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Blind Timing Synchronization for OFDM Systems in Multipath Fading ChannelsChen, Wei-hsiang 23 August 2010 (has links)
In this thesis, a blind symbol timing synchronization algorithm based on cyclic prefix for OFDM systems in multipath fading channels is proposed. It finds the starting point of symbol timing for using appropriate weights which are designed from channel delay spread characteristics. In multipath fading channels, the conventional ML (maximum likelihood) algorithm estimate is biased and has a large variance due to the effect of channel delay spread. The proposed exponential weighting methods not only solve the above problems but also improve the accuracy of symbol timing. Particularly, the proposed method does not require the information of SNR and channel length. From computer simulation results, the proposed method outperforms the other conventional algorithms and is also robust against the effect of multipath fading channels.
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New advances in symbol timing synchronization of single-carrier, multi-carrier and space-time multiple-antenna systemsWu, Yik Chung 01 November 2005 (has links)
In this dissertation, the problem of symbol timing synchronization for the following three different communication systems is studied: 1) conventional single-carrier
transmissions with single antenna in both transmitter and receiver; 2) single-carrier
transmissions with multiple antennas at both transmitter and receiver; and 3) orthogonal frequency division multiplexing (OFDM) based IEEE 802.11a wireless local
area networks (WLANs).
For conventional single-carrier, single-antenna systems, a general feedforward
symbol-timing estimation framework is developed based on the conditional maximum
likelihood principle. The proposed algorithm is applied to linear modulations and two
commonly used continuous phase modulations: MSK and GMSK. The performance
of the proposed estimator is analyzed analytically and via simulations.
Moreover, using the newly developed general estimation framework, all the previously proposed digital blind feedforward symbol timing estimators employing second-order statistics are cast into a unified framework. The finite sample mean-square
error expression for this class of estimators is established and the best estimators are
determined. Simulation results are presented to corroborate the analytical results.
Moving on to single-carrier, multiple-antenna systems, we present two algorithms. The first algorithm is based on a heuristic argument and it improves the
optimum sample selection algorithm by Naguib et al. so that accurate timing estimates can be obtained even if the oversampling ratio is small. The performance of
the proposed algorithm is analyzed both analytically and via simulations.
The second algorithm is based on the maximum likelihood principle. The data
aided (DA) and non-data aided (NDA) ML symbol timing estimators and their cor-
responding CCRB and MCRB in MIMO correlated ??at-fading channels are derived.
It is shown that the improved algorithm developed based on the heuristic argument
is just a special case of the DA ML estimator. Simulation results under different
operating conditions are given to assess and compare the performances of the DA
and NDA ML estimators with respect to their corresponding CCRBs and MCRBs.
In the last part of this dissertation, the ML timing synchronizer for IEEE 802.11a
WLANs on frequency-selective fading channels is developed. The proposed algorithm
is compared with four of the most representative timing synchronization algorithms,
one specically designed for IEEE 802.11a WLANs and three other algorithms designed for general OFDM frame synchronization.
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Polyphase Symbol Timing Synchronization on a Software-Defined RadioLundberg, Georg January 2021 (has links)
Software-defined radio is a continuously developing technology applied in fields of mobile communications and among others. It is a radio communication system where software is used to implement parts of its functionality in an embedded system or computer. Devices which can transmit and receive different radio protocols based on software has major advantages. The ability to be able to reconfigure and change functionality on the fly to adapt to different environments is suited for multiple different applications, one of such is the environment in space. Distortions such as phase, frequency and timing offset all occur in such environment. The effects of these distortions can be reduced using different synchronization techniques in the receiver. A polyphase symbol timing synchronizer with two different timing error detectors, is designed in Simulink consisting of an 8-tap polyphase filter bank, a zero-crossing or Gardner timing error detector, a second order Phase-locked loop and a numerically controlled oscillator. The initial design uses floating-point precision. A fixed-point model is implemented using Xilinx System Generator and is used to generate a custom IP. Simulation is done by implementing a transceiver model with Simulink for the transmitter and parts of the receiver. The polyphase symbol timing synchronizer locks after about 4000 symbols for lower signal-to-noise and the Gardner timing error detector performs better than the zero-crossing error detector at higher signal-to-noise ratios.
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Multiuser communications over frequency selective wired channels and applications to the powerline access networkSartenaer, Thierry 14 September 2004 (has links)
The low-voltage power distribution network is considered today as a serious
candidate to provide residential customers with a high-speed access to
communication services such as Internet. Outdoor Power-Line Communications
(PLC) systems represent an alternative to the other classical 'last-mile
solutions' such as ADSL, cable modems, or wireless access systems.
We developed an accurate powerline channel simulation tool based on the Multiconductor
Transmission Line theory. This tool is able to predict the end-to-end channel
responses on the basis of the multiconductor cable structure and the network topology.
Then the issue of optimal resource allocation in a multiuser environment was
addressed in the light of the Multiuser Information Theory. Simultaneously active
users are in competition for the limited resources that are the power
(constrained by electro-magnetic compatibility restrictions) and the bandwidth
(in the range of 1 to 10 MHz for outdoor PLC). The concept of multiuser balanced capacity was
introduced to characterize the optimal resource allocation providing the
maximum data rates with fairness constraints among the subscribers.
The optimal PLC system was shown to require the shaping of the signal spectrum
in the transmitters, and successive decoding in the receiver. A generic multiple access scheme based on
Filter Banks (FB) was proposed, which offers the required spectral shaping with limited degrees of freedom.
Classical multiple-access techniques (TDMA, CDMA, OFDMA) can be obtained by selecting the
appropriate FB. The Minimum-Mean-Square-Error Decision-Feedback Joint Detector
was shown to approach the performance of the optimal successive decoding
receiver. Finally, the robustness of the proposed system against channel estimation and
timing synchronization errors was addressed. The problem of multiuser timing
synchronization was introduced, and practical multiuser timing error detectors
were proposed.
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Analysis Of Time Synchronization Errors In High Data Rate UltrawidebanBates, Lakesha 01 January 2004 (has links)
Emerging Ultra Wideband (UWB) Orthogonal Frequency Division Multiplexing (OFDM) systems hold the promise of delivering wireless data at high speeds, exceeding hundreds of megabits per second over typical distances of 10 meters or less. The purpose of this Thesis is to estimate the timing accuracies required with such systems in order to achieve Bit Error Rates (BER) of the order of magnitude of 10-12 and thereby avoid overloading the correction of irreducible errors due to misaligned timing errors to a small absolute number of bits in error in real-time relative to a data rate of hundreds of megabits per second. Our research approach involves managing bit error rates through identifying maximum timing synchronization errors. Thus, it became our research goal to determine the timing accuracies required to avoid operation of communication systems within the asymptotic region of BER flaring at low BERs in the resultant BER curves. We propose pushing physical layer bit error rates to below 10-12 before using forward error correction (FEC) codes. This way, the maximum reserve is maintained for the FEC hardware to correct for burst as well as recurring bit errors due to corrupt bits caused by other than timing synchronization errors.
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