Pilot pattern design for high-rank MIMO OFDMA systems

• US 8,724,717 B2
• Filed: 04/08/2009
• Issued: 05/13/2014
• Est. Priority Date: 04/10/2008
• Status: Expired due to Fees

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Lin, Chih-Yuan, Liao, Pei-Kai
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): TAYONG, HELENE E
• Application Number:
  US12/384,705
• Publication Number:
  US 20090257519A1
• Time in Patent Office: 1,861 Days
• Field of Search: 375/260, 714/786, 714/794, 714/795, 370/69.1, 370/323, 370/208, 370/203, 370/206, 370/310, 455/59
• 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 by a wireless communication device 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 by the device based on a set of communications system requirements;

c) determining whether two or more adjacent resource blocks are used for channel estimation; and

d) positioning two pilots by the device near two edges of the resource block in the frequency domain with zero or more spaces from the frequency edges to avoid channel extrapolation based on the determining in c), and positioning remaining pilots of the specified number of pilots to be substantially equally spaced in between the allocated two pilots along the frequency domain; and

e) 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 substantially equally spaced with each other and with other pilots along the frequency domain to improve channel estimation if two or more adjacent resource blocks are available to be used for channel estimation.

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 d) 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 d) is repeated with respect to each stream.

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

7. The method of claim 1, further comprising:

e) 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, 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 for one antenna data stream, and wherein no data symbol is transmitted using the selected frequency tone and the selected time slot for another antenna data stream.

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 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 with zero or more spaces from the frequency edges base on whether two or more adjacent resource blocks are used for channel estimation, and wherein remaining pilots of the specified number of pilots are substantially equally spaced in between the allocated two pilots along the frequency domain, and wherein one or more frequency tones at two edges of the resource block are reserved such that edge pilots of adjacent resource blocks are substantially equally spaced with each other and with other pilots along the frequency domain to improve channel estimation if two or more adjacent resource blocks are available to be used for channel estimation.

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 an approximately equal number of pilot tones are evenly distributed along the time domain to minimize power fluctuation.

12. The wireless communications device of claim 9, wherein at least four streams are transmitted in a high-rank multi-input multi-output (MIMO) system using the same resource block.

13. The wireless communications device of claim 12, wherein an approximately equal number of pilot tones are evenly distributed in each time slot with respect to each stream to minimize transmit power fluctuation.

14. The wireless communications device of claim 9, 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.

15. 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.