2.3 The level diagram

There are internal and external LDs. LD – is the graph of signal’s level dependence during the propagation through the equipment units (internal) or through the transmission system elements (external). Let’s draw the external LD of TrS.

In order to determine the NRS number:

Let’s check the length of the l_sh:

l_sh = L – N_NRS · l_nom = 9.6 km

Let’s check the l_min < l_sh < l_nom condition:

l_min = 0.5 · l_nom = 0,5 · 13.6 = 6.8 km.

6.8 < 9.6 < 13.6 km – in this case we have one shortened section near the TS.

(if l_min > l_sh it’s necessary to recalculate l_sh by using the next formula: l_sh’ = (l_nom + l_sh)/2 . In this case we obtain 2 shortened sections near the both TS).

The shortened section has the different length from nominal section. In order to compensate it we use the artificial line unit. It’s necessary because of the same characteristics of NRS. In CA we’ll determine the l_al by the next formula: l_al = l_nom – l_sh.

p_{rec nom} = p_tr – α_t · l_nom

p_{rec sh} = p_tr – α_t · l_sh

p_rec1 p_rec2 p_rec3 p_{rec n} p_{rec TS}

NRS 1/1

NRS 1/2

NRS 1/3

NRS 1/14

A_sec

A_i

P_{rec nom}

l_sh

l_nom

l_nom

l_nom

P_{rec sh}

L

l_al = 4 km

P_n

Figure 2.5

2.4 The classification of TrS:

1. By the network section at which TrS is being operated: MLN, IAN, SSN, MAN, RAN.

2. By the used propagation media: wireline TrS and radio TrS.

3. By the type of signal’s transformation and the group signal transmission through the line path: analog (ATS) and digital (DTS) (the group signals are an. and d. respectively). ATS can transfer the digital information too (using the modem). DTS can transfer analog signal, but at first it will be transformed to a digital form (by means of pulse code modulation (PCM)).

4. By the way of channeling in receiver: SDC (spectral division ch.) in ATS, TDC (time division ch.) in DTS.

5. By the method of duplex communication organization.

   • by quantity of used frequency band (one-band and two-band);

   • by quantity of used wires (2-wire and 4-wire);

   • by quantity of used cables (1-cable and 2-cable).

The TrSs of primary network provide the bidirectional communication channels to the subscriber (transmission and receiving simultaneously).

2.5 The necessity of the group signal transmission

The economic suitability of TrS usage. Let’s compare two costs variants of communication between two subscribers without using of TrS (C1) and with TrS(C2).

– is for one subscriber,

C_{1km pl} – the cost of 1 km 2 wired physical line, L – the length of circuit.

– is for several subscribers.

C_TS – costs of TS.

– is for one subscriber,

N – is the number of subscribers.

If L = L₀, than C1 = C2. If L > L₀, than C1 > C2. So, it’s profitably to use TrSs when the long distance communication is organized.

The all modern MTS use the grouping idea, in which the result multichannel signal is formed by the sequential transformation of the standard channel groups.

The advantages of the grouping are:

1. Value of TS is lower due to the filters simplification and the lower number of filters number in ATS.

2. The standard frequency group’s bandwidth in ATS is chosen in order to decrease the nonlinear distortions.

There are next groups in MTS FDC:

Groups		VBC	F1 - F2, kHz	ΔF, kHz
The name	The notation
Pregroup	PrG	3	12-24	12
Primary	PG	12	60-108	48
Secondary	SG	60	312-552	240
Master	MG	300	812-2044	1232

3. It gives the possibility to unify the transformation equipment of TS and to decrease the equipment’s value and the maintenance charges.

Several MTSs work over the same transmission line in order to increase the economy.

Figure 2.6