KR0121964B1 - Method for evesdropping voice of a cellular phone - Google Patents

Abstract

A audio signal wiretapping method for the terminal where wiretaps the communication contents between the terminal of the DECT (Digital European Cordless Telecommunication) and the base station.

Description

How to intercept voice signal of terminal

1 is a block diagram showing an embodiment of a general DECT terminal.

FIG. 2 is a flow chart showing step by step an embodiment of general DECT terminal processing of FIG. 1 according to the DECT standard. FIG.

FIG. 3 is a flowchart showing step by step an embodiment of a method of intercepting a voice signal of a terminal according to the present invention using the embodiment of FIG.

The present invention relates to a method of intercepting a voice signal of a terminal, and more particularly, to a method of intercepting a voice signal of a terminal suitable for intercepting a voice signal of a portable terminal of a digital european cordless telecommunications (DECT) method.

In this regard, FIG. 1 is a block diagram illustrating an embodiment of a general DECT terminal, including a central processing unit (CPU) 2 having a baseband processing function for controlling overall operation of the terminal, A power supply unit 4 controlled by the central processing unit 2 to indicate the current power state of the terminal, a power supply unit 6 controlled by the central processing unit 2 to supply power for operating the terminal to the terminal system; A microphone 8 for converting a voice signal into an electrical analog voice signal, an analog-digital converter 10 for converting an analog voice signal of the microphone 8 into a digital signal, The digital voice signal of the analog-to-digital converter 10 is converted into ADPCM (Adaptive Differential Pulse Code Modulation) data and applied to the digital signal processing (DSP) processor 14. Digital signal processing processor 14 which communicates with the ADPCM-PCM (Pulse Code Modulation) conversion unit 12, the central processing unit 2, and digitally processes the digital signal according to the speech coding method used in the DECT standard. A PCM-ACPCM converter 16 for converting ADPEM data of the digital signal processor 14 into PCM data, and a digital-analog converter 18 for converting data from the PCM-ACPCM converter 16 into an analog signal. ), A speaker 20 which is driven by an analog signal of the digital-to-analog converter 18 to output voice, and a carrier for modulating voice data encoded by ADPCM from the central processing unit 2 Amplified signal of the signal synthesizer 22, amplified signal 24 of the signal synthesizer 22, and amplified signal amplified by the DECT. Propagates to the air and emits high frequency signals A low noise amplifier 28 for receiving a high frequency signal from a base station (also called a fixed station) received through the antenna 26 during reception, and amplifying low noise; An intermediate frequency converter 30 which converts the received high frequency signal of the low noise amplifier 28 into an intermediate frequency, and extracts the original signal transmitted from the intermediate frequency of the intermediate frequency converter 30, ), A key input unit 34 for making a call input to the central processing unit 2, and a screen display unit 36 for displaying a longitudinal state by receiving a signal from the central processing unit 2; ), A buzzer 38 for generating a special sound generated for use of a terminal such as a key input and a bell by receiving a signal from the central processing unit 2, and control of the central processing unit 2 This to record the initial status and various phone numbers Pirom (Electrically Erasable Programmable Read Only Memory; EEPROM) 40, a read only memory (ROM) 42 storing data for the operation of the entire processor by the central processing unit 2, and a longitudinal operation by the central processing unit 2; And RAM 44 which temporarily stores the parameters.

Referring to FIG. 2, a general DECT terminal made in this way is as follows.

First, the central processing unit 2 has a baseband processing function for controlling the overall operation of the terminal, and the power display unit 4 is controlled by the central processing unit 2 to indicate the current power state of the terminal. Displayed using a light emitting device such as a diode so that the user can know the state of the power on / off of the local terminal.

Then, the power supply unit 6 is controlled by the central processing unit 2 to supply power for terminal operation, and the microphone 8 converts a voice signal by the user into an electrical analog voice signal, and converts the analog-digital conversion. The unit 10 converts the analog audio signal of the microphone 8 into a digital signal.

The ADPCM-PCM converter 12 converts the digital voice signal of the analog-digital converter 10 into ADPCM data and applies it to the digital signal processing processor 14, and the digital signal processing processor 14 performs central processing. It communicates with the apparatus 2 and processes the digital signal according to the speech coding method used in the DECT standard.

In addition, the PCM-ADPCM converter 16 converts ADPCM data of the digital signal processing processor 14 into PCM data, and the digital-analog converter 18 converts the PCM data of the PCM-ADPCM converter 16 into analog. The signal is converted to a signal, and the speaker 20 outputs a voice by the analog signal of the digital-analog converter 18 so that the user can hear the voice.

Next, the signal synthesizing unit 22 receives the voice data encoded by ADPCM from the central processing unit 2 and modulates it in a carrier for modulation of 1.8 GHz for wireless transmission, and the signal amplifying unit 24 is a signal synthesizing unit 24. The modulated signal 22 is amplified to a level defined by DECT, and the antenna 26 propagates the amplified signal of the signal amplifier 24 in the air and receives the high frequency signal in the air.

Therefore, the low noise amplifier 28 receives the 1.8 GHz signal of the base station received through the antenna 26 during the reception period of the terminal to low noise amplification, the intermediate frequency converter 30 of the low noise amplifier 28 The 1.8 GHz frequency is converted into a 110 MHz intermediate frequency, and the demodulator 32 extracts the original signal transmitted from the 110 MHz intermediate frequency of the intermediate frequency converter 30 and applies it to the central processing unit 2. do.

The key input unit 34 inputs a desired call to the central processing unit 2 by a user's key manipulation, and the screen display unit 36 receives a signal from the central processing unit 2 to display a liquid crystal display (LCD). A bell state is displayed by using a display device such as a display device, and the buzzer 38 receives a signal from the central processing unit 2 to generate a special sound generated for use of a terminal such as a key input and a bell so that the user can hear it. This pyrom 40 records the initial state of the volume and various telephone numbers by the central processing unit 2, and the ROM 42 is non-volatile for operation of the entire terminal by the central processing unit 2; The data is stored, and the RAM 44 temporarily stores the parameters for the longitudinal operation by the central processing unit 2.

FIG. 2 is a flowchart showing step by step an embodiment of the general DECT terminal processing shown in FIG. 1 according to the DECT standard, that is, an algorithm of the central processing unit 2.

In this case, the above-described algorithm is mounted in the Y pyrom 40 or the ROM 42, and the basic operation of each part according to FIG. 1 will be described above.

First, when the power is turned on, the central processing unit 2 reads an initial value for hardware from the ROM 42 or EPI 40, initializes each hardware, inspects the RAM 44, and clears it. (Clear), and then run a self-diagnosis program (Program) or the like to check the basic abnormality of the hardware, and then the antenna 26, low-noise amplification unit 28 of the signal of the wireless base station forming the cell to which it belongs 10 through the intermediate frequency converter 30 and the demodulator 32 to receive radio channels 0 through 9 (100, 102, 104, 106, 108, 110 and 112).

Next, the central processing unit 2 causes the demodulator 32 to examine the received electric field strength for all 10 radio channels, receives the information from the demodulator 32, and sends out the strongest radio signal among them. The connection to the base station is determined, and synchronization is made to be a reference for various timings in the terminal based on the signal sent from the wireless base station (114).

Thereafter, by communicating with the wireless base station through the antenna to check the time slot use state of the wireless base station to check whether there is an empty time slot, and then performs a normal registration procedure to the base station (116).

At this time, after the registration process is entered into the standby state, the operation of the terminal proceeding in the standby state can be largely operated in four.

First, the central processing unit 2 checks the presence or absence of a paging signal from the base station, and if there is a paging signal, first accesses a medium access control (MAC) layer to access a time of a wireless channel. The slot usage rights are secured, and the DLC (Data Link Control) layer connection and the network (Network) layer are sequentially processed to form a call path and then proceed with the call (118, 120, 122, 124, 126).

Thereafter, the network layer is disconnected, the DCL layer is disconnected, and then the MAC layer is disconnected due to any one call disconnection, thereby releasing the license of the wireless channel and entering the standby state again (128, 130, 132).

On the contrary, if there is no paging signal, the terminal user examines a connection request to a specific subscriber, and if a request occurs, if there is an empty time slot by checking the existence of an empty time slot to secure use of the time slot. Immediately requests the use of the time slot to the base station, and if the time slot is not empty, waits until the time delay does not exceed the value set until another user's use of the time slot ends. When the use of another user's time slot ends, an attempt is made to access the MAC layer using the time slot (134, 136).

Subsequently, access to the MAC layer is performed to secure the right to use the time slot of the wireless channel, and the DLC layer and the network layer are sequentially connected to form a call path and then proceed with the call (138, 140, and 142).

Subsequently, the network layer is disconnected, the DLC layer is disconnected, and the MAC layer is subsequently disconnected due to any one call disconnection state, thereby releasing the right to use the radio channel and entering the standby state again (144, 146, 148).

At this time, after there is no paging signal and the user's request for transmission or the processing (step 132 or step 148) is completed, the state check in the terminal is performed.

A typical internal condition check is the voltage level check of the supply battery.

First, the battery voltage is input through a circuit for converting an analog signal into a digital signal to check whether it is at an appropriate level. If the battery is below an appropriate level, a battery charge warning signal is generated to display a message such as, for example, a need for charging. It informs the charging condition and checks whether the signal of the base station is maintained to maintain an appropriate signal level or whether the signal level is too low to attempt to connect to an adjacent base station (150, 152, 154, 156, 158).

If the signal level of the base station is higher than -83dBm, the signal status of the currently registered base station is maintained as it is, and if the signal level drops below a certain value and a mobile connection to the previous station is required, the wireless channel is changed from 0 to 9. First, a process of deregistration of releasing a state registered in a local base station is performed (160).

Subsequently, signals from the radio base station are received again from the radio channels 0 to 9 in ten (162, 164, 166, 168, 170, 172).

Therefore, the total strength received for all ten radio channels is examined to determine the connection to the wireless base station which emits the strongest wireless signal, and the various timing criteria in the terminal are determined based on the signal transmitted from the wireless base station. (174,176)

After that, the time slot usage status of the wireless base station is examined to determine whether there is an empty time slot, and then a new registration procedure is performed (116).

That is, in the standby state, as described above, it is determined whether or not there is a paging signal from the base station and proceeds with the processing thereof, examines the user's transmission request and proceeds with it, and checks whether the battery voltage is at an appropriate level. The basic form of the overall DECT terminal processing is to perform a process for it, inspect the signal level of the base station, proceed with the process, and perform various timer processes of the other terminal.

As described above, in the conventional DECT wireless telephone network, a call channel formed in each time slot encrypts a voice signal encoded by ADPCM by an encryption key value received from a base station and transmits and receives wirelessly.

In such cases, it may be necessary for a third party to receive the contents of the call for official reasons, such as forensic reasons or crimes.

In this case, it is impossible to decrypt the encryption process without a separate device.

Accordingly, an object of the present invention is to provide a method for intercepting a voice signal of a terminal capable of intercepting a call being transmitted and received in a communication path between a DECT terminal and a base station for public reasons.

Hereinafter, with reference to the accompanying drawings an embodiment of the present invention for achieving the above object is as follows.

Referring to FIG. 3, FIG. 3 is a flowchart showing step by step an embodiment of a method of intercepting a voice signal of a terminal according to the present invention using the embodiment of FIG. 1 as hardware.

At this time, the algorithm according to the present invention is mounted in the Ypyrom 40 or the ROM 42 and is operated by the central processing unit 2. In addition, communication between terminals can be made by a switching action of the exchange via a base station (also referred to as a fixed station) having one cell, a base station controller communicating with a plurality of base stations, and an exchange communicating with a plurality of base station controllers. In general, the terminal and the base station communicate wirelessly in the cell of the base station, and the base station, the base station controller, and the switch between the wire communication.

The basic operation of each part according to FIG. 1 showing the hardware of the terminal according to the present invention will be described above.

First, the central processing unit 2 controls the power supply unit 6 by a user's key input so that power is applied to each part of the terminal, and the algorithm according to the present invention from EPI 40 or ROM 42 It is found by receiving a signal from the outside through the number of hardware-initialized parts of the terminal by receiving the stored algorithm, the antenna, the low noise amplifier 28, the intermediate frequency converter 30, and the demodulator 32. All channels from channels 0 to 9 of the base station are received while storing the signal strength of each channel in the RAM 44, and the base station of the strongest signal is selected (200, 202, 204, 206, 208, 210, 212, 214, 216).

At this time, by detecting the strength of the signal strength of the demodulator 32, the information according to the signal strength of each channel described above is received from the demodulator 32.

Next, it receives the contents of the first to 12th time slots in one frame of the transmission channel of the base station described above, selects the terminal number, and encrypts the received data when the terminal connection is established. The presence or absence of a MAC frame for transmitting a key value is checked (218, 220, 222, 224, 226).

When the MAC encryption key value transmission frame is detected among the received data, the encryption key value is stored in the RAM 44, and when the received signal level is low, the signal level moves to an appropriate base station to increase the received signal level (228, 230, 232).

Subsequently, the receiver receives the encrypted encoded speech data from the terminal in the cell to which the cell belongs and decrypts the received encrypted speech (234).

Next, the PCM-ADPCM converter 16 receives the decoded coded speech data through the digital signal processor 14 to convert the PCM data into PCM data, and the digital-to-analog converter 18 converts the PCM data into an analog signal. (236,238).

In addition, the sound signal is output through the speaker 20 so that the user can listen to the converted analog signal, and when the signal level of the base station is less than or equal to the reference value, a sound warning the content is output through the buzzer 38. .

Next, if the call is not terminated, the terminal access determination step 222 is performed again (240).

As described above, the present invention has the effect of intercepting a counterpart DECT terminal in the same cell to which it belongs when an interception is required due to an official reason such as an investigation.

Claims (1)

Initializing the terminal in hardware upon power-on, accepting all channels of the found base station (also called fixed station) and selecting the strongest signal base station (200, 202, 204, 206, 208, 210, 212, 214, 216) and; Receiving the contents of all the time slots in one frame and selecting the number of the terminal, and when the terminal is connected, checking whether there is a MAC frame for transmitting an encryption key value among the received data (218, 220, 222, 224, 226); If the MAC encryption key value transmission frame is detected in the received data, storing the encryption key value and moving the signal level to an appropriate base station (228, 230, 232); Receiving (234) encrypted cipher speech data from a terminal in the same cell to which the cell belongs; Converting the decoded encoded speech data into PCM data and converting the PCM data into an analog signal (236,238); Outputting the converted analog signal as a sound signal and checking a signal level of a base station and outputting a sound warning the content when the signal is below a reference value; If the call is not terminated, the method of listening to the voice signal of the terminal comprising the step (240) of performing again from the terminal connection determination step (222).