Ofdm transmitting and receiving apparatus

Abstract

An OFDM transmitting and receiving apparatus comprises below units. A receiving unit receives an OFDM signal transmitted from a destination transmitting and receiving apparatus. A computing unit computes a value of a channel response characteristic of each of transmission channels corresponding to subcarriers contained in the OFDM signal received, and obtains a computed value. A comparing unit compares the computed value with a predetermined threshold value, and computes a ratio of the number of the subcarriers including the value of the channel response characteristic higher than the predetermined threshold value, to the number of all the subcarriers, and obtaining a computed ratio. A setting unit sets a transmission condition based on at least the computed ratio. A transmitting unit transmits an OFDM signal based on the transmission condition set.

1 . An OFDM apparatus for transmitting an OFDM signal to a destination OFDM apparatus based on a transmission condition, the OFDM signal including a plurality of subcarriers which are transmitted via respective predetermined transmission channels, the OFDM apparatus comprising: 
 a first computing unit configured to compute a value of a channel response characteristic of each transmission channel corresponding to received subcarriers contained in an OFDM signal received from the destination OFDM apparatus;    a second computing unit configured to compute a ratio of a number of received subcarriers having a channel response characteristic value higher than a predetermined threshold value, to a total number of subcarriers, and to output a computed ratio; and    a setting unit configured to set a transmission condition based on at least the computed ratio.    
   
   
       2 . The apparatus according to  claim 1 , wherein: 
 the first computing unit is configured to compute a value of a channel response characteristic of each transmission channel corresponding to known subcarriers contained in data symbols included in the OFDM signal from the destination OFDM apparatus; and    the second computing unit includes a third computing unit configured to compute a ratio of a number of known subcarriers in the data symbols having a channel response characteristic value higher than the predetermined threshold value, to a total number of known subcarriers in the data symbols.    
   
   
       3 . The apparatus according to  claim 1 , wherein: 
 the first computing unit is configured to compute a value of a channel response characteristic of each transmission channel corresponding to known subcarriers contained in preambles included in the OFDM signal from the destination OFDM apparatus; and    the second computing unit includes a third computing unit configured to compute a ratio of a number of known subcarriers in the preambles having a channel response characteristic value higher than the predetermined threshold value, to a total number of known subcarriers in the preambles.    
   
   
       4 . The apparatus according to  claim 1 , wherein the setting unit is configured to set, as the transmission condition, at least one of a modulation form, a coding rate used in error correction coding, a packet length, and a transmission power.  
   
   
       5 . The apparatus according to  claim 1 , further comprising: 
 a measuring unit configured to measure an intensity of the OFDM signal from the destination OFDM apparatus and to output a measured intensity, wherein the setting unit is configured to set the transmission condition based on the measured intensity.    
   
   
       6 . The apparatus according to  claim 1 , further comprising: 
 a measuring unit configured to measure an intensity of the OFDM signal from the destination OFDM apparatus and to output a measured intensity, wherein the setting unit is configured to set the transmission condition based on the measured intensity and a requested communication quality.    
   
   
       7 . The apparatus according to  claim 1 , wherein: 
 the first computing unit is configured to compute a first set of channel response characteristic values corresponding to known subcarriers contained in data symbols included in the OFDM signal from the destination OFDM apparatus, and to compute a second set of channel response characteristic values corresponding to known subcarriers contained in preambles included in the OFDM signal from the destination OFDM apparatus;    the second computing unit is configured to compute a first ratio of a number of known subcarriers in the first set having a channel response characteristic value higher than a first predetermined threshold value, to a total number of known subcarriers in the first set, and to compute a second ratio of a number of known subcarriers in the second set having a channel response characteristic value higher than a second predetermined threshold value, to a total number of known subcarriers in the second set; and    the setting unit is configured to set the transmission condition based on at least the first and second ratios.    
   
   
       8 . The apparatus according to  claim 1 , wherein: 
 the first computing unit is configured to compute a first set of channel response characteristic values corresponding to known subcarriers contained in data symbols included in the OFDM signal from the destination OFDM apparatus, and to compute a second set of channel response characteristic values corresponding to the subcarriers included in the OFDM signal from the destination OFDM apparatus;    the second computing unit is configured to compute a first ratio of a number of known subcarriers in the first set having a channel response characteristic value higher than a first predetermined threshold value, to a total number of known subcarriers in the first set, and to compute a second ratio of a number of subcarriers in the second set having a channel response characteristic value higher than a second predetermined threshold value, to the total number of subcarriers; and    the setting unit is configured to set the transmission condition based on at least the first and second ratios.    
   
   
       9 . An OFDM apparatus for transmitting an OFDM signal to a destination OFDM apparatus based on a transmission condition, the OFDM signal including a plurality of subcarriers which include respective transmission channel responses, the OFDM apparatus comprising: 
 a first computing unit configured to compute a channel response characteristic value of each transmission channel corresponding to received subcarriers contained in an OFDM signal received from the destination OFDM apparatus;    a second computing unit configured to compute a ratio of a number of the received subcarriers having a channel response characteristic value higher than a predetermined threshold value, to a total number of subcarriers, and to output a computed ratio;    a generating unit configured to generate transmission condition setting information which determines the transmission condition which the destination OFDM apparatus uses when the destination OFDM apparatus transmits information to the OFDM apparatus, based on at least the computed ratio; and    a transmitting unit configured to transmit the transmission condition setting information to the destination OFDM apparatus.    
   
   
       10 . The apparatus according to  claim 9 , wherein: 
 the first computing unit is configured to compute a channel response characteristic value corresponding to known subcarriers contained in data symbols included in the OFDM signal from the destination OFDM apparatus; and    the second computing unit includes a third computing unit configured to compute a ratio of a number of known subcarriers in the data symbols having the channel response characteristic value higher than the predetermined threshold value, to a total number of known subcarriers in the data symbols.    
   
   
       11 . The apparatus according to  claim 9 , wherein: 
 the first computing unit is configured to compute a channel response characteristic value of each transmission channel corresponding to known subcarriers contained in preambles included in the OFDM signal from the destination OFDM apparatus; and    the second computing unit includes a third computing unit configured to compute a ratio of a number of known subcarriers in the preambles having the channel response characteristic value higher than the predetermined threshold value, to a total number of known subcarriers in the preambles.    
   
   
       12 . The apparatus according to  claim 9 , wherein: 
 the first computing unit is configured to compute a first set of channel response characteristic values corresponding to known subcarriers contained in data symbols included in the OFDM signal from the destination OFDM apparatus, and to compute a second set of channel response characteristic values corresponding to known subcarriers contained in preambles included in the OFDM signal from the destination OFDM apparatus;    the second computing unit is configured to compute a first ratio of a number of the known subcarriers in the first set having a channel response characteristic value higher than a first predetermined threshold value, to a total number of known subcarriers in the first set, and to compute a second ratio of a number of known subcarriers in the second set having a channel response characteristic value higher than a second predetermined threshold value, to a total number of known subcarriers in the second set; and    the generating unit is configured to generate the transmission condition setting information, which determines the transmission condition which the destination OFDM apparatus uses when the destination OFDM apparatus transmits information to the OFDM apparatus, based on at least the first and second ratios.    
   
   
       13 . The apparatus according to  claim 9 , wherein: 
 the first computing unit is configured to compute a first set of channel response characteristic values corresponding to known subcarriers contained in data symbols included in the OFDM signal from the destination OFDM apparatus, and to compute a second set of channel response characteristic values corresponding to known subcarriers included in the OFDM signal from the destination OFDM apparatus;    the second computing unit is configured to compute a first ratio of a number of the known subcarriers in the first set having a channel response characteristic value higher than a first predetermined threshold value, to a total number of known subcarriers in the first set, and to compute a second ratio of a number of the subcarriers in the second set having a channel response characteristic value higher than a second predetermined threshold value, to the total number of subcarriers; and    the generating unit is configured to generate the transmission condition setting information, which determines the transmission condition which the destination OFDM apparatus uses when the destination OFDM apparatus transmits information to the OFDM apparatus, based on at least the first and second ratios.    
   
   
       14 . An OFDM apparatus for transmitting an OFDM signal to a destination OFDM apparatus based on a transmission condition, the OFDM signal including a plurality of subcarriers which include respective transmission channel responses, the OFDM apparatus comprising: 
 a first computing unit configured to compute a channel response characteristic value of each transmission channel corresponding to received subcarriers contained in an OFDM signal received from the destination OFDM apparatus;    a second computing unit configured to compute a ratio of a number of received subcarriers having a channel response characteristic value higher than a predetermined threshold value, to a total number of subcarriers, and to output a computed ratio;    an integrating unit configured to integrate information concerning transmission condition setting indexes based on at least the computed ratio, the transmission condition setting indexes used to set a transmission condition which the destination OFDM apparatus uses when the destination OFDM apparatus transmits information to the OFDM apparatus; and    a transmitting unit configured to transmit the information concerning the transmission condition setting indexes to the destination OFDM apparatus.