Patent ID: 8472378

Claim:
A radio communication system that performs radio communication by sharing, between a first radio apparatus and at least one second radio apparatus, a frequency band used by another radio communication system without influencing the another radio communication system, wherein: the first radio apparatus comprises: sensing means that observes a surrounding radio wave environment in a frequency band having a possibility of being available for communication; and control means that cognizes, based on a result of observing by the sensing means, as an available frequency band, a frequency band that is not being used by the another radio communication system from the frequency band having the possibility of being available for the communication, to thereby determine a target frequency band to be actually used, and causes transmission means to transmit, to the at least one second radio apparatus, an instruction signal for instructing the at least one second radio apparatus to observe the surrounding radio wave environment in the target frequency band; the at least one second radio apparatus comprises: means that receives the instruction signal and observes the surrounding radio wave environment in the target frequency band specified by the received instruction signal; and means that sends, as a response, a result of observing the radio wave environment to the first radio apparatus under a predetermined condition or a condition specified by the received instruction signal; and the first radio apparatus further comprises determination means that makes a final determination on whether or not the target frequency band is available based on information on the result of observing the radio wave environment, which is received from the at least one second radio apparatus, wherein the control means of the first radio apparatus further has a function of determining, within the frequency band having the possibility of being available for the communication, a candidate ranking in descending order of probability of being available as a free frequency band among a plurality of candidates of a frequency band to be used for the communication, based on the result of the observing by the sensing means with respect to the surrounding radio wave environment in the frequency band having the possibility of being available for the communication; the control means of the first radio apparatus observes, according to the determined candidate ranking, the surrounding radio wave environment with respect to the target frequency band of one of the plurality of candidates through an operation between the first radio apparatus and the at least one second radio apparatus; and the first radio apparatus determines whether or not the target frequency band of the one of the plurality of candidates is available based on the information on the result of observing the radio wave environment, which is received from the at least one second radio apparatus.