Derivation method, communication system and accommodation station apparatus

1. A derivation method performed by a communication system including an access point and a wireless terminal, the access point including an accommodation station device and an extension station device connected to each other through an optical fiber transmitting an optical signal, and the wireless terminal communicating with the extension station device by using a radio-wave signal, the derivation method comprising:

transmitting, to the wireless terminal, a first radio-wave signal according to an optical signal with a first wavelength, and a second radio-wave signal according to an optical signal with a second wavelength;

acquiring information on a first communication start time that is a time at which communication using the optical signal with the first wavelength is started in the accommodation station device, and information on a second communication start time that is a time at which communication using the optical signal with the second wavelength is started in the accommodation station device;

acquiring information on a first reception time that is a reception time related to the first radio-wave signal in the accommodation station device, and information on a second reception time that is a reception time related to the second radio-wave signal in the accommodation station device;

deriving a first round trip time that is a time period from the first communication start time until the first reception time, and deriving a second round trip time that is a time period from the second communication start time until the second reception time; and

deriving a length of the optical fiber, based on the first round trip time, the second round trip time, a group velocity or a group delay time of the optical signal with the first wavelength, and a group velocity or a group delay time of the optical signal with the second wavelength.

2. The derivation method according to claim 1 , further comprising:

deriving the length of the optical fiber, based on a difference between the first round trip time and the second round trip time, the group velocity or the group delay time of the optical signal with the first wavelength, and the group velocity or the group delay time of the optical signal with the second wavelength.

3. The derivation method according to claim 1 , further comprising:

deriving the length of the optical fiber, based on a difference between the first round trip time and the second round trip time, the group velocity or the group delay time of the optical signal with the first wavelength, the group velocity or the group delay time of the optical signal with the second wavelength, a group velocity or a group delay time of an optical signal with a third wavelength, and a group velocity or a group delay time of an optical signal with a fourth wavelength.

4. A communication system, comprising:

an access point including an accommodation station device and an extension station device connected to each other through an optical fiber transmitting an optical signal; and

a wireless terminal that communicates with the extension station device by using a radio-wave signal,

wherein the accommodation station device includes

a transmitter that transmits, to the wireless terminal, a first radio-wave signal according to an optical signal with a first wavelength, and a second radio-wave signal according to an optical signal with a second wavelength,

a communication start time information acquisitor that acquires information on a first communication start time that is a time at which communication using the optical signal with the first wavelength is started in the accommodation station device, and information on a second communication start time that is a time at which communication using the optical signal with the second wavelength is started in the accommodation station device,

a reception time information acquisitor that acquires information on a first reception time that is a reception time related to the first radio-wave signal in the accommodation station device, and information on a second reception time that is a reception time related to the second radio-wave signal in the accommodation station device,

a transmission time period derivator that derives a first round trip time that is a time period from the first communication start time until the first reception time, and derives a second round trip time that is a time period from the second communication start time until the second reception time, and

an optical fiber length derivator that derives a length of the optical fiber, based on the first round trip time, the second round trip time, a group velocity or a group delay time of the optical signal with the first wavelength, and a group velocity or a group delay time of the optical signal with the second wavelength,

wherein each of the transmitter, the communication start time information acquisitor, the reception time information acquisitor, the transmission time period derivator, and the optical fiber length derivator is implemented by:

i) computer executable instructions executed by at least one processor,

ii) at least one circuitry or

iii) a combination of computer executable instructions executed by at least one processor and at least one circuitry.

5. An accommodation station device in a communication system including an access point and a wireless terminal, the access point including the accommodation station device and an extension station device connected to each other through an optical fiber transmitting an optical signal, and the wireless terminal communicating with the extension station device by using a radio-wave signal, the accommodation station device comprising:

a transmitter that transmits, to the wireless terminal, a first radio-wave signal according to an optical signal with a first wavelength, and a second radio-wave signal according to an optical signal with a second wavelength;

a communication start time information acquisitor that acquires information on a first communication start time that is a time at which communication using the optical signal with the first wavelength is started in the accommodation station device, and information on a second communication start time that is a time at which communication using the optical signal with the second wavelength is started in the accommodation station device;

a reception time information acquisitor that acquires information on a first reception time that is a reception time related to the first radio-wave signal in the accommodation station device, and information on a second reception time that is a reception time related to the second radio-wave signal in the accommodation station device;

a transmission time period derivator that derives a first round trip time that is a time period from the first communication start time until the first reception time, and derives a second round trip time that is a time period from the second communication start time until the second reception time; and

an optical fiber length derivator that derives a length of the optical fiber, based on the first round trip time, the second round trip time, a group velocity or a group delay time of the optical signal with the first wavelength, and a group velocity or a group delay time of the optical signal with the second wavelength,

wherein each of the transmitter, the communication start time information acquisitor, the reception time information acquisitor, the transmission time period derivator, and the optical fiber length derivator is implemented by:

i) computer executable instructions executed by at least one processor,

ii) at least one circuitry or

iii) a combination of computer executable instructions executed by at least one processor and at least one circuitry.