JPH06197090A - Data transmitter-receiver - Google Patents

Abstract

PURPOSE:To reduce deterioration due to a strong interfering wave or frequency selective distortion and to eliminate the need of a broad band delay device for delay detection by letting only part of a signal band be a reception band and revising a frequency or a band width of the reception band in response to the reception state. CONSTITUTION:A spread spectrum signal (a) whose period of a spread modulation signal is equal to a symbol period of data are equal to each other is inputted to a variable band pass means 21, in which only a component of a partial band is extracted and an intermediate frequency signal (b) is obtained, A delay detector 12 detects the intermediate frequency signal (b) to obtain a detection output (c). A decoder 16 reproduces data from the detection output (c) and outputs decoding data (d). A reception state discrimination means 24 discriminates the reception state based on the detection output (c) and the decoded data (d) and switches a center frequency or a band width of the variable band pass means 21 when the reception state is defective.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitter / receiver for performing data transmission using spread spectrum signals.

[0002]

2. Description of the Related Art A spread spectrum communication system has good transmission characteristics in a multipath environment and high ability to eliminate interference signals, and therefore is used for wireless LAN and other local wireless data communication and power line carrier data communication. Has attracted attention as a method suitable for. The frequency band of the radio waves provided to the wireless LAN is the industrial scientific medical frequency band (ISM
Band) has become a strong candidate. The ISM band is
Since the frequency band is used by a device that uses a strong electromagnetic wave such as a microwave oven, a transmitter / receiver used in a wireless LAN is required to have a characteristic capable of normally transmitting data even under an extremely high level of interfering waves.

On the other hand, in order to simplify the receiving apparatus in spread spectrum communication, various systems that do not require spread synchronization have been devised. As one of the methods, there is a method (hereinafter, referred to as an SS delay detection method) in which a spread signal cycle is synchronized with a data symbol cycle and reception is performed by differential detection. For example, JP-A-62-257224 discloses an example of this system.

The structure and operation of an example of the spread spectrum communication device based on the SS delay detection method will be described below with reference to the drawings.

FIG. 10 is a block diagram showing an example of an SS differential detection type transmitter and receiver. Further, FIG. 11 shows signal waveforms of respective parts of the apparatus of FIG. In the transmitter 10 of FIG. 10, 11 is a differential encoder, 12 is a phase modulator, 13 is a spread modulation signal generator, and 14 is a spread modulation multiplier. A symbol clock generator 15 supplies a symbol clock CK having a period T to the differential encoder 11, the phase modulator 12, and the spread modulation signal generator 13. Further, in the receiver 20 ′ of FIG. 10, reference numeral 22 is a delay detector, which is composed of a symbol delay device 221, a delay detection multiplier 222, and a low-pass filter 223. Reference numeral 23 is a decoder.

The data d, which is a bit string, is taken in in synchronization with the symbol clock CK, differentially encoded by the differential encoder 11, modulated by the phase modulator 12, and then two-phase phase modulated by the symbol period T. A primary modulated signal p which is a wave is obtained. Therefore, the primary modulated signal p has the same phase as the previous symbol when the data d is 0, and has the opposite phase to the previous symbol when the data d is 1. The spread modulation signal generator 13 generates a spread modulation signal q having the same period as that of the symbol clock CK in synchronization with the symbol clock CK. The spread modulation signal q is a pseudo random pulse waveform having a constant amplitude generated by the pseudo random sequence. The spread modulation multiplier 14 multiplies the primary modulation signal p and the spread modulation signal q to obtain a spread spectrum signal a.

FIG. 11A shows the time waveforms of the primary modulation signal p, the spread modulation signal q, and the spread spectrum signal a. However, for the primary modulation signal p and the spread spectrum signal a, baseband waveforms are shown for convenience.

The spread spectrum signal a thus obtained is input to the receiver 20 'through the transmission line.
In the receiver 20 ′, the delay detector 22 receives the spread spectrum signal “a” and the received signal from the symbol delayer 22.
The delay signal a _d delayed by the symbol period T by 1 is multiplied by the delay detection multiplier 222, and the high-frequency component is removed by the low-pass filter 223 to detect the detection output c.
To get In the detection output c, the multiplication of the spread modulation signal components is always a constant value. Therefore, the detection output c is
Similar to the differential detection output of the normal differential PSK, it takes a positive value when there is no phase change with the previous symbol, and takes a negative value when it has an inverted phase with respect to the previous symbol. The decoder 23 restores the transmission data by outputting 0 as the decoded data d ′ when the detection output c is positive and 1 when the detection output c is negative.

FIG. 11 (b) shows the received spread spectrum signal a, delay signal a _d , and detection output c.
However, as in FIG. 11A, the spread spectrum signal a
A baseband waveform is illustrated for the delay signal a _d and the delay signal a _d . Further, the signal actually received is usually a signal in which noise or an interference component is added to the spread spectrum signal a or distortion is generated in the transmission line.
In 1 (b), the influence of noise and the like is omitted.

With the above configuration, it is possible to obtain a transmitter / receiver having a simple configuration that does not require a complicated mechanism such as spread synchronization while maintaining the high interference rejection capability and the multipath resistance characteristic of the spread spectrum system.

[0011]

However, in the above-mentioned structure, when a very strong interference component is added to the band of the spread spectrum signal, the interference component band is only a part of the signal band. Even if they do not overlap, reception will be impossible. Further, as a symbol delay device used for the delay detector, a wide band delay device having a constant delay characteristic over the entire band of the spread spectrum signal is required.

The present invention solves the above problems, and enables reliable transmission even when a very strong interference component is added to the band of the spread spectrum signal, and does not require a wide band delay device. An object is to provide a transmitting / receiving device.

[0013]

In order to solve the above-mentioned problems, a data transmitting / receiving apparatus of the present invention uses a primary modulation signal obtained by digitally modulating a carrier wave with input data, which has a wider band than the primary modulation signal. It comprises a transmission device that outputs a spread spectrum signal obtained by multiplying a spread modulation signal, and a reception device that demodulates the spread spectrum signal and outputs decoded data, wherein the reception device is a portion within the band of the spread spectrum signal. It is configured to include at least one band-passing means for extracting only a signal component of a specific band and at least one detecting means for detecting an intermediate signal which is an output of the band-passing means.

[0014]

According to the present invention, since only the signal component of a partial band within the band of the spread spectrum signal is detected by the above-described structure, when a very strong interfering wave exists in the signal band or due to multipath, etc. When selective distortion occurs, it is possible to avoid the influence of these deterioration factors and selectively use the signal component in the band in which the reception state is good. Therefore, it is possible to reduce the deterioration of the error rate due to strong interference waves and frequency selective distortion. Also, when detecting with the differential detection method, the signal handled by the differential detector has a narrower band than the bandwidth of the spread spectrum signal,
The delay detector required for the differential detector may be a narrow band one.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A data transmitting / receiving apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a data transmitting / receiving apparatus according to the first embodiment of the present invention. FIG. 2 shows signal waveforms at various parts of the apparatus shown in FIG. However, the baseband waveform is shown for convenience. FIG. 3 shows the outline of the spectrum of the signal of each part.

The operation of the transmitting apparatus 10 of FIG. 1 is the same as the operation of FIG. 10 described in the item "Prior Art". That is, the data d is the symbol clock C of the cycle T.
The signal is captured in synchronization with K, differentially encoded by the differential encoder 11, and then modulated by the phase modulator 12 to obtain the symbol period T.
A primary modulation signal p that is a two-phase modulated wave of is obtained. The spread modulation signal generator 13 generates a spread modulation signal q having the same period as that of the symbol clock CK in synchronization with the symbol clock CK. The spread modulation signal q is a pseudo random pulse waveform having a constant amplitude generated by the pseudo random sequence. The spread modulation multiplier 14 multiplies the primary modulation signal p and the spread modulation signal q to obtain a spread spectrum signal a. FIG. 2A shows a signal waveform of each part of the transmitter.

Spread spectrum signal a passing through the transmission line
Enters the receiving device 20, is band-limited by the variable band pass means 21, and becomes the intermediate signal b. Variable band pass means 2
Reference numeral 1 denotes a first band pass means 211 (hereinafter referred to as BPF1), a second band pass means 212 (hereinafter referred to as BPF2), and a third band pass means 213 (hereinafter referred to as BPF).
3), and any one of them is selected and used. These band pass means BPF
1 to BPF3 are filters having pass band characteristics different from each other as shown in FIG. Variable band pass means 21
When receiving the band switching signal from the reception state determining means 24, the BPF1 is sequentially switched to a filter different from the one currently used in the order of BPF1 → BPF2 → BPF3 → BPF1 (repeated below).

FIG. 3A shows the outline of the spectrum of the received spread spectrum signal a and the pass band of each band pass means. Further, in FIG. 3B, a first intermediate signal b1 output from the first band pass means 211, a second intermediate signal b2 output from the second band pass means 212, and a third band. The outline of the spectrum of the third intermediate signal b3 which is the output of the passing means 213 is shown. Next, the delay detector 22 delay-detects the band-limited intermediate signal b to obtain a detection output c.

FIG. 2 (b) shows the signal waveform of each part of the receiver. The baseband waveform of the spread spectrum signal a has the same shape when the phases of the primary modulation signals are the same in each symbol section, and has the shape in which the positive and negative are inverted when the phases of the primary modulation signals are opposite. . The baseband waveform of the intermediate signal b has a waveform that is considerably different from the shape of the spread spectrum signal a due to band limitation, but has substantially the same shape when the phases of the primary modulation signals are the same in each symbol section. When the phases of the primary modulation signals are opposite, the positive and negative sides are inverted. Strictly speaking, in the vicinity of the boundary with the adjacent symbol, the shape will not be exactly the same due to the influence of the adjacent symbol, and intersymbol interference will occur, but the band of the intermediate signal is compared with the symbol repetition frequency. If it is made large, the intersymbol interference is small, so that it does not become a problem.

In the differential detector, when there is no phase change from the previous symbol, pulses of the same shape are multiplied to generate a positive pulse, and when the phase is inverted from the previous symbol, the positive and negative shapes are inverted. Multiplying the pulses produces a negative pulse. Therefore, the detection output c becomes a negative pulse and a positive pulse depending on whether or not the phase is inverted. Decoder 23
Determines 0 when the detection output c is a positive pulse and 1 when it is a negative pulse, and outputs the decoded data d ′.

Further, the reception state judging means 24 observes the level of the detection output c and the error occurrence state of the decoded data d ', and estimates whether or not good reception is currently performed. As a result, if it is determined that the reception state is not good, the band switching signal is sent to the variable bandpass means 21.

Here, consider a case where the interference wave j shown in FIG. 3A is added to the transmission line. According to the conventional device shown in FIG. 10, most of the energy of the interfering wave j is detected by the delay detector, so that normal reception becomes impossible. According to the apparatus of the present embodiment shown in FIG. 1, the variable band pass means 21 is provided in front of the delay detector 22 to limit the band of the received signal.
In a state in which the bandpass means 211 of 1 is selected, the intermediate signal b is not affected by the interfering wave j, and normal reception is performed. If the variable band pass means 21 is in a state in which the second band pass means 212 or the third band pass means 213 is selected, the intermediate signal b is normally affected by the interference wave. I can't receive. However, if this state continues, the reception state determination means 24 determines that the current reception state is not good, and switches to the next band passage means to change the pass band characteristic of the variable band passage means 21. In this way, the band switching is continued until the first band pass means 211 is selected, and the first band pass means is eventually selected. Since normal reception is performed at that time, the reception state determination means 24 does not output the band switching signal, and stable data transmission that is not affected by the interfering wave can be performed thereafter.

Since the intermediate signal b handled by the delay detector 22 has a narrower band than the original spread spectrum signal a, the symbol delay unit 221 only needs to maintain accuracy within the band of the intermediate signal b. It is not necessary to have high accuracy over the entire band of the spread spectrum signal a.

In the first embodiment, the primary modulation signal p is a two-phase phase modulated wave, but other digital modulation methods such as a four-phase phase modulated wave may be used. Further, although the delay detection is performed by the delay detector 22, another detection method may be used, for example, an envelope detection method may be used as the primary modulation signal p as an amplitude modulation (ASK) wave. Further, the spread modulation signal q is a pseudo random pulse waveform of constant amplitude generated by the pseudo random sequence,
The present invention is not limited to this, and other noise-like signals or chirp signals as shown in the fourth embodiment may be used. The period of the spread modulation signal q is the symbol period T of the primary modulation signal p.
However, it may be 1 / m of the symbol period T of the primary modulation signal p (m is a natural number), or n times the symbol period T of the primary modulation signal p (n is a natural number),
As the symbol delay device 221, a device having a delay time of n times the symbol period T may be used to perform the differential detection. When a detection method other than differential detection is used, the period of the spread modulation signal q can be set independently of the symbol period T of the primary modulation signal p. Further, the variable band pass means 21 is composed of three filters, but it is not limited to three and can be realized by any number. Further, as the variable band pass means 21, instead of switching a plurality of filters, the pass characteristics may be changed by dynamically changing the parameters of a single filter. Alternatively, instead of the variable band pass means 21, a band pass means configured to mix the spread spectrum signal a with the local oscillation signal and frequency-convert it and then pass the band pass filter or the low pass filter is provided. The center frequency may be changed equivalently by changing the frequency. Further, although the reception state determination means 24 observes the level of the detection output c and the error occurrence state of the decoded data d ′,
The present invention is not limited to this, and any parameter that can generally estimate the reception state may be observed, and for example, the aperture ratio of the detection output eye may be observed.

FIG. 4 is a block diagram of a receiver according to the second embodiment of the present invention. In this embodiment, the transmitting device is the same as the transmitting device of the first embodiment shown in FIG. The difference from the first embodiment is that the receiving apparatus 201 in FIG. 4 does not have a receiving state determining means, and is configured to give a band switching signal e to the variable bandpass means 21 from outside the receiving apparatus. is there. Specifically, the external device that connects to the receiving device and uses the decoded data processes the decoded data, and supplies the effective band switching signal using the result, or the band is manually set by the operator's judgment. By performing switching, fine band switching can be performed.

FIG. 5 is a block diagram of a receiver according to the third embodiment of the present invention. In this embodiment, the transmitting device is the same as the transmitting device of the first embodiment shown in FIG. Receiver 202 of FIG.
In, the first bandpass means 211, the second bandpass means 212, and the third bandpass means 213 input the spread spectrum signal a, band-limit the respective passbands, and respectively set the first bandpass means a. The intermediate signal b1, the second intermediate signal b2, and the third intermediate signal b3 are output. The first delay detector 31, the second delay detector 32, and the third delay detector 33 delay the first intermediate signal b1, the second intermediate signal b2, and the third intermediate signal b3, respectively. The first detection output c1 and the second detection output c are detected.
The second and third detection outputs c3 are output. The operation of each of the delay detectors 31 to 33 is similar to that of the delay detector 22 of FIG. 1 shown in the first embodiment. The best band determination means 34 is
The detected outputs c1 to c3 are input, the respective levels are observed, which of the detected outputs c1 to c3 is received is estimated, and the determination result is transmitted to the detected output selecting means 35. . The detection output selection means 35 selects one of the detection outputs c1 to c3 based on the determination result,
The detection output c is output to the decoder 23. The decoder 23 determines the data as in the case of the first embodiment and outputs the decoded data d '.

According to the configuration of this embodiment, the intermediate signals b1 to b3 obtained by the three band pass means 211 to 213 are provided.
Are simultaneously detected, three detection outputs c1 to c3 are obtained, and the best one is selected. Therefore, the time for performing the band switching sequentially as in the first embodiment is unnecessary. Also, even if the reception state changes with time, it is possible to switch to another band before the reception state deteriorates,
The best band can always be selected and received without interruption of data reception.

FIG. 6 is a block diagram of a data transmitting / receiving apparatus according to the fourth embodiment of the present invention. Further, FIG. 7 is a diagram showing a signal waveform of each part of the transmitter of the present embodiment,
FIG. 8 is a diagram showing an outline of a spectrum of an intermediate signal of the receiving apparatus of the present embodiment and a signal waveform of each part.

In this embodiment, the transmitter 10 'is shown in FIG.
It has the same configuration as the transmitter of the first embodiment shown in FIG. However, as shown in FIG. 7, the spread modulation signal q'output from the spread modulation signal generator 13 'is a chirp signal obtained by repeatedly sweeping the frequency of the sine wave, and its cycle is equal to that of the primary modulation signal p. It is equal to the symbol period T.

In the receiving apparatus 202 of FIG. 6, the first band pass means 211, the second band pass means 212, and the third band pass means 213 are the spread spectrum signal a.
Is input and band-limited to each pass band, and a first intermediate signal b1, a second intermediate signal b2, and a third intermediate signal b3 are output. First differential detector 31, second
Delay detector 32 and the third delay detector 33 delay-detect the first intermediate signal b1, the second intermediate signal b2, and the third intermediate signal b3, respectively, and respectively detect the first detection output c1. , Second detection output c2, and third detection output c3. The operation of each delay detector 31-33 is as follows.
This is the same as the differential detector 22 of FIG. 1 shown in the first embodiment.

Since the spread spectrum signal a is a chirp signal, the first part of each symbol section is composed of low frequency components, and the frequency components are composed of higher frequency components toward the rear of each symbol section. . Intermediate signal b
Since 1 has a low frequency component extracted from the original spread spectrum signal a, the amplitude is large in the first half of the symbol section but small in the latter half. Similarly, since the intermediate signal b3 is obtained by extracting high frequency components from the original spread spectrum signal a, the amplitude is small in the first half of the symbol section and large in the latter half. Further, the intermediate signal 2 has a large amplitude at the center of the symbol section and a small amplitude at both ends. However, in both cases, as in the case of the intermediate signal b in the first embodiment, the shapes in each symbol section are almost the same, and the positive and negative signs are inverted according to the phase of the primary modulation signal, so demodulation is performed by differential detection. be able to. Therefore, the detection outputs c1 to c3
As shown in FIG. 8B, is a pulse train having one peak in each symbol section, and the peaks of the pulse are in the first half, the center, and the second half of the symbol section, respectively. This peak position is determined by the frequency sweep parameters of the spread modulation signal q'and the characteristics of each bandpass means. As shown in FIG. 8B, the first
The difference between the peak positions of the pulses of the detection output c1 and the third detection output c3 is t1, and the difference between the peak positions of the pulses of the second detection output c2 and the third detection output c3 is t2.

The detection output synthesizing means 41 has a first detection signal delay means 411, a second detection signal delay means 412, and a third detection signal delay means 413. The first detection signal delay means 411 inputs the detection output c1 and delays it by t1, and the second detection signal delay means 412 receives the detection output c1.
2 is input and delayed by t2, and the third detection signal delay means 413 receives the detection output c3 and delays it by t3. In this way, after the peak positions of the respective detection outputs are matched with the determination timing, these are added by the adder 414 to obtain the combined detection output c ′. The decoder 23 decodes the data depending on whether the detection output is positive or negative at the determination timing and outputs the decoded data d ′.

According to the configuration of the present embodiment, all of the plurality of intermediate signals are detected and combined, so that all the signal components contained in each intermediate signal can be utilized, so the signal-to-noise of the detection output is used. The ratio can be set high and reliable transmission can be performed even when the noise level is high. Further, since the spread modulation signal is a chirp signal, each of the detection outputs c1 to c3
Becomes a shape with one peak in each symbol section,
Since the detection output synthesizing means 41 aligns the peak positions of the respective detection outputs and then synthesizes them, the signal-to-noise ratio at the determination timing can be further improved.

In the fourth embodiment, if the peak position of the pulse of the third detection output c3 is selected as the determination timing, t3 can be set to zero, so that the third detection signal delay means 413 can be used. Can be omitted.
Further, although the adder 414 in the detected signal synthesizing means 41 simply adds the inputs, it is also possible to perform weighted addition in accordance with the reception state of each detected output, whereby the combined detected output c The signal-to-noise ratio of 'can be further increased.

FIG. 9 is a block diagram of a transmitter according to the fifth embodiment of the present invention. The transmitter 10 '' is
It has a shift register 51, a waveform storage means 52, and a carrier wave oscillator 53. The data d, which is a bit string, is input to the m-stage (m is a natural number) shift register 51 and supplied to the address input of the waveform storage means 52 as m-bit parallel data. The waveform storage means 52 pre-calculates a baseband waveform of a spread spectrum signal determined by every m-bit pattern of the input data d, and stores it as waveform data at an address represented by the m-bit pattern for reading only. It is a memory (ROM) and outputs the waveform data stored in the address designated by the output of the shift register 51. The D / A converter 53 converts the waveform data into an analog waveform and outputs it as a spread spectrum signal baseband waveform. Carrier wave oscillator 5
Reference numeral 4 oscillates and outputs a carrier wave, and the modulator 55 multiplies and modulates the carrier wave with the spread spectrum signal baseband waveform to obtain a spread spectrum signal a. With the above configuration, it is possible to generate and transmit a spread spectrum signal a similar to that of the transmitter of the first embodiment.

[0037]

As described above, according to the present invention, an intermediate signal obtained by inputting a spread spectrum signal and extracting only a signal component of a partial band within the band of the signal is output as decoded data. , It is possible to reduce the deterioration of the error rate due to strong interference waves and frequency selective distortion.
Delay detection can be realized without using a broadband delay device.

[Brief description of drawings]

FIG. 1 is a block diagram of a data transmission / reception device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a signal waveform in the same embodiment.

FIG. 3 is a diagram showing a spectrum of a signal in the example.

FIG. 4 is a block diagram of a receiving device according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a receiving device according to a third embodiment of the present invention.

FIG. 6 is a block diagram of a data transmission / reception device according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a signal waveform in the transmitter of the embodiment.

FIG. 8 is a diagram showing a spectrum and a waveform of a signal in the receiving apparatus of the embodiment.

FIG. 9 is a block diagram of a transmission device according to a fifth embodiment of the present invention.

FIG. 10 is a block diagram of a conventional data transceiver.

FIG. 11 is a diagram showing a signal waveform of a conventional data transceiver.

[Explanation of symbols]

 10 transmitter 20 receiver 21 variable band pass means 211-213 band pass means 22 delay detector 23 decoder 24 reception state determination means 34 best band determination means 35 detection output selection means 41 detection output combining means 411-413 detection signal delay Means 52 Waveform storage means

Claims (11)

[Claims] 1. A transmission device which outputs a spread spectrum signal obtained by multiplying a primary modulation signal obtained by digitally modulating a carrier wave with input data by a spread modulation signal having a wider band than the primary modulation signal, A receiving device for demodulating a spread spectrum signal and outputting decoded data is provided, wherein the receiving device includes at least one band pass means for extracting only a signal component of a partial band within the band of the spread spectrum signal, and the band pass. A data transmitting / receiving apparatus comprising at least one detecting means for detecting an intermediate signal which is an output of the means. 2. The primary modulation signal is a digital phase modulation signal, the period of the spread modulation signal is an integral multiple or an integer fraction of the symbol period of the primary modulation signal, and the detecting means detects the intermediate signal and the primary signal. 2. The data transmitting / receiving apparatus according to claim 1, wherein the data transmitting / receiving apparatus is a delay detector that obtains a detection output by multiplying the delay signal delayed by an integer multiple of the symbol period of the modulation signal. 3. The data transmitting / receiving apparatus according to claim 1, wherein the spread modulation signal is a chirp signal obtained by repeatedly sweeping the frequency of a sine wave in each cycle. 4. A transmitting device, a waveform storage means in which a value of a waveform obtained by multiplying a primary modulation signal and a spread modulation signal is calculated in advance and stored, and a D / A connected to the waveform storage means.
A converter, the waveform storage means outputs waveform data corresponding to input data, and the D / A converter outputs a spread spectrum signal by converting the waveform data into an analog waveform. The data transmitting / receiving apparatus according to claim 1. 5. A variable band pass device capable of partially passing a specific frequency band component within a band of a spread spectrum signal and changing at least one of a band width and a center frequency of the pass band. Means for detecting the intermediate signal, which is the output of the variable band pass means, to obtain a detection output, and decoding for decoding data from the detected output and outputting decoded data. The data transmitting / receiving apparatus according to claim 1, further comprising: 6. A receiving device comprises a receiving state judging means for receiving at least one of a detection output and decoded data and judging whether or not the current receiving state is good, and the receiving state judging means receives the current reception. 6. The data transmitting / receiving apparatus according to claim 5, wherein at least one of the bandwidth and the center frequency of the pass band of the variable band pass means is changed when it is determined that the state is not good. 7. The data transmitting / receiving apparatus according to claim 5, wherein the variable band pass means changes its characteristic based on a band switching signal inputted from the outside of the receiving apparatus. 8. A receiving device is cascade-connected to a plurality of band pass means for partially passing signals of different frequency bands within a band of a spread spectrum signal and outputting an intermediate signal, and each of the band pass means. A plurality of detection means for detecting each of the intermediate signals to obtain a detection output, and one of the passbands of the bandpass means for inputting the detection output of each of the detection means, which is the frequency with the best reception state. The best band determination means for determining whether the band is a band, the detection output selection means for selecting one of the detection outputs of the detection means according to the determination result of the best band determination means, and the detection output selection means The data transmission / reception apparatus according to claim 1, further comprising a decoder that decodes data from the detected detection output and outputs the decoded data. 9. A receiving device is cascade-connected to a plurality of band pass means for partially passing signals of different frequency bands within a band of a spread spectrum signal and outputting an intermediate signal, and each of the band pass means. A plurality of detection means for detecting each of the intermediate signals to obtain a detection output, a detection output combining means for combining the detection outputs of the detection means to generate a combined detection output, and data from the combined detection output. The data transmitting / receiving apparatus according to claim 1, further comprising a decoder for decoding and outputting the decoded data. 10. The detection output synthesizing means corrects the difference in the peak position of the amplitude of each detection output determined by the characteristic of each band pass means and the characteristic of the spread modulation signal, and detects the pulse of each detection output. 10. The data transmitting / receiving apparatus according to claim 9, further comprising detection output delay means for matching the timing at which the amplitude becomes maximum, and combining outputs of the detection signal delay means to generate a combined detection output. 11. The data transmitting / receiving apparatus according to claim 10, wherein the spread modulation signal is a chirp signal obtained by repeatedly sweeping the frequency of a sine wave in each cycle.