JP2000209127A - Spread spectrum communication unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spread spectrum communication unit that utilizes an RSSI for a correlation circuit of a receiver and adopts an analog modulation system for primary modulation, can solve a problem of an unstable inverse spread processing due to the saturation of the RSSI when an input level to the receiver is very high. SOLUTION: The communication unit consists of a set of a transmitter 1 and a receiver 11, an inverse spread device 17 of the receiver 11 is provided to a 1st IF section, a limiter amplifier 29 is added to a stage just before the 1st IF section so as to limit an input level to the inverse spread device 17 to be a saturating point of the RSS 115 or below. Thus, the communication unit can stably be operated even when an input level to the receiver 11 is very high.

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 pair of a transmitter and a receiver which are cordlessly connected to each other using a spread-spectrum communication system.

[0002]

2. Description of the Related Art In recent years, Federal Commun
Institutions Commission (FCC) for Industrial, Sc
identific and Medical (ISM)
Since the release of Band, products using this method have appeared in various communication equipment fields such as cordless telephones. 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 method are generally based on digital communication methods, and are more complex than products using conventional analog communication methods.
It is also expensive. Therefore, the conventional analog communication device,
An inexpensive spread spectrum communication device has been devised, in which a simple circuit for performing spreading and despreading is added.

[0003] A spread spectrum communication apparatus based on this analog system will be described below with reference to the drawings. FIG. 4 is a configuration diagram of a conventional spread spectrum communication apparatus. The spread spectrum communication apparatus includes a transmitter 31 and a receiver 41 capable of wirelessly communicating with the transmitter 31 as main components. Transmitter 31
Is a component for putting an information signal on a high frequency as a component.
FM modulator 32 for performing next modulation, PN code generator 36 and spreader 33 for generating a spread spectrum signal
And an RF transmitting unit 34 that converts the modulated signal into a high frequency and amplifies it, and an antenna 35 that transmits a high frequency signal.

[0004] The receiver 41 includes an antenna 49 for receiving a signal from the transmitter 31, an RF receiver 48 for amplifying a received high-frequency signal, and a signal for returning the received spread spectrum signal to the original narrow band signal. A PN code generator 43 and a despreader 47; a synchronizing circuit 42 for synchronizing a signal from a transmitter with a PN code of a receiver; and an A / D converter 46
, An IF unit 45 having an RSSI circuit, and an FM demodulator 44 for demodulating a narrow-band FM signal.

The operation of the spread spectrum communication apparatus configured as described above will be described below. The information input to the transmitter 31 is converted into a narrow-band FM modulated signal 37 by the FM modulator 32 as in the conventional analog system. This narrow-band FM modulation signal 37 is further modulated by a spreader 33 by a spread code 38 generated by a PN code generator 36 to become a spread modulation signal 39. Further, the signal 40 converted and amplified to a high frequency by the RF transmitting unit 34 is radiated from the antenna 35.

On the other hand, the signal transmitted from the transmitter 31 is received by the antenna 49 of the receiver 41 and amplified by the RF receiver 48. This RF spread modulation signal 50 is composed of a despread code 56 generated by the PN code generator 43 and a despreader 4.
Multiplied by seven. At this time, the timing of the PN code generator 43 is controlled by the synchronization circuit 42 and synchronized with the RF spread modulation signal 50, so that the original narrow band FM signal 51 is obtained as the output of the despreader 47. The narrow-band FM signal 51 is converted and filtered to an intermediate frequency 52 by the IF unit 45, and is demodulated to the original information signal by the FM demodulator 44.

[0007] The synchronization circuit 42 is a kind of a sliding correlator using the RSSI voltage of the IF unit 35, and its 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. When the signal level after being converted and filtered to the intermediate frequency 52 by the IF unit 45 is monitored by the RSSI voltage 53, the phase of the despread code 56 and the phase of the RF spread modulation signal 50 are synchronized, and the maximum value is obtained when the correlation value is the maximum. An RSSI voltage is obtained. The despreading is performed by sliding the phase of the despreading code and capturing and tracking the phase at which the maximum RSSI voltage is obtained. Actually, the RSSI voltage 53 is converted into digital data by the A / D converter 46, and the peak position of this data is captured and held.
The synchronization circuit 42 adjusts the phase of the PN code generator 43 using the phase adjustment signal 55.

[0008] The synchronization circuit 42 has two functions of synchronization acquisition and synchronization retention.
It has different operation modes. Hereinafter, examples of these two operation modes will be described. First, in the synchronization acquisition mode, a rough synchronization position in units of 1/2 chip is determined by the following procedure.

1. First, the PN code generator outputs the spread code 56 at an appropriate phase for a certain period of time, and the RSS at that time is output.
The I data 54 and the phase are recorded.

[0010] 2. Next, the spreading code 56 is output for a certain period of time by shifting the phase by チ ッ プ chip, and the R code at that time is output.
If the SSI data 54 is higher than the recorded value, the recorded 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.

3. This content is repeated for all the phases in units of 1/2 chip, and the position at which the RSSI data becomes maximum is set as a synchronization point, and jumping to that phase completes the synchronization acquisition.

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

1. The phase at the time of completion of synchronization acquisition.
6 is output for a certain time, and the RSSI data 5 at that time is output.
Record 4.

2. Set the phase of the spreading code 56 to 1 in an arbitrary direction.
After shifting by / 8 chip, 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 result is used to determine the next phase change direction.

RSSI rise → Next time shift 1/8 chip in the same direction RSSI fall → Next time shift 1/8 chip in the opposite direction No RSSI change → Next time no phase change By repeating this, the phase within ± 1/8 chip from the synchronization point is held.

The spread spectrum communication apparatus based on the analog system as described above has the following advantages as compared with the digital system.

1. The circuit configuration and operation became very simple,
Costs are also lower.

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

3. 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.

[0020]

However, the above-mentioned conventional method and configuration have a problem that when the signal input level to the receiver is very large, the despreader does not operate normally due to RSSI saturation. Was. FIG.
Is a graph showing the effect of conventional RSSI saturation on correlation detection. As shown in this figure, for an input beyond the linear region of the RSSI, the S / N of the RSSI at the time of correlation is obtained.
Is worsened, and a synchronization error is likely to occur.

Generally, an RSSI circuit mounted on a general-purpose IC for an IF has a dynamic range of about 60 dB. This is completely insufficient for a dynamic range required to be actually mounted on a receiver, assuming that it is used for correlation of a spread spectrum signal. For example, I
Considering an application of a cordless telephone using the SM band, the transmission output is often around +20 dBm, and in this case, a dynamic range of about 120 dB is required. An AGC circuit can be considered as a circuit for supplementing the dynamic range. In this case, however, a gain control of about 60 dB is required, and there is a concern that the system becomes complicated and the cost increases.

The present invention solves the above-mentioned conventional problems, and solves the problem of insufficient dynamic range of RSSI with a simple and inexpensive circuit, and realizes a practical spread spectrum communication which operates stably even with a strong input. It is intended to provide a device.

[0023]

In order to solve the above-mentioned problems, a spread-spectrum communication apparatus according to the present invention uses a spread-spectrum communication system and a cordlessly connected transmitter.
The transmitter and the receiver are constituted by a set of receivers, wherein the transmitter and the receiver are analog modulators and demodulators for information modulation, and spreaders and despreaders for modulation and demodulation of spread spectrum signals,
It has a high-frequency transmitter and a receiver, and has a limiter circuit before the despreader.

According to this configuration, the problem of insufficient dynamic range of RSSI can be solved with a simple and inexpensive circuit, and a practical spread spectrum communication apparatus that operates stably even with strong input can be realized.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 comprises a pair of a cordlessly connected transmitter and receiver using a spread spectrum communication system, wherein the transmitter and the receiver are used for information modulation. Analog modulator and demodulator, a spreader and a despreader for modulating and demodulating a spread spectrum signal, a high frequency transmitting unit and a receiving unit, and having a limiter circuit before the despreader. This is a spread spectrum communication apparatus characterized by this configuration, and a stable despreading operation can be realized even for a high-level input signal in a receiver.

According to a second aspect of the present invention, the configuration of the receiver is a double superheterodyne, and the despreader and the limiter circuit are connected to the first. 2. The spread spectrum communication apparatus according to claim 1, wherein the apparatus is provided in an IF unit. With this configuration, it is possible to reduce a deterioration in blocking characteristics caused by adding a limiter, and the like.
Further, the costs of the despreader and the limiter can be reduced.

According to a third aspect of the present invention, there is provided the spread spectrum communication apparatus according to the first aspect, wherein a band pass filter is provided before the limiter circuit. It is possible to further suppress the deterioration of the blocking characteristics and the like.

According to a fourth aspect of the present invention, there is provided the spread spectrum communication apparatus according to the first aspect, wherein the amplitude of the characteristic of the limiter circuit is limited immediately before the saturation point of the RSSI circuit. In addition, it is possible to further suppress the deterioration of the blocking characteristic due to the addition of the limiter, and further minimize the narrowing of the dynamic range of the input level versus the RSSI with the addition of the limiter. Can be held down.

According to a fifth aspect of the present invention, there is provided the spread spectrum communication apparatus according to the first aspect, wherein the high frequency amplifying section of the receiver has an AGC circuit. Therefore, the dynamic range of the RSSI with respect to the input level of the entire receiver system can be improved, and the electric field strength can be monitored up to a high input level.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a spread spectrum communication apparatus according to an embodiment of the present invention.
The spread spectrum communication apparatus includes a transmitter 1 as a main component, and a receiver 11 capable of wirelessly communicating with the transmitter 1.
Is made up of The transmitter 1 includes, as a component, an FM modulator 2 that performs primary modulation for putting an information signal on a high frequency.
And a PN code generator 6 and a spreader 3 for generating a spread spectrum signal, an RF transmission unit 4 for converting and amplifying a modulated signal to a high frequency, and a transmission antenna 5 for transmitting a high frequency signal.

The receiver 11 receives a signal from the transmitter 1, a receiving antenna 19, amplifies the received high-frequency signal, and an RF receiving unit 18 having an automatic gain control (AGC) function. A down-converter 27 for converting to a constant intermediate frequency (1st.IF) lower than 1st. IF passing only the frequency of the first IF. Limiter amplifier 29 for limiting the amplitude of the IF signal, and PN code generator 13 for returning the received spread spectrum signal to the original narrow band signal
And the despreader 17, the signal from the transmitter and the PN of the receiver
It has a configuration including a synchronization circuit 12 and an A / D converter 16 for synchronizing codes, an IF unit 15 having an RSSI circuit, and an FM demodulator 14 for demodulating a narrow-band FM modulation signal.

The feature of this embodiment is that the structure is double superheterodyne and the first. RF receiving unit 1 having a band pass filter 28 and a limiter amplifier 29 in the IF unit, and having an AGC function before the limiter amplifier
8.

The operation of the spread spectrum communication apparatus configured as described above will be described below. FIG.
4 is a graph showing the effect of adding a limiter amplifier to the spread spectrum communication apparatus according to one embodiment of the present invention. The added limiter amplifier 29 is a normal transistor amplifier using the saturation characteristics of a high-frequency transistor. As shown in FIG. 2, the limiter amplifier is set to saturate at a slightly lower level than the saturation characteristics of the circuits after the despreader located after the limiter. By this level setting, no input beyond the saturation point is input after the despreader, and the despreader to RSSI can always operate in the linear region. Due to the addition of this limiter amplifier, the S / S of RSSI can be
N does not deteriorate, and a stable operation of the despreader can be realized.

When a limiter amplifier is added, the limiter operates on a strong interfering signal of another channel to lower the gain, and there is a concern that the blocking characteristic deteriorates, which deteriorates the receiving sensitivity to the target signal. Is done. Since the total NF of the receiver is greatly affected by the NF and gain of the element close to the antenna end, if a gain is reduced by providing a limiter in the high-frequency amplifier, the total NF is greatly deteriorated and the receiving sensitivity is deteriorated. Therefore, in the present embodiment, the limiter amplifier and the despreader are connected to the 1st. I
After conversion to F, total NF deterioration due to limiting is reduced. This also has the effect of reducing the cost of the device of the double balanced mixer and the limiter amplifier used as the despreader by lowering the frequency.

Further, like a general double superheterodyne receiver, the RF receiving section has, for example, 900 MHz.
Passes and amplifies a certain wide band such as the ISM band, and among a plurality of communication channels existing in the band, a desired communication channel is set to a fixed 1st. Converted to IF frequency. 1st. Since the frequency handled after the IF is constant, in the configuration of the present embodiment, a band-pass filter that allows only a single communication channel to pass can be provided before the limiter amplifier. Thus, the blocking by the limiter amplifier when a strong interference signal is present in another communication channel can be solved.

Further, focusing on the characteristics of the limiter amplifier, the object of the present invention can be achieved by limiting the amplitude at such a low level that RSSI does not saturate. However, excessive limiting causes the above-described deterioration of the blocking characteristics. . FIG. 3 is a graph showing the improvement of the dynamic range of RSSI when the spread spectrum communication apparatus according to the embodiment of the present invention is used in combination with AGC. As shown in FIG. 3, by adding a limiter, the dynamic range of the input level versus the RSSI when viewed in the entire receiver becomes narrow. If RSSI is considered for the original purpose of electric field strength detection instead of correlation operation, it is not preferable because a signal of a strong input level is saturated and detection becomes difficult. Due to these circumstances, the added limiter amplifier should not perform unnecessary limiting, and is set to a level slightly lower (considering variation) than the point where the RSSI is saturated.

If the dynamic range between the input level and the RSSI as seen in the entire receiver system is still insufficient, the AGC function can be provided to the RF receiver before the limiter added as shown in FIG. 3 can be easily solved. The AGC function uses RF signals by RSSI signals.
The actual cost increase is small, because it can be realized by controlling the bias of the low noise amplifier of the receiving unit and adjusting the gain thereof.

[0038]

As described above, according to the present invention, a normal correlation operation with respect to a strong input signal, which has been a problem of a conventional spread spectrum communication apparatus based on an analog system, is realized, and a minimum number of circuits are added. And cost up,
It is possible to provide a practical spread spectrum communication device that operates stably even at the time of strong input.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a spread spectrum communication apparatus according to an embodiment of the present invention;

FIG. 2 is a graph showing the effect of adding a limiter amplifier to the spread spectrum communication apparatus according to one embodiment of the present invention;

FIG. 3 is a graph showing an improvement in the dynamic range of RSSI when the spread spectrum communication apparatus according to an embodiment of the present invention is used in combination with AGC.

FIG. 4 is a configuration diagram of a conventional spread spectrum communication apparatus.

FIG. 5 is a graph showing the effect of conventional RSSI saturation on correlation detection.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmitter 2 FM modulator 3 spreader 4 RF transmitter 5 transmission antenna 6 PN code generator 7 narrowband FM signal 8 spreading code 9 spreading modulation signal 10 RF spreading modulation signal 11 receiver 12 synchronization circuit 13 PN code generator 14 FM demodulator 15 2nd. IF section (RSSI) 16 A / D converter 17 Despreader 18 RF receiving section 19 Receiving antenna 20 RF spread modulated signal 21 1st. IF narrowband FM signal 22 2nd. IF output 23 RSSI voltage 24 RSSI data 25 Phase adjustment signal 26 Despread code 27 Down converter 28 Band pass filter 29 Limiter amplifier 30 1st. IF spread modulation signal

Claims (5)

[Claims] The present invention comprises a pair of a cordlessly connected transmitter and receiver using a spread spectrum communication system,
The transmitter and the receiver include an analog modulator and a demodulator for modulating information, a spreader and a despreader for modulating and demodulating a spread spectrum signal, and a high-frequency transmitting unit and a receiving unit. A spread spectrum communication apparatus comprising a limiter circuit in front of a device. 2. The configuration of the receiver is a double superheterodyne, and the despreader and the limiter circuit are 1 s.
t. 2. The spread spectrum communication apparatus according to claim 1, wherein the apparatus is provided in an IF unit. 3. The spread spectrum communication apparatus according to claim 1, further comprising a band pass filter before said limiter circuit. 4. The spread-spectrum communication apparatus according to claim 1, wherein the characteristic of said limiter circuit is amplitude-limited immediately before a saturation point of an RSSI circuit. 5. The spread spectrum communication apparatus according to claim 1, wherein an AGC circuit is provided in a high frequency amplifier of said receiver.