Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-04-21
2001-03-06
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
Reexamination Certificate
active
06198755
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a multiplexing/demultiplexing method, in particular for conveying a plurality of binary digital signals within a single higher rate binary digital signal and which does not require an alignment process at the receiving end in order to decompose the combined signal into its constituant parts and convey them to their correct destinations.
Known multiplexing/demultiplexing methods use a process often referred to as “alignment” in order to unambiguously identify the constituent parts of the combined signal. For example some multiplexing methods use bit or byte interleaving of the lower rate signals, and include in the transmitted signals some extra bits, e.g. those of a frame alignment word, parity coding, or carter coding. Other methods use block coding with parallel inputs and a serial output.
At the receiving end where demultiplexing is to take place the received signal must be disinterleaved or decoded and the start and finish of each frame or code block must be known. This is often referred to as “alignment”, a process which comprises searching in either serial or parallel form for correct alignment by counting the number of correct false and consecutive alignment positions as an aid to stopping or starting the search procedure, or otherwise deducing the start and finish of each frame or block from some property added to them by the multiplexing method. Known examples are the frame structures defined in ITU recommendations G.741 and G.751.
Another known method, which does not of necessity require that the transmitted rate is greater than the sum of the individual rates of the signals being multiplexed together, uses bit or byte interleaving, but depends upon at least one of the individual signals having a known property of its bit sequence which is different from the others, e.g. a frame word, so that it can be identified. This may be regarded as a special case of the method described previously in which extra bits are incorporated into one of the individual signals before multipexing. It still requires a process of alignment during demultiplexing.
SUMMARY OF THE INVENTION
This invention, in one aspect, provides a multiplexing/demultiplexing method comprising, during multiplexing, taking at least one bit from a time slot of each of a plurality of information data signals to form an information data sequence, combining the information data sequence with a fixed binary code to generate a combined data set, sequentially transmitting combined data sets as a signal and, during demultiplexing, analysing the combined data signal in blocks of length equal to that of a combined data set to derive the information data, the code being selected such that any block has, for each possible information data sequence, one of a set of unique values irrespective of the starting point of the block within the combined data signal.
By using the method, there is no need to incorporate any alignment procedures during demultiplexing.
The method enables two or more normally synchronous binary digital signals to be conveyed on a single higher rate binary digital signal whose rate is an integer multiple of the nominal rate of any of the individual signals. The method may also be employed where the individual signals at different rates, for example integer multiple signals of some lower rate, and the multiplexed signal rate is an integer multiple of the HCF (Highest Common Factor), otherwise known as the GCD (Greatest Common Divider), of all the individual signal rates. In such a case, during any time slot, different numbers of bits may be taken from each individual signal. Similarly the higher rate signal may only be a subsidiary signal being conveyed as part of a still higher rate signal using either the same or a different multiplexing method. As used herein “time slot” is a time during which an integer number of bits, preferably the lowest number, can be taken from each signal to be combined.
REFERENCES:
patent: 3912872 (1975-10-01), Callens
patent: 5062105 (1991-10-01), Mcknight et al.
patent: 5729535 (1998-03-01), Rostoker et al.
Kirschstein et al.
Kizou Hassan
Marconi Communications Limited
Mehra Inder Pal
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