JP2516213B2 - Receive path diversity method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to reception diversity capable of suppressing deterioration of transmission characteristics in a wireless transmission system having selective fading.

[Conventional technology]

In wireless communication, the number of radio wave propagation paths from a transmitting antenna to a receiving antenna is not one, but is generally known as a multipath transmission path. In such a transmission line, fading occurs in which the transmission characteristics such as the reception level of the radio waves greatly fluctuate.

In particular, as the transmission bandwidth becomes wider, the transfer function of the radio wave propagation path seen in the frequency domain is not flat but greatly fluctuates due to multipath. Such a phenomenon is called selective fading, and even when the reception level is high, a large waveform distortion remains in the reception waveform, and therefore the transmission characteristics become extremely poor.

A method using a waveform equalizer as shown in FIG. 1 is known as a transmission characteristic improving line often used in a transmission system having such selective fading.

In this figure, the received signal is automatically gain adjusted (AGC).
The attached amplifier 1 amplifies the average output to a constant level. To control this amplifier, level detection and AGC
The control circuit 2 for is used. The amplified signal is input to the in-phase detector 3, and the in-phase detection output I (t) and the quadrature detection output Q (t) are obtained as detection outputs.

The I (t) and Q (t) are input to the equalizer 4 and the distortion due to the delayed wave is removed. This equalizer is composed of a transversal filter 4-1 and an equalization control circuit 4-2 which controls the coefficient of this transversal filter.
The transmission data is reproduced by the determination circuit 5 based on the equalized output.

[Problems to be solved by the invention]

In the circuit described above, since the delayed wave components other than the main wave in the received wave are removed, the waveform distortion in the received wave is eliminated and the transmission characteristics are improved, but only the main wave of the received wave is extracted. Therefore, there is a drawback that components other than the main wave are not used for improving the characteristics.

On the other hand, as a method of coping with selective fading while utilizing components other than the main wave for characteristic improvement, diversity reception as shown in FIG. 2 has been conventionally known.

On the transmitting side of this system, each symbol to be transmitted is associated with one of the signals orthogonal to each other. This orthogonal signal group can be easily obtained by band-spreading the transmission symbols with code sequences orthogonal to each other.

In the receiving system shown in FIG. 2, the received wave is amplified to a constant level while the automatic gain adjusting amplifier 1 is controlled by the level detection / control circuit 2 as in the case of FIG.
An in-phase detection output I (t) and a quadrature detection output Q (t) are obtained.

When I (t) and Q (t) are input to a matched filter (indicated as MF in the figure) 6-1 to 6-4 corresponding to each orthogonal signal, the output is a matched filter output corresponding to the received symbol. The correlation pulse is extracted at. Each correlation pulse corresponds to each delayed wave component. If this correlation pulse is sampled, the phases are matched and superimposed in the combining circuits 7-1 to 7-4, and the data is reproduced by the determination circuit 5 based on this, reception with a diversity effect becomes possible.

According to this method, each component of the received delayed wave can be separated and extracted, and since all the extracted components are utilized, transmission with extremely good characteristics can be expected.

However, there is a drawback that the frequency band is not used very effectively because the signal band is widened to form the orthogonal signal group.

In view of such conventional problems, an object of the present invention is to provide a reception diversity system that combines each component of a delayed wave without widening the band by frequency spreading.

[Means for solving problems]

According to the invention, the above mentioned objects are achieved by the means recited in the claims.

That is, the present invention provides a synchronous detection circuit that receives a received wave, a propagation characteristic estimation circuit that inputs a detection output of the synchronous detection circuit and calculates a complex transfer function T of a radio wave propagation path, and a calculated complex transfer function. A delay wave synthesis coefficient calculation circuit for calculating a complex transfer function D that delays for a fixed time by using a complex conjugate of T as a weight function, and a complex transfer function having a reciprocal of the square of the absolute value of the propagation path complex transfer function T as a weight function. A delay wave equalization coefficient calculation circuit for calculating E, a signal processing circuit whose input is the detection output of the synchronous detector, and a complex transfer function is the product of D and E, and the output of the signal processing circuit is input to transmit data. It is a reception path diversity system having a judgment circuit for reproduction.

The following points are different from the conventional receiving path diversity method.

(I) Since the spectrum is not spread, the modulated wave need only be in the band for transmitting information.

(Ii) Since a quadrature signal is not used, a matched filter corresponding to each quadrature signal is not required.

(Iii) Since diversity combining and equalization are used together, the power of each component of the delayed wave can be efficiently used for transmission as compared with the conventional waveform equalization.

〔Example〕

 A block diagram of one embodiment of the present invention is shown in FIG.

Amplifier 1 with automatic gain adjustment, control circuit 2, synchronous detector 3
Are the same as in FIG.

This circuit includes a propagation characteristic estimation circuit 8, a delayed wave synthesis coefficient calculation circuit 9, a delayed wave equalization coefficient calculation circuit 10 and a signal processing circuit 11, and the determination circuit 5 is based on the signals processed by these.
To play the data.

The operation of these circuits will be specifically described below.

Since the outputs I (t) and Q (t) of the amplifier 1 with automatic gain adjustment are obtained by linear operation, it is considered that they faithfully represent the radio wave propagation characteristics. The frequency characteristic is T
Let (ω). This T (ω) is estimated by the propagation characteristic estimation circuit.

Correlation detection can be considered as an estimation method. This method is, for example, a PN inserted as a frame signal in a transmission signal.
The code is detected by the correlator, and the level and phase corresponding to each component of the delayed wave and the delay time can be observed from the output waveform.

Let the multiple envelopes of each component be {a _i } and its delay time be {τ _i }. The subscript _i indicates the _i- th component. The longer the PN code, the higher the S / N that can be detected, and the higher the estimation accuracy. In this way, the complex transfer function of the radio wave propagation path that can be estimated from the observable {a _i } and {τ _i } is as follows.

However, N is the number of delayed wave components.

| T (ω) | indicates that there is a large frequency dependence and there is selective fading.

The delayed wave synthesis coefficient calculation circuit calculates the complex transfer function D (ω) based on T (ω) by the following equation.

Here, τ ₀ is a value larger than any τ _i .

Therefore, the above expression means that the received detection output is weighted by a _i ^* which is the complex conjugate of each delayed wave component, and is delayed by τ ₀ −τ ₁ .

As a result, the combined characteristic R (ω) of T (ω) and D (ω)
Is Becomes

In addition, the magnitude of the first term is generally larger than the magnitude of the second term and does not depend on the frequency.

Therefore, the variation of | R (ω) |
It is suppressed compared to (ω) |. The above equation can be further modified as follows.

R (ω) = exp (−jωτ ₀ ) R ₀ R _D (ω) (4) Is.

The delayed wave equalization coefficient calculation circuit calculates the complex transfer function E (ω) by the following equation based on R _D (ω) in (6).

E (ω) = R _D ⁻¹ (ω) (7) Therefore, if the total transfer function of T (ω), D (ω), and E (ω) is represented again by R (ω), R
(Ω) is as follows.

R (ω) = T (ω) D (ω) E (ω) = exp (−jωτ ₀ ) R ₀ (8) Having a complex transfer function represented by the product of D (ω) and E (ω) The circuit is realized by a signal processing circuit. This can be easily achieved by a transversal filter.

Although two transversal filters are used in FIG. 3, they can be combined into one. However, when divided into two as in the present embodiment, the output of 11-1 can be fed back to the delay wave synthesis coefficient operation circuit 9 to improve the accuracy of coefficient operation.

Although the synchronous detector 3 is used in FIG. 3, since the diversity combination (3) by the transversal filter has a function of correcting the phase deviation, only the frequency of the reproduced carrier wave matches the carrier wave of the received wave. Alternatively, a quasi-synchronous detector may be used.

In the above equation (8), | R (ω) | is constant regardless of the frequency, and the selective fading is completely eliminated.

Furthermore, the magnitude of the coefficient is R _0, that is, the square of the magnitude of the amplitude of each delayed wave component, and maximum ratio combining diversity is realized in a transmission system in which noise is stationary.

〔The invention's effect〕

As described above, the present invention simultaneously achieves the effects of diversity and waveform equalization, and has the following advantages.

(I) It is not necessary to widen the band of the transmission signal as in frequency spreading.

(Ii) Efficient demodulation can be performed by the maximum ratio combining diversity that can most effectively use each component of the delayed wave. Also,
The diversity is pass diversity and does not require multiple antennas.

(Iii) Good transmission characteristics without deterioration of transmission characteristics due to delay distortion can be obtained.

(Iv) Since it can be realized by digital signal processing, the circuit operation is stable and the size can be reduced.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a receiving system using a conventional waveform equalizer, FIG. 2 is a basic configuration diagram of a conventional bus diversity receiving system, and FIG. 3 is a block diagram of an embodiment of the present invention. . 1 ... Amplifier with automatic gain adjustment, 2 ... Control circuit, 3 ...
Synchronous detector, 4 ... Equalizer, 4-1 ... Transversal filter, 4-2 ... Equalization control circuit, 5 ... Judgment circuit, 6-1 to 6-4 ... Matched filter, 7- 1-7-4
...... Synthesis circuit, 8 ... Propagation characteristic estimation circuit, 9 ... Delayed wave synthesis coefficient arithmetic circuit, 10 ... Delayed wave equalization coefficient arithmetic circuit, 11
...... Signal processing circuit

Claims (1)

(57) [Claims] 1. A synchronous detection circuit which receives a received wave as an input, a propagation characteristic estimation circuit which inputs a detection output of the synchronous detection circuit and calculates a complex transfer function T of a radio wave propagation path, and a complex transfer function of the complex transfer function T. A delay wave synthesis coefficient operation circuit that calculates a complex transfer function D that delays for a fixed time by using a complex conjugate as a weight function, and a complex transfer function E that uses a reciprocal of the square of the absolute value of the complex transfer function T as a weight function. A delay wave equalization coefficient operation circuit, a signal processing circuit having the detection output as an input and a complex transfer function being a product of D and E, and a determination circuit having an output of the signal processing circuit as an input and reproducing transmission data. A receiving path diversity system characterized by having.