Radio communication apparatus and transmission power control method

#This is a continuation application of U.S. patent application Ser. No. 12/055,429 filed Mar. 26, 2008 and claims the benefit of its priority.

#The present invention relates to a radio communication apparatus and a transmission power control method, and more particularly relates to a radio communication apparatus and a transmission power control method, in which a transmission power control is improved.

#A radio communication system such as an inter-automobile communication system is known in which direct communication is carried out between automobile communication apparatuses without any intervention of a base station. In this radio communication system, the communication state changes with movement of the communication apparatus. For example, with the movement of the communication apparatuses, it would be assumed that a communication are has no communication counter end or few communication counter end, or on the contrary, the communication apparatuses are dense in a certain area, in which there are a large number of communicable counter ends.

#The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain exemplary embodiments taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a block diagram showing a configuration of an exemplary embodiment of an on-board communication device as a radio communication apparatus of the present invention;

#FIG. 2 is a block diagram showing a configuration of an exemplary embodiment of an on-board communication device as a radio communication apparatus of the present invention;

#Hereinafter, a radio communication apparatus according to exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. Here, when a transmission power control method is applied to an inter-automobile communication system, the radio communication apparatus mounted on an automobile (a vehicle) will be described. In the inter-automobile communication system, radio communication is carried out between a plurality of on-board communication devices 1 (1-1, 1-2, . . . ). In this case, an on-board communication device transmits a data such as an automobile (vehicle) position data and a setting value of transmission power to peripheral automobiles. Also, the on-board communication device 1 holds the automobile position data and the transmission power setting values, which are received from the peripheral automobiles, and data of reception powers as the data of the peripheral automobiles. Also, the data are updated each time a signal is newly received from any of the peripheral automobile. In accordance with the data of the peripheral automobiles, transmission losses are estimated from the transmission power setting values of the peripheral automobiles and the actual reception powers. Moreover, the number of the receivable automobiles is estimated on the basis of the transmission power setting value at the time of the transmission from the automobile itself. Then, the transmission power is set such that a signal does not reaches many automobiles, more than necessary, and the signal is outputted. The exemplary embodiment of the present invention will be described below in detail.

#FIGS. 1 and 2 are block diagrams showing the configuration of the on-board communication device as the radio communication apparatus according to an exemplary embodiment of the present invention. The on-board communication device 1 contains a transmission power control section 11, an on-board radio section 12 and an on-board control section 13. Here, although the on-board communication device 1-1 will be described, the on-board communication devices 1-2, . . . of the peripheral automobiles have the configuration similar to that of the on-board communication device 1-1.

#The on-board radio section 12 transmits and receives a radio signal to and from the on-board communication devices 1-2, . . . of the peripheral automobiles. That is, at the time of the reception, the on-board radio section 12 receives a radio reception signal from the different on-board communication device 1. The radio reception signal is converted into a reception data, and the reception data and a reception power data are outputted to the on-board control section 13. The reception power data indicates a value of reception power (a reception power measurement value) when the radio reception signal is received. On the other hand, at the time of the transmission, the on-board radio section 12 receives a transmission data from the on-board control section 13 and a vehicle information from the transmission power control section 11. The vehicle information contains a transmission power data indicating a value of transmission power (a transmission power setting value) when a radio transmission signal is transmitted, and an identifier (ID) data indicating this on-board communication device 1-1. The vehicle information may include a position data of the on-board communication device 1-1. The on-board radio section 12 converts the transmission data added with the vehicle information into the radio transmission signal, and transmits the radio transmission signal to the on-board communication devices 1-2, . . . of the peripheral automobiles in the transmission power specified by the transmission power setting value.