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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.
-
-
-
-