9,670 research outputs found
Multi-Channel Random Access with Replications
This paper considers a class of multi-channel random access algorithms, where
contending devices may send multiple copies (replicas) of their messages to the
central base station. We first develop a hypothetical algorithm that delivers a
lower estimate for the access delay performance within this class. Further, we
propose a feasible access control algorithm achieving low access delay by
sending multiple message replicas, which approaches the performance of the
hypothetical algorithm. The resulting performance is readily approximated by a
simple lower bound, which is derived for a large number of channels.Comment: 5 pages, 2 figures, accepted by ISIT 201
Non-Orthogonal Contention-Based Access for URLLC Devices with Frequency Diversity
We study coded multichannel random access schemes for ultra-reliable
low-latency uplink transmissions. We concentrate on non-orthogonal access in
the frequency domain, where users transmit over multiple orthogonal subchannels
and inter-user collisions limit the available diversity. Two different models
for contention-based random access over Rayleigh fading resources are
investigated. First, a collision model is considered, in which the packet is
replicated onto available resources, of which are received
without collision, and treated as diversity branches by a maximum-ratio
combining (MRC) receiver. The resulting diversity degree depends on the
arrival process and coding strategy. In the second model, the slots subject to
collisions are also used for MRC, such that the number of diversity branches
is constant, but the resulting combined signal is affected by multiple
access interference. In both models, the performance of random and
deterministic repetition coding is compared. The results show that the
deterministic coding approach can lead to a significantly superior performance
when the arrival rate of the intermittent URLLC transmissions is low.Comment: 2019 IEEE 20th International Workshop on Signal Processing Advances
in Wireless Communications (SPAWC) - Special Session on Signal Processing for
NOMA Communication System
Age-Optimal Updates of Multiple Information Flows
In this paper, we study an age of information minimization problem, where
multiple flows of update packets are sent over multiple servers to their
destinations. Two online scheduling policies are proposed. When the packet
generation and arrival times are synchronized across the flows, the proposed
policies are shown to be (near) optimal for minimizing any time-dependent,
symmetric, and non-decreasing penalty function of the ages of the flows over
time in a stochastic ordering sense
Simulation Framework for Cooperative Adaptive Cruise Control with Empirical DSRC Module
Wireless communication plays a vital role in the promising performance of
connected and automated vehicle (CAV) technology. This paper proposes a
Vissim-based microscopic traffic simulation framework with an analytical
dedicated short-range communication (DSRC) module for packet reception. Being
derived from ns-2, a packet-level network simulator, the DSRC probability
module takes into account the imperfect wireless communication that occurs in
real-world deployment. Four managed lane deployment strategies are evaluated
using the proposed framework. While the average packet reception rate is above
93\% among all tested scenarios, the results reveal that the reliability of the
vehicle-to-vehicle (V2V) communication can be influenced by the deployment
strategies. Additionally, the proposed framework exhibits desirable scalability
for traffic simulation and it is able to evaluate transportation-network-level
deployment strategies in the near future for CAV technologies.Comment: 6 pages, 6 figure, 44th Annual Conference of the IEEE Industrial
Electronics Societ
A novel approach to detect hot-spots in large-scale multivariate data
Background: Progressive advances in the measurement of complex multifactorial components of biological processes involving both spatial and temporal domains have made it difficult to identify the variables (genes, proteins, neurons etc.) significantly changed activities in response to a stimulus within large data sets using conventional statistical approaches. The set of all changed variables is
termed hot-spots. The detection of such hot spots is considered to be an NP hard problem, but by first establishing its theoretical foundation we have been able to develop an algorithm that provides a solution.
Results: Our results show that a first-order phase transition is observable whose critical point
separates the hot-spot set from the remaining variables. Its application is also found to be more successful than existing approaches in identifying statistically significant hot-spots both with simulated data sets and in real large-scale multivariate data sets from gene arrays,
electrophysiological recording and functional magnetic resonance imaging experiments.
Conclusion: In summary, this new statistical algorithm should provide a powerful new analytical tool to extract the maximum information from complex biological multivariate data
Trade and synchronization in a multi-country economy
Substantial evidence suggests that countries with stronger trade linkages have more synchro-
nized business cycles. The standard international business cycle framework cannot replicate this
finding, uncovering the trade-comovement puzzle. We show that under certain macro-level conditions but irrespective of the micro-level assumptions concerning trade the puzzle arises because
trade fails to substantially increase the correlation between each country's import penetration
ratio and the trade partner's technology shock. Within a large class of trade models, there
are three channels through which bilateral trade may increase business cycle synchronization.
Specifically, increased bilateral trade may (i) raise the correlation between each country's tech-
nology shocks, (ii) raise the correlation between each country's share of expenditure on domestic
goods, and (iii) raise the response of the domestic import penetration ratio to foreign technology
shocks. Empirical evidence strongly supports the first and second channels. We show that the
trade-comovement puzzle can be resolved if productivity shocks are more correlated between
country-pairs that trade more
The complexity of resolving conflicts on MAC
We consider the fundamental problem of multiple stations competing to
transmit on a multiple access channel (MAC). We are given stations out of
which at most are active and intend to transmit a message to other stations
using MAC. All stations are assumed to be synchronized according to a time
clock. If stations node transmit in the same round, then the MAC provides
the feedback whether , (collision occurred) or . When ,
then a single station is indeed able to successfully transmit a message, which
is received by all other nodes. For the above problem the active stations have
to schedule their transmissions so that they can singly, transmit their
messages on MAC, based only on the feedback received from the MAC in previous
round.
For the above problem it was shown in [Greenberg, Winograd, {\em A Lower
bound on the Time Needed in the Worst Case to Resolve Conflicts
Deterministically in Multiple Access Channels}, Journal of ACM 1985] that every
deterministic adaptive algorithm should take rounds
in the worst case. The fastest known deterministic adaptive algorithm requires
rounds. The gap between the upper and lower bound is
round. It is substantial for most values of : When constant and (for any constant , the lower bound is
respectively and O(n), which is trivial in both cases. Nevertheless,
the above lower bound is interesting indeed when poly(). In this
work, we present a novel counting argument to prove a tight lower bound of
rounds for all deterministic, adaptive algorithms, closing
this long standing open question.}Comment: Xerox internal report 27th July; 7 page
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