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.
CONTEXT
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.

APPLICATIONS
- Optical fiber links
- High-capacity (<100 Gbps) coherent transceivers
- Any QAM-Based Transmission Systems Employing Pilot Symbols (RF, Wireless, Optical)
BENEFITS
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
DEVELOPMENT STAGE
TRL 6 - The prototype system was tested in intended environment, with performance close to expected.
COMMERCIAL OFFERING
- Licensing or assignment agreement
- Testing new applications
- Joint further developments
TARGET MARKET
Instituto deTelecomunicações seeks manufacturers of telecommunications equipment, producing coherent optical transceivers.
INTELLECTUAL PROPERTY
Provisional patent application filed in Portugal (priority date: 24/05/2021)
SCIENTIFIC PUBLICATIONS
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.
#OpticalNetworks
#DigitalSignalProcessing
#PilotSymbols
#QuadratureAndAmplitudeModulation
#QAM
TECHNOLOGY ID
PI-1026