Spread spectrum conferencing communication system

• US 4,317,204 A
• Filed: 06/04/1976
• Issued: 02/23/1982
• Est. Priority Date: 06/04/1976
• Status: Expired due to Term

• Current Assignee: E-Systems Incorporated (Rtx Corporation)
• Original Assignee: NCR Corporation (NCR Voyix Corporation)
• Inventors: Sanders, David E., Chambers, Ramon P., Gordy, Robert S.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/693,036
• Time in Patent Office: 2,090 Days
• Field of Search: 325/65, 325/473, 325/474, 325/303, 325/304, 325/323, 325/435, 179/15 AQ, 179/41 A, 179/41 R, 375/1, 370/18, 370/107
• US Class Current: 375/150
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04K 3/25 based on characteristics of target signal or of transmission as countermeasure against surveillance H04K3/827, e.g. using direct sequence spread spectrum or fast frequency hopping spread spectrum techniques H04B1/69

Abstract

An anti-jam PN sequence spread spectrum conferencing communication system is disclosed for simultaneously transmitting and receiving in a plurality of communications channels secure voice communications. All received messages are modulated with the same pseudo noise sequence and arrive at any given channel at random time states, wherein the messages are separated, separately processed and finally conferenced, using a technique based upon the correlation of the PN sequence and dependent upon the randomness of the epoch state of a given PN sequence coded with a message in relation to the other coded messages.

Claims

1. A multiple subscriber random access spread spectrum conferencing communication system comprising:

means for receiving spread spectrum messages in a plurality of channels;

means for detecting said messages and for generating a first signal in each channel in response thereto;

correlation means associated with each channel for correlating said messages with a pseudonoise sequence and for generating a control signal in response thereto;

multiplexing means for assigning a particular channel to said message when said first signal and said control signal in one channel are time coincident and for locking out said other channels not having said time coincidence from said message; and

means associated with each of said channels for decoding said message.

2. A system in accordance with claim 1 wherein said multiplexing means is a time multiplexer.

3. A system in accordance with claim 1 further comprising:

priority means for assigning subsequently received messages to said other channels.

4. A system in accordance with claim 1 wherein said plurality of channels is a number greater than or equal to two and less than or equal to six.

5. A system in accordance with claim 1 wherein said spread spectrum comprises a short repeating PN code.

6. A system in accordance with claim 1 wherein said spread spectrum comprises a long non-repeating sequence.

7. A system in accordance with claim 1 wherein said means for receiving spread spectrum messages includes an IF power splitter for receiving a wideband IF input.

8. A system in accordance with claim 7 wherein said correlation means comprises a correlation mixer for removing the PN code from said wideband messages and for producing a correlated narrowband output.

9. A system in accordance with claim 1 wherein said means for detecting said messages comprises a digital transversal correlator having a processing gain proportional to the product of the bandwidth of the spread spectrum and the correlation period in time.

10. A system in accordance with claim 9 wherein said first signal is a pulse;

and

means for coupling said pulse to said time multiplexing means.

11. A system in accordance with claim 10 wherein said time multiplexing means comprises:

an epoch detector for detecting a particular state of said PN generator associated with said channel; and

having an output when said state is coincident with a predetermined message state;

channel lock detector means for indicating the coincidence of a transversal correlator output and an epoch detector output; and

a priority circuit for assigning a particular channel to said message in response to said channel lock detector indication.

12. A system in accordance with claim 9 wherein said priority circuit includes:

a message selector circuit in each channel multiplexed in time with respect to the other channel message selectors; and

a forbidden time slot generator for comparing said epoch detector outputs in each channel with said message selector outputs to lock out all channels to which said message is not assigned, the assigned channel comprising the channel having an epoch detector output during its multiplexed time slot.

13. A system in accordance with claim 1 wherein said decoder is a PSK decoder.

15. A receiver in accordance with claim 13 further comprising:

combining means for simultaneously processing said messages from said channels at voiceband.

14. A multiple channel spread spectrum receiver for conferencing incoming PN coded spread spectrum messages in a plurality of channels, each channel comprising:

correlation means for despreading said messages;

means for detecting the instantaneous state of said PN code and having an output;

parallel correlation means for detecting said messages and having an output;

means responsive to the outputs of said last two mentioned means when said outputs are coincident in time for gating said message into one channel only and inhibiting said other channels from processing said message; and

means for assigning channel priority for later received messages in said inhibited channels.