Independent Vector Analysis (IVA) has emerged in recent years as an extension of Independent Component Analysis (ICA) into multiple sets of mixtures, where the source signals in each set are independent, but may depend on source signals in the other sets. In a semi-blind IVA (or ICA) framework, information regarding the probability distributions of the sources may be available, giving rise to Maximum Likelihood (ML) separation. In recent work we have shown that under the multivariate Gaussian model, with arbitrary temporal covariance matrices (stationary or non-stationary) of the source signals, ML separation requires the solution of a "Sequentially Drilled" Joint Congruence (SeD-JoCo) transformation of a set of matrices, which is reminiscent of (but different from) classical joint diagonalization. In this paper we extend our results to the IVA problem, showing how the ML solution for the Gaussian model (with arbitrary covariance and cross-covariance matrices) takes the form of an extended SeDJoCo problem. We formulate the extended problem, derive a condition for the existence of a solution, and propose two iterative solution algorithms. In addition, we derive the induced Cramér-Rao Lower Bound (iCRLB) on the resulting Interference-to-Source Ratios (ISR) matrices, and demonstrate by simulation how the ML separation obtained by solving the extended SeD-JoCo problem indeed attains the iCRLB (asymptotically), as opposed to other separation approaches, which cannot exploit prior knowledge regarding the sources distributions.
Discrete multitone transmission (DMT) is a useful approach to cope with the dispersive nature of VLC indoor channels. In such environments, the dispersion occurs either due to the LED in combination with its driver and or the multipath propagation channel. In this paper, we consider the impact of both types of dispersions on the bit error rate performance of a DMT based Li-Fi system. However, the main goal of this work is to compare the DMT scheme results with the transmission strategies employing frequency domain equalization. Here, we distinguish between pulse-amplitude modulation (PAM), partial-response coding, single-subcarrier (SSC) modulation, and "carrier-less amplitude and phase" (CAP) modulation. Keywords: visible light communication (VLC), Li-Fi, orthogonal frequency division multiplex (OFDM), discrete multitone transmission (DMT), block transmission, frequency domain equalization (FDE), wireless infrared (IR) transmission, polymer optical fiber (POF) communication, DC-balanced codes, partial-response coding INTRODUCTIONVisible light communication (VLC) uses the visible light portion of the electromagnetic spectrum to transmit data. It has become more and more attractive, since the LED lighting sources in homes, workplaces, factories or streets can additionally be used for wireless communication. Meanwhile, Li-Fi is an accepted term to describe this Wi-Fi analogy.In this work, we focus on the comparison of suitable transmission schemes for VLC based Li-Fi systems. Specifically, we consider only transmission schemes which ensure a DC-balance and thus a constant, data independent brightness, or schemes which can be easily combined with DC-balanced line codes. In order to take into account the bandwidth limitation caused by the LED in combination with its driver, we employ a Gaussian low-pass filter model at the transmitter. We do not claim that this model is generally valid, but the measurement results presented in [1] suggest rather a steep than a gradually roll-off beyond the upper cut-off frequency, which is said to be between 60 MHz and 180 MHz for a common high-power phosphorescent white-light LED with an optimized driver [1]. We also consider the effect of multipath propagation, if several spatially separated LEDs are used for illumination. Here we use simulated impulse responses, where high order diffuse reflections have been also taken into account.Discrete multitone transmission (DMT) is a promising approach to cope with the bandwidth limitation of the LED/LED-driver combo [2, 3]. Here we consider DC-biased DMT, since it inherently provides a DC-balance. DMT can be interpreted as a real valued variant of orthogonal frequency division multiplex (OFDM), where no quadrature up-conversion takes place after the inverse fast Fourier transform (IFFT) and digital-to-analog conversion at the transmitter. For VLC, it is impossible to modulate the field of a pair of sinusoidal high frequency (optical) carriers with a 90 • phase shift, since the LED-light source is strongly non-coherent. The optical field ap...
OFDM and its real valued version discrete multitone transmission (DMT) are popular schemes to compensate dispersion in direct detection optical systems. They employ an inverse fast Fourier transform (IFFT) at the transmitter and a fast Fourier transform (FFT) at the receiver, whereas the data symbols are processed block-wise. Block transmission combined with frequency domain equalization (FDE) has been recognized as a possible alternative to the DMT schemes, where the IFFT is moved from the transmitter to the receiver. This paper compares various bit loading enhanced DMT schemes such as asymmetrically clipped DMT and DC-biased DMT to PAM block transmission with FDE and to various single subcarrier FDE schemes. Moreover, a new approach termed asymmetrically clipped orthogonal PAM, is proposed in this work. Simulation results are presented for theoretical channels with a Gaussian low-pass profile. It will be shown that PAM-FDE performs best for this kind of channel, and n either bit loading enhanced DMT nor single subcarrier block transmission with FDE can offer a higher data rate at a given average optical power
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