1,781 research outputs found
New advances in symbol timing synchronization of single-carrier, multi-carrier and space-time multiple-antenna systems
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
Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems
Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER
Blind Estimation of Multiple Carrier Frequency Offsets
Multiple carrier-frequency offsets (CFO) arise in a distributed antenna
system, where data are transmitted simultaneously from multiple antennas. In
such systems the received signal contains multiple CFOs due to mismatch between
the local oscillators of transmitters and receiver. This results in a
time-varying rotation of the data constellation, which needs to be compensated
for at the receiver before symbol recovery. This paper proposes a new approach
for blind CFO estimation and symbol recovery. The received base-band signal is
over-sampled, and its polyphase components are used to formulate a virtual
Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system
estimation techniques, the system response is estimated and used to
subsequently transform the multiple CFOs estimation problem into many
independent single CFO estimation problems. Furthermore, an initial estimate of
the CFO is obtained from the phase of the MIMO system response. The Cramer-Rao
Lower bound is also derived, and the large sample performance of the proposed
estimator is compared to the bound.Comment: To appear in the Proceedings of the 18th Annual IEEE International
Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC),
Athens, Greece, September 3-7, 200
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
Synchronisation Issues in Non-coherent MIMO Systems
In this article, we identify some of the key problems that may be encountered when designing Non-Coherent (NC) Multiple-Input Multiple-Output (MIMO) DownLink (DL) synchronisation schemes for communicating over multi-path fading channels. Our main objectives are to illustrate the information theoretic features and to provide design guidelines for the initial synchronisation of NC MIMO systems. We conclude by outlining the relationships between the beneficial and detrimental design factors
Synchronization in wireless communications
The last decade has witnessed an immense increase of wireless communications services in order to keep pace with the ever increasing demand for higher data rates combined with higher mobility. To satisfy this demand for higher data rates, the throughput over the existing transmission media had to be increased. Several techniques were proposed to boost up the data rate: multicarrier systems to combat selective fading, ultra wide band (UWB) communications systems to share the spectrum with other users, MIMO transmissions to increase the capacity of wireless links, iteratively decodable codes (e.g., turbo codes and LDPC codes) to improve the quality of the link, cognitive radios, and so forth
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