A NOVEL FEC SCHEME FOR DIFFERENTIALLY DETECTED QPSK SIGNALS IN MOBILECOMPUTING USING HIGH-SPEED WIRELESS ACCESS

This paper proposes a novel FEC(forward error correction)scheme for hi gh-speed wireless systems aiming at mobile computing applications. The proposed scheme combines inner nonredundant error correction with out er parallel encoding random FEC for differentially detected QPSK(quadr ature phase shift keying)signals. This paper, first, examines error pa tterns after the differential detection with nonredundant error correc tion and reveals that particular double symbol errors occur with relat ively high probability. To improve the outer FEC performance degradati on due to the double symbol errors, the proposed scheme uses I and Q c hannel serial to parallel conversion in the transmission side and para llel to serial conversion in the receiving side. As a result, it enabl es to use simple FEC for the outer parallel encoding random FEC withou t interleaving. Computer simulation results show the proposed scheme e mploying one bit correction BCH coding obtains a required E-b/N-o impr ovement of 1.2 dB at a Pe of 10(-5) compared to that with the same mem ory size interleaving in an AWGN environment. Moreover, in a Rician Fa ding environment where directional beam antennas are assumed to be use d to improve the degradation due to severe multipath signals, an overa ll E-b/N-o improvement at Pe of 10(-5) of 3.0 dB is achieved compared to simple differential detection when the condition of delay spread of 5 nsec, carrier to multipath signal power ratio of 20 dB and Doppler Frequency at 20 GHz band of 150 Hz.