Impact Of Carrier Frequency Offset Research Articles

Understanding Concurrent Transmissions: The Impact of Carrier Frequency Offset and RF Interference on Physical Layer Performance

The popularity of concurrent transmissions (CT) has soared after recent studies have shown their feasibility on the four physical layers specified by BLE 5, hence providing an alternative to the use of IEEE 802.15.4 for the design of reliable and efficient low-power wireless protocols. However, to date, the extent to which physical layer properties affect the performance of CT has not yet been investigated in detail. This article fills this gap and provides an extensive study on the impact of the physical layer on CT-based solutions using IEEE 802.15.4 and BLE 5. We first highlight through simulation how the impact of errors induced by relative carrier frequency offsets on the performance of CT highly depends on the choice of the underlying physical layer. We then confirm these observations experimentally on real hardware and with varying environmental conditions through an analysis of the bit error distribution across received packets, unveiling possible techniques to effectively handle these errors. We further study the performance of CT-based data collection and dissemination protocols in the presence of RF interference on a large-scale testbed, deriving insights on how the employed physical layer affects their dependability.

Impact of carrier frequency offset and in-phase and quadrature imbalance on the performance of wireless precoded orthogonal frequency division multiplexing

<p>Precoding in orthogonal frequency division multiplexing (OFDM) system proved to reduce the peak-to-average power ratio (PAPR), so that it improves BER. However, from the existing literature, the effect of carrier frequency offset (CFO), in-phase and quadrature (IQ) imbalance on precoded wireless OFDM systems has not been carried out. Therefore, this study evaluated the precoded OFDM (P-OFDM) system performance by considering the impact of CFO and IQ imbalance. P-OFDM performance evaluation is expressed in signal-to-interference noise ratio (SINR) and bit error rates (BER). The communication channels used are the additive white Gaussian noise (AWGN) channel and the frequency-selective Rayleigh fading (FSRF) channel, while the channel equalization process is considered perfect. The results of the analysis and simulation show that P-OFDM is greater affected by the presence of CFO and IQ imbalance than conventional OFDM system. In AWGN channel, P-OFDM experiences different SINR for each subcarrier. This is different from conventional OFDM system, where all SINRs are the same for all subcarriers. In the FSRF channel, both the POFDM system and the OFDM system experience different SINR for each subcarrier, where the SINRs fluctuation in the P-OFDM system is much larger than in the OFDM system.</p>

High Resolution Carrier Frequency Offset Estimation in Time-Reversal Wideband Communications

Time-reversal (TR) wideband communication systems enjoy the spatial–temporal focusing effect in a rich-scattering environment. However, the performance degrades in the presence of carrier frequency offset (CFO). The impact of CFO can be mitigated by compensating the estimated CFO values obtained using CFO estimators. Yet, CFO estimators in literature cannot work well in wideband TR systems due to the fact that the normalized CFO values are very small and thus cannot be estimated accurately using conventional schemes. To address this issue, we propose four CFO estimators which are capable of accurate CFO estimations for wideband TR systems. The theoretical performances of the proposed estimators are analyzed. Additionally, realizing that phase wrapping might introduce severe bias into CFO estimations, we present the conditions on the system parameters so that phase wrapping can be avoided. Extensive simulations and experimental results demonstrate the superiority of the proposed methods.

Analysis of Synchronization Impairments for Cooperative Base Stations Using OFDM

Base station cooperation is envisioned as a key technology for future cellular networks, as it has the potential to eliminate intercell interference and to enhance spectral efficiency. To date, there is still lack of understanding of how imperfect carrier and sampling frequency synchronization between transmitters and receivers limit the potential gains and what the actual system requirements are. In this paper, OFDM signal model is established for multiuser multicellular networks, describing the joint effect of multiple carrier and sampling frequency offsets. It is shown that the impact of sampling offsets is much smaller than the impact of carrier frequency offsets. The model is extended to the downlink of base-coordinated networks and closed-form expressions are derived for the mean power of users’ self-signal, interuser, and intercarrier interference, whereas it is shown that interuser interference is the main source of degradation. The SIR is inverse to the base stations’ carrier frequency variance and to the square of time since the last precoder update, whereas it grows with the number of base stations and drops with the number of users. Through user selection, the derived SIR upper bound can be approached. Finally, system design recommendations for meeting synchronization requirements are provided.

Impact of Carrier Frequency Offset on Passive Bistatic Radar with Orthogonal Frequency Division Multiplexing Waveform

Impact of Carrier Frequency Offset on Passive Bistatic Radar with Orthogonal Frequency Division Multiplexing Waveform

Simultaneous Multiple Carrier Frequency Offsets Estimation for Coordinated Multi-Point Transmission in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) combined with the coordinated multi-point (CoMP) transmission technique has been proposed to improve performance of the receivers located at the cell border. However, the inevitable carrier frequency offset (CFO) will destroy the orthogonality between subcarriers and induce strong inter-carrier interference (ICI) in OFDM systems. In a CoMP-OFDM system, the impact of CFO is more severe because of the mismatch in carrier frequencies among multiple transmitters. To reduce performance degradation, CFO estimation and compensation is essential. For simultaneous estimation of multiple CFOs, the performance of conventional CFO estimation schemes is significantly degraded by the mutual interference among the signals from different transmitters. In this work, our goal is to propose an effective approach that can simultaneously estimate multiple CFOs in the downlink by using the composite signal coming from multiple base stations corresponding to CoMP transmission. Based on the Zadoff-Chu sequences, we design an optimal set of training sequences, which minimizes the mutual interference and is robust to the variations in multiple CFOs. Then, we propose a maximum likelihood (ML)-based estimator, the robust multi-CFO estimation (RMCE) scheme, for simultaneous estimation of multiple CFOs. In addition, by incorporating iterative interference cancellation into the RMCE scheme, we propose an iterative scheme to further improve the estimation performance. According to the simulations, our scheme can eliminate the mutual interference effectively, approaching the Cramer-Rao bound performance.

MCMOE-Based CFO Estimator Aided With the Correlation Matrix Approach for Alamouti's STBC MC-CDMA Downlink Systems

This paper addresses the estimation problem of carrier frequency offset (CFO) in the downlink transmission of space-time block-coded multicarrier code-division multiple-access (STBC MC-CDMA) systems over multipath fading. This study proposes a multiply constrained minimum output energy (MCMOE)-based blind CFO estimator, which is simply assisted by the presented correlation matrix approach to efficiently achieve the CFO estimate. We formulate a two-level CFO estimator by optimizing the receiver output power, as well as the data correlation matrix. At the first level, all possible CFO candidates are found by evaluating the well-defined estimated merit figure. Then, exploiting multiple constraints in the design of the MCMOE receiver, a criterion is used in level two to determine the exact CFO estimate. Numerical results are presented to verify that both precise CFO estimation and reliable error performance can be achieved, even when the channel is dominated by noise because the impact of CFO on the output signal-to-interference-plus-noise ratio (SINR) and bit error rate (BER) are effectively removed by the proposed CFO estimator.

On the Impact of CFO for an MC-DS-CDMA System in Weibull Fading Environments

On the basis of CFO (carrier frequency offset) point of view, the system performance results from the analysis by adopting the channel scenarios characterized as Weibull fading for an MC-DS-CDMA (multi-carrier direct-sequence coded-division multiple-access) system is proposed in this article. Moreover, an approximate simple expression with the criterion of BER (bit error rate) versus SNR (signal-to-noise ratio) method is derived for an MC-DS-CDMA system combining with RAKE receiver, which is a special case of MRC (maximal ratio combining) diversity, based on the MGF (moment generating function) formula of Weibull statistics, and it associates with an alternative expression of Gaussian Q-function. In addition, the other point of view on the BER performance evaluation of an MC-DS-CDMA system is not only the assumption of both single-user and multi-user cases applied, but the phenomena of PBI (partial band interference) is also included. Furthermore, with several of the system parameters, such as CFO values, ?, Weibull fading parameter, β, user number, K, spreading chip number, N, branch number, L, and the PBI values, JSR etc., are compared with each other in the numerical results in order to validate the accuracy in the derived formulas. To the best of author's knowledge, it is a brain fresh idea proposed in this paper to evaluate the system performance for an MC-DS-CDMA system on the point of the CFO view over Weibull fading.

Impact of Carrier Frequency Offset on Received SNR in Dual-Hop OFDM Systems with a Fixed Relay

In this letter, we present the impact of carrier frequency offset (CFO) in dual-hop orthogonal frequency division multiplexing (OFDM) systems with a fixed relay for frequency-selective fading channels. Approximate expressions of the average signal-to-noise ratios (SNRs) for both downlink and uplink are obtained and validated by simulations. It is shown that dual-hop systems have slightly worse average SNR degradation than single-hop systems. We also show that the average SNR degradation due to the CFO varies according to the gap between average received SNRs for the first and the second hop.