This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0022106 filed in the Korean Intellectual Property Office on Feb. 25, 2014, the entire contents of which are incorporated herein by reference.
(a) Field of the Invention
The present invention relates to a digital demodulation method and system, and more particularly, to a technique of improving reception performance by changing detection levels at a receiver in a communication system using a digital demodulation scheme.
(b) Description of the Related Art
In a communication system using a conventional digital modulation scheme, reception performance can be improved by changing detection levels at a receiver.
There are many standards that are expected to adopt non-uniform constellation transmission technology in the future to improve system performance. Some standards have already adopted this technology. Due to changes in constellations made at a transmitter, the non-uniform constellation transmission technology can achieve performance improvement only by changing detection levels at a receiver.
The present invention has been made in an effort to provide a digital demodulation method and system which are backward-compatible and have non-uniform detection levels.
An exemplary embodiment of the present invention provides a digital demodulation method for a digital demodulation system that demodulates a received signal, the method including: calculating an I channel value and a Q channel value of a received signal; changing detection levels to obtain non-uniform detection levels; and demodulating the received signal bit by bit by using the changed detection levels, the I channel value, and the Q channel value.
In the changing of detection levels, the detection levels may be changed in accordance with constellation points of a transmitting system.
The changing of detection levels may include: calculating initial soft-decision values for first and second bits by using the I channel value and the Q channel value of the received signal; and changing the detection levels corresponding to an i-th lowest power level by using αi.
Another exemplary embodiment of the present invention provides a digital demodulation system including: a receiver that calculates an I channel value and a Q channel value of a received signal; a detection level calculator that changes detection levels to obtain non-uniform detection levels; and a demodulator that demodulates the received signal bit by bit by using the I channel value and the Q channel value calculated by the receiver and the detection levels changed by the detection level calculator.
The detection level calculator may change the detection levels in accordance with constellation points of a transmitting system.
The detection level calculator may calculate initial soft-decision values for first and second bits by using the I channel value and the Q channel value of the received signal, and change the detection levels corresponding to an i-th lowest power level by using αi.
According to an embodiment of the present invention, the performance of a receiver can be improved by using non-uniform detection levels, compared to a receiver with uniform detection levels.
By adjusting detection levels at a receiving system, performance improvement can be achieved for a system with a modulation order such as 8-VSB, 16-QAM 8-APSK, 8-PSK, or higher that uses non-uniform constellations, and detection and reception performance can also be increased for a system that does not use non-uniform constellations.
In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.
A digital modulation system and method according to an exemplary embodiment of the present invention will now be described in detail with reference to the drawings.
Referring to
A digital demodulation system 200 is a system that is backward compatible and has non-uniform detection levels, and includes a receiver 201, a detection level calculator 203, and a demodulator 205.
The receiver 201 receives the signal sent by the transmitter 100 through the I channel and the Q channel. The detection level calculator 203 determines the value of a detection level. In this instance, the detection level calculator 203 changes the detection level. The demodulator 205 demodulates a received signal bit by bit based on the value of the detection level that is changed by the detection level calculator 203.
First, referring to
Next, the detection level calculator 203 adjusts detection levels (S103).
Then, the demodulator 205 performs detection at the detection levels adjusted in S103, and demodulates a received signal bit by bit (S105).
Hereupon, the receiver 201 calculates initial soft decision values for first and second bits. The initial soft decision values are calculated according to b1=Re{s} and b2=Im{s}, respectively, by using the I channel value and the Q channel value of the received signal s.
Based on the amplitude of the received signal, the received signal is demodulated bit by bit. A demodulation system with uniform constellations is as shown in
In
Referring to
Referring to
αi refers to the value of the detection level for the i-th bit, and the value of αi is determined by repeated tests.
As the value of αi varies depending on the transmitting/receiving system, αi is not fixed to a certain value.
The second, fourth, and sixth bits associated with the Q channel value are detected in the same manner as above.
In a system using non-uniform constellations, detection levels need to be changed in accordance with non-uniform constellation points, as shown in
Referring to
In a system using uniform constellations, detection levels are evenly spaced. For a demodulation system with non-uniform constellations, on the other hand, the detection levels need to be changed in accordance with constellation points, as shown in
Moreover, reception performance can be improved by using αi, as shown in
Although
Detection is then performed at the detection levels adjusted in
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Number | Date | Country | Kind |
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10-2014-0022106 | Feb 2014 | KR | national |
Number | Name | Date | Kind |
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7480342 | Wilhelmsson | Jan 2009 | B2 |
20110044407 | Chang et al. | Feb 2011 | A1 |
Number | Date | Country |
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1020110019691 | Feb 2011 | KR |
Number | Date | Country | |
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20150244550 A1 | Aug 2015 | US |