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Orthogonal frequency division multiplexing (OFDM) is used in many wired and wireless broadband communication systems because of its resilience in the presence of signal dispersion or multipath distortion. OFDM has not been used in practical optical communication systems because the bipolar waveform cannot be used in intensity-modulated direct detec...
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... key feature of OFDM is that data is transmitted in parallel on a number of sinusoidal subcarriers of different frequencies [13]. The frequencies are chosen so that the subcarriers are mutually orthogonal over each OFDM symbol period. Fig. 2 shows a typical OFDM modulator and demodulator. The input data is partitioned into blocks. The i - th block is mapped onto ...
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Citations
... which corresponds to the impulse response (29). If a direct LOS link with delay time t LOS is existent, the frequency response of (30) must be superposed with exp(−j2πf t LOS ). ...
... As a second example, we consider ACO-OFDM [29]. In this modulation scheme, only the odd-indexed OFDM sub-carriers k = 1, 3, ..., 2K − 1 are modulated for which the complex information symbols can be recovered from the clipped signal. ...
... is the electrical power gain factor for ACO-OFDM/M 2 -QAM, which is reduced by a factor of two compared to classical OFDM/M 2 -QAM as a result of clipping loss. It can be shown [16], [29] that the shaping gain factor for ACO-OFDM is approximately given by κ ≈ π. For a channel with frequency response C(f ), the electrical power for each sub-carrier number k is attenuated by a factor |C(f k )| 2 with f k = k/T , cf. (11). ...
Methods for calculating the impulse response of dispersive optical wireless channels have been known for a long time. However, a comprehensive procedure for predicting resulting bit error rates, starting from a highly accurate channel emulation method, has not yet been presented. To fill this gap, we propose a methodology for modeling realistic dispersive optical wireless channels that can be used directly for corresponding bit error rate simulations. The importance of proper power normalization of the multipath components is emphasized. Moreover, the optical channel model is embedded in an end-to-end electrical channel model suitable for intensity-modulation/ direct detection schemes under linear operation. Finally, to significantly reduce the simulation time, a so-called chip-rate model is presented. Finally, based on the proposed modeling approach for dispersive channels, bit error rate simulations are performed for selected intensity modulation schemes with and without equalization at the receiver and are compared within a common and consistent framework.
... Several m could be adopted for a fixed L and M L , which determine the total number of layers and utilized subcarriers, respectively. Normalized optical bit energy to noise power ratio E b(opt) /N 0 proposed in [28] is adopted when evaluating the BER performance of LGABO-OFDM, which is defined as ...
... The BER performance of various optical OFDM schemes is evaluated by utilizing E b(opt) /N 0 similarly to [28] and presented in Fig. 9. 256-QAM and 16-PAM are utilized in these O-OFDM schemes. To obtain the same spectral efficiency, we evaluate the BER performance of HPAM-DMT with G = 3, ALACO-OFDM with 3 layers, LACO-OFDM with 4 layers, GABO-OFDM with m = 16, and ...
Due to the high spectral efficiency and robustness against inter-symbol interference (ISI), orthogonal frequency division multiplexing (OFDM) is attracting increasing attention in sixth-generation (6G) optical wireless communication (OWC) systems. In this paper, based on generalized adaptively biased optical OFDM (GABO-OFDM), we propose a novel power and spectrally efficient scheme of layered GABO-OFDM (LGABO-OFDM). The subcarriers in LGABO-OFDM are divided into several layers and conveyed simultaneously. Each layer employs GABO-OFDM which adds an adaptive bias to generate nonnegative signals. The added bias is orthogonal to the occupied subcarriers in each layer, therefore the transmitted information can be recovered iteratively at the receiver side. Theoretical derivation demonstrates that LGABO-OFDM is more spectrally efficient than traditional asymmetrically clipped optical OFDM (ACO-OFDM) and hybrid ACO-OFDM (HACO-OFDM). In order to optimize the power efficiency and reduce bit error rate (BER), we novelly propose an optical power allocation method and the principle of subcarrier allocation of LGABO-OFDM after analyzing the statistical properties of the adaptive bias. Numerical results further suggest that the proposed LGABO-OFDM has lower BER and peak-to-average power ratio (PAPR) than its conventional counterparts, which demonstrates its high power efficiency and capability of resisting the nonlinear distortion.
... Previous works considering both approaches have focused on comparison of different OFDM schemes in terms of spectral efficiency, sometimes using OOK as a baseline, in the context of simulations or theoretical considerations [12], [13], [14]. As expected OOK generally achieves good results at low signal-to-noise ratio (SNR), but cannot compete in terms of spectral efficiency. ...
... Thus the continuous unipolar signal [20] is given as, ...
In modern homes, the home automation is more preferable to ensure safety and security. Lots of devices can be interconnected in home automation through wireless technologies. The overhead of data communication increases with increasing data transmission through local wireless network like wireless fidelity from the devices used in indoors. Spatial reprocess is not able to meet the current needs with accumulative traffic demand in existing communication technique. The paper focuses the need of visible light communication in future era in home automation system. The sustainable materials in light emitting diodes requires less power than normal forms of lightning. It consumes less energy and impacts positive effect in the environment. Also it has reduced emission effect and supports eco-friendly environment. The proposed work is the usage of Light Fidelity (Li-Fi) with unipolar OFDM (DC biased Optical OFDM (DCO-OFDM)) method to support data transmission with enhanced Signal to Noise Ratio (SNR), data rate and reduced Bit Error Rate (BER) in the home automation system.
... It is critical to analyze the performance of these O-OFDM schemes. In [12] and [13], the performance of Flip-OFDM and ACO-OFDM in additive white Gaussian noise (AWGN) channel were investigated, which demonstrate that Flip-OFDM and ACO-OFDM enjoy high power efficiency. Dimitrov et al. [14] studied the clipping noise and theoretical bit error rate (BER) performance of clipped ACO-OFDM and DCO-OFDM. ...
In optical wireless communications (OWC), hybrid optical orthogonal frequency division multiplexing (O-OFDM) schemes, such as hybrid asymmetrically clipped O-OFDM (HACO-OFDM) and layered asymmetrically clipped O-OFDM (LACO-OFDM), enjoy both high power and spectral efficiency. However, due to the non-orthogonal transmission of signal components induced by the clipping distortion, successive interference cancellation (SIC) is required in these hybrid O-OFDM schemes, leading to notably increased complexity. In this paper, we conceive novel hybrid O-OFDM schemes to offer both high spectral and power efficiency, whilst possessing low complexity. By elaborately designing a time-domain (TD) distortion elimination methodology at the transmitter, a novel distortion-elimination hybrid O-OFDM (DEHO-OFDM) is first proposed, which combines asymmetrically clipped O-OFDM (ACO-OFDM) and pulse-amplitude-modulated discrete multitone (PAM-DMT) in an interference-free manner. In order to further improve the spectral efficiency, an enhance DEHO-OFDM (EDEHO-OFDM) is designed by activating the remaining subcarrier resources. Both DEHO-OFDM and EDEHO-OFDM can be realized through a single-IFFT transmitter and standard OFDM receiver, leading to much lower complexity than the existing hybrid O-OFDM schemes. Simulation results have demonstrated the superiorities of the proposed schemes over HACO-OFDM and LACO-OFDM in terms of peak-to-average-power ratio (PAPR) and bit error rate (BER).
... For ACO-HCM, due to the power loss mentioned above, (27) has to be replaced by ...
... We found δ X (+) = δ for all parameters M and N under consideration. This means that the parameter γ in the error event probability of (26) is the same as for the original M -PAM and given by (27). Consequently, the error event probability and, thus, the asymptotic performance remains the same. ...
... 1) ACO-OFDM System Parameters: As a reference for performance comparison, we consider an ACO-OFDM/4-QAM system [7], [26], [27] with subcarrier positions that just fill this 3 dB bandwidth. For a time-discrete simulation, it must be ensured that sufficient number of samples lie within the time constant τ . ...
In many optical wireless communications systems, power efficiency is paramount. In others, flexibility is important. To achieve these goals, this paper presents a novel transmission scheme dubbed
asymmetrically clipped optical Hadamard coded modulation (ACO-HCM)
. ACO-HCM combines the characteristics of real-valued non-negative orthogonal frequency-division multiplexing (OFDM) and Hadamard coded modulation (HCM). Unlike OFDM, which is based on the Fourier transform and therefore delivers a continuous waveform, ACO-HCM provides a discrete set of amplitudes. This feature is desirable for nonlinear channels. Error probabilities are analytically calculated for a linear receiver similar to the decorrelation receiver in direct-sequence code-division multiple access (DS-CDMA). Maximum-likelihood sequence estimation is also investigated and shown to outperform the linear receiver, particularly in the presence of a time-dispersive channel. The peak-to-average power ratio of ACO-HCM is derived for the electrical as well as the optical domain in closed form.
... The signal must be unipolar, so the OFDM scheme uses DC-bias to make the signal positive. There are other types of ways to make the signal unipolar, but each scheme has positives and negatives, but there are major weaknesses that OFDM modulation suffers from as it suffers from narrow bandwidth due to cyclic prefix (CP) OFDM addition of leakage spectrum because of great side lobes [2], [6], [15], [17]- [19]. Recently, filter bank multi-carrier (FBMC) systems have gained a lot of popularity due to their high bandwidth, power efficiency, flexibility, and spectrum use. ...
... The negative peaks in the signal must be cut first, so a suitable DC bias is added to the X n signal to eliminate the negative peaks. This adds intermittent noise when the DC bias is high, and this noise decreases affecting the sub-carriers [17]. ...
... while Flip-OFDM and ACO-OFDM performance is not feasible for the specific purpose where large DR value and high illumination is required. The simulation and analytical results of BER shown in Fig. 12 show the superiority of ADO and DCO over ACO and FLip optical OFDM schemes compared to Armstrong et al. (2006). It can be seen from the said result that For a DR of -4 dB, the DCO and ADO have better BER performance compared to ACO and Flip OFDM. ...
... Comparing the results of PAPR among DCO, ACO, Flip and ADO-OFDM schemes, it revealed that DCO-OFDM and ADO-OFDM are more attractive for VLC in terms of DR which is the main limitation in OWC. The simulation and analytical results of BER shown in Fig. 12 also proof the superiority of ADO and DCO over ACO and FLip optical OFDM schemes compared to Armstrong et al. (2006). It is evident from the said result that For a DR of -4 dB, the DCO and ADO have better BER performance compared to ACO and Flip OFDM. ...
The trend of high data rates in indoor environments has increased the demand for visible light communication (VLC). This paper investigates the performance of PAPR with dynamic range (DR) of LED in the existing system models of optical OFDM for indoor communication environments based on complimentary cumulative distribution function (CCDF). Four commonly used existing unipolar OFDM schemes which are DC-biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), Flip-OFDM and asymmetrically clipped DC-Biased (ADO-OFDM) Optical OFDM. These schemes have been investigated and compared with the dynamic range of LED in terms of the illumination level requirements in indoor environments for PAPR with and without dynamic range. The PAPR for different system models in optical domain has never been analyzed and compared earlier with the dynamic range of LED. The simulation and analytical results of BER are also compared to show the superiority of ADO and DCO over ACO and FLip optical OFDM schemes. The results indicate the superiority of DCO-OFDM and ADO-OFDM as the best ones among the four schemes in terms of LED’s DR at different indoor illumination levels.
... The wavelength of visible light is much smaller than the typical area of a photodetector, which contributes to neglecting the multipath fading in VLC systems [25]. Therefore, we consider the additive white Gaussian noise (AWGN) in this study without loss of generality and the received signal can be expressed as [26] y = x + w (20) where w is the vector of noise with a variance of δ 2 T . Accordingly, the equivalent frequency-domain input-output relationship of the OFDM scheme is given by ...
... For DCO-IM and ACO-IM systems, only N F /2 − 1 and N F /4 subcarriers are available to transmit information symbols because of the Hermitian symmetry requirement and idle even subcarriers. By using (11) (25) and (26) equals to that of (27) and (28), respectively. On the other hand, the number of index bits of HDCO/HACO-IM is doubled in comparison to DCO/ACO-IM, so that the first term of (27) and (28) is twice that of (25) and (26), respectively, which eventually enhances the overall SE. ...
... By using (11) (25) and (26) equals to that of (27) and (28), respectively. On the other hand, the number of index bits of HDCO/HACO-IM is doubled in comparison to DCO/ACO-IM, so that the first term of (27) and (28) is twice that of (25) and (26), respectively, which eventually enhances the overall SE. ...
This paper investigates optical orthogonal frequency division multiplexing (O-OFDM) systems with index modulation (IM) based on discrete Hartley transform (DHT) for visible light communications (VLC). An interesting trade-off between spectral efficiency (SE), energy efficiency, peak-to-average power ratio (PAPR) and bit error rate (BER) performance can be made by using the IM technique. And the DHT-based O-OFDM-IM systems can achieve higher SE compared with the DFT (discrete Fourier transform)-based counterparts. Employing DHT instead of DFT enables the removal of the Hermitian symmetry requirement, which contributes to transmitting more index bits and results in SE improvement. To acquire the same SE, the proposed systems can significantly lower the constellation order leading to better BER performance by contrast with the DFT-based counterparts. We employ DC (direct current) biasing and AC (Asymmetrically clipped) techniques to investigate the O-OFDM-IM systems in this paper. Simulation results indicate that SNR gains can be obtained by the DHT-based DCO/ACO-IM in comparison to the DFT-based counterparts. We also propose a novel reduced-complexity ML (maximum likelihood) detector specifically applicable to VLC. The new detector exhibits the same BER performance as the ML detector and performs better than the LLR (log-likelihood ratio) detector with reduced computational complexity.
... Orthogonal frequency division multiplexing (OFDM) has been successfully ap-plied to intensity modulated/direct detection (IM/DD) systems. DC-bias optical OFDM (DCO-OFDM) [1][2][3] and asymmetrically clipped optical OFDM (ACO-OFDM) [1,2,4] are basic forms of optical OFDM (O-OFDM) techniques that generate real and unipolar signals required for (IM/DD) transmission mediums. DCO-OFDM has 100% spectral efficiency (SE) as it uses all its subcarriers to process its information. ...
... where , = is a complex QAM symbol for = 1,3 … , 2 − 1 and is the number of subcarriers. The Hermitian constrained input block to the IFFT block generates real time domain signal , has an anti-symmetric property [2,4].This signal is zero clipped to yield the unipolar conventional ACO-OFDM signal generated from odd subcarriers denoted as generated as ...
... where the clipping distortion | , | falls on the even subcarriers and does not affect the data , on the odd subcarriers [1,4]. The even stream of subcarriers are represented as This resultant signal when input to the IFFT block generates real time domain signal and has a symmetric property. ...
A novel spectrally efficient modified asymmetrically and symmetrically clipped optical (mASCO)-OFDM for intensity modulated direct detection (IM/DD) systems is presented. The conventional ASCO-OFDM systems uses two frame to transmit the conventional asymmetrically clipped optical (ACO)-OFDM and symmetrically clipped optical (SCO)-OFDM system. The proposed mASCO-OFDM system replaces the two frame SCO-OFDM by a single frame modified SCO (mSCO)-OFDM. The mSCO-OFDM clips the data only one side of the symmetry and performs an absolute function on the other side of the symmetry. This allows mASCO-OFDM to be 1.333 times more spectral efficient than the conventional ASCO-OFDM. The mASCO-OFDM reduces its receiver’s complexity by estimating and eliminating the clipping noise distortion in time domain. Overall, this system has 43% lower complexity in comparison to ASCO-OFDM system. The mASCO-OFDM shows a better BER performance and a lower Peak Average Power Ratio (PAPR) than ASCO-OFDM. The proposed system also shows better BER performance than ACO-OFDM for the same spectral efficiency.
