Interactive set-top box design based on STB5660 solution

Abstract: This paper discusses the design of an interactive set-top box system based on the STB5660 solution from the aspects of system function, logical structure, hardware and software.

1 Introduction

The dissemination of information mainly consists of three major network systems: communication network, radio and television network, and computer network. With the rapid development of communication technology, television technology, and computer technology, the three major networks have entered a new era of mutual integration. Interactive television (ITV) is the concrete embodiment of this integration. The so-called interactive television is a video distribution service controlled by the audience. The audience can make their own choices and decisions between programs and within programs. It is a new type of television technology with an asymmetric duplex communication mode. Among them, the digital set-top box (STB) is one of the key technologies to realize the interactive function. Through the STB, the audience can realize a variety of services such as video on demand (VOD), home shopping, home office, and electronic games while sitting in front of the TV at home, and can also watch high-definition digital TV programs sent by the TV station on an ordinary TV.

2 System Functional Solution

The system function is based on PHILIPS's STB5660 solution (SAA7214+SAA7215+UAD1320A). It can provide functions including QAM signal reception, demodulation, video and audio processing, user interface, etc. The system adopts a highly open modular structure design. The system front end compresses the analog video and audio signals into digital signals through MPEG-2 video encoding, multiplexes the multi-channel digital signals through a multiplexer, and then performs QAM modulation and transmission as the user's downlink digital signal. The user uses telephone DTMF or BPSK as the uplink, and the information selected by the user can be transmitted to the system service center (system front end) through the uplink channel. In this way, interactive video on demand (VOD), stock information and analysis and timely trading, remote education, information sending and other functions can be realized in the broadband network (i.e. cable TV network).

3 System Logical Structure

According to the basic functions of STB, STB can be divided into six layers according to the logical level, as shown in Figure 1.

Physical layer: Full channel tuning reception and demodulation. It can demodulate the QAM modulated signal transmitted from the HFC network.

Link layer: convolution decoding/deinterleaving, REED SOLOMON decoding, energy dispersion migration. Process the QAM demodulated output signal to generate a data stream that complies with the MPEG-2/DVB standard.

Transport layer: demultiplexing and data unpacking. Separate the generated data stream into video packets, audio packets and data packets, and transmit them to the corresponding chips for processing.

Conditional access layer: controls the operation of the descrambling function. In the set-top box, there is a corresponding permission confirmation function. When the set-top box receives the permission confirmation information, it will decode the digital TV program for the user to watch.

Service layer: video and audio decompression, EPG (electronic program guide) generation and data decoding. Decode and encode the received data stream for video, audio and graphics.

Figure 1 System logical structure

User layer: includes the display, conversion, and remote control of the user interface. The demodulated, decoded, and encoded video and audio signals (i.e., analog signals) are output from the corresponding ports of the set-top box. At the same time, the remote control can be used to control and switch all basic functions.

4 System Hardware Structure Solution

According to the functional characteristics of the STB5660 solution and IC chip, the hardware structure of the system is proposed, as shown in Figure 2.

4.1 Front-end decoding part

The front end receives the signal output by the cable TV cable, and after frequency conversion, QAM decoding, deinterleaving, RS decoding, descrambling and other processing, it outputs the standard code stream before MPEG-2 demultiplexing, namely the transport stream (TS stream). This part is mainly completed by a VES1820X chip.

4.2 Transport Stream and Video and Audio Decoding

The transport stream and video and audio decoding are completed by SAA7214 and SAA7215 chips. Among them, SAA7214 is responsible for MPEG-2 source decoding of TS stream, separating video and audio data streams, and controlling peripheral I/O devices associated with decoding. SAA7215 is responsible for decoding and encoding of audio, video and graphics, and separates the decoded data stream into audio and video signals. SAA7215 also has a complete memory structure, using DRAM, SDRAM, FLASH, etc., and these memory chips greatly speed up the running speed of the software.

[page]

4.3 Backend decoding part

The back-end decoding is completed by SAA7215 and UDA1320A. The video signal is output by SAA7215. The audio signal is output by UDA1320A. UDA1320A is a single-chip positive phase stereo DAC with bit data stream conversion technology. It has low power consumption and low voltage working mode; it has three different system clock frequencies of 256, 384 and 512; different frequencies can be selected through static pin control; it supports sampling frequencies from 16KHZ to 48KHZ; it integrates digital filtering and positive phase DAC.

4.4 Network interfaces for interactive applications

The hardware implementation of the interactive application is completed by SAA7214 and the corresponding network interface.

4.4.1 Telephone network connection using ADSL technology

Telephone network connection using ADSL technology: The set-top box connects to the smart card interface and ADSL Modem through the peripheral serial port, and the parallel port is used to transmit data between the set-top box and the PC. The ADSL Modem is directly connected to the ADSL central office through the telephone line, providing high-speed data communication with a downstream rate of 8Mbits and user control information interaction with an upstream rate of 640kbits. Through ADSL, the set-top box has a faster rate than direct Internet access, thus realizing high-speed interactive services with the ATM/OP network.

4.4.2 Hybrid network connection using fiber/coaxial cable technology (HFC)

A hybrid network connection using fiber/coaxial cable technology (HFC): HFC uses a digital tuner's demodulator to convert the user's selected channel signal into a baseband data stream in the downlink; a modulator is used in the uplink to send the user's control signal into the channel, and its interface also uses a cable modem.

5 System software solution

The software structure of the set-top box system can be divided into three levels: business software application layer, real-time event processing layer, system kernel and driver layer. The system software structure is shown in Figure 3.

5.1 Business Software Application Layer

The business software application layer is equivalent to an interface layer covering the driver and operating system. It is formulated according to the business needs of the system and provides various functional services for user applications to realize the set-top box, such as comprehensive information, e-commerce, electronic games, etc.

5.2 Real-time Event Processing Layer

The real-time event processing layer is a software environment that isolates the application from the low-level operating system and hardware details. It makes the application independent of the specific hardware platform and is the middleware between the business software application and the hardware platform. This software system uses OpenTV middleware. OpenTV middleware provides the user application with a complete application interface, so that the application can realize all the functions that the set-top box system should have by simply calling these functions. In this way, the work of the user application becomes very simple.

5.3 System kernel and driver layer

The operating system used in this system is pSOS. The hardware driver layer mainly provides corresponding drivers for various hardware modules. The main drivers include: interface module, including I2C interface operation control, smart card control, etc.; audio module; video module; demultiplexing module; decoding module, Flash driver module, etc.

6 Conclusion

The above introduces the logical structure, system functions, and the composition and implementation of the interactive digital TV set-top box based on the STB5660 solution. At present, the domestic broadcasting and television system has begun to transform to digital TV. Although the recent digital applications are more about digitizing analog color TV, with the increase in user demand for functions and the enrichment of cable operators' service content, multi-functional interactive digital TV set-top boxes will also be increasingly widely used.

References

〔1〕Xue Huifeng. Information Port Theory and Practice〔M〕. Xi'an: Shaanxi Science and Technology Press, 2000

〔2〕Liu Yuhui. Research on ADSL Application Technology〔J〕 Microcomputer Information, 2004, (8): 111-113

〔3〕Liu Da, Gong Jianrong. Digital Television Technology〔M〕. Beijing: Publishing House of Electronics Industry, 2005.

〔4〕Liu Baofeng, Zhang Wenjun. Design and implementation of set-top box application software module〔J〕. Computer Engineering, 2004, (4) 85-87

〔5〕Leng Gaofeng, Yu Zhensheng, Du Beibei. Software and hardware implementation of HDTV source decoder based on ST20TP4〔J〕.