JP2001094507A - Pseudo-backgroundnoise generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pseudo-backgroundnoise generating method which generates a pseudo-backgroundnoise giving no feeling of physical disorder to a listener irrelevantly to intermittently sent backgroundnoise information. SOLUTION: By the pseudo-backgroundnoise generating method at the time of no telephone call through a moving object communication device, pseudo- backgroundnoise is generated on a base station side on the basis of received encoded energy, an encoded reflection coefficient which is calculated by a reflection coefficient calculation part 11 and smoothed, and the residual code of white noise stored in a memory of a residual code file readout part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of generating pseudo background noise inserted in a silent section during a call used in a mobile communication device, and more particularly, to reducing the power consumption of a mobile station. The present invention relates to a method for generating pseudo background noise when controlling the transmission output of voice information to an off state in a silent section during a call.

[0002]

2. Description of the Related Art In order to prolong the life of a battery in a mobile station (portable terminal) of a mobile communication device, a so-called VOX (Voice O) is used.
There is known an audio signal transmission method called "perated transmitter" control.

In VOX control, when a mobile station detects silence during a call, a postamble signal (hereinafter referred to as P
By transmitting an OST signal), the audio signal output of the next frame is announced in advance. Further, when a sound is detected in the silent state, a preamble signal (hereinafter, also referred to as a PRE signal) is transmitted, thereby notifying that the transmission output of the audio signal is on.

[0004] On the other hand, during a silent period, information on mobile station background noise is included in the POST signal in order to enable the base station to generate pseudo background noise. The information on the mobile station background noise included in the POST signal is a signal obtained by coding the mobile station background noise in accordance with the normal speech coding rules (standard rules of the Radio System Development Center). The mobile station periodically (up to once per second) POS during the silent period
By transmitting the T signal, it is possible to update pseudo background noise generated on the base station side.

[0005] During the silent period, the mobile station has the maximum period,
The background noise information is transmitted only once a second. Therefore, assuming that voice information is transmitted 50 times per second during a voiced period, information of background noise can be obtained only once per second during a silent period at the base station.
This corresponds to only 2% of the audio information during the sound period. However, it is impossible to reproduce actual background noise with this 2% information. So, at the base station,
% Information must be used to insert the pseudo background noise.

From the viewpoint that the pseudo background noise to be inserted is easy to hear, the following (a) to
It is desired to satisfy the point (c).

A) The pseudo background noise must not be disturbing to the receiver.

B) When entering a silent period from a sound period,
When the pseudo background noise is updated in each cycle during the same silence period, it is updated smoothly.

C) The sound quality of the pseudo background noise generated in each cycle during the same silent period does not significantly differ.

In mobile communication, a digital audio signal obtained by converting an analog audio signal into a PCM is converted into a VSELP code (vector sum excitation (residual) linear prediction code (Vector-Sum E) based on the standard rules of the Radio System Development Center.
xcited Linear Predictive Coding)). In order to perform the VSELP encoding, parameters of frame energy and reflection coefficient are calculated based on the digital audio signal, the calculated parameters are quantized, and the code values corresponding to the quantized values are arranged in an order based on the above-mentioned rules. Then, a transmission code is formed and transmitted. In this case,
As for the reflection coefficient, the parameter of the reflection coefficient is -1.
The value of the reflection coefficient is quantized with reference to the quantization table defined by the above-mentioned rules. The frame energy parameter calculated for the frame energy is also quantized. In this specification, a quantization value of a parameter of a reflection coefficient is referred to as a reflection coefficient value before encoding (or a reflection coefficient value before encoding), and a code word corresponding to the quantization value of the reflection coefficient is encoded. The codeword corresponding to the quantized frame energy parameter value is referred to as a coded frame energy value (or coded frame energy value). In this specification, description will be made assuming that background noise information including an encoded frame energy value and an encoded reflection coefficient value is included in a postamble signal.

With respect to the insertion of background noise in a silent section, for example, a method described in Japanese Patent Application Laid-Open No. 5-122165 is known. The configurations of the transmitting side and the receiving side of the mobile station to which this method is applied are as shown in FIGS. 9 (a) and 9 (b). On the transmitting side shown in FIG.
When the voice changes from voiced to silence, the postamble signal is sent from the postamble generation unit 45 to the data switching unit 4.
7 to the transmission unit 47. Following the postamble signal sent from the data switching unit 47 to the transmission unit, the coded frame power (frame energy value) of the speech output from the high-efficiency speech encoder 42, the prediction coefficient, etc. (This is a code processed in order to send the coefficient to the subsequent process).

On the receiving side shown in FIG. 9B, the background frame including the coded frame power and the prediction coefficient of the background noise voice transmitted from the high efficiency voice coder 42 on the transmitting side in the silent section is provided. The noise information is taken into the storage unit 63 and stored. After the background noise information is read from the storage unit 63, the background noise information is input to a background noise synthesizing unit 65 together with a residual signal generated from a random residual generating unit 64, and is synthesized there to generate background noise.

[0013]

However, in the above-described conventional mobile communication device, the method of generating pseudo background noise uses background noise information from a high-efficiency speech coder at random on both the transmitting side and the receiving side. To combine with the residual,
It is unclear whether or not noise that is easy to hear is generated.

The reason is that the frame energy value of the voice determines the sound pressure level of the voice, and the reflection coefficient value determines the pitch (frequency) of the voice. Is determined. However, since the background noise information is transmitted only once per second at maximum during the silent period, if the dispersion between the frame energies and the prediction coefficients is large for each reception, the magnitude and frequency of the generated pseudo background noise are reduced. Variation is large. If the noise having a large variation changes every 1 second at the maximum, it is considered that there is no naturalness and it is difficult to hear.

Furthermore, since the generation of a random residual each time the background noise is generated increases the processing on the base station side, the efficiency is not very high.

An object of the present invention is to provide a pseudo-background noise generation method capable of generating pseudo-background noise that does not cause any discomfort to a receiver regardless of background noise information transmitted intermittently.

[0017]

A pseudo background noise generating method according to the present invention is a method for generating a pseudo background noise during a non-communication in a mobile communication device, wherein a received coded energy value and a coded reflection coefficient value are provided in advance. The base station generates a pseudo background noise signal based on the residual code of the white noise.

According to the pseudo background noise generation method of the present invention,
A pseudo background noise signal is generated at the base station based on the received encoded energy value, encoded reflection coefficient value, and residual code of white noise provided in advance. In this generation, since it is generated based on the residual code of the white noise provided in advance, the processing on the base station side can be reduced.

According to the pseudo-background noise generation method of the present invention, the residual code of white noise is stored in advance as a file, and the stored residual code of white noise is repeatedly read out during a silent period to read out the pseudo-background noise signal. It is characterized by generating.

According to the pseudo background noise generation method of the present invention,
The residual code of the white noise is stored in advance as a file, and the stored residual code of the white noise is sequentially and repeatedly read out during a silent period to generate a pseudo background noise signal. The processing on the base station side is reduced.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

FIGS. 1 and 2 are a schematic configuration diagram on the mobile station side and a schematic configuration diagram on the base station side of a mobile communication device to which the pseudo background noise signal generation method of the present invention is applied, respectively. Both schematic diagrams mainly show the parts related to the method of the present invention.

The mobile station shown in FIG. 1 will be described. The digital audio signal converted into digital data is supplied to the encoding unit 1, and the digital audio signal is encoded by the encoding unit 2. Further, the digital audio signal is supplied to the sound / silence detecting unit 3, and when the sound / silence detecting unit 3 detects that the sound signal is maintained in the sound state, that is, the sound / silence detection is performed. If the output of the unit 3 is {voiced → voiced}, the output speech code from the encoding unit 2 is transmitted via the transmission line encoder 6.

When the sound / silence detecting unit 3 detects that the voice signal has changed from a sound state to a silent state, that is, if the output of the sound / silence detecting unit 3 is {sound → no sound}, the hangover is performed. The section is started, and the speech code is transmitted via the transmission path encoder 6. When the sound / silence detecting unit 3 detects that the sound signal is kept in a silent state, that is, when the output of the sound / silence detecting unit 3 is {silence → silence}, the period between the hangover and the period POST to
Stop transmitting voice codes except when transmitting signals.

At this time, a short burst signal of minimum information required for synchronization is transmitted. The (S−N) frame (S ≧ N) after the start of the hangover section (length S frame) sends the speech code to the transmission path encoder 6 as it is, but the remaining N frames are the reflection signals before encoding the speech signal. The numerical values are smoothed in cooperation with the parameter smoothing unit 4 and the parameter storage unit 5, and the smoothed reflection coefficient values are replaced with the reflection coefficient values before smoothing. The permuted reflection coefficient value is encoded and sent to the transmission path encoder 6 together with other codes.

On the other hand, when the POST signal is transmitted periodically after the end of the hangover section, the frame energy value and the reflection coefficient value of the audio signal are smoothed and averaged in cooperation with the parameter smoothing section 4 and the parameter storage section 5. After processing, it is sent to the transmission path encoder 6 in addition to the POST signal together with other codes.

Further, the frame energy and the reflection coefficient value output from the parameter smoothing unit 4 are stored in the parameter storage unit 5 for the above-mentioned smoothing and averaging processing of the frame energy value and the reflection coefficient value at the next transmission. send. If the output of the sound / silence detecting unit 3 is {silence → voice}, a PRE signal is sent to the transmission line encoder 6 to notify that the transmission of the audio signal is started.

Here, the operation of the multiplexer 61 will be described. If {sound → voice} is detected based on the audio signal, the multiplexer 61 generates a code by the {voice → voice} detection signal. The speech code coded by the coding unit 2 is subjected to transmission path encoding in a transmission path encoder 6 and transmitted. When {sound → no sound} is detected based on the audio signal, the multiplexer 61 is switched by the {sound → no sound} detection signal, and the smoothed encoded reflection coefficient value and the averaged code are output. The encoded frame energy value is transmitted along with other codes in the transmission path encoder 6 and transmitted. When {silence → voice} is detected based on the voice signal, the multiplexer 61 is switched by the {voice → voice} detection signal, and the voice code coded by the coding unit 2 is transmitted through the transmission line. The encoder 6 performs transmission path encoding and transmits the encoded data.

More details will be described later based on the operation flow of the mobile station transmitting side during the silent period shown in FIGS. 3 and 4.

Next, the base station shown in FIG. 2 will be described. The received signal is supplied to a separation circuit 9, and the separation circuit 9 extracts a speech code and voice / non-voice information. Separation circuit 9
If there is an output of only an audio signal from, the switching unit 14 outputs an audio code. If a POST signal is output from the separation circuit 9, the speech code is stored in the storage unit 10, and pseudo background noise is generated in a silent section until the next POST signal or PRE signal comes.

To generate the pseudo background noise, a reflection coefficient value smoothed by the reflection coefficient value calculation section 11 is calculated, and at the same time, a residual code file reading section having a memory in which the white noise residual code is stored in advance as a file. The residual code is read out by 12 and sent to the pseudo background noise synthesizer 13 together with other codes. The switching section during the silent section outputs the background noise code from the pseudo background noise synthesis section. If there is an output of the PRE signal from the separation circuit 9, the silent section ends, and the switching unit 14 outputs a speech code.

More details will be described later based on the operation flow of the base station during the silent period shown in FIG.

Next, the operation on the mobile station side will be described with reference to FIGS.
This will be described based on the flow chart shown in FIG.

On the mobile station side, it is checked whether there is sound or no sound (step S1), and the voice signal is encoded and transmitted until it is determined that there is no sound (step S1).
2). If it is determined in step S1 that there is no sound, a hangover section is started (step S3),
The encoded frame energy value and the reflection coefficient value before encoding are stored (step S4). Usually, even if a silent state is detected from a voiced state, the transmission of the voice code is not immediately interrupted, but a silent signal of several frames is encoded as a voice signal as it is so that the ending in the voiced state is not cut off. And sent. This section is called a hangover section. The length of the hangover section is defined as an S frame.
Also, it is assumed that a POST signal is transmitted every 50 frames during a silent section.

Subsequent to step S4, it is checked whether or not (SN) frames have elapsed (step S5). If it is determined that the frame has not elapsed, the silent signal is directly encoded as a speech signal and transmitted. (Step S
6). N is a natural number and N ≦ S. When it is determined in step S5 that (SN) frames have elapsed, the reflection coefficient value before encoding stored in step S4 is read and smoothed (step S7).
The smoothed reflection coefficient value before encoding is replaced with the reflection coefficient value before smoothing and before encoding, and the replaced reflection coefficient value is encoded and transmitted together with other codes ( Step S8). Subsequent to step S8, the process is executed again from step S4 until the S frame has elapsed (step S8).
9).

When it is determined in step S9 that the S frame has elapsed, it is subsequently checked whether or not silence continues even after the hangover section has elapsed (step S10), and it is determined that silence has not continued. If so, the audio signal is encoded and transmitted following step S10 (step S11). If it is determined in step S10 that silence continues, a smoothing process of the coded frame energy value and a smoothing process of the reflection coefficient value before coding are performed (step S12), and the smoothed code is obtained. The encoded frame energy value is replaced with the encoded frame energy value before smoothing, and the smoothed reflection coefficient value before encoding is replaced with the reflection coefficient value before smoothing, and the smoothed and replaced code is replaced. The reflection coefficient value before conversion is encoded (step S13).

The audio signal coded in step S13 is transmitted together with the first postamble signal (step S14), and it is checked whether or not the next frame is also silent (step S15). The preamble signal is transmitted (step S16), and the process is executed from step S1.

If it is determined in step S15 that there is no sound, it is checked whether (50-M) frames have elapsed since the immediately preceding postamble signal was transmitted (step S17). M is a natural number and M ≦ S (S
Is the number of frames in the hangover section). Step S
If it is determined in step 17 that the (50-M) frame has not elapsed, a short burst signal is transmitted after step S17 to synchronize, and the process is executed again from step S15 (step S18).

If it is determined in step S17 that (50-M) frames have elapsed, the encoded frame energy value and the reflection coefficient value before encoding are stored (step S19). Subsequent to step S19, it is checked whether or not 50 frames have elapsed since the transmission of the immediately preceding postamble signal (step S20).
If it is determined that 0 frames have not elapsed, a short burst signal is transmitted following step S20 to synchronize, and the process is executed again from step S15 (step S21).

If it is determined in step S20 that 50 frames have elapsed, smoothing processing of the coded frame energy value and smoothing processing of the reflection coefficient value before coding are performed (step S22), and the smoothing is performed. The coded frame energy value is replaced with the coded frame energy value before smoothing, and the smoothed reflection coefficient value before coding is replaced with the reflection coefficient value before smoothing, smoothed and replaced. The reflection coefficient value before encoding is encoded (step S
23), the signal coded in step S23 is transmitted together with another code together with the next postamble signal, and is executed again from step S15 (step S24).

Next, the smoothing and averaging processing will be described in detail. First, prior to the description of the smoothing and averaging processing, a VSELP code used in mobile communication for voice encoding and decoding will be described.

One VSELP code has audio information of one audio frame. The length of one voice frame is 160 samples (20 msec), and there are 50 frames per second.
Furthermore, one voice frame has four subframes (5 msec)
Divided into Table 1 below is a list of parameter codes for the VSELP code, where R is the frame energy, soft
in is the soft interpolation bit, ri is the reflection coefficient, Lj is the lag of the jth subframe, Ij is the residual of the jth subframe, and gj is [GS, PO] of the jth subframe. .

[0043]

[Table 1]

In the following, k is the background noise update cycle number in the same-silence period, and t is the number of background noise frames during each cycle. Equation (1) is the sign of the smoothed background noise transmitted by the mobile station in the k-th period during the same-silence period,
It is shown by equation (3). Equation (2) is the sign of the background noise of the t-th frame generated after the k-th cycle is received by the base station during the same-silence period, and is represented by equation (4).

[0045]

(Equation 1)

[0046]

(Equation 2)

[0047]

(Equation 3)

[0048]

(Equation 4)

Here, i = 1 to 10 and j = 0 to 3. k and t vary depending on the length of the silent section and the length of the transmission cycle of the mobile station. When the silent period is 5 seconds and the transmission cycle of the mobile station is 1 second, k = 1 to 5 and t = 1 to 50. FIG. 6 shows an operation sequence of an example of the transmitting side of the mobile station. Hereinafter, the transmission in the k-th cycle is also referred to as a k-th post signal transmission.

The example shown in FIG. 6 has a smooth section of N frames before the end of the sound section and a lapse of the hangover section of the S frame, a silent section continues after the hangover section, and 1 follows the hangover section. The first PO in the frame
An example is shown in which the ST signal is transmitted, the second POST signal is transmitted at the 50th frame after the first POST signal is transmitted, and the same applies to the voiced section after the k times POST signal transmission. .

Next, smoothing of the reflection coefficient value before encoding and correction of the encoded reflection coefficient value in the hangover section on the mobile station side will be described. The smoothing of the reflection coefficient value before encoding and the correction of the encoded reflection coefficient value in the hangover section on the mobile station side are the smoothing and correction in the section a in FIG. In order to smoothly continue the frequency distribution of the speech in the hangover section and the frequency distribution of the pseudo background noise in the silence section, the reflection coefficient value before encoding is smoothed in the hangover section.

After the silence signal of the (S-N) frame after the start of the hangover section is transmitted as an audio signal, the remaining N
For the (N ≦ S) frame, the reflection coefficient value before encoding is subjected to smoothing processing as shown in the following equation (5), and the smoothed reflection coefficient value before encoding is smoothed. Is replaced with the reflection coefficient value before being performed.

[0053]

(Equation 5)

In the equation (5), n = (N-1) -0, i
= 1 to 10. ri (Sn) is the i-th reflection coefficient value of the (Sn) -th frame before encoding, and ri (S-n-
1) is the ith reflection coefficient value before encoding of the frame one frame before (Sn).

In the smoothing by the above equation (5), the reflection coefficient values of two consecutive frames are smoothed, and the smoothed reflection coefficient value is replaced with the reflection coefficient value before smoothing. These processes are processes of the reflection coefficient values before encoding, and the smoothed and replaced reflection coefficient values are encoded (N-
1) The frame is transmitted. In this case, the reflection coefficient values of two or more consecutive frames before encoding may be smoothed.

Next, for the last frame ri (S) of the hangover section, the reflection coefficient value before encoding is similarly smoothed, and the smoothed reflection coefficient value before encoding is obtained before the smoothing. The smoothed and replaced reflection coefficient values are encoded with the reflection coefficients. Only the first reflection coefficient value r1 (S) in the encoded reflection coefficient value is subjected to processing as shown in the following equation (6).

[0057]

(Equation 6)

That is, the first of the encoded reflection coefficient values
Only for the reflection coefficient value r1 (S), rl (S) = rl (S)
The correction of ± 1 or ± 2 is performed, and the coded reflection coefficient values other than the coded first reflection coefficient value are not corrected, and the corrected first reflection coefficient value and the uncorrected second reflection coefficient value are not corrected. To the tenth reflection coefficient value are transmitted.

In equation (5), ri (S−n) is a reflection coefficient value before encoding and is a decimal value (−1 <ri (S−n) <1).
Where rl (S) in the equation (6) is the encoded first reflection coefficient value (0 ≦ rl (S) ≦ 31). Here, the first reflection coefficient value is limited to 0 ≦ rl (S) ≦ 31 because it is encoded into 5 bits. Further, the reason for the processing of equation (6) will be briefly described. The reflection coefficient value has audio frequency information. In particular, the first reflection coefficient value has the largest amount of information. The smaller the code word value, the lower the voice frequency, and the larger the code word value, the higher the voice frequency. Since the frequency is too low or too high, it is difficult to hear. Therefore, the signal when transmitting the POST signal in each silence period described later and the coded first reflection of the last frame of the hangover period described here. The coefficient value is corrected as in equation (6).

Next, the smoothing of the coded frame energy value of the mobile station during the silent period will be described.

The smoothing of the coded frame energy value of the mobile station during the silent period is performed, for example, in the period d in FIG.
And averaging of the encoded frame energy value in the section exemplified in FIG. K-th PO at mobile station during silent period
Let mk be the voice frame number when transmitting the ST signal. The encoded frame energy value to be transmitted together with the k-th POST signal is displayed by equation (7). In order to calculate the encoded frame energy value represented by the equation (7), first, m
Average value of encoded frame energy values from frame k to frame (mk-M-1) preceding M frame ΔR
(K) Find AVR に よ っ て by equation (8).

[0062]

(Equation 7)

[0063]

(Equation 8)

When the k-th POST signal is transmitted, the average value {R (k) AVR} of the coded frame energy value is further reduced by the ｛average value R (1) of the coded frame energy value calculated by the equation (8). ) Take the average with AVR ｛and take this average value as ｛R '
(K) AVR｝. The value in this case is obtained by equation (9). The average value of the coded frame energy value at the time of transmitting the first POST signal is ｛R ′ (1) AVR =
(2 · R (1) AVR / 2) = R (1) AVR｝

[0065]

(Equation 9)

Average value of encoded frame energy value 値 R '
(k) If the value obtained by subtracting p (k) shown in Table 2 from AVR｝ is expressed by equation (10), the value can be obtained by the calculation of equation (11). If the value obtained by the equation (11) is less than 0, the value of the equation (11) is set to 0.

[0067]

[Table 2]

[0068]

(Equation 10)

[0069]

[Equation 11]

Subsequently, using the previously transmitted encoded frame energy value expressed by the equation (12), the next encoded frame energy value transmitted by the equation (13) is corrected.

[0071]

(Equation 12)

[0072]

(Equation 13)

First, the difference between the value of the expression (12) and the value of the expression (13) is determined by the expression (14) in order to correct the energy value of the encoded frame to be transmitted.

[0074]

[Equation 14]

The difference ΔR obtained by the calculation of the equation (14)
When the absolute value of (k) is larger than 1, the transmitted energy value shown in the above equation (7) is obtained by the equation (15).

[0076]

(Equation 15)

The difference ΔR obtained by the calculation of the equation (14)
When the absolute value of (k) does not exceed 1, the transmitted energy value shown in the above equation (7) is obtained by the equation (16).

[0078]

(Equation 16)

The first POST is performed by the calculation of the equation (14).
When calculating the coded frame energy value to be transmitted together with the signal, that is, when calculating ΔR (1) when (k = 1), the code at that time is used as an initial value of the coded frame energy value represented by Expression (17). Frame energy value =
The average value R (k) AVR 用 い る is used. That is, the value of the equation (18) is used.

[0080]

[Equation 17]

[0081]

(Equation 18)

The average value of the coded frame energy values calculated as described above is replaced with the coded frame energy value in the coded voice signal data, and the coded voice signal data with this replacement is transmitted.

The above-described smoothing processing of the frame energy value is all processing of the coded frame energy value. As is apparent from the above equations (9), (11), (14), (15), and (16), in this example, the average of the encoded frame energy values is calculated. The calculated coded frame energy value of the coded average value is corrected by the coded frame energy value in the immediately preceding transmission, and the energy value transmitted each time during the same-silence period has less variation. As a result, the pseudo background noise becomes easier to hear. In a normal state, the average value of the coded frame energy value calculated and transmitted at the beginning of the silent section does not exceed the average value.
And it does not exceed the average value of the energy value of the coded frame transmitted immediately before. Through the above processing, the energy value transmitted each time during the same-silence period becomes less scattered and attenuates gradually, so that the pseudo background noise becomes easier to hear.

Next, the smoothing of the reflection coefficient value of the mobile station during the silent section after the end of the hangover section will be described.

In this case, the reflection coefficient value is smoothed in, for example, sections b and c in FIG. 7, and as in the processing of the coded frame energy value of the mobile station in the silent section, the processing is performed during the silent section. K-th POST at mobile station
The voice frame number when transmitting a signal is mk.

In order to obtain a reflection coefficient value before encoding, which is expressed by the following equation (19), when transmitting the k-th POST signal, first, M frames are traced back from mk frames (m
The average value of the reflection coefficient values ri (i = 1 to 10) before encoding represented by the expression (20) up to (k−M−1) frames is calculated as (21)
Determined by the formula. Here, M is a natural number of M ≦ S.

[0087]

[Equation 19]

[0088]

(Equation 20)

[0089]

(Equation 21)

The average value of the reflection coefficient value before coding ｛ri
(K) Using the AVR｝ and the reflection coefficient value before encoding shown in the equation (22) transmitted previously, the k-th P
A transmission value represented by the above equation (19) when transmitting with the OST signal is obtained.

[0091]

(Equation 22)

[0092]

(Equation 23)

The initial value of the expression (22) used when calculating the reflection coefficient value before encoding shown in the expression (24) transmitted with the first POST signal by the expression (23) is the last code in the hangover section. Reflection coefficient ri (m1-
Use 1). That is, it is as shown in equation (25).

[0094]

(Equation 24)

[0095]

(Equation 25)

How to determine coefficients a and b (a and b are predetermined positive integers) in equation (23) will be described. If the coefficient b is set to be somewhat larger than the coefficient a, the prior transmission value will be emphasized, and thus the dispersion of the value of the expression (23), that is, the reflection coefficient value before encoding is reduced. The reflection coefficient value before encoding smoothed by the above processing is replaced with the reflection coefficient value before encoding.

Next, only the value of the encoded first reflection coefficient value represented by Expression (27) in the encoded reflection coefficient value represented by Expression (26) is converted into the following Expression (28). Correct as shown.

[0098]

(Equation 26)

[0099]

[Equation 27]

[0100]

[Equation 28]

The reflection coefficient value (ri (mk−
h)) and the reflection coefficient values in Expression (23) (reflection coefficient values shown in Expression (29) below) are the reflection coefficient values before encoding and are decimal values, but the reflection coefficient values in Expression (28) Equation (30) is an encoded reflection coefficient value, which is a value in the range shown in equation (31).
This range is because the first reflection coefficient value is encoded into 5 bits.

[0102]

(Equation 29)

[0103]

[Equation 30]

[0104]

(Equation 31)

Here, the processing of the reflection coefficient value during the silent section after the hangover period has elapsed will be summarized. As for the reflection coefficient value transmitted together with the k-th POST signal, first, the reflection coefficient value before encoding of each frame M frames before the k-th POST signal is averaged. (K) obtained in the same manner as the averaged reflection coefficient value before encoding.
-1) The reflection coefficient value before encoding of each frame M frames before the POST signal is averaged. The averaged reflection coefficient values before encoding are weighted and averaged. The weighted averaged reflection coefficient value before encoding (for example, k-th PO
For the reflection coefficient value transmitted with the ST signal)
(For example, the k-th POS
(For the reflection coefficient value transmitted with the T signal), and the replaced reflection coefficient value is encoded.

The encoded first reflection coefficient value in the encoded reflection coefficient value is corrected by the equation (28) and replaced with the encoded reflection coefficient value before being corrected. No correction processing is performed on the encoded second to tenth reflection coefficient values. This is because the first reflection coefficient value occupies the largest weight among other reflection coefficient values.

The first POST signal is transmitted in the first frame, that is, in the (S + 1) frame following the end of the hangover period. In this case, M frames are averaged including the reflection coefficient values of the frames in the overhang section before being encoded. When smoothing (2
As shown in Expression 5), the last reflection coefficient value in the hangover section is used as an initial value.

Next, generation of pseudo background noise by the base station will be described with reference to the flowchart of FIG.

When receiving a signal, the base station checks whether or not a voice signal has been received (step S3).
0), if it is determined that the signal is an audio signal, step S30
Then, after an audio signal is output, the process is executed again from step S30 (step S31). If it is determined in step S30 that the signal is not an audio signal, the type of signal is determined (step S32). If it is determined in step S32 that the signal is a PRE signal, an audio signal is output, and the process is executed again from step S30 (step S33).

If it is determined in step S32 that the received signal is a POST signal, an audio signal is stored (step S34), and a reflection coefficient value is obtained (step S3).
5). If it is determined in step S32 that the signal is a short burst signal, step S34 is skipped and step S35 is performed.

After step S35, the residual code of the white noise previously stored in the memory as a file is read out (step S36), and the pseudo background noise signal is synthesized (step S37), and the pseudo background noise signal is obtained. Is output, the process is executed again from step S30 (step S3).
8).

Next, generation of pseudo background noise in the base station will be described in detail.

During the silent period, the base station receives the k-th POST signal, and during the interval until the next POST signal or PRE signal arrives, the base station is expressed by equation (32) of the background noise input together with the POST signal. VSELP code (= (3) equation)
And the VSELP code (= Equation (4)) of pseudo-background noise expressed by equation (33) using the residual code of white noise prepared as a file in the memory in advance.

[0114]

(Equation 32)

[0115]

[Equation 33]

In order to give the pseudo background noise the characteristics of the actual background noise, the energy value of the received background noise represented by equation (36) is used as the frame energy value represented by equation (34). Also, the reflection coefficient value indicated by the equation (35) includes the reflection coefficient value indicated by the received equation (37) and the reflection coefficient value (48) of the last frame calculated after the last reception by the base station. Is calculated using In order to make the pseudo background noise have randomness, the residual code of the VSELP code represented by the expression (39) generated by white noise is used as the residual code represented by the expression (38). (4
The gain displayed by equation (0) is a constant, and the lag displayed by equation (41) is zero.

[0117]

(Equation 34)

[0118]

(Equation 35)

[0119]

[Equation 36]

[0120]

(37)

[0121]

(38)

[0122]

[Equation 39]

[0123]

(Equation 40)

[0124]

[Equation 41]

If the above relationship is shown, equation (42) and (4
Equations 4) to (47) are obtained. Note that sofin is set to a value {1} as shown in Expression (43).

[0126]

(Equation 42)

[0127]

[Equation 43]

[0128]

[Equation 44]

[0129]

[Equation 45]

[0130]

[Equation 46]

[0131]

[Equation 47]

(T / k) in the above equations indicates the t-th pseudo background noise frame generated by the base station after the k-th reception. The expression (48) in the expression (44) is the reflection coefficient value of the last frame calculated after the last reception by the base station.
The reason why (50-t) is indicated in the equation (44) is that if the transmission cycle of the mobile station is once per second, the base station needs to generate 50 frames of pseudo noise. After the base station receives the first POST signal, (4)
The initial value displayed in equation (50) used when calculating equation 9) is the reflection coefficient value of the last frame in the hangover section. That is, it is as shown in equation (51).

[0133]

[Equation 48]

[0134]

[Equation 49]

[0135]

[Equation 50]

[0136]

(Equation 51)

U in the expression (47) is defined by the standard of the Radio System Development Center [GS, P
O] The index number of the code book. Hereinafter, how to determine U will be described. The gain γ for determining the loudness of the sound of the weighting synthesizer defined in the standard of the Radio System Development Center is calculated by the equation (52). GS and PO in the equation (52) are [GS, PO]
This is the component of the vector selected from the codebook.

[0138]

(Equation 52)

[GS, PO] If the Tu shown in the equation (53) is calculated for the index number (u = 0 to 127) of the codebook, the influence of each index number u on the magnitude of the gain γ is obtained. I understand. When the gain γ is maximized with respect to the pseudo background noise, u (= 11) at which Tu is maximized
You can choose 3). When the gain γ is reduced, Tu is reduced. For example, by selecting u (= 75), the sound volume of the pseudo background noise can be set to a desired value.

[0140]

(Equation 53)

For the residual code of the VSELP code of white noise (formula (54) below), for example, 5 seconds (250 frames) is prepared in advance in the residual code file of white noise.
When the pseudo background noise is generated, the residual code file of the white noise is read out sequentially from the head, and when it is finished, the file is read again from the head.

[0142]

(Equation 54)

[0143]

As described above, according to the method of the present invention, the averaging process and the smoothing process of the frame energy value and the reflection coefficient value of the mobile station and the smoothing process of the reflection coefficient value of the base station are performed. In addition, the magnitude and height of the pseudo background noise sound in the entire silent section are less likely to be affected by the dispersion of the background noise signal at the time of transmission in each cycle, and the effect that the sound can be reproduced without discomfort is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment showing a schematic configuration of a transmission circuit of a mobile station to which the method of the present invention is applied.

FIG. 2 is a block diagram of one embodiment showing a schematic configuration of a receiving circuit of a base station to which the method of the present invention is applied.

FIG. 3 is a flowchart for explaining the operation of the present invention.

FIG. 4 is a flowchart for explaining the operation of the present invention.

FIG. 5 is a flowchart for explaining the operation of the present invention.

FIG. 6 is a schematic explanatory diagram of a sound section and a silent section for explaining the operation of the present invention.

FIG. 7 is a schematic explanatory diagram for explaining smoothing of a reflection coefficient value in the present invention.

FIG. 8 is a schematic explanatory diagram for explaining averaging of encoded frame energy values in the present invention.

FIG. 9 is a block diagram illustrating a configuration of a transmission circuit and a reception circuit on the mobile station side of a conventional example.

[Explanation of symbols]

 Reference Signs List 2 encoding unit 3 voiced / silent detection unit 4 parameter smoothing unit 5 parameter storage unit 6 transmission line encoder 9 separation circuit 10 parameter storage unit 11 reflection coefficient value calculation unit 12 residual signal file reading unit 13 pseudo noise synthesis unit 14 Switching unit 61 Multiplexer

Claims (2)

[Claims] In a method for generating pseudo background noise in a mobile communication device during non-communication, a base station side based on a received coded energy value, a coded reflection coefficient value, and a residual code of white noise provided in advance. Generating a pseudo-background noise signal. 2. The pseudo-background noise generation method according to claim 1, wherein the residual code of the white noise is stored in advance as a file, and the stored residual code of the white noise is repeatedly read out during the silent period in order to generate the pseudo-background noise. A method for generating a pseudo background noise, comprising generating a background noise signal.