30-01-2013, 04:32 PM
A Transmit Diversity Method for DVB-H and IEEE 802.20
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Abstract
We propose a transmitter diversity method to be
used in OFDM systems. The proposed method uses 2 transmit
antennas and 4 distinct subcarriers to obtain eighth order
transmit diversity gain. The proposed method utilizes both space
and frequency diversity. The simulation results show that the
proposed method can provide more gain than QOSTBC for DVBH
and IEEE 802.20.
INTRODUCTION
SPACE time block coding (STBC) [1], [2] can provide
diversity gain by using multiple transmit antennas. Unfortunately,
STBC can cause transmission rate loss when more
than 2 transmit antennas are used [2]. Quasi orthogonal spacetime
block coding (QOSTBC) is proposed in order to use more
than 2 transmit antennas without transmission rate loss [3]–[5].
However, QOSTBC cannot utilize linear maximum likelihood
detection (MLD) while STBC can [3], [4], [6].
Orthogonal frequency division multiplexing (OFDM) converts
a frequency selective fading channel into many parallel
flat fading channels. STBC or QOSTBC can be used in an
OFDM system to utilize space diversity gain [7]. On the other
hand OFDM has the potential to utilize frequency diversity [8],
[9].
In this letter we propose a method to obtain space and
frequency diversity simultaneously in an OFDM system. We
used parameters of DVB-H [10] and IEEE 802.20 [11], where
DVB-H has longer symbol durations and smaller subcarrier
spacing when compared with IEEE 802.20. Simulation results
show that the proposed method can provide more gain than
QOSTBC with the advantage of having less complex transmitter
hardware.
SYSTEM MODEL
We consider an OFDM system which has transmit
antennas, 1 receive antenna and subcarriers. We assumed
the channels between the transmit antennas have the same
power delay profile and taps.
CONCLUSION
We have proposed a method that utilizes both space and
frequency diversity and reduces the hardware complexity
caused by using multiple transmit antennas. The simulation
results show that the proposed method can provide more gain
than QOSTBC for DVB-H and IEEE 802.20. Furthermore, the
proposed method has the flexibility to be used for different
symbol durations and subcarrier spacing.