234,168 research outputs found
A note on implementing combining networks
In shared-memory multiprocessors, combining networks serve to eliminate hot spots due to concurrent access to the same memory location. Examples are the NYU Ultracomputer, the IBM RP3 and the Fluent Machine. We present a problem that occurs when one tries to implement the Fluent Machine`s network nodes with network chips that do not know their position within the network. We formulate the problem mathematically and present two solutions. The first solution requires some additional hardware around nodes that can be put outside network chips. The second solution requires a minor modification of the routing algorithm, but one can prove that there is no performance loss
On the Stability of Isolated and Interconnected Input-Queued Switches under Multiclass Traffic
In this correspondence, we discuss the stability of scheduling algorithms for input-queueing (IQ) and combined input/output queueing (CIOQ) packet switches. First, we show that a wide class of IQ schedulers operating on multiple traffic classes can achieve 100 % throughput. Then, we address the problem of the maximum throughput achievable in a network of interconnected IQ switches and CIOQ switches loaded by multiclass traffic, and we devise some simple scheduling policies that guarantee 100 % throughput. Both the Lyapunov function methodology and the fluid modeling approach are used to obtain our results
Splitting algorithm for DMT optimal cooperative MAC protocols in wireless mesh networks
A cooperative protocol for wireless mesh networks is proposed in this paper. The protocol implements both on-demand relaying and a selection of the best relay terminal so only one terminal is relaying the source message when cooperation is needed. Two additional features are also proposed. The best relay is selected with a splitting algorithm. This approach allows fast relay selection within less than three time-slots, on average. Moreover, a pre-selection of relay candidates is performed prior to the splitting algorithm. Only terminals that are able to improve the direct path are pre-selected. So efficient cooperation is now guaranteed. We prove that this approach is optimal in terms of diversity-multiplexing trade-off. The protocol has been designed in the context of Nakagami-mfading channels. Simulation results show that the performance of the splitting algorithm does not depend on channel statistics
On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff
This paper presents access protocols with optimal Diversity-Multiplexing Tradeoff (DMT) performance in the context of IEEE 802.11-based mesh networks. The protocols are characterized by two main features: on-demand cooperation and selection of the best relay terminal. The on-demand characteristic refers to the ability of a destination terminal to ask for cooperation when it fails in decoding the message transmitted by a source terminal. This approach allows maximization of the spatial multiplexing gain. The selection of the best relay terminal allows maximization of the diversity order. Hence, the optimal DMT curve is achieved with these protocols
Enabling controlling complex networks with local topological information
Complex networks characterize the nature of internal/external interactions in real-world systems
including social, economic, biological, ecological, and technological networks. Two issues keep as
obstacles to fulflling control of large-scale networks: structural controllability which describes the
ability to guide a dynamical system from any initial state to any desired fnal state in fnite time, with a
suitable choice of inputs; and optimal control, which is a typical control approach to minimize the cost
for driving the network to a predefned state with a given number of control inputs. For large complex
networks without global information of network topology, both problems remain essentially open.
Here we combine graph theory and control theory for tackling the two problems in one go, using only
local network topology information. For the structural controllability problem, a distributed local-game
matching method is proposed, where every node plays a simple Bayesian game with local information
and local interactions with adjacent nodes, ensuring a suboptimal solution at a linear complexity.
Starring from any structural controllability solution, a minimizing longest control path method can
efciently reach a good solution for the optimal control in large networks. Our results provide solutions
for distributed complex network control and demonstrate a way to link the structural controllability and
optimal control together.The work was partially supported by National Science Foundation of China (61603209), and Beijing Natural Science Foundation (4164086), and the Study of Brain-Inspired Computing System of Tsinghua University program (20151080467), and Ministry of Education, Singapore, under contracts RG28/14, MOE2014-T2-1-028 and MOE2016-T2-1-119. Part of this work is an outcome of the Future Resilient Systems project at the Singapore-ETH Centre (SEC), which is funded by the National Research Foundation of Singapore (NRF) under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. (61603209 - National Science Foundation of China; 4164086 - Beijing Natural Science Foundation; 20151080467 - Study of Brain-Inspired Computing System of Tsinghua University program; RG28/14 - Ministry of Education, Singapore; MOE2014-T2-1-028 - Ministry of Education, Singapore; MOE2016-T2-1-119 - Ministry of Education, Singapore; National Research Foundation of Singapore (NRF) under Campus for Research Excellence and Technological Enterprise (CREATE) programme)Published versio
Hybrid Analog-Digital Precoding Revisited under Realistic RF Modeling
In this paper we revisit hybrid analog-digital precoding systems with
emphasis on their modelling and radio-frequency (RF) losses, to realistically
evaluate their benefits in 5G system implementations. For this, we decompose
the analog beamforming networks (ABFN) as a bank of commonly used RF components
and formulate realistic model constraints based on their S-parameters.
Specifically, we concentrate on fully-connected ABFN (FC-ABFN) and Butler
networks for implementing the discrete Fourier transform (DFT) in the RF
domain. The results presented in this paper reveal that the performance and
energy efficiency of hybrid precoding systems are severely affected, once
practical factors are considered in the overall design. In this context, we
also show that Butler RF networks are capable of providing better performances
than FC-ABFN for systems with a large number of RF chains.Comment: 12 pages, 5 figure
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