Wireless Transceiver with Reduced Transmit Emissions

• US 20080176523A1
• Filed: 01/19/2007
• Published: 07/24/2008
• Est. Priority Date: 01/19/2007
• Status: Active Grant

• Current Assignee: Wi-LAN Inc.
• Original Assignee: Nextwave Broadband Incorporated (AT&T, Inc.)
• Inventors: Wang, Lei, Sutton, Todd, Gummadi, Srikanth, Hosseini, Walid
• Granted Patent: US 8,290,447 B2
• Time in Patent Office: Days
• US Class Current: 455/76
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/003 Arrangements for allocating sub-channels of the transmission path
• CPC Class Codes: H04L 5/0066 Requirements on out-of-channel emissions

Abstract

Methods and apparatus for reducing transmit emissions are described herein. The transmit out of band emissions in an adjacent band can be reduced while complying with existing wireless communication standards through utilization of one or more of reduced transmit bandwidth, transmit operating band offset, and channel index remapping. The transceiver can support a receive operating band that is substantially adjacent to a band edge. The transmit operating band can be offset from an adjacent frequency band, and can use a narrower operating band than is supported by the receiver. The transmit baseband signal can have a reduced bandwidth to reduce the amount of noise. The frequency offset can introduce a larger transition band between the transmit operating band edges and the adjacent frequency band of interest. The transceiver can remap channel assignments to compensate for the frequency offset such that the frequency offset introduced in the transmitter is transparent to channel allocation.

Claims

1. A method of reducing out of band emissions, the method comprising:

obtaining an uplink resource allocation restricted to a portion of a transmit band;

generating a transmit signal; and

filtering the transmit signal to a signal bandwidth that is less than a bandwidth of the transmit band.

2. The method of claim 1, wherein filtering the transmit signal comprises filtering the transmit signal to a bandwidth equal to or greater than a bandwidth of the uplink resource allocation

3. The method of claim 1, further comprising offsetting a frequency of a Local Oscillator (LO) from a first LO frequency to a second LO frequency.

4. The method of claim 3, wherein a magnitude of a difference between the first LO frequency and the second LO frequency is based at least in part on a difference between the bandwidth of the transmit band and a bandwidth of the portion of the transmit band.

5. The method of claim 3, wherein a magnitude of a difference between the first LO frequency and the second LO frequency is fixed.

6. The method of claim 3, wherein a magnitude of a difference between the first LO frequency and the second LO frequency is determined based on the bandwidth of the uplink resource allocation.

7. The method of claim 3, wherein the first LO frequency is substantially equal to the center frequency of the transmit band and the second LO frequency is substantially equal to a center frequency of the portion of the transmit band.

8. The method of claim 3, wherein the first LO frequency is substantially equal to the center frequency of the transmit band and the second LO frequency is within the portion of the transmit band and is offset from a center frequency of the portion of the transmit band.

9. The method of claim 3, wherein the second LO frequency is further from a band edge of an emissions band of interest than the first LO frequency.

10. The method of claim 3, wherein the first LO frequency comprises a receive LO frequency.

11. The method of claim 3, further comprising remapping at least a portion of the uplink resource allocation to compensate for offsetting the frequency of the LO.

12. The method of claim 11, wherein remapping comprises remapping at least one subcarrier index assigned in the uplink resource allocation to compensate for offsetting the frequency of the LO.

13. The method of claim 11, wherein remapping comprises offsetting a baseband frequency of the transmit signal by a frequency magnitude that is based on a difference between a subcarrier index at a band edge of the portion of the transmit band and a subcarrier index at a band edge of the transmit band.

14. The method of claim 11, further comprising nulling a subcarrier based in part on offsetting the frequency of the LO.

15. The method of claim 14, wherein the subcarrier comprises a DC subcarrier.

16. The method of claim 1, wherein receiving the uplink resource allocation comprises receiving an Adaptive Modulation and Coding resource allocation restricted to a predetermined number of bins in the transmit band.

17. The method of claim 1, wherein receiving the uplink resource allocation comprises receiving at least one index value identifying a subcarrier allocated in an uplink Orthogonal Frequency Division Multiplex (OFDM) symbol.

18. The method of claim 1, wherein receiving the uplink resource allocation comprises receiving the uplink resource allocation which is restricted to the portion of the transmit band furthest from an emissions band of interest.

19. The method of claim 18, wherein the portion of the transmit band is less than or equal to one-half the transmit band.

20. The method of claim 1, wherein generating the transmit signal comprises generating an Orthogonal Frequency Division Multiplex (OFDM) symbol based at least in part on the uplink resource allocation.

21. The method of claim 1, wherein filtering the transmit signal comprises analog filtering a baseband transmit signal.

22. The method of claim 1, wherein filtering the transmit signal comprises filtering an analog baseband transmit signal to a bandwidth less than approximately one half the bandwidth of the transmit band.

23. The method of claim 1, further comprising nulling a subcarrier in the portion of the transmit band.

24. A method of reducing out of band emissions, the method comprising:

obtaining an uplink resource allocation restricted to a portion of a transmit band;

offsetting a Local Oscillator from a first LO frequency to a second LO frequency;

remapping at least a portion of the uplink resource allocation to compensate for a difference between the first LO frequency and the second LO frequency to generate a remapped resource allocation;

generating a transmit signal based at least in part on the remapped resource allocation; and

frequency converting the transmit signal to the portion of the transmit band using the second LO frequency.

25. A method of reducing out of band emissions, the method comprising:

receiving an uplink resource allocation including at least one subcarrier allocation in an Uplink-Map message of a downlink time portion of a Time Domain Duplex (TDD) operating band, the uplink resource allocation constrained to a predetermined portion of the operating band;

offsetting a frequency of a Local Oscillator (LO) from a receive LO frequency by an offset frequency;

remapping the at least one subcarrier allocation based on the offset frequency to determine at least one offset subcarrier allocation; and

generating a transmit signal based in part on the at least one offset subcarrier allocation.

26. The method of claim 25, further comprising:

frequency converting the transmit signal to the predetermined portion of the operating band using the LO to generate a frequency converted transmit signal; and

transmitting the frequency converted transmit signal during an uplink time portion of the TDD operating band.

27. The method of claim 25, wherein receiving the uplink resource allocation comprises receiving the Uplink-Map message which allocates resources in a predetermined number of Adaptive Modulation and Coding (AMC) bins.

28. The method of claim 25, wherein offsetting the frequency of the LO comprises offsetting the frequency of the LO away from an emissions band of interest.

29. The method of claim 25, wherein offsetting the frequency of the LO comprises offsetting the frequency of the LO by a frequency offset that is greater than the difference between a center frequency of the predetermined portion of the operating band and the receive LO frequency.

30. The method of claim 28, wherein the emissions band of interest comprises a Digital Audio Radio Service band.

31. The method of claim 25, wherein offsetting the frequency of the LO comprises offsetting the frequency by a fixed frequency that is based in part on the predetermined portion of the operating band.

32. The method of claim 25, wherein offsetting the frequency of the LO comprises offsetting the frequency by a fixed frequency that is based in part on the uplink resource allocation.

33. The method of claim 25, wherein generating the transmit signal comprises generating at least one Orthogonal Frequency Division Multiplex (OFDM) symbols based on the at least one offset subcarrier allocation.

34. The method of claim 25, further comprising filtering the transmit signal to a bandwidth that is less than a bandwidth of the operating band.

35. The method of claim 34, wherein filtering the transmit signal comprises filtering the transmit signal to a predetermined bandwidth based on a bandwidth of the predetermined portion of the operating band.

36. The method of claim 34, wherein filtering the transmit signal comprises filtering the transmit signal to a bandwidth based on a bandwidth of the uplink resource allocation.

37. An apparatus having reduced out of band emissions, the apparatus comprising:

a receiver configured to receive an uplink resource allocation including at least one subcarrier allocation in a downlink time portion of a Time Domain Duplex (TDD) operating band, the uplink resource allocation constrained to a predetermined portion of the operating band;

a Local Oscillator (LO) selectively tuned to a receive LO frequency during the downlink portion of the TDD operating band and to an uplink LO frequency during an uplink time portion of the TDD operating band, the difference between the receive LO frequency and the uplink LO frequency comprising an offset frequency;

a LO controller configured to selectively tune the frequency of the LO based on an active TDD portion of the operating band;

a channel index remapper configured to remap the at least one subcarrier allocation based on the offset frequency to determine at least one offset subcarrier allocation; and

a signal generator configured to generate a transmit signal based at least in part on the at least one offset subcarrier allocation.

38. The apparatus of claim 37, wherein the uplink resource allocation comprises an IEEE802.16 Orthogonal Frequency Division Multiple Access (OFDMA) PHY UL-MAP.

39. The apparatus of claim 37, wherein the at least one subcarrier allocation comprises at least one Orthogonal Frequency Division Multiple Access (OFDMA) subcarrier in at least one of a predetermined number of Adaptive Modulation and Coding bins.

40. The apparatus of claim 37, wherein the predetermined portion of the operating band comprises a fraction of the operating band furthest from an emissions band of interest.

41. The apparatus of claim 37, wherein the LO controller is configured to tune the LO by a fixed offset frequency.

42. The apparatus of claim 37, wherein the LO controller is configured to tune the LO by a variable offset frequency that is determined, based in part on the uplink resource allocation.

43. The apparatus of claim 37, wherein the signal generator comprises a filter configured to filter the bandwidth of the transmit signal to a signal bandwidth less than the bandwidth of the operating band.

44. The apparatus of claim 43, wherein the signal bandwidth is fixed.

45. The apparatus of claim 43, wherein the signal bandwidth depends at least in part on a bandwidth of the uplink resource allocation.

46. The apparatus of claim 37, wherein the signal generator comprises a transform module configured to generate an Orthogonal Frequency Division Multiplex (OFDM) symbol.

47. An apparatus having reduced out of band emissions, the apparatus comprising:

means for receiving an uplink resource allocation including at least one subcarrier allocation in an Uplink-Map message of a downlink time portion of a Time Domain Duplex (TDD) operating band, the uplink resource allocation constrained to a predetermined portion of the operating band;

means for offsetting a frequency of a Local Oscillator (LO) from a receive LO frequency by an offset frequency;

means for remapping the at least one subcarrier allocation based on the offset frequency to determine at least one offset subcarrier allocation; and

means for generating a transmit signal based in part on the at least one offset subcarrier allocation.

48. The apparatus of claim 47, further comprising means for filtering the transmit signal to a bandwidth that is less than a bandwidth of the operating band.

49. The apparatus of claim 47, wherein the means for offsetting the frequency of the LO comprises a frequency synthesizer.

50. The apparatus of claim 47, wherein the means for remapping the at least one subcarrier allocation comprises means for offsetting the at least one subcarrier allocation by the offset frequency.

51. The apparatus of claim 47, wherein the means for filtering the transmit signal comprises an analog baseband filter.

52. An apparatus having reduced out of band emissions, the apparatus comprising:

means for obtaining an uplink resource allocation restricted to a portion of a transmit band;

means for generating a transmit signal; and

means for filtering the transmit signal to a signal bandwidth that is less than a bandwidth of the transmit band.

53. A processor-readable storage medium containing one or more instructions for a processor, the processor executing the one or more instruction performing the method comprising:

receiving an uplink resource allocation including at least one subcarrier allocation in an Uplink-Map message of a downlink time portion of a Time Domain Duplex (TDD) operating band, the uplink resource allocation constrained to a predetermined portion of the operating band;

controlling a frequency of a Local Oscillator to offset the LO frequency from a receive LO frequency by an offset frequency; and

remapping the at least one subcarrier allocation based on the offset frequency to determine at least one offset subcarrier allocation.

54. The processor readable storage medium of claim 53, the method further comprising controlling a signal bandwidth of a filter configured to filter a transmit signal generated based in part on the at least one offset subcarrier allocation to a bandwidth that is less than a bandwidth of the operating band.

55. The processor readable storage medium of claim 53, wherein the offset frequency comprises a difference between a center frequency of the predetermined portion of the operating band and a center frequency of the operating band.

56. The processor readable storage medium of claim 53, wherein remapping the at least one subcarrier allocation comprises offsetting the at least one subcarrier allocation based on a difference between a subcarrier index at a band edge of the predetermined portion of the operating band and a subcarrier index at a band edge of the operating band.