Increasing the information capacity of optical communications through embedded data modulation over pilot symbols

Summary of the technology

Method to perform modulation over pilot symbols in communications systems employing quadrature amplitude modulation (QAM). It allows to either increase the delivered bit-rate of the transmission system while keeping the same operating bandwidth and/or reduce the required signal-to-noise ratio (SNR) for error-free operation. It does not incur performance penalty or added computational complexity.

Instituto de Telecomunicações
Instituto de Telecomunicações


In modern coherent optical communication systems employing quadrature amplitude modulation (QAM), the use of pilot symbols is very common to aid on the estimation and compensation of carrier-phase noise. These pilot symbols are composed of QAM symbols with pre-defined amplitude and phase, which are knowna priori both by the transmitter and receiver. Pilot symbols are time-multiplexed with regular data symbols (payload), typically in a regularly distributed fashion.

In order to circumvent this loss of information rate imposed by the use of pre-defined pilot symbols, we propose the use of embedded data modulation, in which the amplitude (and possibly also the phase) of the pilot symbols can be modulated, while keeping their underlying properties. This allows to increase the information rate of the transmission system without incurring into additional complexity and/or performance penalty.


  • Optical fiber links
  • High-capacity (<100 Gbps) coherent transceivers
  • Any QAM-Based Transmission Systems Employing Pilot Symbols (RF, Wireless, Optical)


INCREASED TRANSMITTER INFORMATION RATEwhich can be utilized to improve the performance of the transmission systeminvarious ways:

  • DIRECT INCREASE OF BIT-RATEfor the same symbol-rate, modulation format, coding-rate and pilot-rate of the transmission rate
  • IMPROVEMENT OF REQUIRED SNRfor operation, while keeping the same net bit-rate


TRL 6 - The prototype system was tested in intended environment, with performance close to expected.


  • Licensing or assignment agreement
  • Testing new applications
  • Joint further developments


Instituto deTelecomunicações seeks manufacturers of telecommunications equipment, producing coherent optical transceivers.


Provisional patent application filed in Portugal (priority date: 24/05/2021)


F. P.Guiomar, B. M. Oliveira, M. S. Neves, M. A. Fernandes, and P. P. Monteiro, “Squeezing Out the Achievable Information Rate From Coherent QAM Systems Through Amplitude Modulation of CPE-Pilots”, inProc. OpticalFiber Conference (OFC), paper F4D.4, Fully-Virtual Event, March 2021.








Intellectual property status

Attached documents

Related Keywords

  • Electronics, IT and Telecomms
  • IT and Telematics Applications
  • Telecommunications, Networking
  • Broadband Technologies
  • Network Technology, Network Security
  • Signal Processing
  • Communications Protocols, Interoperability
  • Physical Sciences and Exact Sciences
  • Physics
  • Sustainability
  • Communications
  • Data Communications

About Instituto de Telecomunicações

Instituto de Telecomunicações (IT) is a private, not-for-profit organization, of public interest, a partnership of nine institutions with research and development in the field of Telecommunications

IT mission is to create and disseminate scientific knowledge in the field of telecommunications.

IT is actively involved in fundamental and applied research both at national and international levels. Simultaneously it is committed to foster higher education and training, by hosting and tutoring graduate and postgraduate students. it also plays its role towards public society with public awareness initiatives, knowledge transfer to industry, and by providing consulting services on a non-competing basis.

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