Comparison of estimators for frequency offset

Wolf, Jochen; Schwartz, J.W.

doi:10.1109/26.46540

Cited by 6 publications

(1 citation statement)

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“…The expression for the mean square error when only N packets are received is shown in Appendix C to be 160.~x 4 E (2) = (vT) Wolf and Schwartz (1990) use the Cramer-Rao bound (see also Sorenson (1980)), to show that the best estimation of the frequency offset (or rate of the time offset) one can have yields a minimum mean square error of…”

Section: Performance Analysis Of the Fi"equency Offset Estimation Methodsmentioning

confidence: 99%

A synchronization algorithm for distributed multimedia environments

1996

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Network synchronization plays a significant role in transmitting multimedia objects over computer networks. Even packets from a single channel must be synchronized due to the problems in a packet switching environment, such as network jitter, frequency, and time offsets. We present an algorithm that determines the set of packets generated periodically by various participants arriving at a node. The basic advantage of the proposed algorithm is that the receiver estimates the reference times (expected arrival times of the packets) and achieves synchronization, without knowledge of the packet delays. The accuracy is improved and the complexity is reduced by predicting the time/frequency offsets between the clocks at the source and the mixer. The error is calculated by the Chernoff bound, demonstrated by simulation, and shown to be acceptable in practical applications.

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Section: Performance Analysis Of the Fi"equency Offset Estimation Methodsmentioning

confidence: 99%

A synchronization algorithm for distributed multimedia environments

1996

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A robust low-complexity estimation technique for frequency-acquisition over frequency-selective channels

Aggarwal¹,

Chien²

1999 IEEE International Conference on Communications (Cat. No. 99CH36311)

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Conventional estimation algorithms utilize either a tone or squarewave in the preamble for frequency estimation. However, such patterns for the preamble sequence are nonoptimal when the channel is frequency selective. Furthermore, the problem is exacerbated for packet-switched systems which require frequency synchronization on a per-packet basis. This paper presents a low complexity frequency estimation algorithm that is robust in frequency selective fading channels. The algorithm is non-decision aided and does not require apriori frame synchronization. Compared against conventional techniques, a factor of 5-10 reduction in BER and a factor of 3 reduction in convergence time are achieved. .O INTRODUCTIONPacket-switched systems such as wireless LANs have evolved over the past few years and are becoming increasingly important to accommodate the rising demand for data services. The current IEEE 802.11 wireless standard which specifies operation in the ISM bands is limited to primarily provide low data rates up to 2 Mbs in an indoor environment. There has been significant effort recently to improve the performance of IEEE 802.11 to provide high data rates up to ten's of megabits per second in more diverse geographic locations (e.g. outdoors) [ l]. As data rates become higher and coverage extends into outdoor environments, the transmission channel quality degrades significantly. This makes it necessary to use additional signal processing such as channel equalization, antenna diversity and adaptive beamforming to get the desired level of performance. Quite often algorithms for these signal processing functions are based on the assumption that some level of synchronization exists on the transmission link. This synchronization may consist of gain control, clock recovery, frame: synchronization and carrier frequency alignment. Under the more severe channel conditions characterized by higher delay spread and faster time variations, conventional synchronization algorithms [3][4][5][6][8] are no longer adequate and need to be redesigned.This paper focuses on the specific problem of frequency synchronization for wireless transmission over frequency selective channels with large delay spreads, typically encountered in the outdoor environment. One of the inherent difficulties in acquiring the frequency stems from the fact that it is generally not possible to do frame synchronization, channel estimation or to demodulate data before the carrier frequencies are aligned. This means that the estimation techniques must be Non-Decision Aided (NDA). To get *Rockwell Science Center Wireless Systems Group Thousand Oaks, CA around the NDA requirement, most algorithms rely on having a preamble at the beginning of the packet which is either a tone or an alternating pattern of ones and zeros [3][41[51[61[81. However, these preamble sequences arc: inadequate for frequency selective channels, especially, for packet-switched systems which require frequency synchronization on every packet. For robust operation in this case, the frequency must be...

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A study of joint tracking algorithms of carrier frequency offset and sampling clock offset for OFDM-based WLANs

Liu

Chong

IEEE 2002 International Conference on Communications, Circuits and Systems and West Sino Expositions

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We present three joint tracking algorithms of carrier frequency and sampling clock offsets for OFDMbased WLAN systems, such as IEEE 802.11a standard. In such systems, one symbol usually contains a few pilots so that the estimation accuracy mid robustness of conventional methods do not satisfv the system requirement. In this paper. three joint tracking algorithms for accurate frequency and sampling estimation are presented. The first method is performed by one-dimensional least square estimation and averaging over L symbols. The second algorithm compares the phase difference of the current symbol with the subsequent D-th symbol and gives better performance, especially when SNR or synchronization offset is smaller. And the third method uses twodimensional linear least square estimation within the frequency aid time domains. Siniulations using these algorithms have been performed with 16-QAM modulation schemes. Simulation results show that tlu-ee algorithms can improve the estimation accuracy and robustness.

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Comparison of estimators for frequency offset

Cited by 6 publications

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A synchronization algorithm for distributed multimedia environments

A synchronization algorithm for distributed multimedia environments

A robust low-complexity estimation technique for frequency-acquisition over frequency-selective channels

A study of joint tracking algorithms of carrier frequency offset and sampling clock offset for OFDM-based WLANs

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