Base station, controller, communication system, and interference avoidance method

Abstract

A base station transmits an OFDM signal to a mobile station, using carrier frequencies of a frequency band shared with another system. The base station includes a frequency selector that selects an unused frequency band based on an interference level of the frequency band, selects a carrier frequency for systematic-bit mapping, and selects a carrier frequency for parity-bit mapping, and a turbo coder that performs turbo coding processing on transmission data and outputs a systematic bit and a parity bit. The base station also includes a carrier-mapper that performs systematic-bit mapping and parity-bit mapping, and a control-signal generator that generates a control signal containing band-division-count information and signal-type information. The base station further includes an orthogonal frequency division multiplexer that generates the OFDM signal and a transmitter that transmits the OFDM signal to the mobile station.

1 . A base station that transmits an OFDM signal to a mobile station, using some carrier frequencies of a frequency band shared with another system, the base station comprising:
 a frequency selector that selects an unused frequency band not used by the other system in the frequency band, based on an interference level of the frequency band, selects a carrier frequency for systematic-bit mapping from among carrier frequencies each having the interference level lower than a threshold, and selects a carrier frequency for parity-bit mapping from among carrier frequencies other than the carrier frequency for systematic-bit mapping in carrier frequencies of the unused frequency band;   a turbo coder that performs turbo coding processing on transmission data and outputs a systematic bit and a parity bit;   a carrier-mapper that maps the systematic bit to the carrier frequency for systematic-bit mapping and maps the parity bit to the carrier frequency for parity-bit mapping;   a control-signal generator that generates a control signal, when at least one of the systematic-bit mapping or the parity-bit mapping is changed, containing
 band-division-count information, which indicates a number of the carrier frequencies into which the unused frequency band is divided; and 
 signal-type information, which indicates a signal type for every carrier frequency to indicate whether the signal to be mapped is systematic bits or parity bits; 
 an orthogonal frequency division multiplexer that generates the OFDM signal by performing orthogonal frequency division multiplexing processing on the systematic bit and the parity bit mapped to the carrier frequencies, and the control signal; and 
   a transmitter that transmits the OFDM signal to the mobile station.   
     
     
         2 . The base station according to  claim 1 ,
 wherein the frequency selector selects a carrier frequency most distant from a carrier frequency having the largest interference level as the carrier frequency for systematic-bit mapping.   
     
     
         3 . The base station according to  claim 1 ,
 wherein the frequency selector selects an unused frequency band for each of a plurality of streams.   
     
     
         4 . The base station according to  claim 1 , further comprising:
 a transmission-power configurator that configures transmission power for one or more carrier frequencies based on a number of the carrier frequencies for systematic-bit mapping and a number of the carrier frequencies for parity-bit mapping,   wherein the transmitter transmits the OFDM signal using the transmission power configured by the transmission-power configurator.   
     
     
         5 . The base station according to  claim 1 ,
 wherein, when a number of the carrier frequencies for systematic-bit mapping is insufficient in a certain unused frequency band, the frequency selector selects the carrier frequency for systematic-bit mapping in another unused frequency band.   
     
     
         6 . An interference avoidance method in a base station that transmits an OFDM signal to a mobile station, using some carrier frequencies of a frequency band shared with another system, the method comprising:
 selecting an unused frequency band not used by the other system in the frequency band, based on an interference level of the frequency band, selecting a carrier frequency for systematic-bit mapping from among carrier frequencies having the interference level lower than a threshold, and selecting a carrier frequency for parity-bit mapping from among carrier frequencies other than the carrier frequency for systematic-bit mapping in carrier frequencies of the unused frequency band;   performing turbo coding processing on transmission data and outputting a systematic bit and a parity bit;   mapping the systematic bit to the carrier frequency for systematic-bit mapping and mapping the parity bit to the carrier frequency for parity-bit mapping;   generating a control signal, when at least one of the systematic-bit mapping or the parity-bit mapping is changed, containing
 band-division-count information, which indicates a number of the carrier frequencies into which the unused frequency band is divided; and 
 signal-type information, which indicates a signal type for every carrier frequency to indicate whether the signal to be mapped is systematic bits or parity bits; 
 generating the OFDM signal by performing orthogonal frequency division multiplexing processing on the systematic bit and the parity bit mapped to the carrier frequencies, and the control signal; and 
   transmitting the OFDM signal to the mobile station.   
     
     
         7 . A communication system that transmits an OFDM signal from a base station to a mobile station, using some carrier frequencies of a frequency band shared with another system,
 wherein the base station comprises:
 a frequency selector that selects an unused frequency band not used by the other system in the frequency band, based on an interference level of the frequency band, selects a carrier frequency for systematic-bit mapping from among carrier frequencies each having the interference level lower than a threshold, and selects a carrier frequency for parity-bit mapping from among carrier frequencies other than the carrier frequency for systematic-bit mapping in carrier frequencies of the unused frequency band; 
 a turbo coder that performs turbo coding processing on transmission data and outputs a systematic bit and a parity bit; 
 a carrier-mapper that maps the systematic bit to the carrier frequency for systematic-bit mapping and maps the parity bit to the carrier frequency for parity-bit mapping; 
 a control-signal generator that generates a control signal, when at least one of the systematic-bit mapping or the parity-bit mapping is changed, containing
 band-division-count information which indicates a number of the carrier frequencies into which the unused frequency band is divided, and 
 signal-type information which indicates a signal type for every carrier frequency to indicate whether the signal to be mapped is systematic bits or parity bits; 
 
 an orthogonal frequency division multiplexer that generates the OFDM signal by performing orthogonal frequency division multiplexing processing on the systematic bit and the parity bit mapped to the carrier frequencies, and on the control signal; and 
 a transmitter that transmits the OFDM signal to the mobile station.