The present invention relates to a trellis coded modulation (TCM); and more particularly, to a TCM encoder estimating method for transmitting dual stream and an optimal encoder using the same.
Trellis coded modulation (TCM) is a modulation scheme designed through combining an encoding scheme and a modulation scheme, which improves transmission efficiency while minimizing the loss of a frequency width. Dual stream transmission scheme is a transmission scheme for improving transmission efficiency while sustaining backward compatibility with a conventional encoding scheme. That is, the dual stream transmission scheme transmit data stream by interposing a stream encoded by a code having a superior code gain compared to a conventional coding scheme.
Although a TCM encoder using a single stream was introduced, a TCM encoder for dual stream is not developed yet.
It is, therefore, an object of the present invention to provide a method for estimating an optimal ½ rate encoder and an optimal ¼ rate encoder for a dual stream transmission scheme that is introduced to improve a performance for a standard 8-VSB, and an encoder using the same.
In accordance with one aspect of the present invention, there is provided a method of estimating an encoder for dual stream transmission, including the steps of: a) setting up the number of memories required for an encoder, a free distance condition for robust data, and a free distance condition for mixed stream of robust data and normal data; b) obtaining ½ rate encoder combinations that sustain backward compatibility with a conventional trellis encoder; c) obtaining encoder combinations H that satisfy the free distance condition for the robust data and the free distance condition for the mixed stream from the ½ rate encoder combinations; d) obtaining relations between memories and input/output signals, which satisfy the encoder combinations H; and e) configuring an encoder according to the obtained relation between the memories and the input/output signals.
In accordance with another aspect of the present invention, there is provided an encoder for dual stream transmission including: an input terminal; three output terminals; and four memories connected to the input terminal and the output terminals to satisfy an equation:
where st4, st3, st2, and st1 denote states of memories, ot2, ot1 and ot0 denote outputs of an encoder, in denotes an input of encoder, and hj is an octal number.
The method for estimating an encoder for dual stream transmission and an encoder using the same according to the present invention reduce a signal-to-noise ratio (SNR) that satisfies a threshold of visibility (TOV) by improving the receiving performance for normal data as well as robust stream.
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:
Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.
Referring to
At step S120, it obtains a ½ rate encoder combination h that satisfies Eq. 1 and sustains backward compatibility with a conventional encoder. In Eq. 1, st4, st3, st2, and st1 denote the states of the memories, ot2, ot1, and ot0 denote the outputs of the encoder, and the input of the encoder is in.
Herein, the conventional encoder is a typical trellis encoder shown in
In Eq. 1, all of the operations are a modulo 2 operation, simply,
When hj is expressed as octal numbers, hj must be fixed as h4=1, h3=6, and h0=1 in order to sustain the backward compatibility with the conventional encoder. Therefore, a ½ rate encoder that sustains the backward compatibility with the conventional encoder is estimated using h=[h6, h5, h2, h0] with h4, h3, and h1 cancelled. Herein, the ½ rate encoder means that one symbol transmits one bit data.
After calculating the encoder combinations h at step S120, it obtains encoder combinations H that satisfy a free distance condition for robust data and another free distance condition for mixed stream of robust data and normal data from the encoder combinations h. In the present embodiment, the free distance condition R for the robust stream is setup as 164 and 168, and the free distance condition R+N for the mixed stream of the normal steam and the robust stream is setup as a below Table 1.
Table 1 shows 2688 optimal ½ rate encoders H, where R denotes a free distance for a robust stream and R+N denotes a free distance for a robust stream and a normal stream.
Table 1 is obtained by calculating combinations that satisfy the values of R and R+N from h=[h6, h5, h2, h1] through simulations.
After obtaining the optimal ½ rate encoders H that sustain the backward compatibility of the typical encoder, it obtains a relational equation between memories the input/output signals, which satisfy each of the H values at step S140. Finally, an encoder is configured to satisfy the obtained relational equation from step S140. Hereinafter, a method for obtaining the relational equation between the memories and the input/output signals from H values in Table 1, and a method of configuring an encoder from the relational equation will be described.
<relational equation of memories and input/output signal when h=[4 34 20 4]>
st4=0in+0st4+1st3+0st2+0st1
st3=1in+1st4+1st3+0st2+0st1
ot2=1in+0st4+0st3+0st2+0st1
ot1=0in+0st4+1st3+0st2+0st1
As shown in the relational equations, an encoder structure shown in
Referring to
Until now, the ½ rate encoder in which single symbol transmits 1 bit input data is described. However, the present invention can be applied into a ¼ rate encoder in which 2 symbols transmits 1 bit input data. Hereinafter, a method for estimating a ¼ rate encoder and the ¼ rate encoder will be described.
An encoder with a ¼ code rate shown in
The encoder having a ¼ code rate shown in
v(i)=c*g(i) Eq. 2
In Eq. 2, * denotes a convolution operation, and gω=(g0ω, g1ω, . . . , gvω). Therefore, an non-feedback encoder shown in
and gi is expressed as an octal number.
The encoders with n=4 and v=2 in
In Table 4, R denotes a robust steam only case, and R+N denotes a mixed stream of a robust stream and a normal stream.
In
The above described method according to the present invention can be embodied as a program and stored on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by the computer system. The computer readable recording medium includes a read-only memory (ROM), a random-access memory (RAM), a CD-ROM, a floppy disk, a hard disk and an optical magnetic disk.
The present application contains subject matter related to Korean patent application Nos. 2005-0065396 and 2006-0052548, filed in the Korean Intellectual Property Office on Sep. 19, 2005, and Jun. 12, 2006, the entire contents of which is incorporated herein by reference.
While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
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