3 research outputs found
Coherent Detection of Turbo-Coded OFDM Signals Transmitted through Frequency Selective Rayleigh Fading Channels with Receiver Diversity and Increased Throughput
In this work, we discuss techniques for coherently detecting turbo coded
orthogonal frequency division multiplexed (OFDM) signals, transmitted through
frequency selective Rayleigh (the magnitude of each channel tap is Rayleigh
distributed) fading channels having a uniform power delay profile. The channel
output is further distorted by a carrier frequency and phase offset, besides
additive white Gaussian noise (AWGN). A new frame structure for OFDM,
consisting of a known preamble, cyclic prefix, data and known postamble is
proposed, which has a higher throughput compared to the earlier work. A robust
turbo decoder is proposed, which functions effectively over a wide range of
signal-to-noise ratio (SNR). The key contribution to the good performance of
the practical coherent receiver is due to the use of a long preamble (512 QPSK
symbols), which is perhaps not specified in any of the current wireless
communication standards. We have also shown from computer simulations that, it
is possible to obtain even better BER performance, using a better code. A
simple and approximate Cramer-Rao bound on the variance of the frequency offset
estimation error for coherent detection, is derived. The proposed algorithms
are well suited for implementation on a DSP-platform.Comment: 15 pages, 16 figures, 3 table
An average Cramer-Rao bound for frequency offset estimation in frequency-selective fading channels
Several variations of Cramer-Rao bounds for carrier frequency offset (CFO) estimation in frequency-selective fading channels have been used to benchmark practical estimators’ performance or to design training signals for CFO estimation. Among them, the extended Miller-Chang bound (EMCB) provides a tighter bound than the CRB for locally unbiased estimators. However, there is no closed-form expression of the EMCB for the CFO estimation in frequency-selective fading channels with an arbitrary training signal. In this letter, we derive a closed-form exact average CRB (the EMCB) valid for any training signal and any signal structure for the CFO estimation over frequency-selective Rayleigh fading channels with uncorrelated or arbitrarily correlated taps. The accuracy and generality of the proposed average CRB expression, and its advantages over the existing expressions are corroborated by numerical and simulation results
Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last Five Years
Timing and carrier synchronization is a fundamental requirement for any
wireless communication system to work properly. Timing synchronization is the
process by which a receiver node determines the correct instants of time at
which to sample the incoming signal. Carrier synchronization is the process by
which a receiver adapts the frequency and phase of its local carrier oscillator
with those of the received signal. In this paper, we survey the literature over
the last five years (2010-2014) and present a comprehensive literature review
and classification of the recent research progress in achieving timing and
carrier synchronization in single-input-single-output (SISO),
multiple-input-multiple-output (MIMO), cooperative relaying, and
multiuser/multicell interference networks. Considering both single-carrier and
multi-carrier communication systems, we survey and categorise the timing and
carrier synchronization techniques proposed for the different communication
systems focusing on the system model assumptions for synchronization, the
synchronization challenges, and the state-of-the-art synchronization solutions
and their limitations. Finally, we envision some future research directions.Comment: submitted for journal publicatio