Arthur E. Fleek

Low Cost BPSK 2.4 GHz Radio For Wireless LAN

We describe a radio architecture for the IBM Wireless LAN Entry commercial product that achieves low cost and small size by using direct modulation of the master oscillator signal by a vector modulator at the transmitted frequency, and by using a single downconversion to a relatively low IF frequency in the receiver. The transmitter requires only filtering at its output to control harmonic radiation. Spectral control is accomplished by filtering the baseband data signal to the vector modulator ports. The amplified and limited IF signal from the single downconversion is processed digitally for carrier sense, frequency compensation and demodulation. We will describe how this is done with, predominantly, high resolution counting techniques. The receiver passband is determined with an IF filter consisting of lumped L and C elements. The modulation is a form of BPSK with unusual modifications to meet the FCC requirements for the ISM band and still meet the requirements of the simple digital demodulator. We will describe the limits on input signal to noise ratio of these techniques. The data rate is 0.5 Mb/sec. This simple architecture along with only one bandpass filter in the radio, makes for the simplest possible half duplex transceiver, and readily fits into a Type II PCMCIA package with extension for integral antenna, using only off-the-shelf standard (and relatively large) components.