JP2002335191A - Radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct radio communication of a multichannel signal, while keeping secrecy using a simple electronic circuit. SOLUTION: In the radio communication method, where a desired signal is transmitted while being subjected to frequency spread through operation, using a spread code and despread through operation using the spread code thus receiving the desired signal, at least two transmitting/receiving radio channels are prepared, while being arranged such that at least a part of one frequency band of the channel overlaps the frequency band of an adjacent channel in its entirely or partially.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication method for transmitting and receiving signals between a plurality of channels without mutual interference.

[0002]

2. Description of the Related Art A method called CDMA is widely and generally used as a method for transmitting a desired signal by spreading a frequency using a spreading code and obtaining a desired signal by despreading in a receiver. . In this method, even if the channels are allocated to the same frequency band, the channels having different spreading codes can communicate independently without mutual interference. As can be seen from the distribution, a method of multiplexing multiple channels in the same frequency band is used.

[0003] In addition to the above-mentioned feature that a plurality of channels can be multiplexed in the same frequency band to improve the frequency use efficiency, this method also has a feature that secrecy can be ensured unless a spreading code is revealed. ing.

[0004]

By the way, in wireless communication, in order to increase the number of channels to be multiplexed, spreading and despreading are performed using a spreading code having a code length of 100 bits to 1000 bits or more. But
Using the CDMA method, high frequency use efficiency and confidentiality can be achieved, but especially when the spreading code is long,
Since a lot of complicated processing is required for synchronization detection and its maintenance, there is a disadvantage that a transmission / reception system becomes complicated such as an increase in the scale of an electronic circuit.

[0005] However, if the CDMA method is not used and, for example, the FDMA method (a method of allocating different frequencies to each channel) is used, the transceiver can be realized by a relatively simple circuit, but in principle, the confidentiality is low. There is no. Therefore, when confidentiality is required, the data processing portion before and after modulation must be provided with a confidentiality function, resulting in a problem that the circuit becomes complicated. Therefore, before the present invention, there was no method for realizing confidential wireless communication using a simple electronic circuit.

Accordingly, the present invention has been made in view of such a problem,
An object of the present invention is to enable multi-channel signals to be wirelessly communicated in a confidential state with a simple electronic circuit.

[0007]

The above object is achieved by the invention described in the claims. That is, claim 1
The present invention relates to a wireless communication method in which a desired signal is frequency-spread by an operation using a spreading code and transmitted, and a desired signal is extracted and received by despreading by an operation using the spreading code. A wireless communication method characterized in that at least two wireless channels are prepared, and a part of a frequency band of at least one of the channels overlaps with all or a part of a frequency band of an adjacent channel.

[0008] The invention according to claim 2 is the wireless communication method according to claim 1, wherein a difference in center frequency between arbitrary channels is larger than a frequency band of a desired signal. The invention according to claim 3 is the wireless communication method according to claim 1, wherein the frequency bandwidths of all channels are equal and the center frequencies of all channels are different. The invention according to claim 4 is the wireless communication method according to claim 3, wherein a difference in center frequency between any channels is larger than a frequency band of a desired signal.

The invention according to claim 5 is the wireless communication method according to claim 1, wherein at least one channel having the same center frequency exists for an arbitrary channel. The invention according to claim 6 is the wireless communication method according to claim 5, wherein a difference in frequency bandwidth between arbitrary channels having the same center frequency is larger than a frequency bandwidth of a desired signal. The invention according to claim 7 is the wireless communication method according to any one of claims 1 to 6, wherein the desired signal is an FM signal.

[0010]

According to the present invention, transmission / reception is performed by shifting the center frequency of each radio channel or changing the frequency bandwidth of each channel, so that even if the spread code is shortened, resistance to interference from other channels is maintained. Is sufficiently secured. Therefore, since the code length can be shorter than that of the spread code used in the conventional CDMA, the spread and despread operations can be performed with a simple electronic circuit while maintaining secrecy.

[0011]

FIG. 1 is a diagram showing a schematic configuration of a radio channel arrangement according to a first embodiment of the present invention. In FIG. 1, each channel (channel 1, channel 2, channel 3, channel N) has a different center frequency, and the difference between the center frequencies is smaller than each frequency bandwidth.

As a result, a plurality of adjacent channels have overlapping frequency bands. Such an arrangement can be realized by slightly changing the frequency of the carrier on which the spread signal is superimposed.

A receiver trying to receive channel 1
By performing a despreading operation using the corresponding spreading code, a signal as shown in FIG. 2 is obtained, and a sufficient S / N ratio can be secured for an adjacent channel. In addition, in the calculation related to the despreading, integration having the same integration time as the spread code length is usually performed, but in the present invention, the S / N ratio is further improved by setting the integration time longer than that. It is possible.

This effect will be described with reference to FIG. FIG.
Shows an example of the spectrum of a desired wave when the radio wave is spread and an interference wave in a channel adjacent to the desired wave. Here, channel 1 is a desired wave and channel 2 is an interfering wave. As is clear from the figure, the center frequencies of channel 1 and channel 2 are separated by Δf.

When this is despread using a spreading code corresponding to channel 1 in the receiver, the spectrum of channel 1 and channel 2 is as shown in FIG. 3b. This principle will be briefly described using the following mathematical formula.

The transmission signal of channel 1 is represented by the following equation, for example.

[0017]

(Equation 1)

Here, f _Lt1 is a local signal for modulation, m
Is a modulation index, f _d is a transmission signal frequency, s (t) is a spreading code f _Lt2 is a local signal for up-conversion.
In general, the "number 1" as _{f t = f Lt1 + f Lt2} ,

[0019]

(Equation 2)

It can be expressed as The receiving side multiplies the signal of equation 2 by the local signal for down-conversion cos2πf _Lr2 t,

[0021]

(Equation 3)

Is obtained. Next, despreading is performed. If the spreading codes match, s (t) becomes 1, so "Equation 3" becomes:

[0023]

(Equation 4)

## EQU1 ## Normally, the second term moves away to the high frequency side, so considering only the first term side, the frequency of “Equation 4” becomes co
Since the time derivative of the expression in the s function is divided by 2π,

[0025]

(Equation 5)

## EQU1 ## In the case of an interfering wave (in the case of channel 2), since the center frequency of the received signal is shifted with respect to the desired wave (channel 1), if the signal input to the modulator has a spreading code,

[0027]

(Equation 6)

In this case,

[0029]

(Equation 7)

Thus, the demodulated signal appears at a position shifted by Δf _T. The channel 1 returns to the desired signal 1A before spreading by despreading, but the channel 2 is not despread because the code is different, and the spectrum remains in a spread state.

However, due to the intersymbol interference of the spreading codes used for channel 1 and channel 2, ΔF _T
At a remote position, 2A lower than 1A appears. This intersymbol interference tends to appear significantly when the code length is short. However, since the desired signal 1A and the interference signal 2A have different frequencies, they can be removed via a filter or the like. Therefore, the desired signal 1A can be received with a sufficient S / N ratio even if there is a channel 2 or 2A that appears due to the channel 2.

On the other hand, if the channel 1
If channel 2 and channel 2 have the same center frequency, 2A appears on the same frequency as 1A and cannot be removed by the filter.

Therefore, it is necessary to increase the code length so that the above-mentioned intersymbol interference becomes sufficiently small, and the circuit becomes complicated. Therefore, the present invention can realize the above effects with a simpler circuit. Are better.

Since the above-mentioned filter can be easily realized by a combination of passive elements or active elements, this does not sacrifice the simplicity of the circuit. In addition, the filter may be a low-pass filter in the example of FIG. 3A, and can also serve as an integration operation performed in the despreading operation of channel 1. That is, conventionally, the despreading operation is realized by a process corresponding to an integral operation with a time constant equal to the time corresponding to the code length by taking the product of the received signal and the spreading code. A time constant longer than the time corresponding to 2A can be selected so that 2A can be excluded as a result of integration.

For example, assume that the code length is 31 bits, the chip rate is 10 MHz, and the difference between the center frequencies of channel 1 and channel 2 is 100 kHz. The time corresponding to the code length is 3.1.
In microseconds, 1A can be generated but 2A remains even if the product of the received signal and the spreading code is formed and integrated with a time constant of 3.1 microseconds.

Therefore, when integration is performed for a time corresponding to 100 cycles of the code length (ie, 310 microseconds),
1A is the same as the result of one cycle integration, but 2A is attenuated. This is because the integration operation is equivalent to applying a low-pass filter corresponding to a frequency (about 3.2 KHz) corresponding to the reciprocal of 310 microseconds.

Although the above description assumes that channel 1 and channel 2 are spread with different spreading codes, even if the codes are the same, the S / N ratio increases because the intensity of 2A increases. The ratio drops, but can be removed using the frequency difference.

When channel 1 and channel 2 have the same code and the spreading operation is not synchronized, the intensity of 2A is relatively weaker than when synchronized.
It is easier to remove.

As described above, in the present invention, even if a spread code having a relatively short code length is used, a high S which is obtained by using a relatively long code length in the conventional method is obtained.
/ N ratio can be obtained. Generally, in the CDMA according to the conventional method, a sufficient S / N ratio cannot be obtained by spreading / despreading using a relatively short code such as a 31-bit code, but in the present method, a sufficient S / N ratio is obtained. Ratio can be realized.

Further, in the despreading process in the conventional method, even if the integration longer than the code length is performed as in the present invention, the S / N ratio is not improved in principle.

FIG. 4 is a diagram showing a schematic configuration of a wireless channel arrangement according to the second embodiment of the present invention.
In FIG. 4, each channel (channel 1, channel 2,.
Channel 3 and channel N) have different center frequencies, and the difference between the center frequencies is larger than the frequency bandwidth of a desired signal (a signal before spreading or after despreading) transmitted and received by each channel. It is set to be.

Even when integration is performed longer than the above-mentioned code length, if integration is performed with a time constant corresponding to a frequency lower than the frequency band of A ', there is a problem that A' is also eliminated by integration. . On the other hand, in order to sufficiently remove the interference wave B 'from the adjacent channel, it is necessary to integrate at least the time given by the reciprocal of the difference between the center frequencies of the channel to be received and the adjacent channel.

That is, in order for the desired signal not to be lost by this integration, the center frequency intervals of the channels need to be appropriately separated, and for this reason the arrangement is as shown in FIG.

FIG. 5 is a diagram showing a schematic configuration of a wireless channel arrangement according to another embodiment of the present invention. In FIG. 5, each channel (channel 1, channel 2, channel 3, and channel N) has a different band and the same center frequency.

Such an arrangement can be easily realized by changing the chip rate of the spreading code for spreading for each channel. In the case of this method, interference with an adjacent channel can be considered as follows. For example, the cross-correlation of PN codes of two different fifth-order M-sequences is two PN codes.
It changes according to the phase of the code, and has a spectrum as shown in FIG.

Since the PN code of the fifth-order M series has a 31-bit period, the value of the correlation integral value with respect to the relative phase also has a 31-bit period. The peak value of the correlation integral in the above case is 9/31.

Next, consider the cross-correlation of different PN codes, each of which is sent at a different chip rate.
Let the chip rates of the two codes be a [bit / se
Assuming that c] and b [bit / sec], the phase relationship between the two codes changes at a period of 1 / (ab) × 31 [sec].

If the difference between the chip rates of the two codes is not so large, the period of the phase relationship is very long, and the relative phase between the two codes at some time is 0 bit in FIG.
Almost matches. The phase gradually shifts with the passage of time, the relative phase approaches 1 bit, and
The relative phase shifts from 3 bits, and l / (ab) × 31
After [sec], the relative phase is close to 0 bit.
Therefore, both periods 1 / (ab) × 31 [se
The value of the cross-correlation integral during c] can be approximated to the value obtained by integrating the correlation integral value in FIG.

When the correlation integral shown in FIG. 6 is integrated with the relative phase, the value becomes 1/31. In other words, in this method, a difference is made in the chip rate of the spreading code of each channel, and the integration time is set to a relatively long time corresponding to the difference in the chip rate. Also, it is possible to suppress the inter-channel interference to a low level.

Further, FIG. 6 shows the result of discretely plotting the relative phase. More precisely, since the relative phase is continuously displaced during one cycle, each relative phase is displaced. The correlation integral value at the phase behaves such that the bent straight line in FIG. 6 is smoothly connected. When this is integrated for one cycle, the correlation integral value becomes smaller than the above, and as a result, the communication S / N ratio can be increased.

In the same manner as described above, the integration operation based on the relative phase of the correlation integral value is performed only when the relative phase becomes one period when the correlation integral value is obtained (by integrating one cycle of the spread code). If the integration time is extended, a result can be obtained by one operation. However, it is necessary to prevent the desired signal from being attenuated by the integration for one cycle of the relative phase. In this sense, there is an upper limit to the time for one cycle of the relative phase. That is, it is necessary to set the difference between the chip rates to be larger than the lower limit depending on the frequency band of the desired signal.

FIG. 7 shows a sine wave spectrum obtained by spreading and despreading a spread code having a code length of 31 bits using the same code as the code used for spreading, and another code having the same chip rate as another code. FIG. 7 is a diagram plotting, by simulation, a code that is despread with a code and a code that is despread with a code having a different chip rate with another code. From this figure, it can be confirmed that inter-channel interference is large only by changing the spreading code, but inter-symbol interference can be reduced by changing the chip rate.

Therefore, the present invention is superior to the conventional method in that a spread code having a shorter code length than that of the conventional method is used, that is, the inter-channel interference can be reduced by an electronic circuit simpler than the conventional method.

FIG. 8 is a schematic diagram showing a configuration of a modulator and a demodulator according to another embodiment of the present invention. In FIG. 8, a signal to be transmitted wirelessly is an FM analog signal. Since the FM analog signal always transmits a carrier at a constant intensity even in a non-modulated state, it has a feature that the synchronization detection and the maintenance thereof when performing the above despreading operation can be relatively easily performed. In addition, a limiter amplifier can be used in the receiver, and this feature also contributes to simplification of the entire circuit.

As described above, the following two methods are conceivable as a spreading multiplexing method according to the present invention.
A: Carrier shift CDMA, B: Variable chip rate CD
MA. The following three diffusion methods are conceivable. 1: After FM modulation, multiply by a spreading code and upconvert. 2: After FM modulation, up-convert with the local signal spread by the spreading code. 3: After multiplying the BB signal by the spreading code, FM modulation is performed.

The example of FIG. 8 corresponds to the above 1 :, but 2:
Similarly, it is needless to say that the same can be easily realized by using an oscillator, a modulator, a frequency converter, and the like.

[0057]

As described above, according to the present invention, it is possible to make it possible to wirelessly communicate multi-channel signals in a confidential state with an electronic circuit simpler than the prior art. Having.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a wireless channel arrangement according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum after a despreading operation according to the present invention.

FIG. 3 is a diagram for explaining an S / N ratio in the present invention.

FIG. 4 is a diagram showing a schematic configuration of a wireless channel arrangement according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a wireless channel arrangement according to another embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between a relative phase of a PN code and a correlation integral value.

FIG. 7 is a diagram illustrating a degree of interference due to a difference between a spreading code and a chip rate.

FIG. 8 is a schematic diagram showing a configuration of a modulator and a demodulator according to another embodiment of the present invention.

FIG. 9 is a diagram showing a frequency distribution in conventional CDMA.

[Explanation of symbols]

 Reference Signs List 1 FM modulation 2 Spread modulation 3 Frequency conversion 4 First local oscillator 5 Spread code generation 6 Second local oscillator 7 Clock generator 8 Frequency conversion 9 Spread demodulation 10 FM demodulation 11 Second local oscillator 12 Spread code generation 13 First local oscillator 14 Clock generator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuneo Tsukahara 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Mamoru Ugajin 2-3-3, Otemachi, Chiyoda-ku, Tokyo 1 Nippon Telegraph and Telephone Corporation (72) Junichi Kodate Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Junzo Yamada Otemachi 2, Chiyoda-ku, Tokyo F-term (reference) in Nippon Telegraph and Telephone Co., Ltd., 3-1, No. 5K022 EE02 EE11 EE22 5K067 AA42 CC02 CC10 EE02 EE10 EE61 HH21

Claims (7)

[Claims] 1. A wireless communication method in which a desired signal is frequency-spread by an operation using a spreading code and transmitted, and a desired signal is extracted and received by despreading by an operation using the spreading code. A wireless communication method, wherein at least two wireless channels are provided, and a part of a frequency band of at least one of the channels overlaps with all or a part of a frequency band of an adjacent channel. 2. The apparatus according to claim 1, wherein a difference in center frequency between any channels is larger than a frequency band of a desired signal.
The wireless communication method as described. 3. The wireless communication method according to claim 1, wherein the frequency bandwidths of all the channels are equal and the center frequencies of all the channels are different. 4. A difference in center frequency between arbitrary channels is made larger than a frequency band of a desired signal.
The wireless communication method as described. 5. The wireless communication method according to claim 1, wherein at least one channel having the same center frequency exists for any channel. 6. The radio communication method according to claim 5, wherein a difference in frequency bandwidth between any channels having the same center frequency is larger than a frequency bandwidth of a desired signal. 7. The signal according to claim 1, wherein the desired signal is an FM signal.
The wireless communication method according to claim 6.