JP3300611B2 - Digital 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 an improvement in synchronization in a mobile station of a digital radio communication apparatus which performs communication in a TDMA system.

[0002]

2. Description of the Related Art TDMA (Time Division Multiple Access)
ion Multiple Access) wireless communication system
One frame is divided into 3-4 time slots,
By placing the signal of one terminal in one time slot, the signals of up to four terminals can be transmitted at the same frequency.
The receiving side can receive only the signal of the terminal of the communication partner by receiving the frame period in synchronization with the time slot of the transmitting side. In a digital communication system, the base station or a network accommodating the base station defines TDMA timing such as the frame and time slot, and the mobile station operates in synchronization with the timing.

However, in a mobile station immediately after power-on or immediately after moving into a service area from outside the wireless service area,
In the mobile station, the reception clock is not synchronized with the transmission clock of the base station, and the TDMA timing is not known.

For this reason, first, the communication frequency is continuously and asynchronously received and a signal from the base station is waited. The signal from the base station includes a preamble bit that repeats a fixed pattern. The mobile station receives the preamble bit asynchronously, reproduces the transmission clock of the base station, and synchronizes its own reception clock with this (this operation). Is referred to as “reception clock reception”).

Further, a signal from the base station includes a synchronization bit, and the mobile station receives this bit with a clock synchronized with the base station. The mobile station then knows the TDMA timing of the base station from the pre-defined frame structure and the position of the received synchronization bit (this is called "synchronization establishment"). Thereafter, the operation shifts to synchronous reception of only the time slot transmitted by this base station. At the time of synchronous reception, fine adjustment of reception clock and TD by reception of synchronization bit
MA timing maintenance (this is called "synchronization maintenance")
Is performed.

[0006] In the above asynchronous reception for reproducing the transmission clock, if the mobile station erroneously recognizes noise as a signal from the base station and receives the noise, the mobile station erroneously receives TDM.
It shifts to synchronous reception by A timing. As a result, the synchronous reception that should not be received is repeated, and after the reception failure has been performed a certain number of times or more, the loss of synchronization is detected and the process returns to the asynchronous reception. Therefore, a considerable amount of time elapses until synchronization with the base station is established and communication becomes possible.
Since noise is a random pattern, the probability of such a malfunction occurring is quite high. To prevent this, the received signal strength RSSI (Received Signal Strength Indicate) measured by the wireless receiver during asynchronous reception
(r: Indication of received signal strength) A method is used in which the level of a signal is monitored and the reception clock is pulled in and synchronization is established only when the signal level exceeds a threshold value and the signal has reception sensitivity.

Further, even during synchronous reception, for example, when the mobile terminal moves out of the wireless service area, a noise may be received instead of a signal from the base station to prevent malfunction.
A method is used in which the level of the SSI signal is constantly monitored, and synchronization is maintained only when the level exceeds the threshold.

In a conventional system, an RSSI signal output from a radio receiver is input to an analog signal comparator, and a comparison result with a threshold value for determining the presence or absence of reception sensitivity is output. ON / OF of synchronization maintenance
F was controlled.

FIG. 6 is a block diagram of a conventional RSSI signal determination unit 80 and its peripherals in a digital cordless telephone handset. The RSSI signal level output from the RSSI generator 70 is input to one input terminal of the analog signal comparator 801 in the RSSI signal determiner 80. A power supply voltage is connected to the other input terminal of the analog signal comparator by a resistor R1.
(802), the voltage divided by R2 (803) is input as a threshold level. The analog signal comparator 801 outputs to the control unit 90 as a determination signal which of the two input terminals is higher in level.

FIG. 5 shows how the level of the RSSI signal output from the RSSI generator 70 changes.

The RSSI signal level (a) rises to a noise level when the power of the radio receiving unit of the mobile station is turned on. Further, the level rises to the reception level while the radio receiving unit is receiving the signal from the base station from the time of receiving the signal. Then, when the reception is completed, the signal level falls to the noise level again. Further, it drops to 0 when the power of the wireless receiving unit is turned off.

The RSSI signal determination section 80 calculates the RSSI
The signal level is input to the analog signal comparator 801 and R
It is determined that there is reception sensitivity from the point in time when the SSI signal level exceeds the threshold during the reception period, and the determination output becomes true. FIG. 5B shows an analog signal comparator 80.
7 is a waveform of a determination signal output from the first example.

Since the conventional method is such a method, the threshold level input to one input of the analog comparator 801 is a fixed value obtained by dividing the power supply voltage by resistance. Then, this threshold level is set low so that synchronization can be maintained even if the RSSI signal level becomes weak during synchronous reception, and the communicable distance is extended as much as possible. For this reason, in a system in which a plurality of base stations are installed in the same area, even in a distant base station or a base station with poor reception, the RS
The SI signal level may exceed the threshold value, and the mobile station may receive the signal of such a station by asynchronous reception and connect as it is.

FIG. 7 shows an example of the operation at the time of asynchronous reception by the conventional system. When there are a plurality of base stations having a reception level higher than the threshold value, instead of receiving the signal (a) of the base station having the highest level and the stable level, the signal of the base station that first exceeds the threshold value ( Establish synchronization with b).

In such a case, since there is no margin in the reception level necessary for maintaining the synchronization thereafter, the probability that the synchronization is lost and communication becomes impossible on the way is established with the signal (a). Higher than the case.

[0016]

As described above, in the conventional digital communication apparatus, the threshold value of the RSSI signal level is set rather low so that the communicable distance is extended. For this reason, there is a possibility that a base station suitable for communication and a distant base station or a base station with poor reception status may be accepted under equal conditions, and a base station with poor reception status may be selected and terminated. .

An object of the present invention is to improve this point and to realize a digital communication apparatus capable of automatically selecting a base station having a high reception level from a plurality of base stations and performing communication.

[0018]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a receiving intensity detecting means for detecting the receiving intensity of a received signal, and a receiving threshold detected by the receiving intensity detecting means. Receiving strength comparing means for comparing the received signal with the detected receiving signal when the receiving strength comparing means determines that the received strength of the received signal is equal to or greater than the threshold value. In a digital communication apparatus having synchronous communication means for performing communication by means of a communication, the reception intensity comparing means sets the threshold value to an allowable maximum value at the start of the synchronous communication, and thereafter, the synchronous communication means detects the reception signal. A threshold variable setting means for sequentially setting the threshold value to a lower value until the threshold value is changed.

As described above, according to the present invention, by gradually lowering the threshold value for comparing the received electric field strength, synchronization is established from the received signal having the higher received electric field strength.
Without selecting a base station with poor reception,
A base station having a high reception level can be automatically selected from a plurality of base stations to perform communication.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the digital communication apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a digital cordless telephone handset (PS: Personal Station) to which the present invention is applied.

In FIG. 1, reference numeral 1 denotes a receiving side which receives a radio wave from a base station, converts it into a digital baseband signal by performing intermediate frequency processing and receives it, and transmits a digital baseband signal to the base station by performing intermediate frequency processing on the transmitting side. The radio section 2 converts the frequency to power, amplifies the power, and transmits it as a radio wave to the base station. On the receiving side, it performs frame synchronization and bit synchronization from the digital baseband signal, sends the synchronization signal to the control section 5, and shifts the received signal by π / 4. A demodulation unit for performing QPSK demodulation is provided.
The modem unit having a modulator for K modulation, 3 is π on the receiving side.
The own slot signal is extracted from the digital signal demodulated by / 4 shift QPSK, and the transmitting side places a voice-encoded signal in its own slot of the TDMA signal in TDMA (Time).
DivisionMultiple Access), 4 is AD on the receiving side
A communication unit that performs PCM demodulation, demodulates a voice signal from a digital signal by performing PCM demodulation, and sends the demodulated signal to a speaker 43 serving as a receiver; and a transmitting unit that performs PCM modulation and ADPCM modulation on a voice signal from a microphone 44 serving as a transmitter. 5 is a control unit for controlling the entire apparatus, 6 is a display unit for displaying a display necessary for communication, a dial number, etc., 7 is an operation unit for operating a device such as a key dial operation, and 8 is a ringing tone. A sounder 9 is a memory unit for storing information necessary for control, a program, a speed dial, and the like.

The radio section 1 is used in common for transmission and reception. The antenna 11 transmits and receives radio waves, and receives a radio reception signal from the base station received by the antenna 11 via a transmission / reception switch 15 to tune and select a station. The receiving unit 12 converts the received signal to a digital baseband signal by performing intermediate frequency processing on a carrier signal output from the synthesizer 14 and the like, and performs intermediate frequency processing on the π / 4 shift QPSK modulated signal from the modulation unit 22 and finally synthesizer A transmitting unit 13 that modulates with a carrier signal output from 14, amplifies the power to a level required for transmission, and transmits via a transmission / reception switch 15, and a synthesizer 14 that combines and outputs a carrier signal from an oscillation signal from a crystal oscillator 16. The antenna 11 is connected to the receiving unit 12 and the transmitting unit 1 according to the transmission / reception control signal from the control unit 5.
3 is provided with a transmission / reception changeover switch 15 for switching the number to 3.

The modem section 2 demodulates and detects a π / 4-shifted QPSK modulated signal of the received digital baseband signal output from the receiving section 12 and converts it into a serial data signal.
And the serial data signal from the TDMA transmission unit 32
A modulating unit 22 for modulating a / 4 shift QPSK modulated signal;
The RSSI signal generator 23 and the RS
It comprises an SI signal determination unit 24.

Further, the TDMA unit 3 is provided with a TDMA receiving unit 31 for extracting the own slot signal from the serial data signal output from the demodulating unit 21 and performing a time division multiplexing decoding.
It comprises a TDMA transmission unit 32 that encodes an audio signal from the codec 41 into a transmission slot.

The speech unit 4 is an adaptive differential pulse code modulation code composite device that performs speech processing with simple processing and small delay while maintaining speech quality in accordance with the linear prediction of the speech signal using the redundancy of the speech signal. An ADPCM (Adaptive
Pulse Code Modulation (codec) 41 and a PCM (Pu) that digitizes analog voice into PCM code and converts voice digitized into PCM code into an analog signal.
lse Code Modulation) codec 42,
It is connected to a speaker 43 as a receiver and a microphone 44 as a transmitter.

On the other hand, the control section 5 is constituted by a microprocessor or the like, and controls the entire apparatus. A display unit 6 for displaying a display necessary for communication and a dial number, an operation unit 7 for operating a device such as a key dial operation, a sounder 8 for generating a ringing tone, information necessary for control, a program and a speed dial, etc. Is connected.

In the RSSI signal generator 23, the receiver 12
And an analog RSSI signal is generated by searching for the RSSI signal included in the output baseband signal. RSSI
The signal determination unit 24 compares the level of the RSSI signal with a threshold level to determine the presence or absence of reception sensitivity and notifies the control unit 5. The control unit 5 controls the modem demodulation unit 21, the reception unit 12 and the transmission unit 13 based on this information, and turns on / off the reception clock pull-in and synchronization establishment for asynchronous reception, and synchronization for synchronous reception. ON of maintenance /
Control OFF.

FIG. 2 shows an RSSI signal determination unit 2 according to the present invention.
4 is a block diagram of one embodiment of FIG. This circuit includes an analog signal comparator 241, a threshold data register 242, and a D / A converter 243. The output of the D / A converter 243 is connected to a threshold level input terminal of the analog signal comparator 241. I have. The control unit 5 can control the output level of the D / A converter 243 by writing the threshold setting value to the threshold data register 242.

FIG. 3 shows the RSSI signal determination section 2 of this embodiment.
4 is a flowchart of an RSSI signal determination control operation of FIG. FIG. 4 is an explanatory diagram of the receiving sensitivity determination operation in this embodiment. The operation of the RSSI signal determination unit 24 will be described with reference to these drawings.

When the power is turned on in step 100 of FIG. 3, the control unit 5 of the slave unit of the digital cordless telephone sets a higher threshold value for asynchronous reception and stores the value in the threshold data register 242. Memorize (step 101),
Asynchronous reception is started (step 102).

If the asynchronous reception succeeds within a preset time (step 103), the control unit 5 sets a threshold slightly lower than the current threshold for the synchronous reception, and sets the threshold data. The data is stored in the register 242 (step 104), and synchronous reception is started (step 105). If synchronization is lost during synchronous reception, step 101 is performed again.
And start over from asynchronous reception.

If the asynchronous reception is not successful within a preset time (step 103), ie, as shown in FIG.
If the state without reception sensitivity continues for a certain period of time as shown in FIG. 4A, the control unit 5 lowers the threshold value stored in the threshold data register 242 by a certain level as shown in FIG. ), Asynchronous reception is restarted (step 102) within a range where the threshold value does not become equal to the noise level (step 107).

This operation is repeated until the asynchronous reception succeeds. If the threshold value reaches the noise level without reception sensitivity, there is no base station nearby (out of service area).
Thus, the threshold value is set higher again, and the process returns to step 101 to resume the asynchronous reception.

In this way, the controller 5 sets the initial value to a relatively high level for asynchronous reception, and gradually lowers the value if no signal can be received. The signal can be received while receiving the signal from the base station having the highest reception electric field.

[0036]

As described above, according to the present invention, the threshold for comparing the strengths of the received signals is initially set to a relatively high value.
Thereafter, the communication level is gradually lowered so that communication is performed in synchronization with the reception signal that first exceeds the threshold value. Therefore, it is possible to automatically select a base station having a high reception level from among a plurality of base stations and perform communication, and to select a base station having a poor reception state, thereby deteriorating the communication quality or preventing communication. It is possible to reduce the occurrence of problems such as loss of synchronization and communication failure on the way.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital cordless telephone handset to which the present invention is applied.

FIG. 2 is an RSS of the digital cordless telephone handset of FIG. 1;
FIG. 3 is a block diagram of an embodiment of an I signal determination unit.

FIG. 3 is an operation flowchart of the embodiment of the RSSI signal determination unit of FIG. 2;

FIG. 4 is an explanatory diagram of a receiving sensitivity determination operation.

FIG. 5 is a diagram illustrating a change in the level of an RSSI signal and a determination result of an RSSI signal determination unit.

FIG. 6 shows an RSS of a conventional example of a digital communication device mobile station.
FIG. 3 is a detailed block diagram of an I signal determination unit.

FIG. 7 is an explanatory diagram of a reception sensitivity determination operation in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radio part 2 Modem part 3 TDMA part 4 Talking part 5, 90 Control part 6 Display part 7 Operation part 8 Sounder 9 Memory part 11 Antenna 12 Receiving part 13 Transmitting part 14 Synthesizer 15 Transmission / reception switch 16 Crystal oscillator 21 Demodulation part 22 Modulation Units 23, 70 RSSI signal generation unit 24, 80 RSSI signal determination unit 31 TDMA reception unit 32 TDMA transmission unit 41 ADPCM codec 42 PCM codec 43 Receiver (speaker) 44 Transmitter (microphone) 241, 801 Analog signal comparator 242 Threshold data register 243 DA converter 802, 803 Resistance

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-182041 (JP, A) JP-A-8-8808 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 7/24-7/26 H04Q 7/00-7/38

Claims (1)

(57) [Claims] 1. A receiving strength detecting means for detecting a receiving strength of a received signal, a receiving strength comparing means for comparing the receiving strength detected by the receiving strength detecting means with a predetermined threshold value, and a receiving strength comparing means. A digital communication device having synchronous communication means for detecting the reception signal and performing communication in synchronization with the detected reception signal when the reception intensity of the reception signal is determined to be equal to or higher than the threshold value; The reception intensity comparing means sets the threshold value to an allowable maximum value at the start of the synchronous communication, and thereafter variably sets the threshold value to a lower value until the synchronous communication means detects the reception signal. A digital communication device comprising a threshold variable setting unit.