error correction coding (LDPC code) technology and OFDM modulation technology to improve the system's receiving sensitivity requirements, mobility and battery power. Anti-interference ability, support high mobility, and use time slot (time slot) energy-saving technology to reduce terminal power consumption and improve terminal endurance.
The STiMi system operates from 30 MHz to 3000 MHz and the physical bandwidth supports both 8 MHz and 2 MHz modes of operation.
The plurality of data streams from the upper layer independently perform operations of RS coding and byte interleaving, LDPC coding, bit interleaving, and constellation mapping, and then combine with discrete pilots and contiguous pilots carrying transmission indication information to form an OFDM frequency domain. Symbol, then scramble the frequency domain symbol data, perform OFDM modulation, framing, upconversion, etc., and finally send the signal to the air.
The STiMi system uses the Reed-Solomon code as the outer code and the byte interleaver as the outer interleaver. RS coding and byte interleaving are handled in accordance with the column input column output and line coding. The LDPC (Low Density Parity Check Code) code is a type of error correction coding method that can approximate the Shannon limit and has a low decoding complexity. The STiMi system uses an independently developed LDPC code that supports both 1/2 and 3/4 encoding rates. The STiMi system uses bit interleaving as the inner interleaving, and the LDPC encoded bits are input to the bit interleaver for interleaving. The STiMi system supports BPSK, QPSK and 16-QAM constellation mapping schemes, which can flexibly adapt to different transmission rate requirements. The STiMi system employs OFDM modulation, and the frequency domain OFDM symbols are composed of data subcarriers, discrete pilot subcarriers, and contiguous pilot subcarriers. The discrete pilot does not carry any information, and is mainly used to assist the receiver in channel estimation, coherent detection and demodulation. Part of the continuous pilot carries the system transmission indication information. The system data rate of the STiMi system supports different rates from 2.046 Mbps to 16.243 Mbps (8 MHz bandwidth mode) and different rates from 0.409 Mbps to 3.248 Mbps (2 MHz bandwidth mode).
3. Analysis of the solution and development status of CMMB+TD-SCDMA
3.1 Solution Analysis
Mobile operators use their own cellular networks to transmit video programs through streaming media technology. The resources are very expensive. Even in the 3G era, other data needs such as users' Internet access will be affected. In addition, the price of mobile TV live broadcast is too high and lacks the basis for extensive promotion. The mobile TV standard adopting the broadcast mode lacks suitable billing means. If you want to perform billing, you need to develop your own independent CA (Conditional Access) system, which means that the card is separated like a mobile phone, which will result in a large system cost. Rising, while adding cumbersome links to the use of consumers. At the same time, the broadcast mode cannot enable users to experience more novel audio and video services such as interaction and on-demand broadcasting. In summary, combining broadcast and cellular networks is the best solution for mobile TV. Based on the above considerations, this paper designed the following solutions.
The broadcast television program and data service content are integrated on the program integration platform to generate a program source. The program source is forwarded to both the mobile operator and the ground transmitting center to send the signal to the S-band synchronous satellite. The synchronous satellite forwards the received signal, and the forwarded S-band signal is directly received by the receiving terminal on the ground, and can also pass After the supplementary transponder is processed, it is received by the receiving terminal on the ground. At present, due to the cost problem, CMMB adopts the way of adding the transponder on the ground, and the satellite reception has not been put on the schedule. The program sent to the mobile operator is converted by the operator into a system that can be transmitted in the cellular network for the mobile phone user to order on the TD-SCDMA system.
To implement the CMMB function in the terminal, you only need to add the Tuner and Demodulator chips. The source decoding can use the CPU, H.264 decoder chip and display system shared with the original TD-SCDMA mobile phone. In the future, CMMB chips can be fully integrated with TD-SCDMA chips, reducing system cost and power consumption. In terms of billing and user management, the user can subscribe to the service subscription and deduction of the service through the mobile network by establishing a connection between the decryption part of the CMMB chip and the USIM card of the mobile phone. In terms of operations, mobile and broadcasting can be divided by a certain method and ratio. In the process, the two sides need to cooperate fully, put aside disputes and explore the advantages of their respective systems, so as to achieve a win-win situation and maximize the interests of both parties.
3.2 Analysis of development status
After several years of development, China Mobile Multimedia Broadcasting and Television (CMMB) has formed a complete industry and has successfully served the Beijing Olympics to ensure that the Olympic Games will be “anytime, anywhere†during the Olympic Games, providing special athletes, media reporters and other special groups. Quality service. In order to achieve win-win and development of CMMB and TD-SCDMA, the competent national authorities clearly require CMMB to integrate with TD-SCDMA mobile communication technology with independent intellectual property rights. Recently, China Broadcasting Satellite Mobile Broadcasting Co., Ltd., a subsidiary of the State Administration of Radio, Film and Television, and China Mobile officially signed an exclusive cooperation agreement between CMMB and TD-SCDMA. The two sides will aggregate the superior resources of content, network, brand and marketing, and increase cooperation and promotion of new technologies and new products. At this point, the "marriage" of radio and television and communication that has been long-watched by the industry has finally settled, marking that two representative independent innovation technologies in the field of broadcasting and communication in China have entered a stage of coordinated development.
More than 300 prefecture-level cities across the country have completed coverage of mobile multimedia broadcast television networks, and major cities across the country have achieved TD-SCDMA network coverage. Hundreds of millions of users in all "two networks" synchronous coverage areas can enjoy the corresponding services. With the gradual maturity of the market, the number of vendors joining the terminal is increasing, and the result of the final competition will surely enable more consumers to experience the infinite charm of mobile multimedia.
4 Conclusion
With the rapid development of the global consumer electronics industry and the opening of China's 3G curtain, mobile TV will become a hot spot in the entire industry chain. In the next few years, the mobile TV function will gradually become the basic configuration of the mobile phone like a camera. The development of television has grown by leaps and bounds. For decades, the people have witnessed the change of television from black and white to color, and are now experiencing the transition from color television to digital color television. If these two changes are the two nodes of TV's leaping development in China, then moving the fixed TV set in the home to the pocket of the individual, and watching TV on the screen of the mobile phone will be the third in the field of television. Leaping Development.
The significance of the TD-SCDMA standard is to break the monopoly of Western communication standards in China in the past 100 years. CMMB is fully learning the experience of TD-SCDMA in independent innovation and independent innovation in the field of broadcasting and television. The integration of CMMB and TD-SCDMA reflects the new height of the three-network integration proposed by the national “Eleventh Five-Year Plan†on the basis of independent innovation and national industry.
CMMB is a broadcasting technology. Its advantages are wide coverage, relatively low cost, and simultaneous viewing by multiple users. It is difficult to support on-demand and two-way interactive services, and there is no mature mode in charging. Mobile video technologies, such as TD-MBMS, have the advantage of interactive, on-demand and even instant messaging, but it is uneconomical to achieve large-scale, wide-coverage, multi-user video transmission. Therefore, the integration of the two is in full compliance with the principle of triple play, in line with China's national conditions, and also meet the interests of both parties. The two-way transmission standard based on TD-SCDMA and the transmission standard of unidirectional broadcasting based on CMMB are completely complementary. The combination of the two can create an operation mode that is most suitable for ordinary people.
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