Data scrambling system and method and communications system incorporating same

• US 5,917,852 A
• Filed: 06/11/1997
• Issued: 06/29/1999
• Est. Priority Date: 06/11/1997
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Gibson, L Andrew Jr., Steagall, R William, Griffin, Dan M, Perkins, Steven B, Giallorenzi, Thomas R, Butterfield, Lee A, Harris, Johnny M
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): Corrielus, Jean B
• Application Number:
  US08/873,538
• Time in Patent Office: 748 Days
• Field of Search: 375/200, 375/206, 375/207, 375/208, 375/261, 375/285, 375/254, 375/377, 380/6, 380/9, 380/21, 380/43, 380/44, 380/46, 370/310, 370/320, 370/335, 370/342
• US Class Current: 375/141
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

Users or subscribers of a multi-user communications system, such as a spread spectrum communications system, provide signals to the central station or base unit of that system, and receive signals therefrom. Avoidance of interference among those users'"'"' signals is needed to ensure proper operation of the system. To do so, the data of each user is individually scrambled to randomize the data that different users are transmitting, in order to improve tracking performance at a receiver. The data of each user is scrambled independently, in a manner unique to that user in the system, in order to improve tracking performance and detection performance of a receiver. This scrambling makes the multi-user interference zero mean, and makes it possible to integrate out or average out the multi-user interference. The pattern or sequence used for this scrambling, and the pattern or sequence used for spreading here, are preferably identical except in frequency.

Claims

1. A data processor, comprising:

means for scrambling a data stream to produce a scrambled data stream; and

means for spreading the scrambled data stream;

wherein said scrambling means scrambles the data stream at a symbol rate using a predetermined code to reduce multi-user interference resulting from a transmission of correlated data, and wherein said spreading means spreads the scrambled data stream at a chip rate using the same predetermined code.

2. A method for communicating information signals between at least one radio base unit and a plurality of subscriber units, wherein the at least one base unit and each of the plurality of subscriber units is comprised of a transmitter and a receiver for communicating therebetween using a synchronous code division multiple access technique, the method comprising the steps of:

at a source of a communication, scrambling an information signal at a symbol rate with a scrambling pattern that uniquely identifies one of the plurality of subscriber units and that is predetermined to reduce multi-user interference resulting from a transmission of correlated data;

spreading with a spreading code the scrambled information signal at a chip rate over at least a portion of an available transmission bandwidth to produce a spread communication signal;

transmitting the spread communication signal to a channel;

at a destination of the communication, receiving the spread communication signal from the channel; and

despreading and descrambling the received communication signal to obtain the information signal,

wherein

the scrambling pattern and the spreading code both use substantially the name bit pattern.

3. A method for communicating information signals as set forth in claim 2, wherein the scrambling pattern is comprised of series of bits unique for each of the plurality of subscriber units.

4. A method for communicating information signals as set forth in claim 2, wherein the step of scrambling the information signal further comprises the steps of:

providing the scrambling pattern comprised of a series of bits; and

multiplying the information signal with the series of bits to produce the communication signal.

5. A method for communicating information signals as set forth in claim 2, wherein the spreading code is a pseudonoise spreading code having a substantially orthogonal relationship to other pseudonoise spreading codes.

6. A method for communicating information signals as set forth in claim 5, wherein the scrambling pattern for a given one of said subscriber units is comprised of a pattern of bits that are substantially the same as a pattern of bits of the pseudonoise spreading code, and wherein a bit frequency of the scrambling pattern is substantially the same as a bit frequency of the information signal.

7. A method for communicating information signals as set forth in claim 2, wherein the information signal comprises a frame structure for conveying transmission data, the frame structure including a frame synchronization portion which indicates a beginning of a frame, a control portion, and a plurality of transmission data bytes.

8. A method for communicating information signals as set forth in claim 7, wherein the step of scrambling scrambles only the plurality of transmission data bytes within the frame structure.

9. A method for communicating information signals as set forth in claim 7, wherein the step of scrambling scrambles only the control portion and the plurality of transmission data bytes within the frame structure.

10. A method for communicating information signals as set forth in claim 7, wherein the method further comprises the steps of:

prior to the step of scrambling, convolutional encoding and puncturing the plurality of transmission data bytes; and

after the step of descrambling, Viterbi decoding the plurality of transmission data bytes within the frame structure.

11. A synchronous code division multiple access communication system, comprising:

at least one base unit having a transmitter and a receiver;

a plurality of subscriber units, each of said plurality of subscriber units having a transmitter and a receiver;

scrambling control circuitry for providing scrambling patterns which uniquely identify each of said plurality of subscriber units and which are predetermined to reduce multi-user interference resulting from a transmission of correlated data;

means within at least one of said base unit and said plurality of subscriber units for scrambling an information signal at a symbol rate with one of maid scrambling patterns which identifies one of said plurality of subscriber units to produce a communication signal for communicating between said base unit and one of said plurality of subscriber units;

means for spreading said communication signal at a chip rate with a predetermined spreading sequence that uniquely identifies one of said subscriber units; and

means within at least one of said base unit and said plurality of subscriber units for despreading and descrambling said communication signal to obtain said information signal, wherein

the scrambling pattern and the spreading sequence used for a same subscriber unit both use substantially the same bit pattern.

12. A communication system as set forth in claim 11, wherein said scrambling control circuitry provides said scrambling patterns that are comprised of series of bits unique for each of said plurality of subscriber units.

13. A communication system as set forth in claim 12, wherein said means for scrambling said information signal further comprises a multiplier for multiplying said information signal with said series of bits to produce said communication signal.

14. A communication system as set forth in claim 11, wherein said scrambling control circuitry is controlled by a state machine.

15. A communication system as set forth in claim 11, and further comprising:

spreading control circuitry for providing spreading sequences which uniquely identify each of said plurality of subscriber units; and

means for impressing upon said communication signal said spreading sequence which identifies an associated one of said plurality of subscriber units.

16. A communication system as set forth in claim 15, wherein a scrambling pattern for one of said plurality of subscriber units is comprised of a pattern of bits substantially the same as a bit pattern of said spreading sequence for said subscriber unit, and wherein a bit frequency of said scrambling pattern is substantially the same as a bit frequency of said information signal.

17. A communication system as set forth in claim 11, wherein said system further comprises:

a convolutional encoder for encoding said information signal; and

means for puncturing said encoded information signal, said means for puncturing having an input coupled to said convolutional encoder and an output coupled to said means for scrambling.

18. A communication system, comprising:

at least one base unit having a transmitter and a receiver;

a plurality of subscriber units, each of said plurality of subscriber units having a transmitter and a receiver;

scrambling control circuitry for providing scrambling patterns which uniquely identify each of said plurality of subscriber units;

means within at least one of said base unit and said plurality of subscriber units for scrambling an information signal with one of said scrambling patterns which identifies one of said plurality of subscriber units to produce a communication signal for communicating between said base unit and one of said plurality of subscriber units;

means for spreading said communication signal; and

means within at least one of said base unit and said plurality of subscriber units for despreading and descrambling said communication signal to obtain said information signal;

wherein said information signal comprises a frame structure for conveying transmission data, said frame structure includes a frame synchronization flag which indicates a beginning of a frame, a plurality of control bytes and a plurality of transmission data bytes, and wherein said means for scrambling said information signal further comprises;

synchronization control circuitry having a first input, a second input and an output, said first input receiving a frame synchronization signal, said second input receiving a clock signal, said synchronization control circuitry multiplexing said first and said second inputs to provide said frame synchronization flag and said plurality of control bytes at said output; and

a scrambler having a first input coupled to said scrambling control circuitry for receiving said one of said scrambling patterns, a second input coupled to said output of said synchronization control circuitry for receiving said frame synchronization flag and said plurality of control bytes, and a third input for receiving said plurality of transmission data bytes, said scrambler scrambling at least said plurality of transmission data bytes and combining said at least scrambled plurality of transmission data bytes, said first input, and said second input to provide said frame structure.

19. A communication system, comprising:

at least one base unit having a transmitter and a receiver;

a plurality of subscriber units, each of said plurality of subscriber units having a transmitter and a receiver;

scrambling control circuitry for providing scrambling patterns which uniquely identify each of said plurality of subscriber units;

means within at least one of said base unit and said plurality of subscriber units for scrambling an information signal with one of said scrambling patterns which identifies one of said plurality of subscriber units to produce a communication signal for communicating between said base unit and one of said plurality of subscriber units;

means for spreading said communication signal; and

means within at least one of said base unit and said plurality of subscriber units for despreading and descrambling said communication signal to obtain said information signal;

wherein said information signal comprises a frame structure for conveying transmission data, said frame structure includes a frame synchronization flag which indicates a beginning of a frame, a plurality of control bytes and a plurality of transmission data bytes, and wherein said means for scrambling said information signal further comprises;

synchronization control circuitry having a first input, a second input and an output, said first input receiving a frame synchronization signal, said second input receiving a clock signal, said synchronization control circuitry multiplexing said first and said second inputs to provide said frame synchronization flag and said plurality of control bytes at said output; and

a scrambler having a first input coupled to said scrambling control circuitry for receiving said one of said scrambling patterns, a second input coupled to said output of said synchronization control circuitry for receiving said frame synchronization flag and said plurality of control bytes, and a third input for receiving said plurality of transmission data bytes, said scrambler scrambling at least said plurality of transmission data bytes and said plurality of control bytes and combining said at least scrambled plurality of transmission data bytes and scrambled plurality of control bytes, said first input, and said frame synchronization flag to provide said frame structure.

20. A synchronous code division multiple access communication system, comprising:

at least one base unit having a transmitter and a receiver;

a plurality of subscriber units, each of said plurality of subscriber units having a transmitter and a receiver;

a data source providing data for transmission within at least one of said base unit and said plurality of subscriber units;

means for encoding said data source to provide in-phase and quadrature-phase channels each comprised of a bit stream having a frequency of bit occurrence;

a scrambling circuit for scrambling at a symbol rate each of said in-phase channels and said quadrature-phase channels with scrambling sequences; and

a spreading circuit for spreading each of said scrambled in-phase channels and said scrambled quadrature-phase channels at a chip rate with spreading sequences;

wherein within said at least one of said base unit and said plurality of subscriber units, said transmitter transmits said spread, scrambled in-phase channels and said spread, scrambled quadrature-phase channels, wherein

the scrambling patterns and the associated spreading sequences both use substantially the same bit pattern.

21. A communication system as set forth in claim 20, wherein said means for encoding further comprises:

a convolutional encoder for encoding said data to provide encoded in-phase and quadrature-phase channels; and

means for puncturing said encoded in-phase and quadrature-phase channels to provide punctured, encoded in-phase and quadrature-phase channels.

22. A communication system as set forth in claim 21, wherein said system further comprises means within at least one of said base unit and said plurality of subscriber units for despreading, descrambling, depuncturing and decoding said transmitted punctured, encoded, spread, and scrambled in-phase and quadrature-phase channels to obtain said data.

23. In a synchronous code division multiple access communications system having at least one central transceiver and a plurality of subscriber unit transceivers, a method for reducing multi-user interference resulting from a simultaneous transmission of correlated data, comprising steps of:

in a subscriber unit transceiver that is transmitting data to the central transceiver, the transmitted data being spread at a chip rate with a pseudonoise (PN) spreading sequence unique to that subscriber unit, first performing steps of,

encoding the data to be transmitted; and

multiplying the encoded data at a symbol rate with the same PN sequence that is used to spread the transmitted data at the chip rate to produce scrambled data, thereby decorrelating the data from data being transmitted by another subscriber unit transceiver;

then

spreading the scrambled data with the PN sequence at the chip rate; and

up-converting the spread data to a transmission frequency.

24. A method as in claim 23, wherein the data is transmitted in frames having a predetermined duration, each frame comprising a synchronizing portion, a control portion and a data portion, and wherein the step of multiplying operates to generate the scrambled data only from the data portion.

25. A method as in claim 23, wherein the data is transmitted in frames having a predetermined duration, each frame comprising a synchronizing portion, a control portion and a data portion, and wherein the step of multiplying operates to generate the scrambled data only from the control portion and the data portion.

26. A method as in claim 23, wherein the data is transmitted in frames having a predetermined duration, wherein the PN sequence has a predetermined length with a beginning and an end, and wherein at a start of each frame the step of multiplying begins multiplying at the beginning of the PN sequence.