Patent Publication Number: US-7586937-B2

Title: Receiving device and method

Description:
TECHNICAL FIELD 
     The present invention relates to a receiving device and method, and is suitably applied to the case of dividing a wide band of a voice signal into two bands to transmit the voice signal, for example. 
     BACKGROUND ART 
     At present, voice communication using a network such as the Internet has been actively conducted by the use of a VoIP technology. 
     In communication over a network such as the Internet, in which the communication quality is not assured, a packet loss that a packet is lost during transmission frequently causes a phenomenon (voice loss) that a part of voice data, which is supposed to be received in a time series under normal circumstances, is lost. When a voice loss occurs, if the voice data is decoded as it is, voice is frequently interrupted to degrade the voice quality. A technology disclosed in non-patent document 1 to be described below has been already known as a method for compensating this degradation. 
     In this method, the occurrence of a voice loss is monitored for each voice frame (packet) which is a decoding processing unit, and every time the voice loss occurs, compensation processing is performed. In this compensation processing, voice data after decoding a series of encoded voice data is stored in an internal memory or the like, and when a voice loss occurs, a fundamental period near a position where the voice loss occurs is obtained on the basis of voice data read from the internal memory. Then, the voice data is extracted from the internal memory to perform interpolation in regard to a frame in which voice data needs to be interpolated (compensated) because of the voice loss, so that the starting phase of the frame matches the ending phase of an immediately preceding frame to be able to secure continuity in a waveform period (fundamental period). 
     Meanwhile, technologies described in non-patent documents 2 and 3 to be described below are known as a method of voice communication over a network. 
     In the technology described in the non-patent document 2, voice data is transmitted in a single band, but the technology described in the non-patent document 3 relates to a band division method (SB-ADPCM) in which voice data of a wider band (for example, a band of 8 kHz) than usual is divided into two bands and is transmitted so as to realize voice communication of high quality. 
     Non-patent document 1: ITU-T Recommendation G. 711 Appendix I 
     Non-patent document 2: ITU-T Recommendation G. 711 
     Non-patent document 3: ITU-T Recommendation G. 722 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     Incidentally, if the band division method described in the non-patent document 3 is applied as it is to a reception processing device of voice data, it is necessary to provide the reception processing device with processing systems each of which performs the same processing independently for each band, which results in increasing the time complexity and the space complexity. 
     For example, if this processing system is constructed of a general-purpose DSP (digital signal processor), the amount of memory and the amount of processing become large, which inevitably causes an increase in power consumption, an increase in the scale of a device, and an increase in cost. 
     Furthermore, when there are simply provided two independent processing systems are simply provided, the above-mentioned fundamental period is redundantly calculated in both bands because of the voice loss to cause an unnecessary increase in the time complexity and the space complexity. Moreover, when the fundamental period cannot be obtained in any one of the bands because it has a large amount of noise, the communication quality in the processing system of the band is degraded because the above-mentioned interpolation cannot be performed. 
     After all, when the band division method described in the non-patent document 3 is applied as it is to a reception processing device of voice data, the reception processing device will have a construction that degrades the communication quality and reduces efficiency considering a large time complexity and a large space complexity. 
     Means for Solving the Problem 
     In order to solve the problems, according to the first embodiment, a receiving device which receives a transmission unit signal sent from a sending device via a predetermined transmission path, the transmission unit signal containing a plurality of encoded element periodic signals, and which executes a reproduction output corresponding to an element periodic signal that is a decoding result of the plurality of encoded element periodic signals extracted from the transmission unit signal, the plurality of encoded element periodic signals being obtained by dividing an original periodic signal produced from a predetermined source of production in accordance with respective logic channels; the receiving device includes: (1) an interference event detecting means for detecting that a predetermined interference event to interfere with using of the encoded element periodic signals packed in the transmission unit signal for the reproduction output occurs in any of the transmission unit signals received in a time series during transmission via the transmission path; and (2) interpolation means of the number of the logic channels, each of which produces an alternative element periodic signal on the basis of a predetermined period and interpolates the alternative element periodic signal into a series of element periodic signals when the interference event detecting means detects occurrence of the interference event, the alternative element periodic signal being to become alternative to the encoded element periodic signal packed in the transmission unit signal; (3) wherein each of the plurality of interpolation means provided for the respective logic channels includes an element periodic signal storing section for storing the element periodic signal of the decoding result of the encoded element periodic signal extracted from the transmission unit signal received by each corresponding logic channel; (4) wherein any one of the plurality of interpolation means provided for the respective logic channels includes: 
     a period calculating section for calculating a value of the period, which is information to become a base for producing the alternative element periodic signal and is common to the respective element periodic signals obtained by dividing the same original periodic signal, from the element periodic signal stored in the element periodic signal storing section; and (5) a period notifying section for giving a notice of the value of the calculated period to other interpolation means. 
     Further, according to the second invention, a receiving method for receives a transmission unit signal sent from a sending device via a predetermined transmission path, the transmission unit signal containing a plurality of encoded element periodic signals, and for executing a reproduction output corresponding to an element periodic signal that is a decoding result of the plurality of encoded element periodic signals extracted from the transmission unit signal, the plurality of encoded element periodic signals being obtained by dividing an original periodic signal produced from a predetermined source of production in accordance with respective logic channels; the receiving method includes the steps of: (1) detecting, by an interference event detecting means, that a predetermined interference event to interfere with using of the encoded element periodic signals packed in the transmission unit signal for the reproduction output occurs in any of the transmission unit signals received in a time series during transmission via the transmission path; and (2) producing an alternative element periodic signal on the basis of a predetermined period and interpolating the alternative element periodic signal into a series of element periodic signals when the interference event detecting means detects occurrence of the interference event, the alternative element periodic signal being to become alternative to the encoded element periodic signal packed in the transmission unit signal, by each of interpolation means of the number of the logic channels; (3) wherein each of the plurality of interpolation means provided for the respective logic channels causes an element periodic signal storing section to store the element periodic signal of the decoding result of the encoded element periodic signal extracted from the transmission unit signal received by each corresponding logic channel; (4) wherein any one of the plurality of interpolation means provided for the respective logic channels causes a period calculating section to calculate a value of the period, which is information to become a base for producing the alternative element periodic signal and is common to the respective element periodic signals obtained by dividing the same original periodic signal, from the element periodic signal stored in the element periodic signal storing section; and (5) causes a period notifying section to give a notice of the value of the calculated period to other interpolation means. 
     Effect of the Invention 
     According to the present invention, it is possible to realize a construction that can improve the communication quality and can enhance efficiency considering a small time complexity and a small space complexity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a construction example of a main portion of a communication terminal used in the embodiment; 
         FIG. 2  is a schematic diagram showing a construction example of an interpolator included in the communication terminal of the embodiment; 
         FIG. 3  is a schematic diagram showing a construction example of another interpolator included in the communication terminal of the embodiment; and 
         FIG. 4  is a schematic diagram showing a whole construction example of a communication system in accordance with the embodiment. 
     
    
    
     DESCRIPTION OF THE REFERENCE SYMBOLS 
       11 A,  11 B decoder;  12  loss-determining device;  13 A,  13 B interpolator;  14  band combiner;  20  communication system;  21  network;  22 ,  23  communication terminal;  30 ,  40  control section;  31 ,  43  decoded waveform storing section;  32  waveform period calculating section;  33  period notifying section;  34 ,  42  interpolation executing section;  41  notice receiving section; PK 11 -PK 13  packet; CD 1 , CD 2 , CD 11 -CD 13 , CD 21 -CD 23  voice data; DC 1 , DC 2 , DC 11 -DC 13 , DC 21 -DC 23  decoding result; PS fundamental period. 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     (A) Embodiment 
     An embodiment will be described below by taking a case, in which a receiving device and a receiving method in accordance with the present invention are applied to voice communication using a VoIP. 
     (A-1) Construction of Embodiment 
     The whole construction example of a communication system  20  in accordance with the present embodiment is shown in  FIG. 4 . 
     Referring to  FIG. 4 , the communication system  20  includes a network  21  and communication terminals  22  and  23 . 
     Among them, the network  21  may be the Internet and may be an IP network that is provided by a communications carrier and has the communication quality assured to some extent. 
     Moreover, the communication terminal  22  is a communication device, for example, an IP telephone capable of conducting a voice conversation in real time. The IP telephone uses a VoIP technology and makes it possible to conduct a telephone conversation by exchanging voice data on a network using an IP protocol. The communication terminal  23  is also the same communication device as the communication terminal  22 . 
     The communication terminal  22  is used by a user U 1 , and the communication terminal  23  is used by a user U 2 . Commonly, voice is exchanged bidirectionally in the IP telephone so as to establish conversation between the users. Here, voice frames (voice packets) PK 11  to PK 13  are sent from the communication terminal  22  and description will be provided by paying attention to a direction in which these packets are received by the communication terminal  23  via the network  21 . 
     These packets PK 11  to PK 13  include voice data indicating contents (voice information) uttered by the user U 1 . Hence, insofar as this direction is concerned, the communication terminal  23  performs only receiving processing and the user U 2  only hears voice uttered by the user U 1 . 
     The order of sending (which corresponds to the order of reproduction output on a receiving side) is determined among the packets PK 11  to PK 13  of these packets. That is, the packets PK 11  to PK 13  are sent in the order of PK 11 , PK 12 , and PK 13 . 
     In the present embodiment, the band division method disclosed in the non-patent document 3 is employed and the respective bands obtained by dividing a wide band into two bands can be considered to be separate logic channels. For example, when voice information of a wide band having a bandwidth of 8 kHz is divided into two bands at a position of 4 kHz on a frequency axis, voice information can be obtained for two bands (narrow bands) of a narrow bandwidth of 4 kHz. In this case, for example, there are provided a narrow band WA located within a range from 0 to spread in the direction of frequency axis and hence there is a possibility that the same (or similar) waveform will exist in common in the voice information in the narrow band WA and in the voice information in the narrow band WB. For this reason, for example, a waveform corresponding to the fundamental period can also exist in common in both narrow bands WA and WB. 
     When the packets are sent in the order of PK 11 , PK 12 , PK 13 , . . . , in many cases, all of the packets are received by the communication terminal  23  in this order without a dropout. However, a packet loss may be caused by the event of congestion of a router (not shown) on the network  21 . The packet lost by a packet loss may be, for example, PK 12 . 
     The present embodiment is characterized in the function of a receiving side and hence description will be provided hereinafter by paying attention to the communication terminal  23 . The construction example of a main portion of the communication terminal  23  is shown in  FIG. 1 . Naturally, the communication terminal  22  may be provided with the same construction as this so as to perform receiving processing. 
     (A-1-1) Construction Example of Communication Terminal 
     Referring to  FIG. 1 , the communication terminal  23  includes decoders  11 A and  11 B, a loss-determining device  12 , interpolators  13 A and  13 B, and a band combiner  14 . 
     Among them, the decoder  11 A is a decoder for the above-mentioned logic channel CA and is a part that decodes voice data CD 1  extracted from each packet (for example, PK 11 , etc.) received by the communication terminal  23  and outputs a decoding result DC 1 . Here, CD 1  is a symbol used for collectively calling respective voice data CD 11  to CD 13  corresponding to the logic channel CA. Also in the following description, when it is not necessary to discriminate CD 11  to CD 13  from each other, this CD 1  is used. 
     The number of samples included in one voice data (for example, CD 11 ) can be arbitrarily determined and may be approximately 160 samples as one example. 
     The decoding result of the voice data CD 11  by the decoder  11 A is DC 11 , the decoding result of the voice data CD 12  is DC 12 , and the decoding result of the voice data CD 13  is DC 13 . As to the decoding result, when it is not necessary to discriminate DC 11  to DC 13  from each other, a symbol DC 1  is used to call the decoding result collectively. 
     The decoder  11 B is entirely the same in its function as the decoder  11 A. However, this decoder  11 B is a decoder for the logic channel CB, decodes voice data CD 21  to CD 23 , and outputs DC 21  to DC 23  as decoding results. A symbol CD 2  relating to the input/output of the decoder  11 B corresponds to the CD 1  and a symbol DC 2  corresponds to the DC 1 . 
     The loss-determining device  12  is a part that detects the occurrence of the packet loss (voice loss) on the basis of basic information ST 1  and outputs a state-of-loss detection result ER 1 . When a packet loss occurs, interpolation by the interpolators  13 A and  13 B is necessary and hence the loss-determining device  12  provides a notice to this effect according to the state-of-loss detection result ER 1  to the interpolators  13 A and  13 B. 
     Various methods can be used as a method for detecting a packet loss. For example, when a dropout occurs in a sequence number (a serial number that the communication terminal  22  assigns at the time of sending a packet) that is held by a RTP header and the like packed in each packet and is supposed to be a serial number, it is advisable to determine that a packet loss occurs. When a packet is delayed to an excessively large amount in terms of the value of a time stamp (information of a sending time that the communication terminal  22  assigns at the time of sending the packet) held by the RTP header, it is also advisable to determine that a packet loss occurs. In the case of using a sequence number, the basic information ST 1  becomes the sequence number and in the case of using a time stamp, the basic information ST 1  becomes the time stamp. 
     There is a possibility that a packet once determined to be lost by a packet loss will be received later but, in this case, the received packet may be discarded. This is because voice data that is not received before timing to be received cannot be used for outputting voice in real-time communication. 
     However, in the case of determining a packet loss on the basis of a sequence number, when a packet is received at the timing when there is still time to output voice, there is a possibility that the received packet can be used for outputting voice by exchanging the order of the received packet in the communication terminal  23 . Hence, in the case of exchanging the order of the received packet in this manner, it is advisable to make consideration not to make the timing of providing a notice of a packet loss according to the state-of-loss detection result ER 1  too early. 
     The interpolator  13 A is a part that interpolates interpolation voice (interpolation voice information) into a series of decoding result DC 1  outputted from the decoder  11 A and outputs an interpolation result IN 1 . That is, when the state-of-loss detection result ER 1  indicates a voice loss, the interpolator  13 A interpolates interpolation voice produced on the basis of the value of the fundamental period (referred to as “PS”) into a time period corresponding to the voice loss to perform interpolation, and when the state-of-loss detection result ER 1  does not indicate a voice loss, the interpolator  13 A transparently passes the received decoding result DC 1  without executing interpolation. The output of the interpolator  13 A is made the interpolation result IN 1  irrespective of whether or not the interpolator  13 A performs interpolation. 
     Moreover, to produce the interpolation voice, the interpolator  13 A always stores the newest decoding result (for example, DC 11 ). Although there is a possibility that various methods can be used also for executing interpolation, it is assumed here that the method disclosed in the non-patent document 1 is used. When interpolation is performed by the method disclosed in the above-mentioned non-patent document 1, the fundamental period PS is an essential parameter. 
     As far as the function having been hitherto described is concerned, the interpolator  13 B is the same as the interpolator  13 A, but there is an important difference in function between them. 
     That is, the interpolator  13 A has the function of producing a fundamental period PS on the basis of the stored newest decoding result (for example, DC 11 ) and of giving a notice of the fundamental period PS to the other interpolator  13 B. However, the interpolator  13 B has only the function of producing interpolation voice on the basis of the received fundamental period PS and of executing the above-mentioned interpolation. 
     It is also possible to employ a construction that every time the interpolator  13 A receives a new decoding result (for example, DC 11 ), the interpolator  13 A produces a fundamental period PS and gives a notice of the fundamental period PS to the other interpolator  13 B. To reduce load applied to the processing capacity of the communication terminal  23  and to decrease the complexity, however, it is effective to employ a construction that when the loss-determining device  12  indicates the occurrence of a voice loss by the state-of-loss result ER 1 , the interpolator  13 A calculates a fundamental period PS. 
     In the case of the present embodiment, the voice data (for example, CD 11  and CD 21 ) of the logic channels CA and CB are packed in the same packet (for example, PK 11 ) and hence when interpolation is necessary on the interpolation  13 A side, interpolation is necessary also on the interpolation  13 B side. Hence, the fundamental period PS calculated by the interpolator  13 A is used for producing interpolation voice by itself and is used also for producing interpolation voice by the interpolator  13 B. However, when the interpolator  13 B uses the fundamental period PS, the interpolator  13 B needs to be given such a notice of the fundamental period PS that will be described later. 
     The interpolator  13 B may or may not receive the state-of-loss detection result ER 1 . In either of cases, when the interpolator  13 B is given a notice of the fundamental period PS from the interpolator  13 A, the interpolator  13 B produces interpolation voice by the use of this fundamental period PS and performs interpolation to a series of decoding result DC 2 . 
     As shown in  FIG. 2 , the interpolator  13 A includes a control section  30 , a decoded waveform storing section  31 , a waveform period calculating section  32 , a period notifying section  33 , and an interpolation executing section  34 . 
     Among them, the control section  30  is a part that controls the respective constituent sections  31  to  34  in the interpolator  13 A. 
     The interpolation executing section  34  is a part that performs interpolation if necessary to a series of decoding result DC 1  received from the decoder  11 A and outputs an interpolation result IN 1  to the band combiner  14 . This interpolation result IN 1  is nearly identical with the series of decoding result DC 1 , but when interpolation is performed, the interpolation result IN 1  is different from the series of decoding result DC 1  in that interpolation voice is interpolated into a corresponding time period (time period during which a voice loss occurs). 
     At least the newest result of the decoding result DC 1  that the interpolation executing section  34  receives in a time series from the decoder  11 A is stored in the decoded waveform storing section  31 . The amount of decoding result DC 1  stored in the decoded waveform storing section  31  is only an amount necessary for producing interpolation voice. 
     As to the management of a storage area in the decoded waveform storing section  31 , it is also advisable that every time a new decoding result (for example, DC 12 ) is supplied, storage data of the same size is deleted (or invalidated) in the order of storage from oldest (for example, DC 11 ) to newest to secure a storage area for storing its new decoding result. 
     The waveform calculating section  32  is a part that produces a fundamental period PS on the basis of the newest decoding result (for example, DC 12 ) stored in the decoded waveform storing section  31 , when necessary. There is a possibility that various methods can be used for this calculation and, for example, it is also advisable to employ a method of calculating a publicly known autocorrelation coefficient by the use of the newest decoding result DC 12  and of setting the amount of delay to maximize a calculation result for a fundamental period PS. The calculated fundamental period PS is used for interpolation performed in the interpolator  13 A and also for interpolation performed in the other interpolator  13 B, as already described above. 
     For the other interpolator  13 B to perform interpolation, it is necessary to give a notice of the fundamental period PS to the other interpolator  13 B by the use of the period notifying section  33 . When the interpolator  13 A uses the fundamental period PS to perform interpolation, however, the fundamental period PS is passed to the interpolation executing section  34  via the control section  30 . When the interpolation voice is produced, the fundamental period PS is used for determining which decoded waveform of the decoded waveforms stored in the decoded waveform storing section  43  is used for interpolation voice. 
     Meanwhile, the interpolator  13 B, as shown in  FIG. 3 , includes a control section  40 , a notice receiving section  41 , an interpolation executing section  42 , and a decoded waveform storing section  43 . 
     Among them, the control section  40  corresponds to the control section  30 , the interpolation executing section  42  corresponds to the interpolation executing section  34 , and the decoded waveform storing section  43  corresponds to the decoded waveform storing section  31 . Hence, they are not described in detail here. 
     The notice receiving section  41  is a part opposite to the period notifying section  33 , receives a notice of the fundamental period PS given by the period notifying section  33 , and passes it to the control section  40 . The interpolation executing section  42  that receives the fundamental period PS via the control section  40  produces interpolation voice on the basis of the fundamental period PS. 
     As is clear by a comparison of  FIG. 2  and  FIG. 3 , a constituent part corresponding to the waveform period calculating section  32  is not in the interpolator  13 B. Hence, it is possible to reduce the space complexity in that a storage area for operation is hardly necessary and to decrease the time complexity in that a necessary processing capacity is little. 
     An interpolation result IN 1  outputted from the interpolator  13 A and an interpolation result IN 2  outputted from the interpolator  13 B are supplied to the band combiner  14  shown in  FIG. 1 . The band combiner  14  couples these interpolation results IN 1  and IN 2  to restore them to voice V of the same wide band as voice just after collecting voice uttered by the user U 1  on the communication terminal  22  side and outputs the restored voice V. 
     In this regard, when a set of respective decoding results (for example, a set of DC 11  and DC 21 ) corresponding to the above-described set of same voice data (for example, CD 11  and CD 21 ) that are supposed to be processed at the same time can not be obtained at the same time in a strict sense, it is also desirable to employ a construction such that the respective decoding results are temporarily stored, for example, in a memory and are delayed to adjust timing, whereby the respective decoding results belonging to the same set are supplied to the interpolators  13 A and  13 B at the same time. This adjustment of timing is effective also in the case where the sizes of voice data (for example, CD 11  and CD 21 ) constructing the same set are different from each other. 
     The operation of the present embodiment having the above-mentioned construction will be described below. 
     (A-2) Operation of Embodiment 
     When the band division method disclosed in the non-patent document 3 is used, voice uttered by the user U 1  is divided into narrow bands WA and WB. Hence, voice information corresponding to the respective narrow bands WA and WB is decoded to make different voice data (for example, CD 11  and CD 21 ) and is packed in the same packet (for example, PK 11 ) and is sent from the communication terminal  22 . 
     The order of sending of the respective packets from the communication terminal  22 , as described above, is the order of PK 11 , PK 12 , PK 13 , . . . . 
     If a packet loss does not occur when the packets PK 11  to PK 13  are transmitted via the network  21 , the state-of-loss detection result ER 1  outputted by the loss-determining device  14 , shown in  FIG. 1 , in the communication terminal  23  does not indicate the occurrence of a voice loss. Hence, the interpolators  13 A and  13 B passes the decoding results DC 1  and DC 2  received from the decoder  11 A and  11 B transparently without interpolating interpolation voice (as interpolation results IN 1  and IN 2 ) to the band combiner  14 . 
     If this state continues and there is not other cause to degrade the communication quality (the occurrence of large jitters or the like), the communication terminal  73  can continue a voice output at a high level of voice quality. 
     However, when any one of the packets (here, assumed to be PK 12 ) is lost by a packet loss, the above-mentioned state-of-loss detection result ER 1  indicates the occurrence of a voice loss and hence the interpolator  13 A causes the waveform period calculating section  32  to calculate a fundamental period PS on the basis of the decoding result (here, DC 11  (if necessary, including also decoding results before DC 11 )) already stored in the decoded waveform storing section  31 . Here, the calculated fundamental period PS corresponds to the fundamental period of a waveform just before the voice loss. 
     This fundamental period PS is not only used for the interpolator  13 A but also given to the interpolator  13 B. 
     The interpolator  13 A determines which waveform of the decoded waveforms stored in the decoded waveform storing section  31  is used on the basis of the fundamental period PS and produces interpolation voice on the basis of the decoded waveform and interpolates the interpolation voice into the series of decoding result DC 1  to thereby perform interpolation. 
     The interpolation voice is interpolated into a position where DC 12  of the decoding result of the voice data CD 12 , which is supposed to be packed in the PK 12  if the packet loss of the packet PK 12  does not occur, exists in the series of decoding result DC 1 , that is, a position between the DC 11  and DC 13  of the decoding result. 
     Also in the interpolator  13 B that receives the fundamental period. PS from the interpolator  13 A, the same interpolation as in the interpolator  13 A is performed. That is, the interpolator  13 B determine which time of the decoded waveform stored in the decoded waveform storing section  43  is used on the basis of the fundamental period PS and produces interpolation voice on the basis of the decoded waveform and interpolates the interpolation voice into a position where the decoding result DC 22  is supposed to exist in the series of decoding result DC 2 . 
     The series of decoding result IN 2  including the interpolation voice is supplied from the interpolator  13 B to the band combiner  14 , is coupled with the series of interpolation result IN 1  supplied from the interpolator  13 A to the band combiner  14 , and is outputted as voice V of a wide band. The user U 2  on the communication terminal  23  side hears this voice V. 
     In this case, the user U 2  hears the coupled interpolation voice at the time when voice V corresponding to a set of DC 12  and DC 22  of the decoding results is supposed to be outputted. 
     Because the interpolation voice is pseudo voice information, as compared with a case where DC 12  and DC 22  of original decoding results are obtained, it is inevitable that the quality of voice V heard by the user U 2  is degraded. However, as compared with a case where even though a voice loss occurs, even the interpolation of interpolation voice cannot be performed, it can be said that the quality of voice V can be improved. 
     In addition, in the present embodiment, the waveform period calculating section  32  that is a constituent section for making a fundamental period PS necessary for producing interpolation voice needs to be provided only on the interpolator  13 A side of two interpolators  13 A and  13 B. Hence, considering the high voice quality, the time complexity and the space complexity are small and also the size of a device is small. 
     (A-3) Effect of Embodiment 
     According to the present embodiment, because the fundamental period (PS) is calculated only on the one logic channel (CA) side, the time complexity and the space complexity necessary for the calculation can be reduced. Therefore, it is possible to provide the communication terminal ( 23 ) having a construction capable of increasing the communication quality and enhancing efficiency considering a small time complexity and a small space complexity. 
     A small time complexity and a small space complexity result in reducing or decreasing the amount of memory, the amount of processing of operation, the size of a device, and power consumption in a specific package and hence can prevent an increase in cost. 
     (B) Other Embodiments 
     In spite of the above-mentioned embodiment, the construction in  FIG. 2  may be used for the interpolator  13 B for processing the logic channel CB corresponding to the narrow band WB of a higher frequency and the construction in  FIG. 3  may be used for the interpolator  13 A for processing the logic channel CA corresponding to the narrow band WA of a lower frequency. 
     In the above-mentioned embodiment, the narrow bands WA and WB are in contact with each other on a frequency axis. However, two narrow bands that are not in contact with each other (for example, a narrow band of 0 to 4 kHz and a narrow band of 4.5 to 8 kHz) can be set. 
     Naturally, the number of set narrow bands may be three or more. When the number of narrow bands is three or more, the number of interpolators included in one communication terminal is also three or more. 
     Moreover, it is also effective to employ a construction that a plurality of interpolators having the constituent sections  31 ,  32 , and  33  shown in  FIG. 2  exist in one communication terminal. 
     In reality, there is a possibility that a lot of noise will develop only in any one of divided bands (any one of logic cannels) to make it impossible to obtain a fundamental period. In this case, it is effective that one communication terminal is provided with a plurality of interpolators having the construction shown in  FIG. 2 . In this case, however, a construction such that each interpolator includes also a constituent section corresponding to the notice receiving section  41  in  FIG. 3  in addition to the construction in  FIG. 2  and gives a notice of the value of a fundamental period to the other interpolators. 
     This is because if there is provided a construction such that the plurality of interpolators corresponding to the plurality of logic channels can calculate the value of a fundamental period and can give a notice of the value to the other interpolators, when any one of the logic channels has a small amount of noise, the other interpolators can use the value of a fundamental period calculated by the interpolator corresponding to that logic channel and hence can perform effective interpolation. This can decrease the probability of developing a state where effective interpolation cannot be performed in all of the logic channels and hence can further improve the communication quality. 
     Moreover, as described above, it is also advisable to pack the voice information of the respective logic channels (for example, CA and CB) in separate packets to send it. 
     In the above-mentioned embodiments, voice information divided on the frequency axis is transmitted by different logic channels. However, the voice information transmitted by different logic channels is not necessarily such that is divided on the frequency axis. For example, voice information divided on a time axis can be transmitted by the different logic channels. Even if the voice information is divided on the time axis, if the unit of division is sufficiently short time, it is possible to conduct communication of a real time property. 
     In the above-mentioned embodiments, when the packet loss (voice loss) occurs, interpolation is performed by the interpolator but even when the packet loss does not occur, there is a possibility that interpolation can be performed. 
     For example, when the occurrence of an error in transmission or the mixture of noises is detected in a certain packet (frame), interpolation may be performed. This is because when a packet can be received but an error in transmission or noise is detected, voice data in that packet might be destroyed or degraded in quality and hence it might be better to replace the voice data with interpolation voice. 
     While the present invention has been described by taking voice information by the telephone (IP telephone) as the example in the above-mentioned embodiments, the present invention can be applied to voice information other than the voice information by the telephone. For example, the present invention can be widely applied to a case where processing using periodicity such as voice and tone signal is performed in parallel. 
     Further, the range of applications of the present invention is not necessarily limited to the voice and the tone signal, but there is a possibility that the present invention can be applied to image information such as moving image. 
     Still further, naturally, it is not necessary to limit a communication protocol, to which the present invention is applied, to the above-mentioned IP protocol. 
     While the present invention is realized mainly by means of hardware in the above description, the present invention can be also realized by means of software.