JPH1155736A - Wireless base stations for mobile phones - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize uplink communication channel / slot reception in a VOX mode signal format and improve communication quality. SOLUTION: A VOX mode verification / control unit 19 for detecting a unique word of PST0 and PRE is provided in a receiving unit 1
An RSSI value measurement / evaluation unit 36 for measuring and evaluating the RSSI value in response to the RSSI signals received in 6 and 17 and a baseband digital signal demodulated in the demodulation unit 18 for testing the postamble and preamble A postamble / preamble testing unit 37, a likelihood value measurement / evaluation unit 38 which receives the likelihood demodulated by the demodulation unit 18 and measures and evaluates the likelihood value; an RSSI value measurement / evaluation unit 36; -Exchange of information with the preamble testing unit 37 and the likelihood value measuring / evaluating unit 38 and signal timing generation /
It comprises a timing generation / mode verification setting unit 39 for instructing the demodulation unit 18 to adjust the demodulation period via the input / output control unit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio base station for a portable telephone which is used in a home or a building and has a function of detecting and receiving a slot constituted by a VOX mode signal format.

[0002]

2. Description of the Related Art FIG. 10 shows a configuration of a conventional mobile phone radio base station. In FIG. 10, a radio base station 61 for a mobile phone includes a radio section 78, a modulation / demodulation section 79, an encoding / decoding section 80, a public switched telephone network (PSTN) communication section 74, a signal timing generation / input / output signal control section 75, A central control unit 76 is provided. The mobile phone wireless base station 61 and the mobile phone 62 are communicated by wireless digital signals through the first antenna 63 and the second antenna 64. Further, the wireless base station 61 for the mobile phone and the telephone line 81 are connected to a public line network (PST) under the control of a signal timing generation / input / output control unit 75.
N) Communication is performed by a voice analog signal through the communication unit 74.

The radio section 78 includes a first antenna 63 and a second
The antenna 64 and the first antenna 63 have the duplexer 6
5, a transmitting unit (TX) 66 and a first receiving unit 67 (RX1) connected to the second antenna 64, and a second receiving unit (RX2) 68 connected to the second antenna 64. The modulation / demodulation section 79 modulates the encoded audio signal under the control of the signal timing generation / input / output signal control section 75 to transmit the modulated signal to the transmission section 66.
Under the control of the modulating unit 69 for transmitting and the signal timing generation / input / output signal control unit 75, the first and second receiving units 67, 6
And a demodulation unit 77 for demodulating the digital signal received at step 8. The encoding / decoding unit 80 includes a channel codec unit 70, an audio codec unit 71, an echo canceller unit 72, and a PCM conversion unit 73 controlled by a signal timing generation / input / output signal control unit 75.

[0004] Next, a full-rate uplink reception operation will be described with reference to FIGS. 10, 11, 4 and 6 to 9.

[0005] The wireless digital signal transmitted from the portable telephone 62 is received by the first and second receivers 67 and 68 through the first antenna 63 and the second antenna 64. The received wireless digital signal is transmitted to the first and second receivers 67 and 68.
The predetermined band processing and frequency conversion processing are performed by the demodulation unit 77.
Is output to The demodulation unit 77 selects one wireless digital signal from the two wireless digital signals by means represented by diversity, demodulates the signal into a baseband digital signal, and outputs it to the encoding / decoding unit 80.

As shown in FIGS. 4A and 4B, there are two types of baseband digital signals, a physical channel for uplink communication in the TCH mode and a physical channel for uplink communication in the VOX mode. When a voice is detected by the mobile phone 62, a slot having the TCH mode signal format shown in FIG. 4A is received. When no voice is detected by the mobile phone 62, the VOX mode signal format shown in FIG. Receiving the slot that has it.

In the portable telephone 62, when the sound shown in FIG. 6A becomes silence after 3 at the timing of 20 msec shown in FIG. 6B, when the sound shown in FIG.
At the timings of 5 and 5, the slot to which the unique word of the postamble signal PST0 shown in FIGS. 9A and 9B is added is continuously transmitted as a wireless digital signal, and is received by the mobile phone wireless base station 61. The received wireless digital signal is demodulated into a baseband digital signal by the demodulation unit 77, and the first and second slots of the unique word of the postamble signal PST0 shown in FIGS. 9A and 9B are continuously received. When demodulated, the demodulation unit 77
It does not have the function of detecting a unique word of 0, and continues the demodulation period shown in FIG.

In the portable telephone 62, the slot to which the unique word of the postamble signal PST0 shown in FIGS. 9A and 9B is added is continuously transmitted as a wireless digital signal, and is received by the portable telephone wireless base station 61. Also,
As shown in FIG. 7B, the slot in the VOX mode shown in FIG. 11A and the PS shown in FIG.
A slot with a unique word of T0 is transmitted,
It is received by the mobile phone radio base station 61. Demodulation unit 77
Is demodulated in the demodulation period 4 including the guard bit as shown in FIG. 11A even at the time of the slot in the VOX mode shown in FIG. 11A.

[0009] The voice shown in FIG.
When the voice becomes sound after 0 msec timing 1, at the timings 3 and 4 of the encoding process voice detection shown in FIG.
The slots to which the unique words of the preamble signals PRE shown in (c) and (d) are added are continuously transmitted as radio digital signals, and are received by the radio base station 61 for mobile telephone. The received wireless digital signal is demodulated into a baseband digital signal by a demodulation unit 77, and the demodulation unit 77 performs the demodulation in FIG.
When the first slot and the second slot of the unique word of the preamble signal PRE shown in FIG. 11 are continuously received, the demodulation unit 77 does not have the function of detecting the unique word of the PRE, and the demodulation unit 77 shown in FIG. Lasting period.

[0010]

However, in the above-mentioned conventional radio base station for portable telephone, the first and second slots of the PST0 unique word, and the PRE
Since the demodulation unit 77 does not have a function of detecting the unique word when the first slot and the second slot of the unique word are continuously received, the detection of the first or second slot of the PST0 unique word is not possible. At times,
It is impossible to adjust the demodulation period of the demodulation unit at a predetermined timing.

Also, it is not possible to determine whether the received uplink communication channel slot is an uplink communication channel slot having a signal format of TCH mode or an uplink communication channel slot having a signal format of VOX mode. When an uplink communication channel / slot having a signal format of the VOX mode is received, a radio digital signal of a guard time is demodulated, and noise is mixed in a voice analog signal changed by an encoding / decoding unit, thereby deteriorating communication quality. There is.

The radio digital signal of the guard time is
Since a specific frequency band is not satisfied, when an uplink communication channel slot having a signal format of the VOX mode is received, when demodulating a radio digital signal of a guard time, the detection characteristic is significantly reduced, and after demodulation, There is a problem of deteriorating the S / N characteristics of the baseband digital signal.

An object of the present invention is to provide a radio base station for a portable telephone capable of realizing reception of an uplink communication channel / slot in a VOX mode signal format and improving speech quality. Aim.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a radio base station for a portable telephone according to the present invention receives a reception field strength signal received by a radio section and measures and evaluates a reception field strength value. An electric field strength measurement / evaluation unit, a postamble / preamble verification unit that receives a baseband digital signal demodulated from a wireless digital signal by a modulation / demodulation unit, and tests a postamble and a preamble, and a likelihood demodulated by a modulation / demodulation unit. , A likelihood value measurement / evaluation unit for measuring and evaluating likelihood values, a received electric field strength value measurement / evaluation unit, the postamble preamble test unit, and the likelihood value measurement / evaluation unit.
VOX mode test / control configured by a timing generation / mode test setting unit for exchanging information with the evaluation unit and instructing the modulation / demodulation unit to adjust the demodulation period via a signal timing generation / input / output signal control unit. It has a unit.

According to the present invention, uplink communication channel / slot reception of a VOX mode signal format can be realized,
Call quality can be improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a radio unit, a modem unit, an encoding / decoding unit, a public network communication unit, a signal timing generation / input / output signal control unit, and a central control unit. A mobile phone radio base station comprising: a reception field strength measurement / evaluation unit that receives and receives a reception field strength signal received by the radio unit, measures and evaluates a reception field strength value,
A postamble / preamble testing unit for receiving a baseband digital signal demodulated from a wireless digital signal by the modem unit and testing a postamble and a preamble; and a likelihood value receiving a likelihood demodulated by the modem unit. The likelihood value measurement / evaluation unit that measures and evaluates, exchanges information between the reception field strength value measurement / evaluation unit, the postamble preamble test unit and the likelihood value measurement / evaluation unit, and A V composed of a timing generation / mode test setting unit for instructing the modulation / demodulation unit to adjust the demodulation period via a signal timing generation / input / output signal control unit.
An OX mode verification / control unit is provided.

According to a second aspect of the present invention, the VOX mode verification / control unit continuously converts the unique word of the first slot of the postamble and the unique word of the second slot of the preamble with a predetermined number of bit errors. After the detection, the predetermined slot is adjusted at a predetermined timing to a predetermined demodulation period in the VOX mode, and the information channel (T
The change from the (CH) mode to the VOX mode is notified to the modulation / demodulation unit.

According to a third aspect of the present invention, the VOX mode verification / control unit receives a reception field strength signal equal to or more than a specific allowable value from the radio unit during a predetermined period in a predetermined slot changed to the VOX mode. Thereafter, when a likelihood greater than or equal to a specific allowable value is detected from the modem during a predetermined period, the modem corrects the predetermined slot to a predetermined demodulation period at a predetermined timing.

According to a fourth aspect of the present invention, the unique word of the first slot of the preamble is provided for a predetermined period in the predetermined slot corrected by the VOX mode verification / control unit at a predetermined timing during a predetermined demodulation period. When the unique word of the second slot of the preamble one frame later is detected while allowing a predetermined number of bit errors, the predetermined slot is adjusted at a predetermined timing to a predetermined demodulation period in the TCH mode. Then, the change from the VOX mode to the TCH mode is notified to the modem.

According to a fifth aspect of the present invention, in the predetermined slot corrected by the VOX mode verification / control section at a predetermined timing in a predetermined demodulation period, a unique word of a first slot of a preamble is specified in a predetermined period. Is untested and the unique word of the second slot of the preamble one frame later is untested, the predetermined slot is adjusted at a predetermined timing to a predetermined demodulation period in the VOX mode, and the VOX is adjusted. The continuation of the mode is notified to the modem unit.

Therefore, without changing the current internal circuit of the demodulation unit 18 and adding the VOX mode verification / control unit 19 for detecting the unique words of PST0 and PRE,
The timing of changing from the uplink communication channel slot having the VOX mode signal format to the uplink communication channel slot having the TCH mode signal format is as follows:
Without constantly demodulating and detecting guard time information,
The first half of the first slot is discarded, PRE detection is determined by measurement using RSSI and likelihood, and the second half of the first slot and the second slot determine that the PRE has been detected, so that the guard time is always maintained. Therefore, it is not necessary to perform the PRE measurement and the detection processing, and the demodulation of the guard time can avoid the deterioration of the detection characteristic and the influence on the communication quality.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

FIG. 1 is a block diagram showing a configuration of a mobile phone radio base station according to an embodiment of the present invention. In FIG. 1, a radio base station 1 for a mobile phone includes a radio unit 20, a modulation / demodulation unit 21, an encoding / decoding unit 22, and a public switched telephone network (PST).
N) A communication unit 13, a signal timing generation / input / output signal control unit 14, a central control unit 15, and a VOX mode verification / control unit 19 are provided. The mobile phone wireless base station 1 and the mobile phone 2 are communicated by a wireless digital signal through the first antenna 3 and the second antenna 4. The mobile phone wireless base station 1 and the telephone line 24 are communicated by voice analog signals through a PSTN communication unit 13 under the control of a signal timing generation / input / output signal control unit 14.

The radio section 20 includes a first antenna 3 and a second antenna 4, a transmitting section (TX) 7 and a first receiving section (RX 1) connected to the first antenna 3 via an antenna duplexer 6.
16 and a second receiver (RX) connected to the second antenna 4.
2) 17). The modulation / demodulation unit 21 is controlled by the signal timing generation / input / output signal control unit 14,
A modulating unit 8 that modulates the coded audio signal and sends it to a transmitting unit 7; and a digital signal received by a first and second receiving units 16 and 17 under the control of a signal timing generation / input / output signal control unit 14. And a demodulation unit 18 for demodulating. The encoding / decoding unit 22 includes a channel codec unit 9, an audio codec unit 10, and an echo canceller unit 1 controlled by the signal timing generation / input / output signal control unit 14.
1 and a PCM conversion unit 12.

FIG. 2 shows the configuration of the VOX mode verification / control unit 19 and the first VOX mode verification / control unit 19.
FIG. 3 is a block diagram showing a connection relationship between second reception units 16 and 17, a demodulation unit 18, and a signal timing generation / input / output signal control unit 14.

In FIG. 2, a VOX mode verification / control section 19 receives a received field strength (RSSI) signal received by the first and second receiving sections 16 and 17 and measures and evaluates the RSSI value. .Evaluation unit 36 and demodulation unit 18
Receives the baseband digital signal demodulated from the wireless digital signal and tests the postamble and preamble, and receives the likelihood demodulated by the demodulation unit 18 and measures the likelihood value The likelihood value measurement / evaluation unit 38, the RSSI value measurement / evaluation unit 36, the postamble / preamble verification unit 37, and the likelihood value measurement / evaluation unit 38 exchange information and perform signal timing generation / evaluation. A timing generation / mode verification setting unit 39 is provided to instruct the demodulation unit 18 to adjust the demodulation period via the input / output signal control unit 14.

Next, a description will be given, with reference to FIG. 1 to FIG. 9, of the uplink reception operation at the full rate of the VOX mode verification / control section 19 in the mobile phone radio base station 1 configured as described above.

The wireless digital signal transmitted from the mobile phone 2 is transmitted through the first antenna 3 and the second antenna 4 to the first digital signal.
And the second receiving units 16 and 17. The received wireless digital signal is subjected to predetermined band processing and frequency conversion processing in first and second receiving units 16 and 17, and is output to demodulation unit 77. The demodulation unit 18 selects one wireless digital signal from the two wireless digital signals by means represented by diversity, demodulates the signal into a baseband digital signal, and outputs it to the encoding / decoding unit 22. Further, it is output to the postamble / preamble verification section 37 of the VOX mode verification / control section 19, and verifies the postamble and the preamble.

The baseband digital signal is shown in FIG.
As shown in FIG. 4, there are two types of physical channels for uplink communication in the TCH mode and physical channels for uplink communication in the VOX mode, and when the mobile phone 2 detects voice, the TCH shown in FIG. When a slot having a mode signal format is received and no sound is detected by the mobile phone 2, a slot having a VOX mode signal format shown in FIG. 4B is received.

The RSSI signal detected by the first and second receiving units 16 and 17 is output to the RSSI value measuring and evaluating unit 36 of the VOX mode test and control unit 19,
The measurement and evaluation of the SI value are performed.

In the portable telephone 2, when the sound shown in FIG. 6A becomes silence after 3 at the timing of 20 msec shown in FIG. 6B, the timing of 4 and 5 in the encoding process sound detection shown in FIG. Then, the slot to which the unique word of the postamble signal PST0 shown in FIGS. 9A and 9B is added is continuously transmitted as a wireless digital signal, and received by the wireless base station 1 for portable telephone.

The received wireless digital signal is transmitted to the demodulation unit 1
8 demodulated into a baseband digital signal,
The postamble / preamble verification unit 37 of the X-mode verification / control unit 19 allows the arbitrary slot to be set such that the first slot and the second slot of the unique word of the postamble signal PST0 shown in FIGS. Signal timing generation / input / output signal control unit 14
Is notified to the demodulation unit 18 via. After the notification, the demodulation unit 18
The demodulation period from the next slot after one frame to the RCH / SACCH from the preamble shown in FIG.
Then, the mode is changed from the TCH mode to the VOX mode.

That is, as shown in FIG. 3, the VOX mode verification / control section 19 determines whether the mode is the VOX mode (step S1). If the mode is the VOX mode, the process proceeds to step S5. If the mode is not the VOX mode, the process proceeds to step S2. The process proceeds to PST0: It is determined whether the first slot (a bit error equal to or less than a specific number is allowed) is detected. If the first slot has been detected, it is determined in the next step S3 whether or not PST0: the second slot (a bit error of a specified number or less is allowed) is detected. If the second slot is detected, the mode is changed from the TCH mode to the VOX mode in step S4.

The slots changed to the VOX mode are stored in the R shown in FIG. 5A every frame period (every two slots).
In the SSI measurement period, the first and second receiving units 16, 1
7 from the RSSI signal detected in step 7,
The RSSI value measurement / evaluation unit 36 of the control unit 19 measures the RSSI value, compares the RSSI value with the RSSI value before the mode change, and determines whether the comparison result is equal to or greater than a specific allowable value (step S
5). Here, when a value equal to or greater than the specific allowable value is detected, the timing generation / mode test setting unit 39 instructs the likelihood value measurement / evaluation unit 38 to measure the likelihood in the likelihood measurement period shown in FIG. I do. Here, the likelihood is a signal generated as phase information for determining the quality of detection when the demodulation unit 18 detects a wireless digital signal.

The likelihood generated by the demodulation unit 18 is represented by b in FIG.
Is measured and evaluated by the likelihood value measurement / evaluation unit 38 in the likelihood measurement period shown in (1), and it is determined whether the evaluation value of the likelihood is equal to or more than a specific allowable value (step S6). Here, when a value equal to or more than the allowable value is detected, the likelihood value is measured by the timing generation / mode test setting unit 39 in the specific likelihood measurement period shown in FIG. It is determined whether the evaluation value of the likelihood is equal to or larger than an allowable value (step S6). Here, if the likelihood is equal to or larger than the allowable value, it is determined whether the latter half of the slot is the preamble of the first slot, and it is determined whether a unique work of the preamble is detected (step S7). When the determination is affirmative, in the next step S8, it is determined whether it is desired to detect the unique words of the first half and the second half of the preamble of the second slot.

That is, when it is determined that the evaluation value of the likelihood is equal to or larger than the allowable value and the detection quality is determined to be good,
As shown in FIG. 5, the timing generation / mode verification setting unit 39 extends the current slot to the demodulation period 2 and the slot after one frame to the demodulation period 3 to demodulate the baseband digital signal. Instruct the demodulation unit 18 via the timing generation / mode verification setting unit 39 to output the data from the encoding / decoding unit 22 and the postamble / preamble verification unit 37 of the VOX mode verification / control unit 19. The signal timing generation / input / output signal controller 14 instructs the postamble / preamble tester 37 to test.

Postamble / preamble test section 37
Then, when the second half of the PST0 or PRE of the current slot matches the first half and the second half of the PRE second slot shown in FIG.
The timing generation / mode verification setting unit 39 controls the demodulation unit 18 via the signal timing generation / input / output signal control unit 14 so that the demodulation period becomes the demodulation period 3 shown in FIG.
, And change to the TCH mode and set it (step S9). In other cases, the timing generation / mode verification setting unit 39 instructs the demodulation unit 18 via the signal timing generation / input / output signal control unit 14 to change to the demodulation period 1 shown in FIG. I do.

According to the above-described embodiment of the present invention, the PST can be changed without changing the current internal circuit of demodulation section 18.
By adding a VOX mode verification / control unit 19 that detects unique words of 0 and PRE, an uplink communication channel slot having a VOX mode signal format can be changed to an uplink communication channel slot having a TCH mode signal format. The change time is always detected without demodulating and detecting the guard time information, the first half of the first slot is discarded, PRE detection is determined by measurement using RSSI and likelihood, and the second half of the first slot is further determined. With the second slot, the guard time is constantly demodulated by deciding that the PRE has been detected, and there is no need to perform the PRE measurement and detection processing. The effect can be avoided.

[0039]

As described above, according to the present invention, the PST0 and the PRE are not changed without changing the current internal circuit of the demodulation unit 18.
By adding the VOX mode verification / control unit 19 for detecting the unique word of the above, the timing of changing from the uplink communication channel slot having the VOX mode signal format to the uplink communication channel slot having the TCH mode signal format can be changed. Always discard the first half of the first slot without demodulating and detecting the guard time information, judge PRE detection by measurement using RSSI and likelihood, and further determine the second half of the first slot and the second half. Depending on the slot,
By determining that the PRE has been detected, the guard time is always demodulated, and there is no need to perform the PRE measurement and detection processing. By demodulating the guard time, it is possible to avoid the deterioration of the detection characteristics and the influence on the communication quality. A mode signal format uplink communication channel / slot reception can be realized,
Call quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a mobile phone radio base station according to an embodiment of the present invention.

FIG. 2 shows a configuration of a VOX mode verification / control unit and first and second reception units, a demodulation unit, and a signal timing generation / input / output signal control unit related to the VOX mode verification / control unit in the embodiment of the present invention. Block diagram showing connection relationships

FIG. 3 is a flowchart for explaining the operation of a VOX mode verification and control unit according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a signal format of a physical channel for uplink communication and bit allocation.

FIG. 5 is an explanatory diagram of a test and a measurement period in a VOX mode.

FIG. 6 is an explanatory diagram of a transmission timing of a postamble signal at a full rate.

FIG. 7 is an explanatory diagram of a transmission timing of a postamble signal at a full rate.

FIG. 8 is an explanatory diagram illustrating a transmission timing of a preamble signal at a full rate.

FIG. 9 is a diagram showing an example of a unique word pattern of a preamble / postamble signal at a full rate.

FIG. 10 is a block diagram showing a configuration of a conventional mobile phone wireless base station.

FIG. 11 is an explanatory diagram of a test and measurement period in a conventional VOX mode.

[Explanation of symbols]

 Reference Signs List 1 Radio base station for mobile phone 2 Mobile phone 3 First antenna 4 Second antenna 6 Antenna duplexer 7 Transmitter 8 Modulator 9 Channel codec 10 Audio codec 11 Echo canceller 12 PCM converter 13 Public network (PSTN) ) Communication unit 14 Signal timing generation / input / output signal control unit 15 Central control unit 16 First reception unit (RX1) 17 Second reception unit (RX2) 18 Demodulation unit 19 VOX mode verification / control unit 20 Radio unit 21 Modulation / demodulation unit 22 Encoding / decoding section 23 Telephone line 36 RSSI value measurement / evaluation section 37 Postamble / preamble test section 38 Likelihood value measurement / evaluation section

Claims (5)

[Claims] 1. A wireless base station for a mobile phone comprising a wireless unit, a modem unit, an encoding / decoding unit, a public network communication unit, a signal timing generation / input / output signal control unit, and a central control unit. Received electric field strength signal received by the section and measure and evaluate the received electric field strength value
An evaluator, a postamble / preamble tester that receives a baseband digital signal demodulated from a wireless digital signal in the modem and tests the postamble and preamble, and receives a likelihood demodulated in the modem. A likelihood value measurement / evaluation unit that measures and evaluates likelihood values by using the reception field strength value measurement / evaluation unit and the postamble
Timing generation / mode verification for exchanging information between the preamble verification unit and the likelihood value measurement / evaluation unit, and instructing the modulation / demodulation unit to adjust the demodulation period via the signal timing generation / input / output signal control unit. A radio base station for a mobile phone, comprising a VOX mode verification / control unit configured by a setting unit. 2. The VOX mode verification and control unit detects a unique word of a first slot of a postamble and a unique word of a second slot of a preamble continuously by allowing a predetermined number of bit errors, and thereafter, detects a unique word in a predetermined slot. 2. The mobile phone radio according to claim 1, wherein the control unit adjusts the timing to a predetermined demodulation period in the VOX mode at a predetermined timing, and notifies the modem unit of a change from the information channel (TCH) mode to the VOX mode. base station. 3. The VOX mode verification / control unit receives a reception field strength signal equal to or larger than a specific allowable value from a radio unit in a predetermined period in a predetermined slot changed to the VOX mode, and thereafter, in a predetermined period. 3. The mobile phone according to claim 1, wherein, when a likelihood greater than or equal to a specific allowable value is detected from the modem unit, the modem unit corrects the predetermined slot to a predetermined demodulation period at a predetermined timing. For wireless base station. 4. The VOX mode verification / control section, in a predetermined slot corrected for a predetermined demodulation period at a predetermined timing, for a predetermined period, a second half of a unique word of a first slot of a preamble and one frame When the unique word of the second slot of the subsequent preamble is detected by allowing a predetermined number of bit errors, the predetermined slot is adjusted at a predetermined timing to a predetermined demodulation period in the TCH mode, and the VOX mode is changed to the TCH mode. 4. The wireless base station for a cellular phone according to claim 1, wherein the change to the base station is notified to a modem unit. 5. The VOX mode verification / control section, in a predetermined slot corrected at a predetermined timing during a predetermined demodulation period, a second half of a unique word of a first slot of a preamble becomes unverified in a predetermined period. When the unique word in the second slot of the preamble one frame later has not been verified, the predetermined slot is adjusted at a predetermined timing to a predetermined demodulation period in the VOX mode, and the continuation of the VOX mode is modulated and demodulated. The radio base station for a mobile phone according to claim 1, wherein the radio base station is notified of the radio base station.