DE1949132A1 - Method for measuring noise in a frequency or time division multiplex message transmission system - Google Patents

Description

Procedure for measuring noise on a frequency or Time division multiplex message transmission system

The invention relates to a method for making noise solution to a frequency or time division multiplex communication system or individual parts thereof using a measurement signal according to Art a noise voltage as / ie one of the system to be measured or system part downstream, selective measuring device, which measured the noise in at least one further frequency band lying outside the specified frequency band

The noise to be measured is composed of the intermodulation noise, your thermal noise and if necessary, additional type of noise, such as the - in pulse code modulation systems or the like With the help of a special calibration of the selective measuring device ZoB = the zero on the relative useful signal level, d, ho on the system input, related noise power in Measured pW / O or the ratio of the measured noise power for the measured value that results when the "jolection means" is switched off, "This ratio is determined weighted logarithmically and expressed as the signal-to-noise ratio in dB, whereby a correction value is calibrated, the takes into account that the noise power is measured selectively,

The predetermined frequency ba / v'i filled by the measurement signal

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can be used together with the other frequency band (s).:] .., - -for which the selective measuring device is designed, and the frequency gaps in between lie within a channel bandwidth of the message transmission system or a larger part, possibly also the entire width of the transmission frequency band, take, which may also include other, adjacent frequency ranges sindo

The selective measuring device is generally provided with a digital or analog measured value display, which is shown in as is known, is calibrated in such a way that the noise values of interest - z »Bo the noise power or the signal-to-noise ratio - Immediately when the measurement signal is fed in with a predetermined (average) energy distribution or, if necessary, can be displayed directly after a comparison measurement has been carried out ο

The invention is based on the object of the aforementioned method for measuring the noise, in which so far with one limited to the given frequency band Noise voltage has been worked on, particularly in terms of to a shortening of the measuring time. This is achieved according to the invention in that the measuring signal by means of one switched on by periodic clock pulses, feedback shift register is generated whose clock frequency has a value that is significantly greater than the width of the given frequency band »

The advantage achieved with the invention is in particular in a substantial reduction in the fluctuations of the measured value display, which in the known methods of this Type as a result of the random temporal course of the intoxication; spanimngsamplitude occur and especially with narrow given frequency bands are very disruptive »Da-

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with there is on the one hand the possibility of a "üi ^ -. u ..- ron and faster immediate reading and otheri; citij When using gowns that integrate measured values, they are arranged within the "actual" display hysteresis or dioiiem are connected upstream, a faster averaging and thus a shorter curing time. This explains that the quasi-accidental, but actually periodic character of the shift register fed back generated measurement signal the definition of a slowest A; :: plitudenschv / ankung allows the envelope of the. the display system receives Keßsignals supplied and the can no longer be undershot, »It corresponds to the repetition frequency of the sequence of binary characters (bits) output by the shift register - -

The invention is illustrated below with reference to one in the drawing illustrated, preferred embodiment explained in more detail. Ss shows

? ig, 1 the circuit diagram of an arrangement for measuring the signal-to-noise ratio on a telephone channel of a pulse modulation system (PCM system), FIG. 2 the control diagram of a feedback shift register and
FIG. 2 shows the cooling curve of the power distribution of the output voltage output by the shift register according to FIG. 2 over frequency.

Tn Figoi, the low-frequency measurement signal generated by a generator 1, which has the character of a noise voltage, is limited to a predetermined frequency band, for example from 350 to 550 Hs, by means of a downstream bon band filter 2, amplified in 5 and transferred to the n .low-. quenten input of a PCM transmission channel 4 '. After passing through the kartal, the measurement signal recovered by demodulation is tapped at the channel output 5 and

PA 9/150/3239 ■ 1098U71265. * ° ^0RIQ 'N «.

Via a receiver-side low-pass filter 6, Zo- ¹ V "'-.-- ¹ - V of a cut-off frequency of 3 kHz, via switches S2, S2' that can be operated synchronously, one with an effective value voltage.

.-- knife provided measuring means 7 is supplied, permitting noise measurement "In the drawn position of S2 and S2 ¹ is the measuring device 7 upstream of a high-pass filter 8, for example having an intrinsic frequency of 700 Hz, daa together with the low-pass filter 6, 7 evaluable 'frequency band is limited to the range between the two limit frequencies, in the present case to a band from 700 Hz to 3 kHz, in the upper position of the switches S2 and S2' there is an adjustable voltage divider (attenuator) 9 instead of the high-pass filter 8 upstream. The level at the input of the PCM channel 4- is determined after switching S1 to the lower switch position by means of a further measuring device 10 containing an RMS voltmeter

-. displayed, -.- "" ■

The noise measurement on the PCM channel 4- goes in detail so that after dem.Einstell the input level of the measurement signal to a predetermined value with the help of the measuring device 10, the switches S2 and 32 'are initially brought into the position shown, so that a Noise voltage measurement with upstream filters 6 and 8 is carried out within the frequency band from 700 Hz to 3 kHz. Since the transmission side, predetermined frequency band, which is filled by the measurement signal is between 350 and 550 Hz, to the receiving end measures this V ^"r else a noise voltage, which arises due to Quaiitisierungs-, intermodulation and harmonic distortion, and that so far as it in the band from 700 Hz to 3 kHz falls “This also includes the thermal noise that occurs within the band on the receiving side.

Then switch S2 and S2 'are in the upper ΡΛ 9/430/3239 IOiaU / 1266. ■■ "

Switch position brought so that another voltage measurement within the entire Γΐϋς ^ .ϋΐ ^^ ΰα.ϋα υΐι joL'i: --- \ - of 3 kHz takes place »Here the voltage divider 9 is set so that the measuring device 7 of the the same measured value is displayed as for the first measurement mentioned. The attenuation value to be set in the voltage divider 9 for this purpose then provides a measure of the signal-to-noise absorption band.

Appropriately, a correction value is calibrated in the setting scale of the voltage divider 9, which takes into account, shows that the first measurement is only within one 2300 Hz wide frequency band was carried out, while when specifying noises one always uses the full channel band width, e.g. to 3100 Hz for telephone channels. This results in a correction value in the present case K = 10.1g 3100/2300 = 1.3 dB, which is to be subtracted from the set attenuation value. ■

The signal-to-noise ratio measured in this way primarily provides an indication of how large the quantization distortion is when passing through the PCM channel 4, »Since these are, however, of the size of the modulation of the channel it is advisable to carry out several measurements at different input levels. For systems The signal-to-noise ratio gives only relatively little or no quantization distortion at all an indication of the size of intermodulation and distortion and thermal noise.

The generator 1 designed according to the invention as a feedback shift register is shown in principle in FIG. For example, it consists of a chain of ten bistable flip-flops 11, 12 ... 20, each simultaneously by means of the clock pulse generated by a generator 21 e. 2-2 are continued »Here the

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Switching state of a toggle stage when it occurs-Ou-C- '' 'V. impulse is transferred to the next one. The switch off volumes of the last flip-flop 20 and another flip-flop, ZoB. 13, are connected via lines 23 and 24 to a logic circuit 25 is given, which is an output signal therefrom as a function of a predetermined logic function derives and this feeds back via a line 26 to the inputs 11 and 11 'of the first flip-flop, through Insertion of a negation circuit 27 ensures that the two inputs 11 and 11 'of the flip-flop; -] input signals which are complementary to each other »

In Pig. 2 the logic circuit 25 is an exclusive-OR circuit (Half adder) indicated. After that, the logical puncture would be such that a feedback signal "T" is issued when the outputs 13 and 20 'or the Outputs 13 'and 20 each - one: give logical 1 * to two gate circuits 28 and 29 are provided for this purpose, who work according to the so-called NAND puncture (i.e. passing on of a "1" signal when the "O" signal is present at both inputs and output of the signal "0" when signals "1" are present at both inputs and output of the Signal "1" when there are different input signals). These gate circuits are another gate circuit 30 downstream, which works according to the same puncture.

It should be noted, however, that the described logical puncture and the associated circuit structure are only to be adjusted as circuit examples and can be replaced at any time by other punctures or configurations of the logical circuit. In addition, feedback shift register arrangements are also known from the literature which emit signals with comparable statistical properties but do not contain a logic circuit made up of gates. ', ■;' ■ '-

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According to the theory of η-stage, feedback shift registers, which is described for example in the magazine "Electronic Engineering", April 1964, pp.25-3 to 259, a quasi-statistical sequence of 2 -1 binary characters (bits) is output, which is repeated periodically = 'T / ird If the repetition frequency of the clock pulses 22 is designated as f>, then a favorable feedback is obtained Repetition frequency f of the quasi-statistical sequence after the relationship

⁰ 2 ⁿ -1

Each input or output can be any of the bistable Flip-flops can be used as the output of the generator circuit. In Fig * 2, the output 20 was used for this »

The output signal of the feedback shift register, which consists of harmonics of the repetition frequency f, can be represented by a frequency spectrum according to FIG. Here, the power distribution is worn over the individual frequencies, wherein each of the normalized frequency f / f * is used as the abscissa "The de single hull 'of the power spectrum corresponding to the function runs. _n

sin π _ «^ - · _

1Γ ⁶ mZ -ι, ι

The prerequisite for the use of such a feedback shift register within the meaning of the invention = * is that Limitation of the frequency band of the measurement signal to a range that is small compared to the total area below f. It is also useful that f. Relative is large compared to f, which is indicated by the number of tilting "

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step "and, if necessary, by the type of feedback can be set so that numerous harmonics of f fall within the predetermined frequency band. Using of ten flip-flops, for example, f = iO24 ° f So ground the values of f .. and f accordingly ■ the specified frequency band defined by the pass-through curve of the band filter-2 is matched, one obtains an output signal which can be used for the measurement instead of a noise signal, as. special The advantage is the exact reproducibility of this k signal, which », in contrast, ignite purely statistical properties a noise voltage a sufficiently exact (repeatability of the noise measurement.

. In the circuit arrangement shown in FIG. 1 with a frequency band of 35.0 ' ^: to 550 Ez predetermined by the band filter 2, a clock frequency f of 10 kHz, for example, is expedient ο'. "" -. ■■. '■■' ■■■■ .- '. ■''.' ..

The condition,; that the clock frequency f. have a Y / ert should, which is much larger than the width of the vorgo -, .- ■ · Given. Frequency band, also applies to those applications in which the specified frequency band is divided into several sub-bands ^ which dismantles is ». This is particularly the case with the so-called Rausehklirrraessungen in frequency or time division multiplex transmission systems the case where the individual subbands generally have their own message channels to are transmitted separately to the checking system,

Since the repetition frequency f of the sequence of binary characters output by the shift register has the slowest amplitude fluctuation which corresponds to the envelope of the display systems 7. and 10 supplied measuring signals. "- learns: results in a more accurate and faster reading or - at Use of word-integrating means in connection with

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the actual display system - a faster location of the information and thus a shorter heating time. This allows the use of statistical noise symptoms time constants occurring with a measured value integration can be reduced significantly from 1 to 3 s,

4 claims
3 figures

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Claims (3)

Claims .] Method for noise measurement on a frequency or time-division multiplex message transmission system or individual parts thereof using a measurement signal simulating the message occupancy, filling a predetermined frequency band in the manner of a noise voltage and a selective measuring device which can be connected downstream of the system or system part to be measured and which measures the noise in at least measures a further frequency band lying outside the specified frequency band, characterized in that the measuring signal is generated by means of a feedback shift register (11 to 20, 25) which is switched on by periodic clock pulses (22) and whose clock frequency has a value, . which is much larger than the width of the given frequency band (2). 2. The method according to claim 1, d a d ure hg eke η η-ζ e i C h η e t that the given frequency band in several, especially close to one another, r. Subbands is divided and the noise measurement partially or takes place exclusively in the frequency gaps between the sub-bands. 3. The method according to claim 1 or 2, since you rchg ek en wz ei ch η et that the repetition frequency of the sequence of binary characters (bits) output by the shift register (11 to 20, 25) is selected to be much smaller than the repetition frequency of the clock pulses (22) .. ■ ■ '.> ; ΡΛ 9/430/3239 Λ -. ^{:: v} : \, 10981 Circuit arrangement "for implementation"".V ^: ^ ¹ :""^" according to a ;; i of claims 1 to 3, characterized in that the r.essurig des \! ignal-Geiiiusch-Abntandes the selective measuring device consists of an effective value voltmeter (7), which is preceded by a low-pass filter (6) and a series-connected high-pass filter (8) so that the frequency band to be evaluated (700 Hz to 3 kHz) is included by the limit frequency of both filters (6, 8), and that the high-pass filter (8) can optionally be replaced by an adjustable voltage divider (attenuator). ': ■' - ''. ■ ΡΛ 9/430/3239 10 9 8 1 4/1 26 p BATH Lee rs e i t e