In this paper an injection-locked optical orthogonal frequency-division multiplexing (ILO-OFDM) method is presented using an optically injection-locked laser. In an ILO-OFDM system, an optically injected semiconductor laser operating in stable locking is utilized to directly modulate the OFDM signal on the optical carrier intensity. To design this system, we first compute the optimal operating condition for the directly modulated injection-locked laser by numerically solving the rate equations. The goal is to achieve the maximum enhanced modulation bandwidth with desirable flatness and simultaneously reduce signal distortions due to the effects of laser nonlinearity. These properties of the injection-locked laser suggest an appealing solution for high-data-rate transmission using OFDM. Next, we design the ILO-OFDM system by directly modulating the RF OFDM signal on the injection-locked laser with the enhanced features. The performance of the proposed method is assessed by numerical simulations, and the advantages of this method over existing optical OFDM systems are explained.Ayaz Ghorbani received a PG diploma, M.Phil, and Ph.D. degrees in the area of electrical and communication engineering from the University of Bradford, UK, in 1984UK, in , 1985UK, in , and 1987. He received a postdoctorate degree from the University of Bradford, Bradford, UK, in 2004.

In this paper we present a modified model of solid state power amplifiers. Also using the mathematical concept of best approximation in Hilbert spaces, a predistorter structure is suggested to compensate both AM/AM and AM/PM conversion characteristics of a solid state power amplifier. To verify the effects of this linearization we generally consider it in a QAM signal transmission in an additive white Gaussian noise channel and the results are compared with the ideal linear case. It is shown that the presented method is able to compensate the nonlinearity up to a good extent. The performance of proposed method has been analyzed in frequency domain through spectrum simulations. To prove the validity of presented method we have made similar considerations on continuous spectrum.

A modeling approach to power amplifier design for implementation in OFDM radio units is presented. The power amplifier model assesses the impact of linear memory effects within the system using a Wiener representation, and employs a linear novel parametric estimation technique using Hilbert space. In addition, in order to model the nonlinear memory effects the previous topology is generalized by inserting the truncated Volterra filter before the static nonlinearity. Predistortion based on the Hammerstein model is introduced to deal with the nonlinear response. The new general algorithm is proposed to evaluate the Hammerstein model parameters for an OFDM system. A representative test bed was designed and implemented. The assessment of the new methods for PA and PD modeling are confirmed by experimental measurements. The measurement results reveal the preference of the new techniques over the existing approaches.

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