Carrier frequency offsets estimation for uplink OFDMA systems using enhanced PSO and multiple access interference cancellation

ABSTRACTWhile inter-symbol interference is not of concern, inter-carrier interference that is caused by carrier frequency offset (CFO) is more concerned in orthogonal frequency division multiplexing (OFDM) systems. The estimation of channel impulse response (CIR) is another important parameter of interest in the system. Recently, a number of approaches for the joint estimation of CFO and CIR in OFDM systems have been proposed in the literature, and most of them are traditional maximum-likelihood-based approaches. In this paper, we propose a number of mixture cost-reference particle filtering (CRPF) approaches for joint estimation of CIR and CFO, and a couple of them can be applied without the knowledge of both state and measurement noise statistics. Conventional least mean squares algorithm or recursive least squares algorithm is jointly employed with recently developed CRPF for nonlinear and multiple parameters estimation in OFDM systems. The computer simulation results show that mixture CRPFs are more robust against particle impoverishment (PI) problem than standard mixture particle filtering (PF) and mixture regularized PF (RPF) approaches although RPF was particularly developed to tackle the PI problem. In this paper, we investigate a number of mixture PF approaches including ones that do not need the information of noise statistics for the joint estimation of CFO and channel in OFDM systems.

In this paper, we propose a method for joint estimation of carrier frequency offsets (CFO) of multiple active users in an orthogonal frequency division multiple access (OFDMA) uplink using the recently-developed bat algorithm. An initialization technique that can drastically reduce the total computational complexity of joint maximum likelihood (ML) estimation problems is employed to make the metaheuristic bat algorithm more efficient. This initialization improves the convergence rate of the estimator and thus reduces its total computational load in a significant manner. The CFO estimates obtained from the proposed method are also characterized by low mean square error values compared to a conventional implementation of the bat algorithm for the problem. The efficacy of the proposed method is substantiated through computer simulation studies.

In this paper, a complete solution to the initial synchronization for multi-cell OFDMA (orthogonal frequency division multiple access) systems is proposed. The proposed method consists of the following operations: timing synchronization, fractional carrier frequency offset (CFO) estimation, fractional CFO compensation, and joint integer CFO and preamble index estimation. To estimate multiple fractional CFOs with pseudoperiodic preamble, we suggest an over-sampling approach. An ill-condition detection and noise suppression algorithm is also presented. For joint integer CFO and preamble index estimation, we use a differential detection based cross-correlation method. Simulation results have shown that the proposed method gives satisfactory performance for a wide SNR range even when the mobile station (MS) is on the cell boundaries.

In this paper, we deal with the multiple carrier frequency offsets (CFOs) estimation issues for orthogonal frequency-division multiple access (OFDMA) based uplink system. In such system, the interleaved carrier assignment scheme (CAS) has gained much attention for it brings maximum frequency diversity though it undergoes severe CFO problem than other schemes. The multiple-CFO estimation problem in this scheme uses a similar signal structure as that of Direction of Arrival (DOA) estimation problem in array signal processing, so subspace based multiple signal classification (MUSIC) algorithm can be exploited to estimate multiple CFOs. Compared with the conventional MUSIC algorithm utilizing eigenvalue decomposition of complex-value covariance matrix, the proposed unitary MUSIC and unitary root-MUSIC CFO estimation algorithms have comparable performance but lower computational complexity because of real-value covariance matrix used, which is verified by computer simulation.

In this study, the authors propose a blind carrier frequency offset (CFO) estimation method for the tile structure orthogonal frequency division multiple access (OFDMA) uplink with multi‐antenna receiver. They employ an iterative approach to extract the signal component for each user gradually and propose a carefully designed CFO estimator to update the CFO estimate during the iterative procedure. The key ingredient of the proposed method is using few subcarriers on both sides within each tile as the ‘guard subcarriers’, which can greatly mitigate the effect of multi‐user interference. The proposed method supports not only fully loaded transmissions, but also the generalised assignment scheme that provides the flexibility for dynamical resource allocation. The numerical results are provided, which indicate that the proposed method can almost converge to the analytical lower bound within a few iterative cycles. It is seen that the proposed method also outperforms the existing competitor with multi‐antenna receiver in terms of estimation performance, especially with few adopted blocks.

OFDM (orthogonal frequency division multiplexing) is a promising technology for future broadband wireless communications due to its capability in combating multipath fading. Carrier frequency offset (CFO), which can induce the loss of orthogonality among OFDM sub-carriers and significant performance degradation, needs to be estimated and compensated for. In this paper, we propose a general CFO estimator based on the maximum likelihood (ML) estimation criterion. It will be shown that with the same estimator architecture, CFO can be obtained using either training OFDM symbols, pilot tones, null sub-carriers, or a combination of them. Furthermore, by taking advantage of the channel side information, the performance of CFO estimation can be significantly improved. To demonstrate the capability of the proposed CFO estimator, we will consider an OFDM system using the signal structure of the IEEE WLAN standard 802.11a. Compared with previous work using null sub-carriers alone, it will be shown that by taking advantage of the pilot tones, null sub-carriers, and the channel statistics, the performance of CFO estimation can be improved by about 2 dB

Orthogonal Frequency Division Multiple Access (OFDMA) gains increasing attention for broadband, high data rate fixed/mobile communications. As the basic modulation technique in OFDMA is orthogonal frequency division multiplexing (OFDM), it is severely affected by carrier frequency offset (CFO). The CFO causes loss of orthogonality among the subcarriers. In this paper, we propose a method for joint estimation of CFO and cell ID. Cell ID represents the number of the preamble selected by the base station in the downlink. The proposed method is based on the preamble suggested for OFDMA mode of WMAN where the preamble is loaded on every third subcarrier. The proposed method is an extension of Schimdl and Coxpsilas method. We also propose a method for estimation of CP length. Van de Beekpsilas method is adapted for the estimation of CP length in OFDMA mode of WMAN. Simulations are conducted for AWGN and frequency selective channels to demonstrate the performance of the proposed methods.

A low complexity iterative equalization technique for OFDMA and SC-FDMA uplink systems with Tx-Rx IQ imbalance and CFO under doubly selective channels

The carrier frequency offset (CFO) estimation is an important task for orthogonal frequency-division multiple-access (OFDMA) systems. Making use of the intrinsic periodic structure of the received signal samples, an effective Unitary-ESPRIT algorithm based on unitary transformation technique is proposed for the CFO estimation problem. Compared with other recently proposed CFO estimation approaches, the proposed algorithm offers a number of advantages. Firstly, the presented approach can reduce the computation complexity considerably, since it is efficiently formulated in terms of real-valued computation except for the data preprocessing. Secondly, it can provide better CFO estimation performance by incorporating the data stacking technology and the unitary transformation, etc. Simulation results demonstrate the efficacy of the proposed algorithm.

The estimation of carrier frequency offset (CFO) is an important issue in the study of the orthogonal frequency division multiplexing (OFDM) systems. In the past, many CFO estimation methods have been proposed. In this paper, we propose a new blind CFO estimation for OFDM systems based on the so-called remodulated received vectors [8]. The CFO estimate is given by a closed form formula. The proposed method has very low complexity and its performance is robust to different modulation symbols and the presence of virtual carriers.

In uplink orthogonal frequency division multiple access (OFDMA), carrier frequency offsets (CFO) and/or timing offsets (TO) of other users with respect to a desired user can cause significant multiuser interference (MUI). In this paper, we derive analytical bit error rate (BER) expressions that quantify the degradation of BER due to the combined effect of both CFOs as well as TOs; such an analytical BER derivation has not been reported so far for uplink OFDMA in the presence of CFOs and TOs. For the case when the desired user is perfectly frequency/time aligned (and other users have non-zero CFOs/TOs), we obtain an exact closed-form expression for the BER. For the case when the desired user also has non-zero CFO/TO, we obtain an approximate BER expression involving a single integral. Analytical and simulation results are shown to match quite well.

The electrical wireless network build 4G TD-LTE network in 1.8GHz band, orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) are the key technologies. The OFDM system is sensitive to carrier frequency offset (CFO) and hence accurate CFO estimates for the OFDM system are essential. In this paper, we study the problem of carrier frequency offset (CFO) in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, and then a multi-invariance PM algorithm is proposed to estimate CFO in MIMO-OFDM system. The proposed algorithm employs the property of multi-invariance. Simulations show that the proposed algorithm has a better CFO estimation performance than PM.

Orthogonal frequency division multiplexing (OFDM) has been adopted in various wireless communication standards to exploit its high spectral efficiency and robustness against multipath fading channels. Along with the potential benefits of OFDM transmissions, a stringent requirement on orthogonality among subcarriers makes OFDM highly susceptible to synchronization errors, i.e., time and frequency offsets. Addressing the carrier frequency offset (CFO) estimation problem, the paper proposes a pilot-aided CFO estimation scheme for both coarse and fine carrier frequency synchronization in single-input single-output (SISO) OFDM receivers. By exploiting the maximum likelihood (ML) principle, the proposed ML-based CFO estimation algorithm functions properly over a wide range of CFO values and outperforms existing correlation-based schemes.

A turbo receiver combined with CFO compensation in frequency-domain for OFDMA uplink

Low cost video sensors used for streaming video signals to help firefighters, require high bit rate due to uncompressed images. To increase spectral efficiency given a limited bandwidth, very high order constellations in high signal to noise ratio regimes can be used. However, noise is not the only factor effecting the high order constellations. These constellations are also sensitive to hardware impairments and system non‐linearities. Therefore, in this paper, the effect of carrier frequency offset (CFO) on the performance of an orthogonal frequency division multiplexing (OFDM) system with high order quadrature amplitude modulation (QAM) is studied. A closed form expression is derived for the maximum normalized residual CFO that an OFDM system with M ‐QAM constellation can resist to have an error free symbol detection. Finally, the suitability of common previous CFO estimation techniques such as the cyclic prefix based technique and the Moose technique in these systems are investigate. The results show that the maximum residual CFO that an OFDM system with M ‐QAM constellation can resist is proportional to the inverse of . The results also show that very large order QAM constellations such as 4096‐QAM are very sensitive to even small residual CFO values and their performance degrades, significantly. However, the bit error rate analysis indicate that the Moose CFO estimation technique can be used in these systems to compensate the CFO effect, accurately.