2,799 research outputs found
On the Capacity of the Finite Field Counterparts of Wireless Interference Networks
This work explores how degrees of freedom (DoF) results from wireless
networks can be translated into capacity results for their finite field
counterparts that arise in network coding applications. The main insight is
that scalar (SISO) finite field channels over are analogous
to n x n vector (MIMO) channels in the wireless setting, but with an important
distinction -- there is additional structure due to finite field arithmetic
which enforces commutativity of matrix multiplication and limits the channel
diversity to n, making these channels similar to diagonal channels in the
wireless setting. Within the limits imposed by the channel structure, the DoF
optimal precoding solutions for wireless networks can be translated into
capacity optimal solutions for their finite field counterparts. This is shown
through the study of the 2-user X channel and the 3-user interference channel.
Besides bringing the insights from wireless networks into network coding
applications, the study of finite field networks over also
touches upon important open problems in wireless networks (finite SNR, finite
diversity scenarios) through interesting parallels between p and SNR, and n and
diversity.Comment: Full version of paper accepted for presentation at ISIT 201
Performance of wind turbines in a turbulent atmosphere
The effect of atmospheric turbulence on the power fluctuations of large wind turbines was studied. The significance of spatial non-uniformities of the wind is emphasized. The turbulent wind with correlation in time and space is simulated on the computer by Shinozukas method. The wind turbulence is modelled according to the Davenport spectrum with an exponential spatial correlation function. The rotor aerodynamics is modelled by simple blade element theory. Comparison of the spectrum of power output signal between 1-D and 3-D turbulence, shows the significant power fluctuations centered around the blade passage frequency
Construction of Block Orthogonal STBCs and Reducing Their Sphere Decoding Complexity
Construction of high rate Space Time Block Codes (STBCs) with low decoding
complexity has been studied widely using techniques such as sphere decoding and
non Maximum-Likelihood (ML) decoders such as the QR decomposition decoder with
M paths (QRDM decoder). Recently Ren et al., presented a new class of STBCs
known as the block orthogonal STBCs (BOSTBCs), which could be exploited by the
QRDM decoders to achieve significant decoding complexity reduction without
performance loss. The block orthogonal property of the codes constructed was
however only shown via simulations. In this paper, we give analytical proofs
for the block orthogonal structure of various existing codes in literature
including the codes constructed in the paper by Ren et al. We show that codes
formed as the sum of Clifford Unitary Weight Designs (CUWDs) or Coordinate
Interleaved Orthogonal Designs (CIODs) exhibit block orthogonal structure. We
also provide new construction of block orthogonal codes from Cyclic Division
Algebras (CDAs) and Crossed-Product Algebras (CPAs). In addition, we show how
the block orthogonal property of the STBCs can be exploited to reduce the
decoding complexity of a sphere decoder using a depth first search approach.
Simulation results of the decoding complexity show a 30% reduction in the
number of floating point operations (FLOPS) of BOSTBCs as compared to STBCs
without the block orthogonal structure.Comment: 16 pages, 7 figures; Minor changes in lemmas and construction
Synthetic dimensions in ultracold molecules: quantum strings and membranes
Synthetic dimensions alter one of the most fundamental properties in nature,
the dimension of space. They allow, for example, a real three-dimensional
system to act as effectively four-dimensional. Driven by such possibilities,
synthetic dimensions have been engineered in ongoing experiments with ultracold
matter. We show that rotational states of ultracold molecules can be used as
synthetic dimensions extending to many - potentially hundreds of - synthetic
lattice sites. Microwaves coupling rotational states drive fully controllable
synthetic inter-site tunnelings, enabling, for example, topological band
structures. Interactions leads to even richer behavior: when molecules are
frozen in a real space lattice with uniform synthetic tunnelings, dipole
interactions cause the molecules to aggregate to a narrow strip in the
synthetic direction beyond a critical interaction strength, resulting in a
quantum string or a membrane, with an emergent condensate that lives on this
string or membrane. All these phases can be detected using measurements of
rotational state populations.Comment: 5-page article + 4 figures + references; 7 pages + 4 figures in
Supplemen
Reckoning of the Divided Self
Using a personal narrative, this article describes a clinician\u27s journey through a peer-review process after committing a medical error. It strives to identify the limitations of a system that is created to identify medical errors without prioritizing clinician-well being and concludes that a culture of safety needs to acknowledge the humanity and inevitable fallibility of medical providers
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