Introduction to PSI/Si information and functions of digital TV

The Electronic Program Guide (EPG) is usually used in the DVB receiver to quickly find programs. The EPG data generated comes from the business information SI information in the DVB code stream. In digital TV, all the video, audio, text, pictures and so on after digital processing into the data, and according to the MPEG-2 Standard packaging, forming a fixed length (188 bytes) and then the data packets are reused to form a transmission code stream (TS). Generally, a channel corresponds to a TS stream, and a channel's TS stream consists of multiple programs and services. If there is no boot information in the TS stream, the terminal device of the digital TV won't be able to find the desired code stream, so in the MPEG-2, the PSI information is specifically defined, the function is to automatically set and guide the receiver for decoding. PSI information is inserted into the TS stream by means of a multipleth, and identified by a specific PID (package identifier.
The program information PSI defined in the MPEG-2 standard is a description of a single code stream, because the system usually has multiple code streams, in order to enable the user to quickly find the desired business in Multi-code stream, the PSI of MPEG-2 is expanded in DVB, and nine tables are added on the basis of four PSI tables, form Si. Si is a description of all the code streams of the entire system. It describes the data transmitted by the system, the arrangement of broadcast data streams, and the schedule. It includes Psi information.
I. PSI Information PSI is composed of a program Association Table (PAT), a condition receiving table (CAT), a program ing table (PMT), and a network information table (NIT, these tables are inserted to ts for transmission. PSI specifies how to correctly find a specific program from a transfer stream carrying multiple programs. When the receiver wants to receive a specified program, it first obtains the PID value of the program ing table of the program from the program Association table, and then finds the program ing table corresponding to this PID value from ts, obtain the PID value that constitutes the basic code stream of the program from the program ing table, filter the corresponding basic code streams such as video, audio, and data based on the PID value, and then return to the original signal after decoding, delete transfer packets containing other PIDs
1. Pat: to ensure that the TS stream can be normally received in the program Association table, there must be at least one complete and effective Pat in the stream. The program Association Table Pat includes all program ing tables in the TS stream, that is, the pmt pid and transmission stream ID of each program. The PID Number of the Pat table is "0x00", and the demultiplexing always starts by searching for the Pat table. Pat provides the PID that constitutes the PMT of each program business in the transmission stream. You can find the corresponding PMT package based on the Program PID, and also gives the nit pid Number.
2. PMT: The program ing table contains the basic code stream information of each program, that is, the video information, Audio Information, and ECM authorization control information of multiple CA. The PMT table specifies the PID Number of each code stream that constitutes the program service and describes each code stream. PMT table Program The ing between numbers and the original streams that make up them. This ing table is a set defined by all programs in a transfer stream. This table will be transmitted in the group, and its PID value is selected without authorization. Multiple PID values can be used if needed.
3. nit: The network information table includes the physical transmission network information of all transmission streams in the digital TV network, including channel tuning parameters, frequency, and symbol rate of the program, this information allows the receiver to change the channel and tuning parameters with little or no delay according to the user's choice, and correctly decode ts. The nit table is defined by ets300468, it complies with ISO/IEC13818-1 standards and its content is private to provide information about the physical network. If yes, the Network PID value is defined by the user and should be defined in the Pat table. The program number is the reserved 0x0000.
4. cat: the conditional receiving table indicates the authorization of users in a specific CA system. It contains the ca_system_id that identifies the specific CA system and the emm_pid index used to obtain the authorization management information, these two items can be used to obtain the EMM information of the user's CA system. The conditional receiving process of the user end starts from the ca_system_id in the read card and obtains the corresponding Emm. After ECM, the decryption and decryption work starts in the order of inverse to the sending end. The cat table provides one or more ca systems. The PID value is fixed by 0x0001. The cat table provides information for conditional access in the system, specifying the connection between the CA system and the corresponding permission management information EMM (Entitlement management messages), and specifying the PID of the EMM, and other related parameters.
Second, SI information MPEG-2 in PSI provides a lot of information about Program Composition and mutual relationship, so that the receiver can correctly dereuse TS stream. However, this information is still insufficient in actual use. Therefore, the PSI information is further extended using Si information in the DVB standard. The information in PSI is basically related to the current code stream, that is, all the content involved is related to some information in the current code stream. The SI information can include some services and events that are not included in the current code stream, allows users to make more choices and learn more about other services. PSI data only provides the information of a single ts, so that the digital TV set-top box can decode different program streams in a single ts, however, it cannot provide information about the business and program types, programs, and start time of multiple ts. Therefore, the DVB system extends the PSI, it provides various other forms with different types of information to form an SI. In practice, we organize the data provided by Si in an orderly manner to generate similar forms of Program Reports, which can be viewed in real time on the TV, which will greatly facilitate the use of users, this is the EPG guide for Electronic programs.
The SI information table mainly includes the following content:
① Bat: the business group association table provides information about the program business group involved, including the program business group name and the program business list contained in the program business group. BAT can be used to conveniently browse and select related programs or certain types of programs.
② SDT: the service description table is used to describe the service name, service provider, and event description table in the system. The service description table can describe the current transmission stream, you can also describe other transmission streams, which are distinguished by the table ID.
③ EIT: The event information table is the main table for generating EPG. The EIT table contains data about events or programs, such as the name, start time, length of time, and running status of events.
④ Rst: The running status table provides the running status and time of an event or multiple events, that is, information about the running or not running of an event, such: running, about to run, pause, or not running, can be used to automatically switch to the specified event on time.
⑤ TDT: the time and date table provides information about the current time and date. Because this information is frequently updated, you need to use a separate table.
⑥ Tot: The Time Offset Table provides information about the current time, date, and local time offset.
7. St: The Role of the St table is to indicate that its content is invalid. It is only used as a padding byte and does not transmit useful information.
To sum up, by inserting psi/Si information in a digital TV, digital TV users can conveniently and quickly search for and query all Transmitted program names, program categories, weekly program content, and specific playback time, and book programs on digital TV receiving devices as you like, so as to implement the electronic program guide.
Taiyuan cable TV network Co., Ltd. Zhang Juan