JPS6336698B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is a method for combining several reflected waves in a spread spectrum communication system using a direct sequence method, particularly in a spread spectrum communication system in which a synchronization signal is superimposed on a data signal and transmitted in order to maintain synchronization. The present invention relates to a receiving device that employs a diversity method that improves the signal-to-noise ratio.

BACKGROUND ART Conventionally, in the field of wireless communications, particularly mobile communications, a major problem has been that radio waves reflected by buildings, mountains, etc. are received at the same time as the main signal, causing fading. The spread spectrum method has attracted attention because it has the advantage of being able to communicate without being affected by reflected waves. However, conventional spread spectrum receivers only remove the effects of reflected waves, but have the drawback of not being able to make effective use of reflected waves.

The purpose of the present application is to eliminate the disadvantages of the conventional borrowed equipment mentioned above, and not only eliminate the influence of reflected waves, but also actively utilize them to improve the signal-to-reverberation ratio and improve reception quality. The goal is to provide equipment.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram illustrating an example of the configuration of a transmitting station in a system in which the present invention is used. The data sequence {a _i } to be transmitted from the input terminal 100 is multiplied by the square wave g(t). However, g(t)=1 tT/2, g(t)=0 t>T/2, a _i is input in the form of 1 or -1. x(t) is spread-modulated with a pseudo-random waveform PN1(t) whose period is T, which is generated by the pseudo-random sequence generator 11, and y(t)
becomes. Therefore, y(t)=x(t)PN1(t) (2). Furthermore, pseudo-random waveforms PN2(t) of different phases are generated by the pseudo-random sequence generator 11.
is multiplied by k by the attenuator 12 as a periodic signal, then y
(t) and becomes Z(t)=x(t)PN1(t)+kPN2(t)(3). An example of such a pseudo-random generator is detailed in the course "Pseudo-random sequence (4)" written by Hajime Sato and Katsuhiro Nakamura in the February 1975 issue of Vol. 7. No. 2 of the magazine Bit.

FIG. 2 shows the autocorrelation function R(τ) of the pseudorandom sequence PN1(t). As shown in Figure 2, R
(τ) shows a sharp peak where the wavelength τ is an integral multiple of O and T. Z(t) is carrier sin(ω _c t)
It is modulated by u(t)=Z(t) sin(ω _c t) (4) and is transmitted from the terminal 101.

FIG. 3 is a block diagram showing one embodiment of the present invention. It is assumed that the input terminal 102 receives a waveform v(t) in which several reflected waves are added to the transmitted waveform. Now, the reflected waves are Tc,
Assuming that v(t) arrives at the input terminal with a delay of 2Tc, v(t) = u(t) + αu(t-Tc) + βu(t-2Tc)(
u(t), which can be written as 5), is sequentially input to delay circuits 20 and 21 that delay the input signal by Tc. Therefore, the outputs of the delay circuits 20 and 21 are v(t-Tc), respectively.
Indicates u(t-2Tc). PN1 (t-2Tc) obtained from the terminal 104 is added to each of these signals as the first
PN2(t-
2Tc) is applied to the multiplier 24, 2 which is the second despreading circuit.
Multiply by 6,28. Multipliers 23, 24, 25,
The outputs of 26, 27, and 28 are respectively w ₁ (t)=v(t)PN1(t-2Tc) (6) w ₂ (t)=v(t)PN2(t-2Tc) (7) w ₃ ( t)=v(t-Tc)PN1(t-2Tc) (8) w ₄ (t)=v(t-Tc)PN2(t-2Tc) (9) w ₅ (t)=v(t-2Tc )PN1(t-2Tc) (10) w ₆ (t)=v(t-2Tc)PN2(t-2Tc) (11) Furthermore, w ₁ (t), w ₃ (t), w ₅ (t)
are band-limited by band-pass filters 29, 31, and 33, which are the first filter group that passes up to a frequency of approximately 1/T with ω _c as the center frequency, and w ₂ (t), w ₄ (t), Only the carrier component of w ₆ ( _t ) is extracted by narrow band filters 30, 32, and 34, which are the second filter group that allows only the component of ω c to pass. Since PN1(t) and PN2(t) are largely out of phase, 1()2(+)
0-2Tc<τ<2Tc, where the average of x is shown. Also, due to the nature of pseudo-random sequences, 1()1()=1 1()1(-)0 1()1(-2)0 (12) 2()2()=1 2()2(-) 0 2 () 2 (-2) 0 (13) Filter 29, 30, 31, 32, 33, 34
The outputs of w′ ₁ (t), w′ ₂ (t), and w′ ₃ (t) are respectively
,
When w′ ₄ (t), w′ ₅ (t), and w′ ₆ (t), Equation (12)
,
Due to the property of (13), w′ ₁ (t)=βx(t) sinω _c t (14) w′ ₂ (t)=βksinω _c t (15) W′ ₃ (t)=αx(t) sin〓c (t) (16) W′ ₄ (t)=αksin〓ct (17) W′ ₅ (t)=x(t)sin〓ct (18) W′ ₆ (t)=ksin〓ct (19) and Become. These W' ₂ (t), W' ₄ (t), and W' ₆ (t) become the weights of the respective reflected waves. Therefore, multipliers 35, 36, and 37, which are weighting circuits, respectively
W′ ₁ (t)・W′ ₂ (t), W′ ₃ (t)・W′ ₄ (t), W
' _Five
(t)・W′ ₆ (t) and low-pass filter 38,
By removing the harmonic components of the carriers at 39 and 40 and adding them together at the adder circuit 41, a diversity synthesis output D(t)=k/2(1+α ² +β ² )x(t)(20) is obtained, which is sent to the terminal 103. Output from. filter 38,
39, 40 and the adder circuit 41 together constitute a combining circuit.As is clear from equation (20), the receiver using the diversity method of the present invention weights the reflection level α by α. and the level is β
The weighting is given by β. This is the optimal weighting when the noise is white Gaussian noise. According to the receiving device of the present invention, the weight is
Since W' ₂ (t), W' ₄ (t), and w' ₆ (t) are each determined from the received signal, the optimal weights are automatically set even when the size of the reflected wave changes depending on the line condition. can be found. At the same time w′ ₂ (t), w′ ₄ (t),
w' ₆ (t) serves as a carrier for synchronous detection of each reflected wave, and also absorbs carrier phase shifts of delayed waves. Furthermore, if the number of reflected waves generated by the propagation path is even greater, the number of delay circuits can be increased to further enhance the diversity effect. In the embodiment of the present invention, the synchronization signal is added to the data signal and the carrier wave in the same phase, but it is of course possible to add the synchronization signal and the data signal with the carrier wave phase shifted, and in that case, the filters 30, 32, A fixed phase shift circuit may be added to each output of 34 to match the phase of the carrier of the data signal and the carrier of the weighting signal extracted from the synchronization signal.

In addition, in the embodiment shown in Fig. 3, the synthesis circuit is composed of a plurality of low-pass filters followed by an adder circuit. You can get something with similar effects.

As described above, according to the present invention, the reflected waves are used as active waves by automatically combining each reflected wave with an optimal weight on a line where some of the reflected waves arrive, and the signal-to-noise ratio is improved. A receiving device with improved ratio can be provided.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a transmission block diagram of a system in which the present invention is used, Fig. 2 is a diagram showing an autocorrelation function of a pseudorandom sequence, and Fig. 3 is a block diagram showing an embodiment of the present invention. . In the figure, reference numerals 20 and 21 are delay circuits with taps, reference numerals 23, 25 and 27 are first despreading circuits, reference numerals 24, 26 and 28 are second despreading circuits, reference numerals 29, 30, 31, 32, 33 and 34 are filters, reference numbers 35, 36 and 3
7 represents a weighting circuit, and reference numeral 42 represents a combining circuit.

Claims (1)

[Claims] 1. In spread spectrum communication using a direct spread method in which a spread code different from that for the data signal is superimposed on a spread spectrum data signal as a synchronization signal, a delay circuit with a tap that delays a received signal, and a delay circuit with a tap that delays a received signal, a first despreading circuit that multiplies each tap output of the delay circuit by a spreading code for a data signal and despreads the same; and a first despreading circuit that multiplies each tap output of the delay circuit with taps by a spreading code for a synchronization signal and despreads the same. a second despreading circuit;
a first band limiting the output of the first despreading circuit;
a second filter group for band-limiting the output of the second despreading circuit, and a weight for multiplying the output of the first filter group by the output of the second filter group, respectively. 1. A receiving device comprising a weighting circuit and a synthesis circuit for synthesizing low frequency components of respective outputs of the weighting circuits, the output of the synthesis circuit being used as a synthesis output.