2,058 research outputs found
An Efficient Data-aided Synchronization in L-DACS1 for Aeronautical Communications
L-band Digital Aeronautical Communication System type-1 (L-DACS1) is an
emerging standard that aims at enhancing air traffic management (ATM) by
transitioning the traditional analog aeronautical communication systems to the
superior and highly efficient digital domain. L-DACS1 employs modern and
efficient orthogonal frequency division multiplexing (OFDM) modulation
technique to achieve more efficient and higher data rate in comparison to the
existing aeronautical communication systems. However, the performance of OFDM
systems is very sensitive to synchronization errors. L-DACS1 transmission is in
the L-band aeronautical channels that suffer from large interference and large
Doppler shifts, which makes the synchronization for L-DACS more challenging.
This paper proposes a novel computationally efficient synchronization method
for L-DACS1 systems that offers robust performance. Through simulation, the
proposed method is shown to provide accurate symbol timing offset (STO)
estimation as well as fractional carrier frequency offset (CFO) estimation in a
range of aeronautical channels. In particular, it can yield excellent
synchronization performance in the face of a large carrier frequency offset.Comment: In the proceeding of International Conference on Data Mining,
Communications and Information Technology (DMCIT
Discovery Signal Design and Its Application to Peer-to-Peer Communications in OFDMA Cellular Networks
This paper proposes a unique discovery signal as an enabler of peer-to-peer
(P2P) communication which overlays a cellular network and shares its resources.
Applying P2P communication to cellular network has two key issues: 1.
Conventional ad hoc P2P connections may be unstable since stringent resource
and interference coordination is usually difficult to achieve for ad hoc P2P
communications; 2. The large overhead required by P2P communication may offset
its gain. We solve these two issues by using a special discovery signal to aid
cellular network-supervised resource sharing and interference management
between cellular and P2P connections. The discovery signal, which facilitates
efficient neighbor discovery in a cellular system, consists of un-modulated
tones transmitted on a sequence of OFDM symbols. This discovery signal not only
possesses the properties of high power efficiency, high interference tolerance,
and freedom from near-far effects, but also has minimal overhead. A practical
discovery-signal-based P2P in an OFDMA cellular system is also proposed.
Numerical results are presented which show the potential of improving local
service and edge device performance in a cellular network.Comment: arXiv admin note: text overlap with arXiv:1112.1990, arXiv:1207.0557
add reference in page 5 add text in page 5 for explainatio
Spectrum Monitoring Using Energy Ratio Algorithm For OFDM-Based Cognitive Radio Networks
This paper presents a spectrum monitoring algorithm for Orthogonal Frequency
Division Multiplexing (OFDM) based cognitive radios by which the primary user
reappearance can be detected during the secondary user transmission. The
proposed technique reduces the frequency with which spectrum sensing must be
performed and greatly decreases the elapsed time between the start of a primary
transmission and its detection by the secondary network. This is done by
sensing the change in signal strength over a number of reserved OFDM
sub-carriers so that the reappearance of the primary user is quickly detected.
Moreover, the OFDM impairments such as power leakage, Narrow Band Interference
(NBI), and Inter-Carrier Interference (ICI) are investigated and their impact
on the proposed technique is studied. Both analysis and simulation show that
the \emph{energy ratio} algorithm can effectively and accurately detect the
appearance of the primary user. Furthermore, our method achieves high immunity
to frequency-selective fading channels for both single and multiple receive
antenna systems, with a complexity that is approximately twice that of a
conventional energy detector
Efficient implementation of filter bank multicarrier systems using circular fast convolution
In this paper, filter bank-based multicarrier systems using a fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT-based convolution without overlapped processing, and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. First, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Second, the complexity of the system is significantly reduced as the result of using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out-of-band radiation, orthogonality, spectral efficiency, and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot-based channel estimation technique with controlled transmit power is developed and analyzed through lower-bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks
TS-MUWSN: Time synchronization for mobile underwater sensor networks
Time synchronization is an important, yet challenging, problem in underwater sensor networks (UWSNs). This challenge can be attributed to: 1) messaging timestamping; 2) node mobility; and 3) Doppler scale effect. To mitigate these problems, we present an acoustic-based time-synchronization algorithm for UWSN, where we compare several message time-stamping algorithms in addition to different Doppler scale estimators. A synchronization system is based on a bidirectional message exchange between a reference node and a slave one, which has to be synchronized. Therefore, we take as reference the DA-Sync-like protocol (Liu et al., 2014), which takes into account node's movement by using first-order kinematic equations, which refine Doppler scale factor estimation accuracy, and result in better synchronization performance. In our study, we propose to modify both time-stamping and Doppler scale estimation procedures. Besides simulation, we also perform real tests in controlled underwater communication in a water test tank and a shallow-water test in the Mediterranean Sea.Peer ReviewedPostprint (author's final draft
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
Robust Preamble Design for Synchronization, Signaling Transmission and Channel Estimation
The European second generation digital video broadcasting standard (DVB-T2)
introduces a P1 symbol. This P1 symbol facilitates the coarse synchronization
and carries 7-bit transmission parameter signaling (TPS), including the fast
Fourier transform size, single-input/single-output and
multiple-input/single-output transmission modes, etc. However, this P1 symbol
suffers from obvious performance loss over fading channels. In this paper, an
improved preamble scheme is proposed, where a pair of optimal m sequences are
inserted into the frequency domain. One sequence is used for carrier frequency
offset (CFO) estimation, and the other carries TPS to inform the receiver about
the transmission configuration parameters. Compared with the conventional
preamble scheme, the proposed preamble improves CFO estimation performance and
the signaling capacity. Meanwhile, without additional overhead, the proposed
scheme exploits more active pilots than the conventional schemes. In this way,
it can facilitate the channel estimation, improve the frame synchronization
accuracy as well as enhance its robustness to frequency selective fading
channels.Comment: 8 pages 11 figures.
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7001610&tag=
A Survey on Multicarrier Communications: Prototype Filters, Lattice Structures, and Implementation Aspects
Due to their numerous advantages, communications over multicarrier schemes
constitute an appealing approach for broadband wireless systems. Especially,
the strong penetration of orthogonal frequency division multiplexing (OFDM)
into the communications standards has triggered heavy investigation on
multicarrier systems, leading to re-consideration of different approaches as an
alternative to OFDM. The goal of the present survey is not only to provide a
unified review of waveform design options for multicarrier schemes, but also to
pave the way for the evolution of the multicarrier schemes from the current
state of the art to future technologies. In particular, a generalized framework
on multicarrier schemes is presented, based on what to transmit, i.e., symbols,
how to transmit, i.e., filters, and where/when to transmit, i.e., lattice.
Capitalizing on this framework, different variations of orthogonal,
bi-orthogonal, and nonorthogonal multicarrier schemes are discussed. In
addition, filter design for various multicarrier systems is reviewed
considering four different design perspectives: energy concentration, rapid
decay, spectrum nulling, and channel/hardware characteristics. Subsequently,
evaluation tools which may be used to compare different filters in multicarrier
schemes are studied. Finally, multicarrier schemes are evaluated from the view
of the practical implementation issues, such as lattice adaptation,
equalization, synchronization, multiple antennas, and hardware impairments.Comment: Submitted to IEEE Communications Surveys & Tutorials, 27 pages, 14
figures (main), (First Revision
An OFDM Signal Identification Method for Wireless Communications Systems
Distinction of OFDM signals from single carrier signals is highly important
for adaptive receiver algorithms and signal identification applications. OFDM
signals exhibit Gaussian characteristics in time domain and fourth order
cumulants of Gaussian distributed signals vanish in contrary to the cumulants
of other signals. Thus fourth order cumulants can be utilized for OFDM signal
identification. In this paper, first, formulations of the estimates of the
fourth order cumulants for OFDM signals are provided. Then it is shown these
estimates are affected significantly from the wireless channel impairments,
frequency offset, phase offset and sampling mismatch. To overcome these
problems, a general chi-square constant false alarm rate Gaussianity test which
employs estimates of cumulants and their covariances is adapted to the specific
case of wireless OFDM signals. Estimation of the covariance matrix of the
fourth order cumulants are greatly simplified peculiar to the OFDM signals. A
measurement setup is developed to analyze the performance of the identification
method and for comparison purposes. A parametric measurement analysis is
provided depending on modulation order, signal to noise ratio, number of
symbols, and degree of freedom of the underlying test. The proposed method
outperforms statistical tests which are based on fixed thresholds or empirical
values, while a priori information requirement and complexity of the proposed
method are lower than the coherent identification techniques
Frequency Offset Estimation for OFDM Systems with a Novel Frequency Domain Training Sequence
A novel frequency domain training sequence and the corresponding carrier
frequency offset (CFO) estimator are proposed for orthogonal frequency division
multiplexing (OFDM) systems over frequency-selective fading channels. The
proposed frequency domain training sequence comprises two types of pilot tones,
namely distinctively spaced pilot tones with high energies and uniformly spaced
ones with low energies. Based on the distinctively spaced pilot tones, integer
CFO estimation is accomplished. After the subcarriers occupied by the
distinctively spaced pilot tones and their adjacent subcarriers are nulled for
the sake of interference cancellation, fractional CFO estimation is executed
according to the uniformly spaced pilot tones. By exploiting a predefined
lookup table making the best of the structure of the distinctively spaced pilot
tones, computational complexity of the proposed CFO estimator can be decreased
considerably. With the aid of the uniformly spaced pilot tones generated from
Chu sequence with cyclically orthogonal property, the ability of the proposed
estimator to combat multipath effect is enhanced to a great extent. Simulation
results illustrate the good performance of the proposed CFO estimator.Comment: 11 pages, 9 figures, IEICE Trans. Commun., 200
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