JP2593510B2 - Transmission line simulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a transmission line simulator for simulating the characteristics of a transmission line used in communication.

(Conventional technology) When a modulated wave is transmitted via a transmission line, its transmission characteristics fluctuate with time, the level is reduced with respect to the average received power level, and some reflected waves are generated. The transmission characteristics are extremely deteriorated due to the multi-bus state. For such a situation, AGC
The transmission characteristics have been improved by introducing circuits and equalizers. A transmission path simulator is used to confirm the operation of these improvement techniques on an actual device.

Since deterioration in wireless communication is mainly caused by fading of a radio wave propagation path, a transmission path simulator is also called a fading simulator.

FIG. 4 is a circuit block diagram of a conventional fading simulator. In this fading simulator, RF
The modulated wave S (t) of the band is input to the 90-degree hybrid circuit 2 via the input terminal 1 and the real-number component signal αS (t) and the imaginary-number component signal αjS
(T). One signal αS (t) output from the hybrid circuit 2 is supplied to the mixer 3, and the other signal αjS (t) is supplied to the mixer 4. In both signals, α is a real coefficient and j is an imaginary unit.

Both mixers 3 and 4 provide baseband Gaussian noise x (t) and y generated from two-dimensional Gaussian noise generator 5.
(T), and converts the signal αS (t) and the signal αjS (t) from the hybrid circuit 2 into the baseband Gaussian noise x from the two-dimensional Gaussian noise generator 5, respectively.
Multiply with (t) and y (t). The signals multiplied by the mixers 3 and 4 are combined by the combining circuit 6 and output from the output terminal 7.

In the above-described conventional fading simulator, the modulated wave in the RF band is divided by the hybrid circuit 2, multiplied with the baseband Gaussian noise from the two-dimensional Gaussian noise generator 5, and then synthesized to perform Rayleigh fading. It is known that when a modulated wave of an input signal is output as a received signal and has a narrow band, a level variation in radio wave propagation can be well approximated.

By the way, as the signal becomes wider, not only the level modulation but also the frequency characteristic of the radio wave propagation path becomes a problem in the actual transmission path. This frequency characteristic is due to the fact that the actual propagation path is multipath, and the transmission distance from the transmission point to the reception point differs for each path. Such a transmission path cannot be approximated by the conventional simulator shown in FIG.

FIG. 5 is a circuit block diagram of a conventional fading oscillator which considers delay dispersion due to such a multipath phenomenon.

In this fading simulator, an unmodulated carrier wave is supplied to a power distribution circuit 9 via an input terminal 8,
The power is divided into five waves by the power distribution circuit 9. One of the five waves is supplied to the direct wave circuit 10, and the other four
The waves are supplied to delay wave modulation circuits 11, 12, 13, and 14, respectively. The delay wave modulation circuits 11 to 14 are configured by connecting a mixer, an attenuator, and an external phase device in series.

On the other hand, this fading simulator has a Bayband waveform Im (t) and Qm corresponding to the complex envelope of the modulated wave.
(T) is supplied to the baseband input terminal 15. The baseband waveforms Im (t) and Qm (t) are input terminals
The signal is supplied to a delay circuit 16 via a line 15. This delay circuit
Reference numeral 16 supplies the baseband waveforms Im (t) and Qm (t) to the direct wave circuit 10 and four types of delayed baseband waves Im (t-kγ) and Qm (t-kγ) (where k Are integers of 1 to 4), and the four types of delayed baseband waves Im (t-kγ) and Qm (t-kγ) are supplied to the mixer circuits of the delay wave modulation circuits 11 to 14, respectively. ing. As described above, since each delay wave modulation circuit is supplied with the complex envelope baseband waveform via the carrier via the power distribution circuit 9 and the delay circuit 16, each modulation circuit outputs a modulation wave. The level and phase of these modulated waves can be freely varied by the attenuator and the phase shifter in the delay wave modulating circuit 11, and the variable control is performed by the control circuit 17. And the direct wave circuit 10
Are combined by the combining circuit 18, adjusted to an appropriate level by the attenuator 19, and output from the output terminal 20.

Since the conventional fading simulator shown in FIG. 5 configured as described above can form a plurality of delayed waves, it simulates the frequency characteristics of the actual multipath radio wave propagation path as described above. You can do it.

(Problems to be Solved by the Invention) In the conventional simulator shown in FIG. 5 described above, since the level fluctuation and the phase modulation are generated by the analog circuit in the RF band, production and adjustment are difficult, and
Further, there is a disadvantage that the circuit does not operate normally when the fluctuation of the fading becomes faster.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a transmission path simulator which is easy to produce and adjust, and accurately simulates fast-modulating fading.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a transmission path simulator of the present invention is a transmission path simulator for simulating a transmission path through which a modulated wave is transmitted. Delay means for generating a plurality of delay signals obtained by respectively delaying a real component signal and an imaginary component signal obtained by digitizing an in-phase component waveform and a quadrature component waveform each representing a complex envelope by a desired delay time; Complex multiplying means for multiplying each of the complex delay signals output from the means delayed by a predetermined delay time with a complex coefficient, and complex adding means for adding each output signal from the complex multiplying means; ,
Control means for controlling the value of the delay time and the complex coefficient, and conversion means for converting the real component output signal and the imaginary component output signal from the complex addition means into analog signals,
And a quadrature modulation unit to which an output signal from the conversion unit is supplied.

(Operation) In the transmission path simulator of the present invention, the digitized real component signal and imaginary component signal of the in-phase component waveform and the quadrature component waveform, which represent the modulated wave in a complex envelope, are each delayed by a desired delay time. Each signal obtained is multiplied by a complex coefficient and added, and the added output signal is converted into an analog signal to obtain a quadrature modulated wave.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit block diagram of one embodiment of the present invention.
The embodiment shown in the figure is divided into a digital processing section shown in FIG. 1A and a quadrature modulation section shown in FIG. 1B.

First, in the digital processing section shown in FIG. 1 (a), signals Im (t) and Qm (t) representing the complex envelope waveform of the modulated wave S (t) are input to the input terminal 21 respectively.
And are supplied via 22. The modulated wave S (t) is
The following expression shows the complex envelope.

Sm (t) = Im (t) + jQm (t) (1) The signals Im (t) and Qm (t) of the modulated wave S (t) are supplied to a delay circuit 23 including a memory or a shift register. Have been delayed. The delay time γk of the delay circuit 2 is k times the unit time γ. This k is a coefficient, which is controlled by the control circuit 31 as described later. Therefore, the delayed wave output from the delay circuit 23 is S
(T−kγ).

The modulated wave signal S input from the input terminals 21 and 22
(T) is supplied to the complex multiplication circuit 24. This complex multiplying circuit 24 is composed of scalar multipliers 24ma, 24mb, 24mc, 24md and scalar adders 24aa, 24ab, whereby complex coefficients a _k = a _kr + ja _ki are set. That is,
The coefficient a _{1r is set in} the scalar multiplier 24ma, the coefficient −a _{1i is set in} the scalar multiplier 24mb, the coefficient a _1r is set in the scalar multiplier 24mc, and the coefficient a _1i is set in the scalar multiplier 24md. Then, the signals Im (t) supplied from the input terminals 21 and 22 and
Qm (t) is multiplied by each coefficient in each of scalar multipliers 24ma to 24md, and this multiplied output signal is applied to scalar adder 24m.
aa and 24ab are added. Therefore, the output signals If _i (t) and Qf _{i of} the scalar adders 24aa and 24ab
(T) is as follows.

If _i (t) = a _1i Im (t) −a _1i Qm (t) (2-
_{1) Qf i (t) =} a 1i Im (t) + a 1i Qm (t) ...... (2-
Complex envelope Sf ₁ to 2) of these signals is formed is as follows.

Sf ₁ (t) = If ₁ (t) + jQf ₁ (t) = (a _1r + Ja _1i ) [Im (t) + jQm (t)] = a ₁ S (t) (3) S (tk)
γ) is also a scalar multiplier 27ma, 27
mb, 27mc, 27md and scalar multipliers 27aa, 27ab are supplied to a complex multiplication circuit 27 in which complex coefficients a _k = a _kr + ja _ki are set, and are multiplied by the complex coefficients. As a result, the complex multiplying circuit 27 outputs the signal Sf ₂ (t) (t−kγ).

Output signals from the complex multiplication circuits 24 and 27 are synthesized by complex addition circuits 28a and 28b, respectively,
Outputs from a and 28b are output terminals 29 and 30 respectively from If
(T) and Qf (t). The signal Sf (t) formed by these signals is as follows.

Sf (t) = If (t ) + jQf (t) = Sf 1 (t) + Sf 2 (t) (t-kγ) = a 1 S (t) + a 2 S (t-kγ) above synthesized 2-wave Although the description has been given of the case of performing the above, it is also possible to obtain three or more composite waves in any manner.

The complex coefficients a ₁ and a ₂ in the complex multiplication circuits 24 and 27 and the coefficient k for varying the delay time in the delay circuit 23 are controlled by the control circuit 31. These values are calculated based on a specific radio wave propagation model and change with time. Usually, a complex coefficient sequence a =
In {a _k | 0 ≦ k ≦ k}, the magnitude of a _k | a _k | ² is a lognormal distribution, and the phase of a _k is a constant phase component that follows a uniform distribution;
And a component that increases linearly with time using 2πfd as a coefficient. Note that fd is the droop frequency.

Thus, the modulated wave If which fluctuates due to fading
(T) and Qf (t) are supplied from the output terminals 29 and 30 of the digital processing unit in FIG. 1 (a) to the quadrature modulation unit shown in FIG. 1 (b) via the input terminals 39 and 40. .

The quadrature modulation section converts the modulated waves If (t) and Qf (t) supplied from the digital processing section into D / A converters 32, respectively.
The signals are converted into analog signals Ifa (t) and Qfa (t) by a and 32b. These analog signals are supplied to mixers 33a, 3
Supplied to 3b. The mixers 33a and 33b respectively convert these analog signals from the carrier wave supplied from the local oscillator 34 and the local oscillator 34 via the phase shifter 35.
Multiply with the carrier wave advanced by 90 degrees. Mixer 33
Output signals from a and 33b, ie, analog signal If (t)
The two carrier waves multiplied by Qf (t) are combined by the combining circuit 36 and output from the output terminal 37 as a modulated wave subjected to fading.

In the above-described fading simulator, since the baseband component of the composite wave is formed by digital signal processing, the RF circuit includes only the quadrature modulation unit, and the production and adjustment become extremely simple.

In the above embodiment, the fading simulator has been described, but this can be similarly applied to a transmission path simulator.

FIG. 2 is a circuit block diagram of another embodiment of the present invention. In this embodiment, a fading simulator is formed by using four transversal filters constituting the digital signal processing section shown in FIG. 2A as shown in FIG. 2B.

First, the transversal filter shown in FIG. 2 (a) supplies the waveform Im (t) supplied from the input terminal 41 directly to the coefficient multiplication circuit 43a and multiplies the waveform Im (t) by the real number coefficient aI _ri . On the other hand, the waveform Im (t) is delayed via a series of delay circuits 42a, 4ab,..., 42g, and the output signals of these delay circuits are respectively multiplied by coefficient multiplication circuits 43b, 43c,
.., 43h, and multiplied by a real number coefficient a _kri .

Since each delay circuit delays the input signal by the unit time γ, each delay circuit outputs a delay waveform I _mk (tk
γ) (where k is an integer from 1 to k) is output. This delayed waveform I _mk (t−kγ) is applied to a coefficient multiplying circuit 43b.
The product is multiplied by the real number coefficient a _kri at ~ 43h. Output signals from the coefficient multiplying circuit are added by the adding circuit 45, and the sum is obtained. Therefore, the sum I _i f is as shown in the following equation is output via an output terminal 47 from the summing circuit 45.

The fading simulator shown in FIG. 2B uses the transversal filter shown in FIG.
As shown by 2,53,54, the system is configured using four sequences.
The inputs of the transversal filters 51 and 53 are commonly connected and connected to an input terminal 49, and
2, 54 inputs are commonly connected and connected to an input terminal 50. From the input terminals 49 and 50, the signals Im (t) and Qm
(T) are respectively supplied to the transversal filters 51, 53 and 52, 54.

Transversal filter 51-54 is connected to the control circuit 59, the control circuit 59 respectively complex-coefficient transversal 51-54 _{a kr, -a ki, a ki} , is adapted to set the a _kr. The output signal I _i f of the transversal filter _{51,52 (t), I q f} (t) are combined by summing circuit 55,
Output signals Q _q f of transversal filters 53 and 54
(T), Q _i f (t) are combined by adder circuit 56, the adder circuits 55 and 56, the output combined output signal shown in the following equation the If (t) and Contact Qf (t), respectively terminals 57 and 58 Output via.

The complex envelope Sr (t) formed by these is expressed by the following equation.

This equation is similar to the above-described equation (4), and is obtained by synthesizing a k-wave signal with a delay time kγ. If there is no k'th delayed wave, the control circuit 59 may perform control so that _ak '= 0.

The time response of the transversal filter type fading simulator shown in FIG. When the equation (7) is Fourier transformed, the following equation is obtained.

Sf (ω) = T (ω) S (ω) (8) It can be seen that the transversal filter operates as a linear filter, and its frequency characteristic is expanded as in Expression (9). By the way, assuming that the modulation impulse response waveform of the linear modulation wave is g (t) and the propagation delay complex profile representing fading is h (t), these can be easily synthesized because these are linear effects. That is, these convolution integral values g (t) *
Set h (t) as a _k . At this time, the Fourier transform of the Fourier transform of the convolution value is g (t) and h
When G (ω) and H (ω) are obtained by transforming (t) to Fourier, G (ω) H (ω) is obtained. If this value is used as T (ω) in equations (8) and (9), Good. In this case, the inputs Im (t) and Qm (t) of the simulator use impulses corresponding to transmission codes.

Thus, using a transversal filter,
There is an advantage that the spectrum roll-off and the fading phenomenon in the modulation can be dealt with at once, and it is extremely effective for a transmission system simulator.

FIG. 3 is a circuit block diagram of another embodiment of the present invention. The embodiment shown in the figure has a function of suppressing deterioration such as an increase in error due to quantization of the generated signal Sf (t) when the level is reduced by fading.

The embodiment of FIG. 3 includes D / A converters 62 and 63 connected to input terminals 60 and 61, and attenuators 64 and 65 connected to the D / A converters 62 and 63, respectively. A quadrature transformer 66 to which the outputs of the attenuators 64 and 65 are supplied, and a control circuit (not shown) sums the square of the signals If (t) and Qf (t), ie, | Sf (t)
| ² = If ² (t) + Qf ² (t) is calculated in advance, and this value is calculated as D / A
The normalization coefficient α is multiplied and expanded so as to be a sufficiently large value with respect to the minimum unit of the converter, and the expanded digital signal is supplied to the A / D converters 62 and 63 via the input terminals 60 and 61. , And supplied from the D / A converter to the attenuators 64 and 65 as analog signals If (t) and Qf (t). Attenuator 6
4, 65 reduces each analog signal to 1 / α and the signal If
(T) and Qf (t) are returned to the quadrature modulator 66. The quadrature modulator 66 modulates the carrier supplied from the carrier input terminal 68 and outputs the modulated signal to the output terminal 67.

With such a configuration, the D / A converter can always control the quantization error to be small, so that a highly accurate simulator can be realized.

[Effects of the Invention] As described above, according to the present invention, a digitized real component signal and an imaginary component signal of an in-phase component waveform and a quadrature modulation waveform in which a modulated wave is displayed in a complex envelope are respectively delayed by a desired delay time. The delayed analog signal is multiplied by a complex coefficient for each delayed signal, added, and the added output signal is converted to an analog signal to obtain a quadrature modulated wave. In addition, production and adjustment become extremely easy, and processing is performed at the baseband, so in the development of devices that suppress the deterioration of transmission characteristics due to fading on the receiving side, such as the development of equalizers
Even when the RF components are not yet completed, you can check the performance by connecting with baseband.

[Brief description of the drawings]

1 is a circuit block diagram showing a configuration of one embodiment of the present invention, FIG. 2 is a circuit block diagram of another embodiment of the present invention, FIG. 3 is a circuit block diagram of another embodiment of the present invention, FIGS. 4 and 5 are circuit block diagrams of a conventional fading simulator. 23 Delay circuit 24, 27 Complex multiplication circuit 28a, 28b Complex addition circuit 32a, 32b D / A converter 33a, 33b Mixer 34 Local oscillator 35 Phase shifter 36 ... Synthesizer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Hattori 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Examiner, Nippon Telegraph and Telephone Corporation Kazuo Kuna (56) References JP-A-55-37047 (JP, A) JP-A-59-101938 (JP, A) JP-A-59-111435 (JP, A) JP-A-59-230332 (JP, A)

Claims (2)

(57) [Claims] 1. A transmission path simulator for simulating a transmission path through which a modulated wave is transmitted, wherein a real component signal and an imaginary number are provided by digitizing an in-phase component waveform and a quadrature component waveform, respectively, in which the modulated wave is represented by a complex envelope. Delay means for generating a plurality of delay signals obtained by delaying the component signals by a desired delay time, and multiplying each of the complex delay signals output from the delay means by a predetermined delay time by a complex coefficient Complex multiplying means for multiplying, complex adding means for adding each output signal from the complex multiplying means, control means for controlling the value of the delay time and complex coefficient, and real component output from the complex adding means It has a conversion means for converting a signal and an imaginary component output signal into an analog signal, and a quadrature modulation means supplied with an output signal from the conversion means. Transmission line simulator to. 2. A sum-of-squares calculating means for calculating a sum of squares of a real component output signal and an imaginary component output signal from the complex adding means, and wherein the sum of squares has a value sufficiently large with respect to a quantization unit of the conversion means. Multiplying means for multiplying the complex coefficient by a level normalization coefficient so as to supply the complex coefficient to the conversion means,
2. An attenuating means for attenuating an analog signal output from said converting means to one-half of said level normalization coefficient and supplying said signal to said quadrature modulating means.
Transmission line simulator as described.