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|Title: ||Peak to average power ratio reduction for OFDM system|
|Other Titles: ||Xiang di zheng jiao pin fen fu yong xi tong feng zhi ping jun gong lü bi|
|Authors: ||Wang, Chao (王超)|
|Department: ||Department of Electronic Engineering|
|Degree: ||Master of Philosophy|
|Issue Date: ||2008|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Orthogonal frequency division multiplexing.|
Wireless communication systems.
|Notes: ||CityU Call Number: TK5103.484 .W36 2008|
xiii, 138 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references.
|Abstract: ||Wireless communication systems at high data rates and low power consumptions are
currently in high demand. Power efficiency becomes a critical issue for technology that
will be used in 3G and 4G areas. Orthogonal frequency-division multiplexing (OFDM)
is a technique using discrete multi-tone modulation with each subcarrier modulating in a
conventional modulation scheme. OFDM offers many advantages for multi-carrier transmission
at high date rates, particularly in mobile applications. The primary advantage of
OFDM over single-carrier schemes is its ability to cope with severe channel conditions
without complex equalization filters. However, the high time domain peak-to-average
power ratio (PAR) that limits the transmitter power efficiency has been a major obstacle
in the implementation of power efficient transmitter. An OFDM system with high
PAR requires a power amplifier (PA) with large dynamic range, or alternatively, a perfect
linearized saturating PA must back off its maximum output power by approximately the
PAR of the input data for distortion-less transmission. While PA is non-linear, additional
back-off is necessary. Therefore, the PAR reduction is of viral importance for OFDM
systems with power efficient transmitter.
In this thesis, we present a new active constellation extension (ACE) based convex
optimization algorithm which reduces PAR through convex programming. Interior point
methods, also referred to as the barrier methods, are a class of algorithms to solve linear
and non-linear convex optimization problems. These algorithms, in contract to other
optimization methods, reach the optimal solution by traversing the interior of the feasible
region. They consist of self-concordant barrier functions used to encode the convex
sets. The ACE constrained IPM (ACE-IPM) shows that the OFDM signal with globally minimum PAR, subject to the constraint on the allowable constellation region, can
be efficiently computed using convex programming. Moreover, our method can be implemented
by discarding parts of the time-domain signal samples and frequency constellation
variables to reduce the complexity with only slight performance degradation.
Experimental results show that our proposed algorithm outperforms other ACE-based
algorithms with a symbol-error-rate (SER) performance comparable to existing convex
programming methods. We also give a convergence analysis of the ACE-IPM and the
simplified ACE-IPM as well as the suboptimality bound.
Furthermore, the ACE-IPM combined with other techniques are proposed. The first
one is non-linear mapping based ACE-IPM (NM-ACE-IPM). For OFDM with low order
QAM, the ACE-IPM is very effective. However, the PAR reduction capability of the
ACE-IPM will be limited for OFDM with higher order QAM. The NM-ACE-IPM maps
the constellation non-linear to provide more variables for PAR reduction. The second
one is to use data subcarriers combined with free subcarriers and out-of-band subcarriers
to reduce PAR, which gives a general frame work of PAR reduction. For data subcarrier,
they need to satisfy ACE constraint so as to guarantee the BER performance. While for
free and out-of-band subcarriers, they satisfy spectrum flatness requirement and power
spectrum mask constraint, respectively.
Finally, three PAR reduction methods, ACE-IPM, error vector magnitude (EVM)
constrained IPM (EVM-IPM), and repeated clipping and filtering (RCF) based PAR reduction
method (ACE-SGP) are compared and analyzed. Analysis shows that ACE-IPM
guarantees the minimum constellation distance, which explains why the ACE-IPM yields
better SER performance than the EVM-IPM. On the other hand, the ACE-SGP cannot achieve the optimal solution, so the PAR reduction performance is not satisfactory.
In conclusion, we propose a general frame work for OFDM which can achieve better
PAR reduction performance than some existing methods with comparable computational
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2339738|
|Appears in Collections:||EE - Master of Philosophy |
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