Encoding device, decoding device, and communication system for extending voice band

A first encoding unit generates a first encoded signal by encoding a component within a first band in a voice signal. A frequency shifting unit shifts the frequency of a component within a second band in the voice signal, the second band having a frequency higher than that of the first band, to the frequency of a component within the first band. A second encoding unit generates a second encoded signal by encoding the component whose frequency has been shifted in the frequency shifting unit. An output unit outputs both the first encoded signal generated in the first encoding unit and the second encoded signal generated in the second encoding unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-094625, filed on May 10, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a band extension technique, and more particularly to an encoding device, a decoding device, and a communication system for extending a voice band.

2. Description of the Related Art

In order to improve the quality of a voice signal in a communication system, a threshold frequency is defined within a passband defining the maximum frequency and minimum frequency of the voice signal on a transmission side, so that a voice signal having a frequency lower than the threshold frequency is not compressed. On the other hand, a voice signal having a frequency higher than the threshold frequency is compressed and transmitted by being compressed into the region between the threshold frequency and the maximum frequency of the passband. On a reception side, the compressed voice signal is extended and harmonic information is generated based on a non-compressed voice signal, and a suitable harmonic is added to the extended voice signal based on the harmonic information (see, for example, Patent Document 1).

RELATED ART DOCUMENT

Patent Document

When intense compression is applied to a frequency higher than the threshold frequency while a lower frequency is left without being substantially compressed, the quality and clarity of voice may be decreased if the compressed frequency is reproduced as it is without being extended on a reception side. In order to improve the quality and clarity of voice, it is necessary to perform, on the reception side, equalization processing in accordance with a speaker or a language such that adjustment should be made each time. When voice outside a band is reproduced, it is necessary to analyze the received voice, and hence a processing load may increase due to advanced voice signal processing, a speaker output be delayed due to delay processing, or uncomfortable voice be reproduced due to the generation of an unnecessary signal.

SUMMARY

In order to solve the above problems, an encoding device according to an aspect of the present embodiment comprises: an input unit that inputs a voice signal; a first encoding unit that generates a first encoded signal by encoding a component within a first band in the voice signal input in the input unit; a frequency shifting unit that shifts the frequency of a component within a second band in the voice signal input in the input unit, the second band having a frequency higher than that of the first band, to the frequency of a component within the first band; a second encoding unit that generates a second encoded signal by encoding the component whose frequency has been shifted in the frequency shifting unit; and an output unit that outputs both the first encoded signal generated in the first encoding unit and the second encoded signal generated in the second encoding unit.

Another aspect of the present embodiment is a decoding device. The device comprises: an input unit that inputs both a first encoded signal obtained by encoding a component within a first band in a voice signal and a second encoded signal obtained by shifting the frequency of a component within a second band in the voice signal, the second band having a frequency higher than that of the first band, to the frequency of a component within the first band and by encoding the latter component; a first decoding unit that generates a first voice component within the first band by decoding the first encoded signal input in the input unit; a second decoding unit that generates a second voice component within the first band by decoding the second encoded signal input in the input unit; a frequency shifting unit that shifts the frequency of the second voice component generated in the second decoding unit to the frequency of a component within the second band; and a combination unit that combines the first voice component generated in the first decoding unit and the second voice component whose frequency has been shifted in the frequency shifting unit and outputs the combined voice component.

Still another aspect of the present embodiment is a communication system. This communication system comprises an encoding device and a decoding device. The encoding device includes: an input unit that inputs a voice signal; a first encoding unit that generates a first encoded signal by encoding a component within a first band in the voice signal input in the input unit; a frequency shifting unit that shifts the frequency of a component within a second band in the voice signal input in the input unit, the second band having a frequency higher than that of the first band, to the frequency of a component within the first band; a second encoding unit that generates a second encoded signal by encoding the component whose frequency has been shifted in the frequency shifting unit; and an output unit that outputs both the first encoded signal generated in the first encoding unit and the second encoded signal generated in the second encoding unit. The decoding device includes: an input unit that inputs both the first encoded signal and the second encoded signal from the encoding device; a first decoding unit that generates a first voice component within the first band by decoding the first encoded signal input in the input unit; a second decoding unit that generates a second voice component within the first band by decoding the second encoded signal input in the input unit; a frequency shifting unit that shifts the frequency of the second voice component generated in the second decoding unit to the frequency of a component within the second band; and a combination unit that combines the first voice component generated in the first decoding unit and the second voice component whose frequency has been shifted in the frequency shifting unit and outputs the combined voice component.

It is to be noted that any optional combination of the above constituent elements and any embodiment obtained by transforming what are expressed by the present embodiment into a method, an apparatus, a system, a recording medium, a computer program, and so on is also effective as other aspects of the present embodiment.

DETAILED DESCRIPTION

First Embodiment

Prior to the specific description of the present invention, the outline thereof will be given first. First Embodiment relates to a communication system that transmits a voice signal from a transmitter to a receiver. When the communication system is a digital wireless communication system, a vocoder method is often used for transmitting a voice signal. The vocoder method is a voice compression technology for communication. The transmitter transmits parameterized voice signals without directly transmitting waves of voice, and the receiver synthesizes the original voice from the received parameterized signals.

In such a vocoder method, a frequency component higher than the Nyquist frequency is removed. For example, “AMBE (registered trademark) +2” is used as a vocoder method in NXDN (registered trademark) that is a standard of a digital professional-use wireless system, but the sampling frequency is set to 8 kHz in AMBE +2, and hence band limitation is performed at 4 kHz. If a voice having a frequency of 4 kHz or higher is lost, voice quality and clarity may decrease. In order to improve voice quality and clarity, it is necessary to perform band extension either in equalization processing that emphasizes high frequencies in a receiver or in advanced signal processing. In addition, when a voice having a frequency of 4 kHz or higher is reproduced, it is necessary to analyze the received voice, and hence a processing load may increase due to advanced voice signal processing, a speaker output be delayed due to delay processing, or an uncomfortable voice be reproduced due to the generation of even an unnecessary signal, as described above.

In order to easily improve voice quality and clarity under such circumstances, the transmitter according to the present embodiment vocoder-encodes a component of 0 to 4 kHz in a voice signal, and vocoder-encodes a component of 4 to 8 kHz after shifting the frequency thereof to a frequency of 0 to 4 kHz. On the other hand, the receiver vocoder-decodes the latter vocoder-encoded signal and then shifts the frequency thereof to a frequency of 4 to 8 kHz, and reproduces a voice of 0 to 8 kHz by combining the result of the frequency shifting and the result of vocoder-decoding the vocoder-encoded signal of 0 to 4 kHz.

FIG. 1illustrates a configuration of a communication system100according to First Embodiment. The communication system100comprises a transmitter10and a receiver12. The transmitter10includes a microphone20, an IF unit22, an encoding device24, and a transmission unit26, and the receiver12includes a reception unit30, a decoding device32, an IF unit34, and a speaker36. The transmitter10and the receiver12are included in a wireless device or a communication device, such as a terminal device, but herein the transmitter10equivalent to the transmission function of a terminal device and the receiver12equivalent to the reception function thereof are only illustrated in order to clarify description. Additionally, the terminal device may not be directly connected, and may be connected, for example, via a base station apparatus.

The microphone20inputs the voice produced by a speaker and converts this into an electric signal. The microphone20outputs the voice converted into an electric signal (hereinafter, referred to as a “voice signal”) to the IF unit22. The IF unit22inputs the voice signal from the microphone20, and outputs the voice signal to the encoding device24. In this case, the IF unit22may perform any processing on the voice signal. The encoding device24generates both a first encoded signal and a second encoded signal by inputting the voice signal from the IF unit22and vocoder-encoding the voice signal. The details of the first encoded signal and the second encoded signal will be described later. The encoding device24outputs the first encoded signal and the second encoded signal to the transmission unit26. The transmission unit26inputs the first encoded signal and the second encoded signal from the encoding device24, and transmits a wireless signal including these signals. The transmission unit26corresponds to a digital professional-use wireless system like, for example, NXDN.

The reception unit30receives the wireless signal from the transmission unit26. The reception unit30acquires the first encoded signal and the second encoded signal from the wireless signal, and outputs them to the decoding device32. The decoding device32generates a voice signal by vocoder-decoding the first encoded signal and the second encoded signal. The decoding device32outputs the voice signal to the IF unit34. The IF unit34inputs the voice signal from the decoding device32, and outputs it to the speaker36. In this case, the IF unit34may perform processing corresponding to the processing in the IF unit22on the voice signal. The speaker36inputs the voice signal from the IF unit34, and converts it into a voice to be output.

FIG. 2illustrates a configuration of the encoding device24. The encoding device24includes: an input unit40; a first decimation unit42a, a second decimation unit42b, and a third decimation unit42c, which are collectively referred to as a decimation unit42; a frequency shifting unit44; a first encoding unit46aand a second encoding unit46bthat are collectively referred to as an encoding unit46; and an output unit48.

The input unit40inputs the voice signal from the non-illustrated IF unit22. The sampling frequency for the input voice signal is, for example, 48 kHz. The input unit40outputs the voice signal to the first decimation unit42aand the second decimation unit42b.

The first decimation unit42ainputs the voice signal from the input unit40. The first decimation unit42adownsamples the sampling frequency for the voice signal from 48 kHz to 8 kHz. The downsampled voice signal contains a voice component within a band of 0 to 4 kHz. Herein, the band of 0 to 4 kHz is also referred to as a first band, and hence the voice component within the band of 0 to 4 kHz can also be referred to as a component within the first band. The first decimation unit42aoutputs the downsampled voice signal (hereinafter, this is also referred to as the “voice signal”), i.e., the component within the first band to the first encoding unit46a.

The first encoding unit46ainputs the voice signal from the first decimation unit42, i.e., the component within the first band. The first encoding unit46avocoder-encodes the component within the first band. In this case, the sampling frequency of the vocoder processing is 8 kHz. The first encoding unit46aoutputs the vocoder-encoded component within the first band (hereinafter, referred to as the “first encoded signal”) to the output unit48.

The second decimation unit42binputs the voice signal from the input unit40. The second decimation unit42bdownsamples the sampling frequency for the voice signal from 48 kHz to 16 kHz. Herein, the sampling frequency is downsampled up to 16 kHz in order to handle a voice component outside a band of 8 kHz. The second decimation unit42boutputs the downsampled voice signal (hereinafter, this is also referred to as the “voice signal”) to the frequency shifting unit44.

The frequency shifting unit44inputs the voice signal from the second decimation unit42b. The frequency shifting unit44shifts the frequency of a voice component of 4 to 8 kHz contained in the voice signal to the frequency of a component of 0 to 4 kHz. This is equivalent to the fact that the frequency of a voice component of 4 to 8 kHz, outside the band, is shifted to the frequency of a component within the band of 0 to 4 kHz. Herein, the band of 4 to 8 kHz is also referred to as a second band, and hence it can also be said that the frequency shifting unit44shifts the frequency of a component within the second band in the voice signal, the second band having a frequency higher than that of the first band, to the frequency of a component within the first band. This is because: the bandwidth that can be processed in the later-described second encoding unit46bis set up to 4 kHz, and hence a component of a high frequency outside the band is to be processed in the second encoding unit46bby shifting the frequency of the component. Herein, the bandwidth of the second band is the same as that of the first band. The frequency shifting unit44outputs the voice signal whose frequency has been shifted (hereinafter, this is also referred to as the “voice signal”), i.e., the component within the second band whose frequency has been shifted to that of a component within the first band (hereinafter, this is also referred to as the “component within the second band”) to the third decimation unit42c.

The third decimation unit42cinputs the voice signal from the frequency shifting unit44. The third decimation unit42cdownsamples the sampling frequency for the voice signal from 16 kHz to 8 kHz. The third decimation unit42coutputs the downsampled voice signal (hereinafter, this is also referred to as the “voice signal”) to the second encoding unit46b. Herein, the output voice signal also contains the component within the second band.

The second encoding unit46binputs the voice signal from the third decimation unit42c, i.e., the component within the second band. The second encoding unit46bvocoder-encodes the component within the second band. In this case, the sampling frequency of the vocoder processing is 8 kHz. The second encoding unit46boutputs the vocoder-encoded component within the second band (hereinafter, referred to as the “second encoded signal”) to the output unit48.

The output unit48inputs both the first encoded signal from the first encoding unit46aand the second encoded signal from the second encoding unit46b, and outputs these signals. In particular, the output unit48outputs the first encoded signal and the second encoded signal while switching the output order in accordance with the order in which the non-illustrated transmission unit26transmits signals, i.e., the order determined by the frames of a wireless communication channel.

Herein, prior to the description of this, a frame format in a wireless communication channel (RTCH) used during voice communication in an NXDN 9600 bps (Half Rate) system will be described, as a comparison object, by referring toFIG. 3.FIG. 3illustrates a signal format to be used in another communication system to be compared with the communication system100. Herein, “FS” indicates a frame sync word, “LI” a link information channel, “SA” a low-speed accompanying control channel, “VCH” a voice channel, and “FA” a high-speed accompanying control channel 1 (FACCH1). In this case, the first encoded signal is stored in VCH. On the other hand, the second encoded signal is not stored, so that it is not transmitted. Refer back toFIG. 2.

Next, two types of formats for storing the second encoded signal will be described, and either of them may be used. In order to cause to correspond to the first format, the output unit48alternately outputs the first encoded signal and the second encoded signal.FIG. 4illustrates a signal format to be used in the communication system100. Herein, “VCH (extension)”, indicating an extended voice channel, stores the second encoded signal. InFIG. 4, “VCH” and “VCH (extension)” are arranged in a region where “VCH” and “FA” are arranged inFIG. 3. That is, “FA” is not included inFIG. 4. After a telephone call is started, “FA” generally contains only a control code such as, for example, idle information or a message indicating that voice communication is being performed, and hence the telephone call is not affected if such a control code is not transmitted. Therefore, “VCH (extension)” is transmitted instead of transmitting “FA.” In particular, VCH and VCH (extension) are alternately arranged.

In this case, VCH, VCH (extension), VCH, and VCH (extension) are arranged in this order, and hence a combination of the continuous VCH and VCH (extension) becomes a single voice signal. Therefore, the receiver12continuously acquires voice components outside the band by vocoder-decoding VCH to acquire voice components within the band and then by vocoder-decoding VCH (extension). Further, the receiver12reproduces a voice by combining the result of vocoder-decoding VCH and that of vocoder-decoding VCH (extension), and hence the adjustment of the order of the results of vocoder-decoding becomes unnecessary, whereby processing becomes simple.

In order to cause to correspond to the second format, the output unit48continuously outputs a plurality of the first encoded signals, and then continuously outputs a plurality of the second encoded signals.FIG. 5illustrates another signal format to be used in the communication system100. InFIG. 5, “VCH (extension)” is arranged as it is in the region where “FA” is arranged inFIG. 3. In this case, even if a receiver only corresponding to the format ofFIG. 3receives the signal of the frame format ofFIG. 5, it is only necessary to discard VCH (extension), and hence vocoder-decoding of VCH is executed. That is, communication is not affected and compatibility is maintained.

This configuration is implemented in the hardware by any CPU of a computer, memory, and other LSI, and implemented in the software by a program or the like that is loaded in a memory. Herein, functional blocks implemented by the cooperation of hardware and software are depicted. Thus, it is to be understood by a person skilled in the art that these functional blocks can be implemented in various forms, namely, solely in hardware, solely in software, or through a combination of hardware and software.

FIG. 6illustrates a configuration of the decoding device32. The decoding device32includes: an input unit60; a first decoding unit62aand a second decoding unit62bthat are collectively referred to as a decoding unit62; a first interpolation unit64a, a second interpolation unit64b, and a third interpolation unit64c, which are collectively referred to as an interpolation unit64; a delay unit66; a frequency shifting unit68; and a combination unit70.

The input unit60inputs the first encoded signal and the second encoded signal from the non-illustrated reception unit30. When the format of the signal received in the reception unit30corresponds toFIG. 4, the input unit60alternately inputs the first encoded signal and the second encoded signal. On the other hand, when the format of the signal received in the reception unit30corresponds toFIG. 5, the input unit60continuously inputs a plurality of the first encoded signals, and then continuously inputs a plurality of the second encoded signals. The sampling frequency for each of the first encoded signal and the second encoded signal that have been input is, for example, 8 kHz. The input unit60outputs the first encoded signal to the first decoding unit62aand the second encoded signal to the second decoding unit62b.

The first decoding unit62ainputs the first encoded signal from the input unit60. The first decoding unit62avocoder-decodes the first encoded signal. In this case, the sampling frequency of the vocoder processing is 8 kHz. The first decoding unit62aoutputs the vocoder-decoded first encoded signal (hereinafter, referred to as a “first voice component”) to the first interpolation unit64a. The first voice component is a voice component within a band of 0 to 4 kHz, and is a voice component within the first band. Because the first voice component is contained in a voice signal having a sampling frequency of 8 kHz, it can also be said that the voice signal is output to the first interpolation unit64a.

The first interpolation unit64ainputs the voice signal from the first decoding unit62a, i.e., the first voice component. The first interpolation unit64aupsamples the sampling frequency for the voice signal from 8 kHz to 48 kHz. The upsampled voice signal also contains the first voice component within the first band. The first interpolation unit64aoutputs the upsampled voice signal (hereinafter, this is also referred to as the “voice signal”), i.e., the first voice component to the delay unit66.

The delay unit66inputs the voice signal from the first interpolation unit64a, i.e., the first voice component. The delay unit66delays the voice signal only by a period in accordance with the format illustrated inFIG. 4orFIG. 5. The delay unit66outputs the delayed voice signal (hereinafter, this is also referred to as the “voice signal”), i.e., the first voice component to the combination unit70.

The second decoding unit62ainputs the second encoded signal from the input unit60. The second decoding unit62bvocoder-decodes the second encoded signal. In this case, the sampling frequency of the vocoder processing is 8 kHz. The second decoding unit62aoutputs the vocoder-decoded second encoded signal (hereinafter, referred to as a “second voice component”) to the second interpolation unit64b. The second voice component is a voice component outside the band of 4 to 8 kHz, and is a voice component within the second band. Herein, the frequency of the second voice component is shifted to that of a component within the band of 0 to 4 kHz, i.e., within the first band. Also, the second voice component is contained in a voice signal having a sampling frequency of 8 kHz, and hence it can also be said that the voice signal is output to the second interpolation unit64b.

The second interpolation unit64ainputs the voice signal from the second decoding unit62b, i.e., the second voice component. The second interpolation unit64bupsamples the sampling frequency for the voice signal from 8 kHz to 16 kHz. The upsampled voice signal also contains the second voice component within the first band. The second interpolation unit64boutputs the upsampled voice signal (hereinafter, this is also referred to as the “voice signal”), i.e., the second voice component to the frequency shifting unit68.

The frequency shifting unit68inputs the voice signal from the second interpolation unit64b, i.e., the second voice component. The frequency shifting unit68shifts the frequency of the voice component of 0 to 4 kHz contained in the voice signal to that of a component of 4 to 8 kHz. This is equivalent to the fact that a voice component outside the band of 0 to 4 kHz, the frequency of which has been shifted to that of a component within the band thereof, is returned to a voice component within the band of 4 to 8 kHz. Therefore, it is equivalent to the fact that the frequency of the second voice component within the first band is shifted to that of a component within the second band. The frequency shifting unit68outputs the voice signal whose frequency has been shifted (hereinafter, this is also referred to as the “voice signal”), i.e., the second voice component whose frequency has been shifted to a component within the second band (hereinafter, this is also referred to as the “second voice component”) to the third interpolation unit64c.

The third interpolation unit64cinputs the voice signal from the frequency shifting unit68, i.e., the second voice component. The third interpolation unit64cupsamples the sampling frequency for the voice signal from 16 kHz to 48 kHz. The upsampled voice signal also contains the second voice component within the second band. The third interpolation unit64coutputs the upsampled voice signal (hereinafter, this is also referred to as the “voice signal”), i.e., the second voice component to the combination unit70.

The combination unit70inputs the voice signal from the delay unit66, i.e., the first voice component, and inputs the voice signal from the third interpolation unit64c, i.e., the second voice component. The combination unit70combines the first voice component and the second voice component with addition processing. The voice component obtained by combining the first voice component and the second voice component is contained in the voice signal. The combination unit70outputs the voice signal to the non-illustrated IF unit34.

An operation of the communication system100configured as described above will be described.FIG. 7is a flowchart illustrating an output procedure by the encoding device24. The first decimation unit42aand the first encoding unit46aexecute in-band encoding processing (S500). The second decimation unit42b, the frequency shifting unit44, the third decimation unit42c, and the second encoding unit46bexecute out-of-band encoding processing (S510). The output unit48executes output switching processing on an encoded signal (S520).

FIG. 8is a flowchart illustrating a procedure of the in-band encoding processing. The first decimation unit42aexecutes decimation processing (S501). The first encoding unit46aexecutes vocoder-encoding processing (S502).

FIG. 9is a flowchart illustrating a procedure of the out-of-band encoding processing. The second decimation unit42bexecutes decimation processing (S511). The frequency shifting unit44executes frequency shifting processing (S512). The third decimation unit42cexecutes decimation processing (S513). The second encoding unit46bexecutes vocoder-encoding processing (S514).

FIG. 10is a flowchart illustrating a combination procedure by the decoding device32. The input unit60executes input switching processing on an encoded signal (S600). The first decoding unit62a, the first interpolation unit64a, and the delay unit66execute in-band decoding processing (S610). The second decoding unit62b, the second interpolation unit64b, the frequency shifting unit68, and the third interpolation unit64cexecute out-of-band decoding processing (S620). The combination unit70executes combination processing on voice components (S630).

FIG. 11is a flowchart illustrating a procedure of the in-band decoding processing. The first decoding unit62aexecutes vocoder-decoding processing (S611). The first interpolation unit64aexecutes interpolation processing (S612). The delay unit66executes buffering processing (S613).

FIG. 12is a flowchart illustrating a procedure of the out-of-band decoding processing. The second decoding unit62bexecutes vocoder-decoding processing (S621). The second interpolation unit64bexecutes interpolation processing (S622). The frequency shifting unit68executes frequency shifting processing (S623). The third interpolation unit64cexecutes interpolation processing (S624).

Hereinafter, a configuration for further improving voice quality and clarity in each of the encoding device24and the decoding device32described above will be described. The encoding device24and the decoding device32described above do not include an equalizer for reasons such as suppression of an increase in a processing load and the like. On the other hand, at least one of the encoding device24and the decoding device32includes an equalizer herein.

FIG. 13illustrates another configuration of the encoding device24. In the encoding device24, a first EQ unit50aand a second EQ unit50bthat are collectively referred to as an EQ unit50are added to the encoding device24illustrated inFIG. 2. The first EQ unit50ais arranged between the first decimation unit42aand the first encoding unit46a, and the second EQ unit50bbetween the third decimation unit42cand the second encoding unit46b.

The first EQ unit50ainputs the voice signal from the first decimation unit42a, i.e., the component within the first band. The first EQ unit50aexecutes equalization processing on the component within the first band. In the equalization processing, voice quality to a vowel is improved with a formant corresponding to the vowel being further emphasized. The equalization processing may be implemented by any publicly known technique, and thus description thereof will be omitted herein. The first EQ unit50aoutputs the equalization-processed component within the first band (hereinafter, this is also referred to as the “component within the first band”), i.e., the voice signal to the first encoding unit46a.

The second EQ unit50binputs the voice signal from the third decimation unit42c, i.e., the component within the second band. The second EQ unit50bexecutes equalization processing on the component within the second band. In the equalization processing, voice quality to a consonant is improved with a formant corresponding to the consonant being further emphasized. The equalization processing may be implemented by any publicly known technique, and thus description thereof will be omitted herein. The second EQ unit50boutputs the equalization-processed component within the second band (hereinafter, this is also referred to as the “component within the second band”), i.e., the voice signal to the second encoding unit46b.

FIG. 14illustrates another configuration of the decoding device32. In the decoding device32, a first EQ unit72aand a second EQ unit72bthat are collectively referred to as an EQ unit72are added to the decoding device32illustrated inFIG. 6. The first EQ unit72ais arranged between the first decoding unit62aand the first interpolation unit64a, and the second EQ unit72bbetween the second decoding unit62band the second interpolation unit64b. The first EQ unit72aexecutes the same processing as the first EQ unit50aand the second EQ unit72bexecutes the same processing as the second EQ unit50b, and thus description thereof will be omitted herein.

In such a configuration, the encoding device24ofFIG. 2may be included in the transmitter10, and the decoding device32ofFIG. 14in the receiver12. Alternatively, the encoding device24ofFIG. 13may be included in the transmitter10, and the decoding device32ofFIG. 6in the receiver12. Further, the encoding device24ofFIG. 13may be included in the transmitter10, and the decoding device32ofFIG. 14in the receiver12.

According to the present embodiment, the first encoded signal is generated from the component within the first band and the second encoded signal from the component within the second band, and hence a component outside the band can also be encoded. Further, a component outside the band is encoded, and hence voice quality and clarity can be improved. Furthermore, a component within the second band is encoded after the frequency thereof is shifted to that of a component within the first band, and hence a second encoding unit corresponding to the first band can be used. Still furthermore, the first encoded signal is generated from a component within the first band and the second encoded signal from a component within the second band, and hence a voice of 0 to 8 kHz can be reproduced without performing advanced voice signal processing. Still furthermore, the second encoded signal is generated based on a component of 4 to 8 kHz, the unnaturalness of the voice reproduced on the reception side can be reduced. Still furthermore, the first encoded signal and the second encoded signal are alternately output, and hence processing delay can be reduced.

Still furthermore, a plurality of the first encoded signals are continuously output and then a plurality of the second encoded signals are continuously output, and hence changing of the positions of VCH where the first encoded signals are to be stored can be made unnecessary. Still furthermore, changing of the positions of VCH where the first encoded signals are to be stored is made unnecessary, and hence the first encoded signal can be decoded also in a receiver that does not correspond to the decoding of the second encoded signal. Still furthermore, the first encoded signal is decoded also in a receiver that does not correspond to the decoding of the second encoded signal, and hence compatibility can be maintained. Still furthermore, equalization processing is executed in an encoding device, voice quality and clarity can be further improved. Still furthermore, equalization processing is executed in a decoding device, voice quality and clarity can be further improved.

Second Embodiment

Second Embodiment will now be described. Second Embodiment relates to a communication system that transmits a voice signal from a transmitter to a receiver, similarly to First Embodiment. Until now, the NXDN 9600 bps (Half Rate) system has been described as an example of the communication system100. Therefore, a voice signal with a bandwidth of 8 kHz is divided into a component of 0 to 4 kHz and that of 4 to 8 kHz. In Second Embodiment, a voice signal is equally divided into n components. A communication system100according to Second Embodiment is of a type similar toFIG. 1. Herein, description will be made centering on the points different from First Embodiment.

FIG. 15illustrates a configuration of an encoding device24according to Second Embodiment. The encoding device24includes: an input unit40; a first decimation unit42a, a second decimation unit42b, a third decimation unit42c, a fourth decimation unit42d, a fifth decimation unit42e, a sixth decimation unit42f, and a seventh decimation unit42g, which are collectively referred to as a decimation unit42; a first frequency shifting unit44a, a second frequency shifting unit44b, and a third frequency shifting unit44c, which are collectively referred to as a frequency shifting unit44; a first encoding unit46a, a second encoding unit46b, a third encoding unit46c, and a fourth encoding unit46d, which are collectively referred to as an encoding unit46; and an output unit48. The first frequency shifting unit44acorresponds to the aforementioned frequency shifting unit44. Herein, the second frequency shifting unit44band the third frequency shifting unit44care grouped into an additional frequency shifting unit52, and the third encoding unit46cand the fourth encoding unit46dare grouped into an i-th encoding unit54.

The first decimation unit42aand the first encoding unit46agenerate a first encoded signal by vocoder-encoding a component within a first band in a voice signal. The second decimation unit42b, the first frequency shifting unit44a, the third decimation unit42c, and the second encoding unit46bgenerate a second encoded signal by shifting the frequency of a component within a second band in the voice signal to that of a component within the first band and then by vocoder-encoding the component. These are the same processing as in First Embodiment. On the other hand, the fourth decimation unit42d, the second frequency shifting unit44b, the fifth decimation unit42e, and the third encoding unit46cgenerate a third encoded signal by shifting the frequency of a component within a third band in the voice signal to that of a component within the first band and then by vocoder-encoding the component. The sixth decimation unit42f, the third frequency shifting unit44c, the seventh decimation unit42g, and the fourth encoding unit46dgenerate a fourth encoded signal by shifting the frequency of a component within a fourth band in the voice signal to that of a component within the first band and then by vocoder-encoding the component.

That is, the additional frequency shifting unit52shifts the frequency of a component within an i-th (i>2) band in a voice signal, the i-th band having a frequency higher than that of the (i−1)-th band, to that of a component within the first band. The i-th encoding unit54generates an i-th encoded signal by vocoder-encoding the component whose frequency has been shifted in the frequency shifting unit44. The bandwidths of the first band to the fourth band are the same as each other, and they may not be 4 kHz as in First Embodiment. Also, the voice signal is equally divided into “4” components, but the number of equal divisions is not limited to “4.” Also, the sampling frequency in the decimation unit42and the like may be appropriately set. Finally, the output unit48also outputs the i-th encoded signal generated in the i-th encoding unit54.

FIG. 16illustrates a configuration of a decoding device32according to Second Embodiment. The decoding device32includes: an input unit60; a first decoding unit62a, a second decoding unit62b, a third decoding unit62c, and a fourth decoding unit62d, which are collectively referred to as a decoding unit62; a first interpolation unit64a, a second interpolation unit64b, a third interpolation unit64c, a fourth interpolation unit64d, a fifth interpolation unit64e, a sixth interpolation unit64f, and a seventh interpolation unit64g, which are collectively referred to as an interpolation unit64; a delay unit66; a first frequency shifting unit68a, a second frequency shifting unit68b, and a third frequency shifting unit68c, which are collectively referred to as a frequency shifting unit68; and a combination unit70. The first frequency shifting unit68acorresponds to the aforementioned frequency shifting unit68. Herein, the third decoding unit62cand the fourth decoding unit62dare grouped into an i-th decoding unit74, and the second frequency shifting unit68band the third frequency shifting unit68care grouped into an additional frequency shifting unit76.

The first decoding unit62aand the first interpolation unit64agenerate a first voice component by decoding the first encoded signal. The second decoding unit62b, the second interpolation unit64b, the first frequency shifting unit68a, and the third interpolation unit64cgenerate a second voice component obtained by decoding the second encoded signal, and then shift the frequency thereof to that of a component within the second band. These are the same processing as in First Embodiment. On the other hand, the third decoding unit62c, the fourth interpolation unit64d, the second frequency shifting unit68b, and the fifth interpolation unit64egenerate a third voice component obtained by decoding the third encoded signal, and then shift the frequency thereof to that of a component within the third band. The fourth decoding unit62d, the sixth interpolation unit64f, the third frequency shifting unit68c, and the seventh interpolation unit64ggenerate a fourth voice component obtained by decoding the fourth encoded signal, and then shift the frequency thereof to that of a component within the fourth band.

That is, the i-th decoding unit74generates an i-th voice component within the first band by decoding the i-th encoded signal. The additional frequency shifting unit76shifts the frequency of the i-th voice component generated in the i-th decoding unit74to that of a component within the i-th band. Also, herein, the bandwidths of the first band to the fourth band are the same as each other, and they may not be 4 kHz as in First Embodiment. Also, the voice signal is equally divided into “4” components, but the number of equal divisions is not limited to “4.” Also, the sampling frequency in the interpolation unit64and the like may be appropriately set. Finally, the combination unit70also combines the i-th voice component whose frequency has been shifted in the i-th decoding unit74and outputs it.

According to the present embodiment, a voice signal is equally divided into n components and encoding and decoding are executed on each of them, and hence voice quality and clarity can be further improved. Further, a voice signal is equally divided into n components and encoding and decoding are executed on each of them, and hence the flexibility of configuration can be improved.

The present invention has been described above based on embodiments. These embodiments are illustrative in nature, and it should be appreciated by a person skilled in the art that various modifications can be made to the combinations of the components and the processing processes and such modifications also fall within the scope of the present invention.