JPH0752869B2 - Spread spectrum signal reception method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spread spectrum system for receiving radio waves,
In particular, the present invention relates to a spread spectrum signal receiving method using an adaptive antenna.

(Prior Art) In recent years, a spread spectrum (ss: spread spectrum) system has been put into practical use in order to meet the demand for confidentiality or anti-jamming performance for communication.

The spread spectrum communication method is a method for transmitting or receiving electromagnetic energy by spreading it within a relatively wide frequency band, and the desired wave level is below the noise level, that is, the S / N is 0.
Even if it is less than dB, it is possible to improve S / N to more than 0dB by so-called process gain, which is far better than the conventional narrow-band communication method in a noisy malicious channel. You can get good call quality.

On the other hand, as a means for suppressing and removing interfering waves of the same frequency coming from different directions, by performing weighting processing for controlling the amplitude, phase (or delay time), etc. of the array antenna output signals arranged at a predetermined interval, from the desired direction So-called adaptive antennas that extract only the incoming radio waves have been studied.

Therefore, conventionally, it has been proposed to further improve the S / N ratio by using the above-described spread spectrum communication system and an adaptive antenna together.

However, the method of obtaining the weight of the adaptive antenna according to the conventional proposal is mainly based on LMS (Least Mean).
Square: Minimum squared error) method. In this case, it is a prerequisite that the desired wave and the interfering wave can be distinguished by adding some special signal to the desired wave.
In reality, it is rare that the desired wave and the disturbing wave can be clearly distinguished, and it is difficult to realize them.

Incidentally, when it is difficult to distinguish between the desired wave and the interfering wave, it is possible to basically adopt a power inversion adaptive antenna (PI) using the LMS algorithm as the adaptive antenna, Since this PI has the function of suppressing high level signals,
When the disturbing wave level is higher than the desired wave, it is effective in suppressing the disturbing wave and improving the S / N. Conversely, when the desired wave level is higher than the disturbing wave level, the desired wave is eliminated. There is a problem that it kills and deteriorates S / N.

In this way, in PI, even when an interfering wave and a desired wave with a lower level than that are input to the spread spectrum receiver, it is possible to improve the S / N by the processing advantage of the spread spectrum method and to communicate. However, as mentioned above,
Since the signal with a higher input level has the characteristic of being suppressed more, if the level of the desired wave input to the antenna is much higher than the interfering wave, the desired wave will be much The level becomes small, and this signal is S / S even with the processing gain of the spread spectrum method.
There is an inconvenience that the call cannot be made because N cannot be improved to 0 dB or more.

(Object of the invention) The present invention has been made in view of the above-described circumstances, in the case where it is difficult to distinguish between a desired wave and an interfering wave, and the desired wave level is compared with the interfering wave level by PI. Even if it is suppressed below the processing gain of the spread spectrum method, S /
It is an object of the present invention to provide a spread spectrum signal reception method that can improve N to 0 dB or more and is easy to realize.

(Summary of the Invention) In order to achieve this object, in the present invention, a plurality of antenna elements arranged at a predetermined interval, a plurality of weighting means provided with a power inversion algorithm, and the outputs of the plurality of weighting means are added. Means, a means for subtracting the outputs of the plurality of weighting means, a plurality of amplifying means for amplifying the outputs of the adding means and the outputs of the subtracting means, and an output of the amplifying means. And a means for inputting and synthesizing the signals, and of the signals received by the plurality of antenna elements, a high level signal and a low level signal are respectively extracted, and after equalizing the levels of both signals, these signals are combined. It is characterized in that the signals are combined and the combined signal is input to a spread spectrum receiver.

(Example) Hereinafter, the present invention will be described in detail based on an illustrated example.

Prior to the description of the present invention, the PI weight control circuit used in the present invention will be briefly described.

As the PI weight control circuit, for example, a circuit using the above-mentioned LMS (Least Square Error) algorithm or MSN (Maximize)
It is well known that the signal to noise ratio (maximum signal / noise) algorithm is used. Among these, regarding the LMS algorithm, for example, the distribution (RLRiegler, RTCompton: “An adaptive array
for interference rejection ", Proceedings of THE IEE
E, Vol.61, pp.748-758). The LMS algorithm will be briefly described below.

The LMS algorithm is an algorithm that uses the difference between the reference signal prepared on the receiving side and the received signal, that is, the array output, as the error, and controls the weight so that the mean square value of the error is minimized. For this, it is general to use a copy of the desired wave signal extracted from the received signal.

FIG. 2 is a block diagram of an adaptive antenna using the LMS algorithm.

Here, an input signal composed of a desired wave, an interfering wave, and noise is represented by a column vector X, and a weight is represented by a column vector W.

For the i-th weight circuit, if the input signal and weight are x _i (t) and ω _i , respectively, the array output y
(T) is Becomes If the reference signal is γ (t) and the error signal is ε (t), then ε (t) = γ (t) −y (t) (3) Therefore, the mean square of the error signal is
When E [·] is used as the symbol representing the expected value, the result is as follows.

Here, the degree of the influence of the fluctuation of ωi on E [ε ² (t)], that is, the gradient of E [ε ² (t)] with respect to ωi can be expressed by the following equation.

[Ε ² (t)] is a function whose component is the square term of the error signal, and is a downwardly convex function as shown in FIG. Accordingly, the gradient vector of E [ε ^{2 (t)]} regarding omega _2n from weights omega ₁ ▽ When ^{E [ε 2 (t)]} , 2 mean square value of the error component when the gradient vector becomes zero It is the smallest, and at the same time the weight is optimal.

Find the optimal weight by such an algorithm,
By adjusting the phase and amplitude of the received signal and adding the adjusted received signals, a component with a high level is suppressed and a component with a low level is amplified among the signals received by the antenna.

In the LMS algorithm described above, it is necessary to clearly distinguish the desired wave and the interfering wave, but the PI adaptive antenna sets the reference signal γ _(t) in FIG. 2 to 0, that is, the reference signal. It is processed without using the LMS algorithm or the MSN algorithm in principle.

In the present invention, the function of the PI adaptive antenna is used, and the characteristics of the spread spectrum communication system are utilized by the means to be described later to obtain good communication quality.

Hereinafter, a spread spectrum signal receiving method according to the present invention will be described. FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, reference numerals 1 and 1'indicate omnidirectional antenna cords arranged at a predetermined interval, and their outputs are weighting circuits 2 and 2'and a weight control circuit 3 based on a PI algorithm.
3'and input to the PI weight control circuit 3,
By inputting the output of 3'to the weighting circuits 2 and 2 ', a signal whose amplitude and phase are controlled is generated.

That is, when the received signals received by the adaptive antennas 1 and 1'are added to each other by the PI weight control circuits 3 and 3'by the above-described algorithm, the received signal of a low level has a higher level than the received signal of a high level. A control signal for controlling the phase or amplitude of each received signal so as to be output as a signal is generated, and the control signal is weighted by the weighting circuit 2,
By giving it to 2 ', the phases and amplitudes of the received signals output from the antennas 1, 1'in the weighting circuits 2, 2'are adjusted.

The outputs of the weighting circuits 2 and 2'are added by an adder 4 and subtracted by a subtractor 5, respectively. These signals are amplified by the automatic gain control (AGC) amplifiers 6 and 6 ′ so that their gains are adjusted to almost the same level, and are amplified by the adder 7 and input to the spread spectrum receiver 8.

In the system configured as above, the function of the PI adaptive antenna, that is, of the signals arriving at the antennas 1 and 1 ′, the signal with the lower level has a relatively higher level than the signal with the higher level, and Is output.
This function is exactly the function of the PI adaptive antenna, and is shown to be an effective means when the level of the interfering wave is higher than the level of the desired wave.

On the other hand, in the subtractor 5, the signal suppressed in the adder 4 is strengthened, so that of the signals arriving at the antenna, the one with the higher level is further increased and the level ratio is expanded. That is, the main component of the output signal of the adder circuit 4 is the signal with the smaller level among the signals received by the antenna,
The main component of the output signal of the subtraction circuit 5 is the one with the higher level among the signals received by the antenna.

These adder circuit output and subtraction circuit output are fed to amplifiers 6 and 6 '.
In the signal after being aligned at the same level with and synthesized by the adder 7,
Of the signals received by the antenna, the one with the higher level and the one with the lower level are included at substantially the same level.

That is, the signal from the adder 7 is always about 0 dB S / N regardless of the S / N of the signal received at the antenna.

In the spread spectrum receiver 8, if the S / N of the input signal is about 0 dB, the S / N of the output will be higher than that due to the processing gain. Therefore, with the configuration of this embodiment, the S / N of the received signal depends on the S / N. It is possible to always demodulate the spread spectrum signal over a wide range of S / N without being affected.

It should be noted that in the above embodiment, an example of a configuration for keeping the S / N of the signal input to the spread spectrum receiver at 0 dB is shown.
The implementation method of the present invention is not limited to FIG. The antenna used may be a directional antenna.

Further, the weighting control circuit is not limited to the one using the algorithm based on LMS as described above, and may be the one using the MSN algorithm.

(Effects of the Invention) Since the present invention is configured and functions as described above, the characteristics of the spread spectrum communication system can be utilized to obtain a wide range of interference wave level and desired wave level.
It is extremely effective in maintaining a S / N of 0 dB or higher and obtaining good call quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram of an adaptive antenna using the LMS algorithm. FIG. 3 is a diagram showing the concept of E [ε ² (t)] regarding the weight. 1, 1 ... Antenna element, 2, 2 '... Weighting circuit, 3, 3' ... PI weight control circuit, 4 ... Adder, 5 ... Subtractor, 6, 6 '... Automatic gain control amplifier , 7 ... Adder, 8 ... Spread spectrum receiver.

Claims (2)

[Claims] 1. In a spread spectrum reception system for receiving a desired wave using an adaptive antenna, a plurality of weighting means having a power inversion algorithm, a means for adding outputs of the plurality of weighting means, and a plurality of weightings. And means for subtracting the output of the means, a plurality of amplifying means for amplifying the respective outputs of the adding means and the output of the subtracting means, and means for inputting and combining the outputs of the amplifying means. A spread spectrum signal receiving system characterized in that the output of the synthesizing means is input to a spectrum addition receiver. 2. The spread spectrum signal receiving system according to claim 1, wherein the signals induced in a plurality of antenna elements arranged at a predetermined interval are input to a weighting means having a power inversion algorithm.