Communication system and method with orthogonal block encoding

• US 6,215,762 B1
• Filed: 07/22/1997
• Issued: 04/10/2001
• Est. Priority Date: 07/22/1997
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): BOAKYE, ALEXANDER O
• Application Number:
  US08/898,392
• Time in Patent Office: 1,358 Days
• Field of Search: 370/203, 370/208, 370/209, 370/320, 370/335, 375/200, 375/1, 380/37
• US Class Current: 370/208
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence

Abstract

A communication system and method with orthogonal block encoding is provided. Encoded signals are transmitted by repeating transmissions of symbol blocks with a phase or sign change selected for each block from a sequence of phase or sign changes. Different symbols are transmitted using orthogonal sequences. The decoding uses different orthogonal sequences for separating the received encoded signals into corresponding separate channels. The orthogonal encoding is removed from the encoded transmitted signals and corresponding ones of the repeated symbols are added in successively received repeated blocks after the orthogonal encoding is removed. A transmitter uses a digital source encoder to encode information into symbols, and each symbol is repeated a preselected number of times to successively produce groups of repeated bits. Each repeat bit is changed in phase or sing by application of a sign or phase change determined by a selected assigned orthogonal code associated with the transmitter. The sign changed bits are interleaved from a number of such groups to successively generate a number of blocks, each composed of the different sign or phase changed bits of the preselected number of repeated groups and having a collective sign or phase change corresponding to a common sign change or phase shared by all bits of the block. The interleaved blocks then modulate a radio signal for transmission.

Claims

1. A spread spectrum communication system for transmitting information signals overlapping in time comprising:

a transmitter for transmitting said overlapping information signals, wherein each of said information signals is orthogonally encoded prior to transmission according to a different one of a set of mutually orthogonal coding sequences, said orthogonally encoded information signals comprising successively repeated blocks of information symbols having a modification factor applied to each repeated block, said sequence of modification factors applied to successive repeats of said information block forming one of said set of mutually orthogonal coding sequences; and

a receiver for receiving and decoding the orthogonally encoded information signals.

2. The communication system as recited in claim 1 wherein the receiver employs different orthogonal codes to separate the information signals from different transmitters into corresponding separate channels.

3. The communication system as recited in claim 1 comprising:

a memory for storing an orthogonal code; and

a phase shifter for responding to the stored orthogonal code for imposing a corresponding sequence of phase changes onto the repeated information blocks.

4. The communication system as recited in claim 1 wherein the receiver comprises:

an orthogonal block code remover for removing the orthogonal encoding from the encoded information signals; and

an adder for adding corresponding ones of the symbols in successively received repeated information blocks from the transmitter after the orthogonal encoding is removed by the orthogonal code remover to form a summed signal for each symbol within the repeated information blocks.

5. The communication system as recited in claim 4 comprising a transmitter for transmitting the repeated information blocks at a preselected rate and for adding symbols in successive ones of the repeated blocks.

6. The communication system as recited in claim 4 wherein the receiver comprises an equalizer for processing the summed signal from the adder to compensate for multipath propagation.

7. The communication system as recited in claim I comprising a digital source encoder for producing the symbols as digital bits of information.

8. The communication system as recited in claim 7 comprising:

bit repeater for repeating each bit of information produced by the digital source encoder a preselected number of times to successively produce groups of repeated bits;

sign imposer for selectively imposing a sign change on the repeated bits of each of a number of successive groups of repeated bits equal to the preselected number of bits in each group in accordance with an orthogonal code;

interleaver for interleaving the sign changed bits from the preselected number of groups to successively generate a number of blocks each composed of the different sign changed bits of the preselected numbers of repeated groups and having a collective sign change corresponding to a common sign change shared by all signed changed bits of the block; and

a signal modulator for transmitting a signal modulated in accordance with the generated information blocks with sign changes corresponding to the orthogonal code.

9. A spread spectrum communication system comprising:

a plurality of transmitters for transmitting mutually orthogonally encoded information signals overlapping in time, each transmitter applying a different on of a set of mutually orthogonal coding sequences, said orthogonally encoded signals including successively repeated blocks of information symbols having a modification factor applied to each repeated block, said sequence of modification factors applied to successive repeats of said information block forming one of said set of mutually orthogonal coding sequences; and

a receiver for receiving and decoding the orthogonally encoded information signals.

10. The communication system as recited in claim 9 wherein each of the transmitters comprises:

a memory for storing an orthogonal code; and

a responder responsive to the stored orthogonal code for imposing a corresponding sequence of phase changes onto the repeated information blocks.

11. The communication system as recited in claim 10 wherein the responder selectively imposes a 180°

phase shift onto the repeated information blocks in accordance with the stored orthogonal code.

12. The communication system as recited in claim 11 wherein the memory comprises a memory for storing a Walsh-Hadamard code having a number of bits equal to the number of times the transmitters repeatedly transmits the repeated information blocks.

13. The communication system as recited in claim 9 wherein the receiver comprises:

an orthogonal code remover for removing the orthogonal encoding from the encoded information signals; and

an adder for adding corresponding ones of the symbols in successively received repeated information blocks from one of the plurality of transmitters after the orthogonal encoding is removed by the orthogonal code remover to form a summed signal for each symbol within the repeated information blocks.

14. The communication system as recited in claim 13 wherein

the blocks of an information signal are transmitted at a preselected block repetition rate which results in a preselected repetition period;

and

the adder comprises another adder for adding the corresponding symbols in successive repeated information blocks which are separated from each other by an amount equal to the repetition period.

15. The communication system as recited in claim 14 wherein each of the transmitters comprises:

an orthogonal encoder for selectively imposing phase shifts to the repeated information blocks while being transmitted in accordance with an associated one of a plurality of the different orthogonal codes; and

the receiver comprises a block remover for removing each of the repeated information blocks received from each of the plurality of transmitters in accordance with the orthogonal code respectively associated with the transmitters being decoded before being applied to the adder.

16. The communication system as recited in claim 13 wherein each of the transmitters comprises:

an orthogonal encoder for selectively imposing phase shifts onto the repeated information blocks while being transmitted in accordance with an associated one of a set of different orthogonal codes; and

the receiver comprises a block remover for removing each of the repeated information blocks received from each of the plurality of transmitters in accordance with the associated one of the set of mutually orthogonal codes being decoded before being applied to the adder.

17. The communication system as recited claim 13 wherein the receiver comprises an equalizer for processing the summed signal from the adder to compensate for multipath propagation effects.

18. The communication system as recited in claim 9 wherein each of the plurality of transmitters comprises a digital source encoder for producing the symbols as digital bits of information.

19. The communication system as recited in claim 18 wherein each of the plurality of transmitters comprises:

a repeater for repeating each bit of information produced by the digital source encoder a preselected number of times to successively produce groups of repeated bits;

a sign changer for selectively imposing a sign change on the repeated bits of each of a number of successive groups of repeated bits equal to the preselected number of bits in each group in accordance with an orthogonal code associated with the transmitter

an interleaver for interleaving the sign changed bits from the preselected number of groups to successively generate a number of blocks each composed of the different sign changed bits of the preselected number of repeated groups and having a collective sign change corresponding to a common sign change shared by all signed changed bits of the block; and

a sign modulator for transmitting a signal modulated in accordance with the generated information blocks with sign changes corresponding to the orthogonal code.

20. The communication system as recited in claim 19 wherein each of the transmitters comprises an error correction encoder for imposing error correction encoding upon each of the digital bits of information from the digital source encoder.

21. The communication system as recited in claim 19 wherein each of the transmitters comprises:

an access code generator for generating access code sequences at the rate at which digital bits of information are produced by the digital source encoder; and

an access code imposer for imposing the access code onto the individual digital bits of each of the orthogonally encoded information blocks.

22. The communication system as recited in claim 21 wherein the receiver comprises an access code decoder for decoding the individual digital bits of information received at the receiver.

23. The communication system as recited in claim 19 wherein the decoder comprises a deinterleaver for separating the information blocks into individual digital bits.

24. The communication system as recited in claim 23 comprising a maximum likelihood equalizer for equalizing the individual digital bits from the deinterleaver.

25. The communication system as recited in claim 23 wherein the receiver comprises an error correction decoder.

26. A method for transmitting orthogonally encoding information signals overlapping in time comprising:

coding each one of said information signals to produce corresponding information blocks containing coded information symbols;

repeating each information block a predetermined number of times according to a predetermined spectrum spreading factor;

orthogonally encoding said repeated information blocks by applying a modification factor to each repeat of said information block, the sequence of modification factors applied to successive repeats of said information block forming one of a set of mutually orthogonal coding sequences; and

transmitting said orthogonally encoded information blocks.

27. The method as recited in claim 26 further comprising the step of decoding the orthogonally encoded information blocks by employing different orthogonal codes respectively for separating the information blocks corresponding to different information signals into corresponding separate channels.

28. The method as recited in claim 26 comprising the steps of.

storing an orthogonal code; and

imposing a corresponding sequence of phase changes onto said repeated information blocks in response to the stored orthogonal code.

29. The method as recited in claim 26 wherein said decoding comprises the steps of:

removing the orthogonal encoding from encoded information blocks; and

adding corresponding ones of the symbols in repeated information blocks after the orthogonal encoding is removed.

30. The method as recited in claim 29 comprising the step of processing the summed signal to compensate for multipath propagation effects.

31. The method as recited in claim 29 wherein the steps of removing the orthogonal coding comprising the steps of:

forming a summed signal for each symbol within the repeated information blocks; and

processing the summed signal with an equalizer.

32. The method system as recited in claim 31 comprising the step of encoding the symbols as digital bits of information.

33. The method as recited in claim 32 comprising the steps of:

repeating each bit of information produced by the digital source encoder a preselected number of times to successively produce groups of repeated bits;

imposing a sign change on the repeated bits of each of a number of successive groups of repeated bits equal to the preselected number of bits in each group in accordance with an orthogonal code;

interleaving the sign changed bits from the preselected number of groups to successively generate a number of repeated groups and having a collective sign change corresponding to a common sign change shared by all signed changed bits of the information blocks; and

transmitting a signal modulated in accordance with the generated information blocks with sign changes corresponding to the orthogonal code.

34. The method as recited in claim 33 comprising the steps of:

generating access code sequences at the rate at which digital bits of information are produced by the digital source encoder; and

imposing the access code onto the individual digital bits of each of the orthogonally encoded information blocks.

35. The method as recited in claim 26 comprising the steps of:

transmitting the blocks by a preselected block repetition rate which results in a preselected repetition period; and

adding the corresponding symbols in successive repeated information blocks which are separated from each other by an amount equal to the repetition period.

36. The method as recited in claim 35 comprising the steps of.

selectively imposing phase shifts to the repeated information block with an orthogonal encoder while being transmitted in accordance with an associated one of a plurality of the different orthogonal codes;

and

removing each of the repeated information blocks received from each of the plurality of transmitters in accordance with the orthogonal code respectively associated with the transmitters being decoded before adding the corresponding one of the symbols.

37. The method of claim 26 wherein said orthogonal sequences are Walsh-Hadamard sequences and

38. The method of claim 26 wherein said orthogonal sequences are Fourierr sequences and wherein said modification factors apply phase rotations to said repeated blocks.

39. The method of claim 26 wherein said modification factors are applied by changing the phase of signal segments corresponding to said repeated information blocks.

40. The method of claim 26 wherein said change of phase is 180°

.

41. The method of claim 26 in which the step of transmitting said encoded information blocks includes combining blocks corresponding to different ones of said information signals.

42. A method of transmitting a spread-spectrum encoded signal with improved tolerance of multipath propagation, comprising the steps of:

encoding information to produce symbol blocks each containing a predetermined number of different symbols;

repeating transmission of each symbol block a selected number of times;

changing a sign of each successively repeated block according to one of a set of orthogonal sequence of sign changes; and

wherein the number of repetitions is equal to the length of the orthogonal sequence.

43. The method as recited in claim 42 in which the spread-spectrum coded signal is further conditioned prior to transmission by combining with a spread-spectrum access code.

44. The method as recited in claim 43 in which the spread-spectrum access code is used in common by different transmitters.

45. The method as recited in claim 42 in which the selected sequence of sign or phase changes is different for a different transmitter.

46. The method as recited in claim 45 in which the different sequences are orthogonal to one another.

47. A method for decoding a spread-spectrum coded signal, comprising the steps of:

receiving a composite signal, the composite signal being a sum of a number of overlapping orthogonally encoded signals including said coded signal and sampling the composite signal to produce signal samples;

combining selected ones of the signal samples separated by a predetermined number of samples using a phase change selected from a predetermined orthogonal sequence of phase changes comprising one of a set of orthogonal sequences, associated with said coded signal to produce despread samples; and

processing the despread samples using an equalizer to compensate for multipath propagation.

48. A transmitter for use in a communication system employing orthogonal block encoding, the transmitter comprising:

a producer of an information source signal;

a transmitter circuit for repetitively transmitting information blocks representing samples of the source signal, each of said information blocks containing a plurality of different symbols;

a memory for storing an orthogonal code; and

a phase shifter responsive to the stored orthogonal code for applying one of a set of orthogonal sequences of phase changes to repeated information blocks, wherein the number of repetitions of the information block is equal to the length of the orthogonal sequence.

49. The transmitter as recited in claim 48 comprising a digital source encoder for producing the symbols as digital bits of information.

50. The transmitter as recited in claim 49 comprising:

a repeater for repeating each bit of information produced by the digital source encoder a preselected number of times to successively produce groups of repeated bits;

a sign changer for selectively applying a sign change on the repeated bits of each of a number of successive groups of repeated bits equal to the preselected number of bits in each group in accordance with an orthogonal code associated with the transmitter;

an interleaver for interleaving the sign changed bits from the preselected number of groups to successively generate a number of blocks each composed of the different sign changed bits of the preselected number of repeated groups and having a collective sign change corresponding to a common sign change shared by all signed changed bits of the block; and

a sign modulator for transmitting a signal modulated in accordance with the generated blocks with sign changes corresponding to the orthogonal code.

51. The transmitter as recited in claim 50 comprising an error correction encoder for imposing error correction encoding upon each of the digital bits of information from the digital source encoder.