Receiving apparatus and receiving method

1. A receiving apparatus comprising:

first correlation value computation means for receiving an orthogonal frequency division multiplexing signal based on a predetermined standard for transmitting data in unit of a frame arranged, at a beginning of said frame, with a preamble signal having a correlation between a first section and a second section that are parts of an entire signal, thereby computing a first correlation value which is a correlation value of signals in two sections separated from each other by a time equal to a time interval between said first section and said second section;

operation means for performing Fourier transform processing on said preamble signal including the signals of the two sections with said first correlation value equal to or higher than a threshold value obtained, thereby generating said orthogonal frequency division multiplexing signal of frequency domain;

second correlation value computation means for computing a second correlation value which is a correlation value between a sequence of subcarriers for use in data transmission among subcarriers of said orthogonal frequency division multiplexing signal of frequency domain and a known sequence;

decoding means for computing third correlation values, each of said third correlation values being a correlation value between data transmitted by subcarriers of a sequence with said second correlation value with said known sequence equal to or higher than a threshold value and a plurality of known items of data having a same number of bits as a bit train indicative of a transmission parameter for use in demodulation of a signal subsequent to said preamble signal, thereby decoding known data having a maximum value of said third correlation values as said transmission parameter; and

determination means for determining whether said maximum value of said plurality of third correlation values computed by said decoding means is less than a predetermined threshold value and, if said maximum value is found to be less than said predetermined threshold value, outputting a signal indicative that said orthogonal frequency division multiplexing signal based on said predetermined standard is not being transmitted on a channel being received.

2. The receiving, apparatus according to claim 1 , wherein, if a maximum value of said first correlation value is higher than a first threshold value and a value of said second correlation value is higher than a second threshold value, said determination means makes comparison between a maximum value of said plurality of third correlation values and said predetermined threshold value.

3. The receiving apparatus according to claim 1 , wherein said predetermined standard is the digital video broadcasting—terrestrial 2 standard and said preamble signal is a P 1 symbol.

4. The receiving apparatus according to claim 3 , wherein

said decoding means includes

first decoding means for computing a correlation value between data transmitted by subcarriers of a sequence and said known sequence with said second correlation value equal to or higher than a threshold value and eight types of 3-bit data making up S 1 in the digital video broadcasting—terrestrial 2 standard, thereby decoding the 3-bit data having a highest correlation value as S 1 ; and

second decoding means for computing a correlation value between data transmitted by subcarriers of a sequence and said known sequence with said second correlation nine with equal to or higher than a threshold value and sixteen types of 4-bit data making up S 2 in the digital video broadcasting—terrestrial 2 standard, thereby decoding the 4-bit data having a highest correlation value as S 2 .

5. The receiving apparatus according to claim 4 ,

wherein, if a maximum value in a plurality of correlation values computed by said first decoding means and a maximum value of a plurality of correlation values computed by said second decoding means are less than said predetermined threshold value, said determination means outputs a signal indicative that said orthogonal frequency division multiplexing signal of said predetermined standard is not being transmitted on a channel being received.

6. A receiving method comprising the steps of;

receiving an orthogonal frequency division multiplexing signal based on a predetermined standard for transmitting data in unit of a frame arranged, at a beginning of said frame, with a preamble signal having a correlation between a first section and a second section that are parts of an entire signal, thereby computing a first correlation value, that is a correlation value of signals in two sections separated from each other by a time equal to a time interval between said first section and said second section;

performing Fourier transform processing on said preamble signal including the signals of the two sections with said first correlation value equal to or higher than a threshold value obtained, thereby generating said orthogonal frequency division multiplexing signal of frequency

computing a second correlation value which is a correlation value between a sequence of subcarriers for use in data transmission among subcarriers of said orthogonal frequency division multiplexing signal of frequency domain and a known sequence;

computing third correlation values, each of said third correlation values being a correlation value between data transmitted by subcarriers of a sequence with said second correlation value with said known sequence equal to or higher than a threshold value and a plurality of known items of data having a same number of bits as a bit train indicative of a transmission parameter for use in a demodulation of a signal subsequent to said preamble signal, thereby decoding known data having a maximum value of said third correlation values as said transmission parameter; and

determining whether said maximum value of said plurality of third correlation values computed in the decoding step is less than a predetermined threshold value and, if said maximum value is found to be less than said predetermined threshold value, outputting a signal indicative that said orthogonal frequency division multiplexing signal based on said predetermined standard is not being transmitted on a channel being received.

7. A receiving apparatus having processor programmed to include:

a first correlation value computation section configured to receive an orthogonal frequency division multiplexing signal based on a predetermined standard for transmitting data in unit of a frame arranged, at a beginning of said frame, with a preamble signal having a correlation between a first section and a second section that are parts of an entire signal, thereby computing a first correlation value which is a correlation mine of signals in two sections separated from each other by a time equal to a time interval between said first section and said second section;

an operation section configured to perform Fourier transform processing on said preamble signal including the signals of the two sections with said first correlation value equal to or higher than a threshold value obtained, thereby generating said orthogonal frequency division multiplexing signal of frequency domain;

a second correlation value computation section configured to compute a second correlation value which is a correlation value between a sequence of subcarriers for use in data transmission among subcarriers of said orthogonal frequency division multiplexing signal of frequency domain and a known sequence;

a decoding section configured to compute third correlation values, each of said third correlation values being a correlation value between data transmitted by subcarriers of a sequence with said second correlation value with said known sequence equal to or higher than a threshold value and a plurality of known items of data having a same number of bits as a bit train indicative of a transmission parameter for use in demodulation of a signal subsequent to said preamble signal, thereby decoding known data having a maximum value of said third correlation values as said transmission parameter; and

a determination section configured to determine whether said maximum value of said plurality of third correlation values computed by said decoding section is less than predetermined threshold value and, if said maximum value is found to be less than said predetermined threshold value, output a signal indicative that said orthogonal frequency division multiplexing signal based on said predetermined standard is not being transmitted on a channel being received.