We analyze the performance of a wideband orthogonal frequency division multiplexing (OFDM) signal in estimating the micro-Doppler frequency of a rotating target having multiple scattering centers. The use of a frequency-diverse OFDM signal enables us to independently analyze the micro-Doppler characteristics with respect to a set of orthogonal subcarrier frequencies. We characterize the accuracy of micro-Doppler frequency estimation by computing the Cramer-Rao bound (CRB) on the angular-velocity estimate of the target. Additionally, to improve the accuracy of the estimation procedure, we formulate and solve an optimization problem by minimizing the CRB on the angular-velocity estimate with respect to the OFDM spectral coefficients. We present several numerical examples to demonstrate the CRB variations with respect to the signal-to-noise ratios, number of temporal samples, and number of OFDM subcarriers. The improvement in estimation accuracy due to the adaptive waveform design is also analyzed numerically. A grid-based maximum likelihood estimation technique is applied to evaluate the corresponding mean-squared error performance.

Adaptive OFDM Radar Waveform Design for Improved Micro-Doppler Estimation

We propose a multi-objective optimization (MOO) technique to design an orthogonal frequency division multiplexing (OFDM) radar signal for detecting a moving target in the presence of multipath reflections We employ an OFDM signal to increase the frequency diversity of the system Moreover, the multipath propagation increase the spatial diversity by providing extra “looks” at the target First, we develop a parametric measurement model by reformulating the target detection problem as a sparse estimation method At a particular range cell, we exploit the sparsity of multiple paths and the knowledge of the environment to estimate along which path the target responses are received Then, we formulate a constrained MOO algorithm, to optimally design the spectral parameters of the OFDM waveform, by simultaneously optimizing two objective functions: minimizing the upper bound on the estimation error to improve the efficiency of sparse-recovery and maximizing the squared Mahalanobis-distance to increase the performance of the underlying detection problem We present numerical examples to demonstrate the performance improvement due to adaptive waveform design

Multi-objective optimized OFDM radar waveform for target detection in multipath scenarios

In this paper the authors discuss the feasibility of a constant envelope optical OFDM based on fast Hartley transform. The digital signal processing output drives an optical phase modulator for obtaining a 0 dB PAPR signal at the transmission side, whereas the use of a Hartley transform increases power efficiency and relaxes the level of the constellation used. Additionally, a set of simulations of the system are presented, showing a back-to-back sensitivity of −34.6 dBm for a 10−3 BER.

Constant envelope coherent optical OFDM based on fast Hartley transform

Two key technology enablers for next generation networks are examined in this thesis, namely Cognitive Radio (CR) and Spectrally Efficient Frequency Division Multiplexing (SEFDM). The first part proposes the use of traffic prediction in CR systems to improve the Quality of Service (QoS) for CR users. A framework is presented which allows CR users to capture a frequency slot in an idle licensed channel occupied by primary users. This is achieved by using CR to sense and select target spectrum bands combined with traffic prediction to determine the optimum channel-sensing order. The latter part of this thesis considers the design, practical implementation and performance evaluation of SEFDM. The key challenge that arises in SEFDM is the self-created interference which complicates the design of receiver architectures. Previous work has focused on the development of sophisticated detection algorithms, however, these suffer from an impractical computational complexity. Consequently, the aim of this work is two-fold; first, to reduce the complexity of existing algorithms to make them better-suited for application in the real world; second, to develop hardware prototypes to assess the feasibility of employing SEFDM in practical systems. The impact of oversampling and fixed-point effects on the performance of SEFDM is initially determined, followed by the design and implementation of linear detection techniques using Field Programmable Gate Arrays (FPGAs). The performance of these FPGA based linear receivers is evaluated in terms of throughput, resource utilisation and Bit Error Rate (BER). Finally, variants of the Sphere Decoding (SD) algorithm are investigated to ameliorate the error performance of SEFDM systems with targeted reduction in complexity. The Fixed SD (FSD) algorithm is implemented on a Digital Signal Processor (DSP) to measure its computational complexity. Modified sorting and decomposition strategies are then applied to this FSD algorithm offering trade-offs between execution speed and BER.

Spectrum optimisation in wireless communication systems : technology evaluation, system design and practical implementation

We propose a multi-objective optimization (MOO) technique to design an orthogonal frequency division multiplexing (OFDM) radar signal for detecting a moving target in the presence of multipath reflections. We employ an OFDM signal to increase the frequency diversity of the system, as different scattering centers of a target resonate variably at different frequencies. Moreover, the multipath propagation increases the spatial diversity by providing extra “looks” at the target. First, we develop a parametric OFDM measurement model for a particular range cell under test, and convert it to an equivalent sparse-model by considering the target returns over all the possible signal paths and target velocities. Then, we propose a constrained MOO problem to design the spectral-parameters of the transmitting OFDM waveform by simultaneously optimizing three objective functions: maximizing the Mahalanobis distance to improve the detection performance, minimizing the weighted trace of the Cramer–Rao bound matrix for the unknown parameters to increase the estimation accuracy, and minimizing the upper bound on the sparse-recovery error to improve the performance of the equivalent sparse-estimation approach.

https://www.ese.wustl.edu/~nehorai/paper/Satyasen_Tang_MultiObjective_Chapter3.pdf

Designing OFDM Radar Waveform for Target Detection Using Multi-objective Optimization

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation scheme that provides efficient bandwidth utilization and robustness against time dispersive channels This paper deals with the basic system model for OFDM based systems and with self-interference, or the corruption of desired signal by itself in OFDM systems A simple transceiver based on OFDM modulation is presented Important impairments in OFDM systems are mathematically analyzed

Sharma Kanchan

Papers

Orthogonal Frequency Division Multiplexing: An Overview