Controlled superposition coding in multi-user communication systems

• US 7,411,895 B2
• Filed: 02/19/2004
• Issued: 08/12/2008
• Est. Priority Date: 02/19/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi, Srinivasan, Murari
• Primary Examiner(s): Trost; William
• Assistant Examiner(s): PEREZ, JULIO R
• Application Number:
  US10/782,186
• Publication Number:
  US 20040166869A1
• Time in Patent Office: 1,636 Days
• Field of Search: 455/509, 455/450, 455/513, 455/522, 370/32, 370/342, 370/345, 370/224, 370/335
• US Class Current: 370/203
• CPC Class Codes: H04L 1/1607 Details of the supervisory signal
• CPC Class Codes: H04L 1/1861 Physical mapping arrangements for ACK signaling see also H04L5/0053
• CPC Class Codes: H04L 27/2604 Multiresolution systems by means of multiresolution subcarriers H04L27/183, H04L27/3488
• CPC Class Codes: H04L 27/3488 Multiresolution systems
• CPC Class Codes: H04L 5/04 the signals being represented by different amplitudes or polarities, e.g. quadriplex
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/283 Power depending on the position of the mobile

Abstract

Methods of using superposition coding in a communications systems, e.g., a multi-user communications system. Superpostion coding in accordance with the invention occurs in the case of an uplink by transmissions of different wireless terminals transmitting using the same communications resource, e.g., simultaneously transmitting using the same frequencies. The signals combine in the communications channel resulting in one transmission being superimposed on the other transmission. The device, e.g., base station, receiving the superimposed signals uses superposition decoding techniques to recover both signals. To obtain the benefit of the superposition, assignments of channel segments to multiple wireless terminals is controlled by the base station and/or transmission power levels are controlled by on or more wireless terminals sharing the same uplink communications resource, e.g., time slot, to make sure that the received signals from the different devices will have different received power levels making superposition decoding possible.

Claims

1. A communications method for use in a communications system including a base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the method comprising:

operating the base station to;

i) maintain a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examine the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a pre-selected minimum amount; and

iii) assign a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount.

2. The method of claim 1, further comprising:

operating the base station to repeat said steps of maintaining, examining and assigning.

3. The method of claim 1, further comprising:

operating the base station to repeat said steps of maintaining and examining; and

wherein when said examining step fails to identify at least two wireless terminals having channel conditions which differ by the pre-selected minimum amount having signals to be transmitted in a communications channel segment which is available to be assigned, operating said base station to;

assign the available communications channel segment to a single one of said plurality of wireless terminals.

4. A communications method for use in a communications system including a base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the method comprising:

operating the base station to;

i) maintain a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examine the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a pre-selected minimum amount; and

iii) assign a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount;

wherein the maintained set of channel condition information includes channel signal to noise ratio information;

wherein said at least two different wireless terminals include a first and a second wireless terminal; and

wherein the minimum preselected amount by which the channel conditions of the first and second wireless terminals differ is 3 dB.

5. A communications method for use in a communications system including a base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the method comprising:

operating the base station to;

i) maintain a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examine the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a pre-selected minimum amount; and

iii) assign a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount; and

operating the base station to transmit a first superimposed signal to the first and second wireless terminals in said assigned communication channel segment, said first superimposed signal including a low power signal portion intended for said first wireless terminal and a high power signal portion intended for said second wireless terminal, the low power signal portion being transmitted by said base station with lower power than said high power signal portion or having less coding protection than said high power signal portion;

wherein said at least two different wireless terminals includes a first wireless terminal and a second wireless terminal;

wherein said assigned communications channel segment is a segment of a downlink channel; and

wherein the first wireless terminal has a better channel quality than said second wireless terminal.

6. The communications method of claim 5, wherein said assigned communications channel segment is a segment of an assignment channel used to communicate communications channel segment assignments to wireless terminals.

7. The communications method of claim 6, further comprising:

operating said base station to;

receive a second superimposed signal from said first and second wireless terminals, said received second superimposed signal including first and second signal portions transmitted by said first and second wireless terminals, respectively, said first signal portion being received by said base station at a higher power level than said second signal portion.

8. The communications method of claim 7, further comprising:

operating said base station to;

decode said first signal portion;

subtract said first signal portion from said second superimposed signal; and

decode said second signal portion.

9. The communications method of claim 7, further comprising:

operating the first wireless terminal to determine which one of a plurality of received target power levels to use in determining the transmission power to use to transmit said first signal portion from said first superimposed signal transmitted to said first and second wireless terminals in said segment of an assignment channel.

10. The communications method of claim 9, wherein operating the first wireless terminal to determine which one of a plurality of received target power levels to use includes:

determining whether the portion of the first superimposed signal used to communicate uplink channel assignment information to the first wireless terminal was transmitted as a low power signal portion or a high power signal portion.

11. A base station for use in a communications system including a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the base station comprising:

a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

means for examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by a pre-selected minimum amount; and

means for assigning a communications channel segment to be used to communicate superimposed signals corresponding to a least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount.

12. The base station of claim 11, further comprising:

means for assigning an available communications channel segment to a single one of said plurality of wireless terminals when said examining means fails to identify at least two wireless terminals having channel conditions which differ by the pre-selected minimum amount which have signals to be transmitted in the communications channel segment which is available to be assigned.

13. A base station for use in a communications system including a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the base station comprising:

a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

means for examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by a pre-selected minimum amount; and

means for assigning a communications channel segment to be used to communicate superimposed signals corresponding to a least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount;

wherein said at least two different wireless terminals includes a first and a second wireless terminal;

wherein the maintained set of channel condition information includes channel signal to noise ratio information; and

wherein the minimum pre-selected amount by which the channel conditions of a first and second wireless terminals differ is 3 dB.

14. A base station for use in a communications system including a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the base station comprising:

a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

means for examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by a pre-selected minimum amount; and

means for assigning a communications channel segment to be used to communicate superimposed signals corresponding to a least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount;

means for assigning an available communications channel segment to a single one of said plurality of wireless terminals when said examining means fails to identify at least two wireless terminals having channel conditions which differ by the preselected minimum amount which have signals to be transmitted in the communications channel segment which is available to be assigned; and

a receiver for receiving a superimposed signal from said first and second wireless terminals, said received superimposed signal including first and second signal portions transmitted by said first and second wireless terminals, respectively, said first signal portion being received by said base station at a higher power level than said second signal portion, said first wireless terminal having a better channel condition than said second wireless terminal.

15. The base station of claim 14, further comprising:

a superposition decoder for decoding said first and second signal portions of the received superimposed signal.

16. The base station of claim 15, wherein said superposition decoder includes:

a decoder device for decoding said first signal portion;

a subtracter for subtracting said first signal portion from said superimposed signal to produce said second signal portion; and

a second decoder device for decoding said second signal portion.

17. A communications method for use in a communications system including a base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the method comprising:

operating a first wireless terminal having a first channel quality to transmit a first portion of a superimposed communications signal to said base station; and

operating a second wireless terminal having a second channel quality to transmit a second portion of said superimposed communications signal to said base station, the first and second channel qualities being different by at least a first pre-selected amount, said first and second signal portions combining in the air during transmission to the base station to form said superimposed communications signal.

18. The communications method of claim 17,

wherein the at least a first minimum pre-selected amount by which the channel quality of the first and second wireless terminals differ is 3 dB.

19. The communications method of claim 17, further comprising:

operating the first and second wireless terminals to receive, prior to transmission of said first and second superimposed signal portions, a superimposed assignment signal including a low power signal portion intended for said first wireless terminal and a high power signal portion intended for said second wireless terminal, the lower power signal portion being transmitted by said base station with lower power than said high power signal portion, said first wireless terminal having a better channel quality than said second wireless terminal, said superimposed assignment signal assigning an uplink communications channel segment.

20. The communications method of claim 19, wherein the first and the second signal portions transmitted by said first and second wireless terminals, respectively, are transmitted with power levels that cause said first signal portion to be received by said base station at a higher power level than said second signal portion.

21. The communications method of claim 20, further comprising:

operating the first wireless terminal to determine which one of a plurality of received target power levels to use in determining the transmission power to use to transmit said first signal portion from said superimposed assignment signal.

22. The communications method of claim 21, wherein operating the first wireless terminal to determine which one of a plurality of received target power levels to use includes:

determining whether the superimposed signal portion used to communicate uplink channel assignment information to the first wireless terminal was transmitted as a low power signal portion or a high power signal portion.

23. A wireless terminal including:

receiver means for receiving a superimposed assignment signal including a first signal portion and a second signal portion one of said signal portions being intended for said wireless terminal with the other one of said signal portions being intended for another wireless terminal, the first signal portion being received with at a lower power level than said second signal portion;

superposition decoder means for decoding said first and second signal portions;

means for determining from information included in one of said first and second signal portions which portion is intended for said wireless terminal; and

a transmitter for transmitting signals in uplink communications channel segments to which received superimposed assignment signals intended for said wireless terminal correspond.

24. The wireless terminal of claim 23, further comprising:

stored received target level power information for a plurality of different received power target levels; and

means for determining which one of the plurality of received target power levels to use when transmitting a signal in a particular uplink communications channel segment from a received superimposed assignment signal corresponding to the particular uplink communications channel segment.

25. The wireless terminal of claim 24, wherein said means for determining determines whether the superimposed signal portion used to communicate uplink channel assignment information to the wireless terminal was transmitted as a low power signal portion or a high power signal portion.

26. A communications method for use in a communications system including a base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the communications channel quality for the particular wireless terminal, signals transmitted from the wireless terminals to the base station combining in the communications channel, the method comprising:

operating the base station to;

assign an uplink communications channel segment to be used simultaneously by a first and second device;

receive a composite signal from said uplink communications channel segment, said composite signal including a first signal transmitted by said first device and a second signal transmitted by said second device; and

perform a superposition decoding operation on the received composite signal to decode the first and second signals included in said composite signal.

27. The communications method of claim 26, wherein operating the base station to assign an uplink communications channel segment includes operating the base station to:

select based on communications channel quality information, a first wireless terminal and a second wireless terminal, the first and second wireless terminals having different wireless terminal communications channel qualities, to share an uplink traffic segment; and

wherein the method further comprises operating the base station to;

transmit to the selected first and second wireless terminals information indicating the assigned traffic channel segment and which one of the first and second wireless terminals should transmit signals to be received by said base station at a higher power level.

28. The method of claim 27, wherein the one of the first and second wireless terminals having the better channel conditions is to be received at the base station at the higher power level, the method further comprising:

operating the first wireless terminal to transmit to the base station in the assigned traffic channel segment a first signal portion; and

operating the second wireless terminal to transmit to the base station in the assigned traffic channel segment a second signal portion, the first and second signal portions superimposing during transmission to said base station.

29. The method of claim 28, wherein the first wireless terminal transmits the first signal portion using less power than the power used by said second wireless terminal to transmit said second signal portion but the first signal portion is received by said base station with a power level that is higher than the power level of the second signal portion received by said base station.

30. The method of claim 29,

wherein said at least two different wireless terminals includes a first wireless terminal and a second wireless terminal;

wherein said communications channel segment to be assigned is a segment of a downlink channel;

wherein the first wireless terminal has a better channel quality than said second wireless terminal; and

wherein the base station further comprises;

means for transmitting a superimposed signal to the first and second wireless terminals in said assigned communication channel segment, said superimposed signal including a low power signal portion intended for said first wireless terminal and a high power signal portion intended for said second wireless terminal, the lower power signal portion being transmitted by said base station with lower power than said high power signal portion.

31. A computer readable medium encoded with computer executable instructions for controlling a base station to implement a communications method in a communications system including the base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the communications method comprising:

i) maintaining a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a pre-selected minimum amount; and

iii) assigning a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount.

32. A computer readable medium encoded with computer executable instructions for controlling a base station to implement a communications method in a communications system including the base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the communications method comprising:

i) maintaining a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a pre-selected minimum amount; and

iii) assigning a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount;

wherein the maintained set of channel condition information includes channel signal to noise ratio information;

wherein said at least two different wireless terminals include a first and a second wireless terminal; and

wherein the minimum pre-selected amount by which the channel conditions of the first and second wireless terminals differ is 3 dB.

33. The computer readable medium of claim 32, wherein the communications method further comprises:

repeating said steps of maintaining, examining and assigning.

34. A device comprising a processor configured to control a base station to implement a communications method in a communications system including the base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the communications method comprising:

i) maintaining a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a pro-selected minimum amount; and

iii) assigning a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount.

35. A device comprising a processor configured to control a base station to implement a communications method in a communications system including the base station and a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the communications method comprising:

i) maintaining a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

ii) examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by at least a preselected minimum amount; and

iii) assigning a communications channel segment to be used to communicate superimposed signals corresponding to at least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount;

wherein the maintained set of channel condition information includes channel signal to noise ratio information;

wherein said at least two different wireless terminals include a first and a second wireless terminal; and

wherein the minimum pre-selected amount by which the channel conditions of the first and second wireless terminals differ is 3 dB.

36. The device of claim 35, wherein the communications method further comprises:

repeating said steps of maintaining, examining and assigning.

37. A base station for use in a communications system including a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the base station comprising:

memory including a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

a channel condition information examination module for examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by a pre-selected minimum amount; and

an assignment module for assigning a communications channel segment to be used to communicate superimposed signals corresponding to a least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount.

38. A base station for use in a communications system including a plurality of wireless terminals, a different communications channel existing between each wireless terminal in said plurality of wireless terminals and said base station, the communications channel existing between each particular wireless terminal and the base station having a quality which is the channel quality for the particular wireless terminal, the base station comprising:

memory including a set of channel condition information indicating the channel quality of each of said plurality of wireless terminals;

a channel condition information examination module for examining the set of channel condition information to identify wireless terminals having channel conditions which differ from one another by a pre-selected minimum amount; and

an assignment module for assigning a communications channel segment to be used to communicate superimposed signals corresponding to a least two different wireless terminals identified as having channel conditions which differ by at least said pre-selected minimum amount;

wherein said at least two different wireless terminals includes a first and a second wireless terminal;

wherein the maintained set of channel condition information includes channel signal to noise ratio information; and

wherein the minimum pre-selected amount by which the channel conditions of a first and second wireless terminals differ is 3 dB.

39. The base station of claim 38, further comprising:

a receiver for receiving a superimposed signal from said first and second wireless terminals, said received superimposed signal including first and second signal portions transmitted by said first and second wireless terminals, respectively, said first signal portion being received by said base station at a higher power level than said second signal portion, said first wireless terminal having a better channel condition than said second wireless terminal.

40. A wireless terminal including:

a receiver for receiving a superimposed assignment signal including a first signal portion and a second signal portion one of said signal portions being intended for said wireless terminal with the other one of said signal portions being intended for another wireless terminal, the first signal portion being received with at a lower power level than said second signal portion;

a superposition decoder for decoding said first and second signal portions;

a determination module for determining from information included in one of said first and second signal portions which portion is intended for said wireless terminal; and

a transmitter for transmitting signals in uplink communications channel segments to which received superimposed assignment signals intended for said wireless terminal correspond.

41. The wireless terminal of claim 40, further comprising;

stored received target level power information for a plurality of different received power target levels; and

a target power level determination module for determining which one of the plurality of received target power levels to use when transmitting a signal in a particular uplink communications channel segment from a received superimposed assignment signal corresponding to the particular uplink communications channel segment.

42. A method of operating a wireless terminal comprising:

receiving a superimposed assignment signal including a first signal portion and a second signal portion one of said signal portions being intended for said wireless terminal with the other one of said signal portions being intended for another wireless terminal, the first signal portion being received with at a lower power level than said second signal portion;

decoding said first and second signal portions;

determining from information included in one of said first and second signal portions which portion is intended for said wireless terminal; and

transmitting signals in uplink communications channel segments to which received superimposed assignment signals intended for said wireless terminal correspond.

43. The method of claim 42, further comprising:

storing received target level power information for a plurality of different received power target levels; and

determining which one of the plurality of received target power levels to use when transmitting a signal in a particular uplink communications channel segment from a received superimposed assignment signal corresponding to the particular uplink communications channel segment.

44. The method of claim 43, wherein said determining includes determining whether the superimposed signal portion used to communicate uplink channel assignment information to the wireless terminal was transmitted as a low power signal portion or a high power signal portion.

45. A computer readable medium encoded with computer executable instructions for controlling a wireless terminal to implement a method, the method comprising:

receiving a superimposed assignment signal including a first signal portion and a second signal portion one of said signal portions being intended for said wireless terminal with the other one of said signal portions being intended for another wireless terminal, the first signal portion being received with at a lower power level than said second signal portion;

decoding said first and second signal portions;

determining from information included in one of said first and second signal portions which portion is intended for said wireless terminal; and

transmitting signals in uplink communications channel segments to which received superimposed assignment signals intended for said wireless terminal correspond.

46. The computer readable medium of claim 45, wherein the method, further comprises:

storing received target level power information for a plurality of different received power target levels; and

determining which one of the plurality of received target power levels to use when transmitting a signal in a particular uplink communications channel segment from a received superimposed assignment signal corresponding to the particular uplink communications channel segment.

47. The computer readable medium of claim 46 wherein said determining includes determining whether the superimposed signal portion used to communicate uplink channel assignment information to the wireless terminal was transmitted as a low power signal portion or a high power signal portion.

48. A device including a processor configured to control a wireless terminal to implement a method, the method comprising:

receiving a superimposed assignment signal including a first signal portion and a second signal portion one of said signal portions being intended for said wireless terminal with the other one of said signal portions being intended for another wireless terminal, the first signal portion being received with at a lower power level than said second signal portion;

decoding said first and second signal portions;

determining from information included in one of said first and second signal portions which portion is intended for said wireless terminal; and

transmitting signals in uplink communications channel segments to which received superimposed assignment signals intended for said wireless terminal correspond.

49. The device of claim 48, wherein the method, further comprises:

storing received target level power information for a plurality of different received power target levels; and

determining which one of the plurality of received target power levels to use when transmitting a signal in a particular uplink communications channel segment from a received superimposed assignment signal corresponding to the particular uplink communications channel segment.

50. The device of claim 49 wherein said determining includes determining whether the superimposed signal portion used to communicate uplink channel assignment information to the wireless terminal was transmitted as a low power signal portion or a high power signal portion.