Iman Tavakkolnia

Signalling over nonlinear fibre-optic channels by utilizing both solitonic and radiative spectra

Using the inverse scattering method known for solving partial differential equations such as nonlinear Schrödinger equation, we analyse a fibre optic communication system which maps data on both discrete and continuous spectra defined by nonlinear Fourier transform. By signalling over both spectra, the degrees of freedom of the channel can be exploited to potentially increase the achievable data-rate in an attempt to approach the capacity of the optical fiber. Considering such a system, our results demonstrate the signal-dependency of the noise mapped to the nonlinear frequency domain. The temporal broadening factor is also studied for different pulse shapes and pulse sequence lengths modulated over the continuous spectrum. Finally, the error rate performance of the communication system signalling over both discrete and continuous spectra is presented.

Capacity Analysis of Signaling on the Continuous Spectrum of Nonlinear Optical Fibers

This paper investigates the capacity of signaling on the continuous spectrum (CS) of optical fibers as defined by the nonlinear Fourier transform (NFT). The channel model of such NFT-based optical fiber communication systems is studied based on the behavior of the propagated optical signal in the time domain for an asymptotically long fiber length. The derived channel model is validated using simulation for different scenarios of practical interest. An important characteristic of the channel in the nonlinear spectral domain is the strong dependence of noise to signal. A variance normalizing transform is applied as a tool to obtain an estimate on the capacity of the underlying channel. The results predict a remarkable capacity for signaling on CS, which can be utilized as an extra degree of freedom along with discrete spectrum (i.e., soliton transmission). It is further observed that the channel capacity of signaling on CS saturates at high signal power despite the linearizing capability of the NFT.

Signaling on the Continuous Spectrum of Nonlinear Optical Fiber

This paper studies different signaling techniques on the continuous spectrum (CS) of nonlinear optical fiber defined by nonlinear Fourier transform. Three different signaling techniques are proposed and analyzed based on the statistics of the noise added to CS after propagation along the nonlinear optical fiber. The proposed methods are compared in terms of error performance, distance reach, and complexity. Furthermore, the effect of chromatic dispersion on the data rate and noise in nonlinear spectral domain is investigated. It is demonstrated that, for a given sequence of CS symbols, an optimal bandwidth (or symbol rate) can be determined so that the temporal duration of the propagated signal at the end of the fiber is minimized. In effect, the required guard interval between the subsequently transmitted data packets in time is minimized and the effective data rate is significantly enhanced. Moreover, by selecting the proper signaling method and design criteria a distance reach of 7100 km is reported by only singling on CS at a rate of 9.6 Gbps.

Variance normalizing transform for performance improvement in radio-over-fiber systems

Radio-over-fiber (ROF) will be an indispensable part of future wireless communication networks to support backhaul connectivity. The performance of ROF communication system is impaired with signal-dependent distortions in the optical fiber link such as shot noise and relative intensity noise. In this paper, these signal-dependent distortions of the ROF channel are analyzed in more details and a variance normalizing technique is proposed to normalize the noise power. In effect, the signal-dependent noisy ROF channel is converted to a signal-independent additive white Gaussian noise channel for which the conventional signaling techniques are efficient. The results show significant performance improvements for the proposed technique in terms of signal-to-noise ratio.

Effect of PMD on the continuous spectrum of nonlinear optical fibre

Nonlinear Fourier transform (NFT) can be used as a tool to overcome nonlinearity in optical fibre communication systems [1-5]. Signalling on the continuous spectrum (CS), defined by NFT, can be performed as well as on solitons. The feasibility of this technique is demonstrated by simulation and experiment [2-5]. Amplified spontaneous emission (ASE) noise is considered as the main perturbation that limits the capacity of the CS channel [1-5]. However, it is important to include other optical fibre impairments such as polarization mode dispersion (PMD) as well. Coupled nonlinear Schrödinger equations (CNLSE) should be considered to model the effect of random birefringence on the propagation of light in the fibre. CNLSE can be simplified to scalar NLSE if the input optical field is initialized in a single polarization state and PMD is negligible [6]. However, PMD is usually not negligible in long-haul fibre links. Hence, in this paper, we investigate the effect of PMD, as a perturbation, on the continuous spectrum in systems designed based on NFT in single-polarization NLSE [1-5]. In NFT-based systems, data is mapped on the CS, and the time domain signal obtained from the inverse NFT is launched into one of the orthogonal polarizations of the fibre. Taking into account the CLNSE, almost half of the energy will be coupled into the other polarization at the end of the fibre. Therefore, some kind of PMD compensation is needed. Since CS represents the quasi-linear regime, it is expected that even a linear PMD compensation would be effective.

Efficient signalling on the continuous spectrum of nonlinear optical fibre

Due to the so-called capacity crunch, an increasing number of research have been focused on the subject of efficient signalling on nonlinear optical fibres and particularly methods based on nonlinear Fourier transform (NFT) [1-6]. This field of research includes the design of optical transmission using discrete spectrum, continuous spectrum (CS) [1], and combination of all degrees of freedom [2]. Recently in [4, 5], the capacity of the continuous spectrum is estimated and it is demonstrated that CS can be a suitable alternative for application in long-haul optical fibre links. A very important and unique property of the CS channel is the dependence of noise variance in nonlinear frequency domain on the signal amplitude [4, 5]. In this abstract, based on the statistical behaviour of noise in nonlinear frequency domain, we propose a simple but efficient method for signalling and performance improvement. Using this method, the channel is converted into an additive white Gaussian noise (AWGN) channel.

Secure and robust watermarking using arnold transform and Neyman-Pearson decoder

In this paper, we propose an adaptive multiplicative method to watermark binary data by scaling low frequency wavelet coefficients in the first level of decomposition. We decode message using hypothesis testing with optimum threshold value according to Neyman-Pearson test. We define a detection factor, k0, which is equivalent to Lagrange Multiplier and use PSO optimization algorithm to obtain optimum threshold value. To increase security, we impose Arnold transform with optimum iteration number both on the host image and logo before embedding data. The robustness of the method is analyzed against well-known Stir-Mark attack set and compared with similar methods. Experimental results confirm the imperceptibility of the proposed method and more robustness against attacks.

Multiuser orthogonal signal division multiplexing for doubly-selective fading channel in autonomous vehicular communications

Communication networks with highly mobile users are emerging rapidly. Autonomous vehicular communication is an interesting example of such systems. High mobility speed causes drastic change in channel states, and consequently a doubly selective fading scenario is a proper model for such channels. In this paper, by considering this proper model, we introduce a multiuser system based on orthogonal signal division multiplexing in a cognitive radio scenario. Carrier interferometry codes are also utilized in this system. By designing the transmitter and receiver, the performance of such system is investigated. We show that this system works properly when users are moving rapidly, and moreover the random delay of different users can be dealt with effectively.