Patent Publication Number: US-2005136985-A1

Title: Power consumption reducing method in a comunication terminal, communication system, communication terminal, and computer program thereof

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a technical field of a communication terminal that transmits and receives image data. Also, the present invention relates to a technical field of a communication terminal having, for example, a so-called video phone function.  
      2. Description of the Rerated Art  
      Conventionally, in a mobile communication system that is operated by a communication operator, a second-generation cellular phone communication system using a narrow-band communication system has widely spread. A PDC/GSM system has spread as the narrow-band communication system. The PDC (personal digital cellular) is the representation of the mobile communication system of the second-generation cellular phone used in Japan. On the other hand, a GSM (global system for mobile communications) is the representation of a standard system of the second-generation cellular phone that has been standardized in Europe.  
      Then, in the recent years, the conventional second-generation cellular phone communication system has been shifting to a third-generation cellular phone system using a wideband communication system that is represented by a wideband-CDMA (code division multiple access) system. A so-called video phone function is one of the killer contents in the third-generation cellular phone system. The video phone function is expected to widely spread as a standard function in the communication terminal (cellular terminal) in the future.  
      In general, in the communication terminal such as the cellular phone on whose portability emphasis is placed, because a battery (chargeable battery) mounted for its operation is also downsized, a power capacity is restricted. For that reason, in the communication terminal, a maximal reduction in power consumption during operation has been demanded. However, in the third-generation cellular phone system, there arises a problem on the amplitude of the power consumption in the radio communication circuit of the communication terminal, which is attributable to the communication system. For that reason, there arises a problem in that the battery life of the communication terminal becomes short, and the usability of a user remarkably deteriorates. In the present specification, the battery life represents the battery lifetime of the chargeable battery that is required to be again charged by power consumption accompanied by use after the communication terminal has been charged into a fully charged state.  
      Also, in the communication terminal of the third-generation cellular phone system, the power consumption further increases with an additional function such as the so-called video phone function in addition to the problem on the power consumption that is attributable to the above communication system. Then, the problem on the power consumption which is attributable to the inclusion of the video phone function is caused by a sequential processing of until transmitting and receiving a photographed motion picture as image data. For that reason, in the communication terminal of the third-generation cellular phone system, it is anxious to reduce the power consumption by using some means.  
      By the way, JP 2001-136423 A has proposed that in order to reduce the power consumption in a communication terminal with a video phone function, when there is no change in an image photographed by a camera provided in the terminal, a power of the camera turns off.  
      That is, in JP 2001-136423 A, the communication terminal stores the image data of the photographed image in a storage device, and judges whether there is a change in the photographed image, or not, by comparing the stored image data with image data of a newly photographed image, during the photograph by the camera. Then, the communication terminal stops dispatching of a power to an image photographing circuit including the camera until a predetermined period of time elapses or a user conducts restart operation, when it is judged that there is no change between both of image data. Accordingly, the communication terminal disclosed in JP 2001-136423 A can suppress the useless power consumption.  
      However, a method of reducing the power consumption in the communication terminal according to JP 2001-136423 A suffers from the following problem.  
      That is, in the communication terminal according to JP 2001-136423 A, only when there is no change in the photographed image (that is, a variation between the image data to be compared is 0), dispatching of the power to the image photographing circuit is stopped in order to reduce the power consumption. Accordingly, a reduction effect on the total power consumption of the communication terminal is restrictive.  
      Also, in the communication terminal according to JP 2001-136423 A, the dispatching of the power to the camera stops when there is no change in the photographed image as described above. For that reason, in the communication terminal, after the above predetermined period of time has elapsed, or when the user conducts the restart operation, some period of time is required since the dispatching of the power to the image photographing circuit and the camera is restarted until image data of the newly photographed image is outputted. Accordingly, an operating response is low, and the operationality is not good.  
      Accordingly, a technique of reducing the power consumption of the communication terminal without lowering the operationality of the use has been desired.  
      By the way, in the case where the video phone function is a high-load function that much occupies (consumes) individual system resources in the case where it is treated as the overall system including the cellular phone and its equipment side. For that reason, in order to efficiently supply the video phone service to a larger number of users in the radio system of the cellular phone, there is something that radio traffic needs to be reduced. In this matter, in JP 2001-136423 A, even during dispatching of a power to the image photographing circuit including the camera stops (that is, no change in the image data is found), the image data that is stored in the storage device is transmitted to a communication terminal as a receiver. Accordingly, the technique that is disclosed in JP 2001-136423 A does not obtain the reduction effect on the radio traffic.  
      Accordingly, there is a tendency that the radio graphic increases with a high function such as the video phone function in the radio communication system in the recent years, and a technique of reducing the radio traffic has been desired in such a radio communication system.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in view of the above problems, and therefore a main object of the present invention is to efficiently reduce the power consumption of a communication terminal without deterioration of the operationality of a user.  
      In addition, another object of the present invention is to reduce the power consumption of a communication terminal without deterioration of the operationality of a user, and to reduce radio traffic in a radio communication system.  
      That is, according to the present invention, there is provided a method of reducing power consumption in a communication terminal that transmits and receives image data, including: stopping transmission of new image data from a transmission side communication terminal ( 1 A) to a reception side communication terminal ( 1 B) in a duration where a difference between image data inputted in time series is smaller than a predetermined value; and displaying an image, on the reception side communication terminal ( 1 B), on the basis of image data that has already been received in a duration where the reception side communication terminal cannot receive the new image data from the transmission side communication terminal ( 1 A).  
      In a preferred embodiment, the image displayed on the reception side communication terminal ( 1 B) is a still picture based on the latest image data that is received before the reception side communication terminal ( 1 B) cannot receive the new image data.  
      In addition, input image data to be compared with the predetermined value is, for example, image data of two frame images in question among image data of a plurality of frame images that are inputted in time series, and the image data of two frame images in question is, for example, image data of two frame images that are continuous in time series, or image data of two frame images that are at a predetermined frame interval among the image data of a plurality of frame images that are inputted in time series.  
      The above object is achieved even by a communication system that corresponds to the power consumption reducing method in the communication terminal having each of the above structures, and the communication terminal that constitutes the communication system.  
      Also, the above object is achieved even by a computer program that realizes the above communication terminal by means of a computer, and a computer readable storage medium in which the computer program is stored.  
      Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein:  
       FIG. 1  is a block diagram showing a structure of a cellular phone in accordance with an embodiment of the present invention;  
       FIG. 2  is a flowchart showing an image transmission control process which is performed by a cellular phone in this embodiment; and  
       FIG. 3  is a flowchart showing an image reception control process which is performed by the cellular phone in this embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.  
      Hereinafter, a description will be given in more detail of a cellular phone which is a typical communication terminal according to an embodiment of the present invention with reference to the accompanying drawings.  
      First of all, in this embodiment, in order to realize a reduction in the power consumption of the cellular phone and a reduction in the radio traffic in a radio communication system that accommodates the cellular phone, attention is paid to the following points.  
      An attempt has been made to spread the video phone function in the third-generation cellular phone system using the wideband communication system under the above circumstances as described above. The wideband CDMA communication system, which is one example of the wideband communication system, is of a system that spreads a signal energy to a frequency band that is far wider than the band width of the information to perform communication. A spreading factor SF in the wideband CDMA communication system is in the range of 4 to 512. In the present specification, the spreading factor SF has the following relationship: 
 
 ST=T (bit section)/ Tc (chip section) 
 
      In the communication system, one chip section represented by Tc is a fixed value. Then, a one-bit information section represented by T is variable according to the amount of communicated information. Accordingly, in the case where the amount of information to be communicated is small, a data rate is lowered so that communication can be performed. For that reason, since T per Tc becomes long, the spreading factor SF becomes resultantly a large value. Then, in the case where the spreading factor SF is larger, because more chips (unit power) are required in transmission of data of one symbol, a power peak of a desired wave after dispreading becomes large.  
      From the above viewpoint, in the wideband CDMA communication system, the power peak after dispreading at a reception side communication terminal can ensure a sufficient level as required even in the case where the radio transmission power is lowered by positively reducing the amount of information to be transmitted. Then, a reduction in the radio transmission power at a transmission side communication terminal means a reduction in the power consumption of the communication terminal.  
      In addition, an SIR (signal interference ratio) of another communication terminal having the transmission wave of the communication terminal as an undesired wave is relatively improved as the radio transmission power of the transmission side communication terminal is lowered. As a result, this contributes to the efficient use of a limited line subscriber capacity of the overall radio communication system.  
      As described above, it is found that a reduction in the radio transmission power of the transmission side communication terminal contributes not to only a reduction in the power consumption of the communication terminal but also a reduction in the radio traffic as the overall communication system. Then, a cellular phone  1  according to this embodiment has a structure for realizing the above knowledge. Hereinafter, its structure will be described.  
      (Description of Device Structure and Operation)  
      First, the device structure of the cellular phone according to this embodiment will be described.  FIG. 1  is a block diagram showing the structure of a cellular phone according to an embodiment of the present invention. The cellular phone  1  shown in the figure is a cellular phone (mobile communication terminal) having a so-called video phone function.  
      The cellular phone  1  includes, as shown in  FIG. 1 , a control circuit  101 , an antenna  102 , a radio circuit  103 , a base band circuit  104 , a camera (image pickup device)  105 , an image processing circuit  106 , a display device  107 , a key operation device  108 , a storage device (image memory)  109 , a microphone  121 , a speaker  122 , and a battery  150 . The cellular phone  1  is operated by an electric power that is supplied from a battery (chargeable battery)  150 .  
      The control circuit  101  includes a CPU (central processing unit)  151 , a RAM (random access memory)  152 , a ROM (read only memory)  153 , and peripheral circuits (not shown). In this embodiment, the control circuit  101  controls the entire operation (the video phone function, a communication function such as transmission and reception of e-mail, etc.) of the cellular phone  1  having the structure shown in  FIG. 1 . In this situation, the CPU  151  executes a software program group that is read out of the ROM  53  while using the RAM  152  as a work area. In particular, the CPU  151  executes the respective programs of a comparison judgment function  112 , a notice monitor function  113 , and a notice generation function  114  so as to realize the characteristic transmission and reception operation in this embodiment (which will be described in more detail later).  
      Then, the outline of the operation that is realized by the cellular phone  1  will be described. The cellular phone  1  transmits and receives image data and voice data with respect to another cellular phone  1  that is a communicated party during calling at the time when the video phone function is executed. Accordingly, the cellular phone  1  functions not only as a transmission side communication terminal but also as a reception side communication terminal.  
      In the following description, for convenience of description, in the case of emphasizing the cellular phone  1  having the above device structure is a transmission side communication terminal, the cellular phone  1  may be called “cellular phone  1 A”, and in the case of emphasizing that the cellular phone  1  is a reception side communication terminal, the cellular phone  1  may be called “cellular phone  1 B”.  
      The key operation device  108  is an input device such as a ten key or a pointing device via which a user inputs a variety of operations. In this embodiment, the user starts a communication operation through the video phone communication by using the key operation device  108 . In this situation, the camera  105  starts the photograph of a moving picture on the basis of an instruction from the control circuit  101 . The camera  105  is an image pickup device using an image pickup device such as a CCD (charge coupled device) or a CMOS (complementary metal-oxide semiconductor). The camera  105  inputs an image signal (image data) of a frame unit which represents a photographed image to the image processing circuit  106  in time series. The control circuit  101  transmits image data of the photographed image and voice data that represents a voice that is inputted from the microphone  121  to the cellular phone  1 B through the base band circuit  104 , the radio circuit  103 , and the antenna  102 .  
      The image processing circuit  106  has a differential operation function  111 . The differential operation function  111  calculates a variation (difference) Dv of a position of an object to be photographed at real time on the basis of image data of two frame images which are inputted to the image processing circuit  106  from the camera  105  in time series. In this situation, the object to be photographed by the camera  105  is a user per se of the cellular phone  1  in the general use of the video phone function.  
      The control circuit  101  compares the variation (difference value) Dv between two frame images by the differential operation function  111  of the image processing circuit  106  with a predetermined specific value Th by means of the comparison judgment function  112 . As a result of comparison, in the case where it is judged that the variation is equal to or lower than the specific value (predetermined threshold value) Th, and there is no change between those two frame images, the control circuit  101  generates control information (hereinafter referred to as “transmission stop notice SI”) which is for announcing that the transmission of the image data to the cellular phone  1 B is stopped. The control circuit  101  of the cellular phone  1 A generates the transmission stop notice SI by means of the notice generation function  113 . In addition, the control circuit  101  transmits the transmission stop notice SI to the cellular phone  1 B through the base band circuit  104 , the radio circuit  103 , and the antenna  102 . Then, the control circuit  101  stops only the transmission of the image data among the transmission and reception operation of the image data and the voice data which is performed after the start of the video phone communication. The operation state continues until that the variation between two new frame images that are sequentially inputted to the image processing circuit  106  exceeds a predetermined value (specific value Th) is detected by the differential operation function  111 , or the call end operation by the user is detected.  
      On the other hand, in the cellular phone  1 B, the reception of the transmission stop notice SI is monitored by the notice monitor function  114  of the control circuit  101 . Then, upon receiving the transmission stop notice SI, the control circuit  101  starts the display of the still image on the basis of the image data (latest image data) that has been finally received from the cellular phone  1 A and continues the voice call.  
      The control circuit  101  of the cellular phone  1 A generates control information (hereinafter referred to as “transmission restart notice TI”) for announcing that the transmission of the imaged data to the cellular phone  1 B is restarted in accordance with the detected result of the differential operation function  111 . More specifically, the control circuit  101  of the cellular phone  1 A generates the transmission restart notice TI when it is detected, by the differential operation function  111 , that the variation between the two new frame images that are sequentially inputted to the image processing circuit  106  exceeds the specific value Th. In addition, the control circuit  101  transmits the transmission restart notice TI to the cellular phone  1 B through the base band circuit  104 , the radio circuit  103 , and the antenna  102 . Then, the control circuit  101  restarts the transmission of the image data which has been stopped after the transmission stop notice SI has been transmitted. The operation state continues until that the variation between two new frame images that are sequentially inputted to the image processing circuit  106  is again equal to or lower than specific value Th is detected by the differential operation function  111 , or the call end operation by the user is detected.  
      On the other hand, in the cellular phone  1 B, the reception of the transmission restart notice TI is monitored by the notice monitor function  114  of the control circuit  101 . Then, upon receiving the transmission restart notice TI, the control circuit  101  starts the display of the moving picture on the basis of the image data that is sequentially received from the cellular phone  1 A and continues the voice call.  
      Then, the functions of the respective parts of the cellular phone  1  shown in  FIG. 1  will be described in more detail along a flow of image data at the time of video phone communication.  
      (Operation as a Transmitter)  
      First, the operation of the cellular phone  1  (cellular phone  1 A) as a transmitter will be described. The cellular phone  1 A principally transmits the voice data and the image data to a base station (not shown) during the video phone communication. In this embodiment, the transmission of the image data is performed in the case where there is a difference that exceeds the predetermined value (specific value Th) between two time-series frame images of the image photographed by the camera  105  as described above.  
      That is, during the execution of the video phone communication, the camera  105  photographs the user of the cellular phone  1 A according to an instruction from the control circuit  101 . The camera  105  outputs image data of the photographed image to the image processing circuit  106  in one frame unit. The image processing circuit  106  subjects inputted image data to arbitrary image processing (for example, adjustment of brightness or contrast, etc.). The control circuit  101  saves the image data that has been subjected to the image processing in the storage device  109  once. In this embodiment, the storage device  109  saves image data of two frames which are continuous in time series and consists of image data of the frame image before one frame and image data of the latest frame.  
      The control circuit  101  transfers the image data of the two new and old frames which are saved within the storage device  109  to the image processing circuit  106 . The image processing circuit  106  calculates the amount of difference between image data of the two frames by means of the differential operation function  111 . Then, the image processing circuit  106  notifies the data difference amount to the control circuit  101  as a difference value Dv obtained by quantifying the data difference value.  
      In the calculation procedure of the difference amount between the image data of the two frames, various general methods can be applied currently. Therefore, the detailed description in this embodiment will be omitted.  
      Also, in this embodiment, for convenience of description, the control circuit  101  and the image processing circuit  106  are constituted as separate devices. However, the control circuit  101  and the image processing circuit  106  are not limited to the above device structure, but the device structure including the image processing circuit  106  in the control circuit  101  may be applied.  
      Subsequently, in the control circuit  101 , the comparison judgment function  112  compares the notified difference value Dv with the predetermined specific value Th, and judges the magnitude relation of the calculated difference value Dv and the specific value Th. The control circuit  101  reads the image data of the latest frame that is saved in the storage device  19  from the RAM  152  in the case where the judgment result is equal to or higher than the specific value Th. Then, the control circuit  101  converts the image data of the latest frame and the voice data corresponding to the voice of the user which is inputted to the microphone  121  into modulated signals by means of the base band circuit  104  as data within the transmission traffic channel (TCH) data. The radio circuit  103  radiates the modulated signals toward an aerial through the antenna  102  as radio signals after the modulated signals have been up-converted to a predetermined ling frequency.  
      The control circuit  101  realizes the data transmission of the moving picture and the voice while executing the above sequence of operations for each of the image data of the two frames that are continuous in time series.  
      Also, the control circuit  101  generates the transmission stop notice SI by means of the notice generation function  114  in the case where it is judged by the comparison judgment function  112  that the difference value Dv that has been notified from the image processing circuit  106  is equal to or lower than the specific value Th. Then, the control circuit  101  notifies the transmission stop notice SI to the cellular phone  1 B, which functions as a receiver, through the radio circuit  103  and the base band circuit  104  by using an additional information bit within the TCH data to be transmitted. After that, the control circuit  101  stops the transmission operation of the image data, and switches to the voice call operation including no image data within the TCH data.  
      After that, the control circuit  101  generates the transmission restart notice TI by means of the notice generation function  114  in the case where the comparison operation result between the difference value Dv and the specific value Th is returned to the specific value Th or higher. The control circuit  101  notifies the transmission restart notice TI to the cellular phone  1 B through the radio circuit  103  and the base band circuit  104  by using the additional information bit within the TCH data to be transmitted. After that, the control circuit  101  restarts the video phone operation including the moving picture and voice by restarting the transmission operation of the image data.  
      (Operation as a Receiver)  
      Then, the operation of the cellular phone  1  (cellular phone  1 B) as the receiver will be described. The cellular phone  1 B receives the voice data and the image data from the base station (not shown) in principle during the video phone communication. In this embodiment, the reception of the image data is performed in the case where there is a difference that exceeds the specific value Th between the two time-series frame images of the images photographed by the camera  10 , as described above.  
      That is, during the execution of the video phone communication, the radio circuit  103  receives a radio signal from the aerial through the antenna  102 . Then, the radio circuit  103  demodulates the received radio signal by means of the base band circuit  104  after being down-converted from the line frequency. The demodulated data includes image data and voice data, and each of the image data and the voice data is inputted to the control circuit  101 .  
      The control circuit  101  outputs the inputted voice data by means of a speaker  122  as a voice. Also, the control circuit  101  outputs the inputted image data to the image processing circuit  106 . In this situation, the image processing circuit  106  subjects the image data to arbitrary image processing (for example, the adjustment of brightness or contrast, etc.), to thereby restore the image data of one frame. The control circuit  101  saves the image data of one frame which has been restored by the image processing circuit  106  in the storage device  109  once. Then, the control circuit  101  displays a moving picture on the display device  107  on the basis of the image data that has been saved in the storage device  109 .  
      The above operation is performed for the respective received frame image data, to thereby realize the reception and display of the moving picture data.  
      Also, in the cellular phone  1 B as the receiver, the control circuit  101  always monitors the reception of the following signals by means of the notice monitor function  113  during the execution of the above series of operations. That is, there is a case where the transmission stop notice SI or the transmission restart notice TI is included in the additional information bit within the received TCH data which is transmitted from the cellular phone  1 A as described above. Accordingly, the cellular phone  1 B as the receiver monitors whether or not the transmission stop notice SI or the transmission restart notice TI is included in the additional information bit within the received TCH data which is demodulated on the basis of the received radio signal.  
      The control circuit  101  cannot receive new image data after the notice monitor function  113  detects the transmission stop notice SI within the received TCH data. Accordingly, the control circuit  101  displays the still picture on the display device  107  on the basis of the image data (latest image data) that has been finally saved in the storage device  109 , and continues the voice call operation on the basis of the voice data.  
      Also, the control circuit  101  can sequentially receive the new image data after the notice monitor function  113  detects that the transmission restart notice TI is included in the received TCH data. Accordingly, the control circuit  101  displays the moving picture on the display device  107  on the basis of the image data that is sequentially updated in the storage device  109  according to the newly received TCH data, and continues the voice call operation on the basis of the voice data.  
      The RAM  152  and the storage device  109  may be realized in two separate areas within the physically same device.  
      Also, in a procedure of transmitting the user&#39;s voice that is inputted to the microphone  121  as the radio signal, and in a procedure of outputting the voice that has been received as the radio signal to the speaker  122  as a voice (acoustic), a general procedure can be applied. Accordingly, the detailed description of this embodiment will be omitted.  
      (Image Transmission Control Process)  
      Then, a description will be given of image transmission control that is executed by the cellular phone  1  (cellular phone  1 A) as the transmitter in order to realize the operation as the above-mentioned transmitter.  
       FIG. 2  is a flowchart showing an image transmission control process which is executed by the cellular phone  1  in this embodiment. The flowchart represents a processing procedure of a software program that is executed by the CPU  151  in the control circuit  101  shown in  FIG. 1 .  
      The CPU  151  of the control circuit  101  instructs a photograph operation to the camera  105  and stores the image data of the photographed two frames in the storage device  109  according to the user&#39;s selection of execution of the video phone function (step  201 ). That is, the CPU  151  stores the image data of the continuous two frame images among the frame images that are inputted to the image processing circuit  106  from the camera  105  in the time series in the storage device  109 . In this situation, the storage device  109  stores the image data of the frame image before one frame and the image data of the latest frame, which are continuous in time series.  
      In the following description, the image data of the frame image before one frame is called “image data (A)”, and the image data of the latest frame is called “image data (B)”. In addition, a third frame image that is acquired newly is called “image data (C)”.  
      The CPU  151  updates the image data that has been temporarily stored within the storage device  109  (Step S 202 ). That is, the CPU  151  deletes the image data (A) that has been stored before from the storage device  109  when the CPU  151  stores the image data (C) subsequent to the image data (B) in the storage device  109 . Then, the CPU  151  saves the image data (B) as the image data (A) and the image data (C) as the image data (B).  
      Subsequently, the CPU  151  transfers the image data (A) and the image data (B) within the storage device  109  to the image processing circuit  106  so as to detect the presence and absence of the movement between the stored two frame images. In this situation, the image processing circuit  106  calculates an amount of difference between the image data of the two frames by means of the differential operation function  111 . Then, the CPU  151  acquires the difference value Dv obtained by quantifying the difference value from the image processing circuit  106  (Step S 203 ). In the case where the control circuit  101  per se has the function of the image processing circuit  106  (differential operation function  111 ), the difference value Dv may be directly calculated by the control circuit.  
      The CPU  151  executes the comparison judgment function  112  to compare the difference value Dv with the specific value Th that has been registered in the storage device  109  or the like in advance. Then, the CPU  151  proceeds with Step S 205  if the difference value Dv is larger than the specific value Th, and proceeds with Step S 206  if the difference value Dv is equal to or lower than the specific value Th (Step S 204 ). In this case, the CPU  151  has the image data (B) of the latest frame which has been saved in the storage device  109  as effective data.  
      In the case where it is judged in Step S 204  that the difference value Dv is larger than the specific value Th, the CPU  151  should transmit the image data to the cellular phone  1 B. In the case where the CPU  151  stops transmitting the image data before a previous control cycle, the CPU  151  must notify the restart of transmission of the image data to the cellular phone  1 B. Therefore, the CPU  151  judges whether the transmission of the image data to the cellular phone  1 B has been already stopped, or not (Step S 205 ). This judgment can be readily made with the general processing structure, for example, turning on a predetermined internal flag, in accordance with the transmission of the transmission stop notice S 1 , for example, in Step S 207  which will be described later.  
      Then, in the case where it is judged in Step S 205  that the transmission of the image data has been already stopped, the CPU  151  transmits the transmission restart notice TI to the cellular phone  1 B, and restarts the transmission of the image data (B) which is the latest frame (Step S 209 ). On the other hand, in the case where it is judged in Step S 205  that the image data is being transmitted, the CPU  151  continues to transmit the image data (B) which is the latest frame to the cellular phone  1 B (Step S 208 ).  
      On the other hand, in the case where it is judged in Step S 204  that the difference value Dv is smaller than the specific value Th, there is substantially no difference between the two frame images to be compared (that is, the movement of the object to be photographed). Accordingly, in this case, the radio transmission power of the cellular phone  1 A should be reduced (that is, the power consumption should be reduced) by stopping the transmission of the unnecessary image data.  
      Therefore, the CPU  151  sets the image data (B) of the latest frame which has been saved in the storage device  109  as invalid data (Step S 206 ). Then, the CPU  151  transmits the transmission stop notice S 1  to the cellular phone  1 B, and stops the transmission of the image data (B) (Step S 207 ). As a result, the CPU  151  stops the transmission of the image data (B) which has been continuously performed till the previous control cycle.  
      Then, the CPU  151  returns the processing to Step S 201  after executing the processing of S 207  to S 209 , and also continues the above sequence of processing until the call end operation by the user is detected. That is, in this embodiment, the cellular phone  1 A continues photographing by means of the camera  105  and updating of the image data within the storage device  109  even during stopping of transmission of the image data.  
      (Image Reception Control Process)  
      Subsequently, a description will be given of the image reception control that is executed by the cellular phone  1  (cellular phone  1 B) as the receiver in order to realize the operation as the above receiver.  
       FIG. 3  is a flowchart showing an image reception control process which is executed by the cellular phone  1  in this embodiment. The flowchart represents a processing procedure of a software program which is executed by the CPU  151  in the control circuit  101  shown in  FIG. 1 .  
      In the control circuit  101 , the CPU  151  reproduces the image data of a frame unit by demodulating and binarizing the received signal that has been received from the cellular phone  1 A by means of the radio circuit  103  and the base band circuit  104  (Step S 301 ).  
      The CPU  151  stores the reproduced image data of one frame in the storage device  109  (Step S 302 ). Then, the CPU  151  displays an image on the display device  107  on the basis of the image data that has been stored in the storage device  109  in Step S 302  (Step S 303 ).  
      Subsequently, the CPU  151  executes the notice monitor function  113 , to thereby judge whether the transmission stop notice SI is included in the radio signal that has been received from the cellular phone  1 A, or not (Step S 304 ). In this embodiment, the transmission stop notice SI and the transmission restart notice TI are notified by using the additional information within the received TCH data.  
      The cellular phone  1 A stops the transmission of the image data which has been performed up to now after transmitting the transmission stop notice SI. Accordingly, the cellular phone  1 B cannot acquire the image data of a new frame image for displaying the moving picture in the case where the reception of the transmission stop notice SI is detected by the judgment in Step S 304 . Therefore, the CPU  151  displays the image (still picture) on the display device  107  on the basis of the latest image data that has been finally received from the cellular phone  1 A (Step S 305 ). Then, the CPU  151  continues the display of the still picture in Step S 304  until it is judged in Step S 306  that the transmission restart notice TI is included in the radio signal that has been received from the cellular phone  1 A. In this situation, the CPU  151  continues to reproduce the voice data since the CPU  151  receives the transmission stop notice SI until the CPU  151  receives the transmission restart notice TI (Step S 305 , Step S 306 ). Accordingly, during that, the user continues the voice call while viewing the still picture that is displayed on the display device  107 .  
      By the way, while the still picture is displayed in Step S 305  and Step S 306 , the CPU  151  continuously uses the image data that has been finally saved in the storage device  109 . In this example, the image data that has been finally saved is image data of one frame which has been saved in the storage device  109  in Step S 301  in the control cycle immediately before receiving the transmission stop notice SI. In other words, this means that while the still picture continues to be displayed in a loop of Step S 305  and Step S 306 , the CPU  151  does not execute the following processes: 
          a process of reproducing the image data on the basis of the radio signal (Step S 301 );     a process of storing the reproduced image data (Step S 302 ); and     a process of reading the image data that is stored in the storage device  109  and displaying the new frame image on the display device  107  on the basis of the read image data (Step S 303 ).        

      Accordingly, in the cellular phone  1 B, the power consumption can be reduced as much as Step S 301  to Step S 303  are not executed while the still picture is continuously displayed as compared with a case where Steps S 301  to S 303  are executed in every control cycle. Accordingly, even in the cellular phone  1 B, the battery life of the battery  150  can be extended.  
      The CPU  151  returns the processing to Step S 301  in the case of detecting the transmission restart notice TI in Step S 305 . Then, the CPU  151  displays a moving picture based on image data that is received newly in the storage device  109  on the display device  107  while sequentially updating the image data until again detecting the transmission stop notice SI in Step S 303 . Accordingly, the user conducts voice call while viewing the moving picture that is displayed on the display device  107 .  
      (Advantages of the Embodiment)  
      The present invention described above provides the following advantages.  
      That is, the cellular phone  1 A stops the transmission of the image data even during execution of the video phone communication in the case where the difference (movement) Dv between the image data of two frame images that are continuous in time series is smaller than the specific value Th. As a result, the transmission power of the cellular phone  1  as the transmitter can be reduced, and hence the power consumption can be reduced. Accordingly, the battery life of the battery  150  can be extended, and hence the convenience of the cellular phone  1  is improved.  
      Also, in this embodiment, the still picture is displayed by the cellular phone  1 B in the case where no large change (movement) is found in the state of the object to be photographed at the transmission side. Then, in the case where the object to be photographed is changed, the display of the moving picture is restarted immediately in the cellular phone  1 B. Accordingly, there is no case where an uncomfortable feeling is given to the user of the cellular phone  1  as the receiver.  
      In addition, in this embodiment, the cellular phone  1 B is not required to perform the process of reproducing the image data based on the received radio signal and the process of storing the reproduced image data since the cellular phone  1 B receives the transmission stop notice SI until the cellular phone  1 B receives the transmission restart notice TI. Accordingly, even in the cellular phone  1  as the receiver, the power consumption can be reduced. Therefore, the battery life of the battery  150  can be extended, and hence the convenience of the cellular phone  1  is improved.  
      Also, the cellular phone  1 A stops the transmission of the image data as described above, to there by reduce the radio traffic in the communication system. As a result, this contributes to the efficient use of a limited line subscriber capacity of the radio communication system.  
      Also, in this embodiment, the cellular phone  1 A continues photographing by the camera  105  and updating of the image data within the storage device  109  even during the stop of transmission of the image data. That is, there is no case where the power supply to the camera  105  is interrupted during the video phone communication. Accordingly, in this embodiment, in the cellular phone  1  as the transmitter, there is no need to take a period of time taken till the stabilization of operation with restart of power dispatching to the camera into account, which is different from JP 2001-136423 A described in the above “background of the invention”. That is, according to the cellular phone  1  of this embodiment, there is no case where the operation feeling is sacrificed for achieving a reduction in power consumption.  
      (Modification of this Embodiment)  
      (First Modification)  
      In the above embodiment, the cellular phone  1  that realizes the video phone function by means of voice and moving picture has been exemplified. However, in the present invention, from the viewpoint of realizing the reduction in power consumption of a communication terminal and reduction in radio traffic in a radio communication system that accommodates the communication terminal, the video phone function and the transmission and reception of the voice data are not essential. That is, the present invention is preferably applied to a system in which image data for reproducing a moving picture by means of a reception side communication terminal is sequentially transmitted to the reception side communication terminal from a transmission side communication terminal.  
      More specifically, in the above embodiment, the reduction in the power consumption of the cellular phone  1 A at the time of the video phone communication is realized, and the reduction in the radio traffic by stopping the transmission of the image data is also realized. However, the present invention is not limited to the communication system of the cellular phone. For example, the present invention can be also applied to a monitor system that is made up of an image monitor terminal that sends moving picture data and an image processing device that receives the moving picture data.  
      (Second Modification)  
      In the above embodiment, in the cellular phone  1 A, attention is paid to the difference between the image data of the frame image before one frame and the image data of the latest frame among the image data of the frame images which are sequentially produced in time series to constitute the processing. However, the present invention is not limited to the above processing structure. That is, the present invention may be constituted to select two frame images whose difference is to be calculated by using a frame interval (for example, five-frame interval) specified in advance instead of calculating the difference at every frame interval (two continuous frame images) Also, in the case where the second modification is applied to, for example, the structure of the cellular phone  1  shown in  FIG. 1 , the selection of the two frame images may be autonomously performed by the image processing device  106 , or may be performed in the process of updating the image data within the storage device  109  by the control circuit  101 . The second modification is preferably applied to a case where the frame rate of the camera  105  (that is, the number of frame images that are photographed per unit time) is high in speed. Then, when the frame images which should be subjected to difference calculation are selected as in this modification, a load of the operation processing can be reduced, and hence power saving of the terminal and an improvement in the performance of the device can be expected.  
      (Third Modification)  
      In the above embodiment, in the process of updating the image data (Step S 202  in  FIG. 2 ), the image data (A) is deleted, and the image data (B) is updated to the image data (A) whereas the image data (C) is updated to the image data (B). That is, in the updating process, the frame image as a reference is updated to the latest frame image in every control cycle. In contrast, in this modification, the frame image as the reference of comparison is fixed to the image data (A) during stop of transmission of the image data. More specifically, the image data (A) is kept as it is, the image data (B) is deleted, and the image data (C) is updated to the imaged data (B) during stop of transmission of the image data. According to such a processing structure, the load of the operation processing can be reduced, and hence the power saving of the terminal and an improvement in the performance of the device during stop of transmission of the image data can be further expected.  
      In the above embodiment, the cellular phone  1  having the device structure in which the camera  105  that photographs a frame image is integrated with the communication terminal has been exemplified. However, the present invention is not limited to the above device structure. That is, the present invention can be applied to even a device structure in which a communication terminal that transmits image data is separated from an image pickup device that photographs a frame image which is the original of the image data.  
      Also, in the above embodiment, for convenience of description, the reference value Th to which the CPU  151  refers at the time of executing the difference operation has the same value (threshold value) between a case where the transmission of the image data is stopped and a case where the transmission of the image data is restarted. However, a different value may be applied to the threshold value at the time of executing the difference operation. In this case, the reference value (Th 1 ) at the time of stopping the transmission is set to be larger than the reference value (Th 2 ) at the time of restarting the transmission, thereby permitting the transmission operation in the cellular phone  1 A to be stabilized.  
      Also, the present invention that has been exemplified by way of the above embodiment and its modifications is achieved by reading a computer program that can realize the functions of the flowcharts ( FIGS. 2 and 3 ) referred to in the above description to the CPU  151  of the device and executing the computer program after the computer program is supplied to the above cellular phone  1 . Also, the computer program that is supplied to the device may be stored in a storage device such as a readable and writable memory.  
      In the above case, a method of supplying the computer program to each device can currently adopt a general procedure such as a method involving installing the computer program into the device by using an appropriate jig or a method involving downloading the computer program from the external through a communication line such as the Internet, at the manufacturing stage before shipping, at the maintenance stage after shipping, or the like. Then, in this case, the present invention is constituted by codes or storage medium of the computer program.  
      While this invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of this invention is not limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternative, modification and equivalents as can be included within the spirit and scope of the following claims.