arXiv subjects

Nima Taherkhani

Publications and source records attributed to Nima Taherkhani.

4 recordsLinked to original sources

arXiv2021

Performance Improvement of Dimmable OFDM-Visible Light Communication using Subcarrier Index Modulation and Reed Solomon Encoding

In this paper, we propose a new subcarrier index modulation scheme for orthogonal frequency division multiplexing (OFDM), which incorporates the Reed-Solomon (RS) encoding in a visible light communication (VLC) system. In this scheme, the incoming bits are first encoded using the RS encoder, then a set of symbols in the resulting RS codeword are punctured, and the remaining symbols are modulated and mapped onto the OFDM subcarriers. This system is referred to as RS-OFDM-IM. Unlike the traditional subcarrier index modulation (SIM) schemes, the proposed scheme operates based on conveying extra information by inactivating the selected subcarriers, which facilitates simultaneous clipping noise reduction and spectral efficiency enhancement in OFDM-VLC. The bit error rate (BER) and throughput of the proposed technique is theoretically and numerically analyzed. The simulation results show the superiority of the proposed technique as compared to the coded DCO-OFDM without SIM and the classical SIM in OFDM-VLC in a system with practical clipping conditions.

cs.IT↗

arXiv2019

Analysis and Comparison of the LDPC and Reed Solomon Encodings in Mitigating the Impact of Clipping Noise in OFDM-Based VLC

The linear error-correcting codes are known to be well suited for battling and correcting the burst errors caused by noise in the wireless data transmission system. However, different types of codes offer different decoding and burst-error-correcting capabilities. This paper compares the Low-Density-Parity Check (LDPC) and Reed Solomon (RS) encoding schemes in battling and correcting the burst error caused by the clipping distortion occurred due to the dynamic range constraints in an Orthogonal Frequency Division Multiplexing (OFDM) based Visible Light Communication (VLC). The unipolar conversion applied to the output of the multiplexer in this system results in a clipping noise which distorts the data symbols on the subcarriers in OFDM block. Considering that such distortion impacts the data symbol on each subcarrier differently, RS and LDP are used to encode the data block before being modulated for mapping the OFDM block. In order to control the extreme value of the output of the multiplexer, the transmitter applies puncturing to the generated codeword before mapping OFDM subcarriers, leaving the corresponding subcarriers of the punctured symbols empty. This will lead to the reduction of clipping events in the optical front-end and will mitigate the impact of nonlinear distortion on the modulated symbols for the occupied subcarriers. The redundancy in the codeword generated by the encoder is used not only to control the clipping probability by shortening the number of active subcarriers but also for the reconstruction of the original codeword and correction of the errors caused by channel noise. This work investigates the ability of LDCP and RS encoders in battling the effects of clipping noise in the frequency domain and compares their performances in improving the bit error ratio (BER) performance of an OFDM-based VLC.

eess.SP↗

arXiv2019

Sum Rate Capacity of MIMO HetNet Systems in the Presence of Channel Estimation Error

In this paper, the impact of channel estimation error (CEE) on the sum-rate capacity of multiple-input-multiple-output (MIMO) heterogeneous networks (HetNets) is investigated. It is assumed that the receiver is a linear minimum mean-square (LMMS) receiver. The architecture is based on the deployment of macro base stations with large antenna arrays and a secondary tier of small cell base stations having fewer number of antenna arrays. The key contribution of the paper is to highlight the noticeable impact of CEE on the sum-rate capacity of macro-cells. Furthermore, it is shown that CEE has only marginal impact on the sum-rate capacity of small cells. Simulations for the sum rate of macro users versus that of the small cell users for time-division duplex (TDD) are performed and the results are compared with the case when channel estimation error is present.

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arXiv2019

Statistical Modelling of the Clipping Noise in OFDM-based Visible Light Communication System

This paper analyses the statistics of the clipping noise in orthogonal frequency-division-multiplex (OFDM) based visible light Communication systems. The clipped signal is generally modelled as the summation of the scaled original signal and clipping noise, which is treated by the linear equalizer in the receiver. Generally, it is assumed that the clipped and original signal share the same statistics. Although valid in some cases, we show that such assumption is invalid when the transmitter is tightly constrained. We derive closed-form probability distribution function (pdf) for the clipping noise and use the pdf for statistical hypothesis testing in an optimum receiver

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