4,507 research outputs found
A New Class of Multiple-rate Codes Based on Block Markov Superposition Transmission
Hadamard transform~(HT) as over the binary field provides a natural way to
implement multiple-rate codes~(referred to as {\em HT-coset codes}), where the
code length is fixed but the code dimension can be varied from
to by adjusting the set of frozen bits. The HT-coset codes, including
Reed-Muller~(RM) codes and polar codes as typical examples, can share a pair of
encoder and decoder with implementation complexity of order .
However, to guarantee that all codes with designated rates perform well,
HT-coset coding usually requires a sufficiently large code length, which in
turn causes difficulties in the determination of which bits are better for
being frozen. In this paper, we propose to transmit short HT-coset codes in the
so-called block Markov superposition transmission~(BMST) manner. At the
transmitter, signals are spatially coupled via superposition, resulting in long
codes. At the receiver, these coupled signals are recovered by a sliding-window
iterative soft successive cancellation decoding algorithm. Most importantly,
the performance around or below the bit-error-rate~(BER) of can be
predicted by a simple genie-aided lower bound. Both these bounds and simulation
results show that the BMST of short HT-coset codes performs well~(within one dB
away from the corresponding Shannon limits) in a wide range of code rates
Symbol error rate analysis for M-QAM modulated physical-layer network coding with phase errors
Recent theoretical studies of physical-layer network coding (PNC) show much interest on high-level modulation, such as M-ary quadrature amplitude modulation (M-QAM), and most related works are based on the assumption of phase synchrony. The possible presence of synchronization error and channel estimation error highlight the demand of analyzing the symbol error rate (SER) performance of PNC under different phase errors. Assuming synchronization and a general constellation mapping method, which maps the superposed signal into a set of M coded symbols, in this paper, we analytically derive the SER for M-QAM modulated PNC under different phase errors. We obtain an approximation of SER for general M-QAM modulations, as well as exact SER for quadrature phase-shift keying (QPSK), i.e. 4-QAM. Afterwards, theoretical results are verified by Monte Carlo simulations. The results in this paper can be used as benchmarks for designing practical systems supporting PNC. © 2012 IEEE
PSR B0809+74: Understanding Its Perplexing Subpulse-separation (P2) Variations
The longitude separation between adjacent drifting subpulses, , is
roughly constant for many pulsars. It was then perplexing when pulsar B0809+74
was found to exhibit substantial variations in this measure, both with
wavelength and with longitude position within the pulse window. We analyze
these variations between 40 and 1400 MHz, and we show that they stem primarily
from the incoherent superposition of the two orthogonal modes of polarization.Comment: Submitted for publication Astronomy and Astrophysic
Construction of Capacity-Achieving Lattice Codes: Polar Lattices
In this paper, we propose a new class of lattices constructed from polar
codes, namely polar lattices, to achieve the capacity \frac{1}{2}\log(1+\SNR)
of the additive white Gaussian-noise (AWGN) channel. Our construction follows
the multilevel approach of Forney \textit{et al.}, where we construct a
capacity-achieving polar code on each level. The component polar codes are
shown to be naturally nested, thereby fulfilling the requirement of the
multilevel lattice construction. We prove that polar lattices are
\emph{AWGN-good}. Furthermore, using the technique of source polarization, we
propose discrete Gaussian shaping over the polar lattice to satisfy the power
constraint. Both the construction and shaping are explicit, and the overall
complexity of encoding and decoding is for any fixed target error
probability.Comment: full version of the paper to appear in IEEE Trans. Communication
Ramsey interference with single photons
Interferometry using discrete energy levels in nuclear, atomic or molecular
systems is the foundation for a wide range of physical phenomena and enables
powerful techniques such as nuclear magnetic resonance, electron spin
resonance, Ramsey-based spectroscopy and laser/maser technology. It also plays
a unique role in quantum information processing as qubits are realized as
energy superposition states of single quantum systems. Here, we demonstrate
quantum interference of different energy states of single quanta of light in
full analogy to energy levels of atoms or nuclear spins and implement a Ramsey
interferometer with single photons. We experimentally generate energy
superposition states of a single photon and manipulate them with unitary
transformations to realize arbitrary projective measurements, which allows for
the realization a high-visibility single-photon Ramsey interferometer. Our
approach opens the path for frequency-encoded photonic qubits in quantum
information processing and quantum communication.Comment: 16 page
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