Demodulation of nonuniform QAM signals

Patent metadata

Field	Value
Publication number	US-10038587-B2
Application number	US-201515551092-A
Country	US
Kind code	B2
Filing date	Oct 22, 2015
Priority date	Oct 22, 2015
Publication date	Jul 31, 2018
Grant date	Jul 31, 2018

Abstract

There is provided a device and method for demodulating a pulse amplitude modulated, hereinafter referred to as PAM, signal. The device comprises memory storing a set of boundaries of regions in which the log likelihood ratio, hereinafter referred to as LLR, for each bit to be determined is represented by a linear function of the received signal, along with the properties of the linear function for each bit for each region; and a controller. The controller is configured to: receive a PAM signal to be demodulated; determine which region the signal falls within; for each bit to be determined, retrieve the properties of the linear function for the LLR for the bit within the determined region and determine, from this linear function, the LLR value for the bit; and demodulate the signal based on the determined LLR values.

First claim

The invention claimed is:

1. A device for demodulating a pulse amplitude modulated, hereinafter referred to as PAM, signal, the device comprising:
memory storing a set of boundaries of regions in which the log likelihood ratio, hereinafter referred to as LLR, for each bit to be determined is represented by a linear function of a received signal, along with the properties of the linear function for each bit for each region; and
a controller configured to:
receive a PAM signal to be demodulated;
determine which region the signal falls within;
for each bit to be determined, retrieve the properties of the linear function for the LLR for the bit within a determined region and determine, from this linear function, the LLR value for the bit; and
demodulate the signal based on the determined LLR values.

2. The device of claim 1 wherein:
the received signal is Gray coded according to a predefined set of symbols, each symbol having its own assigned signal value;
the properties of the linear function for each region comprise the gradient and the y-intercept of the linear function within the region; and
the gradient, α i , and y-intercept, β i , for the i th bit for each region obey the following equations:
α i =2( x 1 (i) −x 0 (i) ); and

β i =( x 0 (i) ) 2 −( x 1 (i) ) 2 ,

wherein x 0 (i) and x 1 (i) are signal values assigned to the closest symbols to the region out of the symbols in which the i th bit equals 0 and 1 respectively.

3. The device of claim 2 wherein determining the LLR value for each bit comprises calculating:

LLR
i

=

α
i

⁢
y

+

β
i

σ
2

wherein LLR i is the log likelihood ratio for the i th bit, α i is the gradient for the i th bit, β i is the y-intercept for the i th bit, y is the received signal and σ is a noise variance for the signal.

4. The device of claim 1 wherein determining which region the signal falls within comprises:
(a) ordering the set of boundaries according size, setting a search index to identify a middle boundary of the set of boundaries and setting an initial step size of a quarter of the total number of regions;
(b) determining whether the received signal is greater than the boundary identified by the search index;
(c) if the signal is greater than the boundary identified by the search index, increasing the search index by the step size; otherwise, decreasing the search index by the step size; and
(d) determining whether a single region containing the signal has been identified and, if so, determining this region to be the region within which the signal falls; otherwise, halving the step size and repeating steps (b)-(d).

5. The device of claim 4 wherein a single region is identified when the number of times, k′, the received signal has been compared to a boundary has reached log 2 L, wherein L is the total number of regions.

6. The device of claim 1 , wherein the received signal is Gray-coded according to a predefined set of symbols, each symbol having its own assigned signal value, α i , and wherein the boundaries are located at signal values described by the union of:

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i

+

a

i
+
1

2

}

,

i
=
1

,
…
⁢

,

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2

-
1

;

{

±

a

(

4
⁢
k

+
1

)

⁢

2

m
-
i

+

a

(

4
⁢
k

+
3

)

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m
-
i

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Assignees

• Toshiba Kk

Inventors

• Sandell Magnus Stig Torsten
• Tosato Filippo
• Ismail Amr

Classifications

• H04L27/389 Primary

  with separate demodulation for the phase and amplitude components · CPC title

• H04L25/067

  providing soft decisions, i.e. decisions together with an estimate of reliability (H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178) · CPC title

• H03M13/45

  Soft decoding, i.e. using symbol reliability information (H03M13/41 takes precedence) · CPC title

• H04L27/22

  Demodulator circuits; Receiver circuits · CPC title