QAM signal decoding

• US 20050002465A1
• Filed: 06/25/2004
• Published: 01/06/2005
• Est. Priority Date: 07/03/2003
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Jeong, Jun-young
• Granted Patent: US 7,706,460 B2
• Time in Patent Office: Days
• US Class Current: 375/261
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

A demodulator recovers a transmitted symbol represented by a received quadrature amplitude modulation (QAM) signal. Such a demodulator may include: a QAM-decoding block operable to map a received signal vector onto a constellation so as to yield a first symbol, and identify a next-most probable second symbol based upon the signal vector; and a selection unit operable to select, among the first and second symbols, the one having the lower error content as corresponding to the transmitted symbol. A corresponding method may include similar steps.

Claims

1. A demodulator for recovering a transmitted symbol represented by a received quadrature amplitude modulation (QAM) signal, the demodulator comprising:

a QAM-decoding block operable to

map a received signal vector onto a constellation so as to yield a first symbol, and

identify a next-most probable second symbol based upon the signal vector; and

a selection unit operable to select, among the first and second symbols, the one having the lower error content as corresponding to the transmitted symbol.

2. The demodulator of claim 1, wherein:

the QAM-decoding block includes

at least two decoders operable to produce at least first and second bit streams corresponding to the first and second symbols, respectively; and

the selection unit includes

at least two error-checking units operable upon the first and second bit streams; and

logic to select the one of the first and second bit streams having the lower error content as corresponding to the transmitted symbol.

3. The demodulator of claim 2, wherein the error-checking units are operable to perform cyclic redundancy code (CRC) error checking.

4. The demodulator of claim 2, wherein each decoder includes:

a mixer to produce a symmetric version of the signal vector;

first and second conversion units to convert the signal vector and symmetric version thereof into the first and second bit streams, respectively.

5. The demodulator of claim 1, wherein the QAM-decoding block is further operable to

evaluate whether a sub-channel to which the first symbol corresponds is extra-noisy;

determine, if the sub-channel is extra-noisy, whether the signal vector is mapped to an overlap region;

proceed, if the signal vector is mapped to an overlap region, to the identification and selection.

6. The demodulator of claim 5, wherein the QAM-decoding block is further operable to:

skip, if either the sub-channel is not extra-noisy or the signal vector is not mapped to an overlap region, the identification and selection and instead treat the first symbol as corresponding to the transmitted symbol.

7. The demodulator of claim 5, wherein:

the constellation is organized as a grid of square cells;

symbols forming the constellation are located at the centers of the cells, respectively;

each side of the cells is of length, ^d;

each cell has overlap regions corresponding to each adjoining cell, respectively;

each overlap region for a given cell is defined as the intersection of the given cell and a circle of radius, r, for the corresponding adjoining cell, where

$\frac{d}{2}<<br><br>r\le <br><br>\frac{\sqrt{2}}{2}<br><br>d$

and r is centered upon the adjoining cell.

8. The demodulator of claim 1, wherein:

there are a plurality of neighbor symbols adjacent to the first symbol; and

the second symbol is the one among the neighbor symbols that is located closest to the signal vector.

9. The demodulator of claim 1, wherein the QAM signal is also a multiple-carrier modulated signal.

18. A method comprising steps that together represent the operation of the demodulator of claim 1.

10. A method of recovering a transmitted symbol represented by a received quadrature amplitude modulation (QAM) signal, the method comprising:

mapping a received signal vector onto a constellation to yield a first symbol;

identifying a next-most probable second symbol based upon the signal vector; and

selecting, among the first and second symbols, the one having the lower error content as corresponding to the transmitted symbol.

11. The method of claim 10, further comprising:

receiving an indication of whether a sub-channel to which the first symbol corresponds is extra-noisy;

determining, if the sub-channel is extra-noisy, whether the mapping step has mapped the signal vector to an overlap region; and

proceeding, if the signal vector is mapped to an overlap region, to the identifying and selecting steps.

12. The method of claim 11, further comprising:

skipping, if either the sub-channel is not extra-noisy or the signal vector is not mapped to overlap region, the identifying and selecting steps and instead treating the first symbol as corresponding to the transmitted symbol.

13. The method of claim 11, wherein:

the constellation is organized as a grid of square cells;

symbols forming the constellation are located at the centers of the cells, respectively;

each side of the cells is of length, ^d;

each cell has overlap regions corresponding to each adjoining cell, respectively; and

each overlap region for a given cell is defined as the intersection of the given cell and a circle of radius, ^r, for the corresponding adjoining cell, where

$\frac{d}{2}<<br><br>r\le <br><br>\frac{\sqrt{2}}{2}<br><br>d$

and r is centered upon the adjoining cell.

14. The method of claim 10, wherein:

there are a plurality of neighbor symbols adjacent to the first symbol; and

the second symbol is the one among the neighbor symbols that is located closest to the signal vector.

15. The method of claim 10, wherein the selecting step includes performing cyclic redundancy code (CRC) error checking on each of the first and second symbols.

16. The method of claim 10, wherein the QAM signal is also a multiple-carrier modulated signal.

17. A demodulator comprising components operable together to perform the method of claim 10.