5.1 The multiplex plan structure for dwdm dts

SDH interface for DWDM with using of two optical fibers (fig. 5.1)

1 2 … 622 1 2 … 622

Figure 5.1 – SHD interface for DWDM with using of two optical fibers

In this case one duplex optical channel (OCh) is assigned for SDH network.

Table 5.1 – The matrix of DWDM node-to-node load

NN	1	2	3	4	5	6	7	8
1	-	1						+1
2		-	1					+1
3			-	1				+1
4				-	1			+1
5					-	1		+1
6						-	1	+1
7							-	1+1
8								-

Transfer of Ethernet traffic in WDM ring is arranged according to a star topology (between SNN and each DNN). It should be allocated to 1 OCh for each connection SNN-DNN. General view of the multiplex plan is shown in fig.5.2, table 5.1. The maximal load on DWDM section is 5 OCh.

Choice of multiplexing equipment type

Selected type of DWDM system must provide the transfer of two types of traffic: SDH and Ethernet. Ethernet technology uses a linear code 8B10B (which increases the linear bitrate in1,25 times). We define the maximum transmission rate of the optical channel as a maximum of two given:

In WDM systems modulation of intensity is used, therefore, the signal

spectrum is similar to the case of AM modulation, containing spectral lobes. We

will focus on the need of four spectral lobes transfer ( width each) in the optical channel.Also note the presence of a transponder code FEC (forward error correction) encoder with the code RS (239,255), which leads to an increase of the modulated signal transmission rate by 7%.

Frequency band of oneoptical channel is:

Let us choose an interval between the carrier frequencies of adjacent channels from the standard row of the minimal one according to the so that (in this case according to table 5.2 choose =12,5 GHz).

Table 5.2 – WDM types

WDM type (ITU recommendation)	Interchannel interval , GHz	The n-th channel central frequency, THz
DWDM (G.694.1)	100	193,1 + n*0.1
	50	193,1 + n*0.05
	25	193,1 + n*0.025
	12.5	193,1 + n*0.0125

Optical fiber bandwidth is subdivided into series of ranges within the frequency windows, that is shown below.

Optical erbium doped fiber amplifier (EDFA) allows to amplify the signal within the O band (1260 nm...1360 nm). Therefore, carrier frequencies of optical channels (in THz) will be chosen within this specified band, where n –the optical channel’s quantity (n≥1).

Table 5.3 – Optical ranges of WDM systems

Bandwidth	Name	Range, nm
O	Original	1260…1360
E	Extended	1360…1460
S	Short wave length	1460…1530
C	Conventional	1530…1565
L	Long wave length	1565…1625
U	Ultra long wave length	1625…1675

Lets fill the 5.4 table with the carrier frequencies according to the calculated optical channel’s number in the maximum loaded section in the 5.1 subsection.

The results of calculations for this and other channels are shown in the table 5.4

Table 5.4 – Carrier frequency DWDM for =12,5 GHz.

n	1	2	3	4	5
, THz	193,1125	193,125	193,1375	193,15	193,1625

Let us adduce the system’s spectrum for the section with the maximal number of OCh (fig. 5.3)

5.3. The organization scheme of communication network using SDH and DWDM technologies.

OCh is chosen from the multiplex plan (OCh that passes through the highest number of transit nodes). Suppose there are two optical EDFA amplifiers in each node: preamplifier and booster. Optical channel between the 3^st and the 7^th nodes contains the highest number of transit nodes (fig. 5.4).

Figure 5.5 – Structure scheme of optical channel SNN-8-DNN-4

Let’s take optical signal’s power at the input of amplifier in DNN-1 as = -10 dBp ( =-0,1 mW) and optical signal’s power at the outputs of

amplifiers as = +8 dBp. There is optical signal and quantum noise

power at the input of amplifier:

where h – Plank’s constant (

v – central wavelength of optical emission

- bandwidth of optical filter of DWDM demultiplexer (

If there is no signal, on the optical amplifier’s input there is noise of amplified spontaneous emission (ASE) with power:

where - coefficient of spontaneous emission (

G – gain factor of EDFA.

where - the optical amplifiers in gain section ;

–quantity of optical amplifiers in considering section (

Now let us calculate ASE noise power:

There is ASE noise accumulation in the linear path with several amplifiers. The noise power at the output of the amplifier equals to:

Let us determine the total noise power at the outputs of each of 5 amplifiers from our example by using this expression:

;

;

;

;

.

The transmission quality of optical is determined by the optical signal/noise ratio at the input of photo receiving unit:

where and - signal and noise powers, which correspond to the optical section.

Let us perform calculations:

;

In order to determine the error probability for detected signal let is calculate Q-factor:

Where and - bandwidth of optical filter of DWDM demultiplexer and electrical filter of photoreceiving module (

Let us determine the BER value from Q-factor:

;

=

All calculations results fill into the table 5.5.

Table 5.5 – Quality parameters of the DNN1-SNN5 optical channel

Line trunk point of OTL WDM

Amplifier 1

Amplifier 2

Amplifier 3

Amplifier 4

Amplifier 5

input

output

input

output

input

output

input

output

input

output

, dBm

, dBm

G, dB

OSNR, dB

Q