Method and apparatus for communicating variable length messages between a primary station and remote stations of a data communications system

{
  "publication_number": "US4519068A",
  "country": "US",
  "kind": "A",
  "title": "Method and apparatus for communicating variable length messages between a primary station and remote stations of a data communications system",
  "abstract": "A data communications system is described in which variable length messages are communicated between a general communications controller (GCC) and a plurality of portable and mobile radios. The variable length messages include a bit synchronization field, a message synchronization field and a plurality of channel data blocks for efficiently and reliably handling long strings of data or text. Each channel data block includes an information field, a parity field for error-connecting the information field and a channel state field indicating whether or not the radio channel is busy or free. The GCC is coupled to a cellular arrangement of channel communications modules (CCM's), which each include a radio transmitter and/or radio receiver. The mobile and portable radios communicate with the GCC by way of the CCM's.",
  "claims": [
    "1. A signalling system for communicating messages via a communications medium between a primary station and a plurality of remote stations in a data communications system, said signalling system including a variable length message which is transmitted between an originating station and received by at least one destination station and is comprised of: a bit synchronization field; a message synchronization field; and a plurality of channel data blocks being comprised of: said first channel data block including: an information field including at least one command, a station address and a check word coded from the command and station address; and a parity field coded from the information field according to a predetermined code; the bits of the fields being interleaved such that consecutive bits of a field are separated by a predetermined number of bits; said second channel data block including: an information field including a block count; a message sequence number incremented for each message and a check word coded from the block count and message sequence number; and a parity field coded from the information field according to a predetermined code; the bits of the fields being interleaved such that consecutive bits of a field are separated by a predetermined number of bits; and said third and following channel data blocks each including: an information field including data; and a parity field coded from the information field; the bits of the fields being interleaved such that consecutive bits of a field are separated by a predetermined number of bits; and the information field of the last channel data block further including a check word coded from the data in the information field of the third and following channel data blocks.",
    "2. A method for use in a signalling system for communicating messages via a communications medium between a primary station and a plurality of remote stations in a data communications system, said signalling system including a variable length message which is transmitted between an originating station and received by at least one destination station, said method for producing the variable length message comprised of the steps of: producing a bit synchronization field; producing a message synchronization field; and producing a plurality of channel data blocks; for said first channel data block, producing an information field including at least one command, a station address and a check word coded from the command and station address; coding a parity field from the information field according to a predetermined code; and interleaving the bits of the fields such that consecutive bits of a field are separated by a predetermined number of bits; and for said second channel data block, producing information field including at least a block count, a message sequence number incremented for each message and a check word coded from the block count and message sequence number; coding a parity field from the information field according to a predetermined code; and interleaving the bits of the fields such that consecutive bits of a field are separated by a predetermined number of bits; for said third and following channel data blocks, producing an information field including data; coding a parity field from the information field; and interleaving the bits of the fields such that consecutive bits of a field are separated by a predetermined number of bits; and for the information field of the last channel data block, coding a check word from the data in the information field of the third and following command data blocks.",
    "3. A signalling system for communicating messages via a communications medium between a primary station and a plurality of remote stations in a data communications system, said signalling system including a variable length message which is transmitted between an originating station and received by at least one destination station and is comprised of: a bit synchronization field; a message synchronization field; and a plurality of channel data blocks being comprised of: said first channel data block including: an information field including at least one command, a station address and a check word coded from the command and station address; a parity field coded from the information field according to a predetermined code; and a channel state field dynamically changing to indicate whether the communications medium is busy or free; the bits of the fields being interleaved such that consecutive bits of a field are separated by a predetermined number of bits; said second channel data block including: an information field including at least a block count; a message sequence number incremented for each message and a check word coded from the block count and message sequence number; a parity field coded from the information field according to a predetermined code; and a channel state field dynamically changing to indicate whether the communications medium is busy or free; the bits of the fields being interleaved such that consecutive bits of a field are separated by a predetermined number of bits; and said third and following channel data blocks each including: an information field including data; a parity field coded from the information field; and a channel state field dynamically changing to indicate whether the communications medium is busy or free; the bits of the fields being interleaved such that consecutive bits of a field are separated by a predetermined number of bits; and the information field of the last channel data block further including a check word coded from the data in the information field of the third and following channel data blocks.",
    "4. A method for use in a signalling system for communicating messages via a communications medium between a primary station and a plurality of remote stations in a data communications system, said signalling system including a variable length message which is transmitted between an originating station and received by at least one destination station, said method for producing the variable length message comprised of the steps of: producing a bit synchronization field; producing a message synchronization field; and producing a plurality of channel data blocks; for said first channel data block, producing an information field including at least one command, a station address and a check word coded from the command and station address; coding a parity field from the information field according to a predetermined code; dynamically producing a channel state field to indicate whether the communications medium is busy or free; and interleaving the bits of the fields such that consecutive bits of a field are separated by a predetermined number of bits; and for said second channel data block, producing an information field including at least a block count, a message sequence number incremented for each message and a check word coded from the block count and message sequence number; coding a parity field from the information field according to a predetermined code; dynamically changing a channel state field to indicate whether the communications medium is busy or free; and interleaving the bits of the fields such that consecutive bits of a field are separated by a predetermined number of bits; for said third and following channel data blocks, producing an information field including data; coding a parity field from the information field; dynamically changing a channel state field to indicate whether the communications medium is busy or free; and interleaving the bits of the fields such that consecutive bits of a field are separated by a predetermined number of bits; and for the information field of the last channel data block, coding a check word from the data in the information field of the third and following command data blocks.",
    "5. A remote station having a pre-assigned remote station address, for receiving variable length messages via a communications medium from a primary station in a data communications system, said variable length messages including a bit synchronization field, a message synchronization field, and a plurality of channel data blocks, each channel data block including an information field, a parity field coded from the information field according to a predetermined code and a channel state field dynamically changing to indicate whether or not the communications medium is busy or free, the information field of the first channel data block including a remote station address and a command, and the information field of the second channel data block including a block count indicating the number of following channel data blocks, said remote station comprising: means for receiving variable length messages from the communications medium; means for transmitting variable length message via the communications medium to the primary station; register means for storing data; memory means for storing data; and processing means responsive to the channel state field in the received variable length messages for inhibiting transmissions by said transmitting means when the channel state field indicates that the communications medium is busy and responsive to the parity field for error-correcting the information field of each received variable length message, said processing means further being responsive to detection of the pre-assigned remote station address in the error-corrected information field for executing the command therein, error-correcting and storing the block count of the information field of the second received channel data block in the register means, and error-correcting and storing the contents of the information field of the following received channel data blocks in the memory means until a number of channel data blocks substantially the same as the block count in the register means have been received.",
    "6. A method for receiving variable length messages communicated via a communications medium of a data communications system from a primary station to a remote station having a pre-assigned remote station address, said remote station including receiving means, transmitting means, register means and memory means, said variable length messages including a bit synchronization field, a message synchronization field, and a plurality of channel data blocks, each channel data block including an information field, a parity field coded from the information field according to a predetermined code and a channel state field dynamically changing to indicate whether or not the communications medium is busy or free, the information field of the first channel data block including a remote station address and a command, and the information field of the second channel data block including a block count indicating the number of following channel data blocks, said method comprising the steps of: receiving variable length messages from the communications medium; and inhibiting transmissions by said transmitting means when the channel state field of a received variable length message indicates that the communications medium is busy; error-correcting the information field of each received variable length message in response to the parity field; and in response to detection of the pre-assigned remote station address in the error-corrected information field, executing the command therein, error-correcting and storing the block count of the information field of the second received channel data block in the register means, and error-correcting and storing the contents of the information field of the following received channel data blocks in the memory means until a number of channel data blocks substantially the same is the block count in the register means have been received.",
    "7. The remote station according to claim 5, wherein said processing means applies variable length messages to the transmitting means.",
    "8. The remote station according to claim 5, wherein said processing means applies variable length messages to the transmitting means, said processing means dynamically changing the channel state field to indicate pre-selected status of said remote station.",
    "9. The remote station according to claim 5, wherein said processing means interleaves and applies bits of variable length messages to the transmitting means.",
    "10. The remote station according to claim 5, wherein said communications medium comprises a radio channel, said receiving means includes radio receiving means coupled to antenna means for receiving variable length messages from the radio channel, and said transmitting includes radio transmitting means coupled to the antenna means for transmitting variable length messages via the radio channel."
  ],
  "description_excerpt": "The present invention relates generally to radio communications systems, and more particularly to an improved method and apparatus for communicating variable length messages between a primary station and remote stations of a data communications system.\n\nIn prior art data communications sytems, as exemplified by the system described in U.S. Pat. No. 4,156,867, messages communicated from a central station to mobile stations included a start code followed by one or more data blocks each including a parity word and a number of digital words with a data and parity portions. No information is provided in the first or second block as to the number of following blocks, and no provision was made for efficiently and reliably accomodating long strings of data. The bits of the data block were interleaved so as to be more tolerant of burst errors. However, the interleaving scheme of these prior art data communications systems typically rendered blocks susceptible to the loss of either a group of data bits or a group of parity bits due to burst errors. Furthermore, simultaneous transmissions from two or more mobile stations could interfere with one another such that neither was adequately received by the central station.\n\nIt is an object of the present invention to provide an improved method and apparatus for communicating variable length messages between a primary station and remote stations of a data communications system.",
  "cpc": [
    "H04W 28/06"
  ],
  "ipc": [
    "H04W 28/06"
  ],
  "assignees": [
    "Motorola Inc"
  ],
  "inventors": [
    "Jay Krebs",
    "Thomas A. Freeburg"
  ],
  "filing_date": "1983-07-11",
  "publication_date": "1985-05-21",
  "grant_date": "1985-05-21",
  "priority_date": "1983-07-11",
  "application_number": "US-51280183-A",
  "family_id": "24040626",
  "cited_by_count": 236,
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}