Signal processing device, signal processing method, and program

Abstract

In the signal processing device, which is capable of performing an FFT and performing a window function process as preprocessing before the FFT and achieves OFDM demodulation, the window function process is skipped to perform an FFT on a received signal if the frequency of narrow-band noise included in the received signal coincides with the subcarrier frequency of OFDM within a predetermined range. If the frequencies do not coincide with each other, the FFT is performed after the window function process is performed on the received signal. The signal processing device includes an NBN detection/determination section, which determines whether narrow-band noise is included in a subcarrier, and a window function determination section, which determines, in accordance with the degree of coincidence between the frequency of narrow-band noise and the frequency of a subcarrier, whether or not to perform the window function process.

What is claimed is: 
     
         1 . A signal processing device that outputs received data upon receipt of a modulated signal that is orthogonal frequency division modulated by a plurality of subcarriers, the signal processing device comprising:
 an input section that extracts a predetermined number of input data from the modulated signal that is in a time series;   a window function processing section that is capable of exercising control to determine whether or not to perform a window function process on the predetermined number of input data;   an FFT processing section that performs an FFT process on data output from the window function processing section; and   a narrow-band noise detection/determination section;   wherein the narrow-band noise detection/determination section detects the degree of coincidence between the frequency of narrow-band noise included in the modulated signal and the frequencies of the subcarriers, and exercises control to determine in accordance with the detected degree of coincidence whether the window function processing section should perform the window function process on the input data and supply the resulting processed data to the FFT processing section or supply the input data to the FFT processing section without performing the window function process on the input data.   
     
     
         2 . The signal processing device according to  claim 1 ,
 wherein the FFT processing section acts as a first FFT processing section,   wherein the narrow-band noise detection/determination section includes a second FFT processing section that performs an FFT process on the input data to calculate electrical power at the frequency of each of the subcarriers,   wherein, if a predetermined threshold value is exceeded by the electrical power at two neighboring subcarrier frequencies, the narrow-band noise detection/determination section allows the window function processing section to perform the window function process, and   wherein, if the threshold value is exceeded by the electrical power at only one subcarrier frequency, the narrow-band noise detection/determination section inhibits the window function processing section from performing the window function process.   
     
     
         3 . The signal processing device according to  claim 2 ,
 wherein the narrow-band noise detection/determination section calculates an average value of electrical power at all subcarrier frequencies within the band of the modulated signal from the electrical power calculated by the second FFT processing section, and prescribes the threshold value in accordance with the average value.   
     
     
         4 . The signal processing device according to  claim 1 ,
 wherein the FFT processing section acts as first FFT processing section,   wherein the signal processing device further includes a standby FFT processing section,   wherein the narrow-band noise detection/determination section includes a second FFT processing section,   wherein, while the modulated signal is being input, the second FFT processing section performs an FFT process on the input data to calculate reception state electrical power at the frequency of each of the subcarriers,   wherein, while the modulated signal is not being input, the standby FFT processing section performs an FFT process on standby state input data, which corresponds to the input data, to calculate standby state electrical power at the frequency of each of the subcarriers, and   wherein, in accordance with the reception state electrical power and with the standby state electrical power, the narrow-band noise detection/determination section exercises control to determine whether the window function processing section should perform the window function process on the input data and supply the resulting processed data to the first FFT processing section or supply the input data to the first FFT processing section without performing the window function process on the input data.   
     
     
         5 . The signal processing device according to  claim 4 ,
 wherein, if a predetermined standby state threshold value is exceeded by the standby state electrical power at only one subcarrier frequency and a predetermined reception state threshold value is exceeded by the reception state electrical power at the only one subcarrier frequency, the narrow-band noise detection/determination section inhibits the window function processing section from performing the window function process.   
     
     
         6 . The signal processing device according to  claim 1 , further comprising:
 a processor; and   a memory;   wherein the window function processing section, the FFT processing section, and the narrow-band noise detection/determination section function when a program stored in the memory is executed by the processor.   
     
     
         7 . The signal processing device according to  claim 1 , further comprising:
 a demodulation processing section that performs a demodulation process on data output from the FFT processing section; and   a decoding processing section that performs a decoding process on data output from the demodulation processing section and outputs the received data;   wherein the input section includes an analog front-end section that can be coupled through a plug to a transmission path for power-line communication, and a guard interval elimination section that receives an output from the analog front-end section and performs predetermined preprocessing to extract the predetermined number of input data.   
     
     
         8 . The signal processing device according to  claim 7 ,
 wherein the signal processing device is formed over a single semiconductor substrate.   
     
     
         9 . The signal processing device according to  claim 7 ,
 wherein the signal processing device is divided into some parts that are formed over multi-chip semiconductor integrated circuits and incorporated into a single package.   
     
     
         10 . A signal processing method that outputs received data upon receipt of a modulated signal that is orthogonal frequency division modulated by a plurality of subcarriers, the signal processing method comprising the steps of:
 detecting the degree of coincidence between the frequency of narrow-band noise included in the modulated signal and the frequencies of the subcarriers; and   determining in accordance with the detected degree of coincidence whether to perform a window function process on a predetermined number of input data extracted from the modulated signal that is in a time series and then perform an FFT process or to perform the FFT process without performing the window function process.   
     
     
         11 . The signal processing method according to  claim 10 , further comprising the steps of:
 performing the FFT process as a first FFT process;   performing a second FFT process in which an FFT process is performed on the input data to calculate electrical power at the frequency of each of the subcarriers;   if a predetermined threshold value is exceeded by the electrical power at two neighboring subcarrier frequencies, performing the first FFT process after the window function process; and   if the threshold value is exceeded by the electrical power at only one subcarrier frequency, performing the first FFT process without performing the window function process.   
     
     
         12 . The signal processing method according to  claim 11 , further comprising the steps of:
 calculating an average value of electrical power at all subcarrier frequencies within the band of the modulated signal from the electrical power calculated in the second FFT process; and   prescribing the threshold value in accordance with the average value.   
     
     
         13 . The signal processing method according to  claim 10 , further comprising the steps of:
 performing the FFT process as a first FFT process;   while the modulated signal is being input, performing a second FFT process on the input data to calculate reception state electrical power at the frequency of each of the subcarriers;   while the modulated signal is not being input, performing a third FFT process on standby state input data, which corresponds to the input data, to calculate standby state electrical power at the frequency of each of the subcarriers; and   in accordance with the reception state electrical power and with the standby state electrical power, determining whether to perform the window function process on the input data and then perform the first FFT process or to perform the first FFT process without performing the window function process.   
     
     
         14 . The signal processing method according to  claim 13 , further comprising the step of:
 if a predetermined standby state threshold value is exceeded by the standby state electrical power at only one subcarrier frequency and a predetermined reception state threshold value is exceeded by the reception state electrical power at the only one subcarrier frequency, performing the first FFT process on the input data without performing the window function process.