Inter-symbol and inter-carrier interference canceller for multi-carrier modulation receivers

• US 20070019746A1
• Filed: 10/24/2005
• Published: 01/25/2007
• Est. Priority Date: 07/21/2005
• Status: Active Grant

• Current Assignee: Realtek Semiconductor Corp.
• Original Assignee: Realtek Semiconductor Corp.
• Inventors: Lin, Chia-Liang, Yeh, Heng-Cheng, Li, Cheng-Hsian
• Granted Patent: US 7,693,225 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

A MCM (multi-carrier modulation) receiver that utilizes a plurality tones to transmit information. Identify a first subset of tones that have negligible ISI (inter-symbol interference) and ICI (inter-carrier interference), and a second subset of tones that ISI/ICI cancellation is needed to improve the performance. For tones in the first subset, conventional FEQ (frequency-domain equalization) is performed to obtained soft decisions from the raw decisions. For those tones in the second subset, perform FEQ along with ICI/ISI cancellation. For tones in the second subset, identify a third subset (one for each of the tones in the second subset) to perform ICI cancellation and a series of fourth subsets (one for each of the tones in the second subset) to perform ISI cancellation. The selection of the first subset, the second subset, the third subset (for each of the tone in the second subset), and the fourth subset (for each of the tone in the second subset) are based on examining the frequency response of the communication channel.

Claims

1. A method of receiving multi-carrier data, the method comprising:

receiving a sequence of blocks of frequency domain data comprising N elements, each representing the modulation onto a certain sub-carrier;

selecting a first subset U among the N elements and performing frequency-domain equalization for each element u in U; and

selecting a second subset A among the N elements performing both frequency-domain equalization and interference cancellation for each element a in A.

2. The method of claim 1, wherein performing frequency-domain equalization further comprises multiplying the element with a respective equalization coefficient.

3. The method of claim 2, wherein performing interference cancellation for each element a in subset A further comprises:

selecting a third subset M and performing inter-carrier interference cancellation for removing the interference caused to element a by the elements in M in current time instant; and

selecting a fourth subset P and performing inter-symbol interference cancellation for removing the interference caused to element a by the elements in P in previous time instants.

4. The method of claim 3, wherein performing the inter-carrier interference cancellation further comprises:

multiplying each of the elements in M with a respective inter-carrier coupling coefficient;

summing all the multiplication products; and

subtracting the summing result from element a.

5. The method of claim 4, wherein performing the inter-symbol interference cancellation further comprises:

multiplying each of the elements in P with a respective inter-carrier coupling coefficient;

summing all the multiplication products; and

subtracting the summing result from element a.

6. The method of claim 2, wherein performing frequency domain equalization further comprises:

making a most likely decision on the element after performing frequency domain equalization or both frequency domain equalization and interference cancellation;

calculating the difference between the most likely decision and the element after equalization or both equalization and cancellation; and

using the difference to adapt the equalization coefficient to minimize the difference.

7. The method of claim 3, wherein performing inter-carrier interference further comprises:

making a most likely decision on the element after performing both frequency domain equalization and interference cancellation;

calculating the difference between the most likely decision and the element after equalization and cancellation; and

using the difference to adapt the inter-carrier coupling coefficient to minimize the difference.

8. The method of claim 4, wherein performing inter-symbol interference further comprises:

making a most likely decision on the element after performing both frequency domain equalization and interference cancellation;

calculating the difference between the most likely decision and the element after equalization and cancellation; and

using the difference to adapt the inter-symbol coupling coefficient to minimize the difference.

9. A device comprising:

a receiver including a frequency domain equalizer/interference canceller, the frequency domain equalizer/interference canceller including an input, a tone selector, and an output;

the input adapted to receive a discrete multi-tone signal including a plurality of tones;

the tone selector adapted to generate a first subset of tones that have negligible inter-carrier interference and negligible inter-symbol interference, and a second subset of tones that have significant inter-carrier interference and significant inter-symbol interference;

and the output adapted to provide a soft decision for each of a first subset of the plurality of tones and a soft decision for each of a second subset of the plurality of tones.

10. The device of claim 9, further including a decision device coupled to the output of the frequency domain equalizer/interference canceller, the decision device adapted to generate a set of most likely constellation points, said hard decisions from the soft decision of each of the first subset and the second subset of the plurality of tones.

11. The device of claim 10, further including a feedback loop coupling an output of the decision device with a feedback input of the frequency domain equalizer/interference canceller, the feedback loop adapted to provide the frequency domain equalizer/interference canceller with a set of hard decisions generated by the decision device from the soft decision for each of the second subset of the plurality of tones.

12. The device of claim 11, wherein the frequency domain equalizer/interference canceller is adapted generate a soft decision for each of the second subset of tones based on the hard decisions provided at the feedback input.

13. The device of claim 9, further including a memory coupled to the frequency domain equalizer/interference canceller, adapted to store hard decisions from one or more discrete multi-tone symbols known to be transmitted from a transmitter.

14. The device of claim 13, wherein the frequency domain equalizer/interference canceller is adapted to generate a soft decision for each tone in the second subset of tones based on the hard decision generated for each tone of a discrete multi-tone symbol stored in the memory.

15. The device of claim 10, further including a decoder coupled to the frequency domain equalizer/interference canceller, the decoder adapted to perform forward error correction on the output of the frequency domain equalizer/interference and generate an alternative hard decision for each of the first subset and the second subset of the plurality of tones.

16. The device of claim 15, further including a feedback loop coupling an output of the decoder with a feedback input of the frequency domain equalizer/interference canceller, the feedback loop adapted to provide the frequency domain equalizer/interference canceller with a set of alternative hard decisions generated by the decoder for each of the first subset and the second subset of the plurality of tones.

17. A system comprising

a transmitter adapted to generate a multi-carrier modulation signal, the signal including a plurality of tones utilized to transmit information;

a communication channel having a frequency response coupled to the transmitter, the communication channel adapted to transmit the multi-carrier modulation signal generated by the transmitter;

a receiver including a frequency domain equalizer/interference canceller;

wherein the frequency domain equalizer/interference canceller is adapted to receive a first set of frequency domain samples, and to determine from the plurality of tones a first subset of tones that are close to being orthogonal to one another under the influence of the communication channel and a second subset of tones that are far from being orthogonal to one another under the influence of the communication channel.

18. The system of claim 17, wherein the first subset of tones includes tones that are at least a number of tones away from the transition band between two non-overlapping frequency bands or a transition edge in the frequency response of the communication channel.

19. The system of claim 17, wherein the second subset of tones includes one or more tones that are closest to the transition band between two non-overlapping frequency bands or a transition edge in the frequency response of the communication channel.

20. The system of claim 17 further including a decision device coupled to the output of the frequency domain equalizer/interference canceller, the decision device adapted to receive a soft decision regarding a constellation point for each of the tones in the first set of tones, and a soft decision regarding a constellation point for each of the tones in the second subset of tones.

21. The system of claim 20, wherein the decision device is further adapted to generate a hard decision regarding the a most likely constellation point for each of the tones in the first set of tones, and a hard decision regarding a most likely constellation point for each of the tones in the second subset of tones.

22. The system of claim 21, wherein the frequency domain equalizer/interference canceller processes each of the tones in the first subset by multiplying the frequency domain sample of each tone with an equalization constant.

23. The system of claim 21, wherein the frequency domain equalizer/interference canceller processes each of the tones in the second subset by multiplying the frequency domain sample of each tone with an equalization constant and subtracting from the multiplication product the coupling from each of other tones in the second subset.

24. The system of claim 23, wherein the coupling from each of other tones in the second subset, said the coupling from tone X to tone Y in the second subset is a multiplication product between an coupling coefficient and the frequency domain data for tone X, or the soft decision for tone X, or the hard decision for tone X.