Design and implementation of low complexity OFDM modulator for broadband wireless devices
The modulation technique plays significant role as a component of communication systems. A novel technique known as orthogonal frequency division multiplexing (OFDM), which can be implemented in broadband wireless systems, has been designed and developed to fulfill the requirements of high data...
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/71099/1/FK%202017%2016%20-%20IR.pdf |
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| Summary: | The modulation technique plays significant role as a component of communication
systems. A novel technique known as orthogonal frequency division
multiplexing (OFDM), which can be implemented in broadband wireless
systems, has been designed and developed to fulfill the requirements of high
data rate signals. One of the major drawbacks of OFDM systems is its high
crest factor (CF) in the time domain. The large CF causes the transmit power
amplifier to enter the non-linear region, distorting the signal and resulting in a
significant increase in the bit error rate (BER) at the receiver.
This thesis focuses on the design and implementation of a proposed techniques
approach to reduce CF, and the computational complexity of the proposed
techniques will increase linearly with the increase of the number of subcarriers.
This research presents three novel low complexity techniques for reducing CF
in OFDM systems followed by an efficient hardware co-simulation implementation
of two of these techniques by using a Xilinx system generator on a field
programmable gate array (FPGA).
The first part of this thesis presents a new subblocks interleaving partial transmit
sequence (SBI-PTS) technique having low complexity for reducing the CF in
OFDM systems followed by an efficient hardware co-simulation implementation
of this technique by using a Xilinx system generator on a field programmable
gate array (FPGA). In this technique, a new subblocks interleaver is proposed.
The subblocks interleaver can be applied in the frequency domain before
the inverse fast Fourier transforms (IFFT) or in the time domain after (IFFT).
Moreover, a new optimization scheme is introduced, in which the number of
iterations is made to be equal to the number of subblocks only which results in reduced processing time and less computation that leads to reduced complexity.
A new low complexity high efficiency hybrid multiplicative-additive CF reduction
technique for OFDM systems is presented in the second part of the thesis.
This technique consists of two IFFT blocks. First, the output of the two IFFT
blocks is partitioned into four subblocks, which are subsequently used to rearrange
the subblocks with padding zeros in a specific manner. Then, a new optimization
scheme is introduced, in which only a single two-phase sequence and
four iterations needs to be applied. Numerical analysis shows that the hybrid
proposed technique achieves better CF reduction performance with significantly
lower complexity and better bit error rate performance than the existing scrambling
(multiplicative) and additive CF techniques. The other salient feature of
this scheme is that no side information (SI) is needed which increases transmission
efficiency.
The last part of this thesis presents a new low complexity scrambling technique
for reducing the CF in OFDM systems followed by an efficient hardware cosimulation
implementation of this technique by using a Xilinx system generator
on a FPGA. In this technique, the output of a single IFFT is duplicated M times
and partitioned into M subblocks, which are subsequently interleaved. Then,
a new optimization scheme is introduced in which only a single two phase
sequence need to be applied. Unlike the C-PTS which needs M- IFFT blocks and 2M-1 iterations, the proposed technique requires only a single IFFT block
and M iterations. These features significantly reduce processing time and less
computation that leads to reduced complexity. Simulation results demonstrate
that the new technique can effectively reduce the complexity up to 99:95%
compared with the conventional PTS (C-PTS) technique and yields good CF
performance. |
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