'Institute of Electrical and Electronics Engineers (IEEE)'
Doi
Abstract
Multipath dispersion and fluorescent light
interference are two major problems in indoor
wireless infrared communications systems. Multipath
dispersion introduces intersymhol interference
at data rates above 10 Mb/s, while
fluorescent light induces severe narrowband
interference to baseband modulation schemes
commonly used such as OOK and PPM. This
article reviews the research into the application
of direct sequence spread spectrum techniques
to ameliorate these key channel impairments
without having to resort to complex signal processing
techniques. The inherent properties of a
spreading sequence are exploited in order to
combat the ISI and narrowband interference. In
addition, to reduce the impact of these impairments,
the DSSS modulation schemes have
strived to be bandwidth-efficient and simple to
implement. Three main DSSS waveform techniques
have been developed and investigated.
These are sequence inverse keying, complementary
sequence inverse keying, and M-ary biorthogonal
keying (MBOK). The operations of
the three systems are explained; their performances
were evaluated through simulations and
experiments for a number of system parameters,
including spreading sequence type and length.
By comparison with OOK, our results show that
SIK, CSIK, and MBOK are effective against
multipath dispersion and fluorescent light interference
becausc the penalties incurred on the
DSSS schemes are between 0-7 dB, while the
penalty on OOK in the same environment is
more than 17 dB. The DSSS solution for IR
wireless transmission demonstrates that a transmission
waveform can he designed to remove
the key channel impairments in a wireless IR
system