Scattered pilot pattern and channel estimation method for MIMO-OFDM systems

• US 8,254,246 B2
• Filed: 05/19/2009
• Issued: 08/28/2012
• Est. Priority Date: 10/17/2001
• Status: Expired due to Term

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Ma, Jianglei, Jia, Ming, Zhu, Peiying, Tong, Wen
• Primary Examiner(s): Jagannathan, Melanie
• Application Number:
  US12/468,624
• Publication Number:
  US 20090225891A1
• Time in Patent Office: 1,197 Days
• Field of Search: None
• US Class Current: 370/208
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0234 by non-linear interpolation
• CPC Class Codes: H04L 25/0244 with inversion
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/26035 Maintenance of orthogonality, e.g. for signals exchanged between cells or users, or by using covering codes or sequences using different training sequence per antenna H04B7/0684; code allocation H04J13/16
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/2627 Modulators
• 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
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

A method and apparatus are provided for reducing the number of pilot symbols within a MIMO-OFDM communication system, and for improving channel estimation within such a system. For each transmitting antenna in an OFDM transmitter, pilot symbols are encoded so as to be unique to the transmitting antenna. The encoded pilot symbols are then inserted into an OFDM frame to form a diamond lattice, the diamond lattices for the different transmitting antennae using the same frequencies but being offset from each other by a single symbol in the time domain. At the OFDM receiver, a channel response is estimated for a symbol central to each diamond of the diamond lattice using a two-dimensional interpolation. The estimated channel responses are smoothed in the frequency domain. The channel responses of remaining symbols are then estimated by interpolation in the frequency domain.

Claims

1. A method of inserting pilot symbols into Orthogonal Frequency Division Multiplexing (OFDM) frames at an OFDM base station having a plurality of transmitting antennas, the OFDM base station neighboring an adjacent OFDM base station having a plurality of transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols, the method comprising the steps of:

for each antenna, inserting scattered pilot symbols in an identical scattered pattern in time-frequency, wherein the scattered patterns are offset from the adjacent OFDM base station.

2. The method of claim 1, wherein inserting scattered pilot symbols comprises:

inserting scattered pilot symbols in a respective location within the scattered pattern on a same sub-carrier.

3. The method of claim 1, wherein inserting scattered pilot symbols in an identical scattered pattern in time-frequency comprises:

inserting scattered pilot symbols at locations that form at least one diagonal arrangement in time-frequency.

4. The method of claim 1 further comprising transmitting the scattered pilot symbols with a power level greater than a power level of data symbols, depending upon a value reflective of channel conditions.

5. The method of claim 1 further comprising transmitting the scattered pilot symbols with a power level which is dynamically adjusted to ensure sufficiently accurate reception as a function of a modulation type applied to sub-carriers carrying data.

6. The method of claim 1, wherein the scattered pattern in time-frequency includes a first plurality of pilot symbols, each pilot symbol of the first plurality of pilot symbols spaced six subcarriers apart.

7. The method of claim 6 wherein the scattered pattern in time-frequency includes a second plurality of pilot symbols, each pilot symbol of the second plurality of pilot symbols spaced six subcarriers apart, the second plurality of pilot symbols offset from the first plurality of pilot symbols by three subcarriers.

8. The method of claim 7, wherein the second plurality of pilot symbols is offset in time from the first plurality of pilot symbols.

9. The method of claim 1, wherein the offset is in at least one of time or frequency.

10. The method of claim 1, wherein the adjacent OFDM base station transmits, for each of its plurality of antennas, a scattered pattern of pilot symbols in time-frequency.

11. A system comprising:

a first Orthogonal Frequency Division Multiplexing (OFDM) base station having a plurality of transmitting antennas, the first OFDM base station configured to insert scattered pilot symbols into OFDM frames, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols; and

a second OFDM base station adjacent the first OFDM base station, the second OFDM base station having a plurality of transmitting antennas, the second OFDM base station configured to insert scattered pilot symbols into OFDM frames;

wherein, for each antenna of the first OFDM base station and each antenna of the second OFDM base station, the scattered pilot symbols are in an identical scattered pattern in time-frequency, wherein the scattered patterns for the first OFDM base station are offset from the scattered patterns for the second OFDM base stations.

12. The system of claim 11, wherein the offset is in at least one of time and frequency.

13. The system of claim 11, wherein the scattered pilot symbols for the first and second base stations are in a respective location within the scattered pattern on a same sub-carrier.

14. The system of claim 11, wherein the first OFDM base station transmits, for each of its plurality of antennas, a scattered pattern of pilot symbols in time-frequency;

and the second OFDM base station transmits, for each of its plurality of antennas, a scattered pattern of pilot symbols in time-frequency.

15. An Orthogonal Frequency Division Multiplexing (OFDM) base station comprising:

a plurality of transmitting antennas; and

an OFDM frame generator that inserts pilot symbols into OFDM frames, the OFDM base station neighboring an adjacent OFDM base station having a plurality of transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols, wherein for each antenna, scattered pilot symbols are inserted in an identical scattered pattern in time-frequency, wherein the scattered patterns are offset from the adjacent OFDM base station.

16. The OFDM base station of claim 15, wherein the scattered pilot symbols are inserted in a respective location within the scattered pattern on a same sub-carrier.

17. The OFDM base station of claim 15, wherein the scattered pilot symbols are inserted at locations that form at least one diagonal arrangement in time-frequency.

18. The OFDM base station of claim 15 further comprising a transmitter configured to transmit the scattered pilot symbols with a power level greater than a power level of data symbols, depending upon a value reflective of channel conditions.

19. The OFDM base station of claim 15 further comprising a transmitter configured to transmit the scattered pilot symbols with a power level which is dynamically adjusted to ensure sufficiently accurate reception as a function of a modulation type applied to sub-carriers carrying data.

20. The OFDM base station of claim 15 wherein the scattered pattern in time-frequency includes a first plurality of pilot symbols, each pilot symbol of the first plurality of pilot symbols spaced six subcarriers apart.

21. The OFDM base station of claim 20 wherein the scattered pattern in time-frequency includes a second plurality of pilot symbols, each pilot symbol of the second plurality of pilot symbols spaced six subcarriers apart, the second plurality of pilot symbols offset from the first plurality of pilot symbols by three subcarriers.

22. The OFDM base station of claim 21, wherein the second plurality of pilot symbols is offset in time from the first plurality of pilot symbols.

23. The OFDM base station of claim 15, wherein the offset is at least one of time and frequency.