Cellular spacecraft TDMA communications system with call interrupt coding system for maximizing traffic throughput

• US 5,717,686 A
• Filed: 01/21/1997
• Issued: 02/10/1998
• Est. Priority Date: 01/21/1997
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Schiavoni, Maryanne Theresa
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): VU, HUY DUY
• Application Number:
  US08/786,599
• Time in Patent Office: 385 Days
• Field of Search: 370/528, 370/527, 370/522, 370/523, 370/310, 370/315, 370/316, 370/321, 370/324, 370/319, 370/322, 370/326, 370/345, 370/347, 370/431, 370/436, 370/442, 370/433, 370/458, 370/350, 370/252, 370/465, 370/503, 370/509, 370/473, 370/472, 370/470, 370/476, 370/478, 370/241, 370/242, 370/243, 371/47.1, 371/48, 371/30, 371/37.1, 371/37.2, 371/37.4, 371/37.7, 371/43, 371/44, 371/45, 371/46, 455/11.1, 455/12.1, 455/13.1, 455/13.2, 455/13.3
• US Class Current: 370/321
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]
• CPC Class Codes: H04J 3/125 One of the channel pulses or the synchronisation pulse is also used for transmitting monitoring or supervisory signals

Abstract

Improved throughput is provided in a spacecraft TDMA cellular communications system by in-call signalling without the need for flag bits, while still allowing the in-call signaling to be differentiated from other traffic. The terrestrial locations include mobile user terminals and gateways which provide connections to the land telephone line system. The spacecraft includes a transmitter and receiver, and an antenna which forms a plurality of spot beam footprints, in which the terrestrial terminals are located. Each of the terrestrial terminals transmits signals to, and receives signals from, the spacecraft. Each of the terrestrial terminals includes an encoder/decoder, for encoding at least call maintenance control signals, for temporarily interrupting the traffic signals to allow another action. The control signals may have bit content which exceeds the bit-carrying capability of the TDMA bursts, so transmission of the control signals must extended over a plurality of bursts.

Claims

1. A spacecraft TDMA cellular communications system, for communicating traffic signals between disparate terrestrial locations, said system comprising:

a spacecraft including transmitting and receiving means, and an antenna arrangement coupled to said transmitting and receiving means, for forming a plurality of spot beams, each of which defines a footprint, which footprints of said spot beams may partially overlap;

a plurality of terrestrial terminals, some of which may be mobile user terminals, at least some of said terrestrial terminals being located in said footprints, each of said terrestrial terminals being for transmitting electromagnetic signals to said spacecraft within a predetermined first frequency band, and for receiving electromagnetic signals within a second frequency band, different from said first frequency band, each of said terrestrial terminals further including encoding/decoding means, for encoding control signals to generate encoded control signals including at least call maintenance control signals, which call maintenance signals are for interrupting said traffic signals, said terrestrial terminals also transmitting said encoded control signals to another one of said terrestrial terminals by way of said electromagnetic signals, and for decoding received encoded control signals, wherein said control signals may have bit content which exceeds the bit carrying capability of the TDMA bursts of said communications system, whereby transmission of said control signals must extend over a plurality of said bursts, said encoding/decoding means encoding said control signals by dividing said control signals into a plurality of equal-content portions, and encoding each of said equal-content portions for transmission on a single burst rather than on a set of multiple bursts;

a network control system coupled to said terrestrial terminals, for controlling the timing of TDMA burst signals transmitted between said terrestrial stations by way of said spacecraft;

each of said terrestrial terminals including means for inserting said call maintenance signals into said burst only when a call is to be interrupted, whereby bits are allocated to said call maintenance signals only when a call is to be interrupted, and not otherwise, whereby no interrupt flag signals are used in a burst, which thereby makes more bits in each burst available for traffic, to thereby increase the traffic throughput, and whereby the interrupt of current traffic by said call maintenance signal can be received on each burst rather than on a group of bursts;

said encoding/decoding means of said terminals including means for (a) further encoding said equal-content-portions with error correction codes to form error-corrected portions, whereby the length of each error-corrected portion is no greater than the bit-carrying capacity of a single TDMA slot, so that each slot may be independently decoded, thereby reducing the amount of memory required in decoding said control signal, (b) at said decoder of said encoder/decoder, error correcting said error-corrected portions individually within each TDMA slot to produce decoded equal-content portions, (c) at said decoder of said encoder/decoder, examining symmetries in said decoded equal-content portions to determine the presence of said call maintenance control signals, and for (d) routing said decoded equal-content portions in accordance with one of the presence and absence of said call maintenance control signals.

2. A system according to claim 1, wherein said encoding/decoding means further comprises means for adding error detection codes to said call maintenance signal prior to division into said equal portions, to identify errors in the call maintenance message which are not corrected by said error correction codes.