Symbol-Wise Channel Tracking For SUN OFDM

• US 20140307813A1
• Filed: 12/31/2013
• Published: 10/16/2014
• Est. Priority Date: 04/10/2013
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: HOSHYAR, Reza, BATRA, Anuj, SCHMIDL, Timothy Mark
• Granted Patent: US 9,083,571 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/023 with extension to other symbols
• CPC Class Codes: H04L 27/26 Systems using multi-frequency codes H04L27/32 takes precedence
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A device for updating complex channel gain estimates for orthogonal frequency division multiplexed (OFDM) symbols that includes a receiver to receive a plurality of OFDM symbols, wherein each OFDM symbol includes a plurality of pilot tones at a subset of odd positions and a finite impulse response (FIR) filter. The FIR filter configured to filter a plurality of initial channel estimates of odd tones of an OFDM symbol using a first set of coefficients to generate an updated estimate of the channel estimates of the plurality of odd tones for that OFDM symbol, and filter the plurality of the initial channel estimates of the odd tones of the OFDM symbol using a second set of coefficients to generate estimates for a plurality of initial channel estimates of even tones for that OFDM symbol.

Claims

1. A device for updating channel gain estimates for orthogonal frequency division multiplexed (OFDM) symbols, comprising:

a receiver to receive a plurality of OFDM symbols, wherein each OFDM symbol includes a plurality of pilot tones at a subset of odd positions; and

a finite impulse response (FIR) filter configured to;

filter a plurality of channel estimates of odd tones of an OFDM symbol using a first set of coefficients to generate an updated estimate of the channel estimates of the plurality of odd tones for that OFDM symbol, and

filter the plurality of the channel estimates of the odd tones of the OFDM symbol using a second set of coefficients to generate estimates for a plurality of initial channel estimates of even tones for that OFDM symbol.

2. The device of claim 1, wherein the device further comprises a buffer to store the channel estimates of a previous OFDM symbol of the plurality of OFDM symbols.

3. The device of claim 1, wherein the odd tones of each OFDM symbol comprise that symbol'"'"'s plurality of pilot tones and all other odd tones of the OFDM symbol are taken from a previous OFDM symbol.

4. The device of claim 1, wherein a first OFDM symbol of the plurality of symbols is a preamble symbol containing the channel estimates for all tones of the first OFDM symbol.

5. The device of claim 1, wherein a FIR filtering window is longer for filtering the odd tones than for filtering the even tones.

6. The device of claim 1, wherein the FIR filter filters edge and close-to-edge tones of the OFDM symbols differently than middle tones of the OFDM symbol.

7. The device of claim 1, wherein the FIR filter is implemented with a shift register.

8. The device of claim 7, wherein the shift register receives the odd tones as inputs and the positions of the shift register are multiplied by different coefficients to generate the updated odd tones and the even tones of the OFDM symbols.

9. A low complexity channel tracking orthogonal frequency-division multiplexed (OFDM)-based device, comprising:

a receiver to receive OFDM symbols and to update estimates of the channel gain of the tones of the OFDM symbols and to smooth the channel estimates of the OFDM symbols along a time-domain;

the receiver comprising a finite impulse response (FIR) filter and a buffer, the FIR filter configured to;

filter a plurality of initial channel gain estimates of a plurality of odd tones of an OFDM symbol based on a first set of coefficients to generate an updated estimate of the channel gain for the plurality of odd tones of the OFDM symbol; and

filter the plurality of gain estimates of the plurality of the odd tones of the OFDM symbol based on a second set of coefficients to generate an estimate of the channel gain for a plurality of even tones of the OFDM symbol.

10. The device of claim 9, wherein the buffer is configured to store the channel gain estimates of a previous OFDM symbol.

11. The device of claim 10, wherein the channel gain of the plurality of the odd tones of the OFDM symbol other than the pilot tone are taken from the previous OFDM symbol'"'"'s odd tones.

12. The device of claim 11, wherein the odd tones of a first OFDM symbol other than the pilot tone are taken from a long training field (LTF) symbol.

13. The device of claim 9, wherein middle tones of the OFDM symbol are filtered differently than edge tones of the OFDM symbol.

14. The device of claim 13, wherein the edge tones and middle tones are filtered differently due to a length of the filtering window.

15. The device of claim 9, wherein the FIR filter is a shift register.

16. The device of claim 15, wherein inputs to the shift register are the channel gain estimates of the odd tones of the OFDM symbol and positions of the shift register are multiplied by the first set of coefficients to generate the updated channel gain estimates of the odd tones and the second set of coefficients to generate the estimate of the channel gain for the even tones.

17. A method to update the channel gain of each tone of an orthogonal frequency-division multiplexed (OFDM) symbol, comprising:

buffering, by a receiver, a first OFDM symbol, wherein the first OFDM symbol comprises estimates of a channel gain for each odd tone of the OFDM symbol;

receiving, by the receiver, a second OFDM symbol, wherein the second OFDM symbol includes a plurality of pilot tones at a subset of odd tone positions;

replacing, by the receiver, all of the odd tones of the second OFDM symbol other than the plurality of pilot tones with the initial estimates of the channel gain from corresponding odd tones of the first OFDM symbol;

filtering, by a finite impulse response (FIR) filter, the replaced odd tones and the plurality of pilot tones of the second OFDM symbol using a first set of FIR filter coefficients to generate updated channel gain estimates for the odd tones of the second OFDM symbol; and

filtering, by the FIR filter, the replaced odd tones and the plurality of pilot tones of the second OFDM symbol using a second set of FIR filter coefficients to generate an estimate of the channel gain for even tones of the second OFDM symbol.

18. The method of claim 17, wherein the first OFDM symbol is a long training format symbol.

19. The method of claim 17, wherein a length of the FIR filter is different for generating the updated channel gain estimates for the odd tones than for generating the estimate of the channel gain for even tones of the second OFDM symbol.

20. The method of claim 17, wherein middle tones of the second OFDM symbol are filtered differently than edge tones of the second OFDM symbol.

21. The method of claim 17, further comprising, replacing the first OFDM symbol with the replaced odd tones and the plurality of pilot tones of the second OFDM symbol.