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A versatile digital front-end architecture is designed and implemented on field-programmable gate array (FPGA) technology. The architecture includes the digital up-conversion, and peak-to-average power ratio (PAPR) reduction blocks that are applicable to down-link data paths in multi-band wireless base stations such as WCDMA or Wimax systems. Transmitter linearity requirements are addressed and tradeoff analysis for design and optimization of the PAPR reduction algorithm within the context of the error vector magnitude and adjacent channel leakage ratio quality metrics are studied. Statistical characteristics of the clipping noise are analyzed and a novel method for clipping the multi-band signal under the phase invariant constraint is proposed. Our study also includes mapping of the signal processing algorithms onto Xilinx Virtex-4[TM] FPGA device and addresses the resource utilization and efficient hardware implementation of the above signal processing blocks. Performance assessments and hardware validation of the proposed architecture are also addressed. Index Terms--Adjacent channel leakage ratio (ACLR), crest factor reduction, error vector magnitude (EVM), field-programmable gate array (FPGA), multi-band transmitters, peak-to-average power ratio (PAPR) reduction, reconfigurable transmitter.

In this paper, we present a new class of blind cyclic-based estimators for carrier frequency offset and symbol-timing error estimation of orthogonal frequency-division multiplexing (OFDM) systems. The proposed approach exploits the properties of the cyclic prefix subset to reveal the synchronization parameters in the likelihood function of the received vector. In this paper, a new likelihood function for the joint timing and frequency-offset estimation is derived, which globally characterizes the estimation problem. The resulting probabilistic measure is used to develop three classes of unbiased estimators, namely, maximum-likelihood, minimum variance unbiased, and moment estimator. In comparison to the previously proposed methods, the proposed estimators in this study are computationally and statistically efficient, which makes the estimators more attractive for real-time applications. Performance of estimators is assessed by simulation for an OFDM system. Index Terms--Frequency synchronization, likelihood metric, minimum variance unbiased estimation, multicarrier (MC) modulation, OFDM, timing recovery.

This paper presents a new iterative equalization algorithm that maximizes capacity for discrete multitone (DMT) systems. The research modifies a previously proposed criterion and applies an appropriate transformation to map the objective function and the constraint set into a canonical region. The resulting constraint set exhibits an identifiable geometric characteristic. Using the gradient projection method in conjunction with projection onto convex sets (POCS) provides us with an iterative search algorithm that facilitates the gradient descent method. We also generalize the approach to two important subclasses of equalizers, namely linear phase and unit tap filters. We also derive a fundamental limit on the performance of the proposed approach. In comparison with the previous methods, the proposed equalization algorithm is less computationally complex and more geometrically intuitive. Simulation experiments confirm the validity of the proposed method for equalization of DMT systems. Index Terms--Capacity maximization, convex optimization, discrete multitone systems, multicarrier systems, optimum equalization, projection onto convex set.