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1993-06-26
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ANNEX 2
(to draft Recommendation G.136)
SOURCE: THE USSR TELECOMMUNICATION ADMINISTRATION
TITLE: INTERRELATION BETWEEN ERRORS IN A DIGITAL CIRCUIT AND IMPULSE NOISE IN
VOICE-FREQUENCY CHANNELS OF THE PCM SYSTEM
ÄÄÄÄÄÄÄÄÄÄ
1. Introduction
Voice-frequency channels of PCM as well as FDM systems should be fit for
transmitting various types of signals. It is well known that the transmission
quality of discrete signals in voice-frequency channels is affected by impulse
noise. At present, Recommendation G.712 has no requirements to voice- frequency
PCM-channels regarding impulse noise. However, under real-life conditions in a
v.-f. PCM channel impulse noise contributes to the error-rate of digital links.
The present contribution gives the investigation results of impulse noise in v.-
f. PCM-channels.
2. Influence of digital circuit errors on impulse noise in an idle v.-f. _
PCM-channel
Evaluation of error influence on digital links on the value of impulse
noise in v.-f. channels was conducted experimentally on a channel equipment
(satisfying Recommendation G.712) of a PCM transmission system (2048 kbit/s).
With the help of an error simulator, errors had been introduced into one or
several bits corresponding to a chosen idle v.-f. channel of a digital link
(Figure 1). In the v.-f. channel impulse noise could be observed with the help
of an oscillograph. The shape of the pulse response in the v.-f. channel is
presented in Figure 2.
The parameters of pulse response are given in Table 1 (the values are
chosen for the point of the relative zero level at a resistance of 600 ohm).
These data allow us to formulate the following conclusions:
- the pulse amplitude of the response depends on the bit number
which contains the error; the errors in the more significant
bits cause a greater amplitude of the response;
- with single errors the maximum value of the pulse peak A1 (in
case of an error in the second bit) is -22.1 dBmO;
- with burst-building and with an increase in the number of errored
bits in the code word of the prime digital path (2048 kbit/s) the
response amplitude values A1, A2, A3, ... grow, but their duration,
as determined by the response of the channel's low frequency
receiving filter, remains unchanged. This applies to the cases where
in a prime digital path, the error bursts affect the digital stream
for not more than one discretization period, i.e. the number of the
errors in a burst does not exceed 256. With errors in code words
occurring every 125 s the superposition of responses takes place as
a result of the receiving filter reaction on the error pulses in
each following
discretization period.
TABLE 1
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
Duration of
Amplitude of pulse response pulse response
Errored bits ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
in a frame of A1 A2 A3 t1 t2 t3
primary multiplex ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
dBmO dBmO dBmO s s s
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
2 -22.1 -28.2 -33.8 320 160 130
3 -34.1 -40.2 -45.8 320 160 130
2 and 3 -10.1 -16.2 -21.8 320 160 130
2 and 3 and 4 -4.1 -10.2 -15.8 320 160 130
from 2 to 8,
2 discretization
periods +4.3 -6.7 -14.8 440 180 100
from 2 to 8,
3 discretization
periods +4.3 -4.9 -14.8 600 200 100
from 2 to 8,
4 discretization
periods +4.3 -4.7 -14.8 680 180 120
from 2 to 8,
5 discretization
periods +4.3 -6.7 -14.8 840 200 120
from 2 to 8,
6 discretization
periods +3.8 -4.3 -14.8 930 200 100
from 2 to 8,
7 discretization
periods +5.25 -8.7 -14.8 1100 180 140
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
Thus, when errors on a 2048 kbit/s digital path grow into bursts of
2 errors and more there is a certain probability that the value of the impulse
noise in a PCM v.-f. channel exceeds -21 dBmO given in Recommendation M.1020,
2.6.
With error bursts of 256 and more bits, the above-mentioned impulse noise
will always be present.
The quantitative relationship between the number of bursts, the number of
errors in them within a definite time interval and the number of impulse noise
interferences and the BER in a v.-f. channel is under study at present.