Abstract
In this thesis the performance of selected carrier frequency offset
(CFO) estimators is studied in an ultrawideband (UWB) slow frequencyhopping
orthogonal frequency division multiplexing (FHOFDM) system. A challenge in a
very high data rate FHOFDM system is to minimize self interference such as
intercarrier interference (ICI) and constellation rotation due to the CFO
under several nonidealities. Various transmission techniques are first
represented emphasising UWB transmission, orthogonal frequency division
multiplexing (OFDM), frequencyhopping spread spectrum (FHSS) and the
combination of these schemes. The synchronization requirements in wireless
communications are considered next, followed by the review of the existing CFO
estimation methods. After presenting the characteristics of the target
system model the simulation results are shown with the appropriate analysis.
First, the basic algorithms from each defined estimation category are compared
in additive white Gaussian noise (AWGN) channel. The effects of nonidealities
in despreading the frequencyhopped signal are considered next in a
frequencyselective fading channel. The nonidealities may introduce a residual
frequencyhopping timing offset (FHO) and phase offset (PHO) due to the
nonideal hoptiming estimator, frequencyhopping synthesiser and
frequencyselective channel. The main class of the studied CFO estimators is
based on the autocorrelation of the received samples. The algorithms have two
parameters to adjust for mitigating the noise. These include an averaging
length and a distance between correlative samples.
The simulation results indicate the kind of hop timing estimator, preamble
structure, frequencyhopping synthesiser and signaltonoise ratio (SNR)
operation point that are required before the CFO estimation can be performed
with the given estimators. Simulations show that Lank’s CFO estimator is
suitable for the target scenario and requirements when using relatively high
SNR. For the lower SNR operation points Fitz’s, Luise’s or Mengali’s
algorithms give better performance at the cost of increased complexity or
reduced estimation range. Furthermore, the CFO estimators are quite robust to
the FHO less than half the hopping duration, which causes a slight increase in
standard deviation. It is shown that this degradation can be compensated
using the CFO algorithm itself and utilizing the available preamble. The
estimators are, however, sensitive to the PHO caused by the possible lack of
phase memory in the frequencyhopping synthesizer or frequencyselective
channel, resulting in a significant bias to the CFO estimate.
Original language  English 

Qualification  Licentiate Degree 
Awarding Institution 

Place of Publication  Oulu 
Publisher  
Publication status  Published  2005 
MoE publication type  G3 Licentiate thesis 
Keywords
 Nonideal frequency synthesiser
 multicarrier modulation
 performance analysis
 timing offset
 phase memory
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Cite this
Anttonen, A. (2005). Carrier frequency offset estimation in a frequencyhopping ultrawideband OFDM system: Licenciate thesis. University of Oulu.