SELF-SUPPORTING SIMPLEX PACKETS

• US 20080117952A1
• Filed: 11/07/2007
• Published: 05/22/2008
• Est. Priority Date: 11/17/2006
• Status: Active Grant

• Current Assignee: Comtech Mobile Datacom Corporation (Comtech Telecommunications Corporation)
• Original Assignee: Comtech Mobile Datacom Corporation (Comtech Telecommunications Corporation)
• Inventors: JORDAN, Luis G.
• Granted Patent: US 8,275,080 B2
• Time in Patent Office: Days
• US Class Current: 375/130
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 3/0608 Detectors therefor, e.g. correlators, state machines
• CPC Class Codes: H04L 1/0042 Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape H04L1/0067 takes precedence
• CPC Class Codes: H04L 1/0079 Formats for control data H04L1/16 takes precedence; training sequences H04L25/00 and H04L27/00

Abstract

Existing message fields and/or message parameters are configured to facilitate the packet and message synchronization and decoding tasks that conventionally rely upon a known bit sequence in each packet, thereby eliminating the need for a predefined message preamble in each packet. In example embodiments, the unique identifier of each transmitter is structured to facilitate determination of bit polarity and the start of each packet; packet sequence numbers use an unconventional counting sequence to assure synchronizing bit transitions; and so on. Other techniques, such as the use of run-length limited (RLL) message encoding, or 8b/10b encoding, to assure within-packet bit transitions, are also used to enhance clock synchronization and proper header location determination.

Claims

1. A method of encoding a packet at a transmitter, comprising:

creating a header of the packet,

creating a body of the packet that includes information that is to be transmitted by the transmitter, and

encoding the packet for transmission using a spreading code,

wherein

the header is configured to include a sequence of bit transitions that enables a receiver to determine a start of the packet without prior knowledge of the particular sequence of bit transitions.

2. The method of claim 1, wherein

the sequence of bit transitions corresponds to an identifier of the transmitter.

3. The method of claim 1, wherein

the sequence of bit transitions is configured to enable the receiver to determine a polarity of bits in the packet.

4. The method of claim 1, wherein

the sequence of bit transitions is configured to include a minimum number of transitions to enable synchronization of the receiver to the packet.

5. The method of claim 1, wherein:

the header of the packet includes a plurality of identifiers, and

the identifiers are configured to include a minimum number of transitions to enable synchronization of the receiver to the packet.

6. The method of claim 1, including

providing an error correcting sequence within the packet,

wherein the error correcting sequence is configured to include a minimum number of transitions to enable synchronization of the receiver to the packet.

7. The method of claim 6, wherein

the error correcting sequence is configured to enable the receiver to determine an end of the packet.

8. The method of claim 1, wherein

the sequence of bit transitions is based on a self-correcting code.

9. The method of claim 1, wherein

the body of the packet is encoded so as to include a minimum number of transitions to enable synchronization of the receiver to the packet.

10. The method of claim 1, wherein

the packet includes a polarity-independent encoding having a maximum span of non-transitions.

16. The method of claim 1, including

synchronizing a demodulation of the packet based on the sequence of bit transitions.

11. A method of decoding a packet that does not include a preamble of known bit values, comprising:

despreading the packet using a spreading code,

identifying a header of the packet that includes a sequence of bit transitions, and

identifying a body of the packet that includes information that has been transmitted by the transmitter,

wherein identifying the header includes identifying a start of the packet based on the sequence of bit transitions.

12. The method of claim 11, wherein

the sequence of bit transitions identifies a transmitter of the packet.

13. The method of claim 11, including:

determining a first bit transition rate based on transitions in the header,

identifying an end of packet sequence,

determining a second bit transition rate based on transitions in the end of packet sequence, and

estimating a bit transition rate for decoding bits in the body of the packet based on the first and second bit transition rates.

14. The method of claim 13, wherein

the end of packet sequence corresponds to an error correction code.

15. The method of claim 11, including

determining a polarity of bits in the packet based on the sequence of bit transitions.

17. A transmitter comprising:

a packet creator that is configured to;

create a header of a packet that includes a sequence of bit transitions that enables a receiver to determine a start of the packet without prior knowledge of the particular sequence of bit transitions, and

create a body of the packet that includes information that is to be transmitted by the transmitter, and

a spread-spectrum encoder that is configured to encode the packet for transmission using a spreading code.

18. The transmitter of claim 17, wherein

the sequence of bit transitions corresponds to an identifier of the transmitter.

19. The transmitter of claim 17, wherein

the sequence of bit transitions includes a minimum number of transitions to enable synchronization of the receiver to the packet.

20. The transmitter of claim 17, wherein

the packet creator is configured to create an error correcting sequence that includes a minimum number of transitions to enable synchronization of the receiver to the packet.

21. A receiver comprising:

a receive buffer that is configured to receive a composite signal,

a phase detector that is configured to detect a code-phase of a message that does not include a sequence of known bit values,

a demodulator that is configured to;

identify a header of the packet that includes a sequence of bit transitions,

identify a start of the packet based on the sequence of bit transitions, and

identify a body of the packet that includes information that has been transmitted by the transmitter.

22. The receiver of claim 21, wherein

the sequence of bit transitions identifies a transmitter of the packet.

23. The receiver of claim 21, wherein

the demodulator is configured to:

determine a first bit transition rate based on the bit transitions in the header,

identify an end of packet sequence,

determine a second bit transition rate based on transitions in the end of packet sequence, and

determine a bit transition rate for decoding bits in the body of the packet based on the first and second bit transition rates.

24. The receiver of claim 21, wherein

the demodulator is configured to determine a polarity of bits in the packet based on the sequence of bit transitions.

25. A system comprising:

a spread-spectrum receiver, and

a plurality of spread spectrum transmitters,

wherein

each transmitter is configured to transmit packets using a common spreading code, and

each packet includes a header that includes a sequence of bit transitions that enables a receiver to determine a start of the packet without prior knowledge of the particular sequence of bit transitions.