JP2974448B2 - Mobile radio communication device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile radio communication device used in a mobile radio communication system employing a cellular system, such as a portable / automobile radio telephone system and a private radio telephone system.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic structure of a portable / car radio telephone system adopting a conventionally known cellular system. This system includes a control station CS connected to a wired telephone network NW and a plurality of base stations B connected to the control station CS via wired lines CL1 to CLn, respectively.
S1 to BSn and a plurality of mobile stations PS1 to PSm. Each of the base stations BS1 to BSn includes a radio zone E1 to En called a cell in a different area.
To form Each of the mobile stations PS1 to PSm is connected to a base station in a wireless zone in which the mobile station is located via a wireless line, and further connected from this base station to a wired telephone network NW via a control station CS. Then, in this state, the wired telephone network N
It is possible to talk with the telephone connected to W.

In this type of system, when a mobile station PS1 to PSm during a call moves to another wireless zone, control called so-called handover for switching a connection-destination base station is performed. This handover control is performed by transmitting and receiving a predetermined control signal between the corresponding base station and the mobile station according to the instruction of the control station CS.

[0004] For example, a base station BSi is a mobile station P during a call.
It monitors the received electric field strength of the radio wave sent from Sk,
When the received electric field strength falls below a certain level, the control station CS is notified of the fact. The control station CS sends a request for monitoring the received electric field strength to each of the base stations located around the base station BSi where the deterioration of the received electric field strength is detected. Then, each base station detects the received electric field strength of the radio wave transmitted from the target mobile station PSk, and notifies the control station CS of the detection result. The control station CS selects the best base station BSj from these detection results and determines a new radio communication channel. Then, a handover command including the new wireless communication channel designation information is transferred to the communicating base station BSi, and the selected base station BSj is instructed to set the new wireless communication channel. Base station BS
i transmits the handover command to the mobile station PSk. On the other hand, upon receiving the handover command, the mobile station PSk transmits a short burst to the base station BSj. The short burst is for measuring the propagation delay between the base station and the mobile station, and is composed of, for example, a pattern obtained by combining several types of frame patterns and “0” bit patterns. The base station BSj measures the propagation delay time from the reception result of the short burst, inserts the time alignment command created based on the measurement result into the operation state control signal, and returns it. Upon receiving the operation state control signal from the base station BSj, the mobile station PSk sets the transmission timing of the transmission time slot according to the time alignment command. And
A response signal is returned to the base station BSj, and thereafter, the mobile station returns to the talking state.

By the way, during the handover control, the mobile station receives a call during the handover period as shown in FIG. 5 so as to prevent various control signals and switching noises caused by switching of radio channels from being output from the receiver. The system is set to mute (silence). In this way, unpleasant noise is not output, thereby preventing the degradation of speech quality.

[0006]

However, in such a conventional configuration, the received voice is suddenly silenced during a call, so that the speaker has an illusion that the call has been disconnected, thereby causing, for example, the volume to be reduced. Incorrect operation such as up, redial, and end call was sometimes performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. It is an object of the present invention to prevent annoying noises from being output at the time of handover and to prevent a reception output from being in a silent state, thereby improving speech quality. While keeping
It is an object of the present invention to provide a mobile radio communication device that can always perform a smooth handover process without giving a speaker an unnatural feeling.

[0008]

In order to achieve the above object, the present invention provides a plurality of base stations each forming a radio zone, and these base stations are selectively connected to each other via a radio line. In a mobile radio communication device used as the mobile station in a system including at least one mobile station, when moving to a radio zone of another base station different from the connected base station during a call, In addition to switching control means for transmitting and receiving a control signal in a predetermined procedure between the base station and switching the connection destination base station, a noise generating means for generating a pseudo background noise, and a reception output control means, During the switching operation by the switching control unit, the pseudo-background noise generated by the noise generation unit is output from the receiver as a reception signal by the reception output control unit. It should be noted that the pseudo background noise is noise that is harsh.

[0009]

As a result, according to the present invention, annoying pseudo background noise is output from the receiver of the mobile station during handover. For this reason, even if the received voice is interrupted, the speaker can respond with a natural feeling without an illusion that the call is disconnected, thereby performing an erroneous operation such as increasing the volume, redialing, ending the call, etc. Inconvenience is prevented. Also, since no annoying noise such as switching noise is output, it is possible to maintain good communication quality.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a circuit block diagram illustrating a configuration of a mobile wireless communication device according to an embodiment of the present invention. The mobile radio communication device includes a transmission system,
It is roughly divided into a receiving system and a control system. Incidentally, reference numeral 40 denotes a battery as a power supply.

First, a transmission system includes a transmitter 11, a speech encoder (SPCOD) 12, and an error correction encoder (CHCOD).
13, a digital modulator (MOD) 14, and an adder 1
5, a power amplifier (PA) 16, a high-frequency switch circuit (SW) 17, and an antenna 18. The speech encoder 12 encodes a transmission signal output from the transmitter 11. The error correction encoder 13 performs error correction encoding of the digitized transmission signal output from the voice encoder 12 and a digitized control signal output from a control circuit 30 described later. The digital modulator 14 generates a modulation signal corresponding to the digitized transmission signal output from the error correction encoder 13. In the adder 15, the modulated signal is added to the carrier signal output from the frequency synthesizer 31, and the frequency is converted by this. In the power amplifier 16, the wireless transmission signal output from the adder 15 is amplified to a predetermined transmission power. The high-frequency switch 17 includes a control circuit 30
Is turned on only during a transmission time slot designated by the user. During this period, the wireless transmission signal output from the power amplifier 16 is supplied to the antenna 18 so that the antenna 1
8 to a base station (not shown).

Next, the receiving system includes a receiver (RX) 21, a digital demodulator (DEM) 22, and an error correction decoder (C
HDEC) 23, an audio decoder (SPDEC) 24,
A receiver 25 is provided. The receiver 21 performs frequency conversion of a radio reception signal received by the antenna 18 and the high-frequency switch 17 in a reception time slot of a predetermined radio frequency. In the digital demodulator 22, bit synchronization and frame synchronization with respect to the reception signal output from the receiver 21 are performed, and the synchronization signal is supplied to the control circuit 30. In the error correction decoder 23,
The digital demodulated signal output from the digital demodulator 22 is subjected to error correction decoding. Then, the digitized reception signal obtained by the error correction decoding is output to the audio decoder 24, and the digitization control signal is supplied to the control circuit 30. In the voice decoder 24, the digitized speech signal is decoded. Then, the analog reception signal restored by the decoding process is output from the receiver 25 as loudspeaker.

The control system includes a control circuit (CONT) 30
, A frequency synthesizer (SYN) 31, a reception field strength detection circuit (RSSI) 32, and a transmission request switch (S
W) 33. The frequency synthesizer 31 generates a local oscillation signal corresponding to each channel frequency for control, communication, and synchronization specified by the control circuit 30. In the reception electric field strength detection circuit 32, the reception electric field strength of the radio wave transmitted from the base station is detected, and the detection signal is notified to the control circuit 30 in order to search for an empty channel or monitor outside the communication range.

The receiving system is provided with a noise generator (NG) 34, and a switch 35 is provided between the speech decoder 24 and the receiver 25.
The noise generator 34 is composed of, for example, a random noise generator, and generates noise similar to background noise that can be heard when the talker of the other party is not speaking, that is, pseudo background noise. The changeover switch 35 is formed of a semiconductor switch and operates in accordance with a changeover control signal output from the control circuit 30 to connect the speech decoder 24 and the noise generator 34 to the receiver 25 alternatively.

The control circuit 30 includes, for example, a microcomputer as a main control unit. In addition to the conventional control functions such as setting control of a wireless communication channel and communication control in connection with outgoing / incoming, handover control is also provided. Means 30
a and the reception output control means 30b. The handover control means 30a monitors the arrival of a handover command transmitted from the base station during a call, and executes a series of controls for handover in a predetermined procedure when the handover command is received. On the other hand, receiving output control means 30
b is the switch 3 during the execution of the handover control.
A switching control signal is output to the receiver 5 so that the noise generator 34 is connected to the receiver 25 instead of the speech decoder 24 only during the handover control period.

Next, the operation of the apparatus configured as described above will be described in accordance with a handover control procedure. During the call, the mobile station apparatus monitors the arrival of the handover command in step 2a as shown in FIG. 2 while executing various controls related to the call by the control circuit 30.

In this state, it is assumed that the mobile station moves to another wireless zone, for example, and a handover command is transmitted from the current base station during communication as shown in FIG. Then, the control circuit 30 of the mobile station apparatus shifts from step 2a to step 2b, where it captures a new radio communication channel in accordance with the new radio communication channel designation information included in the handover command, and The current wireless communication channel is switched to the new wireless communication channel. Then, in step 2c, a changeover control signal is output to the changeover switch 35. Therefore, the changeover switch 35
Is switched from the voice decoder 24 to the noise generator 34. As a result, as shown in FIG. 3D, the noise generator 34 replaces the received voice signal output from the receiver 25 until then. Pseudo background noise is output.

Next, at step 2d, the control circuit 30 sends a short burst to the new base station as the destination via the new radio communication channel as shown in FIG. 3 (c). The short burst is used by the base station to measure the propagation delay between the base station and the mobile station, as described above. For example, the short burst includes a pattern obtained by combining several types of frame patterns and a “0” bit pattern. Has become. The new base station receives the short burst to measure a propagation delay time with the mobile station, and generates a time alignment command for adjusting the transmission timing of the mobile station based on the measurement result. . Then, the operation state control signal into which the time alignment command is inserted is transmitted to the mobile station as shown in FIG. Note that, in addition to the time alignment command, a transmission power control command, a command for controlling characteristics of an equalizer provided in the digital code decoder, and the like are also inserted into the operation state control signal.

When the transmission of the short burst is started, the control circuit 30 of the mobile station device monitors the arrival of the operation state control signal in step 2e. Then, when the operation state control signal is transmitted from the base station, the transmission of the short burst is stopped at that point, and the process proceeds to step 2f. In step 2f, the timing of the transmission time slot is adjusted according to the time alignment command included in the operation state control signal. At the same time, the transmission power of the power amplifier 16 is set to a predetermined value in accordance with the transmission power control command, and the characteristics of the equalizer are set to predetermined characteristics in accordance with the equalization characteristic control command. After completion of the setting of the operation state, a response signal is returned to the new base station as shown in FIG. 3C in step 2g.

After returning the response signal, a switch control signal is output to the switch 35 in step 2h. Therefore, the changeover switch 35 is connected to the noise generator 34.
Side returns to the audio decoder 24 side. Therefore, the pseudo background noise output from the receiver 25 during the handover period is stopped, and the receiver 25 outputs a received voice signal reproduced by the voice decoder 24 instead. Thus, the mobile station thereafter returns to the talking state.

As described above, according to the present embodiment, during the handover control period from the reception of the handover command to the return of the response signal, the noise generator 34 replaces the reception signal output from the voice decoder 24. Since the pseudo background noise generated from is output from the receiver 25,
The speaker can overhear the interruption of the received voice during the handover control period without much discomfort. For this reason, for example, as in the conventional case where the reception output is set to a mute state during the handover period, for example, the speaker performs an ending operation in an illusion of the disconnection of the call or performs an operation for increasing the transmission power. As a result, a reliable handover can always be performed.

During the handover control period, the receiver 2
Since 5 is disconnected from the audio decoder 24, the switching noise generated during the handover control period and the noise due to the control signal are not output from the receiver 25. For this reason, a problem in which harsh noise is output from the handset 25 is also prevented, so that good call quality can be maintained.

The present invention is not limited to the above embodiment. For example, the power supply to the noise generator 34 may be turned on / off in conjunction with the switching operation of the switch 35. In this way, the power consumption of the noise generator 34 can be extremely reduced, and the life of the battery 40 can be extended.

In the above-described embodiment, the switching between the received voice signal and the pseudo background noise is instantaneously performed at one time. However, the signal levels of the received voice signal and the pseudo background noise cross each other. As described above, the switching may be performed by gradually increasing or decreasing each of them. In this manner, the switching from the received voice to the pseudo background noise and the switching from the pseudo background noise to the received voice can be smoothly performed, and the discomfort given to the speaker can be further reduced.

Further, as the noise generating means, pseudo background noise may be generated by, for example, randomly scrambling the received data to an audio decoder and supplying the data, and the operation state of the audio decoder is intentionally changed. It may be configured such that pseudo background noise is generated from the audio decoder by making it incomplete. By doing so, it is not necessary to newly provide a noise generator, and the circuit configuration of the mobile station apparatus can be simplified and downsized accordingly.

In addition, the control sequence between the control station, the base station and the mobile station at the time of performing the handover, the control procedure and control contents of the handover at the mobile station, the frequency characteristic of the pseudo background noise, the output period of the pseudo background noise, and the like are also described. Various modifications can be made without departing from the spirit of the present invention.

[0027]

As described above in detail, according to the present invention, there is provided a noise generating means for generating pseudo background noise, and a receiving output control means. The output control means causes the pseudo background noise generated from the noise generation means to be output from the receiver as a reception signal instead of a reception signal, so that annoying noise is output at the time of handover and the reception output does not go into a silent state. As a result, it is possible to provide a mobile radio communication device capable of maintaining a good call quality and always performing a smooth handover process without giving the speaker an unnatural sensation.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a configuration of a mobile wireless communication device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure and control contents of a handover of the apparatus shown in FIG. 1;

FIG. 3 is a timing chart used for explaining the operation of handover.

FIG. 4 is a schematic configuration diagram of a portable wireless telephone system employing a cellular system.

FIG. 5 is a signal waveform diagram showing a state of a reception output at the time of handover in the conventional device.

[Explanation of symbols]

NW: Wired telephone network, CS: Control station, CL, CL1 to CL
n: Wired line, BS1, BS2, ... base station, PS1, P
S2: mobile station, E1, E2: radio zone, 11: transmitter, 12: voice encoder, 13: error correction encoder, 14 ...
Digital modulator, 15 ... adder, 16 ... power amplifier,
17 high frequency switch, 18 antenna, 21 receiver, 22 digital demodulator, 23 error correction decoder,
24: voice decoder, 25: receiver, 30: control circuit, 3
0a handover control means, 30b reception output control means, 31 frequency synthesizer, 32 reception electric field strength detection circuit, 33 transmission request switch, 34 noise generator, 35 changeover switch, 40 battery.

Claims (1)

(57) [Claims] 1. A mobile station comprising: a plurality of base stations each forming a wireless zone; and at least one mobile station selectively connected to the base stations via a wireless line. In the mobile radio communication device used, when moving to a radio zone of another base station different from the connected base station during a call, transmission and reception of a control signal with a corresponding base station in a predetermined procedure. Switching control means for switching the connection destination base station, a noise generation means for generating pseudo background noise, and a pseudo background noise generated from the noise generation means as a reception signal during the switching operation by the switching control means. A mobile radio communication device comprising: a receiver output control means for outputting from a receiver.