Pilot pattern design for small size resource block in OFDMA systems

• US 20090257520A1
• Filed: 04/08/2009
• Published: 10/15/2009
• Est. Priority Date: 04/10/2008
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Liao, Pei-Kai, Lin, Chih-Yuan
• Granted Patent: US 8,724,718 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

In OFDMA wireless communications systems, pilot pattern design is optimized based on predefined resource block size. The number of pilots and the spacing between pilots within a resource block is determined based on a set of system requirements. In one novel aspect, if resource block size is smaller than three in either frequency or time domain, then the pilots are allocated such that average pilot-to-data distance is minimized and that pilot-to-pilot distance is as large as possible. In one example, m pilots are allocated in an i×j resource block. The resource block is partitioned into n equal sub blocks, where m is a multiple of n. Within each sub block, m/n pilots are positioned such that average pilot-to-data distance is minimized. On the other hand, if resource block size is larger than or equal to three in both frequency and time domain, then pilots are allocated to avoid channel extrapolation.

Claims

1. A method comprising:

a) defining a resource block in an orthogonal Frequency Division Multiple Access (OFDMA) communications system, wherein the resource block is a two-dimensional block having a first number of frequency tones along frequency domain and a second number of time slots along time domain;

b) determining a specified number of pilot tones to be allocated within the resource block based on a set of communications system requirements; and

c) positioning the specified number of a plurality of pilot tones such that average distance between the allocated pilot tones and data tones is minimized and that pilot-to-pilot spacing is as large as possible.

2. The method of claim 1, wherein the set of communications system requirements is specified by at least one of maximum Doppler spread, maximum delay spread, peak data rate, and throughput.

3. The method of claim 1, wherein the specified number is equal to m, wherein the resource block is partitioned into n equal sub-blocks, wherein m is a multiple of n, and wherein the positioning in c) involves allocating m/n pilots in each of the partitioned sub-blocks such that average pilot-to-data distance is minimized.

4. The method of claim 3, wherein the second number is smaller than three, wherein the first number is a multiple of n, and wherein the resource block is partitioned along the frequency domain.

5. The method of claim 3, wherein the first number is smaller than three, wherein the second number is a multiple of n, and wherein the resource block is partitioned along the time domain.

6. The method of claim 1, wherein the positioning in c) also involves allocating an approximately equal number of pilot tones along the time domain to minimize power fluctuation.

7. The method of claim 1, wherein the positioning in c) is repeated for multiple data streams, and wherein an approximately equal number of pilot tones are maximally evenly distributed along the time domain with respect to each data stream to minimize power fluctuation.

8. The method of claim 1, wherein a selected frequency tone and a selected time slot are adapted for transmitting a pilot tone of the specified number of the plurality of pilot tones, and wherein no data symbol is transmitted using the selected frequency tone and the selected time slot.

9. A wireless communications device, comprising:

a transmitter that transmits a plurality of pilot tones for a data stream using a two-dimensional resource block having a first number of frequency tones along frequency domain and a second number of time slots along time domain; and

a pilot allocation module that allocates a specified number of the plurality of pilot tones, wherein the specified number is determined based on a set of communications system requirements, and wherein the specified number of pilot tones is allocated such that average distance between the allocated pilot tones and data tones is minimized and that pilot-to-pilot spacing is as large as possible.

10. The wireless communications device of claim 9, wherein the set of communications system requirements is specified by at least one of maximum Doppler spread, maximum delay spread, peak data rate, and throughput.

11. The wireless communications device of claim 9, wherein the specified number is equal to m, wherein the resource block is partitioned into n equal sub-blocks, wherein m is a multiple of n, and wherein m/n pilot tones are allocated in each of the partitioned sub-blocks such that average pilot-to-data distance is minimized.

12. The wireless communications device of claim 11, wherein the second number is smaller than three, and wherein the first number is a multiple of n and the resource block is partitioned along the frequency domain.

13. The wireless communications device of claim 11, wherein the first number is smaller than three, and wherein the second number is a multiple of n and the resource block is partitioned along the time domain.

14. The wireless communications device of claim 9, wherein an approximately equal number of pilot tones are maximally evenly distributed along the time domain to minimize power fluctuation.

15. The wireless communications device of claim 9, wherein a second plurality of pilot tones for a second data stream is transmitted using the resource block, and wherein an approximately equal number of pilot tones are maximally evenly distributed along the time domain with respect to each data stream to minimize power fluctuation.

16. The wireless communications device of claim 9, further comprising:

multiple antennas used in a Multi-Input Multi-Output (MIMO) system, wherein one pilot tone is transmitted by one antenna using a selected frequency tone and a selected time slot, and wherein no data symbol is transmitted by other antennas using the selected frequency tone and the selected time slot.

17. An apparatus, comprising:

an antenna; and

means for transmitting via the antenna a plurality of pilot tones located within a two-dimensional resource block having a first number of frequency tones along frequency domain and a second number of time slots along time domain, wherein a specified number of pilot tones are determined based on a set of communications system requirements, and wherein the specified number of the plurality of pilot tones is allocated such that average distance between the allocated pilot tones and data tones is minimized and that pilot-to-pilot spacing is as large as possible.

18. The apparatus of claim 17, wherein the specified number is equal to m, wherein the resource block is partitioned into n equal sub-blocks, wherein m is a multiple of n, and wherein m/n pilot tones are allocated in each of the partitioned sub-blocks such that average pilot-to-data distance is minimized.

19. The apparatus of claim 18, wherein the second number is smaller than three, and wherein the first number is a multiple of n and the resource block is partitioned along the frequency domain.

20. The apparatus of claim 18, wherein the first number is smaller than three, and wherein the second number is a multiple of n and the resource block is partitioned along the time domain.

21. The apparatus of claim 17, wherein an approximately equal number of pilot tones are maximally evenly distributed along the time domain to minimize power fluctuation.

22. A wireless communications device, comprising:

a transmitter that transmits two pilots using a two-dimensional resource block having a first number of consecutive frequency tones along frequency domain and a second number of consecutive time slots along time domain; and

a pilot allocation module that generates and allocates the two pilots into the resource block, wherein the resource block is partitioned into two equal sub-blocks, wherein each pilot is positioned near the center of each sub-block such that pilot-to-data distance is minimized, and wherein each pilot is positioned in different time slot or frequency tone such that pilot-to-pilot distance is as large as possible.

23. The wireless communications device of claim 22, wherein the first number is six and the second number is two, wherein the resource block is partitioned along the frequency domain, and wherein each pilot is positioned at the center frequency tone of each sub-block and two pilots are positioned in different time slots.

24. The wireless communications device of claim 22, wherein the first number is two and the second number is six, wherein the resource block is partitioned along the time domain, and wherein each pilot is positioned at the center time slot of each sub-block and two pilots are positioned in different frequency tones.

25. A wireless communications device, comprising:

one or more than one transmitter that transmits two pairs of pilots for two data streams using a two-dimensional resource block having a first number of consecutive frequency tones along frequency domain and a second number of consecutive time slots along time domain; and

a pilot allocation module that generates and allocates the two pairs of pilots into the resource block, wherein one pair of pilots for one data stream is positioned diagonally at two corners of the resource block, and wherein the other pair of pilots for another data stream is positioned diagonally at the other two corners of the resource block.

26. The wireless communications device of claim 25, wherein the first number is six and the second number is four.

27. The wireless communications device of claim 25, wherein the first number is four and the second number is six.

28. A wireless communications device, comprising:

a transmitter that transmits four pilots using a two-dimensional resource block having a first number of consecutive frequency tones along frequency domain and a second number of consecutive time slots along time domain; and

a pilot allocation module that generates and allocates the four pilots into the resource block, wherein the four pilots are positioned at four corners of the resource block, and wherein two diagonal pilots are shifted inside by one time slot such that power fluctuation is minimized.

29. The wireless communications device of claim 28, wherein the first number is six and the second number is four.

30. The wireless communications device of claim 28, wherein the first number is four and the second number is six.