Chip-interleaved, block-spread multi-user communication

• US 6,912,241 B2
• Filed: 04/19/2001
• Issued: 06/28/2005
• Est. Priority Date: 03/08/2001
• Status: Active Grant

• Current Assignee: Regents of The University of Minnesota (University of Minnesota), University of Minnesota
• Original Assignee: Regents of The University of Minnesota (University of Minnesota)
• Inventors: Zhou, Shengli, Giannakis, Georgios B.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/838,621
• Publication Number:
  US 20020126740A1
• Time in Patent Office: 1,531 Days
• Field of Search: 375140-153, 714/761, 714/762, 714/787
• US Class Current: 375/141
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27

Abstract

Techniques are described for maintaining the orthogonality of user waveforms in multi-user wireless communication systems, such as systems using the code division multiple access (CDMA) modulation scheme in the presence of frequency-selective fading channels. Unlike conventional systems in which spreading is performed on individual information-bearing symbols, the “chip-interleaved block-spreading” (CIBS) techniques described herein spread blocks of symbols. A transmitter includes a block-spreading unit to form a set of chips for each symbol of a block of information-bearing symbols and to produce a stream of chips in which the chips from different sets are interleaved. A pulse shaping unit within the transmitter generates a transmission signal from the stream of interleaved chips and transmits the signal through a communication channel. A receiver includes a block separator to de-interleave the chips, followed by a match filter to separate signals from different users, and followed by any single-user equalizer.

Claims

1. A method comprising:

applying a user-specific orthogonal spreading code to a block of K information bearing symbols to form a set of M chips for each symbol;

storing the chips in an array having M columns and K+L rows, where L is a function of a channel length of a wireless communication channel;

selectively interleaving the chips from the chip sets; and

generating a transmission signal from the interleaved chips.

2. The method of claim 1,

wherein the wireless communication comprises a frequency selective communication channel, and

wherein applying the spreading code comprises an orthogonal spreading code selected such that the interleaved chips retain their orthogonality after passing through the frequency selective communication channel.

3. The method of claim 1, further comprising communicating the transmission signal through the wireless communication medium.

4. The method of claim 1, wherein generating the transmission signal further comprises:

padding each column of the array with L guard chips; and

generating the transmission signal by reading the chips from the array in column wise fashion.

5. The method of claim 4, wherein the guard chips comprise null values.

6. The method of claim 4, wherein the guard chips are selected from a common modulation constellation.

7. The method of claim 1 further comprising:

receiving the signal; and

de-interleaving the chips from the received signal.

8. The method of claim 7 further comprising separating the data according to a user.

9. The method of claim 8, wherein separating the data comprises applying a matched filter and a single-user decoding technique.

10. The method of claim 7, wherein de-interleaving the data comprises storing the chips in an array having M columns and K+L rows, wherein M represents a number of spreading codes within a set of spreading codes, and father wherein the M chips within each row of the array correspond to a common symbol.

11. The method of claim 10, wherein de-interleaving the data further comprises producing a stream of chips by reading the array in row wise fashion.

12. The method of claim 11, further comprising:

applying a matched filter to the stream of chips to separate signals from different users based on their code orthogonality and produce a stream of user-specific symbols;

applying a single-user detecting scheme to remove channel effects and output user-specific symbol estimates; and

converting the stream of user-specific symbol estimates into a serial data stream.

13. A computer-readable medium having instructions thereon to cause a programmable processor to:

apply a user-specific orthogonal spreading code of length M to a block of K information-bearing symbols to form a set of M chips for each symbol; and

store the chips in an array having M columns and K+L rows, where L is a function of the communication channel length;

select chips from the chip sets to produce a stream of chips in which the chips from different sets are interleaved; and

generate a transmission signal from the stream of interleaved chips.

14. The computer-readable medium of claim 13, further including instructions to cause the processor to transmitting the signal through a wireless communication channel.

15. The computer-readable medium of claim 13, further including instructions to cause the processor to:

pad each column of the array with L guard chips; and

generate the transmission signal by reading the chips from the array in column wise fashion.

16. A computer-readable medium having instructions to cause a processor to:

receive a signal having interleaved chips generated from a block of K information-bearing symbols;

write the interleaved chips column-wise into an may such that each row contains chips generated from the same received symbol, wherein the array has M columns and K+L rows, wherein L is a function of the communication channel length and M represents a number of spreading codes within a set of spreading codes applied to generate the signal; and

produce a stream of de-interleaved chips by reading the rows of the array.

17. The computer-readable medium of claim 16, wherein the M chips within each row of the array are generated from a common received symbol.

18. The computer-readable medium of claim 16, wherein the instructions cause the processor to:

apply a matched filter to the stream of de-interleaved chips to produce a stream of user-specific symbols;

apply a single-user channel equalization and symbol detection scheme to remove channel effects and output user-specific symbol estimates; and

convert the stream of user-specific symbol estimates into a serial data stream.

19. A transmitting device comprising:

a block-spreading unit to form a set of M chips for each symbol of a block of K information-bearing symbols and to produce a stream of chips in which the chips from different sets of chips are interleaved and separated by L guard chips, wherein L is a function of a channel length of a wireless communication; and

a pulse shaping unit to generate a transmission signal from the stream of interleaved chips.

20. The transmitting device of claim 19, wherein the block-spreading unit comprises:

a symbol-spreading unit to generate M user-specific orthogonal spreading chips for each symbol within the block of K symbols;

a buffer to store the sets of chips; and

a chip-interleaving unit to read chips from the buffer and output a stream of chips in which the chips from different sets are interleaved.

21. The transmitting device of claim 20, wherein the buffer stores the chips in an array having M columns and K+L rows, where M represents a maximum number of users.

22. The transmitting device of claim 19, wherein the buffer pads each column of the array with L guard chips.

23. The transmitting device of claim 19, wherein the chip-interleaving unit reads the chips from the array in column wise fashion.

24. The transmitting device of claim 20, wherein the transmitting device comprises a cellular phone.

25. A system comprising:

a transmitter to transmit a signal through a wireless communication channel according to interleaved chips generated from a block of K information-bearing symbols, wherein the transmitter interleaves the chips in an array having M columns and K+L rows, where L is a function of a channel length of the wireless communication channel and M represents a maximum number of users; and

a receiver to receive the signal and de-interleave the chips.

26. The system of claim 25, wherein the transmitting device comprises

a block-spreading unit to form a set of chips for each symbol of the block and to produce a stream of chips in which the chips from different sets are interleaved;

and

a pulse shaping unit to generate the signal from the stream of interleaved chips.

27. The system of claim 26, wherein the block-spreading unit comprises:

a symbol-spreading unit to generate user-specific orthogonal spreading chips codes for each symbol within the block of symbols;

a buffer to store the sets of chips in the array form; and

a chip-interleaving unit to read chips from the buffer and output a stream of chips in which the chips from different sets are interleaved.

28. The system of claim 25, wherein the receiver comprises:

a block separator to store the interleaved chips column-wise into an array such that each row contains chips generated from the same received symbol with intersymbol interference, and to produce a stream of de-interleaved chips by reading the rows of the array;

a single-user detector to apply a matched filter to the stream of de-interleaved chips to produce a stream of user-specific symbols; and

a single-user channel equalization and symbol detection scheme to remove channel effects and output the estimated symbols.

29. The system of claim 28, wherein the single-user detector achieves performance equivalent to a set of M single user detectors.

30. A system comprising:

a transmitter to transmit a signal according to interleaved chips generated from a block of symbols; and

a receiver to receive the signal and de-interleave the chips, wherein the receiver comprises;

a block separator to store the interleaved chips column-wise into an array such that each row contains chips generated from the same received symbol with intersymbol interference, and to produce a stream of de-interleaved chips by reading the rows of the array wherein the array has M columns and K+L rows wherein L is a function of the communication channel length and M represents a number of spreading codes with a set of spreading codes applied to generate the signal;

a single-user detector to apply a matched filter to the stream of de-interleaved chips to produce a stream of user-specific symbols; and

a single-user channel equalization and symbol detection scheme to remove channel effects and output the estimated symbols, wherein the single-user detector that achieves performance equivalent to a set of M single user detectors.