4,187 research outputs found
On the Design of a Novel Joint Network-Channel Coding Scheme for the Multiple Access Relay Channel
This paper proposes a novel joint non-binary network-channel code for the
Time-Division Decode-and-Forward Multiple Access Relay Channel (TD-DF-MARC),
where the relay linearly combines -- over a non-binary finite field -- the
coded sequences from the source nodes. A method based on an EXIT chart analysis
is derived for selecting the best coefficients of the linear combination.
Moreover, it is shown that for different setups of the system, different
coefficients should be chosen in order to improve the performance. This
conclusion contrasts with previous works where a random selection was
considered. Monte Carlo simulations show that the proposed scheme outperforms,
in terms of its gap to the outage probabilities, the previously published joint
network-channel coding approaches. Besides, this gain is achieved by using very
short-length codewords, which makes the scheme particularly attractive for
low-latency applications.Comment: 28 pages, 9 figures; Submitted to IEEE Journal on Selected Areas in
Communications - Special Issue on Theories and Methods for Advanced Wireless
Relays, 201
The serial harness interacting with a wall
The serial harnesses introduced by Hammersley describe the motion of a
hypersurface of dimension d embedded in a space of dimension . The height
assigned to each site i of Z^d is updated by taking a weighted average of the
heights of some of the neighbors of i plus a ``noise'' (a centered random
variable). The surface interacts by exclusion with a ``wall'' located at level
zero: the updated heights are not allowed to go below zero. We show that for
any distribution of the noise variables and in all dimensions, the surface
delocalizes. This phenomenon is related to the so called ``entropic
repulsion''. For some classes of noise distributions, characterized by their
tail, we give explicit bounds on the speed of the repulsion.Comment: 18 pages. Version almost identical to the one published in SP
On Secure Transmission over Parallel Relay Eavesdropper Channel
We study a four terminal parallel relay-eavesdropper channel which consists
of multiple independent relay-eavesdropper channels as subchannels. For the
discrete memoryless case, we establish inner and outer bounds on the
rate-equivocation region. For each subchannel, secure transmission is obtained
through one of the two coding schemes at the relay: decoding-and-forwarding the
source message or confusing the eavesdropper through noise injection. The inner
bound allows relay mode selection. For the Gaussian model we establish lower
and upper bounds on the perfect secrecy rate. We show that the bounds meet in
some special cases, including when the relay does not hear the source. We
illustrate the analytical results through some numerical examples.Comment: 8 pages, Presented at the Forty-Eighth Annual Allerton Conference on
Communication, Control, and Computing, September 29 - October 1, 2010,
Monticello, IL, US
The microaerophilic microbiota of de-novo paediatric inflammatory bowel disease: the BISCUIT study
<p>Introduction: Children presenting for the first time with inflammatory bowel disease (IBD) offer a unique opportunity to study aetiological agents before the confounders of treatment. Microaerophilic bacteria can exploit the ecological niche of the intestinal epithelium; Helicobacter and Campylobacter are previously implicated in IBD pathogenesis. We set out to study these and other microaerophilic bacteria in de-novo paediatric IBD.</p>
<p>Patients and Methods: 100 children undergoing colonoscopy were recruited including 44 treatment naïve de-novo IBD patients and 42 with normal colons. Colonic biopsies were subjected to microaerophilic culture with Gram-negative isolates then identified by sequencing. Biopsies were also PCR screened for the specific microaerophilic bacterial groups: Helicobacteraceae, Campylobacteraceae and Sutterella wadsworthensis.</p>
<p>Results: 129 Gram-negative microaerophilic bacterial isolates were identified from 10 genera. The most frequently cultured was S. wadsworthensis (32 distinct isolates). Unusual Campylobacter were isolated from 8 subjects (including 3 C. concisus, 1 C. curvus, 1 C. lari, 1 C. rectus, 3 C. showae). No Helicobacter were cultured. When comparing IBD vs. normal colon control by PCR the prevalence figures were not significantly different (Helicobacter 11% vs. 12%, p = 1.00; Campylobacter 75% vs. 76%, p = 1.00; S. wadsworthensis 82% vs. 71%, p = 0.312).</p>
<p>Conclusions: This study offers a comprehensive overview of the microaerophilic microbiota of the paediatric colon including at IBD onset. Campylobacter appear to be surprisingly common, are not more strongly associated with IBD and can be isolated from around 8% of paediatric colonic biopsies. S. wadsworthensis appears to be a common commensal. Helicobacter species are relatively rare in the paediatric colon.</p>
Densities of primes and realization of local extensions
In this paper we introduce new densities on the set of primes of a number
field. If is a Galois extension of number fields, we associate to any
element a density on primes of
. In particular, the density associated to is the usual Dirichlet
density on . After establishing some properties of these densities, we use
them to show that the maximal solvable extension of a number field unramified
outside an almost Chebotarev set realize the maximal local extension at each
prime lying outside this set.Comment: 19 pages; the main theorem appears now in a slightly generalized
version compared to v1. A section recalling stable sets is added. Several
small corrections are mad
Computationally Tractable Algorithms for Finding a Subset of Non-defective Items from a Large Population
In the classical non-adaptive group testing setup, pools of items are tested
together, and the main goal of a recovery algorithm is to identify the
"complete defective set" given the outcomes of different group tests. In
contrast, the main goal of a "non-defective subset recovery" algorithm is to
identify a "subset" of non-defective items given the test outcomes. In this
paper, we present a suite of computationally efficient and analytically
tractable non-defective subset recovery algorithms. By analyzing the
probability of error of the algorithms, we obtain bounds on the number of tests
required for non-defective subset recovery with arbitrarily small probability
of error. Our analysis accounts for the impact of both the additive noise
(false positives) and dilution noise (false negatives). By comparing with the
information theoretic lower bounds, we show that the upper bounds on the number
of tests are order-wise tight up to a factor, where is the number
of defective items. We also provide simulation results that compare the
relative performance of the different algorithms and provide further insights
into their practical utility. The proposed algorithms significantly outperform
the straightforward approaches of testing items one-by-one, and of first
identifying the defective set and then choosing the non-defective items from
the complement set, in terms of the number of measurements required to ensure a
given success rate.Comment: In this revision: Unified some proofs and reorganized the paper,
corrected a small mistake in one of the proofs, added more reference
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