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A communications system for communications by a multicarrier transmission mode between a plurality of communications apparatuses, wherein an overall frequency band assigned to the communications system is divided into a plurality of frequency bands each having a constant bandwidth and a specific ban

A communications system for communications by a multicarrier transmission mode between a plurality of communications apparatuses, wherein an overall frequency band assigned to the communications system is divided into a plurality of frequency bands each having a constant bandwidth and a specific band. The divided bands are used to transmit used frequency band information thereby indicating the assignment of the remaining bands used between said communications apparatuses. The specific band is defined as a main band for transmitting control channel information including used frequency band information and data channel information. The main band may be added with an extension band for transmitting further data channel information. The main band and extension band can be changed in the frequency band used along with time or can be changed in the number thereof. Both the main band and the extension bands are preferably used for multiplexing by some of communications apparatuses.

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1. A communications apparatus accommodated in a communications system for exchange of information between communications apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication apparatus comprising: a transmission data generator configured to generate freq

1. A communications apparatus accommodated in a communications system for exchange of information between communications apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication apparatus comprising: a transmission data generator configured to generate frequency band information indicating which frequency band is to be used for transmission of data information between said communication apparatuses; anda transmitter configured to transmit the frequency band information by using a specific frequency band which is set from among a plurality of frequency bands assigned to the communications system, and to transmit data information by using at least one frequency band set from among said plurality of frequency bands, other than the specific frequency band. 2. A communications apparatus as set forth in claim 1, wherein said specific frequency band also transmits data information. 3. A communications apparatus as set forth in claim 2, wherein said specific frequency band is set at the time of establishing a wireless channel between said communications apparatuses. 4. A communications apparatus as set forth in claim 2, wherein when there are a plurality of said communications apparatuses, specific frequency bands are individually set for said plurality of frequency bands and each of the specific frequency bands is assigned corresponding to each of the plurality of communications apparatuses. 5. A communications apparatus as set forth in claim 4, wherein two or more of said communications apparatuses simultaneously use the same specific frequency band by time division multiplexing and/or code division multiplexing. 6. A communications apparatus as set forth in claim 2, wherein a frequency band to be occupied as said specific frequency band among said plurality of frequency bands is made variable along with time. 7. A communications apparatus as set forth in claim 6, wherein whether or not a propagation environment between said communications apparatuses is good is judged, and a frequency band having the best propagation environment among said plurality of frequency bands or a frequency band which is next best to this is selected and set as said specific frequency band. 8. A communications apparatus as set forth in claim 7, wherein at the time of a new setting of said specific frequency band, a change of the frequency band thereof is notified to the communications apparatus of the other party. 9. A communications apparatus as set forth in claim 7, wherein whether or not said propagation environment is good is judged by using a detection result of transmission quality obtained in response to a transmitted pilot channel or pilot signal between said communications apparatuses. 10. A communications apparatus as set forth in claim 9, wherein said judgment of whether or not the propagation environment is good is sequentially or simultaneously carried out for all of said plurality of frequency bands. 11. A communications apparatus as set forth in claim 7, wherein the result of judgment of whether or not said propagation environment is good is transmitted to the communications apparatus of the other party through a control channel of a specific frequency band. 12. A communications apparatus as set forth in claim 7, wherein the judgment of whether or not said propagation environment between said communications apparatuses is good is individually carried out for each of said plurality of frequency bands, and the judgment result thereof is individually transmitted to the communications apparatus of the other party for each frequency band. 13. A communications apparatus as set forth in claim 12, wherein said judgment result is transmitted to said communications apparatus of the other party by using either of said specific frequency band, said at least one frequency band set, other than the specific frequency band, or said frequency band having a good propagation environment. 14. A communications apparatus as set forth in claim 7, wherein the judgment of whether or not said propagation environment between said communications apparatuses is good is individually carried out for each of said plurality of frequency bands, and judgment results for all frequency bands are multiplexed and transmitted to the communications apparatus of the other party all together. 15. A communications apparatus as set forth in claim 1, wherein the number of said least one frequency band set from among said plurality of frequency bands, other than the specific frequency band, is changed in accordance with a predetermined transmission rate of said data information. 16. A communications apparatus as set forth in claim 1, wherein the frequency band set as said at least one frequency band set from among said plurality of frequency bands, other than the specific frequency band, is made variable along with time. 17. A communications apparatus as set forth in claim 16, wherein whether or not the propagation environment between said communications apparatuses is good is judged, and the frequency band which is next best to the frequency band having the best propagation environment among said plurality of frequency bands is selected and set as said at least one frequency band set, other than the specific frequency band. 18. A communications apparatus as set forth in claim 17, wherein the setting information of the frequency band to be set as said least one frequency band set, other than the specific frequency band, is notified to the communications apparatus of the other party in advance. 19. A communications apparatus as set forth in claim 17, wherein the result of judgment of whether or not said propagation environment is good is transmitted to the communications apparatus of the other party through a control channel of a specific frequency band. 20. A communications apparatus as set forth in claim 17, wherein the judgment of whether or not said propagation environment is good is carried out by using a detection result of transmission quality returned in response to a pilot channel or pilot signal sent between said communications apparatuses. 21. A communications apparatus as set forth in claim 17, wherein at the time of setting a new at least one frequency band set, other than the specific frequency band, the change of the frequency band thereof is notified to the communications apparatus of the other party in advance. 22. A communications apparatus as set forth in claim 16, wherein at the time of establishing the wireless channel, the frequency band usable by the communications apparatus is restricted, and said specific frequency band and said at least one frequency band set, other than the specific frequency band, are dynamically assigned within that restricted frequency band. 23. A communications apparatus as set forth in claim 22, wherein frequency band setting information is received from the communications apparatus of the other party for the change of said at least one frequency band set, other than the specific frequency band, or said specific frequency band. 24. A communications apparatus as set forth in claim 23, wherein change timing information concerning the timing of said change is further received. 25. A communications apparatus as set forth in claim 16, wherein a necessity of setting or change of said at least one frequency band set, other than the specific frequency band, is judged based on at least one of the available frequency bands of the communications apparatus, quality of the propagation environment at each of said frequency bands, usage situation of each frequency band, and a predetermined transmission rate of said data information. 26. A communications apparatus as set forth in claim 1, wherein both of the frequency band to be occupied as said specific frequency band among said plurality of frequency bands and the frequency band to be occupied as said at least one frequency band set among the plurality of frequency bands, other than the specific frequency band, are made variable along with time so that the two will not overlap. 27. A communications apparatus as set forth in claim 26, wherein one said specific frequency band and at least one said at least one frequency band set, other than the specific frequency band, are simultaneously changed. 28. A communications apparatus as set forth in claim 1, wherein, for each of said plurality of frequency bands, at least one of information of a frequency band identification number, used/not yet used state as said specific frequency band, used/not yet used state as said at least one frequency band set, other than the specific frequency band, and current status maintained is encoded and transmitted to the communications apparatus of the other party. 29. A communications apparatus as set forth in claim 1, wherein one or more of said at least one frequency band set, other than the specific frequency band, set continuous are assigned to a frequency band consecutive with said specific frequency band along a frequency axis. 30. A communications apparatus as set forth in claim 29, wherein an isolated at least one frequency band set, other than the specific frequency band, not consecutive with any other set bands is further included on said frequency axis. 31. A communications apparatus as set forth in claim 30, wherein a meaningless signal is inserted for a not yet used frequency band accompanied with said isolated set frequency band and transmitted to the communications apparatus of the other party. 32. A communications apparatus as set forth in claim 1, wherein bandwidths of said plurality of frequency bands are made a predetermined constant value, and also numbers of said series of subcarriers in each of the bands are made a predetermined constant value. 33. A communications apparatus as set forth in claim 1, wherein bandwidth of each of said plurality of frequency bands is made a predetermined constant value, and also bandwidth of each of said subcarriers in each of the bands is made a predetermined constant value. 34. A communications apparatus as set forth in claim 33, wherein the number of said subcarriers in each said band is made a predetermined constant value. 35. A communications apparatus as set forth in claim 1, wherein in order to judge the necessity of said at least one frequency band set, other than the specific frequency band, a difference between a predetermined transmission rate S1 assumed to be necessary for the exchange of said information and an actual transmission rate S2 which is actually achieved (S1−S2) is calculated, and it is judged whether the at least one frequency band set, other than the specific frequency band, is required or not required in accordance with a positive or negative sign of this difference. 36. A communications apparatus as set forth in claim 35, wherein said actual transmission rate is found from the number of transmission data information calculated from the number of used frequency bands and a transmission interval of the transmission data information. 37. A communication method for exchange of information between communication apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication method comprising: in a case where usage of only a part of divided frequency bands is allowed at present among a plurality of divided frequency bands formed by dividing an overall frequency band, operating the part of divided frequency bands allowed to be used at present by further dividing the part into one or more frequency bands;dividing each of the remaining said divided frequency bands restricted from usage at present into one or more frequency bands;when the restriction thereof is lifted, operating each of said plurality of divided frequency bands formed by dividing said overall frequency band, but not used at present, by the same operation as dividing the divided frequency band already allowed for use into one or more frequency bands; andexchanging information between the communication apparatuses regarding the one or more frequency bands indicating which frequency band is to be used for transmission of data information between said communication apparatuses. 38. The communication method of claim 37, wherein a plurality of divided frequency bands formed by dividing said overall frequency band have constant bandwidths with respect to each other, and the number and bandwidth of said subcarriers in each of the divided frequency bands have constant values with respect to each other. 39. A communication system for exchange of information between communication apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication system comprising: a transmission data generator configured to generate frequency band information indicating which frequency band is to be used for transmission of data information between said communication apparatuses;a transmitter configured to transmit the frequency band information by using a specific frequency band which is set from among a plurality of frequency bands assigned to the communication system, and to transmit data information by using at least one frequency band set from among the plurality of frequency bands, other than the specific frequency band; anda receiver configured to receive the frequency band information transmitted by the specific frequency band and receive the data information transmitted by the at least one frequency band set from among the plurality of frequency bands, other than the specific frequency band. 40. A communication system in which multicarrier transmission is conducted by using a plurality of frequency bands, the communication system comprising: a communication apparatus configured to transmit control information by using a specific frequency band and to transmit data information by using another frequency band, other than the specific frequency band, wherein the control information addressed to another communication apparatus designates the other frequency band from among the plurality of frequency bands, other than the specific frequency band, to transmit the data information to the other communication apparatus;the other communication apparatus configured to receive the control information addressed to the other communication apparatus and the data information transmitted in accordance with the control information. 41. A communication method in which multicarrier transmission is conducted by using a plurality of frequency bands, the communication method comprising: transmitting control information by using a specific frequency band and transmitting data information by using another frequency band, other than the specific frequency band, from a communication apparatus, wherein the control information addressed to another communication apparatus designates the other frequency band from the plurality of frequency bands, other than the specific frequency band, to transmit data information to the other communication apparatus;receiving, by the other communication apparatus, the control information addressed to the other communication apparatus and data information transmitted in accordance with the control information. 42. A communications apparatus accommodated in a communications system for exchange of information between communications apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication apparatus comprising: a receiver configured to receive frequency band information by using a specific frequency band which is selected from among a plurality of frequency bands assigned to the communication system, the frequency band information which indicates a used frequency band which includes at least one frequency band other than the specific frequency band, the used frequency band which is to be used for transmission data information between said communication apparatuses,wherein after the receiver receives the frequency band information, the receiver receives data information by using the used frequency band indicated by the frequency band information. 43. A communications system for exchange of information between communications apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication system comprising: a transmission data generator configured to generate frequency band information indicating which frequency band is to be used for transmission of data information between said communication apparatuses; anda transmitter configured to transmit the frequency band information by using a specific frequency band which is set from among a plurality of frequency band assigned to the communications system, and to transmit data information by using at least one frequency band set from among said plurality of frequency bandsa receiver configured to receive the frequency band information by using the specific frequency band. 44. The communications system as set forth in claim 43, wherein said specific frequency band also transmits data information. 45. The communications system as set forth in claim 44, wherein said specific frequency band is set at the time of establishing a wireless channel between said communications apparatuses. 46. The communications system as set forth in claim 43, wherein the number of said least one frequency band set from among said plurality of frequency bands, other than the specific frequency band, is changed in accordance with a predetermined transmission rate of said data information. 47. The communications system as set forth in claim 43, wherein in order to judge the necessity of said at least one frequency band, other than the specific frequency band, a difference between a predetermined transmission rate S1 assumed to be necessary for the exchange of said information and an actual transmission rate S2 which is actually achieved (S1−32) is calculated, and it is judged whether the at least one frequency band, other than the specific frequency band, is required or not required in accordance with a positive or negative sign of this difference. 48. The communications system as set forth in claim 47, wherein said actual transmission rate is found from the number of transmission data information calculated from the number of used frequency bands and a transmission interval of the transmission data information. 49. The communications system as set forth in claim 43, wherein one said specific frequency band and at least one said at least one frequency band, other than the specific frequency band, are simultaneously changed. 50. A communications system for exchange of information between communications apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication system comprising: a transmission data generator configured to generate frequency band information indicating which frequency band is to be used for transmission of data information between said communication apparatuses;a transmitter configured to transmit the frequency band information by using a specific frequency band which is set from among a plurality of frequency band assigned to the communications system, and to transmit data information by using at least one frequency band set from among said plurality of frequency bands; anda receiver configured to receive the frequency band information by using the specific frequency band, wherein said specific frequency band also transmits data information, andwhen there are a plurality of said communications apparatuses, specific frequency bands are individually set for said plurality of frequency bands and each of the specific frequency bands is assigned corresponding to each of the plurality of communications apparatuses. 51. The communications system as set forth in claim 50, wherein two or more of said communications apparatuses simultaneously use the same specific frequency band by time division multiplexing and/or code division multiplexing. 52. A communication system for exchange of information between communication apparatuses by a multicarrier transmission mode using a plurality of subcarriers, the communication system comprising: a transmission data generator configured to generate frequency band information indicating which frequency band is to be used for transmission of data information between said communication apparatuses;a transmitter configured to transmit the frequency band information by using a specific frequency band which is set from among a plurality of frequency bands assigned to the communication system, and to transmit data information by using at least one frequency band set from among the plurality of frequency bands, other than including the specific frequency band; anda receiver configured to receive the frequency band information transmitted by the specific frequency band and receive the data information transmitted by the at least one frequency band set from among the plurality of frequency bands.