Evaluation of DSL potential characteristics at parallel work on high-capacity telephone cables.

One of the main factors which limit the speed and distance of transmission in subscriber lines are transitive noises, appeared at parallel work of DSL in multipair telephone cables. The algorithm of calculation transitive influences between DSL are shown on figure 2.1 where shown two influencing DSL (DSL_i and DSL_j) and one influenced DSL (DSL_k). Power of incoming signal at the input of i-th SL is P_{i trans} . On the input of DSL_k receiver comes attenuated useful signal with power P_{k rec} and transitive noises (from near P_{near i,k} , P_{near j,k} and far P_{far , i,k} и P_far,j,k ends) caused by transmitting signals DSL_i и DSL_j .

Signal – noise ratio at the input of receiving device DSL is:

,

where

PSD – dependence of signal on frequency at the output of transmitter of k -th DSL;

H – amplitude-frequency characteristic of SL (communication channel);

– sum of other noises, acting on the input of receiving device DSL_k .

		j		Pj tran
			DSLj

Figure 2.1 − Model of electromagnetic interaction between DSL in multipair cable

Values P_{nea i,k} и P_{far i,k} can be defined by analogy accordingly to formulas, where H ²(f) is substituted frequency functions of transitive characteristics between i -th and и k- th SL on near and far end H_{near i,k} (f) и H _{far i,k} (f) accordingly:

In accordance to model of electromagnetic compatibility it is possible to calculate acceptable lengths of SL and their transmission rates into upstream and downstream directions along DSL at different variants of xDSL equipment, loading, level of noise, number of pairs, diameter of core, using of homogeneous and non-homogeneous cables.

In the Figure 2.2, 2.3 are shown examples of calculations (with the help of program «xDSL-Liner») the maximum length ADSL2+ line at the using 10-pair ТП cables with bunchy twisting of core where diameters of wire are 0,32 mm; 0,4 mm; 0,5 mm and 0,64 mm for different types of white noise at the input of receiver. It also depends on percent of cable pairs using for transmitting of ADSL2+.

а) White noise equals minus 140 dBm/Hz

b) White noise equals minus 120 dBm/Hz

c) White noise equals minus 100 dBm/Hz

Figure 2.2 - Accessible length of ADSL2+ line for rate 19648 kbps for upstream and 928 kbps for downstream, direction at using of 10-pair TП cable and white noise 140, 120, 100 dBm/Hz which depend on percent of loading by cable at ADSL2+

а) White noise equals minus 140 dBm/Hz

b) White noise equals minus 120 dBm/Hz

c) White noise equals minus 100 dBm/Hz

Figure 2.3 - Accessible length of ADSL2+ line for rate 19648 kbps for upstream and 928 kbps for downstream, direction at using of 10-pair TП cable and white noise 140, 120, 100 dBm/Hz which depend on percent of loading by cable at ADSL2+

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