FQPSK-2 high speed modem for infrared wireless LAN

The design and evaluation of a modem prototype, based on FQPSK-2 modulation, is presented. Its main application is wireless infrared local area networks. The bit rate of this prototype is 2 Mb/s, but this magnitude can be taken up to 4.8 Mb/s just by substituting the quartz crystals on the oscillator and the A/D and D/A converters in the emitter low-pass filters of the receiver. The design is full-digital in order to allow its integration on a single chip. We have chosen FQPSK-2 modulation due to its high spectral efficiency (300% better than GMSK), robustness against jitter and the constant amplitude of its complex envelope. This permits the possibility of using non-linear amplifiers and reducing power consumption. This is the most important characteristic when the system is based on portable equipment, such as laptops. Finally, extensive experimental results are presented, and BER measurements of this prototype are also given.