20-07-2012, 11:36 AM
Orthogonal Frequency Division Multiplexing
Orthogonal Frequency.pdf (Size: 424.69 KB / Downloads: 91)
Applications of OFDM
Digital Television
! European and Australian standard
! Wireless Local Area Networks (LANs)
! Hiperlan 2
! ADSL (asymmetric digital subscriber loop)
! High speed data transmitted along existing
telephone lines
! Future mobile telephony?
Multicarrier systems
! Single carrier system
! signal representing each bit
uses all of the available
spectrum
! Multicarrier system
! available spectrum divided
into many narrow bands
! data is divided into parallel
data streams each
transmitted on a separate
band
Why is OFDM so popular for new broadband systems?
! Most broadband systems are subject to
multipath transmission
! Conventional solution to multipath is an
equalizer in the receiver
! high data rates - equalizers too complicated
! With OFDM there is a simple way of dealing
with multipath
! relatively simple DSP algorithms
What is Multipath?
! More than one
transmission path
between transmitter
and receiver
! Received signal is the
sum of many versions
of the transmitted
signal with varying
delay and attenuation
Spectrum of Received Signal
! Multipath fading causes
some frequencies to be
attenuated
! Fading is approximately
constant over narrow band
! This is corrected in the
receiver