Techniques are described for maintaining the orthogonality of user waveforms
in multi-user wireless communication systems, such as systems using the code division
multiple access (CDMA) modulation scheme in the presence of frequency-selective
fading channels. Unlike conventional systems in which spreading is performed on
individual information-bearing symbols, the "chip-interleaved block-spreading"
(CIBS) techniques described herein spread blocks of symbols. A transmitter includes
a block-spreading unit to form a set of chips for each symbol of a block of information-bearing
symbols and to produce a stream of chips in which the chips from different sets
are interleaved. A pulse shaping unit within the transmitter generates a transmission
signal from the stream of interleaved chips and transmits the signal through a
communication channel. A receiver includes a block separator to de-interleave the
chips, followed by a match filter to separate signals from different users, and
followed by any single-user equalizer.
