Abstract:
A technique is provided that can avoid radio zone interference in a radio controlled model apparatus, which employs the frequency hopping system in the spread spectrum radio techniques. In the controller for maneuvering, for example, model airplanes, a process for detecting whether or not a radio zone is in an occupied state is initiated, with an initial radio zone represented by information (M) stored in a nonvolatile memory, acting as a starting point. Until an unoccupied radio zone is detected, the process of detecting occupation of radio zones continues, according to a predetermine sequence. Thus, an available radio zone can be detected. Moreover, information (M) representing an initial radio zone, stored in a nonvolatile memory, is updated immediately after power-on of the controller.

Description:
CROSS REFERENCES TO RECATED APPLICATIONS 
       [0001]    This application claims the priority benefit of Japanese Patent Application No. 2007-255349 filed on Sep. 28, 2007, which is fully incorporated herein by reference. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a radio controlled model apparatus, a controller for a radio controlled model apparatus, and a frequency hopping pattern selection method. Particularly, the present invention relates to a radio controlled model apparatus and a controller for a radio controlled model apparatus, each of which uses frequency hopping spread spectrum communication, and to a frequency hopping pattern selection method used in radio frequency hopping spread spectrum communication. 
         [0005]    2. Description of the Prior Art 
         [0006]    The use of the spread spectrum radio technique for wireless control of radio controlled model apparatuses, such as model airplanes, has now become widespread. The 2.4 GHz band is commonly used in the spread spectrum radio technique. The spread spectrum radio technique involves either a frequency hopping spread spectrum system or a direct sequence spread spectrum system. To use the entire given frequency range at the same time, the direct sequence spread spectrum system is a communication method which does not perform channel separation. In contrast, the frequency hopping spread spectrum system is a communication method which uses ten or more frequencies obtained through time division mapping by employing a specific algorithm. In Japan, for example, the frequencies are obtained by shifting the 26 MHz band by 1 MHz. A variety of frequency hopping patterns can be created using the algorithm. When the frequency hopping spread spectrum system is applied to radio controlled model apparatuses, one frequency hopping pattern is used to communicate between a transmitter and a receiver included in model aircraft including model airplanes, helicopters, airships, dragonflies, and so on. The apparatus incorporates the transmitter as a part of the controller that functions as a radio parent station for the radio controlled model apparatus, and the receiver that functions as a radio mobile station for the apparatus. The communication path, created using a single frequency hopping pattern, is referred to hereinafter as a radio zone. 
         [0007]    In order to facilitate the understanding of the technical content to be described hereinafter, the whole configuration of a radio controlled model apparatus will be briefly explained here. The radio controlled model apparatus includes a controller, or control device, which functions as a radio parent station, and the controller comprises a transmitter and an operation unit. The transmitter, which transmits control information to a model aircraft for example, employs the frequency hopping spread spectrum system when transmitting radio waves. The operation unit has a wheel or joystick for controlling a model aircraft. The transmitter and the operation unit are normally integrated into a single, portable device. The integrated device is referred to as a controller, or control device. 
         [0008]    The power transmission unit has a different configuration depending on the type of model aircraft, including model airplanes, helicopters, airships, and so on. The power source may be a fuel engine or an electric motor depending on the type of model aircraft. A different mechanism may be used for directional control and speed control depending on the type of model aircraft. Generally, the aircraft is provided with a receiver, servos, motors for driving rudders attached, for example, to a horizontal stabilizer and a vertical fin in a model airplane, amplifiers for supplying power to motors, and a frame for carrying them. In the above configuration, the receiver receives radio waves from the controller and sends the necessary control information to the servos. The amplifier receives the signals from the servos to operate the motors. 
         [0009]    In the radio controlled model apparatus with the above configuration, the same radio zone is shared by a single controller and a single model aircraft, while other radio zones are shared by other controllers and their respective model aircraft. Thus, different frequency hopping patterns, independent of each other, are used. A different frequency hopping pattern is used for each radio zone. A specific controller can thereby control a specific aircraft without radio signal interference from another radio zone, even if the controller&#39;s radio zone is overlapped by a neighboring radio zone. A neighboring radio zone refers to a different radio zone, whose hopping pattern results in the temporary sharing of a particular radio frequency. One such radio controlled model apparatus is disclosed in Japanese Patent Publication No. 10-252884, the contents of which are hereby incorporated by reference. 
       SUMMARY OF THE INVENTION 
       [0010]    Since technical advances have reduced the price of radio controlled model apparatuses, the number of people enjoying radio controlled models as a hobby is increasing. However, the number of radio zones is finite. There is therefore increasing concern that radio signals of radio zones may interfere with each other when using the frequency hopping system. The mutual interference between radio zones means that two or more model aircraft controlled by human operators occupy the same radio zone simultaneously. As a conceived approach for avoiding the occurrence of such a situation, the controller that functions as the radio parent station checks previously whether or not the radio zone to be used by the apparatus including the controller has been occupied by any other apparatus. Thereafter, an unoccupied radio zone is used by the apparatus. Such an approach may be advantageous in avoiding interference between radio zones. For that reason, it may be considered that controllers should include the function of detecting radio zones occupied by others. Specifically, a radio zone initialized set by default is initially set as the radio zone to be used at the start. The controller detects whether or not this radio zone is currently in an occupied state. When the target radio zone is not occupied, the setting of the initialized radio zone is maintained. However, when the initial radio zone is in an occupied state, a radio zone which is not being used by other controllers, identified in a predetermined order, may be used as the apparatus&#39; own radio zone. 
         [0011]    A study by the inventor et al., described in the present application, proved that interference between radio zones cannot be avoided using only the procedure described above. Such a situation will be explained in detail below. 
         [0012]    The controller is usually controlled by a human operator on the ground. Accordingly, when two or more controllers are used, some distance apart, the case may arise where a controller trying to use a particular radio zone cannot detect radio waves being transmitted by another controller that has already started to use that same radio zone. The operator of one controller and the operator of another controller may operate their respective radio controlled apparatuses in model aircraft airports, or in other suitable places such as empty lots, established at some distance from each other. In this case, a radio wave in the 2.4 GHz band, which is a ground wave, transmits between the controllers, and the traveling distance is relatively short. More specifically, the direct wave propagating between the controllers and reflected waves from the ground surface with opposite phase to the direct wave interfere with each other, and thus the traveling distance is shortened. Moreover, radio waves in the 2.4 GHz band are inclined to travel in straight lines, so buildings and other objects act as barriers to the direct travel of signals between the controllers in their respective model aircraft airports, thereby also shortening the traveling distance. 
         [0013]    On the other hand, since radio waves propagate directly in free space between the controller and the model aircraft, there is no phase interference due to propagation between the two paths, and no radio wave absorption due to obstacles. The traveling range of the radio signal becomes relatively long. In such a situation, controllers cannot receive radio waves from other controllers. However, when two or more controllers can transmit radio waves in the same radio zone, the receivers installed in both the model aircraft can receive the radio waves from each of the controllers. For that reason, it becomes possible for a single controller to control both its own and another controller&#39;s aircraft. As a result, an aircraft may fly out of control and may crash, or indeed one controller may be used, not to operate its own aircraft, but to seize a model aircraft belonging to an unrelated person. 
         [0014]    The present invention is designed to overcome the problems described above. The object of the present invention is to provide a technique capable of avoiding interference between radio zones in a radio controlled model apparatus employing the frequency hopping system in the spread spectrum radio techniques. 
         [0015]    According to the present invention, a radio controlled model apparatus comprises a mobile model device to be controlled by radio, and a controller capable of using a plurality of radio zones, which are created by switching plural frequencies sequentially and respectively, the controller controlling the mobile model device using one of the radio zones. The controller includes a radio zone use detector for detecting whether or not the radio zones are in an occupied state before the controller is used, and a transmitter for selectively transmitting through an unoccupied radio zone detected by the radio zone use detector. The radio zone use detector starts by detecting whether or not an initial radio zone, represented by information stored in a nonvolatile memory, is in an occupied state, continues to detect sequentially in a predetermined order whether or not radio zones are in an occupied state until an unoccupied radio zone is detected, and thereby updates the value of the information stored in the nonvolatile memory before the controller is used. 
         [0016]    According to the present invention, the controller for a radio controlled model apparatus capable of using a plurality of radio zones, which are created by switching plural frequencies sequentially and respectively, controls the mobile model device using one of the radio zones. The controller includes a radio zone use detector for detecting whether or not the plurality of radio zones are occupied before the controller is used, and a transmitter for selectively transmitting via an unoccupied radio zone detected by the radio zone use detector. The radio zone use detector starts detecting whether or not an initial radio zone, represented by information stored in a nonvolatile memory, is in an occupied state, continues to detect in a predetermined order whether or not radio zones are in an occupied state until an unoccupied radio zone is detected, and thereby updates the value of the information stored in the nonvolatile memory before the controller is used. 
         [0017]    According to the present invention, in a frequency hopping pattern selection method for a radio controlled model apparatus, the radio controlled model apparatus comprising a mobile model device to be controlled by radio, and a controller capable of using a plurality of radio zones created by switching plural frequencies sequentially and respectively, the controller controlling the model mobile device using one of the radio zones, and the frequency hopping pattern selection method comprises the following steps. The frequency hopping pattern selection method commences by detecting whether or not an initial radio zone, represented by information stored in a nonvolatile memory, is in an occupied state before the controller is used, continues detecting whether or not radio zones are in use in a predetermined order until an unoccupied radio zone is detected, and thereby updates the value of the information stored in the nonvolatile memory before the controller is used. 
         [0018]    According to the present invention, each of the radio controlled model apparatus, the controller for the radio control model apparatus, and the frequency hopping pattern selection method share common novel technical features. That is, the present invention is characterized by the control technique where a mobile model device is controlled wirelessly, plural radio zones are created by sequentially switching plural frequencies, respectively, and the mobile model device is manipulated using one of the radio zones. Before the controller is used, the detection process commences to determine whether or not an initial radio zone, represented by information stored in a nonvolatile memory and acting as a starting point, is in use. Until an unoccupied radio zone is detected, the process continues detecting sequentially in a predetermined order whether or not radio zones are in an occupied state. Information values stored in the nonvolatile memory are updated prior to using the controller. In such a manner, by changing the initial radio zone due to the detection process for occupation or non-occupation of a radio zone, every time the controller is used, the probability of radio zone interference is reduced. 
         [0019]    In a radio controlled model apparatus employing the frequency hopping system in the spread spectrum radio techniques, the present invention can provide the means of updating information values stored in a nonvolatile memory before the use of the controller starts, thereby avoiding radio zone interference. 
         [0020]    Other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part thereof, and in which there is shown by way of illustration a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram illustrating how to use a radio controlled model apparatus according to an embodiment of the present invention; 
           [0022]      FIG. 2  is a flowchart illustrating a process for operating a receiver incorporated into, for example, a model airplane, according to an aspect of the present invention; and 
           [0023]      FIG. 3  is a flowchart illustrating a process for setting radio zones, according to another aspect of the present invention. 
       
    
    
       [0024]    Before an embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    The present invention will be explained more specifically by referring the examples shown in the attached drawings. Explanation will be made in the following order: “an embodiment of using a radio controlled model apparatus”, “an embodiment of a frequency hopping system”, “an embodiment of using a frequency hopping system”, “a conventional example for comparison”, and “an embodiment of a receiver”. Thereafter, explanation will be made as to “an embodiment of setting radio zones”. In addition, various other embodiments will be explained. Thus, embodiments are fully disclosed below. 
         [0026]    First, how to use a radio controlled mode apparatus will be explained with reference to an embodiment according to the present invention shown in  FIG. 1 . In a model aircraft airport  10 , a controller  20 , a second controller  21 , and a third controller  22 , are used simultaneously. The controller  20  controls a model airplane  30 , the second controller  21  controls another model airplane  31 , and the third controller  22  controls a model helicopter  32 . The radio zone for the controller  20  and the model airplane  30 , the radio zone for the controller  21  and the model airplane  31 , and the radio zone for the controller  22  and the model helicopter  32 , are mutually distinct. This allows each controller to control its respective model aircraft freely, even in concurrent use, without causing interference with unrelated model aircraft. 
         [0027]    In this manner, even when three controllers are used simultaneously in the model aircraft airport  10 , flight vehicles, such as model aircraft, can be controlled arbitrarily and respectively. That is, the controllers  20  to  22  recognize the radio zones occupied by other controllers, which have previously started to transmit radio waves. As a result, the controllers  20  to  22  avoid the use of the occupied radio zones and use other radio zones distinct from one another, so that interference between radio zones can be avoided. 
         [0028]    Similar to the model aircraft airport  10 , a fourth controller  40 , a fifth controller  41 , and a sixth controller  42 , are used simultaneously in a second model aircraft airport  11 . The controller  40  controls a model airplane  50 , the controller  41  controls a model airplane  51 , and the controller  42  controls a model airship  52 . The radio zones for the controller  40  and the model airplane  50 , for the controller  41  and the model airplane  51 , and for the controller  42  and the model airship  52 , are mutually distinct. This allows each controller to control its respective model flight vehicles freely, even in concurrent use, without causing interference with unrelated model flight vehicles. 
         [0029]    In this manner, even when three controllers are used simultaneously in the model aircraft airport  11 , model flight vehicles can be controlled arbitrarily and respectively. That is, the controllers  40  to  42  recognize the radio zones occupied by other controllers which have previously started to transmit radio waves. The controllers  40  to  42  use other radio zones, avoiding the use of the occupied radio zones, so that interference between radio zones can be avoided. 
         [0030]    Table 1 illustrates an embodiment of a frequency hopping system. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 (Hopping pattern code) 
               
             
          
           
               
                 Y □X 
                 X1 
                 X2 
                 . . . 
                 Xn 
               
               
                   
               
               
                 1 
                 f1 
                 f2 
                   
                 fn 
               
               
                 2 
                 f2 
                 f4 
                   
                 f10 
               
               
                 — 
               
               
                 n 
                 fn 
                 f10 
                   
                 f1 
               
               
                   
               
             
          
         
       
     
         [0031]    In Table 1, the vertical column represents the frequencies of the radio waves output sequentially. The sequence of the frequencies indicated in each column represents a frequency hopping pattern, being characteristics of a radio zone. In the radio zone X 1 , the frequency changes in the order f 1 , f 2 , . . . , to fn. After reaching the frequency fn, the process repeats again from frequency f 1 . Similarly, in the radio zone X 2 , the frequency changes in the order of f 2 , f 4 , . . . , to f 10 . After reaching the frequency f 10 , the process repeats again from frequency f 2 . A pattern in which different frequencies are repeated in a predetermined sequence is also set previously in the other radio zones. The frequencies f 1  to fn are different for each radio zone. A single cycle of the radio zones X 1  to Xn is designed to generate the same frequency once. As described above, broadband frequencies are used with time division mapping to improve the signal-to-noise (S/N) ratio. Airborne vehicles can be controlled wirelessly from a long distance using low-level electric power, and without interference from other signals. 
         [0032]    In the present embodiment, a total of 36 frequencies are used for f 1  to fn. The number of frequency hopping patterns is represented by the number of columns in Table 1 or 36 kinds of patterns. Hence, this radio controlled model apparatus has 36 radio zones. The time between changes of frequency is 8 milliseconds, and the occupation time, namely, communicable time, of one frequency is 2 milliseconds. The time taken to cycle through each frequency in one radio zone is 288 msec (=36×8). When a radio controlled model apparatus having 36 radio zones is used, 36 human operators can control model aircraft, using 36 controllers at the same time. 
         [0033]    Next, how to use a frequency hopping system in the radio control mode apparatus will be explained. The model aircraft airports  10  and  11 , are generally located away from each other at a distance of about 2 km. In such a situation, none of the controllers  20  to  22  and  40  to  42 , can detect radio waves transmitted from a controller used in the other airport. It is possible for any one of the controllers  20  to  22  (referred to as the first group), and any one of the controllers  40  to  42  (referred to as the second group), to use the same radio zone. For example, the controller  20  in the first group and the controller  42  in the second group may use the same radio zone. 
         [0034]    Radio controlled model apparatuses generally use an ID code. The ID code that authorizes the operation of a model aircraft is set previously to the receiver installed in the model aircraft. The receiver only accepts incoming signals that include the ID code. Before a model aircraft flies, the ID code sent by the controller is identified to match with the ID code of the receiver. Hence, in principle, controllers having a different ID code cannot operate other unrelated aircraft even in the same radio zone. However, when ID codes match with each other by accident, or if an ID code is stolen, or various ID codes are transmitted in an attempt to operate other model aircraft, the ID codes become ineffective. 
         [0035]    If ID codes become ineffective in this manner, when the controller  20  in the first group and the controller  42  in the second group use the same radio zone, the situation may arise where the controller  20  controls the airship  52  from the other airport  11 , together with its own related airplane  30 . The reason is that radio waves propagating from the controller  20  to the controller  42  are ground waves of which phases have damped each other and which have a large attenuation characteristic. In contrast, radio waves propagating from the controller  20  to the model airship  52  propagate in free-space with less attenuation, so that they have sufficient radio field strength to operate the model airship  52 . 
         [0036]    For purposes of comparison to the present invention, a brief explanation will be made here as to how radio zones are determined conventionally, when one controller in the first group and one controller in the second group is used. When the controller  20  in the first group, for example, is powered on, it detects whether or not a predetermined radio zone to be used in the controller  20  is in an occupied state, prior to transmission of radio waves. When the predetermined radio zone is in an unoccupied state, transmission of radio waves commences. In this case, even when the wheel or joystick is not operated, the controller continues to transmit radio waves in a predetermined frequency hopping pattern in the predetermined zone. Thus, any controller, powered on later, can certainly detect the existence of the controller in the first group, powered on in advance. 
         [0037]    A constant default value is set to the predetermined radio zone, for example, radio zone X 1 , to be used by the controller  20 . In the receiver side of the model airplane  30 , the radio zone X 1  is set as a default value. As described above, the same default value is set to all the controllers. This is because when the frequency hopping pattern is known beforehand, the receiver side can be synchronized easily with the hopping pattern, and the necessity for the operator to set the transmitter&#39;s frequency hopping pattern can be omitted. Moreover, in fabrication of controllers, it is convenient for product inspection to set the radio zone X 1  uniformly as the initial radio zone. The radio zone is determined in the following procedure according to whether the radio zone X 1  is in use, namely, in an occupied state or not in use, namely, in an unoccupied state. 
         [0038]    First, the controller  20  checks whether or not the radio zone X 1  to be used by the controller  20  is in an occupied state. When the radio zone X 1  is in an unoccupied state, both the controller  20  and the model airplane  30  start to use the radio zone X 1 . Similarly, when the radio zone X 1  to be used by the controller  42  in the second group is in an unoccupied state, both the controller  42  and the model airship  52  start to use the radio zone X 1 . Thus, interference in the radio zone X 1  in air occurs with a probability of 1. 
         [0039]    Further explanation will be made as to the use of two controllers in the first group and two controllers in the second group. When the controller  20  is powered on, it detects whether or not the radio zone X 1  is in an occupied state, prior to radio transmission. When the radio zone X 1  is determined as being in an unoccupied state, the controller  20  starts to transmit radio waves via the radio zone X 1 . When the controller  21  is powered on after the power-on of the controller  20 , the controller  21  detects whether or not the radio zone X 1  is in an occupied state, prior to radio transmission. When the radio zone X 1  is determined as being in an occupied state, the controller  21  does not transmit radio waves via radio zone X 1 . Next, the controller  21  detects whether or not radio zone X 2  is in an occupied state. When the radio zone X 2  is determined as being in an unoccupied state, the controller  21  starts to transmit radio waves through the radio zone X 2 . Similarly, the controller  42  in the second group commences the use of the radio zone X 1 . When the controller  40  is powered on after the power-on of the controller  42 , the controller  40  starts to detect whether or not the radio zone X 1  is in an occupied state, prior to transmission of radio waves. The controller  40  detects that the radio zone X 1  is in an occupied state and thus does not transmit radio waves through the radio zone X 1 . Next, the controller  40  detects whether or not the radio zone X 2  is in an occupied state. Then, the controller  40  detects that the radio zone X 2  in an unoccupied state and thus starts to transmit radio waves through the radio zone X 2 . Thus, interferences in the radio zone X 1  and the radio zone X 2  in air occur with a probability of 1, respectively. 
         [0040]    As described above, interference occurs between the radio zone X 1  occupied by the controller  20  and the model airplane  30 , and the radio zone X 1  occupied by the controller  42  and the model airship  31 . Moreover, interference occurs between the radio zone X 2  occupied by the controller  21  and the model airplane  31 , and the radio zone X 2  occupied by the controller  40  and the model airplane  50 . 
         [0041]    In the conventional radio zone determination process, the radio zone X 1  is set as a default value. When a controller detects that the radio zone X 1  is in an occupied state, the detection sequence moves on to radio zone X 2 . When the controller detects that the radio zone X 2  is in an occupied state, the sequence moves on to radio zone X 3 . When the controller detects that the radio zone X 3  is in an occupied state, the sequence moves on to the radio zone X 4 . Thus, the radio zones are changed according to a predetermined detection sequence, with the use or non-use of each radio zone being detected at every step. When a radio zone is determined as being in an unoccupied state, the controller and the model aircraft start to use that particular radio zone. For that reason, even when the use of a radio zone by another controller is not confirmed between different model aircraft airports, the probability of interference between radio zones becomes high in the order of radio zones X 1 , X 2 , X 3 , . . . , Xn, in the predetermined radio zone selection order. 
         [0042]    Next, operation of the receiver for the model aircraft according to one aspect of the present invention will be explained with reference to a process illustrated in the flowchart of  FIG. 2 . In step ST 300 , the receiver is powered on and the model aircraft is powered on. In step ST 301 , the same radio zone is set to the receiver by tuning it to the radio zone of the transmitter in the controller. The same ID code as that of the controller is set to the receiver. The radio zone and ID may be set manually, or the setting may be performed automatically by bringing the transmitter close to the receiver. 
         [0043]    In step ST 302 , the receiving frequency of the receiver is set to a coordinate (Xm, 01), where (Xm, 01) represents an initial frequency in the radio zone Xm. For example, when the radio zone X 1  is selected, the coordinate (Xm, 01) represents frequency f 1  as shown in Table 1. In step ST 303 , the process is halted until the carrier is detected at the frequency f 1 . In ST 303 , when the carrier is detected (YES), the process goes to step ST 304 . 
         [0044]    In ST 304 , the radio waves at the frequency f 1  are demodulated to detect the ID code. The detected ID code is checked to determine whether it is the same as the set ID code. Since an ID code is inserted every time the frequency changes, the ID code is detected every time the frequency hops. When the detected ID code is the same as the set ID code (YES), the process goes to step ST 305 . When the detected ID code is not the same as the set ID code (NO), the process returns to step ST 302 . 
         [0045]    In step ST 305 , control information is received. The control information relates to, for example, control of a rudder of a horizontal stabilizer and so on. The control signal also includes information regarding conditions where no control is exercised. In step ST 306 , control information such as that regarding control of the rudder of a horizontal stabilizer and so on, is sent to the servomechanisms. 
         [0046]    In step ST 307 , the next frequency is received after a predetermined time. With the radio zone X 1 , the frequency f 2  is set as the next frequency. The predetermined time is the time elapsed since immediately after the ID was detected in step ST 304 . The time between the ID detection and the change from the current frequency to the next frequency is always constant. In the present embodiment, the time period is less than 8 milliseconds, as described above. In this process, the time until the current frequency changes to the next frequency is reset after the detection of the ID, every time the frequency changes. Therefore, synchronization is maintained even, for example, when there is a discrepancy between the transmitter&#39;s reference clock and the receiver&#39;s reference clock. After completing the process in step ST 307 , the process returns to step ST 304 . 
         [0047]    When they occupy the same radio zone, the transmitter operates as a master while the receiver operates as a slave. If radio contact is lost or a stronger radio disturbance occurs, the receiver performs a pull-in operation, in which the receiver operates as a slave when the ID codes match, for example, when the same ID code is set in another controller, because of a breach in the security of the ID code. This situation may result in information from the transmitter in another controller being decoded accurately. 
         [0048]    The receiver, which has decoded information from the transmitter regarding flight control, operates the servomechanisms based on the decoded information, thereby obtaining the desired flight control including, for example, nose-up, nose-down, circular flight, landing, takeoff, and the like. 
         [0049]    Explanation will now be made to a process for setting radio zones by referring to a flowchart shown in  FIG. 3 . The flowchart describes processes of the central processing unit (CPU) in a controller, together with processes of hardware related to the CPU. The CPU functions in the embodiment as part of the radio zone use detector for detecting whether or not plural radio zones are in an occupied state. Similarly, a radio level, namely, RSSI level, detector, to be described later, functions in the embodiment as the other part of the radio zone use detector. 
         [0050]    In step ST 100 , the controller is powered on (abbreviated as “power-ON”). The operator manually operates the power switch attached to the controller to energize the controller. Every time the power source is turned on, the process begins at step ST 100 . The process terminates at step ST 110  or step ST 118  to be described later. The power-ON operation means not only power distribution to the whole controller, but also power distribution to the transmitter alone, with some part of the controller being energized previously. That is, power-ON provides impetus for a series of operations, or uses of the controller, initiated to maintain radio transmission in such a way that, after the controller has confirmed radio conditions emitted from another controller, this another controller can recognize the existence of the corresponding controller. The power-ON operation indicates the embodiment of this impetus. 
         [0051]    In ST 101 , the number of radio zones (M) is incremented by 1. In ST 102 , it is determined whether or not M=n+1. When M=n+1 (YES), the process goes to step ST 103 , so that M becomes 1, wherein n is the maximum number of radio zones (the number of columns in Table 1). When M is not n+1 (NO), where n is the number of channels, the process goes to step ST 104 . 
         [0052]    In step ST 104 , the values for a number of variables are set, substituting M for N, Y=1 and K=3. Values in the radio zone use table are cleared (n table values of the first to n-th relative addresses, corresponding to respective radio zones X 1  to Xn, are set to “0”). After the setting of the variables, the process goes to step ST 105 , wherein Y is a frequency number, namely the line number in Table 1 in each radio zone, K is a value specifying the maximum execution cycle in step ST 105 , and M is the number of radio zones or hopping patterns, or 1 to 36 in the embodiment. N is the number of channels, or 36 in the embodiment. N is a variable in the process and corresponds to the number of radio zones, namely hopping patterns. Value M is stored in a nonvolatile memory built into the controller, and is sustained even after power is turned off namely, power-OFF. In contrast, values of the radio zone use table and the values for Y, K and N are stored in the controller&#39;s “volatile” memory. 
         [0053]    In step ST 105 , a radio level, namely, received signal strength indication (RSSI) level, of a frequency on the coordinate (XN, Y) is detected. Whether or not a format of information obtained from the received signal matches with a predetermined format is determined within 300 msec. The frequency of the coordinate (XN, Y) is the frequency of the Y-th line shown in Table 1 in the radio zone XN corresponding to the N-th line in Table 1. When step ST 105  terminates, the process goes to step ST 106 . 
         [0054]    In step ST 106 , it is determined whether or not the RSSI level is more than a predetermined reference value during the measuring time of 300 msec. To ensure detection of radio waves from other controllers, this measuring time is larger than 288 msec (=36×8 msec), which is the cycle time of one radio zone with frequencies. When the RSSI level is more than a predetermined reference value (YES), the process goes to step ST 107 . When the RSSI level is less than the predetermined reference value (NO), the process goes to step ST 110 . In step ST 110 , the radio zone XN is set, that is, M=N is written in the nonvolatile memory. This process is thereby terminated. 
         [0055]    In step ST 107 , it is determined whether or not the detection format is the predetermined format. When the detection format has the predetermined format (YES), the process goes to step ST 112 . When the detection format is not the predetermined format (NO), the process goes to step ST 108 . 
         [0056]    In step ST 108 , it is determined whether or not Y=K. When Y=K (YES), the process goes to step ST 110 . When Y≠K (NO), the process goes to step ST 109 . In step ST 109 , the value Y is incremented by 1, and the process then goes again to step ST 105 . 
         [0057]    In step ST 112 , radio zones of the predetermined format are detected for 800 msec at frequency Y. All detected radio zones are stored. An “occupied” flag is set to the corresponding number in the radio zone use table. After that process ends, the process goes to step ST 113 . 
         [0058]    In step ST 113 , it is determined whether or not an N-th flag, namely, the radio zone to be used, in the “in-use table” is 1. When the flag is 1 (YES), the process goes to step ST 114 . When the flag is not 1 (NO), the process goes to step ST 119 . 
         [0059]    In step ST 119 , an empty radio zone is selected. Thereafter, the process goes to step ST 110 . In step ST 114 , the value N is incremented by 1. Thereafter, the flow goes to step ST 115 . In step ST 115 , it is determined whether or not N is equal to n+1. When N is equal to n+1 (YES), the process goes to step ST 116 . When N is not equal to n+1 (NO), the process goes to step ST 117 . In step ST 116 , N is set to 1. Thereafter, the process goes to step ST 117 . 
         [0060]    In step ST 117 , it is determined whether or not N=M. When N=M (YES), the process goes to step ST 118 . When N≠M (NO), the process goes to step ST 113 . 
         [0061]    In step ST 118 , “no radio zone currently available” is indicated to terminate the process. The “no radio zone currently available” message may be displayed on a liquid crystal display (LCD) installed on the controller, or may be indicated by blinking a specific lamp. 
         [0062]    The radio zone setting procedure of the above embodiment has the following notable features. As to the first feature, every time the controller is powered on, the number of the initial radio zone at the beginning of a search is incremented by 1, compared with the number in the previous power-ON mode. When the number of the radio zone reaches 36, the number is reset to 1. 
         [0063]    Implementing such a procedure enables a reduction in the probability of radio zone interference occurring between one controller and a different controller, used in another model aircraft airport and separated to the extent that the first controller cannot recognize the different controller. 
         [0064]    The probability of radio zone interference occurring is described below. The initial radio zone value for radio zone detection depends on the number of power-ON, namely, the number of power-OFF+1 of each controller. It is believed that initial radio zone values for radio zone detection in respective controllers are substantially distributed uniformly. As a result, the probability of the radio zone interference due to the matching of an initial value is 1/n, that is, 1/36 in the present embodiment. 
         [0065]    The occupation time of one frequency, that is, 2 msec in the present embodiment, is shorter than one cycle time, that is, 288 msec (=36×8 msec) in the present embodiment. The probability of overlap in the occupation time of one frequency is represented by the formula, that is, (occupation time of one frequency)/(time of one cycle), or, 2 msec/288 msec in the present embodiment. 
         [0066]    The probability that the same radio zone with perfect synchronization is selected is (1/n)×((occupation time of one frequency)/(time of one cycle)). In the present embodiment, that probability is very small, namely, (1/36)×(2 msec/288 msec) =1/5184. 
         [0067]    As to the second feature, prior to detection of an available radio zone, whether or not a radio level, RSSI level exceeds a predetermined reference value is determined, thereby indicating whether or not another controller is using the same frequency. This allows detection accuracy to be improved. 
         [0068]    In the radio zone setting procedure in the above-mentioned embodiment, the number of the initial radio zone to be searched every power-ON is incremented by 1, compared with the number in the previous power-ON. After the radio zone number reaches 36, it is reset to 1. However, the setting order may be changed randomly. The CPU may be set to generate the necessary random numbers to change the order randomly. Alternatively, a counter may be provided that divides the controller&#39;s clock and repeatedly counts 1 to n, namely, 1 to 36 in the present embodiment, to determine the count value. 
         [0069]    It is to be understood that the controllers of the above-mentioned embodiments can be used as devices for manipulating volume controls and trims in radio control transmitters. Moreover, various applications are possible as embodiments of the present invention. The present invention should not be restricted to only the above-mentioned embodiments. Needless to say, variations not described in the embodiments, but within the technical concept of the present invention, are within the scope of the present invention. 
         [0070]    For example, if the CPU can inspect radio zones sequentially, the priority of the detection or search order of radio zones is not limited to the embodiments described above. Moreover, the value M, for example, stored in the nonvolatile memory, may be updated not only through increment or random number generation, but also through decrement. The value M may be updated according to a predetermined array order of 1 to n. Moreover, the present invention has been explained, by way of example, as used in wireless control of mobile model devices, but the invention should not be limited only to use with model aircraft. In other words, when the radio propagation distance between a mobile model device and a controller is larger than the radio propagation distance between the model mobile device and a different airport, the probability of radio zone interference can be reduced effectively.