a few preferred embodiments of the present invention will be described below with reference to the accompanying drawings . a radio communication system of the present invention is comprised of base stations b 1 , b 2 , . . . , b n which are fixed or semi - fixed in a movable state and mobile stations t 1 , t 2 , . . . , t m which move inside and outside the radio zones formed by the base stations b 1 , b 2 , . . . , b n . each of the base stations b 1 , b 2 , . . . , b n forms a radio zone by transmitting a polling signal . when a mobile station enters this radio zone and receives a polling signal from the base station , the mobile station makes some response to the base station to notify the base station of the presence of the mobile station . when data to be transmitted to the base station or mobile station is generated , the polling signal is temporarily stopped by corresponding communication control , and data communication is performed . fig3 shows the first embodiment of the radio communication system of the present invention , and more specifically , adjacent base stations b i and b i + 1 , of the base stations b 1 , b 2 , . . . , b n , and mobile stations t j , t j + 1 , t j + 2 , and t j + 3 located around the base stations . fig3 does not show base stations other than the base stations b i and b i + 1 , and mobile stations other than the mobile stations t j , t j + 1 , t j + 2 , and t j + 3 . fig4 shows an example of the arrangement of the base station b i ( i = 1 , 2 , . . . , n ). the base station b i includes an antenna 10 ( b i ) for transmitting a polling signal to mobile stations and transmitting / receiving data , a reception section 12 ( b i ) for receiving data , a transmission section 13 ( b i ) for transmitting a polling signal and data , and a transmission output control section 131 ( b i ) for controlling the transmission output of the transmission section 13 ( b i ). the base station b i further includes a control section 14 ( b i ) for controlling the overall base station b i , a mobile station position determination section 15 ( b i ) for determining the position of each mobile station in the radio zone in accordance with a response from each mobile station to a polling signal , a polling transmission interval generating timer 17 ( b i ) for generating time intervals at which polling signals are transmitted , a switch 11 ( b i ) for switching the transmission / reception state of the base station b i under the control of the control section 14 ( b i ), and an interface section 19 ( b i ) connected to , for example , a network that connects base stations . fig5 shows an example of the mobile station t j ( j = 1 , 2 , . . . , m ). the mobile station t j includes an antenna 10 ( t j ) for receiving a polling signal from the base station b i and transmitting / receiving data , a reception section 12 ( t j ) for receiving a polling signal and data , a transmission section 13 ( t j ) for transmitting data , and a pooling response determination section 132 ( t j ) for determining whether to respond to a polling signal from the base station b i . the mobile station t j further includes a control section 14 ( t j ) for controlling the overall mobile station t j , a self - position determination section 16 ( t j ) for determining the position of the self - station in the radio zone from the transmission output value obtained from a polling signal from the base station b i , a polling response timing generation timer 18 ( t j ) for generating the timing of a response to a polling signal , a switch 11 ( t j ) for switching the transmission / reception state of the mobile station t j under the control of the control section 14 ( t j ), and an interface section 19 ( t j ) connected to a display , input button , or the like . in the base station b i in fig4 the control section 14 ( b i ) controls the polling transmission interval generating timer 17 ( b i ) to generate the timing of transmission of a polling signal . in accordance with this timing , the control section 14 ( b i ) sends , to the transmission section 13 ( b i ), an instruction to transmit a polling signal . the control section 14 ( b i ) controls the transmission output control section 131 ( b i ) to adjust the transmission output of a polling signal , as shown in fig6 . fig6 shows a case wherein polling signals are output at predetermined intervals ( time ti ). however , the control section 14 ( b i ) may control the polling transmission interval generating timer 17 ( b i ) to transmit polling signals irregularly instead of transmitting them at predetermined intervals . the transmission section 13 ( b i ) changes the transmission output of a polling signal in accordance with the transmission output value sent from the transmission output control section 131 ( b i ), and transmits the polling signal through the switch 11 ( b i ) and the antenna 10 ( b i ). at this time , the switch 11 ( b i ) has already been switched to the transmission section 13 ( b i ) side . the switch 11 ( b i ) is switched to the transmission side when a polling signal or other data is to be transmitted , but is always switched to the reception side except for such an occasion . as shown in fig6 the base station b i changes the transmission output of a polling signal to transmit a long - distance polling signal having a large transmission output and a short - distance polling signal having a small transmission output , thereby forming a radio zone constituted by a large zone bz i having a large coverage and a small zone sz i having a small coverage . at this time , as shown in fig1 or 7 , such radio zones are formed such that the small zones sz i and sz i + 1 formed by the adjacent base stations b i and b i + 1 do not overlap . fig8 shows an example of the data format of a polling signal transmitted from the base station b i . the polling signal is made up of flags indicating the start and end of the polling signal , a base station id for identifying the base station b i that has originated the polling signal , a transmission output value set when the polling signal is transmitted , and data consisting of other control codes and various information . the control section 14 ( b i ) generates a polling signal in accordance with this data format and sends it to the transmission section 13 ( b i ). this signal is then transmitted through the switch 11 ( b i ) and the antenna 10 ( b i ). upon reception of the polling signal from the base station , the mobile station t j processes the polling signal through the control section 14 ( t j ) to obtain the base station id and the transmission output value . the control section 14 ( t j ) sends the base station id and the transmission output value to the self - position determination section 16 ( t j ). the self - position determination section 16 ( t j ) processes the base station id and the transmission output value to check whether the mobile station t j is located in the large or small zone in the radio zone formed by the base station . when the mobile station t j receives the polling signal from the base station , the control section 14 ( t j ) instructs the polling response timing generation timer 18 ( t j ) to generate the timing of transmission of a polling response signal . as shown in fig9 the polling response timing generation timer 18 ( t j ) generates a response timing td by randomly selecting one of random slots . the control section 14 ( t j ) generates a polling response signal and sends it to the transmission section 13 ( t j ) in accordance with the response timing td . this signal is then transmitted through the switch 11 ( t j ) and the antenna 10 ( t j ). when a polling response signal or another data is to be transmitted , the switch 11 ( t j ) is switched to the transmission side , but is always switched to the reception side except for such an occasion . the transmission timing of a polling response signal is set such that a plurality of slots are generated a predetermined period of time after reception of a polling signal , one slot is randomly selected from the generated slots , and the polling response signal is transmitted in the selected slot . the time required for the generation of random slots , the number of slots , and the time per slot remain constant throughout all the mobile stations . for this reason , polling response signals do not interfere with each other unless mobile stations that are to respond to the same polling signal select the same slot . fig1 shows an example of the data format of a polling response signal . the polling response signal is made up of flags indicating the start and end of the polling response signal , a mobile station id for identifying the mobile station t j that has originated the polling response signal , a base station id for identifying the base station that has received the polling response signal , and data consisting of other control codes and various information . the control section 14 ( t j ) generates a polling response signal in accordance with this data format and sends it to the transmission section 13 ( t j ). this signal is then transmitted through the switch 11 ( t j ) and the antenna 10 ( t j ). upon reception of the polling response signal from the mobile station , the base station b i processes the polling response signal through the control section 14 ( b i ) to obtain the mobile station id . the mobile station position determination section 15 ( b i ) checks whether the received polling response signal is a response to a long - distance polling signal or short - distance polling signal , thereby checking whether the mobile station corresponding to the obtained mobile station id is located inside or outside the small zone sz i of the radio zone formed by the base station b i . fig1 shows how polling signals and polling response signals are exchanged in a case wherein base stations and mobile stations are arranged as shown in fig3 . fig1 shows the output levels of the respective signals along the time axis extending to the right . the base stations b i and b i + 1 alternately originate long - distance polling signals and short - distance polling signals at predetermined time intervals t . at this time , synchronization is not necessarily established between the base stations b i and b i + 1 . since the mobile station t j is located inside the small zone of the base station b i , the mobile station t j receives both short - and long - distance polling signals from the base station b i , and hence responds to them . since the mobile station t j + 1 is located in a place where the large zone of the base station b i overlaps the large zone of the base station b i + 1 , the mobile station t j + 1 responds to long - distance polling signals from the two base stations . the mobile station t j + 2 is located inside the large zone of the base station b i + 1 , and hence responds to a long - distance polling signal from the base station b i + 1 . the mobile station t j + 3 is located outside the radio zones of the two base stations , and hence originates no polling response signal . as described above , since the timing of transmission of a polling response signal is generated by selecting one of random slots through the polling response timing generation timer , the probability that polling response signals responding to the same polling signal interfere with each other is low . referring to fig1 , the output level of each polling response signal is set to be almost equal to that of each long - distance polling signal . however , the output level of a polling response signal may be changed in accordance with the transmission output value contained in a polling signal . when a polling signal with a small transmission output value is received , the power consumed by the mobile station can be saved by returning a polling response signal with an output value similar to the transmission output value . as described above , a polling signal and a polling response signal respectively contain the corresponding base station id or mobile station id . for this reason , when these signals are received , specific stations from which the signals originated can be determined . therefore , the base station can determine whether the mobile station located around the base station is located inside or outside the small zone . the mobile station can also determine , from the received polling signal , the position of itself within a specific zone of a specific base station . although a given base station may receive a polling signal originated from another base station , since a base station id is contained in the polling signal , the signal does not interfere with a polling response signal . although a given mobile station may receive a polling response signal originated from another mobile station , since a mobile station id is contained in the polling response signal , the signal does not interfere with a polling signal from a base station . information originated from the base station includes various data as well as a polling signal . when different data need to be transmitted from the base station b i to a plurality of mobile stations , the base station b i transmits first the data to mobile stations located outside the small zone in the radio zone formed by the base station b i on the basis of the determination result obtained by the mobile station position determination section 15 ( b i ). after completion of data communication to mobile stations outside the small zone , the base station b i transmits the data to mobile stations inside the small zone . fig1 shows another arrangement of a base station in the present invention . according to this arrangement , a mobile station presence determination section 20 ( b i ) is added to the arrangement of the base station described above and is connected to the control section 14 ( b i ). as described above , the base station b i alternately transmits long - and short - distance polling signals . if a polling response signal is returned in response to a long - distance polling signal , the mobile station presence determination section 20 ( b i ) determines that the mobile station is present inside the large zone formed by the base station b i . otherwise , the mobile station presence determination section 20 ( b i ) determines that the mobile station is not present in the large zone . the mobile station presence determination section 20 ( b i ) then sends the corresponding information to the control section 14 ( b i ). when the control section 14 ( b i ) determines , on the basis of the determination result sent from the mobile station presence determination section 20 ( b i ), that the mobile station is not present in the large zone formed by the base station b i , the control section 14 ( b i ) stops the origination of a short - distance polling signal , and continuously transmits a long - distance polling signal . if it is determined that the mobile station is present in the large zone , long - and short - distance polling signals are alternately originated , as described above . fig1 shows another arrangement of the mobile station in the present invention . according to this arrangement , a response determination section 30 ( t j ), a transmission output value buffer 31 ( t j ), and a transmission output value determination section 32 ( t j ) are added to the arrangement of the above mobile station and are connected to the control section 14 ( t j ). upon reception of a polling signal from a base station , the control section 14 ( t j ) processes the polling signal to obtain the transmission output value of the polling signal in the above - described manner . the control section 14 ( t j ) sends the transmission output value to the response determination section 30 ( t j ). the response determination section 30 ( t j ) sends the transmission output value sent from the control section 14 ( t j ) to the transmission output value buffer 31 ( t j ). the transmission output value buffer 31 ( t j ) includes two transmission output value memories 311 ( t j ) and 312 ( t j ) capable of storing transmission output values . upon reception of a transmission output value from the response determination section 30 ( t j ), the transmission output value buffer 31 ( t j ) stores the transmission output value , stored in the transmission output value memory 311 ( t j ), in the transmission output value memory 312 ( t j ), and stores the transmission output value , sent from the response determination section 30 ( t j ), in the transmission output value memory 311 ( t j ). if no data is stored in the transmission output value memory 311 ( t j ), the transmission output value sent from the response determination section 30 ( t j ) may be simply stored in the transmission output value memory 311 ( t j ). with this operation , the transmission output value of the currently received polling signal and the transmission output value of the previously received polling signal are respectively stored in the transmission output value memories 311 ( t j ) and 312 ( t j ). if no transmission output value is sent from the control section 14 ( t j ) for a predetermined period of time , the response determination section 30 ( t j ) clears the transmission output value memories 311 ( t j ) and 312 ( t j ) in the transmission output value buffer 31 ( t j ). the transmission output value determination section 32 ( t j ) refers to / processes the transmission output value in the transmission output value buffer 31 ( t j ) to check whether the polling signal is a long - or short - distance polling signal , and sends the determination result to the response determination section 30 ( t j ). the response determination section 30 ( t j ) generates and outputs a determination result indicating whether to transmit a polling response signal on the basis of the determination result sent form the transmission output value determination section 32 ( t j ). fig1 shows the determination results sent from the transmission output value determination section 32 ( t j ) and the response determination results obtained by the response determination section 30 ( t j ). as shown in fig1 , the determination results sent from the transmission output value determination section 32 ( t j ) are classified into six patterns . of the six patterns , patterns 1 to 4 correspond to whether the mobile station is located inside the large or small zone in the radio zone formed by the base station . pattern 1 corresponds to a case wherein the mobile station is located inside the large zone of the base station . patterns 2 and 3 correspond to a case wherein the mobile station is located inside the small zone . pattern 4 corresponds to a case wherein the mobile station is located in the small zone but fails to receive a long - distance polling signal for some reason , and the short - distance polling signal received before last is left in the transmission output value buffer 31 ( t j ). patterns 5 and 6 correspond to a case wherein the transmission output value buffer 31 ( t j ) is empty because , for example , the mobile station is located in an area that does not belong to any of the radio zones of the base stations , and no polling signal is received within a predetermined period of time . the response determination section 30 ( t j ) determines , on the basis of the determination result obtained by the transmission output value determination section 32 ( t j ), a specific pattern , of the six patterns , to which the current and previous polling signals correspond . assume that the response determination section 30 ( t j ) determines pattern 2 , in which the currently received polling signal is a long - distance polling signal and the previously received polling signal is a short - distance polling signal . in this case , a determination result indicating that no response is to be made is output to the control section 14 ( t j ). if pattern 1 , 3 , 4 , 5 , or 6 is determined , a determination result indicating that a polling response signal is to be output to the base station in response to the polling signal is output to the control section 14 ( t j ). on the basis of this determination result , the control section 14 ( t j ) controls transmission / non - transmission of a polling response signal . according to the above description of the embodiment of the present invention , the transmission output of a polling signal is controlled in two steps . however , the transmission output of a polling signal may be controlled in three or more steps . however , since the propagation of radio waves is influenced by environments , when transmission output control is performed in multiple steps , a distinctive radio zone may not be formed in some case . for this reason , the number of steps must be set within the range in which the boundaries between radio zones remain distinct . in addition , according to the description of the embodiment of the present invention , small zones are formed by base stations such that the small zones formed by the respective adjacent base stations do not overlap , as shown in fig7 . however , the present invention is not limited to this arrangement . the sizes of large and small zones can be arbitrarily set in accordance with the system to which the present invention is applied . although the number of radio channels is not specifically limited in the present invention , the present invention is effective especially for radio communication using a signal frequency .