OFDM/OFDMA FRAME STRUCTURE FOR COMMUNICATION SYSTEMS

• US 20090122771A1
• Filed: 10/17/2008
• Published: 05/14/2009
• Est. Priority Date: 10/17/2007
• Status: Active Grant

• Current Assignee: ZTE Corporation
• Original Assignee: ZTE Corporation
• Inventors: CAI, Sean
• Granted Patent: US 8,369,301 B2
• Time in Patent Office: Days
• US Class Current: 370/338
• CPC Class Codes: H04J 11/00 Orthogonal multiplex systems, e.g. using WALSH codesH04J13/00 takes precedence
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2607 Cyclic extensions

Abstract

An OFDM/OFDMA frame structure technology for communication systems is disclosed. The OFDM/OFDMA frame structure technology comprises a variable length sub-frame structure with efficiently sized cyclic prefixes and efficient transition gap durations operable to effectively utilize OFDM/OFDMA bandwidth. Furthermore, the frame structure provides compatibility with multiple wireless communication systems. An uplink frame structure and a downlink frame structure are provided.

Claims

1. An OFDM communication system comprising:

a plurality of radio frequency (RF) channels, wherein the RF channels comprise dissimilar bandwidths; and

a transmitter for providing a plurality of OFDM subcarriers, wherein the OFDM subcarriers comprise a fixed subcarrier spacing chosen such that the OFDM subcarriers are scalable in number to utilize any of the RF channels.

2. The OFDM communication system of claim 1, wherein the fixed subcarrier spacing that can divide the allocated bandwidth evenly is chosen to optimize bandwidth efficiency.

3. The OFDM communication system of claim 1, wherein the fixed subcarrier spacing that can divide a channel raster of 200 KHz or 250 KHz evenly is chosen to optimize bandwidth efficiency.

4. The OFDM communication system of claim 1, wherein the fixed subcarrier spacing comprises one of the group consisting of about 10 kHz, 12.5 KHz, and multiple of 10 kHz or 12.5 kHz, such as 20 kHz, and 25 KHz.

5. The OFDM communication system of claim 1, wherein the fixed subcarrier spacing comprises 10.9375 kHz or 21.875 kHz.

6. The OFDM communication system of claim 1, wherein the OFDM communication system is an OFDMA communication system.

7. An OFDM communication system comprising a plurality of radio frequency (RF) channels, wherein the RF channels comprise dissimilar bandwidths, the OFDM communication system comprising:

a transmitter for providing a plurality of OFDM subcarriers, wherein the OFDM subcarriers comprise a fixed subcarrier spacing chosen such that the OFDM subcarriers are scalable in number to utilize any of the RF channels; and

a processor module operable to provide a flexible radio frame structure comprising a plurality of variable length cyclic prefixes operable for the RF channels.

8. The OFDM communication system of claim 7, wherein the variable length cyclic prefixes comprise a set of predefined cyclic prefix durations for each RF channel.

9. The OFDM communication system of claim 8, wherein the same set of cyclic prefix durations is used by multiple or all RF channels.

10. The OFDM communication system of claim 7, wherein each of the variable length cyclic prefixes can be dynamically selected for each of the RF channels.

11. The OFDM communication system of claim 7, further comprising a plurality of OFDM frames each comprising one of the variable length cyclic prefixes, and one of a plurality of data symbols.

12. The OFDM communication system of claim 11, further comprising a plurality of variable size sub-frames each comprising a subset of the OFDM frames.

13. The OFDM communication system of claim 12, further comprising a plurality of timing gaps associated with at least one of the variable size sub-frames, wherein the timing gaps are calculated based, at least in part, on a duration of at least one of the variable length cyclic prefixes.

14. The OFDM communication system of claim 13, wherein the timing gaps provide protection for timing variations at signal reception.

15. The OFDM communication system of claim 14, wherein the timing gap is placed at the end of a downlink sub-frame.

16. The OFDM communication system of claim 14, wherein the timing gap is placed at the beginning of an uplink sub-frame.

17. The OFDM communication system of claims 15 and 16, wherein the transmit-transition gap (TTG) of a frame is consisted of the timing gap from downlink sub-frame (TTG-DL) plus the timing gap from uplink sub-frame (TTG-UL).

18. The OFDM communication system of claim 12, further comprising a plurality of variable radio frame configurations for transmission through one of the RF channels, wherein the variable radio frame configurations comprise a subset of the variable size sub-frames.

19. The OFDM communication system of claim 7, wherein the set of cyclic prefix durations are chosen based at least in part on a condition of each of the RF channels.

20. A communication system comprising:

at least one base station supporting variable cyclic prefix durations, wherein the variable cyclic prefix durations are chosen based on a cell coverage area of the at least one base station; and

a processor module for providing a flexible radio frame structure utilizing the variable size cyclic prefix durations, wherein the flexible radio frame structure is used by the at least one base station for transmitting data wirelessly to a mobile station.

21. The communication system of claim 20, wherein the variable cyclic prefix durations are chosen based on a fixed subcarrier spacing.

22. The communication system of claim 21, wherein the fixed subcarrier spacing comprises 12.5 KHz.

23. The communication system of claim 22, wherein the variable cyclic prefix durations, plus a timing window, comprise one of the group consisting of:

about 3.125 μ

s, 10 μ

s, and 16.875 μ

s for a n×

1.25 MHz bandwidth series.

24. The communication system of claim 22, wherein the variable cyclic prefix durations, plus a timing window, comprise one of the group consisting of:

about 3.281 μ

s, 10 μ

s, and 16.178 μ

s for a n×

3.5 MHz bandwidth series.

25. The communication system of claim 22, wherein the variable cyclic prefix durations, plus a timing window, comprise one of the group consisting of:

about 2.5 μ

s, 9.375 μ

s, and 16.875 μ

s for a n×

1.25 MHz and a n×

3.25 MHz bandwidths series.

26. The communication system of claim 22, wherein the variable cyclic prefix durations comprise one of the group consisting of:

about 2.5 μ

s, 10 μ

s, 15 μ

s, and 20 μ

s for a 5 MHz bandwidth series.

27. The communication system of claim 21, wherein the fixed subcarrier spacing comprises about 10.9375 KHz.

28. The communication system of claim 27, wherein the variable cyclic prefix durations comprise one of the group consisting of:

about 2.857 μ

s, 11.428 μ

s, 17.142 μ

s, and 22.857 μ

s for a 5 MHz bandwidth series.

29. The communication system of claim 21, wherein the fixed subcarrier spacing comprises about 25 KHz.

30. The communication system of claim 29, wherein the variable cyclic prefix durations comprise one of the group consisting of:

about 2.5 μ

s, 10 μ

s, 15 μ

s, and 20 for a 5 KHz bandwidth series.

31. The communication system of claim 20, wherein a first cyclic prefix duration for a first base station differs from a second cyclic prefix duration for a second base station.

32. The communication system of claim 20, wherein the flexible radio frame structure comprises a 10 ms radio frame.

33. The communication system of claim 20, wherein the flexible radio frame structure comprises sub-frames which comprise sub-frame duration options based on the variable cyclic prefix durations.

34. The communication system of claim 33, wherein the sub-frame duration options comprise one of the group consisting of:

about 0.5 ms, 0.675 ms, 1 ms, 1.25 ms, 1.5 ms, 2 ms, and 2.5 ms.

35. The communication system of claim 33, wherein the sub-frame duration options allow a system to reduce interference with systems based on a plurality of industry standards.

36. The communication system of claim 35, wherein the industry standards comprise one of the group consisting of:

Third Generation Partnership Project Long Term Evolution (3GPP LTE), Third Generation Partnership Project 2 Ultra Mobile Broadband (3Gpp2 UMB), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA), and Wireless Interoperability for Microwave Access (WiMAX).

37. The communication system of claim 33, wherein the sub-frames comprise a plurality of sub-frame sizes.

38. The communication system of claim 37, wherein the variable cyclic prefix durations are selected for each of the sub-frame sizes.

39. The communication system of claim 33, wherein the processor module is further operable to calculate a plurality of timing gaps associated with at least one of the sub-frames, wherein the timing gaps are calculated based in part on the variable cyclic prefix durations.

40. The communication system of claim 39, wherein the timing gaps comprise one of the group consisting of:

a transmission timing gap for an uplink TTG(UL), a transmission timing gap for a downlink uplink TTG(DL), and a transmit-receive timing gap (RTG).

41. An OFDM/OFDMA radio frame structure for communication in an RF channel in a wireless network, the radio frame structure comprising:

a plurality of OFDM symbols each comprising a variable cyclic prefix duration and an at least one OFDM data symbol;

a plurality of variable size sub-frames formed from a subset of the OFDM symbols;

a plurality of radio frames for transmitting a subset of the variable size sub-frames through the RF channel; and

a plurality of timing gaps associated with the radio frames for providing a protection for timing variations at signal reception, wherein the timing gaps are calculated based at least in part on the variable cyclic prefix duration.

42. The OFDM/OFDMA radio frame structure of claim 41, further comprising a sub-frame structure for the variable size sub-frames comprising:

a downlink sub-frame; and

an uplink sub-frame, wherein the uplink sub-frame and the downlink sub-frame use the same RF channel for communication, and wherein the downlink sub-frame operates with the uplink sub-frame to achieve a maximum transmit-receive transition time gap.

43. The OFDM/OFDMA radio frame structure of claim 42, wherein the transmit-receive transition time gap is larger than a round-trip delay from a mobile station at the edge of a communication cell of a base station to the base station.

44. The OFDM/OFDMA radio frame structure of claim 41, wherein the variable cyclic prefix duration is based on a number of OFDM subcarriers used on the RF channel.

45. The OFDM/OFDMA radio frame structure of claim 41, wherein the network comprises an IEEE 802.16m standard network.

46. A communication system comprising a plurality of RF channels, wherein the RF channels comprise dissimilar channel bandwidths, the communication system comprising:

an inverse fast Fourier transform module operable for transforming a plurality of frequency domain data symbols into a plurality of time domain data symbols respectively;

a cyclic prefix selector module operable for selecting a cyclic prefix from a plurality of variable length cyclic prefixes to obtain a selected cyclic prefix; and

an add cyclic prefix module operable for adding the selected cyclic prefix into each of the time domain data symbols to obtain a plurality of OFDM frames.

47. The communication system of the claim 46, further comprising a processor module operable for:

providing a plurality of variable size sub-frames formed from a subset of the OFDM frames;

providing a plurality of radio frames for transmitting a subset of the variable size sub-frames through at least one of the RF channels; and

calculating a plurality of timing gaps associated with at least one of the variable size sub-frames for providing a protection for timing variations at signal reception, wherein the timing gaps are calculated based at least in part on a cyclic prefix duration of the selected cyclic prefix.

48. The communication system of the claim 47, wherein a cyclic prefix duration of the selected cyclic prefix is determined based on a sampling rate of one of the RF channels.

49. A method for communication in a communication system, the method comprising:

receiving a plurality of time domain data symbols for transmission on a radio channel;

selecting a cyclic prefix from a plurality of variable length cyclic prefixes to obtain a selected cyclic prefix; and

adding the selected cyclic prefix into each of the time domain data symbols to obtain a plurality of OFDM frames.

50. The method of claim 49, further comprising transmitting the OFDM frames on the radio channel.

51. The method of claim 50, further comprising adding the OFDM frames to a flexible sub-frame prior to transmitting.

52. The method of claim 51, wherein the flexible sub-frame comprises a timing gap for providing a protection for timing variations at signal reception, wherein the timing gap is calculated, based at least in part, on a cyclic prefix duration of the selected cyclic prefix.

53. The method of claim 51, further comprising forming a radio frame comprising the flexible sub-frame prior to transmitting.

54. A computer-readable medium for a communication system, comprising program code for:

receiving a plurality of time domain data symbols for transmission on a radio channel;

selecting a cyclic prefix from a plurality of variable length cyclic prefixes for the radio channel to obtain a selected cyclic prefix; and

adding the selected cyclic prefix into each of the time domain data symbols to obtain a plurality of OFDM frames.

55. The computer-readable medium of claim 54, further comprising program code for adding the OFDM frames to a flexible sub-frame prior to transmitting the OFDM frames on the radio channel.

56. The computer-readable medium of claim 55, further comprising program code for:

providing a plurality of variable size sub-frames formed from a subset of the OFDM frames;

providing a plurality of radio frames for transmitting a subset of the variable size sub-frames through the radio channel; and

calculating a plurality of timing gaps associated with at least one of the variable size sub-frames for providing a protection for timing variations at signal reception, wherein the timing gaps are calculated based at least in part on a cyclic prefix duration of the selected cyclic prefix.

57. The computer-readable medium of claim 55, further comprising program code for forming a radio frame comprising the flexible sub-frame prior to transmitting.