Experimental Demonstration of Visible Light Communications with OFDM/OQAM Modulation
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Date
2019
Authors
Sawalmeh, Rasha
Damiri, Yasmin
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Abstract
An OFDM/Offset QAM (OQAM)-IOTA system uses the isotropic orthogonal transform algorithm (IOTA) function, which is employed instead of the guard interval used in a conventional OFDM/QAM system in order to be robust for multi-path channels. The drawbacks of the conventional OFDM system have been discussed in graduation project 1 report. That included also a study of the OFDM modulation over a multipath Rayleigh channel in order to see how it affects the bit error rate in the system. Then an enhancement of the bit error rate performance was done by using a multiple access method called Multicarrier Code Division Multiple Access (MCCDMA) under the same multipath channel. Finally, the report discussed the architecture of the VLC system and the modified OFDM/OQAM modulation technique which aimed to enhance the data rate of the system. In this report we will proceed with the channel estimation methods for both OFDM and FBMC systems.
The estimation of the channel is an important factor in the transmission of the data, for OFDM system; there are two feasible methods, until now, which are; blind channel estimation and pilot-aided channel estimation. In this report the pilot-based channel estimation is discussed, which includes three different pilot arrangements, namely block-type pilot arrangement, comb-type pilot arrangement and lattice-type pilot arrangement. The comb type pilot channel estimation is the one we will take into consideration; this type can be based on LS or MMSE estimators which will be discussed in details.
The simplicity of the channel estimation in OFDM is lost in FBMC/OQAM systems, because the real-valued pilots also are "polluted" by this imaginary-valued contribution of their neighbors, so a number of training schemes and associated channel estimation methods that take this under consideration have recently been studied. One of these approaches is the Interference Approximation Method (IAM); this method has a low computational complexity and promising robustness against ISI.
This report concentrates mainly on the channel estimation methods (LS, MMSE and IAM) used for OFDM/QAM and OFDM/OQAM in order to reduce the BER and enhance the performance. It also includes the usage of the VLC in indoor environment with OFDM/OQAM as a modulation technique of indoor VLC system.