224,965 research outputs found
Mixed Coherent and Non-Coherent Transmission for Multi-CPU Cell-Free Systems
Existing works on cell-free systems consider either coherent or non-coherent
downlink data transmission and a network deployment with a single central
processing unit (CPU). While it is known that coherent transmission outperforms
noncoherent transmission when assuming unlimited fronthaul links, the former
requires a perfect timing synchronization, which is practically not viable over
a large network. Furthermore, relying on a single CPU for geographically large
cell-free networks is not scalable. Thus, to realize the expected gains of
cellfree systems in practice, alternative transmission strategies for realistic
multi-CPU cell-free systems are required. Therefore, this paper proposes a
novel downlink data transmission scheme that combines and generalizes the
existing coherent and non-coherent transmissions. The proposed transmission
scheme, named mixed transmission, works based on the realistic assumption that
only the access points (APs) controlled by a same CPU are synchronized, and
thus transmit in a coherent fashion, while APs from different CPUs require no
synchronism and transmit in a non-coherent manner. We also propose extensions
of existing clustering algorithms for multi-CPU cell-free systems with mixed
transmission. Simulation results show that the combination of the proposed
clustering algorithms with mixed transmission have the potential to perform
close to the ideal coherent transmission.Comment: Submitted for possible publication in IEEE conferenc
Towards generic satellite payloads: software radio
Satellite payloads are becoming much more complex with the evolution towards multimedia applications. Moreover satellite lifetime increases while standard and services evolve faster, necessitating a hardware platform that can evolves for not developing new systems on each change. The same problem occurs in terrestrial systems like mobile networks and a foreseen solution is the software defined radio technology. In this paper we describe a way of introducing this concept at satellite level to offer to operators the required flexibility in the system. The digital functions enabling this technology, the hardware components implementing the functions and the reconfiguration processes are detailed. We show that elements of the software radio for satellites exist and that this concept is feasible
Expanded delta networks for very large parallel computers
In this paper we analyze a generalization of the traditional delta network, introduced by Patel [21], and dubbed Expanded Delta Network (EDN). These networks provide in general multiple paths that can be exploited to reduce contention in the network resulting in increased performance. The crossbar and traditional delta networks are limiting cases of this class of networks. However, the delta network does not provide the multiple paths that the more general expanded delta networks provide, and crossbars are to costly to use for large networks. The EDNs are analyzed with respect to their routing capabilities in the MIMD and SIMD models of computation.The concepts of capacity and clustering are also addressed. In massively parallel SIMD computers, it is the trend to put a larger number processors on a chip, but due to I/O constraints only a subset of the total number of processors may have access to the network. This is introduced as a Restricted Access Expanded Delta Network of which the MasPar MP-1 router network is an example
Real Time Global Tests of the ALICE High Level Trigger Data Transport Framework
The High Level Trigger (HLT) system of the ALICE experiment is an online
event filter and trigger system designed for input bandwidths of up to 25 GB/s
at event rates of up to 1 kHz. The system is designed as a scalable PC cluster,
implementing several hundred nodes. The transport of data in the system is
handled by an object-oriented data flow framework operating on the basis of the
publisher-subscriber principle, being designed fully pipelined with lowest
processing overhead and communication latency in the cluster. In this paper, we
report the latest measurements where this framework has been operated on five
different sites over a global north-south link extending more than 10,000 km,
processing a ``real-time'' data flow.Comment: 8 pages 4 figure
Conversational Sensing
Recent developments in sensing technologies, mobile devices and context-aware
user interfaces have made it possible to represent information fusion and
situational awareness as a conversational process among actors - human and
machine agents - at or near the tactical edges of a network. Motivated by use
cases in the domain of security, policing and emergency response, this paper
presents an approach to information collection, fusion and sense-making based
on the use of natural language (NL) and controlled natural language (CNL) to
support richer forms of human-machine interaction. The approach uses a
conversational protocol to facilitate a flow of collaborative messages from NL
to CNL and back again in support of interactions such as: turning eyewitness
reports from human observers into actionable information (from both trained and
untrained sources); fusing information from humans and physical sensors (with
associated quality metadata); and assisting human analysts to make the best use
of available sensing assets in an area of interest (governed by management and
security policies). CNL is used as a common formal knowledge representation for
both machine and human agents to support reasoning, semantic information fusion
and generation of rationale for inferences, in ways that remain transparent to
human users. Examples are provided of various alternative styles for user
feedback, including NL, CNL and graphical feedback. A pilot experiment with
human subjects shows that a prototype conversational agent is able to gather
usable CNL information from untrained human subjects
A topology-oblivious routing protocol for NDN-VANETs
Vehicular Ad Hoc Networks (VANETs) are characterized by intermittent
connectivity, which leads to failures of end-to-end paths between nodes. Named
Data Networking (NDN) is a network paradigm that deals with such problems,
since information is forwarded based on content and not on the location of the
hosts. In this work, we propose an enhanced routing protocol of our previous
topology-oblivious Multihop, Multipath, and Multichannel NDN for VANETs
(MMM-VNDN) routing strategy that exploits several paths to achieve more
efficient content retrieval. Our new enhanced protocol, i mproved MMM-VNDN
(iMMM-VNDN), creates paths between a requester node and a provider by
broadcasting Interest messages. When a provider responds with a Data message to
a broadcast Interest message, we create unicast routes between nodes, by using
the MAC address(es) as the distinct address(es) of each node. iMMM-VNDN
extracts and thus creates routes based on the MAC addresses from the strategy
layer of an NDN node. Simulation results show that our routing strategy
performs better than other state of the art strategies in terms of Interest
Satisfaction Rate, while keeping the latency and jitter of messages low
Operating-system support for distributed multimedia
Multimedia applications place new demands upon processors, networks and operating systems. While some network designers, through ATM for example, have considered revolutionary approaches to supporting multimedia, the same cannot be said for operating systems designers. Most work is evolutionary in nature, attempting to identify additional features that can be added to existing systems to support multimedia. Here we describe the Pegasus project's attempt to build an integrated hardware and operating system environment from\ud
the ground up specifically targeted towards multimedia
Dissociating word frequency and age of acquisition: The Klein effect revived (and reversed).
The Klein effect (G. S. Klein, 1964) refers to the finding that high-frequency words produce greater interference in a color-naming task than low-frequency words. The present study used the Klein effect to investigate the relationship between frequency and age of acquisition (AoA) by measuring their influence on color naming. Two experiments showed reliable effects of frequency (though in the opposite direction to that reported by Klein) but no effects of AoA. Experiment 1 produced a dissociation between frequency and AoA when manipulated orthogonally. Experiment 2 produced the same dissociation using different stimuli. In contrast, both variables reliably influenced word naming. These findings are inconsistent with the view that frequency and AoA are 2 aspects of a single underlying mechanism
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