Power Balance

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					6.3 Power Balance and Dispersion

This section is addressed to giving an explanation on how the number of amplifiers has
been chosen, and which fiber has been deployed at each link and why.

The maximum distance available for each link is determined by two main factors:
attenuation and dispersion.

6.3.1 Dispersion

It is important to keep in mind that dispersion is the most negative effect, because
compensating it is more expensive than deploying fiber with a better dispersion

To calculate the dispersion of our links, we are based on recommendation G.957. This
recommendation indicates the maximum value of dispersion for a link. The maximum
value varies depends on the STM used as shown in the table below:

Fig…..Dispersion values for STM cards

         Type of STM card                   STM 1       STM 4      STM 16
    Maximum dispersion (ps/nm)               1600        1600       1600

For the calculation of dispersion of a fiber we have used the following formula,
taking into accunt that the fiber that we has a Single-Mode behavior:

Where:             optical fiber bandwidth (nm)= 1 nm

                = dispersion coefficient (ps/nm*km)

         L = fiber length (km)
The value of       changes according to the fiber that we will use in each link. In our
case, we have chosen the followings types of Corning fabricant:

Fig… Dispersion values for chosen fiber

                                                              Maximum Dispersion
                      Type of fiber
                                                                 (pm/nm km )
Corning SMF-28e+ Optical Fiber G.652                                   18
Corning LEAFTM G.655-Compliant (NZDS) Fiber                            4,6
According with this we obtained the maximal distance allowed to transmit over the link,
without dispersion.

    Maximal distance (Corning SMF-28e+ Optical Fiber G.652) = 88 km

      Maximal distance (Corning LEAFTM G.655-Compliant (NZDS) Fiber) = 347 km

6.3.2 Technical characteristics of the equipment

All along a transmission link, characteristics of the equipment influence the power balance
of the link. In this part of the project we will analyze the attenuation introduced by the
equipment’s used in our network. Losses in signal quality are modeled by: optical fiber
losses, connectors, splices and losses due to multiplexers and de-multiplexers. The
general equation for obtaining the total link losses is:

Where:         is the attenuation factor through the distance [dB/km];

               L is the link distance in km

                  is the mean splice loss (dB)

               x is the total number of splices for any given link

                  is the mean loss due to the STM connectors, mux/de mux

               connectors, amplifiers connectors

               y is the total number of connectors

6.3.3 Fibers

Optical fiber typically consists of a transparent core surrounded by a transparent cladding
material with a lower index of refraction. Light is kept in the core by total internal reflection.
This causes the fiber to act as a waveguide. Fibers which support many propagation paths or
transverse modes are called multi-mode fibers (MMF), while those which can only support a
single mode are called single-mode fibers (SMF).

The single mode optical fibers have a diameter of the nucleus smaller than multimode
fibers, allowing a single way forward is (propagation mode and not oscillation mode) and
prevent the multimodal dispersion. Single mode fibers are also characterized by a lower
attenuation than multimode fiber, but the coupling of light becomes more complicated
and the tolerances of connectors and splices are stricter.
In contrast to the multimode fibers, single mode fibers allow to be up to great distances
and transmit higher bit rates, which are mainly limited by the chromatic dispersion and
non-linear effects. For all these reasons we have chosen to use single mode fibers in
onCAT network.

Fig… Type of Single Mode Fiber

                                             Maximum                           Att. Fusion
           Type of fiber                 Dispersion (pm/nm      No Channels    Fibers (dB/
                                                km )                              5km)
   Corning SMF-28e+
                                    0,2            18                16           0,02
   Optical Fiber G.652
   Corning LEAFTM G.655-
                                   0,25            4,6               80           0,02
   Compliant (NZDS) Fiber

System fiber-mux/de-mux in coupled by connectors. Each system fiber + mux/demux is
composed by 6 connectors.

Fig…Connectors loss

                               Att Connectors (dB)

Losses associated to the connecters are known as Insertion Losses and they are usually
lower than 1 dB. Those losses define the power loss when coupling the fiber ends or in
other words, the power loss due to coupling mismatch and small differences in reflection

6.3.4 Optical Amplifier
An optical amplifier is used in long fiber links to make useful the low power received signal.
This device decoder the received data, regenerates the digital pulses and overwrites the
regenerator section of the frame (RSOH). Finally, sends it again over the path to the next
Fig …Type of amplifier

      EDFA OA 4500             Total input signal power       -30 to 2 dBm
     Amplifiers Series         Total ouput signal power         21,5 dBm
                                      Signal Gain             19 to 32 dBm

Fig…Gain performance of EDFA OA 4500 Amplifiers Series


                                                           Maximum output
      32 dB                                                power = 21,5 dBm

      19 dB

        Sensitivity                     -10,5 dBm         Pr max         received
         -30 dBm                                          2 dBm

Fig…Power performance of EDFA OA 4500 Amplifiers Series

  21,5 dBm

     2 dBm
        Sensitivity                     -10,5 dBm         Pr max         received
         -30 dBm                                          2 dBm
Fig…. STM cards characteristics

      Type of STM card                STM 1            STM 4             STM 16
Transmited Power (dBm)                   -5               -3                -2
      Sensitivity (dBm)                 -34              -28               -27
Maximum dispersion (ps/nm)             1600             1600              1600
  Source linewidth (nm) (SM
                                         1                1                 1

We will work with STM 16 characteristics , because this card is more restrictive. We use
for transmitted power Tx= -2 dBm and for sensitivity Rx= -27 dBm.

Total Attenuation

We make the attenuation calculation using the following formula:

 In order to fix the maximal distance Lmax that allows us to transmit a signal without using
amplifiers we will use the following formula:

Considering the characteristics of optical multiplexers and demultiplexers presented in the
chapter number 6.2.1, we make the calculation of Lmax considering next cases:

         WDM technology                 Att Mux/Demux                L max
        CWDM 1 channels                  0 (No use mux)              120,59
        CWDM 2 channels                        4,6                    94,12
        CWDM 8 channels                        7,4                    80,4
        DWDM 8 channels                         8                     62,20
        DWDM 13 channels                        7                     66,14
        DWDM 40 channels                       12                     46,46

After we obtain the maximal distance Lmax that allows us to transmit the signal without
using amplifiers, we look to links that are bigger than Lmax. In order to have a proper
transmission, for this links we use amplifiers.
For links with one amplifier we calculate the new maximal distance, Lmax, at which the
amplifier can transmit the signal. There can be situations in which the amplifier is not able
to cover all the link distance, when transmitting the signal. For this case we will use the
same formula when we make the new Lmax calculation, but we will use the transmitted
power from datasheet of the amplifier and the sensibility from datasheet of the de-
multiplexer. For the value of new Lmax we obtain the links that needs 2 amplifiers.

When we calculate the Lmax for links that need more than one amplifier we have to
calculate also the maximal distance between 2 amplifiers. For this distance we use the
input power 2 dBm, representing the addition between the signal gain of the amplifier and
the sensibility of the amplifier.

For links that are using 2 Fibers SP-Ring Protection, we take in count also the traffic for
the protection. That means we have double number of STM cards representing protection
and working traffic.

For the value of new Lmax, representing the maximal distance at which we can transmit a
signal using an amplifier and adding the maximal distance at which the signal can be
transmitted without using an amplifier, we obtain the number of AO that we need in each
link. In our case we have links for which we don’t use amplifiers and links in which we
needs one or two amplifiers.

Fig…. Link with one amplifier

        ADM/DXC          Mux                            Demux               ADM/DXC

Fig … Lmax calculate for links with one or more amplifiers

                    No. Channels               Pt             Sensibility             Lmax
   Lmax from
                   DWDM 13 channels           -2              -30              93,31
   STM to AO
   Lmax from
                   DWDM 13 channels           2               -27              97,25
   AO to STM
   Lmax from
                   DWDM 13 channels           2               -30             109,06
    AO to AO
   Lmax from
                   DWDM 8 channels            -2              -30              91,34
   STM to AO
   Lmax from
                   DWDM 8 channels            2               -27              91,34
   AO to STM
   Lmax from
                   DWDM 8 channels            2               -30              99,21
    AO to AO

   Fig… Link with 2 amplifier

                                      AO           AO
         ADM/DXC     Mux                                    Demux       ADM/DXC

   Fig… Lmax calculated for links with one amplifier and 2 amplifiers

                            Real      No.                     Lmax    # AOs L max with 1 AO
            Link          Distance channels WDM technology without AO used      or 2 AO
    Igualada-Manresa        78,8      6     DWDM 8 channels    62,2     1       182,68
  Tarragones – Montsia       74       6     DWDM 8 channels    62,2     1       182,68
    Lerida - Tarragona      104       13    DWDM 13 channels  66,14     1       190,55
   Lerida - Tarragona 2     97,9      13    DWDM 13 channels  66,14     1       190,55
Lerida - Manresa- Gerona    223       13    DWDM 13 channels  66,14     2        299,6
 Lerida - Monjo- Gerona     254       13    DWDM 13 channels  66,14     2        299,6
  Tarragona - Barcelona     97,4      13    DWDM 13 channels  66,14     1       190,55
 Tarragona - Barcelona 2     87       13    DWDM 13 channels  66,14     1       190,55
Barcelona - Blanes-Gerona 119,9       13    DWDM 13 channels  66,14     1       190,55
   Barcelona - Gerona       102       13    DWDM 13 channels  66,14     1       190,55
In this section of the project we assure the proper signal transmission in all our network.

Using optical amplifiers we get sure that signal transmission over the fiber has the needed power
to travel all along the network.

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