Top PDF Estimation of carrier frequency offset with I/Q mismatch using pseudo offset injection in OFDM systems

Estimation of carrier frequency offset with I/Q mismatch using pseudo offset injection in OFDM systems

Estimation of carrier frequency offset with I/Q mismatch using pseudo offset injection in OFDM systems

I/Q Mismatch Using Pseudo-Offset Injection in OFDM Systems Ming-Fu Sun, Student Member, IEEE, Jui-Yuan Yu, and Terng-Yin Hsu, Member, IEEE Abstract—This work presents a novel carrier frequency offset (CFO) estimation algorithm, based on pseudo-CFO (P-CFO), to es- timate the CFO value under the conditions of I/Q mismatch for di- rect conversion structures with 2-dB gain error and 20-deg. phase error in frequency selective fading channels. To circumvent CFO with I/Q mismatch, the proposed P-CFO algorithm rotates three training symbols by adding extra frequency offset into the received sequence to improve CFO estimation. Simulation results indicate that the estimation error of the proposed method is about 0.3 ppm, which is lower than those of two-repeat preamble-based methods.
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Maximum Likelihood Timing and Carrier Frequency Offset Estimation for OFDM Systems With Periodic Preambles

Maximum Likelihood Timing and Carrier Frequency Offset Estimation for OFDM Systems With Periodic Preambles

Fig. 3. Performance comparison of CFO estimation, the algorithm in [17], and proposed algorithm I; SNR = 10 dB. Fig. 4. BER comparison for systems with and without CFO. frequency-domain binary-phase-shift-keying-modulated signal, has ten periods, and each period has 16 samples. The data following the preamble are transmitted using a 16-quadratic- amplitude-modulation scheme. The mean square error (MSE) of the estimated CFO is used as a performance measure. We first consider the CFO-only estimation problem. In this case, the first received N samples are discarded. As previously mentioned, we term the proposed approach for this scenario as algorithm I (as described in Section III). We compare the proposed ML estimator with that in [17]. One optimum algorithm (algorithm A) and two suboptimum algorithms (algorithm A and B) in [17] are simulated. Fig. 3 shows the simulation result for SNR at 10 dB. In the figure, we can see that the performances of algorithms A and B are poorer. Algorithm A and the proposed algorithm offer a similar level of performance that is very close to the CRLB. To evaluate the impact of CFO on system perfor- mance, we conduct simulations for systems with and without CFO. For the system with CFO, we first use the proposed method to estimate CFO and then conduct CFO compensation.
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A 62.8 mW 4x4 MIMO-OFDM Modem with One-Symbol-Locked Timing Recovery, Frequency-Dependent I/Q Mismatch Estimation and Adaptive Equalization

A 62.8 mW 4x4 MIMO-OFDM Modem with One-Symbol-Locked Timing Recovery, Frequency-Dependent I/Q Mismatch Estimation and Adaptive Equalization

This chip occupies 4.6×4.6 mm 2 and consumes 62.8 mW at 1.2 V. I. I NTRODUCTION The combination of multi-input multi-output (MIMO) transmission, orthogonal frequency-division multiplexing (OFDM) technology, and space-time block code (STBC) scheme comprises a potential solution for next-generation wireless communications [1]. However, MIMO-OFDM systems are sensitive to sampling clock offset and carrier frequency offset (CFO). In addition, direct-conversion receivers suffer from I/Q mismatch (IQM). IQM arises when the phase and gain differences between I and Q branches are not exactly 90° and 0 dB, respectively. Due to the impairment in the analog components, the mismatched low-pass filters result in frequency-dependent IQM (FD-IQM) [2]. In an MIMO-OFDM system with FD-IQM, the FD-IQM parameters for every subcarrier are different. Moreover, the ability of adaptive equalization is required due to time-varying environments. For successful transmissions, obtaining accurate channel frequency response (CFR) is extremely important. Owing to the above considerations, an MIMO- OFDM modem is proposed for fast timing recovery, anti-IQM frequency recovery, FD-IQM estimation and adaptive frequency-domain equalization.
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Iterative ML estimation for frequency offset and time synchronization in OFDM systems

Iterative ML estimation for frequency offset and time synchronization in OFDM systems

According to the proposed iterative approaching algorithm, the global maximum of log-likelihood function can be definitely found to achieve both frequency and time synchronization[r]

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Pilot-assisted maximum-likelihood frequency-offset estimation for OFDM systems

Pilot-assisted maximum-likelihood frequency-offset estimation for OFDM systems

the channel’s maximum delay spread is shorter than the length of the cyclic prefix. Assuming a mobile speed of 100 km/h, cor- responding to a Doppler frequency of approximately 463 Hz when the carrier frequency is 5 GHz, we plot the corresponding MSE performance in Figs. 7 and 8. As our derivations assume a quasi-static channel that remain unchanged during the preamble period, the estimation performance is degraded due to the fact that the received signal model (4) is no longer valid. In sum- mary, Algorithms and and the MTB estimate render the best performance, followed by Algorithm , and then the other correlation-based algorithms. When is small, Algorithms , , and yield almost the same MSE performance. The pro- posed methods can be used when an arbitrary number of identical pilot symbols are available.
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Joint weighted least squares estimation of frequency and timing offset for OFDM systems over fading channels

Joint weighted least squares estimation of frequency and timing offset for OFDM systems over fading channels

The carrier frequency offset can he estimated by first calculating the pilot-suhcarrier phase difference between two OFDM symbols, removing the quantity contributed by the [r]

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An approximately MAI-free multiaccess OFDM system in carrier frequency offset environment

An approximately MAI-free multiaccess OFDM system in carrier frequency offset environment

C. Hadamard–Walsh Code in the Uplink Transmission In the uplink transmission, it is difficult to guarantee that every user transmits his/her signal simultaneously. This will lead to timing mismatch among users. If the Hadamard–Walsh code is used in the uplink transmission in conventional CDMA sys- tems, a small timing mismatch among users will result in great MAI even if the channel is perfect. For instance, consider the case with processing gain . If the fourth user has a delay of one chip duration while the other three users are per- fectly synchronized, the receiver cannot distinguish the fourth user from the third one because . There- fore, Hadamard–Walsh code is seldom used in the uplink trans- mission unless the timing mismatch problem can be well re- solved by some other mechanism. In conventional CDMA or MC-CDMA systems, quasiorthogonal codes that have less cross correlation such as the Gold code or the Kasami code are usu- ally used to mitigate the timing mismatch problem. In contrast, since the proposed system is robust to timing mismatch [23], we can adopt the low complexity Hadamard–Walsh code in the uplink transmission.
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Blind Maximum-Likelihood Carrier-Frequency-Offset Estimation for Interleaved OFDMA Uplink Systems

Blind Maximum-Likelihood Carrier-Frequency-Offset Estimation for Interleaved OFDMA Uplink Systems

very high. The distinct feature of the proposed algorithm is that it only requires a root-searching procedure. The main idea is to use a series expansion when evaluating the ML function. The performance of the expansion is also analyzed. The operations of the proposed method are simple, and the computational complexity is low. Simulations show that the proposed method can approach the CRB. As shown in Fig. 1, a large EVS will be induced in the full-loaded scenario (Δq = 1), and the perfor- mance of the proposed method will seriously be affected. The problem can be solved by an expectation-maximization (EM) algorithm referred to as iterative space alternating generalized EM (SAGE) [23], [24]. However, the complexity of the SAGE algorithm can be very high for large N s . Note that in real- world applications, only a number of users will be activated at a specific time [24]. Thus, only the CFOs of the newly activated users have to be estimated, and the knowledge of the previously estimated CFOs can be exploited in each new estimation. It is interesting to incorporate the SAGE algorithm into the proposed method, which may serve as a topic for further research.
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Blind recursive tracking of carrier frequency offset (CFO) vector in MC-CDMA systems

Blind recursive tracking of carrier frequency offset (CFO) vector in MC-CDMA systems

power in dealing with a broad range of estimation problems with incomplete observations [12], [13]. Estimation of the symbol arrival time and the carrier phase was considered in [14] with the transmitted symbol being treated as the missing data. A blind CFO estimation scheme in MC-CDMA systems using the EM algorithm was studied in [15], where the gradient decent technique was proposed to deal with the nonlinear optimization problem in the CFO estimate. However, since there exist multiple local optima in the cost function, the solution is sensitive to the initialization of the optimiza- tion process, which could be problematic for a hill-climbing adaptive algorithm. Besides, all these schemes were operated in a block-based manner assuming that the target parameters were time invariant inside this time block. However, timely updates of system parameters would be more desirable in real time applications, which motivates the development of online algorithms to track possibly time-varying unknowns.
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Preamble-Assisted Estimation for Frequency-Dependent I/Q Mismatch in Direct-Conversion OFDM Receivers

Preamble-Assisted Estimation for Frequency-Dependent I/Q Mismatch in Direct-Conversion OFDM Receivers

In practice, frequency-dependent IQ-M and CFO arise simultaneously. However, only some references consider the frequency-dependent IQ-M with CFO. This study mainly concentrates on the estimation of frequency- dependent IQ-M with CFO. To maintain and realize sys- tems with imperfect front-end modules, a preamble-assisted estimation scheme is developed. Simulation results show that the performance loss is in the range of 1.6 to 1.8 dB at 10 −4 bit error rate. Experiment results demonstrate that the proposed method could overcome joint impairments of frequency-dependent IQ-M and CFO, enabling a high per- formance receiver. The remainder of the paper is organized as follows. Section 2 introduces the system model. Sec- tion 3 then presents the proposed method. Simulation and experiment results are shown in Sect. 4. Conclusions are fi- nally drawn in Sect. 5.
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Novel sampling clock offset estimation for DVB-T OFDM

Novel sampling clock offset estimation for DVB-T OFDM

National Taiwan University, Taipei 10617, Taiwan Abstract – Sampling clock offset estimation and compensation are important problems in an OFDM system. Sampling clock offset can cause a severe drift in symbol-timing, thus causing inter-carrier and inter-OFDM-symbol interference. In this paper, we propose a novel sampling clock offset estimator for OFDM systems that use scattered pilots. The proposed algorithm makes use of the received pilot phases and the least-squares algorithms. Simulation results show that when applied to the DFB-T standard, the performance of the proposed estimator is very accurate and robust against multipath fading and Doppler Spread.
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A low-complexity frame synchronization and frequency offset compensation scheme for OFDM systems over fading channels

A low-complexity frame synchronization and frequency offset compensation scheme for OFDM systems over fading channels

A. Residual Frequency Tracking Error In the acquisition stage, we assume that the residual fre- quency error after the frequency tracking stage is an integral multiple of the subcarrier spacing. However, there exists a residual frequency tracking error that introduces ICI and de- grades the performance of the acquisition scheme. To explore how the residual frequency tracking error affects the acquisi- tion scheme, a computer simulation is taken. Fig. 15 shows the plots of versus the normalized residual frequency tracking error. The solid-line curve and the dashed-line curve represent the estimated by (22) for SNR dB and SNR dB, respectively. In Fig. 15, the “ ” symbols and the “ ” symbols represent the Monte Carlo simulations results for SNR dB and SNR dB, respectively. To speed up our simulation, the acquisition range is set to ten. We can see that the missed lock probability of the acquisition scheme is still very low even the residual frequency tracking error is as large as 0.47 times of the subcarrier spacing. That is, the proposed acquisition scheme is insensitive to the tracking error. As shown in Fig. 7, the residual tracking error after the frequency detector without averaging process is smaller than 0.15 times of the subcarrier spacing, which is tolerable to the proposed acquisition scheme.
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A fully digital noncoherent and coherent GMSK receiver architecture with joint symbol timing error and frequency offset estimation

A fully digital noncoherent and coherent GMSK receiver architecture with joint symbol timing error and frequency offset estimation

Assume that we first convert the received signal from radio frequency (RF) to baseband and the real and imaginary compo- nents of the base-band complex signal are and . These two signals are oversampled, digitally frequency discriminated, and low-pass filtered to obtain raw digital data. This data goes through an FFT for synchronization preamble bits detection. If detected, both frequency offset and sampling time error are es- timated from the FFT results. Symbol timing sychronization is done in a feedforward manner. Carrier frequency offset com- pensation is done in a hybrid manner. On one hand, frequency offset estimation is fed back to a VCO during the preamble pe- riod. On the other hand, this estimation can be used to change the decision threshold in a noncoherent detection mode or rotate the signal constellation in a coherent detection mode. After syn- chronization is finished, we obtain the demodulated data. The whole synchronization and data detection process can be un- derstood in more detail by examining the flowchart shown in Fig. 2.
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Maximum-likelihood estimation of frequency and time offsets in OFDM systems with multiple sets of identical data

Maximum-likelihood estimation of frequency and time offsets in OFDM systems with multiple sets of identical data

Therefore, an accurate estimation of the frequency offset is critical. Existing approaches for the frequency-offset estimation using the pre- amble data [6], [7], the cyclic prefix data [8], [9], or the cyclostationary property [10] of the received signals have been proposed. Extensive coverage of techniques for digital synchronization is also provided in textbooks [11]–[13]. Here, we focus on the data-aided maximum-like- lihood (ML) estimation in OFDM systems. The ML estimation of fre- quency and time offsets in OFDM systems using the two sets of iden- tical cyclic prefix data has been derived in [8]. In the IEEE 802.11a [14] standard for wireless LAN communications, the preamble con- tains multiple sets of identical data for channel estimation and syn- chronization. Hence, an extension for the ML estimation algorithm to include for multiple sets of identical data is practically useful and worth studying. Therefore, in this paper, by using the matrix inversion lemma [15], we generalize the ML algorithm for the estimation of frequency and time offsets to include for the number of the identical data set more than two. Moreover, we also derive the Cramér–Rao bound for the fre- quency-offset estimate. Since the resulting ML algorithm requires high realization complexity, we further develop a simplified algorithm that can reduce significantly the realization complexity but at the cost of modest performance degradation. Simulations are then carried out to evaluate the performance of all proposed algorithms using the ten short identical symbols in the preamble of IEEE 802.11a standard.
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Cross-Validation Estimation for Frequency-Dependent I/Q Imbalance in MIMO-OFDM Receivers

Cross-Validation Estimation for Frequency-Dependent I/Q Imbalance in MIMO-OFDM Receivers

Received: 4 March 2008 / Revised: 4 August 2009 / Accepted: 6 August 2009 / Published online: 8 September 2009 # 2009 Springer Science + Business Media, LLC. Manufactured in the United States Abstract The effects of variation in RF, such as I/Q imbalance and filter mismatch, are extremely important for OFDM wireless accesses. This work presents a low- computational estimation of I/Q imbalances with filter mismatches to improve performance in MIMO-OFDM receivers. For N×N MIMO-OFDM systems, the proposed cross-validation estimation is such that, only N+1 preambles are required to extract the mismatches of filters, gains and phases. With the estimated parameters, frequency-domain filters are exploited to correct frequency-dependent I/Q imbalances. Through performance evaluation of a 2 ×2 MIMO-OFDM system, with ideal channel estimations this study incurs a SNR loss of 1–1.2 dB to maintain a 10% PER at 1-dB gain error, 10°-phase error and the worst 180°-filter mismatch. In addition, this algorithm is well-matched to IEEE 802.11n and new specifications discussed in IEEE 802.11 VHT study group.
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An iterative maximum SINR receiver for multicarrier CDMA systems over a multipath fading channel with frequency offset

An iterative maximum SINR receiver for multicarrier CDMA systems over a multipath fading channel with frequency offset

adaptive filter bank, copied from the lower branch, performs despreading and MAI suppression, and pilot symbols assisted frequency offset estimation, channel vector estimation and RAKE combining give the desired signal symbols. With signal subtraction in the lower branch, the proposed MC-CDMA re- ceiver can achieve nearly the performance of the ideal MSINR receiver within a few iterations. Finally, a low-complexity PA realization of the GSC adaptive filters is presented for a multiuser scenario. The new PA receiver is shown to be robust to multiuser channel errors, and offer nearly the same perfor- mance of the fully adaptive receiver. In summary, the proposed MC-CDMA receiver with PA MAI suppression performs near optimal signal detection with tolerance to large frequency offsets and resistance to strong MAI. More importantly, it can be initialized in the blind mode without the aid of channel estimation and frequency offset compensation.
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Frequency-domain interpolation-based channel estimation in pilot-aided OFDM systems

Frequency-domain interpolation-based channel estimation in pilot-aided OFDM systems

With its low hardware complexity and accurate estimation performance, the raised-cosine frequency- domain interpolation channel estimator will find many appli- cations in OFDM co[r]

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Noncoherent block detection in the presence of DC offset

Noncoherent block detection in the presence of DC offset

Fig. 7. BEP comparison among block detection scheme with L = 4, iterative detection scheme with I = 3 and L = 4, and TSA-4PSK detection scheme with R = 1/8. Digital simulation has been conducted to evaluate the BEP performance of the iterative detection scheme for demodu- lating the Gray-labeled data phasor block-modulated signals composed by the transform in Example One of Table I. It is found by the author that the iterative scheme can provide better performance by increasing iterations. Particularly, significant performance improvement is achieved by making final deci- sion at the second iteration than at the first iteration and the improvement become infinitesimal by making final decision after more than three iterations. Figs. 7 and 8 illustrate the sim- ulated BEP results of the iterative detection scheme with I = 3 for L = 4 and 8, respectively, and compare the results with the approximate bound results of the block detection scheme.
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Noncoherent Block Detection in the
Presence of DC Offset

Noncoherent Block Detection in the Presence of DC Offset

Fig. 7. BEP comparison among block detection scheme with L = 4, iterative detection scheme with I = 3 and L = 4, and TSA-4PSK detection scheme with R = 1/8. Digital simulation has been conducted to evaluate the BEP performance of the iterative detection scheme for demodu- lating the Gray-labeled data phasor block-modulated signals composed by the transform in Example One of Table I. It is found by the author that the iterative scheme can provide better performance by increasing iterations. Particularly, significant performance improvement is achieved by making final deci- sion at the second iteration than at the first iteration and the improvement become infinitesimal by making final decision after more than three iterations. Figs. 7 and 8 illustrate the sim- ulated BEP results of the iterative detection scheme with I = 3 for L = 4 and 8, respectively, and compare the results with the approximate bound results of the block detection scheme.
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Failure Probability Estimation of Anisotropic Conductive Film Packages With Asymmetric Upper-to-Lower Pad Size and Misalignment Offset

Failure Probability Estimation of Anisotropic Conductive Film Packages With Asymmetric Upper-to-Lower Pad Size and Misalignment Offset

V. C ONCLUSION This paper has used the V-shaped curve method to analyze the failure probability of ACF packages in which the upper and lower pads have a different side length and are subject to alignment errors. In formulating the V-shaped curve, the opening probability has been modeled using a Poisson function, suitably modified to take into account the effects of the pad- width difference and the misalignment offset on the effective conductive area between opposing pads. Meanwhile, the bridg- ing probability has been modeled using an enhanced bridging model, modified to take into account the effects of asymmetry and misalignment on the lengths of the bridging paths between neighboring pad pairs. The major findings of this paper can be summarized as follows.
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