Pilot pattern design for high-rank MIMO OFDMA systems

• US 20090257519A1
• 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 8,724,717 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, in a high-rank MIMO system, pilots are allocated within a resource block to avoid channel extrapolation in frequency domain only. Because high-rank MIMO only supports low-mobility environment, time-domain extrapolation is no longer a dominant factor. For uplink transmission, one or more frequency tones at one or more edges of the resource block are reserved to be pilot-free to reduce multiuser synchronization error effect. When continuous resource blocks are jointly used for channel estimation, the upper and lower edges of each resource block are left with blanks such that edge pilots of adjacent resource blocks are not too close to each other to improve channel estimation.

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 an array of frequency tones along frequency domain and an array of time slots along time domain;

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

c) positioning two pilots near two edges of the resource block in the frequency domain to avoid channel extrapolation, and then positioning remaining pilots of the specified number of pilots to be maximally equally spaced in between the allocated two pilots along the frequency domain.

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 2, wherein the determining in b) involves calculating pilot spacing constraints based on two-dimensional sampling theory.

4. 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.

5. The method of claim 1, wherein the OFDMA communications system is a high-rank multi-input multi-output (MIMO) system with at least four streams, wherein the positioning in c) is repeated with respect to each stream.

6. The method of claim 5, wherein an approximately equal number of pilot tones are evenly distributed along the time domain with respect to each stream to minimize power fluctuation.

7. The method of claim 1, further comprising:

d) reserving one or more frequency tones at one or more edges of the resource block to be pilot-free such that multiuser synchronization error effect is reduced.

8. The method of claim 1, further comprising:

d) reserving one or more frequency tones at two edges of the resource block in the frequency domain such that edge pilots of adjacent resource blocks are sufficiently apart with each other to improve channel estimation if two or more adjacent resource blocks are available to be used for channel estimation.

9. 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.

10. 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 an array of frequency tones along frequency domain and an array 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, wherein two pilots are allocated near two edges of the resource block in the frequency domain, and wherein remaining pilots of the specified number of pilots are maximally equally spaced in between the allocated two pilots along the frequency domain.

11. The wireless communications device of claim 10, 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.

12. The wireless communications device of claim 10, wherein an approximately equal number of pilot tones are evenly distributed along the time domain to minimize power fluctuation.

13. The wireless communications device of claim 10, wherein at least four streams are transmitted in a high-rank multi-input multi-output (MIMO) system using the same resource block.

14. The wireless communications device of claim 13, wherein an approximately equal number of pilot tones are evenly distributed along the time domain with respect to each stream to minimize power fluctuation.

15. The wireless communications device of claim 10, wherein one or more frequency tones at one or more edges of the resource block are reserved to be pilot-free such that multiuser synchronization error effect is reduced.

16. The wireless communications device of claim 10, wherein one or more frequency tones at two edges of the resource block are reserved such that edge pilots of adjacent resource blocks are sufficiently apart with each other to improve channel estimation if two or more adjacent resource blocks are available to be used for channel estimation.

17. The wireless communications device of claim 10, 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.

18. A wireless communications device, comprising:

a plurality of transmitters that transmit a plurality sets of three pilot tones for a plurality of data streams respectively using a predefined two-dimensional resource block having eighteen consecutive frequency tones along frequency domain and six consecutive time slots along time domain; and

a pilot allocation module that generates and allocates each set of the pilot tones for each data stream respectively, wherein a first pilot of each set is allocated at one of the two smallest frequency tones, wherein a second pilot of each set is allocated at one of the two largest frequency tones, wherein a third pilot of the same set is allocated at one of the two frequency tones in the middle of the resource block along the frequency domain, and wherein the middle two time slots are pilot-free.

19. The wireless communications device of claim 18, wherein the number of sets of pilots and the number of data streams have an equal value range from five to eight.

20. The wireless communications device of claim 18, wherein no more than one pilot is allocated with respect to each data stream along the same time slot to minimize power fluctuation.

21. The wireless communications device of claim 18, wherein the resource block is reduced to have five consecutive time slots, and wherein one of the pilot-free middle time slots is removed.

22. The wireless communications device of claim 18, wherein the resource block is extended to have seven consecutive time slots, and wherein one more pilot-free time slot is added as a largest time slot without reallocating any of the pilots.

23. A wireless communications device, comprising:

a plurality of transmitters that transmit a plurality of sets of two pilots for a plurality of data streams using a predefined two-dimensional resource block having eighteen frequency tones along frequency domain and six time slots along time domain; and

a pilot allocation module that generates and allocates each set of pilots for each data stream respectively, wherein a first pilot of each pilot set is allocated at the fourth or the fifth frequency tones, wherein a second pilot of each pilot set are allocated at the fourteenth or the fifteenth frequency tones, and wherein the middle two time slots are pilot free.

24. The wireless communications device of claim 23, wherein the number of sets of pilots and the number of data streams have an equal value range from five to eight.

25. The wireless communications device of claim 23, wherein no more than one pilot is allocated with respect to each data stream along the same time slot to minimize power fluctuation.

26. The wireless communications device of claim 23, wherein continuous resource blocks are jointly used for channel estimation.

27. The wireless communications device of claim 23, wherein the second pilot of each pilot set is shifted by one frequency tone to be allocated at the thirteenth or the fourteenth frequency tones.

28. The wireless communications device of claim 23, wherein the resource block is reduced to have five consecutive time slots, and wherein one of the pilot-free middle time slots is removed.

29. The wireless communications device of claim 23, wherein the resource block is extended to have seven consecutive time slots, and wherein one more pilot-free time slot is added as a largest time slot without reallocating any of the pilots.