Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-01-21
2001-05-08
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S756000
Reexamination Certificate
active
06230298
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system and method for the transmission and reception of digital messages. The invention particularly relates to a system and method employing a telecommunications link. In greatest particularity, the present invention relates to a system and method for conveying messages in satellite communications.
BACKGROUND OF THE INVENTION
Digital Messages comprise a sequence of binary digits conveying information. The binary digits are transmitted, in sequence, and received in sequence, to reconstruct the original digital message.
Digital Messages are extensively used for conveying data from one point to another. The digital message is modulated onto a carrier frequency which is then conveyed by a telecommunications channel to the receiving point where the modulated carrier is demodulated to recover the original digital message.
While transmission via, cable and telephone lines is generally of high quality and requires no particular sophistication beyond that already stated, many situations exist where the viability of the communications link is marginal and where the digital message must be conveyed under circumstances which are less than ideal.
One such environment is in satellite communications. A user terminal, perhaps in the form of a telephone handset, is in radio contact with a satellite which, in turn, conveys messages to and from the user terminal respectively from and to an earth station. There are circumstances where the satellite finds difficulty in establishing radio contact with the user terminal. The user terminal may be shielded by buildings, locked within a motor vehicle or in a desk, or unavailable for a host of other reasons. None the less, it is a function of a satellite communications system periodically to poll user terminals to determine their location or to instruct the user terminal to re-register with the satellite communication system as soon as radio contact with the satellite can be established. In order to achieve this purpose, the satellite sends a digital message, to the user terminal, at higher power than would be employed in normal communications. This is known as high power notification. There is a limit to the amount of power that a satellite can devote to attempting to poll a particular user terminal. While it is desirable to use as much available power as one can, there is a limit. Another approach is to use the available bandwidth to best effect and to ensure and improve the reliability of the decoding of the digital message.
SUMMARY OF THE INVENTION
The present invention does not concern itself with the particular contents of a digital message. The invention is directed solely towards ensuring that the available bandwidth and decoding capacity are used to best advantage.
When sending a digital message, especially a short digital message as is desirable when using limited high power, there is a problem that a true spread spectrum signal is not generated. A spread spectrum signal best utilises the available bandwidth. However, short recursive messages tend to produce spectral peaks such that the signal transmitted, instead of appearing to have a largely flat spectrum across the available bandwidth, as is desirable with a true spread spectrum system, exhibits, instead, a finite number of spectral peaks which fail best to utilise the available bandwidth.
The present invention concerns itself with a method and system for sending digital messages, particularly short digital messages, while avoiding the generation of spectral peaks and while adapting the spectrum of the digital message to be closer to the ideal, flat spread spectrum.
According to a first aspect, the present invention consists in a method for transmitting a digital message, said digital message comprising an ordered sequence of binary message digits, said method including the steps of: rearranging said ordered sequence of binary message digits into a re-ordered sequence where no binary message digit in said re-ordered sequence is adjacent to any binary message digit whereto it was adjacent in said ordered sequence; dividing said re-ordered sequence into a plurality of smaller elements; selecting each of said smaller elements, in turn; and repeatedly transmitting each selected smaller element, according to the sequentially ordered digits of a preferred binary polynomial, selecting each ordered binary digit in said binary polynomial in turn, and selectively, as an ordered sequence of binary signals, transmitting either the logically uninverted form or the logically inverted form of the selected smaller element according to the logical polarity of the selected digit of the binary polynomial, until each ordered binary digit of the binary polynomial has been selected.
According to a second aspect, the present invention consists in a method for receiving a digital message, for use in conjunction with the first aspect of the invention, including the steps of; receiving said sequence of binary signals; employing the sequence of binary terms of said preferred polynomial to separate said sequence of binary signals into a plurality of supposedly identical smaller elements; correcting any errors between said plurality of supposedly identical smaller elements to create a corrected smaller element; assembling all of said plurality of smaller elements as a plurality of said smaller corrected elements into said re-ordered sequence; and deriving said ordered sequence from said re-ordered sequence.
According to a third aspect, the present invention consists in an apparatus for transmitting a digital message, said digital message comprising an ordered sequence of binary message digits, apparatus being operative to rearrange said ordered sequence of binary message digits into a re-ordered sequence where no binary message digit in said re-ordered sequence is adjacent to any binary message digit whereto it was adjacent in said ordered sequence; wherein said apparatus is operative to divide said re-ordered sequence into a plurality of smaller elements; wherein said apparatus is operative to select each of said smaller elements, in turn; and repeatedly to transmit each selected smaller element, according to the sequentially ordered digits of a preferred binary polynomial, selecting each ordered binary digit in said binary polynomial in turn, and selectively, as an ordered sequence of binary signals, transmitting either the logically uninverted form or the logically inverted form of the selected smaller element according to the logical polarity of the selected digit of the binary polynomial, until each ordered binary digit of the binary polynomial has been selected.
According to a fourth aspect, the present invention consists in an apparatus for receiving a digital message, for use in conjunction with apparatus according to the third aspect, operative to receive said sequence of binary signals; operative to employ the sequence of binary terms of said preferred polynomial to separate said sequence of binary signals into a plurality of supposedly identical smaller elements; operative to correct any errors between said plurality of supposedly identical smaller elements to create a corrected smaller element; operative to assemble all of said plurality of smaller elements as a plurality of said smaller corrected elements into said re-ordered sequence; and operative to deriving said ordered sequence from said re-ordered sequence.
The apparatus may be operative to rearrange said ordered sequence of binary message digits by assembling said ordered binary digits as the sequential elements of sequential rows of a matrix and by taking the ordered elements of sequential columns of said matrix as said re-ordered sequence. The apparatus may take, as said smaller elements, the sequences of said message binary digits in each of said columns of said matrix. The preferred binary polynomial may be a PN sequence or an m-sequence or an alternating binary digits of mutually inverse logical polarity.
The apparatus may be operative to employ, as said digital message a first digita
De'cady Albert
ICO Services Ltd
Lamarre Guy
McDermott & Will & Emery
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