CPL - Chalmers Publication Library
| Utbildning | Forskning | Styrkeområden | Om Chalmers | In English In English Ej inloggad.

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

Hongxia Zhao (Institutionen för signaler och system, Kommunikationssystem) ; Erik Agrell (Institutionen för signaler och system, Kommunikationssystem) ; Magnus Karlsson (Institutionen för mikroteknologi och nanovetenskap, Fotonik)
European Transactions on Telecommunications Vol. 19 (2008), 8, p. 895-906 .
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: unequal BER, coherent QPSK fiber optic



Denna post skapades 2007-04-25. Senast ändrad 2016-04-28.
CPL Pubid: 40892