1. Field of the Invention
The present invention relates to a wireless communication device and a communication terminal that perform a communication by use of sound packets.
2. Description of the Related Art
When a user carries a wireless voice communication system in one's hand, such as a cellular phone and a cordless phone, or uses the system at a location where ambient circumstances change, variations occur in received signal strength indicator, a distance between devices, and an interference radio wave, which greatly affects communication quality. A known countermeasure against the problems is; for instance, a technique described in relation to a wireless telephone system as disclosed in JP-T-2002-509387.
The wireless telephone system of JP-T-2002-509387 is made up of a base unit that has a base transceiver and at least one wireless handset and that is connectable with one external phone line. The wireless handset and the base unit implement communication by means of fixed-size audio packets, each of which is composed of a plurality of audio data samples and error correction bits. Moreover, JP-T-2002-509387 includes descriptions about changing a relative number of bits assigned to an audio data sample and an error correction bit in connection with a packet configuration of a subsequent audio packet by means of monitoring the quality of a digital link set on a wireless channel and determining whether or not a change has occurred in error rate.
Specifically, when the error rate becomes worse, the wireless telephone system performs processing for decreasing an amount of data pertinent to an audio data sample contained in a packet and increasing an amount of data pertinent to error correction bits to thus assign a larger number of bits to error correction, thereby broadening a distance range and enhancing a tolerance to the interference radio wave.
JP-A-2010-154163 discloses a technique of reversing least significant bits in “n” bits in accordance with the number of “1s” in the “n” bits of n-bit ADPCM data, thereby letting the least significant bits act like a parity signal and enabling detection of an error without involvement of an increase in the number of bits. As a result, when a communication environment becomes worse, sound quality is somewhat distorted, but accuracy in error detection is increased. When an error occurs in ADPCM data, the ADPCM data themselves can be switched to a muted or attenuated state.
In addition, JP-A-7-143074 discloses a technique of converting an ADPCM code for which an error is detected into an ADPCM code which may cause a much smaller amplitude change in a decoded signal, thereby preventing occurrence of high-level unusual noise and avoiding a situation in which a level of a normal decoded sound will fall more than necessary to thus prevent a listener from feeling unpleasant sensation.
When the error rate is increased as a result of deterioration of the communication environment, the wireless telephone system described in connection with JP-T-2002-509387 switches a quality level from the highest quality level to an intermediate quality level or a low quality level by decreasing a data rate of sound in order to increase the amount of data pertinent to the error correction bits. For this reason, sound quality is considered to become deteriorated. However, if the sound quality changes for the worse in sequence as the communication environment becomes worse, the user will experience inconvenience in using the wireless telephone system.
Moreover, the techniques described in connection with JP-A-2010-154163 and JP-A-7-143074 make it possible to perform audio processing that inhibits muting of a sound or occurrence of unpleasant unusual noise, which would otherwise arise at the time of occurrence of an error, without greatly degrading sound quality even when the communication environments become worse, thereby preventing the listener from feeling unpleasant sensation. In the meantime, these techniques are based on the premise that the system uses a signal band employed in a popular telephone line. However, even in the field of wireless communication, a demand exists for extending a frequency band to a broader band to implement communication of more natural sound quality.
Accordingly, an object of the present invention is to provide a wireless communication device and a communication terminal that can maintain sound quality without changing a sound data rate through use of a fixed-size packet even when the communication environments become worse and, hence, can enhance accuracy in error detection.
A wireless communication device according to an aspect of the present invention is configured to include: an ADPCM encoding unit that divides a sampled sound signal into a high frequency signal and a low frequency signal and individually encodes the high frequency signal and the low frequency signal by means of adaptive differential pulse code modulation to thereby convert the high frequency signal into high frequency ADPCM data having a first number of bits, and convert the low frequency signal into low frequency ADPCM data having a second number of bits; an error detection code generation unit that generates an error detection code that is pertinent to the high frequency ADPCM data having the first number of bits and the low frequency ADPCM data having the second number of bits; a transmission data conversion unit replaces data pertinent to some of a plurality of bits which configure the low frequency ADPCM data with the error detection code formed from the error detection code generation unit; and a received data processing unit that receives the high frequency ADPCM data and the low frequency ADPCM data, which are sent along with the error detection code, and that individually processes the high frequency ADPCM data and the low frequency ADPCM data in accordance with a value of the error detection code.
The wireless communication device according may be configured so that the error detection code generation unit generates a first error detection code pertaining to the high frequent ADPCM data and a second error detection code pertaining to the low frequency ADPCM data, and the transmission data conversion unit replaces at least two bits of data among the plurality of bits that configure the low frequency ADPCM data with at least two bits of an error detection code including the first error detection code and the second error detection code.
The wireless communication device may be configured so that the error detection code generation unit generates a third error detection code that acts as a parity signal for reversing bits in accordance with the number of “1s” in a series of data that include the high frequency ADPCM data and the low frequency ADPCM data.
The wireless communication device may be configured so that when an error is detected by means of the received error detection code, the received data processing unit performs first signal processing on the high frequency ADPCM data that are received along with the error detection code and performs second signal processing on the low frequency ADPCM data that are received along with the error detection code.
The wireless communication device may be configured so that the received data processing unit performs third signal processing on the high frequency ADPCM data received along with the error detection code and fourth signal processing on the low frequency ADPCM data received along with the error detection code when an error in a high frequency signal is detected by means of the received first error detection code, and the received data processing unit performs fifth signal processing on the high frequency ADPCM data received along with the error detection code and sixth signal processing on the low frequency ADPCM data received along with the error detection code when an error in a low frequency signal is detected by means of the received second error detection code.
According to the present invention, in a wireless wideband voice communication, high frequency ADPCM data and low frequency ADPCM data are individually processed by means of an error detection code that is transmitted after replacement of some of bits of the low range ADPCM data. Therefore, even when the communication environments become worse, wideband sound quality can be maintained by a fixed-size packet without changing a data rate of sound.
By reference to the drawings, a wireless communication device according to an embodiment of the present invention is described by taking a cordless telephone as an example.
The cordless telephone includes the master device 10 and one or more slave devices 20, as shown in
The master device 10 includes a sound input unit 11, a PCM conversion unit 12, an ADPCM encoding unit 13, a transmission conversion table 14, a transmission conversion table switching unit 15, a transmission packet generation unit 16, and a wireless transmission circuit 17.
The sound input unit 11 inputs a sound signal formed from signal that is delivered by way of a telephone line network or an IP network. The sound input unit 11 corresponds to a microphone that is built in a handset if the master device 10 is provided with the handset.
The PCM conversion unit 12 samples the sound signal at a predetermined cycle and quantizes the thus-sampled signal into an integral value including a predetermined number of bits.
The ADPCM encoding unit 13 generates digital sound data (hereinafter referred to simply as “sound data”) by means of G.722 wideband ADPCM (Adaptive Differential Pulse Code Modulation). The ADPCM encoding unit 13 first separates input data into a high frequency signal and a low frequency signal by means of a quadrature mirror filter and performs ADPCM encoding on the high frequency signal and the low frequency signal, respectively.
The 15-level adaptive dequantizer 13c calculates a quantized differential signal from data pertinent to the core bits (four bits), outputting a calculation result. The differential signal output from the 15-level adaptive dequantizer 13c is delivered to the adaptive predictor 13d and an adder 13f. The adder 13f adds a prediction signal generated in the encoder to the differential signal, to thus generate a regenerative signal. The adaptive predictor 13d generates a prediction signal from the differential signal originating from the 15-level adaptive dequantizer 13c and the regenerative signal originating from the adder 13f.
An input signal sent from the PCM conversion unit 12 is delivered to the adder 13e, and the adder 13e calculates a difference between the input signal sent from the PCM conversion unit 12 and the prediction signal sent from the adaptive predictor 13d. A resultant difference signal generated by the adder 13e is delivered to the 60-level adaptive quantizer 13a, and the 60-level adaptive quantizer 13a generates a 6-bit low frequency ADPCM code.
In the meantime, the high frequency ADPCM encoder performs 2-bit high frequency ADPCM encoding on an input high frequency signal according to G.722 standards. The high frequency ADPCM encoder does not have a bit mask unit and is configured so as to input all bits into the adaptive dequantizer. The high frequency ADPCM encoder can be analogous to the low frequency ADPCM encoder except this configuration, and hence its detailed explanations using the drawings are omitted. The ADPCM encoding unit 13 multiplexes the thus-generated 6-bit low frequency ADPCM code and the 2-bit high frequency ADPCM code by use of a multiplexer as shown in
In the embodiment, the ADPCM encoding unit 13 of the master device 10 generates ADPCM data that are a low frequency signal having a data rate of 48 kbps. In the ADPCM data, low frequency sound data are assigned six bits, and highest order bits include a positive code bit and a negative code bit. Accordingly, as shown in
In conformance with G.722 standards, four bits of the 6-bit low frequency ADPCM code are set as core bits, and remaining two bits are set as enhancement bits in the embodiment. Specifically, the ADPCM encoding unit 13 generates ADPCM data while taking four higher order bits as core bits, and the decoding unit of the receiving side also performs decoding operation while taking the four higher order bits as core bits. As above, so long as the same number of core bits is set on the encoder and the decoder, respectively, a prediction signal generated by the adaptive predictor 13d assumes the same value at both the encoder and the decoder. Accordingly, even when enhancement bits are used in another application, like a data communication, great degradation of sound quality cannot be avoided.
In
In short, in relation to the two lower order bits of the table T2; namely, b6 (the next least significant bit (LSB)) and b7 (the least significant bit), the “next least significant bit” is reversed such that the number of “is” in the two bits becomes even according to the number of “is” in the two bits of the high frequency ADPCM data, and the “least significant bit” is reversed such that the number of “is” in the four bits become even according to the number of “1s” in the four higher order bits of the low frequency ADPCM data, thereby letting the two bits act as a parity signal. By means of converting the sound data by use of the table T2, the two lower order bits b6 and b7 of eight bits per one sample value of a sound data sequence to be transmitted; for instance, eight bits b0, b1, b7 shown in
In
By use of a changeover switch 15a intended for connection with the ADPCM encoding unit 13 and a changeover switch 15b intended for connection with the transmission packet generation unit 16, the transmission conversion table switching unit 15 toggles between the table T1 and the table T2 in accordance with the receiving error information so as to apply any one of the tables to the ADPCM encoding unit 13 and the transmission packet generation unit 16. When an excellent communication environment is maintained and when there is no need for transmission conversion, the changeover switches 15a and 15b are switched to the table T1. When transmission conversion is required as a result of deterioration of the communication environment, the changeover switches 15a and 15b are switched to the table T2, thereby converting transmission data such that two lower order bits of the transmission data act as a parity signal.
In
The sound packet shown in
In the embodiment, wideband ADPCM sound data to be stored in the field B are assigned eight bits per sample value, and two lower order bits (b6, b7) of the eight bits are allocated for a parity signal. In addition, two higher order bits (b0, b1) are assigned for high frequency ADPCM data, and subsequent four bits (b2, b5) are assigned for four core bits of the lower frequency ADPCM code.
Further, in the embodiment, when conversion is carried out by reference to the table T2, the transmission side sends per sample, as low frequency ADPCM data, 5-bit data that are made up of four bits of ADPCM data (core bits) and one least significant bit that is to act as a parity bit. The transmission side also sends per sample, as high frequency ADPCM data, 3-bit data that are made up of two bits of ADPCM data and one next least significant bit that is to act as a parity bit. Thus, the transmission side transmits both the parity bit for a low frequency signal and the parity bit for a high frequency signal without changing the number of bits (eight bits) per sample.
The CRC for the field B does not take the entirety of 320-bit field B as a target and partially takes only data pertinent to predetermined bit positions as a target. To be specific, the field-B CRC takes, as a target, sound data that are distributed in ten locations every 16 bits. The sound data are only a total of 160 bits that are represented by bit numbers: b48 to b63, b112 to b127, b176 to b191, . . . , b560 to b575, and b624 to b639.
In
As above, in the master device 10, data transmission section is configured by the transmission conversion table 14 that converts a portion of the ADPCM sound data into a parity bit, the transmission packet generation unit 16 that generates a sound packet including the thus-converted sound data, and the wireless transmission circuit 17 that transmits the sound packet as a wireless signal to the slave device 20.
The slave device 20 is now described by reference to (B) in
The wireless reception circuit 21 acts as a reception circuit unit that receives by way of an antenna 21a the wireless signal output from the master device 10, demodulates the thus-received signal, and outputs the thus-demodulated signal as a sound packet to the received packet processing unit 22. The wireless reception circuit 21 measures a received strength indicator (RSSI) of the received sound packet, outputting the thus-measured indicator to received field strength processing.
The received packet processing unit 22 detects a sync error when a predetermined sync word is not acquired, a CRC error for the field A or the field B, and a parity error in sound data, sending the error to the receiving error processing unit 24 and extracting the sound data and outputting the thus-extracted sound data to the reception conversion table 23.
The reception conversion table 23 converts the 4-bit sound data received from the master device 10, outputting a conversion result. By reference to
In
During the conversion performed by the table R2 of the reception conversion table 23, sound data are exactly output without change unless a parity error occurs. In contrast, if occurrence of a parity error is identified (when the number of “is” in target bits is determined to be odd), sound data are replaced with mute data. In the embodiment, high frequency signal mute data are assigned “11,” and low frequency signal mute data are assigned “111111” or “000000.” However, the mute data are not limited to them, and another mute data can also be used. As above, in response to occurrence of a parity error, the reception conversion table 23 converts the sound data including the error with mute data, thereby preventing reproduced sound from being affected by the error.
In connection with high frequency data, the table R3 converts data including a parity error with mute data as does the table R2. In addition to this, in connection with low frequency data, the table R3 is configured so as to add one to four higher order bits of data that are free of an error, thereby replacing the data with sound data that will attenuate a sound. In the case of; for instance, “1001,” “1010,” and “1100,” they are converted into “1010,” “1011,” and “1101” by addition of one.
The table R4 is configured so as to replace all of the sound data with mute data regardless of occurrence of the parity error; in other words, the high frequency data with “11” and the low frequency data with “111111” or “000000.”
In (B) of
The reception conversion table switching unit 25 acts as a data conversion section (a receiving side processing unit) along with the reception conversion table 23 by switching among four tables (the tables R1 to R4) of the reception conversion table 23 in accordance with a command from the slave device 20 by way of the receiving error processing unit 24 or a received signal strength indicator signal originating from the received signal strength indicator processing unit 29. The reception conversion table switching unit 25 is now described by reference to
By means of changeover switches 25a and 25b, the reception conversion table switching unit 25 switches among the tables (R1 to R4) used in the reception conversion table 23. For instance, when conversion processing is not performed, the received packet processing unit 22 and the ADPCM decoding unit 26 are switched to the table R1. In the meantime, when parity processing is practiced, the received packet processing unit 22 and the ADPCM decoding unit 26 are switched to the table R2. In addition, when parity processing and attenuation processing are performed, the received packet processing unit 22 and the ADPCM decoding unit 26 are switched to the table R3.
The ADPCM decoding unit 26 shown in (B) of
The feedforward adaptive quantizer 26b calculates a quantized differential signal by use of all bits in the ADPCM data, outputting a calculation result. When the low frequency sound data are 48 kbps, a 6-bit ADPCM code input is output. The adder 26f adds the prediction signal calculated only from the core bits to the quantized differential signal calculated from all six bits, whereby a low frequency regenerative signal is output.
In the meantime, the essential requirement for the high frequency ADPCM decoder of the ADPCM decoding unit 26 is to perform processing conforming to the known G722 standard. The bitmask unit is not necessary, and all of the bits are input to the adaptive dequantizer. The high frequency ADPCM decoder is analogous to the low frequency ADPCM decoder except absence of the bitmask unit, and hence its detailed explanations are unnecessary.
The ADPCM decoding unit 26 combines the thus-decoded low frequency signal and the high frequency signal together by means of a receiving rectangular mirror filter, to thus generate a wideband sound signal. Even when a parity bit is transmitted without changing the number of bits per sample (eight bits), the receiving side uses the low frequency ADPCM data as they are without changing four core bits thereof to generate a prediction signal. The receiving side also processes the high frequency ADPCM data while taking them as two bits, so that deterioration of sound quality is small, and a conversation can be performed while a certain degree of sound quality is maintained.
In (B) of
The received electric field strength processing unit 29 functions as the received electric field strength level determination means that determines the change of the received electric field strength measured by the wireless reception circuit 21 and outputs the result of the determination to the reception conversion table switching unit 25. This determination is made in a manner such that, in the case where the master device 10 and the slave device 20 are spaced apart from each other, the received electric field strength is lowered, and if the received electric field strength is lower than a threshold value A (a first threshold value), the communication environment is inferior. Further, in the case where the master device 10 and the slave device 20 are close to each other, the communication environment becomes good and the received electric field strength is elevated. If the received electric field strength exceeds a threshold value B (a second threshold value), the communication environment becomes good. However, in determination, the threshold value B is set to be higher than the threshold value A.
The received electric field strength processing unit 29 outputs information on the communication environment to the reception conversion table switching unit 25, and the reception conversion table switching unit 25 selects the table R1 that does not perform the parity check if the communication environment is good. Further, if the communication environment is inferior, the reception conversion table switching unit 25 performs the parity check (the transmission side: table T2), the reception side selects any one of other tables (tables R2 to R4) to be sound-processed. The received electric field strength processing unit 29 performs the synchronization between the master device 10 and the conversion table by transferring the determination result information that is obtained by determining the change of the received electric field strength to the master device 10 using a control packet.
By setting the threshold value B to be larger than the threshold value A, switching is performed from the table R1 in which the parity check is not performed to the tables R2 to R4 in which the parity check is performed and the sound process is performed when the communication environment is deteriorated, and even if the communication environment becomes good thereafter, the switching is not performed at the same electric field strength as that switched by the reception conversion table 23. Since the parity check is stopped after the communication environment reaches a sufficiently good level, the reception conversion table 23 and the transmission conversion table 14 are prevented from being frequently switched.
A communication method of the cordless telephone as configured above according to the embodiment of the present invention will be described based on the drawings. First, in communication between the master device 10 and the slave device 20, a case where the communication environment is good and no reception error occurs will be described. In this case, it is assumed that the table T1 illustrated in
The sound signal from the sound input unit 11 is quantized by the PCM conversion unit 12, and one code is compressed into 8-bit sound data through ADPCM by the ADPCM encoding unit 13.
This 8-bit sound data is input to the table T1 of the transmission conversion table 14, and then the sound data having the same value as the input is output from the table T1 as the transmission data. The sound data output from the transmission conversion table 14 is included in the sound packet by the transmission packet generation unit 16, and is transmitted to the slave device 20 through the antenna 17a by the wireless transmission circuit 17 as the wireless signal.
In the slave device 20, the wireless signal from the master device 10 is received in the wireless reception circuit 21 through the antenna 21a. The wireless signal received in the wireless reception circuit 21 is demodulated and output to the received packet processing unit 22 as the sound packet.
The received packet processing unit 22 checks the occurrence of the reception error of the sound packet, extracts the 8-bit sound data included in the sound packet, and outputs the extracted sound data to the reception conversion table 23.
If the sound data is input to the table R1 of the reception conversion table 23, 8-bit sound data having the same value as the input is output from the table T1. The sound data output from the reception conversion table 23 is input to and expanded by the ADPCM decoding unit 26, converted into a sound signal by the PCM conversion unit 27, and is reproduced by the sound output unit 28.
In this case, since the master device 10 that is the transmission side transmits the sound to the slave device 20 as it is without processing all the 8-bit ADPCM sound data, high-quality sound can be transmitted.
Next, a case where the slave device 20 detects the reception error will be described.
If the received packet processing unit 22 of the slave device 20 detects the reception error such as a sync error or a CRC error, it transmits reception error information regarding the effect that the reception error has occurred to the master device 10 using a transmission function (not illustrated). The master device 10 can recognize that the communication environment is deteriorated through the notification of the reception error information. Accordingly, the transmission conversion table switching unit 15 performs switching of the connections of the transmission conversion table 14 to be applied between the ADPCM encoding unit 13 and the transmission packet generation unit 16 from the table T1 to the table T2. By doing so, the two lower order bits of the 8-bit sound data is converted into the parity bit (see
The slave device 20 instructs, in synchronization with the notification of the reception error to the master device 10, the reception conversion table switching unit 25 to perform switching of the reception conversion table 23 from the table R1 to the table R2. That is, the reception conversion table 23 is switched to the table R2 as a reception conversion table pertinent to the low frequency signal as shown in
Next, the influence on the sound packet in the related art and the influence on the sound of the sound packet according to the embodiment of the present invention will be described based on
In the sound packet in the related art as illustrated in
In the sound packet according to the embodiment, a parity bit is added for each 8-bit sound data, and thus the error can be detected every 8 bits. Accordingly, as illustrated in
The sound data output from the reception conversion table 23 is input to and expanded by the ADPCM decoding unit 26, converted into a sound signal by the PCM conversion unit 27, and is reproduced by the sound output unit 28. In reproducing the sound, since the two lower order bits are used as the parity bit while the data rate is maintained, the sound quality is somewhat deteriorated in comparison to the case where all the 8 bits are used as the sound data, but high sound quality can be secured in comparison to the case where sound data for one frame is processed in a state of the sync word error or the CRC error due to the deterioration of the communication environment.
Next, a method of switching transmission and reception conversion tables that is performed by the reception error processing unit 24 will be described based on
As shown in
As illustrated in
Next, the reception error processing unit 24 determines whether or not the reception conversion table 23 that is currently used is the table R1 (S125). If the reception conversion table 23 is the table R1, the reception error processing unit 24 determines whether or not the frame error counter value is equal to or larger than a threshold value C (S130). If the frame error counter value is equal to or larger than the threshold value C, the reception error processing unit 24 invalidates a flag of the table R1 (S135). That is, as illustrated in
Further, if it is determined that the reception conversion table 23 that is currently used is not the table R1 in S125 as illustrated in
Next, the received electric field strength processing unit 29 determines whether or not the reception conversion table 23 currently used is the table R1 (S160). If the reception conversion table 23 is the table R1, the received electric field strength processing unit 29 determines whether or not the received electric field strength measured by the wireless reception circuit 21 is lower than the threshold value A (S170). If the received electric field strength is lower than the threshold value A, the received electric field strength processing unit 29 invalidates the flag of the table R1 (S180). That is, as illustrated in
Further, if it is determined that the reception conversion table 23 currently used is not the table R1 in S160 shown in
Next, as illustrated in
Next, the reception error processing unit 24 determines whether or not the flag of the table R1 is valid (S240). If the flag of the table R1 is valid, it means that the frame error rate is low and the communication environment is good, and thus regardless of the count value of the sound data error counter C2, the side of the master device 10 is switched to the table T1 and the side of the slave device 20 proceeds to S300 to be switched to the table R1.
Next, the reception error processing unit 24 determines whether or not the sound data error counter C2 is within a range of the level B (S250). This level B is in a range where the frame system error rate has been elevated, but the sound data error rate is determined to be still low. Accordingly, in order to perform the parity check of the sound data, the reception conversion table 23 validates the flag of the table R2 that selects the table R2 (S260), and then proceeds to S300.
If the sound data error counter C2 is not within the range of the level B, the reception error processing unit 24 then determines whether or not the sound data error counter C2 is within the range of the level C (S270). This level C is in a range where it is determined that the sound data error rate has been gradually elevated. Accordingly, the reception error processing unit 24 validates the flag of the table R3, which selects the table R3 that not only replaces the sound data with the mute data in the case where the parity error of the sound data has occurred but also replaces the sound data with the sound data that mutes the high frequency sound and attenuates the low frequency sound even in the case where the parity error has not occurred (S280), and then proceeds to S300.
If the sound data error counter C2 is not within the range of the level C, it means that the sound data error counter C2 is within the level D, and the reception error processing unit 24 validates the flag of the table R4. This level D is in the range where the communication environment is worst. Accordingly, the table R4 which replaces all the sound data with the mute data is selected in the reception conversion table 23 (S290).
In S300, the reception error processing unit 24 performs the switching of the reception conversion table 23 according to the flag. For example, if the flag of the table R1 is valid, the reception error processing unit 24 instructs the reception conversion table switching unit 25 to perform switching of the reception conversion table 23 to the table R1. Further, the reception error processing unit 24 transmits a control packet to the master device 10 so that the master device 10 switches the transmission conversion table 14 to the table T1.
Further, if any one of flags of the tables R2 to R4 is valid, the reception error processing unit 24 instructs the reception conversion table switching unit 25 to perform switching of the reception conversion table 23 to any one of the tables R2 to R4. Further, the reception error processing unit 24 notifies the master device 10 of the error information, and instructs the master device 10 to perform switching of the transmission conversion table 14 to the table T2.
As described above, since the reception error processing unit 24 determines the increase/decrease of the error rate by adding the frame system error, such as the sync word error, the A-field CRC error, or the B-field CRC error, to the parity error of the sound data, it can cope with the occurrence of the error with higher accuracy.
Further, if it is determined that the error has occurred by the parity bit value of the sound data, the reception error processing unit 24 makes the sound data error counter C2 count up, while if it is determined that the error has not occurred, the reception error processing unit 24 makes the sound data error counter C2 count down. By increasing/decreasing the error rate by the sound data error counter C2, the reception error processing unit 24 can cope with the communication environment in which the reception level is deteriorated or becomes good.
Further, in the table R2 of the reception conversion table 23, the sound data in which the parity error has occurred is converted into the mute data. However, a click noise may occur depending on the sound data. Accordingly, by performing switching of the reception conversion table 23 to the table R3, the sound data for which the error does not occur in the same frame is converted so that the sound is attenuated, and thus the influence of the click noise can be suppressed.
Further, in the case where the communication environment is further deteriorated, by performing switching of the reception conversion table 23, which converts the whole sound data in the same frame into the mute data, to the table R4, the click noise can be suppressed more effectively.
As described above, the embodiment of the present invention has been described thus far, but the present invention is not limited to the embodiment. For instance, in the embodiment, the high frequency signal is muted by means of a parity error for a high frequency signal, and the low frequency signal is muted by means of a parity error for a low frequency signal. However, both the high frequency signal and the low frequency signal can be muted by means of either of the two parity errors.
In an example shown in
In the example shown in
In the example shown in
In the examples shown in
In the example shown in
In the example shown in
In the example shown in
Third to fifth signal processing corresponds to the following processing in the example shown in
In the embodiment, lower order bits of sound data are employed as error detection bits; namely, parity bits. However, the least significant bit can also be generated by means of another error detection method.
In the above embodiment, an error detection code including a total of two bits; namely, the high frequency signal parity bit P1 and the low frequency signal parity bit P2, is generated, and the error detection codes are assigned to two lower order bits of the sound data. However, in another embodiment, only one parity bit of entire data that include both a high frequency signal and a low frequency signal is assigned to the error detection code, and both the high frequency signal and the low frequency signal can also be muted in accordance with the parity error code. Specifically, there may be generated a parity bit (the third parity bit: P3) that reverses bits in accordance with the number of “1s” in a series of data including both high frequency ADPCM data and low frequency ADPCM data, and a least significant bit of the low frequency ADPCM data can be also replaced with the third parity bit P3.
In the embodiment shown in
Moreover, in the embodiment, when the sound data error counter C2 shows “level C,” or a threshold value which is more than one to less than two, “mute” processing is performed for the high frequency sound when the high frequency signal parity bit P1 represents “NG.” Further, when the sound data error counter C2 represents “level C,” “attenuation” processing is performed for the low frequency sound regardless of whether the parity bit P3 is normal, that is, “OK,” or “NG.”
Furthermore, in the example, when the sound data error counter C2 shows a threshold value of more than two, or deterioration proceeding up to “level D,” both the high frequency signal and the low frequency signal are muted regardless of whether the parity bit P3 represents “OK” or “NG.”
Since the system that is based on a wideband fixed-size sound packet can enhance accuracy in error detection while assuring a certain degree of sound quality when a communication environment becomes worse, the present invention is preferable for a wireless communication device and a communication terminal that practice a communication by means of a wideband sound packet.
The present application is a continuation-in-part of international patent application No. PCT/JP2013/077016 filed on Sep. 27, 2013 claiming the priority of Japanese Patent Application No. 2012-215890 filed on Sep. 28, 2012, the contents of which are incorporated herein by reference in its entirety.
Number | Date | Country | Kind |
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2012-215890 | Sep 2012 | JP | national |
Number | Date | Country | |
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Parent | PCT/JP2013/077016 | Sep 2013 | US |
Child | 14668198 | US |