Unequal bit error probabiltiy in coherent QPSK fiber-optic systems using phase modulator based transmitters
Journal article, 2008

We report on the occurrence of unequal bit error probability in a coherent quadrature phase shift keying (QPSK) fiber optic system. The bit error rates (BER) of two QPSK bits are derived individually based on the developed system model, and they turn out to differ by more than an order of magnitude for a phase modulator based transmitter. The phenomenon, previously unreported, arises because such a transmitter introduces a controlled form of inter-symbol-interference (ISI), and the receiver low-pass filters affect this ISI differently for the two bits. The optimum bandwidth of the receiver low-pass filter is obtained from the analytic derivation, which is about 0.7 times the symbol rate. We propose two simple system modifications, one in the transmitter and one in the receiver, to compensate for the phenomenon and equalize the two BER's. Those modifications improve the system performance by about 2~dB without adding any extra hardware.

coherent QPSK fiber optic

unequal BER

Author

Hongxia Zhao

Chalmers, Signals and Systems, Communication and Antenna Systems, Communication Systems

Erik Agrell

Chalmers, Signals and Systems, Communication and Antenna Systems, Communication Systems

Magnus Karlsson

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

European Transactions on Telecommunications

1124-318X (ISSN) 1541-8251 (eISSN)

Vol. 19 8 895-906

Subject Categories

Telecommunications

Signal Processing

DOI

10.1002/ett.1222

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Latest update

3/29/2018