Main strategies for WDM system capacity enhancement

  1. Optimize spectral utilization
  2. Expanding bandwidth
  3. Increase modulation

Let’s start with spectral utilization:

To optimize spectral utilization we can use flex grid technology.

Flex grid allow us to fix more channels in the same bandwidth, this is done by allowing fiber granularity of channels.

We can divide the bandwidth in to slices and assign based on customers demand.

Using flex grid instead of fixed grid can support increasing the throughput by 33%

Let’s go to the next point, to expand the bandwidth we can use C band plus L band.

Both of them are Good from attenuation coefficient point of view.

We can expand the bandwidth by using C + L.

Last point is the modulation.

As we know increasing the capacity can be done by using higher orders of modulation

Increase the order of modulation can increase the amount of bits per unit of time

By transferring Alot of bits over one symbol we can reach higher but rates

  • bits / second is the bit rate
  • symbols / second is the baud rate

We are using M ary modulation.

Note : increasing the modulation order will also lead to higher bit errors too because symbols become more closer.

In case of we decide to use higher modulation orders, we have to find out how can we tolerate the system OSNR.

In WDM systems we can use Qpsk, 16 QAM, 64 QAM.

Note : there’s a trade-off between transmission capacity and distance can be reached based on different modulation orders.

Distance decreased as modulation order increase.

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