DE2360654C1 - Device for measuring distortions in the transmission of radio signals - Google Patents

Description

50

The invention relates to a device for measuring distortions of all kinds caused by Multipath propagation of a preferably modulated high-frequency signal arise.

In the radio fields of earth-based radio systems, there are many in addition to the direct path of propagation Detect additional detours caused by reflectors in the area. For fixed services the influence of detours can be minimized by using appropriate antenna heights and directional antennas. In the case of mobile services, on the other hand, the situation has changed for almost every location, and it has to be Signal distortions due to multipath propagation are expected. This also applies to stationary ones Radio connections and even for directional radio connections in which signal distortions cannot be masked out Detours can occur.

The signal distortions arise with the vectorial Addition of the incoming signals from different directions. Arising from the addition both amplitude and time-of-flight distortions, which are discussed in detail below. The strenght the distortion depends on the relative attenuation of the reflected beam to and from the direct signal the difference in length between the detour and the direct route, based on the electrical length of a bit of the information transmitted.

In nature it is extremely difficult to determine the influence of the individual parameters involved in the distortion to be recognized quantitatively, since on the one hand it is often impossible to be completely clear about the propagation mechanism analyze and on the other hand also the individual parameters, such as length of detours and their attenuation, during the measurement cannot be varied. If one considers the further circumstances, such as weather-dependent Reflection attenuation, which a certain propagation situation during the day and also from day to day can fundamentally change and the circumstances associated with the measurement (such as arrival with Special vehicles that have always been extremely limited for reasons of space and power supply Situation of the measuring equipment park to be carried, the fact that for measurements of phase and Runtime distortions, apart from the radio field subject to distortion to be examined, no reference connection whatsoever for the radio frequency to the other vehicle [distance e.g. B. 30 ... 50 km] is possible), so it becomes clear that the analysis of the parameters causing the distortions in this way only with very high expenditure of time and money can be achieved.

This applies to all types of modulation, especially to the digital ones that are mostly used today Modulation types.

The invention is based on the object of specifying a device with which it can be used in a laboratory Means is possible to detect all distortions of the signal caused by the radio path and analyze.

This object is achieved in a device of the type described in that for Simulation of the transmission path, the signal on the one hand (direct beam) via an adjustable attenuation line and an adjustable phase delay element and on the other hand (reflected beam) via at least one delay line with adjustable delay time and an element for balancing basic attenuation on an addition circuit with a subsequent analysis device for the delay is given.

In order to achieve the delay lines, which are easier to implement at low frequencies, even at higher frequencies To be able to use it, it is advantageous if the RF signal is initially set to a lower frequency range is implemented, which the simulation device runs through to return to the original frequency position to be implemented and if the two frequency converter stages using a common oscillator preferably adjustable frequency are fed. For this it is advantageous to use the delay line as Train ultrasonic line with electromechanical transducers on both sides.

To simulate difficult propagation fields, π delay lines are advantageously switched through in parallel and / or in series.

It is useful to compensate for the basic attenuation of the direct path and the at least one

3 4

Reflection path adjustable damping elements in detected, delayed by the transit time A t of the distance Al

intended every way. and in the receiving antenna the addition of the two

In order to simulate diffuse reflection, the ultra-signals are done, which results in a relatively simple one

sound line advantageous, z. B. by attaching the principle equivalent circuit diagram (Fig. 4).
Bores, kinks or the like, with possi- 5 5 A transmission signal applied to point 1 reaches once

opportunities for sound refraction. via a direct connection (electrical length = 0)

To simulate disturbances of any kind (ECM) it is point 1 'and in parallel via a delay line

advantageous, disturbance signals in the to be simulated with the electrical length Al the point Xa '. In order to

Fade in radio field. the same electrical state prevails at point 1 a as

The invention is illustrated below with reference to FIGS. 10 at 1 '. The state la'is around the running time of the route Al

explained in more detail. In the drawing means: delayed. The point 1 a thus corresponds to the point a in

FIG. 1 shows the principle of multiple propagation in FIG. 1.

a radio beam; In the adding network add that of the receiving antenna

Fig. 2 shows the result of the superposition of two corresponding, the two components 1 'and la'

Signals from different directions; 15 are added and result in the receiver level (SWR), which is set in

F i g. 3 shows the standing wave distortion resulting therefrom. 2 is shown in principle.

ratio as a function of the difference Ap of the level In F i g. 5 the device is shown as it is for

of the two signals; practical investigations are suitable, d. H. all at the

F i g. 4 shows the principle of simulating the propagation- Signal distortion parameters involved are changeable-

tung; 20 bar.

F i g. 5 shows an expanded image for the measurement according to The basic attenuation in the radio field can be determined by means of the

F i g. 4; Attenuator 1 can be changed so far that all

F i g. 6 shows a measuring device in which the signal-to-noise ratios occurring in the principle are measured

the double mixture can be reduced to one. With the z. B. change in steps

lower intermediate frequency use is made; 25 Delay line 2 can take any desired detour

F i g. 7 shows a measuring circuit diagram for length or length Al can be set. The delay line

Dual spread; has a damping that corresponds to the basic damping 1

Fig. 8 shows the principle of diffuse reflection; elevated. With the attenuator 3, the level difference

F i g. 9 shows the replication principle of the diffuse between direct route and detour so set that

Reflection; 30 the desired SWR is created. The location of a minimas

Fig. 10 shows an extension of the simulation for on the frequency axis, in which 180 ° phase shift

diffuse reflection. Exercise prevails (Fig. 2), can be with the help of the

A radio signal according to FIG. 1, transmitted by A, adjust phase shifter 4 (Αφ = 360 °). Through this

reaches the receiver B both on the direct can the standing wave characteristic compared to a

Path Si as well as on the detour 52. The detour is 35 fixed measuring frequency (ie without detuning of

the distance Al longer than the direct route. Transmitter and receiver) continuously by the distance

This causes the signal to be delayed in a detour. two minima can be shifted. So the

Between the two received signals PX / P2 there is a measurement of the signal distortion at any one

thus a runtime difference that is possible at the vectorial point of the characteristic,

len addition of the two signals at the same time 40. B. all critical detour differences Al

Variation of the frequency from a center frequency k for all that occur in digital radio tasks

leads to a standing wave characteristic, as shown in FIG. To reproduce 2 Biraten (approx. 0.1 kBd ... 1 MBd), the

shown. The difference between maxima and delay times is between approx. 0.5 μβεο and 5 msec

Minima, in the following SWR (Standing Wave Ratio) can be changed. The realization of detour differences

called, depends on the difference in the reception level 45 zen around 1 μβεο does not yet make unsolvable with cables

ρ 1 and ρ 2. The frequency spacing between the minima difficulties. Since digital radios are mainly

is inversely proportional to the path difference Al. borrowed the digital voice transmission e.g. by means of

_c Vocoder and delta modulation (1.8 kBd / 19.2 kBd) inter-

I / = - yy. eats, delay times of z. B. 25 to

50 280 μβεϋ realized according to Al from 7.5 to 90 km

At the minima the phase shift will be. For this purpose, ultrasonic delay

180 ° between the signals, but approximate lines are used for the maxima.

0 °. Such delay lines consist of the simple

The dependence of the SWR on the level difference is the most common, as is known per se, from a rod, its

in Fig. 3 shown. 55 material that delays sound waves (e.g. Trolitul or

First of all, the detour situation in Plexiglas) with the appropriate length depending on the desired

F i g. 1 must be considered. The signal which at a ter delay time. For implementation in sound waves

at a certain point in time via the direct path which are piezoelectric transducers on both sides of the rod

Reached the receiving location, meets at the same time about attached, which then when a relatively broad

the detour at a point a. As a result, between eo measuring frequency band is required, accordingly

the direct signal at the receiving location and which must be broadband.

Detour signal at point a Time-of-flight and in-phase A certain disadvantage of such delay lines

Ness. If one further assumes that between the two lines it is that they inevitably adhere to a certain one

Signals are completely equal in amplitude (same converter frequency, ζ. Β. 4 MHz, are bound

Path attenuation), then these two states 65 are usually not directly in the simulation arrangement

completely identical. frequency range of interest can be used, rather

Since the detour signal at the receiving point opposite must e.g. in the intermediate frequency response of the to

The direct signal at the receiving location, as already inserted into the radio systems that have already been investigated.

In order to be able to use the simulation arrangement also at higher frequencies, it is necessary to use the apply double implementation mentioned at the beginning. A block diagram for this arrangement is shown in FIG. 6th shown.

The high-frequency radio signal (225 to 400 MHz) by means of a subcarrier, generated in the generator HG, in a mixer Ml into the frequency position of the delay line 2, z. B. 4 MHz, implemented as previously delayed and added and reset to the original radio frequency position with the same subcarrier and another mixer M 2.

As a generator for the subcarrier is here, especially if long detours Al are examined (Minimaabstand Af very small), advantageously a synthesizer used. A standard measuring transmitter is sufficient for small Al (large Af). Because of the double mixing, the absolute frequency of this auxiliary generator has no influence on the accuracy of the radio frequency, but it can be used to change the operating frequency of the delay line. This provides a further, very advantageous possibility for continuous scanning of the standing wave characteristics.

It should be emphasized that in principle this means that the simulation can be applied to all conceivable radio frequencies is possible.

The previous block diagrams were limited to a detour. In general, the system can be expanded as required, e.g. B. according to FIG. 7, and thus difficult detour situations can also be simulated. However, it is necessary here to equip each delay line L I to Ln with an attenuator line E 1 to En and a phase shifter ψ 1 to φη.

For the implementation of processes as they occur with diffuse reflection (length of the reflectors > λ and a strongly structured surface, e.g. in the case of mountains and hills, also forest edges), according to the method shown in FIG. 7 means a relatively high effort. It is therefore proposed as a further advantageous embodiment to incorporate the diffuse refraction processes into the sound line itself.

A case of diffuse reflection in a radio field is shown in Fig. 8. The from a transmitting antenna 11 outgoing rays are refracted at a structured reflector 12 and in principle in all Directions scattered. In Fi g. 7 in this case, however, only the rays are shown, which in turn are a Have a chance to hit the receiving antenna 13 (hatched field). It is easy to see here that different detour lengths occur. The direct beam is at least strong through an obstacle 14 muffled.

The same result must be achieved in the simulation. But since the piezoelectric transducers do not Point emitters, but surface emitters from which the rays exit parallel, must be different Arrangement are made (see Fig. 9). Parallel beams emerge from the transducer 15. Certain Beams have the chance to close a joint 16 (e.g. hole) introduced into the delay section in this way meet that they are reflected from there to the transducer 17. This means that signals now also reach different levels Running time the converter 17. The two arrangements according to FIGS. 8 and 9 thus have a equivalent basic behavior.

The delay section offers even more variation options if several joints (e.g. Row of holes) with a corresponding inclination, based on the arrangement of the transducers, are arranged so that There is already a different transit time for the individual hole centers, as in FIG. 10 indicated here For the sake of clarity, only a few lines have been drawn again

A particularly large number of simulation options arise when using different delay lines according to FIG. 10 in an arrangement according to FIG. 7 in parallel or partly switched in series.

The simulation options of the system (Fig. 7) are also significantly expanded if interfering signals (ECM) are faded in via an additional attenuator. This means that route disturbances, colored noise and, for tactical simulations, all conceivable types of targeted ÜCM disturbances can also be displayed.

Measurements carried out e.g. B. on the system according to F i g. 4 make the basic route behavior completely clear. The amplitude, phase and runtime behavior can be relative between input and output simply record it by measurement. This means that the propagation mechanism is basically the same as the usual one Means of filter theory can be represented.

In addition to the simulation options for radio fields that have already been described in detail, showing interference and ECM , the following tasks can still be managed very efficiently:

a) Clarification of further propagation and process details and investigation of the various types of modulation (Frequency shift keying, phase shift keying, amplitude modulation and possibly optimization and preamphasis etc.);

b) Laboratory use for special radio systems under operating conditions;

c) Creation of measuring devices to test the behavior of other radio systems in the case of multipath propagation (e.g. mobile radio relay systems);

d) Creation of measuring devices for series testing of devices in the test field;

e) Measuring device for examining and determining all parameters necessary for the equalization of already distorted signals according to amount and phase in the transmission frequency position are necessary.

With the radio field simulator shown, a large number of difficult and information that is usually extremely cumbersome to obtain is relatively easy to obtain.

For this purpose 3 sheets of drawings

Claims (7)

Patent claims: 1. Device for measuring distortions of all kinds caused by multipath propagation of a preferably modulated high-frequency signal arise, characterized in that To simulate the transmission path, the signal on the one hand (direct beam) via an adjustable Attenuation line and an adjustable phase delay element and on the other hand (reflected Beam) via at least one delay line with adjustable transit time and an element for Compensation of basic attenuation on an addition circuit with subsequent analysis device for the distortion is given. 2. Device according to claim 1, characterized in that the signal is initially transmitted to a frequency converter stage, then on the radio field simulation, then again on a frequency converter stage and that the two frequency converter stages are fed by a common oscillator with preferably adjustable frequency. 3. Device according to claim 2, characterized in that the line with variable transit time is designed as an ultrasonic line with electromechanical transducers on both sides. 4. Device according to claim 3, characterized in that η delay lines are connected in parallel and / or in series to simulate difficult propagation fields. 5. Device according to claim 4, characterized in that to compensate for the basic attenuation the direct path and the at least one reflection path adjustable damping elements in are provided for each path. 6. Device according to claim 3, characterized in that to simulate diffuse reflections the ultrasonic line, for example, by making holes, kinks or the like is provided with possibilities for sound refraction. 7. Device according to one of claims 3.5 or 6, characterized in that interference signals are faded into the simulated radio field to simulate interference of any kind (ECM).