1,721,037 research outputs found
A Comparison of Pilot-Aided Channel Estimation Methods for OFDM Systems
No full textThis paper deals with the estimation of the channel impulse response (CIR) in orthogonal frequency division multiplexed (OFDM) systems. In particular, we focus on two pilot-aided schemes: the maximum likelihood estimator (MLE) and the Bayesian minimum mean square error estimator (MMSEE). The advantage of the former is that it is simpler to implement as it needs no information on the channel statistics. On the other hand, the MMSEE is expected to have better performance as it exploits prior information about the channel. Theoretical analysis and computer simulations are used in the comparisons. At SNR values of practical interest, the two schemes are found to exhibit nearly equal performance, provided that the number of pilot tones is sufficiently greater than the CIRs length. Otherwise, the MMSEE is superior. In any case, the MMSEE is more complex to implement
Joint Frequency and Timing Recovery for MSK-Type Modulation
No full textWe investigate a novel nondata-aided method for jointly estimating timing and carrier frequency offset in MSK-type modulation. The algorithm has a feedforward structure and lends itself to a simple digital implementation. Its estimation accuracy depends on a design parameter that may be varied to trade performance for computational complexity. Setting the parameter to unity yields a synchronization scheme already known in the literature. Computer simulations are used to assess the synchronizer performance on AWGN Rayleigh fading channels with MSK and Gaussian MSK modulation
Carrier-Frequency Estimation for Transmissions over Selective Channels
No full textThis paper deals with carrier-frequency estimation
for burst transmissions over frequency-selective channels. Three
estimation schemes are proposed, all based on the use of known
training sequences. The first scheme employs an arbitrary sequence
and provides joint maximum-likelihood (ML) estimates
of the carrier frequency and the channel response. Its implementation
complexity is relatively high but its accuracy achieves
the Cramer–Rao bound. The second scheme is still based on
the ML criterion, but the training sequence is periodic, which
helps to reduce the computational load. The third scheme also
employs periodic sequences, but its structure comes from heuristic
reasoning. Theoretical analysis and simulations are employed to
assess the performance of the three schemes
Code-multiplexed UWB Transmitted-Reference Radio
No full textIn traditional transmitted reference (TR) ultrawideband
systems the reference component is time-shifted and
orthogonal relative to the data-bearing signal. This paves the
way to a correlation receiver in which the local template is
derived from the incoming waveform using a delay line. As analog
delay lines are difficult to implement with current technology,
an alternative TR system has recently been proposed in which
reference and data components are made orthogonal by a
frequency shift rather than a time shift. The resulting receiver
has no delay lines and has better performance compared to
the traditional scheme. In the present paper we discuss a third
way to achieve orthogonality, i.e., by modulating reference and
data components with two distinct code sequences. Even in this
case the receiver has no delay lines. However, it is simpler to
implement and has better performance than the frequency-shift
based receiver
Frame Frequency Estimation in Ultra-Wideband Communications
No full textThis paper investigates the estimation of the frame
frequency in ultrawideband (UWB) communication systems. An
estimation method is proposed that exploits the transmission of a
periodic pulse sequence at the frame frequency. The samples of
the received waveform are used to compute a cost function that
depends on a trial value of the incoming pulse frequency. The
location of the maximum provides an estimate of the transmitted
frequency. The performance of the estimator is assessed theoretically
and is compared to the Cramer–Rao lower bound. It is shown
that in certain conditions the estimator achieves the bound at high
SNR values. Simulations validate the theory and show the degradations
in the estimation performance caused by multiple-access
interference. They also give an idea of the estimation accuracy
needed in a correlation receiver
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