Joint Estimation Of Carrier Frequency Research Articles

Joint estimation of carrier frequency and two-dimensional arrival angle based on L-shaped delay array modulation wideband converter

As the signal spectrum in modern information technology becomes wider and wider, multi-band signals are distributed in a frequency range of tens of GHz. It covers a very wide spectrum but each RF signal has a very narrow band, and the distribution location of the band (or carrier frequency) is completely unknown. For the receiver, the single-band signals transmitted together constitute a multi-band signal. The sampling rate required to jointly estimate the space domain and frequency domain parameters of these signals is getting higher and higher. Modulated wideband converter system is an analog information conversion system for multiband analog signals, which is based on compressed sensing theory and greatly reduces the sampling rate. First, we propose an L-shaped delay array structure based on modulated wideband converter, which can estimate carrier frequency and two-dimensional arrival angles with a small number of samples. Secondly, two parameter-estimating algorithms are proposed based on the proposed structure. One is based on the estimating of signal parameter via rotational invariance technique (ESPRIT), which requires a small number of computations and is suitable for real-time processing application scenarios; the other algorithm is based on CANDECOMP/PARAFAC (CP) technique, which has better robustness and is suitable for applications with low signal-to-noise ratio. The samples of the delay channels can be directly used to estimate the carrier frequencies, and then the two-dimensional arrival angles are calculated. No additional pairing issue is required between the parameters. Then we give the time complexity analysis and space complexity analysis of the two methods. It can be found that the computational complexity and space storage occupation of the method based on ESPRIT are lower than those of the CP decomposition method. Then the conditions for unique parameter estimation are given. Finally, simulation experiments show that the proposed methods can estimate the carrier frequencies and two-dimensional arrival angles from sub-Nyquist samples. It can be found that the estimation method based on CP decomposition is more robust than the method based on ESPRIT, but at the cost of increased complexity of the algorithm.

Sequential Estimation of Frequency and Direction-of-Arrival Based on the Relaxed Coprime Array for Multiple Targets

Recently, extensive researches focus on the joint estimation of carrier frequency and direction-of-arrival, whereas the heavy computation burden and affordable hardware cost are always required therein. To alleviate the problem, we propose a relaxed coprime array based two-stage estimator, which can sequentially detect the frequencies and direction-of-arrival for multiple targets. Guided by the closed-form robust algorithm, this relaxation yields a higher array sparsity compared with existing sparse arrays. Specifically, the first stage aims to achieve the classification of the frequency and angle remainders arising from temporal-spatial undersampling, which is realized by combining spectrum correction with pattern clustering. By incorporating the closed-form robust Chinese Remainder Theorem into the remainder classification result, we obtain all the frequencies and direction-of-arrival in the second stage. Both performance analysis and numerical results were conducted to verify the effectiveness of the proposed estimator in the multi-target case.

Suboptimal training sequence design for synchronisation of burst‐mode CPM

In this study, they authors introduce a suboptimal training sequence for burst-mode continuous phase modulation. The optimum training sequence has been prove to be optimal for the estimates of carrier frequency offset, carrier phase error and timing error. However, the optimum sequence brings high side-lobe of the log-likelihood function (LLF), that is not benefit for detecting the start of the sequence (SOS). Thus, the suboptimal sequence is designed to improve the SOS performance through decreasing the side-log effect of the LLF. Meanwhile, the proposed sequence can minimise the Cramer-Rao bound for the joint estimation of carrier frequency offset, carrier phase error and symbol timing error. The data-aided maximum likelihood algorithms for timing error and phase error estimation are derived for evaluating the performance of the proposed sequence. The simulation results demonstrate that the new sequence provides better performance on start detection of the sequence than the optimal one. The performance of timing and carrier phase recovery is also close to the ideal synchronisation performance.

Joint estimation of carrier frequency and phase offset based on pilot symbols in quasi-constant envelope OFDM satellite systems

Spectral efficiency and energy efficiency are two important performance indicators of satellite systems. The Quasi-Constant Envelope Orthogonal Frequency Division Multiplexing (QCE-OFDM) technique can achieve both high spectral efficiency and low peak-to-average power ratio (PAPR). Therefore, the QCE-OFDM technique is considered as a promising candidate multi-carrier technique for satellite systems. However, the Doppler effect will cause the carrier frequency offset (CFO), and the non-ideal oscillator will cause the carrier phase offset (CPO) in satellite systems. The CFO and CPO will further result in the bit-error-rate (BER) performance degradation. Hence, it is important to estimate and compensate the CFO and CPO. This paper analyzes the effects of both CFO and CPO in QCE-OFDM satellite systems. Furthermore, we propose a joint CFO and CPO estimation method based on the pilot symbols in the frequency domain. In addition, the optimal pilot symbol structure with different pilot overheads is designed according to the minimum Cramer- Rao bound (CRB) criterion. Simulation results show that the estimation accuracy of the proposed method is close to the CRB.

Blind joint estimation of carrier frequency offset and I/Q imbalance in OFDM systems

This paper proposes a blind estimator of the carrier frequency offset (CFO) and in-phase/quadrature (I/Q) imbalance in orthogonal frequency-division multiplexing (OFDM) systems, which does not require any prior knowledge of training symbols or channel side information. The key element behind this algorithm is the null sub-carriers commonly existed in many OFDM systems. This blind joint estimation is carried out in a sequential manner that the frequency offset is estimated first and then based on which, the I/Q imbalance estimation is performed. Important issues including the identifiability problem of the CFO estimator involving whether minimizing the cost function would yield a unique and exact estimate of the frequency offset, performance analysis of the I/Q imbalance estimator and complexity analysis are addressed. Furthermore, this algorithm is proved to be applicable in multiple-input multiple-output (MIMO) systems. Finally, numerical simulation results are presented to validate the effectiveness of the proposed scheme and carry out performance comparison with other existing approaches.

Joint Iterative Carrier Synchronization and Signal Detection Employing Expectation Maximization

In this paper, joint estimation of carrier frequency, phase, signal means and noise variance, in a maximum likelihood sense, is performed iteratively by employing expectation maximization. The parameter estimation is soft decision driven and allows joint carrier synchronization and data detection. The algorithm is tested in a mixed line rate optical transmission scenario employing dual polarization 448 Gb/s 16-QAM signal surrounded by eight on-off keying channels in a 50 GHz grid. It is shown that joint carrier synchronization and data detection are more robust towards optical transmitter impairments and nonlinear phase noise, compared to digital phase-locked loop (PLL) followed by hard decisions. Additionally, soft decision driven joint carrier synchronization and detection offers an improvement of 0.5 dB in terms of input power compared to hard decision digital PLL based carrier synchronization and demodulation.

A Robust Joint Frequency Offset Estimation for the OFDM System Using Cyclic Delay Diversity

Cyclic delay diversity (CDD) is a low-complexity transmit diversity technique for orthogonal frequency division multiplexing (OFDM), which transforms a multiple-input channel into an equivalent single-input channel with a large delay spread. Consequently, high frequency selectivity makes channel and frequency estimation a challenging task. This paper proposes an improved joint estimation of carrier frequency offset and sampling frequency offset for the OFDM system using CDD technique. By finding the amount of a transmit-antenna specific delay which reduces the variance of the frequency estimation scheme, these parameters improve the robustness of the joint frequency estimation scheme against the frequency selectivity of the channel. Computer simulation shows that the joint frequency-offset estimation scheme with properly designed cyclic delay parameters performs robustly, with the performance better than the conventional scheme.

Joint estimation of carrier frequency offset, dc offset and I/Q imbalance for OFDM systems

Orthogonal frequency division multiplexing (OFDM) systems with direct-conversion receiver (DCR) are vulnerable to carrier frequency offset (CFO), dc offset (DCO) and in-phase/quadrature (I/Q) imbalance. In this paper, we propose blind estimator for joint estimation of CFO, DCO and I/Q imbalance in OFDM systems with DCR. Simulation results show that performance of proposed estimator approaches Cramér–Rao lower bound (CRLB) asymptotically, which demonstrates its effectiveness.

Joint Fine Frequency Synchronization for UWB-OFDM Signals

In this paper, a joint estimation of carrier frequency offset and sampling frequency offset is suggested for multi-band ultra-wideband orthogonal frequency division multiplexing (UWB-OFDM) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the UWB-OFDM system, thus removing the need of pilot symbols. The system performance of using our algorithm is demonstrated in terms of mean square error and bit error rate.

Joint Frequency Offset and Channel Estimation for OFDM Systems Using Pilot Symbols and Virtual Carriers

We consider joint estimation of carrier frequency offset and channel impulse response (CIR) for orthogonal frequency division multiplexing (OFDM) systems with pilot symbols and virtual subcarriers (VCs). We derive the receive-signal correlation structure due to the pilots and VCs, give the evidence of joint multivariate Gaussian distribution of the received samples, and derive an approximate maximum likelihood (ML) frequency offset estimator. We also derive the asymptotic mean-square error (MSE) and an approximate Cramer-Rao bound (CRB) and establish the asymptotic unbiasedness. Without pilots, in high signal-to-noise ratio, our estimator is equivalent to Liu and Tureli's estimator with Nv virtual carriers. When the pilot number (Np) is greater than the channel length L, our estimator acts as a subspace-based estimator with Nv + Np - L virtual carriers. A decision-directed joint ML estimator is derived to iteratively update the estimates of frequency offset, data symbols and CIR. The optimal pilot and virtual carrier placement strategies are also discussed. The resulting decision-directed joint estimator performs within 0.8 dB of the ideal case even when the frequency offset is as large as 20%

The modified Cramer-Rao bound in vector parameter estimation

In this paper we extend the scalar modified Cramer-Rao bound (MCRB) to the estimation of a vector of nonrandom parameters in the presence of nuisance parameters. The resulting bound is denoted with the acronym MCRVB, where V stands for vector. As with the scalar bound, the MCRVB is generally looser than the conventional CRVB, but the two bounds are shown to coincide in some situations of practical interest. The MCRVB is applied to the joint estimation of carrier frequency, phase, and symbol epoch of a linearly modulated waveform corrupted by correlated impulsive noise (encompassing white Gaussian noise as a particular case), wherein data symbols and noise power are regarded as nuisance parameters. In this situation, calculation of the conventional CRVB is infeasible, while application of the MCRVB leads to simple useful expressions with moderate analytical effort. When specialized to the case of white Gaussian noise, the MCRVB yields results already available in the literature in fragmentary form and simplified contexts.