Patent Abstract:
Switching a mobile telephone for selectively receiving or transmitting a voice signal in a speakerphone mode by counting the number of the full-rate voice data received from the sender, and blocking the transmission path from the receiver to prevent the received voice data from being retransmitted through the receiver&#39;s microphone to the sender if the number of the full-rate voice data exceeds a predetermined value.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mobile telephone, and more particularly to a method for switching a mobile telephone for selectively transmitting or receiving a voice signal. 
     2. Description of the Related Art 
     Recently, a more compact sized mobile telephone, such as the folder-type mobile telephone, has been developed. These newer mobile telephones incorporate an additional function of a speakerphone mode that enables the user to conduct a voice communication without holding the mobile telephone by his ear. However, the conventional mobile telephone with such an additional function inherently suffers particular drawbacks. One of these drawbacks is that the received voice signal emanating from a speaker may unintentionally feedback through the microphone to the sender, thus causing unwanted interference. This interference, or garble, is known as a howling phenomenon. Moreover, the mobile telephone only operates in either a receive mode or transmit mode at any point in time based on the voice signal (i.e. the transmitted voice signal or the received voice signal) with the greater intensity. This limitation creates a problem in that the user cannot be assured that his voice signal input through the microphone is being transmitted to the other user. The present invention solves this longstanding problem in the present technology. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for switching a mobile telephone for selectively receiving or transmitting a voice signal in the speakerphone mode so as to prevent the howling phenomenon. 
     According to one embodiment of the present invention, a method for switching the mobile telephone for selectively receiving or transmitting a voice signal in the speakerphone mode, comprises the steps of counting the number of the full-rate voice data received from the sender, and blocking the transmission path from the receiver to prevent the received voice data from being retransmitted back through the microphone of the receiver to the sender if the number of the full-rate voice data exceeds a predetermined value. 
    
    
     The present invention will now be described more specifically with reference to the drawings attached only by way of example. 
     BRIEF DESCRIPTION OF THE ATTACHED 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 in which: 
     FIG. 1 is a block diagram for illustrating the structure of a mobile telephone according to an embodiment of the present invention; and 
     FIG. 2 is a flow chart for illustrating the steps of switching a mobile telephone for selectively receiving or transmitting a voice signal in the speakerphone mode according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a microprocessor  112  controls the functions of the mobile telephone  200 . A duplexer  100  delivers a signal received by an antenna ANT to a radio receiver  102  or transmits the signal of a radio transmitter  108  through the antenna ANT. The radio receiver  102  delivers the non-voice data to the microprocessor  112 . The radio receiver  102  also delivers the voice signal to a signal level detector  122 . The voice signal is then delivered to a voice signal processor  104 . A frequency synthesizer  106  generates a carrier eliminator signal delivered to the microprocessor  112  to eliminate the received carrier signal corresponding to the receiving channel. The frequency synthesizer  106  also generates a transmitter carrier signal that is applied to the output signal of the radio transmitter  108 . The radio transmitter  108  combines the carrier signal from the frequency synthesizer  106  and the voice signal from the voice signal processor  104 , and outputs it to a duplexer  100  for transmission through the antenna ANT. 
     The voice signal processor  104  decodes the coded voice signal from the radio receiver  102 , delivers it through a speakerphone part  107 , and outputs it to a speaker SPK. The voice signal processor  104  also encodes the voice signal delivered from the microphone MIC through the speakerphone part  107 , and ultimately to the radio transmitter  108 . A signal level detector  122  detects the levels of the received and transmitted voice signals delivered to the microprocessor  112 . A ringer  114  generates a ringing sound when a ring signal is received. A memory device  110  includes a ROM for storing a control program of the microprocessor  112 , a non-volatile memory for storing a plurality of names and associated telephone numbers, and a RAM for temporarily storing data generated when operating the mobile telephone. A key input part  118  includes various functional keys for establishing and terminating communication and dialing a telephone number. A display  116  displays the characters and images representing the various operational states of the mobile telephone. 
     Referring to FIG. 2, the switching operation of the mobile telephone for selectively receiving or transmitting a voice signal in the speakerphone mode according to an embodiment of the present invention will be described. The microprocessor  112  determines in step  201  whether the mobile telephone has received a call. If a call is received, the microprocessor  112  generates a ring signal and sends it to the ringer  114  in step  202 . Accordingly, the user, in step  203 , presses a key of the key input part  118  to establish a communication channel and the microprocessor  112  establishes a single communication path between the sender and receiver. 
     In step  204 , the microprocessor  112  determines whether the mobile telephone is set in the speakerphone mode. If so, it enables the speakerphone part  107  to make the sender and receiver communicate in the speakerphone mode. Otherwise, the microprocessor  112  proceeds to step  205  to operate the mobile telephone in the ordinary communication mode. If speakerphone mode is selected the signal level detector  122  compares the level of the voice signal from the radio receiver  102  with that from the voice signal processor  104 . The signal with the greater level is delivered to the microprocessor  112 . 
     If the voice signal from the radio receiver  102  is delivered to the microprocessor  112 , the microprocessor  112  proceeds to step  206  to determine whether the received voice data is of a full-rate. This is accomplished by reading the configuration byte contained in the voice data information. Generally, a single voice data has a length of 20 ms. If the received voice data is determined to have a full-rate in step  206 , the microprocessor  112  proceeds to step  207  to count the full-rate value of the received voice data. The voice data is continuously received until the counted value reaches a predetermined value, at which point the microprocessor  112  determines it to be the valid voice data. Then, if the counted full-rate value exceeds the predetermined value in step  208 , the microprocessor  112  proceeds to step  210  to control the rate of the transmitted voice data from the microphone. 
     Each block of received voice data is checked to determine if it is at full-rate. If is it at full-rate, an accumulator, stored in the memory device  110 , is increased by 1. Each time a full-rate voice data block is received the accumulator is increased by 1. The value stored in the accumulator is referred to as the counted value. If the received voice data is not of a full-rate the accumulator is decreased by a value of 1. When a full-rate signal is received, the microprocessor  112  checks if the counted value exceeds a predetermined value, signifying that the received voice signal is at a level to begin controlling the transmission rate of the mobile telephone. If the counted value does not exceed the predetermined value, the counted value, stored in the accumulator, is increased by 1, transmission is not controlled, and the process returns to check the level of the next received voice data block. This process of receiving the voice data, checking for full-rate, and increasing or decreasing the counted value continues until the predetermined value is exceeded, at which time transmission control begins. The process then returns to check the next received voice data block for full-rate. 
     The transmitted voice data is divided into four different rates according to the amount of the sound, e.g., full-rate, ½ rate, ¼ rate, and ⅛ rate. In addition, the voice data with no voice information is called the blank rate. In order to control the packet rate of the transmitted voice data, the value ‘1’ is assigned to the bit of the configuration byte, representing that the voice data is presently the blank rate, while the other bits representing the other rates are all assigned with the value ‘0’. Thus, no changes are made to the configuration byte with the information of the voice data. When the counted value exceeds the predetermined value one of two events occur. Either the voice data is deleted from the transmitted data or the voice data is changed into ⅛ rate data to minimize the echoing effect. 
     Subsequently, if the communication is terminated in step  211 , the microprocessor  112  cuts off the communication path between the sender and receiver, or otherwise returns to step  206 . Meanwhile, if the received voice data is not of full-rate in step  206 , the microprocessor  112  proceeds to step  212  to determine whether the counted value is ‘0’. If so, it directly proceeds to step  211 . Or otherwise, it proceeds to step  213  to reduce the counted value by ‘1’, returning to step  206 . Alternatively, if the counted full-rate value does not exceed the predetermined value in step  208 , it proceeds to step  209  to increase the counted value by ‘1’, returning to step  206 . 
     Thus, the inventive switching method in the speakerphone mode employs the full-duplex operation to enable the mobile telephone to function in speakerphone mode with no additional device. It also reduces the number of cases where the communication is interrupted in the VOX (voice operated switch) function. In addition, the voice data of one user is prevented from being transmitted in the speakerphone mode when the voice data of the other user is transmitted with the full-rate, thus preventing voice communication garbling. 
     While the present invention has been described in connection with specific embodiments accompanied by the attached drawings, it will be readily apparent to those skilled in the art that various changes and modifications may be made thereto without departing the gist of the present invention.

Technology Classification (CPC): 7