scheme to overcome multi-path interference.
At the transmitter, raw data is encoded by a rate-½
convolutional encoder, and then interleaved. The
interleaving process is performed to decorrelate errors in
the radio channel, making the channel appear Gaussian.
The interleaved data is then packed into frames of blockdifferentially-
modulated quadrature phase-shift-keyed
(DQPSK) symbols suitable for generating a multi-tone
signal. These frames are passed to a 16-point Inverse Fast
Fourier Transform (IFFT) processor, where the DQPSK
symbols in the frame set the phase of 16 individual tones.
The output of the IFFT is a complex time domain signal
consisting of the sum of these 16 tones – a multi-tone
signal. This signal is passed to a radio-frequency (RF)
transmitter, where it is mixed up to RF frequencies (5
GHz in our system) and transmitted.
At the receiver the RF radio signal is down-converted to a
pair of signal components (in-phase and quadraturephase)
at baseband (30 MHz). These recovered signal
components are used by the demodulator to reconstruct