Is the digital TV set-top box really coming to an end?

Abstract: This paper describes the latest developments in the architecture of digital terrestrial TV set-top boxes (DTT/STB) worldwide, following the widespread adoption of broadcast DTT standards and the latest video compression technologies. The last part describes how DiBcom solutions can help OEMs continue to use cost-optimized hardware without compromising the scalability of the set-top box, while extending its lifespan.

After LCD TVs integrated DTT receivers, some people thought that set-top boxes would soon be obsolete. However, television is undergoing a revolution, with Internet connectivity, high-capacity, low-cost PVRs and VOD, etc. This has led to more and more powerful set-top boxes that can receive content from a variety of broadcast and broadband networks. With greater flexibility, set-top boxes are also changing in structure, providing manufacturers with new business opportunities to design low-cost, high-performance set-top boxes for different markets.

For many years, the functional components of DTT STB front-end/back-end have been divided into the following parts:

Based on the "three-chip solution" (tuner + demodulator + video decoder)

Or based on a “two-chip solution”, an RF tuner is connected to a SoC chip that integrates a baseband DTT demodulator and a video decoder , as shown in Figure 1:

This structure is a natural result of chip manufacturers and set-top box OEMs trying to reduce costs and provide affordable products for a relatively stable market. Since DTT standards were very limited before 2007 (see Figure 2), it was natural to integrate the DTT demodulator in the back-end processor SoC.

Figure 2: Distribution of DTT standards related to video compression standards around the world in 2007

However, this structure became obsolete a few years later due to the emergence of more efficient DTT standards and video compression standards driven by high-definition television content.

Since 2007, new DTT broadcasting standards have emerged, such as DTMB in China and ISDB-Tb in Latin America. At the same time, DVB-T2 networks, which can increase spectrum efficiency by 30% to 50%, have also begun to be built in the UK and Scandinavia.

On the other hand, new video compression standards, such as MPEG-4 AVC/H264 and AVS (China), are gradually replacing MPEG-2. With the use of H264, the required transmission bandwidth can be saved by up to 50% or more, which accelerates the introduction of HDTV. The result is further fragmentation of the market, as shown in the different sectors in Figure 3.

Figure 3 Distribution of DTT standards related to video compression standards around the world in 2010

If chipmakers wanted to deliver the best chip integration for all markets, they would have to design more than a dozen different SoC chips, not even factoring in satellite and cable broadcasting. If chipmakers were to meet all of those criteria, the volume wouldn’t be enough to realize a return on their investment.

Looking ahead

Therefore, in order to quickly adapt to the development of this market, a more flexible STB structure has emerged, as shown in Figure 4, which includes all the latest integrated technologies (tuner + demodulator) in a single chip. Its advantage is that the video decoder will not be overloaded by a large number of channel decoding. This helps to avoid the risks caused by imperfectly designed or non-competitive SoCs.

Figure 4: STB DTT front-end/back-end block diagram after 2010

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This architecture addresses the challenges that the STB industry currently and in the future will face, namely scalability and adaptability in a fragmented market.

The following table (Table 1) details the video compression standard specifications (P) and levels (L) for each DTT standard.

Table 1: Video compression standards for each DTT standard

Based on the video compression standards of all DTT standards, we can draw Figure 6, which shows the DTT standards launched globally in 2010, and Figure 7, which shows the global distribution of a subset of video compression standards.

Figure 6: DTT standard introduced in 2010 (front end)

Figure 7: Video compression standards introduced in 2010 (backend)

From Figures 6 and 7, it can be seen that developing a front-end SoC that supports the five current demodulation standards and a back-end processor that supports decoding the five current video compression standards is more effective than designing ten dedicated SoCs that support the ten different combinations in Figure 3.

Looking ahead to 2011 and beyond, the market development trend will also be more favorable to this structure:

· "IP STB" is becoming more and more popular, especially in Western European countries that have successfully implemented "triple play". Global analysts agree that 10% of global STB shipments in 2009 were IP STBs. This trend will also accelerate the development of Internet TV (web2.0), and access to video-on-demand content and online applications (such as through smartphones) will become simpler. However, TV programs transmitted through cable networks may not always provide stable linear TV programs (due to distance to DSLAM and network stability issues), and they are not necessarily free services. Therefore, the rise of IP STB will increase the demand for "Hybrid-Box", while the back-end chips will tend to value-added services on the Internet, and the front-end chips can also be used interchangeably according to the region and the target terminal market.

The latest video compression standards not only save bandwidth, but also reduce the demand for storage capacity. Coupled with the increasingly low cost of storage units (hard disk or Flash memory), the price of personal video recorders (PVRs) is becoming more and more attractive. With this structure, STB OEMs only need one, two or more tuners to easily expand from the initial platform to various products, and a back-end processor can support one, two or more video streams separately and synchronously.

PVRs are the digital replacements for the old VCRs that we all had just a few years ago that recorded our favorite shows on tape.

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DiBcom now offers cost-effective front-end chips for DVB-T and ISDB-T, fully pin-compatible, especially for the current STB market in Europe, Asia and Latin America:

DIB 7090: Integrated tuner + demodulator for DVB-T

DIB 8096: Integrated tuner + demodulator for ISDB-T and ISDB-Tb (Full seg and one seg)

The block diagrams of these two chips are exactly the same as Figure 4. Compared with the old front-end structure in Figure 1, the new integrated solution has the following advantages:

Front-end SoC:

The two chips use system-on-chip (SoC) technology to integrate all devices on a single chip chassis. This approach brings real advantages in performance, size and cost reduction for DTT applications (fixed and mobile). Integrating a single-chip RF tuner and demodulator on a single chassis solves the space, feature differences and cost issues of the front end. It facilitates the implementation of highly integrated solutions, whether simple mode or dual antenna (PVR or diversity).

Better indoor signal reception

Years of experience developing signal processing technology for portable devices has enabled us to implement more powerful digital channel estimation, thus improving indoor signal reception, which is particularly important when indoor antennas cannot be used.

No SAW filter required:

Integration efficiency is very high when using “Zero IF” (I&Q) tuners, since a separate digital filter in the demodulator replaces the expensive external RF SAW filter.

Integrated AGC:

Tuner-demodulator coupling has a significant impact on AGC optimization, avoiding module duplication in both circuits. Customers no longer have to develop a complex hardware/software AGC interface between an external RF tuner and a baseband demodulator. The AGC is able to work immediately even with high dynamic range input signals and adjacent channels.

PVR/PIP or Diversity mode

In dual mode (see Figure 8 below) when using both chips, the main chip provides an MPEG-2 transport stream that transmits:

- Data provided by two independent front ends

- or data obtained by Maximum Ratio Combining (MRC) of two single data

This makes dual receiver configurations extremely simple, whether for PVR/PIP (A-Mode) providing two independent video/audio channels, or diversity mode (B-Mode) for increased receiver sensitivity when signals are weak.

in conclusion

In addition to Soc chips for DVB-T and ISDB-T, DiBcom has also developed "Octopus", a programmable/multi-standard platform that supports most existing TV broadcast standards. Due to the diversity of TV broadcast standards around the world, this highly adaptable platform should soon become the best solution for LCD TV integrated digital TV front-ends.

This is not the end of STBs. In many countries, a large number of CRT and even LCD flat-panel TVs do not have any DTT front-end integrated. In addition, DTT technology innovations are constantly ongoing, which take some time to be integrated into LCD TVs (such as HDTV, PIP, PVR, 3D…). Generally, people replace their flat-panel TVs every five to seven years, so it is much easier to launch a set-top box with new technology than to integrate it into the flat-panel TV. Only STBs can keep pace with technological innovations.