Modulation scheme boosts data throughput

Modulation scheme boosts data throughput

Technology News |
By Christoph Hammerschmidt

During the experiment which was part of the Safe and Secure European Routing project (SABER), the project partners achieved a net data rate of 1 terabit per second within a narrow frequency band. The bandwidth achieved is close to the theoretical maximum rate of the optical channel, defined by the Shannon Limit. The latter has been discovered by Bell Labs researcher Claude Shannon in 1948, one of the fathers of information theory.


During the field test, the project participants utilised a modulation scheme known as Probabilistic Constellation Shaping (PCS). It leverages the Quadrature Amplitude Modulation (QAM) technique to effectuate a higher transmission capacity across a defined channel and thus to significantly improve the spectral efficiency in optical communications.


PCS modifies the likelihood at which constellation points are used. Constellation points can be regarded as something like a transmission alphabet. Normally, all constellation points are driven at the same incidence. PCS, in contrast, utilises high-amplitude constellation points less often than average. To create a signal, the PCS approach makes greater use of low-amplitude constellation points. These points are less susceptible to noise and interferences. The bottom line: They makes it possible to optimize the transmission rate for the respective channel; at the same time, the range is increased up to 30%.


The research activities at hand are regarded as a significant milestone to find out of PCS can be used to increase future optical communications channels. The demand is high: Globally the data traffic is growing at a rate of up to 100%. PCS could contribute increase throughput and flexibility of optical networks without adding to the complexity.

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