Constellation shaping is an energy efficiency enhancement method for digital signal modulation that improves upon amplitude and phase-shift keying (APSK) and conventional quadrature amplitude modulation (QAM) by modifying the continuous uniform distribution of the data symbols to match the channel.
[2] This technique gathered more interest in September 2016 when Nokia Bell Labs demonstrated working 1 Tbit/s data transmission channels between German cities.
[3] In October 2016, Alcatel-Lucent and Bell Labs claimed to have achieved 65 Tbit/s transmission over a 6,600 km (4,100 mile) single mode fiber in laboratory trials.
Other types of channels require that high-amplitude points are clipped altogether, due to e.g. problems with amplifier efficiency.
The benefits of geometric constellation shaping is that no distribution matcher is required, which simplifies the digital signal processing at the transmitter and receiver.