Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-01-30
2001-05-08
Marcelo, Melvin (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S514000
Reexamination Certificate
active
06229826
ABSTRACT:
BACKGROUND OF THE INVENTION
According to ITU Standard G. 728, encoded voice signals are transmitted in packet-oriented fashion in PCM-oriented, multiplexed data streams. A packet thereby respectively comprises 10 bits (625 &mgr;s) or, respectively, one PCM data word (125 &mgr;s). For example, four data streams representing compressed encoded voice signals are multiplexed in PCM data words in a multiplexed, serial data stream. This means that 2 bits for the respective packet-oriented data stream are transmitted in each PCM data word according to G. 728, whereby a packet (10 bits) is formed of 5 sub-packets of 2 bits each.
Further, predetermined bit patterns, i.e. synchronization words are inserted into every data stream according to the ITU Recommendation G. 728. The bits of the bit pattern or of the synchronization words are continuously inserted into every n
th
packet of the data stream—for example into every 16
th
packet or G. 728 data word. When a predetermined bit pattern or synchronization word is formed by m bits, for example 4 bits, then a predetermined bit pattern or synchronization word is transmitted after n×m×10 (packet length) bits of a packet-oriented data stream; given a word width of 4 bits and a repetition rate of 16 packets (of 10 bits each), a synchronization word is transmitted after 640 bits of the packet-oriented data stream.
In multiplexed data streams, at least one bit is allocated to a data stream in the respective packet. For example, four data streams encoded according to G. 728 are combined to form a multiplexed, PCM-oriented data stream. Respectively 2 bits (sub-packet) of a packet are thereby allocated to the respective PCM-oriented data stream. The individual bits of the synchronization word are thereby transmitted in the first bit, i.e. the “most significant bit”.
SUMMARY OF THE INVENTION
An object of the invention is to find synchronization words in serial, packet-oriented and potentially multiplexed data streams in the shortest time.
According to a method of the present invention for searching a bit pattern formed by m predetermined bits in a serial, packet-oriented data stream where m≧1, bits of the bit pattern being continuously inserted into every n
th
packet of the data stream, where n≧1, one bit of bits of the serial data stream that are acquired and comprise n packets is stored in a memory cell of allocated memories that are m memory cells wide, the memory cell representing a bit position within n packets, whereby the number of memories is determined by n×number of bits per packet. The memories are checked for the presence of a bit pattern. Upon recognition of a bit pattern in one of the memories, the bit position of the bit pattern in the serial data stream is defined by this. Given multiplexed, packet-oriented data streams, an identical number of successive bits is allocated to each data stream in each multiplexed packet, whereby the bits of the bit patterns are inserted into every n
th
packet of the respective data stream. Upon recognition of a bit pattern in one of the memories allocated to a data stream, the bit position of the respective bit pattern in the multiplexed, serial data stream is defined by this.
According to an advantageous development of the method of the invention given x (x≧1) successive bits (sub-packet) of a packet of a data stream in a multiplexed packet, respectively one predetermined bit of the x bits is stored in an allocated memory that is m memory cells wide, whereby the respectively predetermined bit of x successive bits with in the multiplexed packets is copied into a memory cell of the memory that is m memory cells wide. This technique is particularly advantageous given synchronous words whose bits are respectively inserted at the beginning of a packet. Particularly given multiplexed bit streams, the bits that follow the first bit of a sub-packet of a data stream in the respective, multiplexed packet are no longer investigated, i.e. stored and evaluated.
According to a first version, bit patterns (SW) recognized in a memory after respectively n×m packets of the respective data stream are counted by a counter reading of a first counter unit allocated to the memory and are defined as a recognized bit pattern after a predetermined plurality of recognized bit patterns. A multiple locating of predetermined bit patterns or synchronization words in the data streams can be avoided with this technique.
According to a more advantageous, further version, a recognition of a bit pattern after respectively n×m packets of the respective data stream is counted by a corresponding allocated counter reading of a first counter unit. Given a non-recognition of the corresponding bit pattern, the corresponding counter reading of the first counter unit is reset, and the appertaining bit pattern or synchronization word is defined as recognized bit pattern or synchronization word when a predetermined number of a recognized bit patterns is reached. The dependability in view of the recognition of a predetermined bit pattern or synchronization word in a data stream is considerably enhanced by this technique. This is achieved in that the counter is reset, i.e. set back to an initial value, even given a one-time non-recognition of a bit pattern. When a predetermined number of recognized bit patterns occur in the respective data stream, then the predetermined number is to be increased. The dependability of recognizing a predetermined bit pattern or synchronization word is enhanced further by the increase of the predetermined number.
The method of the invention is explained in greater detail below on the basis of two block circuit diagrams and a flowchart.
REFERENCES:
patent: 4847877 (1989-07-01), Besseyre
patent: 5742647 (1998-04-01), Chaisemartin
International Telecommunication Union—CCITT—Recommendation G.728—Coding of Speech At 16 kbit/s Using Low-Delay Code Excited Linear Prediction—Geneva 1992.
Egler Gerhard
Lenger Manfred
Marcelo Melvin
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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