JP2001069037A - Spread spectrum communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spread spectrum communication equipment that can discriminate the presence of use of a channel affected by a different kind of PN codes and a side lobe. SOLUTION: The spread spectrum communication receiver 11 is provided with an inverse spread device 17 that uses an inverse spread code to generate a primary modulation signal from a spread spectrum signal as a high frequency signal, an intermediate frequency section 15 that generates an intermediate frequency signal 22 from the primary modulation signal 21, detects a reception electric field strength value from the generated intermediate frequency signal and discriminates whether or not the detected reception electric field strength value exceeds 1st and 2nd reception electric field strength threshold values, an analog demodulator 14 that demodulates the intermediate frequency signal to provide an output of an information signal, a noise squelch circuit 28 that discriminates whether or not a white noise level outputted from the analog demodulator exceeds a noise squelch threshold value, and an idle channel discrimination circuit 29 that discriminates whether or not an idle channel is in existence on the basis of the discrimination results by the intermediate frequency section and the noise squelch circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication apparatus comprising a transmitter using a spread spectrum communication system and a receiver.

[0002]

2. Description of the Related Art In recent years, FCC (Federal Com
communications-Communications-Communications (ISM) for spread spectrum communications.
1, Scientific and Medical)
Since the band was released, products using this method have appeared in various communication equipment fields such as cordless telephones.

[0003] The spread spectrum system is characterized by excellent anti-interference and confidentiality. Also, by using this method, transmission with a larger output than in the case of the conventional analog communication method is approved by the FCC, which is advantageous in terms of communication distance. On the other hand, products using this system are generally based on digital communication systems, and are more complicated and expensive than products using conventional analog communication systems. Therefore, an inexpensive spread spectrum communication apparatus in which a simple circuit for performing spreading and despreading is added to a conventional analog communication apparatus has been devised.

Hereinafter, a spread spectrum communication apparatus based on the analog communication system will be described with reference to the drawings.

FIG. 2 is a block diagram showing a conventional spread spectrum communication apparatus.

The spread spectrum communication apparatus shown in FIG. 2 has, as main components, a transmitter 31 and a receiver 41 capable of communicating with the transmitter 31 by radio. The transmitter 31 includes, as constituent elements, an FM modulator 32 as an analog modulator for performing primary modulation for putting an information signal on a high frequency, and a PN code generator 3 for generating a spread spectrum signal.
6, a spreader 33, an RF transmitter 34 for converting a modulated signal (spread spectrum signal) into a high frequency and amplifying the signal, and an antenna 35 for transmitting a high frequency signal. The receiver 41 includes an antenna 49 for receiving a signal from the transmitter 31, an RF receiving unit 48 for amplifying a received high-frequency signal and converting the signal to a spread spectrum signal, and a narrowband signal based on the received spread spectrum signal. P for returning to FM modulated signal
An N code generator 43, a despreader 47, a synchronizing circuit 42 for synchronizing a signal from a transmitter with a PN code of a receiver, an A / D converter (ADC) 46, and a signal from the despreader 47 An RS for generating an intermediate frequency signal from the primary modulation signal and detecting a received electric field strength value from the generated intermediate frequency signal
An IF unit (intermediate frequency unit) 45 having an SI circuit, an FM demodulator 44 as an analog demodulator for demodulating the intermediate frequency signal from the IF unit 45, and a noise squelch threshold value. A noise squelch circuit 58 for determining whether or not the output white noise level exceeds the noise squelch threshold; and an empty channel for determining whether there is an empty channel based on the determination result in the noise squelch circuit 58. A determination circuit 59;

The operation of the spread spectrum communication apparatus configured as described above will be described below.

In order to establish good communication, the receiver 41 first determines an empty channel. The noise squelch circuit 58 is used for this. A channel in which the white noise level of the FM demodulator 44 input to the noise squelch circuit 58 is equal to or higher than a certain threshold (noise squelch threshold) is determined to be empty, and communication is performed on that channel.

[0009] The information input to the transmitter 31 is converted by the FM modulator 32 into the narrow band F, which is the same as that of the conventional analog communication system.
An M-modulated signal 37 is obtained. This narrow-band FM modulation signal 37
Is the spreading code 38 generated by the PN code generator 36.
The signal is modulated by the spreader 33 and becomes a spread spectrum signal 39, which is input to the RF transmitter 34. A high frequency signal 40 obtained by converting and amplifying the spread spectrum signal 39 to a high frequency in the RF transmitting unit 34 is radiated from the antenna 35. On the other hand, the signal transmitted from the transmitter 31
The signal is received by one antenna 49 and amplified by the RF receiver 48. The RF spread modulated signal (spread spectrum signal) 50 output from the RF receiver 48 is multiplied by a despreader 47 by a despread code 56 generated by the PN code generator 43. At this time, the timing of the PN code generator 43 is controlled by the synchronization circuit 42 and is synchronized with the RF spread modulation signal 50, so that the original narrow band FM modulation signal 51 is obtained as the output of the despreader 47. The narrow-band FM modulated signal 51 is converted and filtered into an intermediate frequency signal 52 by an IF unit 45, and is demodulated to an original information signal by an FM demodulator 44.

The synchronization circuit 42 is a kind of a sliding correlator using the RSSI voltage (voltage indicating the received electric field strength) of the IF unit 35, and the correlation operation will be described. The despreading code 56 used for despreading and the spreading code 38 at the time of spreading have exactly the same code and speed. I
When the signal level after being converted and filtered into the intermediate frequency signal 52 by the F section 45 is monitored by the RSSI voltage 53, the phases of the despreading code 56 and the RF spread modulated signal 50 are synchronized, and the maximum is obtained when the correlation value is the maximum. Is obtained. By sliding the phase of the despreading code, this maximum RSS
Despreading is performed by capturing and tracking the phase at which the I voltage is obtained. In practice, the synchronizing circuit 42 adjusts the phase of the PN code generator 43 with the phase adjustment signal 55 so that the RSSI voltage 53 is converted into digital data by the A / D converter 46 and the peak position of the data 54 is captured and held. I do.

The synchronizing circuit 42 has two functions of synchronizing acquisition and synchronizing.
It has different operation modes. Hereinafter, examples of these two operation modes will be described.

In the synchronous acquisition mode, the following procedure is taken to reduce
Determine the approximate synchronization position for each chip.

First, the spreading code 56 is output from the PN code generator 43 at an appropriate phase for a fixed time, and the RSS at that time is output.
The I data 54 and the phase are recorded. Next, the phase is shifted by チ ッ プ chip, and the spreading code 56 is output for a certain period of time. If the RSSI data 54 at that time is higher than the recording value, the recording value of the RSSI data and the phase at that time are recorded. By repeating this, the maximum value of the RSSI data and the phase at that time are recorded. Such an operation is 1 /
Repeat for all phases in 2-chip units, RS
With the position where the SI data becomes maximum as the synchronization point, the phase jumps to that phase to complete the synchronization acquisition.

After completion of the synchronization acquisition, the mode is shifted to the synchronization holding mode for further fine phase adjustment and the holding thereof. The procedure of the synchronization holding mode is as follows.

At the phase at the time of completion of synchronization acquisition, the spreading code 56 is output for a fixed time, and the RSSI data 54 at that time is recorded. The phase of the spreading code 56 is shifted by 1/8 chip in an arbitrary direction, the spreading code 56 is output for a certain period of time, the RSSI data 54 at that time is compared with the previously recorded data, and the results are used as a1 to a3. Is determined.

A1. RSSI rise → Next time shift 1/8 chip in the same direction a2. RSSI down → Next time shift 1/8 chip in the reverse direction a3. No RSSI change → No phase change next time By repeating this, the phase within ± 1/8 chip from the synchronization point is held.

The spread spectrum communication apparatus based on the analog communication system as described above has the following merits as shown in b1 to b3 as compared with the digital system.

B1. The circuit configuration and operation are greatly simplified, and the cost is reduced.

B2. The FM demodulator 44 is advantageous in terms of reception sensitivity over the demodulator of the digital system, and can extend the communication limit distance.

B3. Particularly, in a system for transmitting voice, there is no need to code voice, so that voice delay due to the coding circuit does not occur.

[0021]

However, in the above-mentioned conventional spread spectrum communication apparatus, whether or not a channel is used is determined only by the determination result 57 of the noise squelch circuit 58. There is a problem that a channel used by another signal of the electric field may be determined to be empty. This is PN
If the type of the code is different, the FM demodulation signal cannot be demodulated, or even if the FM demodulation can be performed to a certain extent, the FM demodulated signal is greatly distorted (10 kHz of one period of the PN code or 2 times of double frequency).
This is because the white noise component exceeds the noise squelch threshold value. For this reason, there is a problem in that communication is attempted to be established on a channel used by another signal, and a case where a call is not established or a case where a call state in which a call can be established cannot be secured cannot be ensured.

In order to perform communication in a good state, it is necessary to accurately search for an available channel (a channel that can be used for communication, that is, a channel that is not being used) and perform communication using that channel. In a normal analog communication system, it is possible to easily determine whether a channel is used by using either the noise squelch circuit 58 or the RSSI circuit of the IF unit 45. However, in the case of an analog communication system using spread spectrum technology, it is necessary to determine whether or not to use a channel using a different type of PN code or a channel to which a sidelobe component of a relatively strong electric field signal is applied. Squelch circuit or RSS
It is difficult with a method using either of the I circuits.

This spread spectrum communication apparatus is required to be able to determine whether or not to use a channel affected by different PN codes and side lobes, which is difficult with a conventional spread spectrum communication apparatus based on an analog communication system. I have.

An object of the present invention is to provide a spread spectrum communication apparatus capable of determining whether or not a channel affected by different PN codes or side lobes is used.

[0025]

In order to solve the above problems, a spread spectrum communication apparatus according to the present invention is a spread spectrum communication apparatus comprising a transmitter and a receiver using a spread spectrum communication system, wherein the transmitter is An analog modulator that modulates an information signal to output a primary modulation signal, a spreader that generates a spread spectrum signal from the primary modulation signal output from the analog modulator, and a spread spectrum signal from the spreader as a high frequency signal. A high-frequency transmitting unit for transmitting, the receiver includes a high-frequency receiving unit that receives a high-frequency signal, and an inverse generating unit that generates a primary modulation signal using a despread code from a spread spectrum signal as a high-frequency signal from the high-frequency receiving unit. An intermediate frequency signal is generated from a primary modulation signal from a spreader and a despreader, and a received electric field strength value is detected from the generated intermediate frequency signal. An intermediate frequency unit for determining whether the detected received electric field intensity value exceeds the first and second received electric field intensity thresholds, an analog demodulator for demodulating the intermediate frequency signal and outputting an information signal, A noise squelch circuit that determines whether the white noise level output from the analog demodulator exceeds a noise squelch threshold value, and whether there is an empty channel based on the determination result in the intermediate frequency section and the determination result in the noise squelch circuit And an empty channel determination circuit for determining whether or not the channel is empty.

Thus, a spread spectrum communication apparatus capable of determining whether or not a channel affected by different PN codes or side lobes is used can be obtained.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A spread spectrum communication apparatus according to a first aspect of the present invention is a spread spectrum communication apparatus comprising a transmitter and a receiver using a spread spectrum communication system, wherein the transmitter is an information signal. An analog modulator that modulates the signal to output a primary modulation signal, a spreader that generates a spread spectrum signal from the primary modulation signal output from the analog modulator, and a high frequency that transmits the spread spectrum signal from the spreader as a high frequency signal Having a transmitting unit, the receiver is a high-frequency receiving unit that receives a high-frequency signal, and a despreader that generates a primary modulation signal using a despread code from a spread spectrum signal as a high-frequency signal from the high-frequency receiving unit. , Generates an intermediate frequency signal from the primary modulation signal from the despreader, and detects and detects the received electric field strength value from the generated intermediate frequency signal. An intermediate frequency unit for determining whether or not the received electric field intensity value exceeds the first and second received electric field intensity thresholds; an analog demodulator for demodulating the intermediate frequency signal to output an information signal; and an analog demodulator A noise squelch circuit that determines whether or not the white noise level output from the noise squelch threshold value is exceeded, and whether there is an empty channel based on the determination result in the intermediate frequency unit and the determination result in the noise squelch circuit. And an empty channel determining circuit for determining.

With this configuration, it is possible to determine whether or not there is an empty channel based on the three thresholds of the noise squelch threshold and the first and second reception field strength thresholds. It is possible to reliably determine an empty channel before the start, and to perform communication on a channel without interference or a channel that minimizes interference even if it is received.

A spread spectrum communication apparatus according to a second aspect of the present invention is the spread spectrum communication apparatus according to the first aspect, wherein: noise squelch threshold <first reception field strength threshold <second reception field strength. It is assumed that there is a threshold value relationship.

With this configuration, the vacant channel determination circuit can accurately determine a vacant channel, and the provision of only three thresholds minimizes the number of parts and increases the cost of the vacant channel. This has the effect of making a determination.

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

(Embodiment 1) FIG. 1 is a block diagram showing a spread spectrum communication apparatus according to Embodiment 1 of the present invention.

The spread spectrum communication apparatus shown in FIG. 1 comprises, as main components, a transmitter 1 and a receiver 11 capable of communicating with the transmitter 1 by radio. The transmitter 1 has, as a component, an F that performs primary modulation for putting an information signal on a high frequency.
An M modulator 2, a PN code generator 6 and a spreader 3 for generating a spread spectrum signal, an RF transmitter 4 for converting and amplifying the modulated signal to a high frequency, and an antenna 5 for transmitting a high frequency signal. Having. The receiver 11 has an antenna 19 for receiving a signal from the transmitter 1 and an R 19 for amplifying the received high-frequency signal and converting it to a spread spectrum signal.
F receiving unit 18 and a PN code generator 13 for returning the received spread spectrum signal to the original narrow band FM modulation signal
And a despreader 17, a synchronizing circuit 12 for synchronizing a signal from the transmitter 1 with the PN code of the receiver 11, an A / D converter (ADC) 16, and an RSSI circuit. Is converted to the intermediate frequency signal 22
An IF unit (intermediate frequency unit) 15, an FM demodulator 14 for demodulating the intermediate frequency signal from the IF unit 15, a noise squelch (Noise Squelch) circuit 28,
And an empty channel determination circuit 29. In this embodiment, the spreading code and the despreading code are 1.28M
cps / 2.56 Mcps (mega cycle), 127c
A hip (chip) M-sequence PN code is used.

The function and operation of the spread spectrum communication apparatus configured as described above will be described.

First, the general function and general operation will be described. As can be seen from a comparison between FIG. 1 and FIG. 2, in the present embodiment, the components are the same as in FIG.
5 and the empty channel determination circuit 29 have different functions and operations. That is, the feature of the present embodiment is that the receiver 11
Noise squelch circuit 2 having noise squelch threshold
8, an IF unit 15 having an RSSI circuit having two thresholds of first and second reception electric field strength thresholds, and an idle channel determination for determining an empty channel based on the outputs of these two circuits 28 and 15. Circuit 29, the presence or absence of a correlation (use / non-use of a channel) is determined based on the determination result of the noise squelch circuit 28. If it is determined that there is no correlation (no use), then the IF unit That is, an operation of determining whether or not a channel is used by a different PN code (no correlation) using the 15 RSSI circuits. When the determination is made by the RSSI circuit, it may be erroneously determined that all channels are in use due to side lobe components of other channels. Therefore, two thresholds are provided, and all channels are used with the first reception field strength threshold RSSI1. Only when the determination is made, the erroneous determination is eliminated by using the second reception field strength threshold RSSI2 which is a higher threshold.

Next, the function and operation of the spread spectrum communication apparatus of FIG. 1 will be described in detail. Note that the general operation of the spread spectrum communication apparatus is the same as that of the related art, and a description thereof will be omitted. That is, the signals 37 to 37 in FIG.
40 corresponds to the signals 7 to 10 in FIG. 1 and the signals 50 to 50 in FIG.
57 corresponds to the signals 20 to 27 in FIG.

The noise squelch circuit 28 is an analog FM
The same cut-off frequency 2 used for the receiver
It has a high-pass filter of 0 kHz and outputs 20 kHz as a white noise component from the detection output signal of the FM demodulator 14.
The above band is extracted, the level of the white noise component is detected as a DC level, and the magnitude of the white noise amount is determined based on a threshold (noise squelch threshold) set by a comparator.

The threshold value of the noise squelch circuit 28 is adjusted so that the threshold value comes to the reception sensitivity point of the receiver 11, as in the case of the conventional analog FM receiver used for weak electric field determination. The two threshold values of the RSSI circuit of the IF unit 15 are noise squelch threshold value <first reception field strength threshold RSSI1 <second reception field strength threshold RSSI2
Set so that

As a procedure for determining an empty channel, first, a determination is made by the noise squelch circuit 28 set to the lowest threshold value. When the noise squelch circuit 28 determines that the white noise output from the FM demodulator 14 is equal to or smaller than the noise squelch threshold value, the channel determined to be in use by the idle channel determination circuit 29 is regarded as a busy channel, and thereafter, The channel is not used until it is determined that the channel is an empty channel or after it is determined that all channels are busy (in use), and then selected as a channel in good use.

If the vacant channel determination circuit 29 determines that the channel is an empty channel based on the determination result from the noise squelch circuit 28, the RSSI circuit then changes the received signal power level (received field intensity value) to the first received electric field strength. Compare with threshold RSSI1. Here, the channel is determined to be empty only when the received signal power level is determined to be equal to or lower than the threshold RSSI1. A signal 30 a indicating the determination result based on the threshold RSSI 1 is input from the IF unit 15 to the empty channel determination circuit 29.

If it is determined that the received signal power level is equal to or higher than the first received electric field strength threshold RSSI1, this channel is performing communication using a different type of PN code, or performing communication in a nearby channel. Since it is considered that the side lobe which is the diffusion component is applied to this channel, the channel is determined to be a busy channel.
When it is determined that all channels are busy in the determination with the threshold RSSI1, it is necessary to select a channel having a better use status from among them and perform communication. The channel determined to be busy here is one of the following a1 to a3.

A1. Channels communicating with the same PN code (determined by noise squelch circuit 28) a2. Channel on which communication is performed using different PN codes a3. Communication is performed by a relatively strong radio wave on a nearby channel, and a channel with side lobes is applied. In the case of a3, communication is not actually performed on that channel. We can keep good situation. In the case of a2, a relatively good situation can be maintained if communication is performed at a radio wave level that is equal to or more than the cross-correlation from the interference wave (that is, different PN codes). Therefore, the threshold RSSI2 is set to (RSSI2 + α)
> RSSI1 is set, and it is determined which of the above a1 to a3. The value α is set so that the simultaneous use status of a plurality of receivers is created and an optimum level difference is provided. When it is determined that all channels are busy with the first reception field strength threshold RSSI1, communication is performed on a channel determined to be free using the second reception field strength threshold RSSI2.

In the above-described determination, the channel determined to have a radio wave of the threshold RSSI2 or more is transmitted on the same channel using a different PN code at a short distance or is transmitted on a nearby channel. Even if characteristics such as cross-correlation and process gain are utilized, good communication cannot be ensured. A signal 30 b indicating the determination result based on the threshold RSSI 2 is input from the IF unit 15 to the empty channel determination circuit 29.

As described above, the noise squelch threshold, the first
By determining whether to use or not use the channel in three stages, such as the reception field strength threshold RSSI1 and the second reception field strength threshold RSSI2, it is possible to reliably determine an empty channel before starting communication, Communication can be performed on a channel without interference.

As described above, according to the present embodiment, the intermediate frequency section 15 determines whether or not the detected received field strength value has exceeded the first and second received field strength thresholds RSSI1 and RSSI2. A noise squelch circuit 28 that determines whether the white noise level output from the FM demodulator 14 exceeds a noise squelch threshold value, and a determination result in the intermediate frequency unit 15 and a determination result in the noise squelch circuit 28. And a vacant channel determination circuit 29 for determining whether there is a vacant channel, based on the three thresholds of the noise squelch threshold and the first and second reception field strength thresholds. Since it is possible to determine whether or not there is an empty channel, it is possible to reliably determine an empty channel before starting communication, and It is possible to perform communication with no channel.

Further, since the relationship of noise squelch threshold value <first received electric field intensity threshold value <second received electric field intensity threshold value is established, the empty channel judgment circuit 29 judges an empty channel. Can be performed accurately, and only three thresholds are provided, so that the determination of an empty channel can be performed with a minimum number of parts and an increase in cost.

[0047]

As described above, according to the spread spectrum communication apparatus of the first aspect of the present invention, a spread spectrum communication apparatus including a transmitter and a receiver using a spread spectrum communication system, The modulator modulates an information signal and outputs a primary modulation signal, a spreader that generates a spread spectrum signal from the primary modulation signal output from the analog modulator, and a high frequency spread spectrum signal from the spreader. The receiver has a high-frequency transmitting unit that transmits a signal, and the receiver generates a primary modulation signal using a despread code from a high-frequency receiving unit that receives the high-frequency signal and a spread spectrum signal as a high-frequency signal from the high-frequency receiving unit. A despreader that generates an intermediate frequency signal from the primary modulation signal from the despreader and detects the received electric field strength value from the generated intermediate frequency signal An intermediate frequency section for determining whether or not the detected received electric field strength value has exceeded the first and second received electric field strength threshold values; and an analog demodulator for demodulating the intermediate frequency signal and outputting an information signal. A noise squelch circuit that determines whether the white noise level output from the analog demodulator exceeds a noise squelch threshold, and an empty channel based on the determination result in the intermediate frequency section and the determination result in the noise squelch circuit. And a vacant channel determination circuit for determining whether or not there is a vacant channel based on three thresholds of a noise squelch threshold and first and second reception field strength thresholds. Can be reliably determined before communication starts, and a channel without interference or interference can be determined. Advantageous effect of it even only can communicate with the channel to suppress to a minimum is obtained.

According to the spread spectrum communication apparatus of the second aspect, in the spread spectrum communication apparatus of the first aspect, the noise squelch threshold <the first reception electric field strength threshold <the second reception electric field Due to the relationship of the intensity threshold value, the determination of the empty channel in the empty channel determination circuit can be accurately performed, and the minimum number of parts and the increase in cost can be attained by providing only three threshold values. , An advantageous effect of being able to judge an empty channel can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a spread spectrum communication apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional spread spectrum communication apparatus.

[Explanation of symbols]

 Reference Signs List 1 transmitter 2 FM modulator 3 spreader 4 RF transmitter 5, 19 antenna 6, 13 PN code generator 11 receiver 14 FM demodulator 15 IF section (intermediate frequency section) 16 A / D converter (ADC) 17 reverse Spreader 18 RF receiver 28 Noise squelch circuit 29 Free channel determination circuit

Claims (2)

[Claims] 1. A spread-spectrum communication device comprising a transmitter and a receiver using a spread-spectrum communication method, wherein the transmitter modulates an information signal and outputs a primary modulation signal; A spreader that generates a spread spectrum signal from a primary modulation signal output from an analog modulator, and a high frequency transmission unit that transmits a spread spectrum signal from the spreader as a high frequency signal, wherein the receiver has the high frequency A high-frequency receiving unit that receives a signal, a despreader that generates a primary modulation signal using a despread code from a spectrum spread signal as a high-frequency signal from the high-frequency receiving unit, and a primary modulation signal from the despreader. An intermediate frequency signal is generated, and a received electric field intensity value is detected from the generated intermediate frequency signal, and the detected received electric field intensity value is first, 2, an intermediate frequency section for determining whether or not the received electric field strength threshold value has been exceeded, an analog demodulator for demodulating the intermediate frequency signal and outputting an information signal, and a white noise level output from the analog demodulator A noise squelch circuit for determining whether or not a threshold value exceeds a noise squelch threshold, and an empty channel determination for determining whether or not there is an empty channel based on a determination result in the intermediate frequency section and a determination result in the noise squelch circuit. And a circuit. 2. The spread-spectrum communication apparatus according to claim 1, wherein a relation of the noise squelch threshold value <the first reception electric field intensity threshold value <the second reception electric field intensity threshold value is satisfied. .