Abstract:
A method of eliminating irritating noise at the end of communication for a walkie-talkie which has a receiving loop. The method includes providing a first detector, determining whether a radio frequency signal in a predetermined frequency range received by the walkie-talkie belongs to a non-standard squelch signal by using the first detector, and if so, stopping the walkie-talkie from receiving subsequent radio frequency signals.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of preventing from generating noise for a walkie-talkie, more specifically, to a method of preventing noise at the receiving end at the moment of the end of conversation.  
           [0003]    2. Description of the Prior Art  
           [0004]    A continuous tone-coded squelch system (CTCSS) has been widely applied to wireless transmission, and is used to let a plurality of users communicate with each other within a predetermined communication area. The CTCSS adopts a low-frequency CTCSS tone signal to distinguish signals transmitted via the same physical channel. For instance, a prior art walkie-talkie utilizes the CTCSS to achieve group communication. Please refer to FIG. 1, which is a schematic diagram showing frequency bands used by the prior art CTCSS. As shown in FIG. 1, a band ranging from 62.5 Hz to 250 Hz is used to transmit the above-mentioned low-frequency CTCSS tone signal, and another band ranging from 300 Hz to 3.4 KHz is used to transmit speech signals spoken by a user. The operation of the CTCSS is described as follows. With regard to the prior art walkie-talkie, 14 channels P 1 -P 14  generally are adopted to carry signals, and the 14 channels are physical channels. In addition, 38 CTCSS tone signals T 1 -T 38  individually corresponding to different frequencies are used. One of the 38 CTCSS tone signals T 1 -T 38  annexed to one physical channel generates a specific logical channel, and the 14 physical channels are capable of forming 532 (14*38) logical channels in total. When a speaker sets the walkie-talkie with a physical channel P 1  and a desired CTCSS tone signal T 1 , the logical channel set by the speaker becomes P 1  (T 1 ). After the speaker presses a push-to-talk (PTT) button on the walkie-talkie, the speaker is capable of outputting speech signals via the walkie-talkie toward the predetermined communication area specified by the walkie-talkie. If there are three listeners in the predetermined communication area, and the three listener set their own logical channels as P 1  (T 1 ), P 1  (T 38 ), P 2  (T 1 ) respectively. For the first listener with a logical channel P 1  (T 1 ), because his walkie-talkie receives and transmits signals through the physical channel P 1 , the walkie-talkie of the first listener will start receiving speech signals spoken by the speaker. In addition, the walkie-talkie of the first listener judges that the CTCSS tone signal used by the speaker is T 1 . In other words, the speaker and the first listener both adopt the same logical channel P 1  (T 1 ). Therefore, the walkie-talkie of the first listener then outputs the received speech signals via an audio speaker. The first listener is capable of hearing the speech signals spoken by the speaker. For the second listener with a logical channel P 1  (T 38 ), because his walkie-talkie receives and transmits signals through the physical channel P 1 , the walkie-talkie of the second listener will start receiving speech signals spoken by the speaker. However, the walkie-talkie of the second listener judges that the CTCSS tone signal used by the speaker is not T 1 , but T 38 . In other words, the speaker and the second listener adopt different logical channels P 1  (T 1 ) and P 1  (T 38 ). Therefore, the walkie-talkie of the second listener then does not output the received speech signals via an audio speaker, and the second listener cannot hear the speech signals spoken by the speaker. For the third listener with a logical channel P 2  (T 1 ), because his walkie-talkie receives and transmits signals through the physical channel P 2 , the walkie-talkie of the third listener and that of the speaker use different physical channels. With the unmatched physical channel, the walkie-talkie of the third listener cannot acknowledge an adequate signal strength indicated by a received signal strength indicator (RSSI). Therefore, the walkie-talkie of the third listener will not receive any speech signals spoken by the speaker. That is, no speech signal is played by an audio speaker of the walkie-talkie. The second and third listeners cannot hear any speech signals spoken by the speaker, that is, the walkie-talkies of the second and third listeners both detect the CTCSS tone signal related to the received speech signals for actuating a signal squelch function. To sum up, only the users using the same logical channel can communicate with each other to achieve group communication.  
           [0005]    Please refer to FIG. 2, which is a block diagram of a prior art walkie-talkie  10 . The walkie-talkie  10  has an antenna  11 , a transceiver  12 , a selector  14 , a processor  16 , a speaker  17 , a microphone  18 , and a speech signal processor  20 . The walkie-talkie  10  can receive and transmit radio frequency (RF) signals through the antenna  11 . With regard to receiving RF signals, the transceiver  12  converts the high-frequency RF signal into a low-frequency baseband signal Rx, and transmits the baseband signal Rx to the selector  14 . The selector  14  then outputs the baseband signal Rx from an output port A. The processor  16  determines frequency of a CTCSS tone signal according to the received baseband signal Rx. Generally speaking, the processor  16  has a low-pass filter (LPF) for extracting signals with frequencies ranging from 62.5 Hz to 250 Hz, and then the processor  16  judges the CTCSS tone signal related to the baseband signal Rx to decide whether the walkie-talkie  10  and the baseband signal Rx use the same logical channel. If the walkie-talkie  10  and the baseband signal Rx use the same logical channel, the processor  16  activates the speaker  17  to proceed following signal output operation. That is, the speech signal processor  20  has two analog filter circuits for extracting signals with frequencies ranging from 300 Hz to 3.4 KHz, and the extracted signals are played by the speaker  17 . On the contrary, if the walkie-talkie  10  and the baseband signal Rx use different logical channels, the processor  16  does not actuate the speech signal processor  20  and the speaker  17 . The walkie-talkie  10 , therefore, does not output any speech signals transmitted by unmatched logical channels. With regard to transmitting RF signals, when the user presses the PTT button, the selector  14  will chose the input port B, and the processor  16  simultaneously actuates the microphone  18 . Therefore, the speech signals spoken by the user are inputted into the speech signal processor  20 . As mentioned above, the speech signal processor  20  uses filter circuits to extract signals with frequencies ranging from 300 Hz to 3.4 KHz, and the speech signal processor  20  outputs the extracted signals to the CTCSS encoder  18 . Based on a CTCSS code (CTCSS tone signal with a specific frequency) set in the walkie-talkie  10 , the processor  16  adds a corresponding CTCSS tone signal in the extracted signals outputted from the speech signal processor  20  for forming a baseband signal Tx. In the end, the transceiver  12  converts the low-frequency baseband signal Tx into a high-frequency RF signal, and the RF signal is then outputted via the antenna  11 .  
           [0006]    Theoretically, during receiving RF signal, while the RSSI at the receiving end is higher than a receivable threshold, the speaker  17  is turned on, on the contrary, while the RSSI is lower than the receivable threshold, the speaker  17  is turned off. At the moment of end of communication, that is, the moment of releasing the PTT, the RF signal is thus terminated to transmit. However, in the course of the strength of receiving signal going from receivable to unreceivable, the transceiver  12  is still in receiving state, meanwhile the speaker  17  is still turned on. Therefore, the noise whose transient strength may be higher than the receivable threshold is demodulated and outputted by the speaker  17  to generate an irritating noise to make the user uncomfortable.  
         SUMMARY OF INVENTION  
         [0007]    It is therefore a primary objective of the claimed invention to provide a method used in a walkie-talkie for preventing from generating an irritating noise at the moment of the end of conversation to solve the aforementioned problem.  
           [0008]    Briefly summarized, the claimed invention provides a method for a walkie-talkie having a receiving loop comprising the steps of providing a first detector; determining whether a non-standard CTCSS tone signal in a predetermined frequency range is included in a radio frequency signal received by the walkie-talkie by using the first detector; and stopping receiving subsequent radio frequency signals if the non-standard CTCSS tone signal in the predetermined frequency range is included in the radio frequency signal.  
           [0009]    These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the invention, which is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic diagram showing frequency bands used by the prior art CTCSS.  
         [0011]    [0011]FIG. 2 is a block diagram of a prior art walkie-talkie.  
         [0012]    [0012]FIG. 3 is a schematic diagram of walkie-talkies according to the present invention.  
         [0013]    [0013]FIG. 4 is a block diagram of the walkie-talkies according to the present invention.  
         [0014]    [0014]FIG. 5 is a timing diagram at transmission end depicted in FIG. 4.  
         [0015]    [0015]FIG. 6 is an operation flowchart with respect to the walkie-talkie according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Please refer to FIGS. 3, 4, and  5 . FIG. 3 is a schematic diagram of the walkie-talkies  30 ,  40  according to the present invention. FIG. 4 is a block diagram of the walkie-talkies  30 ,  40  according to the present invention.  
         [0017]    [0017]FIG. 5 is a timing diagram at transmission end depicted in FIG. 4. The walkie-talkie  30  comprises a push-to-talk (PTT) button  32 , a microphone  34 , a processor  36 , and a transmitter  38 . The walkie-talkie  40  comprises a receiver  41 , a select button  42 , a processor  43 , a speaker  44 , a first detector  46 , a second detector  48 , and a receiving loop  45 . When pressing the PTT button  32  (time at t 0  shown in FIG. 5), the processor  36  activates the microphone  34  to receive a speech signal, which is converted from human sound or ambient sound, and generates a standard CTCSS tone signal according to a predetermined frequency. Finally, the speech signal and the standard CTCSS tone signal T 38  both combining a predetermined carrier is broadcasted. For example, as shown in FIG. 1, since 38 channels corresponding to the standard CTCSS tone signals are distributed in the frequency range of 62.5 Hz-250 Hz, if the walkie-talkie  30  is set by using a logical channel P 1 (T 38 ), i.e. using a physical channel P 1  carrier, and a 38 th  standard CTCSS tone signal (given its frequency is 250 Hz), the speech signal is broadcasted by using the logical channel P 1 (T 38 ). After releasing the PTT button  32 , i.e. time at t 1  shown in FIG. 5, the speech signal and the standard CTCSS tone signal T 38  are not broadcasted with the predetermined carrier. However, in the meantime, a non-standard CTCSS tone signal T 39  is generated and is broadcasted with the carrier by the walkie-talkie  30  for an interval Î         . If the PTT  32  is pressed at time t 2  and released at time t 3 , the non-standard CTCSS tone signal T 39  is generated and is broadcasted with the carrier by the walkie-talkie  30  for an interval Î          again. Notice that frequency range of the non-standard CTCSS tone signal is between 62.5 Hz-250 Hz but is not overlapping the frequency range used by the standard CTCSS tone. Since the standard CTCSS tone signal and the non-standard CTCSS tone signal belong to the same frequency range, for preventing error, while the standard CTCSS tone signal is being transmitted, the non-standard CTCSS tone signal fails to be transmitted.  
         [0018]    The receiver  41  of the walkie-talkie  40  is used for receiving RF signal from the walkie-talkie  30 . In the illustrative embodiment, the receiver  41  is set to receive the physical channel P 1  carrier. The select button  42  is used to determine whether to use the first detector  46  and the second detector  48 , or only the second detector  48 , the first detector  46  is used to determine whether the non-standard CTCSS tone signal T 39  is included in the RF signal received by the receiver  41 . The second detector  48  is used to determine whether the standard CTCSS tone signal T 38  is included in the RF signal received by the receiver  41 . The receiving loop  45  is used to transform the speech signal within the RF signal into sound waves. The speaker  44  is used for outputting the sound waves. For the following explanation, assume that frequency of the non-standard CTCSS tone signal T 39  is defined as 65 Hz, not used by any standard CTCSS tone signal, and frequency of the standard CTCSS tone signal T 38  is defined as 250 Hz.  
         [0019]    Please refer to FIG. 6, which shows an operation flowchart with respect to the walkie-talkie according to the present invention. The operation of the walkie-talkie  40  occurs as follows:  
         [0020]    Step  100 : start;  
         [0021]    Step  102 : the receiver  41  receives RF signal using the physical channel P 1 ;  
         [0022]    Step  104 : determine if the select button  42  is triggered? If it is, go to step  106 ; if not, go to step  108 ;  
         [0023]    Step  106 : determine whether the non-standard CTCSS tone signal T 39  is included in the RF signal by using the first detector  46 . If it is, go to step  112 , if not, go to step  102 ;  
         [0024]    Step  108 : determine whether the standard CTCSS tone signal T 38  is included in the RF signal by using the second detector  48 . If it is, go to step  110 , if not, go to step  114 ;  
         [0025]    Step  110 : deliver the RF signal to the receiving loop  45  to transform the speech signal within the RF signal into sound waves, and then use the speaker  44  to output the sound waves; and  
         [0026]    Step  112 : end.  
         [0027]    After the receiver  41  receives the RF signal using the physical channel P 1  (step  102 ), if the select button  42  is pressed, the processor  43  controls the first detector  46  to detect whether the non-standard CTCSS tone signal T 39  is included in the RF signal received by the receiver  41 , and controls the second detector  48  to detect whether the standard CTCSS tone signal T 38  is included in the RF signal received by the receiver  41 . For example, assume that frequency for the non-standard CTCSS tone signal T 39  is 65 Hz (and the frequency does not belong to any defined standard CTCSS tone signals), when the select button  42  is pressed, the first detector  46  detects whether a 65 Hz signal is included within the RF signal (step  106 ), if the 65 Hz signal is detected, (i.e. time at t 1 -t 1 +Î          and t 3 -t 3 +Î          shown in FIG. 5), meaning that the PTT  32  of the walkie-talkie  30  is released, the walkie-talkie  40  stops receiving the subsequent RF signal. Since the walkie-talkie  40  stops receiving the RF signal, the speaker  44  also stops outputting the speech signal within the RF signal. If the 65 Hz is not detected, meaning that the walkie-talkie  40  is still under standby state (i.e. time at t 1 +Î         −t 2 ), the walkie-talkie  40  keeps detecting the RF signal. If the select button  42  is not pressed, the processor  43  only controls the second detector  48  to detect whether the standard CTCSS tone signal T 38  with 250 Hz exists within the RF signal (step  108 ). If the standard CTCSS tone signal T 38  with 250 Hz exists (i.e. time t 0 -t 1  and t 2 -t 3  shown in FIG. 5), the processor  43  controls the receiving loop  45  to transform the speech signal with 300 Hz to 3.4 Khz into sound waves (step  110 ). Finally, the speaker  44  outputs the sound waves so that the user using the walkie-talkie  40  can listen to sound from the user using the walkie-talkie  30 .  
         [0028]    When the PTT  32  is pressed (time t 0 -t 1 , t 2 -t 3  shown in FIG. 5), the transmitter  38  of the walkie-talkie  30  broadcasts the speech signal received by the microphone  34  and the standard CTCSS tone signal T 38  with 250 Hz. When the PTT  32  is released (time t 1 -t 2  shown in FIG. 5), the transmitter  38  of the walkie-talkie  30  sends neither the speech signal received by the microphone  34  nor the standard CTCSS tone signal T 38  but the non-standard CTCSS tone signal T 39  with 65 Hz. Because the receiver  41  of the walkie-talkie  40  stops receiving the subsequent radio frequency signals when the receiving loop  45  receives the non-standard CTCSS tone signal T 39  with 65 Hz, hence, the walkie-talkie  40  can prevent from generating an irritating noise at the moment of the end of conversation.  
         [0029]    In contrast to prior art walkie-talkie, when the conversation is finished, the walkie-talkie at the receiving end still receives white noise in air at the moment of turning off the speaker. Therefore the prior art speaker generates an irritating noise. Instead, the present invention walkie—sends a non-standard CTCSS tone signal T 39  at a later time, when the PTT is released. Then, the walkie-talkie turns off the speaker in the interval. By using such method, the speaker does not generate an irritating noise at the end of conversation.  
         [0030]    Those skilled in the art will readily observe that numerous modifications and alterations of the method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.