Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-02-26
2001-01-16
Felber, Joseph L. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S535000, C348S423100
Reexamination Certificate
active
06175577
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to a transmission system for transmitting a multiplex signal from a transmitter to a receiver, said multiplex signal comprising at least one information section carrying information about the multiplex signal, the receiver comprising evaluation means for evaluating said information section, said evaluation means being arranged to select information sections with symbol values corresponding to a predetermined sequence of symbol values, the receiver further comprises processing means for processing the multiplex signal in dependence on information present in the selected information sections.
The present invention is also related to a receiver, a decoder, a transmission method, a receiving method and a decoding method for use with such a transmission system.
A transmission system according to the preamble is known from the MPEG-2, DVB, JSAT Transport Demultiplexer, Preliminary Technical Manual published by LSI Logic under document number DB14-000007, Draft Jul. 30, 1996, pp. 4-12-4-15.
Digital broadcast systems as they are being standardized, or are already standardized are based on the so-called MPEG-2 transport stream. The MPEG-2 transport stream offers the possibility of transporting digital video signals and other signals, such as related audio or data signals associated therewith in a very flexible way. The MPEG-2 transport stream is based on 188 byte transport packets, which carry a plurality of so-called elementary streams. Each of said elementary streams is identified by a so-called Packet ID (PID). This elementary streams can be (encoded) video streams, audio streams, and related data signals as required for functions like conditional access or electronic program guides (EPG,s).
The relation between a program and the corresponding elementary streams is defined by a plurality of tables. First there is the Program Map Table (PMT) in which the relation between each program in the transport stream and the PID of the related audio and video signals is stored. Second, there is the Program Association Table (PAT) in which the number of programs transported by the transport stream is stored. Further the PAT gives for each of the programs the PID of the elementary stream which carries the entries of the Program Map Table. Finally there is the Conditional Access Table (CAT) which holds the relation between the different types of conditional systems that may be used and the combination of conditional access PID's, table ID's and table ID's associated therewith.
These tables are stored in the receiver and are initialized and updated by information carried by the information sections. These information sections are also identified by a PID. The PID for the PAT is “00”, and the PID for the CAT is “10”. The PID for the PMT is stored in the PAT at the position corresponding to the program actually to be decoded.
When a program with number i has to be decoded, the PMT table has to be reconstructed from the transport stream. The decoder reads from the Program Association Table the PID for program number i. Using said PID, all elements of the PMT are read from the transport stream, and the complete PMT is built up using said elements. If the PMT is constructed, the demultiplexer can find the elementary streams in the multiplex signal.
Sometimes during a transmission of a multiplex signal the PMT has to be updated due to a change of said multiplex signal. This can be caused by the addition of programs and/or elementary streams. This change is indicated by a changed version number of the Program Association Table entries. In order to be able to find PAT entries of which the version number has changed, the receiver must perform a filtering operation to distinguish between all possible version numbers. Because 5 bits are reserved for the version number of the PAT, 32 different version numbers are possible. This requires 32 filter operations for each PAT entry, resulting in a substantial computational effort.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the transmission system according to the present invention is to provide a transmission system according to the preamble in which the required computational effort has been reduced.
Therefor the invention is characterized in that the evaluation means are arranged for selecting information sections with symbol values differing from a further predetermined sequence of symbol values.
By selecting (filtering) only the information sections with a changed symbol value (e.g. the version number), it is possible to detect that an update of the information carried by the information section (e.g. the PAT) takes place without having to filter all possible symbol values (e.g. version numbers). This reduces the computational effort considerably. It is observed that the scope of the present invention is not limited to the example presented above, but that the invention is applicable in each transmission system in which a change in the constitution of a multiplex signal has to be communicated to a receiver.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the invention is that the information section is arranged for identifying a sequence of symbols corresponding to a conditional access message and in that the processing means are arranged for changing the value of the conditional access message if the string differs from the previous string corresponding to said conditional access message. In conditional access systems often a changing control word is transmitted at regular intervals. In the receiver the received signal is filtered using the expected value of the next conditional access control word. To obtain the expected value of the next conditional control word, the receiver comprises a state machine which stores the conditional access control words in dependence of the state of said state machine. If the state machine is to be initialized at the beginning of transmission, the first conditional access control word is received, and via a table stored in the receiver the corresponding state of the state machine is found. Subsequently the state machine is forced into the state corresponding to the received conditional access control word. It may happen that in the time required for initializing the state machine, already a next conditional access control word is received, leading to a wrong state of the state machine. By filtering only conditional access control words having a value different from the previous value, the state machine can completely be dispensed with resulting in a substantially increased reliability of the system.
REFERENCES:
patent: 5477263 (1995-12-01), O'Callaghan et al.
patent: WO9720413 (1997-06-01), None
MPEG-2, DVB, JSAT Transport Demultiplexer, Preliminary Technical Manual published by LSI Logic under document No. DB14-000007, Draft Jul. 30, 1996, pp. 4-12-4-15.
Biren Steven R.
Felber Joseph L.
U.S. Philips Corporation
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