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Emerging applications like distributed coordinated beamforming (DCB), intelligent reflector arrays, and networked robotic devices will transform wireless applications. However, for systems-centric work on these topics, the research community must first overcome the hurdle of implementing fine-grained, over-the-air timing synchronization, which is critical for any coordinated operation. To address this gap, this paper presents an open-source design and implementation of 'RFClock' that provides timing, frequency and phase synchronization for software defined radios (SDRs). It shows how RFClock can be used for a practical, 5-node DCB application without modifying existing physical/link layer protocols. By utilizing a leader-follower architecture, RFClock-leader allows follower clocks to synchronize with mean offset under 0.107Hz, and then corrects the time/phase alignment to be within a 5ns deviation. RFClock is designed to operate in generalized environments: as standalone unit, it generates a 10MHz/1PPS signal reference suitable for most commercial-off-the-shelf (COTS) SDRs today; it does not require custom protocol-specific headers or messaging; and it is robust to interference through a frequency-agile operation. Using RFClock for DCB, we verify significant increase in channel gain and low BER in a range of [0 -- 10--3] for different modulation schemes. We also demonstrate performance that is similar to a popular wired solution and significant improvement over a GPS-based solution, while delivering this functionality at a fractional price/power point.Keywords:
Carrier frequency offset
Preamble
Carrier frequency offset
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OFDM is a practical and efficient modulation technology. Frequency synchronization for OFDM is very important because the carrier frequency offset (CFO) will damage the performance. Based on the correlation between the front half-symbol and the back half-symbol, a cost function is deduced which varies with the carrier frequency offset as a sine function, and then a new carrier frequency offset estimation algorithm is presented. The papers will all be in a 2-column format and the final publication will be A4 size
Carrier frequency offset
Sine
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The conventional physical-layer (PHY) security approaches, e.g., transmit beamforming and artificial noise (AN)-based design, may fail when the channels of legitimate user (LU) and eavesdropper (Eve) are close correlated. Due to the highly directional transmission feature of millimeter-wave (mmWave), this may occur in mmWave transmissions as the transmitter, Eve and LU are aligned in the same direction exactly. To handle the PHY security problem with directionally-aligned LU and Eve, we propose a novel frequency diverse array (FDA) beamforming approach to differentiating the LU and Eve. By intentionally introducing some frequency offsets across the antennas, the FDA beamforming generates an angle-range dependent beampattern. As a consequence, it can degrade the Eve's reception and thus achieve PHY security. In this paper, we maximize the secrecy rate by jointly optimizing the frequency offsets and the beamformer. This secrecy rate maximization (SRM) problem is hard to solve due to the tightly coupled variables. Nevertheless, we show that it can be reformulated into a form depending only on the frequency offsets. Building upon this reformulation, we identify some cases where the SRM problem can be optimally solved in closed form. Numerical results demonstrate the efficacy of FDA beamforming in achieving PHY security, even for aligned LU and Eve.
PHY
Artificial Noise
Secure transmission
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In this paper, the impact on carrier capture of high dynamic and low SNR signal in satellite communication caused by the rate of change of the carrier frequency offset is analyzed. Firstly, the existing large carrier frequency offset estimate technology is described. Secondly, the rate of change of the carrier frequency offset impact on the carrier frequency offset is analyzed. Finally, the Doppler shift characteristics of Low SNR high dynamic signal and performance impact on the capture carrier are simulated by MATLAB. The results showed that the rate of change of Doppler shift will seriously affect the number of non-coherent accumulation times of the carrier frequency offset estimate.
Carrier frequency offset
Carrier recovery
Doppler frequency
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A new aspect of carrier frequency offset (CFO) estimation is studied in a frequency-hopping (FH) orthogonal frequency division multiplexing (OFDM) system.Unlike in a traditional nonhopped OFDM system,in FH-OFDM system it is important to verify how accurately frequency-switching must be performed before the CFO estimation can take place with adequate performance.The accuracy of frequency-switching is evaluated through frequency-hopping timing offset (FHO) and frequency-hopping phase offset (PHO) between the received signal and the signal produced by the local frequency-hopping synthesizer of the receiver.The performance of selected autocorrelation algorithms is simulated in multi-path fading channel under the FHO and PHO,and the results are compared with the performance of ideal frequency-switching and the corresponding analytical Cramer-Rao bound.It is found that the CFO estimators based on autocorrelation principle are quite robust to the FHO less than half the hopping period.
Carrier frequency offset
Frequency-hopping spread spectrum
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Abstract In order to address the challenge of carrier blind synchronization and blind demodulation for non-cooperative burst signals, a modification scheme of carrier frequency offset estimation is proposed in this paper. Due to the existence of carrier frequency offset and phase offset, the received signal constellation is circular. In the absence of prior information, a non-data-aided method is adopted to estimate carrier frequency offset of the received signal. Then the loop processing method is used to compensate and correct the carrier frequency offset and phase offset to complete the carrier recovery. Simulation results show that the proposed method has high accuracy in carrier frequency offset and phase offset correction when the signal to noise ratio is close to or higher than that of demodulation. Moreover, it has wide extension in engineering practice.
Carrier frequency offset
Carrier recovery
DC bias
Carrier-to-noise ratio
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A new coarse carrier frequency synchronization algorithm is proposed that can estimate a coarse carrier frequency offset using only two symbols in the frequency domain for orthogonal frequency division multiplexing (OFDM) systems. The problem of conventional carrier frequency synchronization algorithms is that they require many symbols to compensate for a carrier frequency offset when the offset is close to +0.5 or -0.5, where the frequency is normalized to the subcarrier space. In contrast, the proposed algorithm estimates a coarse carrier frequency offset of around +0.5 or -0.5, thereby reducing the remaining carrier frequency offset to within -0.25/spl sim/+0.25. As a result, the proposed algorithm can significantly reduce the time required to synchronize a carrier frequency.
Carrier frequency offset
Frequency deviation
Carrier recovery
Frequency-division multiplexing
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OFDM is one of technology that can be utilized in a variety of telecommunication systems that being widely developed today, for application in LAN, WLAN, 3G, 4G, or 5G. One of the problem faced by the OFDM technology that its sensitivity to Carrier Frequency Offset (CFO) and the lack of synchronization in the OFDM signal. This research aims to design the synchronization that estimates Carrier Frequency Offset (CFO) to obtain synchronization of OFDM signal, where the error of the estimated Carrier Frequency Offset can be obtained, minimized and better than previous studies. The CFO estimation method in this research is using the training symbol on the OFDM symbol and utilize the statistical characteristics of the timing metric. This researchs result shows the Mean Square Error (MSE) of estimated Carrier Frequency Offset to Carrier Frequency Offset input, with range MSE 9.43 x 10-3 at 0 dB SNR input and MSE 1.687 x 10-5 at 30 dB SNR input. If Signal to Noise Ratio is greater, then the value of the mean square error (MSE) will be smaller. The position of the timing metric for timing estimation also affects to CFO estimation. CFO estimation accuracy will be maximized when using maximum timing metric.
Carrier frequency offset
Carrier-to-noise ratio
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OFDM is a practical and efficient modulation technology. Frequency synchronization for OFDM is very important because the carrier frequency offset (CFO) will damage the performance. Based on the correlation between the front half-symbol and the back half-symbol, a cost function is deduced which varies with the carrier frequency offset as a sine function, and then a new carrier frequency offset estimation algorithm is presented. The papers will all be in a 2-column format and the final publication will be A4 size. (5 pages)
Carrier frequency offset
Symbol (formal)
Symbol rate
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This paper discusses the effect of carrier frequency offset on the performance of OFDM communications systems. The sensitivity of OFDM systems to frequency offset compared with single carrier systems is a major disadvantage. In general, Frequency offset is defined as the difference between the nominal frequency and actual output frequency. In OFDM, the uncertainty in carrier frequency, which is due to a difference in the frequencies of the local oscillators in the transmitter and receiver, gives rise to a shift in the frequency domain. This shift is also referred to as frequency offset. The frequency offset disturbs the orthogonality of the sub-carriers and eventually gives rise to lower SNR and ISI which affects the overall performance of the OFDM system. The demodulation of a OFDM signal with an frequency offset in the carrier frequency can cause large bit error rate and it may to make contemptible the performance of a symbol synchronizer. It is therefore important to estimate the frequency offset and minimize/eliminate its impact. In this paper we will study the effects of CFO upon signal to noise ratio (SNR) for an OFDM system, and also estimate the amount of frequency offset. In the first part of paper we discusses Conjugate ICI Cancellation scheme. method for estimating of frequency offset. In second part we will discuss another method i.e Extended Kalman Filtering (EKF) for estimating CFO and then Simulation results illustrate comparison of performance of these two methods for BPSK modulation scheme for different values of frequency offset.
Carrier frequency offset
Symbol rate
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