1,652 research outputs found
A low complexity SI sequence estimator for pilot-aided SLM–OFDM systems
Selected mapping (SLM) is a well-known method for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. However, as a consequence of implementing SLM, OFDM receivers often require estimation of some side information (SI) in order to achieve successful data recovery. Existing SI estimation schemes have very high computational complexities that put additional constraints on limited resources and increase system complexity. To address this problem, an alternative SLM approach that facilitates estimation of SI in the form of phase detection is presented. Simulations show that this modified SLM approach produces similar PAPR reduction performance when compared to conventional SLM. With no amplifier distortion and in the presence of non-linear power amplifier distortion, the proposed SI estimation approach achieves similar data recovery performance as both standard SLM–OFDM (with perfect SI estimation) and also when SI estimation is implemented through the use of an existing frequency-domain correlation (FDC) decision metric. In addition, the proposed method significantly reduces computational complexity compared with the FDC scheme and an ML estimation scheme
Fifty Years of Noise Modeling and Mitigation in Power-Line Communications.
Building on the ubiquity of electric power infrastructure, power line communications (PLC) has been successfully used in diverse application scenarios, including the smart grid and in-home broadband communications systems as well as industrial and home automation. However, the power line channel exhibits deleterious properties, one of which is its hostile noise environment. This article aims for providing a review of noise modeling and mitigation techniques in PLC. Specifically, a comprehensive review of representative noise models developed over the past fifty years is presented, including both the empirical models based on measurement campaigns and simplified mathematical models. Following this, we provide an extensive survey of the suite of noise mitigation schemes, categorizing them into mitigation at the transmitter as well as parametric and non-parametric techniques employed at the receiver. Furthermore, since the accuracy of channel estimation in PLC is affected by noise, we review the literature of joint noise mitigation and channel estimation solutions. Finally, a number of directions are outlined for future research on both noise modeling and mitigation in PLC
SYNCHRONIZATION AND RESOURCE ALLOCATION IN DOWNLINK OFDM SYSTEMS
The next generation (4G) wireless systems are expected to provide
universal personal and multimedia communications with seamless connection
and very high rate transmissions and without regard to the users’ mobility and
location. OFDM technique is recognized as one of the leading candidates to
provide the wireless signalling for 4G systems. The major challenges in
downlink multiuser OFDM based 4G systems include the wireless channel, the
synchronization and radio resource management. Thus algorithms are required
to achieve accurate timing and frequency offset estimation and the efficient
utilization of radio resources such as subcarrier, bit and power allocation.
The objectives of the thesis are of two fields. Firstly, we presented the
frequency offset estimation algorithms for OFDM systems. Building our work
upon the classic single user OFDM architecture, we proposed two FFT-based
frequency offset estimation algorithms with low computational complexity.
The computer simulation results and comparisons show that the proposed
algorithms provide smaller error variance than previous well-known algorithm.
Secondly, we presented the resource allocation algorithms for OFDM
systems. Building our work upon the downlink multiuser OFDM architecture,
we aimed to minimize the total transmit power by exploiting the system
diversity through the management of subcarrier allocation, adaptive
modulation and power allocation. Particularly, we focused on the dynamic
resource allocation algorithms for multiuser OFDM system and multiuser
MIMO-OFDM system. For the multiuser OFDM system, we proposed a lowiv
complexity channel gain difference based subcarrier allocation algorithm. For
the multiuser MIMO-OFDM system, we proposed a unit-power based
subcarrier allocation algorithm. These proposed algorithms are all combined
with the optimal bit allocation algorithm to achieve the minimal total transmit
power. The numerical results and comparisons with various conventional nonadaptive
and adaptive algorithmic approaches are provided to show that the
proposed resource allocation algorithms improve the system efficiencies and
performance given that the Quality of Service (QoS) for each user is
guaranteed.
The simulation work of this project is based on hand written codes in the
platform of the MATLAB R2007b
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