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

A communication system wherein a mobile station and a base station communicate with each other using some carrier frequencies of a frequency band shared with another system and a controller controls a plurality of the base stations,

• 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 in carrier frequencies of the unused frequency band and selects a carrier frequency for parity-bit mapping from among carrier frequencies other than the carrier frequency for systematic-bit mapping;
• a controller communicator that transmits to the controller frequency information indicating a carrier frequency having the interference level lower than the threshold, the carrier frequency for systematic-bit mapping and the carrier frequency for parity-bit mapping, the carrier frequency for systematic-bit mapping and the carrier frequency for parity-bit mapping being selected by the frequency selector, and receives from the controller signal-assignment-information indicating the carrier frequency for systematic-bit mapping and the carrier frequency for parity-bit mapping which are assigned by the controller;
• a control-signal generator that generates a control-signal including the signal-assignment-information during handover;
• and
• a transmitter that transmits the control signal to the mobile station,
• wherein, the controller comprises:
• a receiver that receives first frequency information from a first base station in communication with the mobile station and second frequency information from a second base station, the first frequency information indicating a carrier frequency having an interference level lower than a threshold in an unused frequency band, a carrier frequency to which a systematic bit is mapped, and a carrier frequency to which a parity bit is mapped, the second frequency information indicating a carrier frequency having an interference level lower than the threshold in carrier frequencies of an unused frequency band, the second base station being a handover destination;
• the frequency selector that selects a carrier frequency for systematic-bit mapping and a carrier frequency for parity-bit mapping based on the first frequency information and the second frequency information;
• a signal-assignment-information generator that generates signal assignment information indicating the carrier frequency for systematic-bit mapping and the carrier frequency for parity-bit mapping;
• and
• a transmitter that transmits the signal assignment information to the first and the second base stations,
• wherein the mobile station comprises:
• a receiver that receives the control signal;
• 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 based on the signal-assignment-information contained in the control signal;
• an orthogonal frequency division multiplexer that generates an OFDM signal by performing orthogonal frequency division multiplexing processing on the systematic bit and the parity bit mapped to the carrier frequencies;
• and
• a transmitter that transmits the OFDM signal to the base station.

A handover method by a controller that controls a plurality of base stations each configured to communicate with a mobile station using some carrier frequencies of a frequency band shared with another system, the handover method comprising:

• receiving first frequency information from a first base station in communication with the mobile station and second frequency information from a second base station, the first frequency information indicating a carrier frequency having an interference level lower than a threshold in an unused frequency band, a carrier frequency to which a systematic bit is mapped, and a carrier frequency to which a parity bit is mapped, the second frequency information indicating a carrier frequency having an interference level lower than the threshold in carrier frequencies of an unused frequency band, the second base station being a handover destination;
• selecting a carrier frequency for systematic-bit mapping and a carrier frequency for parity-bit mapping based on the first frequency information and the second frequency information;
• generating signal assignment information indicating the carrier frequency for systematic-bit mapping and the carrier frequency for parity-bit mapping;
• and
• transmitting the signal assignment information to the first and the second base stations.