09-05-2012, 11:32 AM
Broadband MIMO-OFDM Wireless Communications
[attachment=21639]
INTRODUCTION
Orthogonal frequency division multiplexing (OFDM)
has become a popular technique for transmission of signals
over wireless channels. OFDM has been adopted in several
wireless standards such as digital audio broadcasting (DAB),
digital video broadcasting (DVB-T), the IEEE 802.11a [1]
local area network (LAN) standard and the IEEE 802.16a [2]
metropolitan area network (MAN) standard. OFDM is also
being pursued for dedicated short-range communications
(DSRC) for road side to vehicle communications and as
a potential candidate for fourth-generation (4G) mobile
wireless systems.
MIMO-OFDM SYSTEM MODEL
A multicarrier system can be efficiently implemented in
discrete time using an inverse FFT (IFFT) to act as a modulator
and an FFT to act as a demodulator. The transmitted data
are the “frequency” domain coefficients and the samples at
the output of the IFFT stage are “time” domain samples of the
transmitted waveform. Fig. 1 shows a typical MIMO-OFDM
implementation.
SYNCHRONIZATION IN THE ACQUISITION MODE
Time and frequency synchronization can be performed sequentially
in the following steps [28].
Step 1) Coarse Time Synchronization and Signal Detection—
Coarse time acquisition and signal detection
locates the start of an OFDM frame over an
approximate range of sample values. Due to the
presence of the CP (or suffix), coarse time acquisition
during the preamble can be performed
by correlating the received samples that are at a
distance of from each other over a lengthwindow
([25], [29]), viz.
MIMO-OFDM CHANNEL ESTIMATION
Channel state information is required in MIMO-OFDM
for space–time coding at the transmitter and signal detection
at receiver. Its accuracy directly affects the overall performance
of MIMO-OFDM systems. In this section, we present
several approaches for MIMO-OFDM channel estimation.
A. Basic Channel Estimation
Channel estimation for OFDM can exploit time and
frequency correlation of the channel parameters. A basic
channel estimator has been introduced in [31].
As discussed before, for a MIMO system with transmit
antennas, the signal from each receive antenna at the th subchannel
of the th OFDM block can be expressed as1
[attachment=21639]
INTRODUCTION
Orthogonal frequency division multiplexing (OFDM)
has become a popular technique for transmission of signals
over wireless channels. OFDM has been adopted in several
wireless standards such as digital audio broadcasting (DAB),
digital video broadcasting (DVB-T), the IEEE 802.11a [1]
local area network (LAN) standard and the IEEE 802.16a [2]
metropolitan area network (MAN) standard. OFDM is also
being pursued for dedicated short-range communications
(DSRC) for road side to vehicle communications and as
a potential candidate for fourth-generation (4G) mobile
wireless systems.
MIMO-OFDM SYSTEM MODEL
A multicarrier system can be efficiently implemented in
discrete time using an inverse FFT (IFFT) to act as a modulator
and an FFT to act as a demodulator. The transmitted data
are the “frequency” domain coefficients and the samples at
the output of the IFFT stage are “time” domain samples of the
transmitted waveform. Fig. 1 shows a typical MIMO-OFDM
implementation.
SYNCHRONIZATION IN THE ACQUISITION MODE
Time and frequency synchronization can be performed sequentially
in the following steps [28].
Step 1) Coarse Time Synchronization and Signal Detection—
Coarse time acquisition and signal detection
locates the start of an OFDM frame over an
approximate range of sample values. Due to the
presence of the CP (or suffix), coarse time acquisition
during the preamble can be performed
by correlating the received samples that are at a
distance of from each other over a lengthwindow
([25], [29]), viz.
MIMO-OFDM CHANNEL ESTIMATION
Channel state information is required in MIMO-OFDM
for space–time coding at the transmitter and signal detection
at receiver. Its accuracy directly affects the overall performance
of MIMO-OFDM systems. In this section, we present
several approaches for MIMO-OFDM channel estimation.
A. Basic Channel Estimation
Channel estimation for OFDM can exploit time and
frequency correlation of the channel parameters. A basic
channel estimator has been introduced in [31].
As discussed before, for a MIMO system with transmit
antennas, the signal from each receive antenna at the th subchannel
of the th OFDM block can be expressed as1