3,650 research outputs found
Location-Quality-aware Policy Optimisation for Relay Selection in Mobile Networks
Relaying can improve the coverage and performance of wireless access
networks. In presence of a localisation system at the mobile nodes, the use of
such location estimates for relay node selection can be advantageous as such
information can be collected by access points in linear effort with respect to
number of mobile nodes (while the number of links grows quadratically).
However, the localisation error and the chosen update rate of location
information in conjunction with the mobility model affect the performance of
such location-based relay schemes; these parameters also need to be taken into
account in the design of optimal policies. This paper develops a Markov model
that can capture the joint impact of localisation errors and inaccuracies of
location information due to forwarding delays and mobility; the Markov model is
used to develop algorithms to determine optimal location-based relay policies
that take the aforementioned factors into account. The model is subsequently
used to analyse the impact of deployment parameter choices on the performance
of location-based relaying in WLAN scenarios with free-space propagation
conditions and in an measurement-based indoor office scenario.Comment: Accepted for publication in ACM/Springer Wireless Network
Splitting Algorithms for Fast Relay Selection: Generalizations, Analysis, and a Unified View
Relay selection for cooperative communications promises significant
performance improvements, and is, therefore, attracting considerable attention.
While several criteria have been proposed for selecting one or more relays,
distributed mechanisms that perform the selection have received relatively less
attention. In this paper, we develop a novel, yet simple, asymptotic analysis
of a splitting-based multiple access selection algorithm to find the single
best relay. The analysis leads to simpler and alternate expressions for the
average number of slots required to find the best user. By introducing a new
`contention load' parameter, the analysis shows that the parameter settings
used in the existing literature can be improved upon. New and simple bounds are
also derived. Furthermore, we propose a new algorithm that addresses the
general problem of selecting the best relays, and analyze and
optimize it. Even for a large number of relays, the algorithm selects the best
two relays within 4.406 slots and the best three within 6.491 slots, on
average. We also propose a new and simple scheme for the practically relevant
case of discrete metrics. Altogether, our results develop a unifying
perspective about the general problem of distributed selection in cooperative
systems and several other multi-node systems.Comment: 20 pages, 7 figures, 1 table, Accepted for publication in IEEE
Transactions on Wireless Communication
Sidelobe Control in Collaborative Beamforming via Node Selection
Collaborative beamforming (CB) is a power efficient method for data
communications in wireless sensor networks (WSNs) which aims at increasing the
transmission range in the network by radiating the power from a cluster of
sensor nodes in the directions of the intended base station(s) or access
point(s) (BSs/APs). The CB average beampattern expresses a deterministic
behavior and can be used for characterizing/controling the transmission at
intended direction(s), since the mainlobe of the CB beampattern is independent
on the particular random node locations. However, the CB for a cluster formed
by a limited number of collaborative nodes results in a sample beampattern with
sidelobes that severely depend on the particular node locations. High level
sidelobes can cause unacceptable interference when they occur at directions of
unintended BSs/APs. Therefore, sidelobe control in CB has a potential to
increase the network capacity and wireless channel availability by decreasing
the interference. Traditional sidelobe control techniques are proposed for
centralized antenna arrays and, therefore, are not suitable for WSNs. In this
paper, we show that distributed, scalable, and low-complexity sidelobe control
techniques suitable for CB in WSNs can be developed based on node selection
technique which make use of the randomness of the node locations. A node
selection algorithm with low-rate feedback is developed to search over
different node combinations. The performance of the proposed algorithm is
analyzed in terms of the average number of trials required to select the
collaborative nodes and the resulting interference. Our simulation results
approve the theoretical analysis and show that the interference is
significantly reduced when node selection is used with CB.Comment: 30 pages, 10 figures, submitted to the IEEE Trans. Signal Processin
ALOHA With Collision Resolution(ALOHA-CR): Theory and Software Defined Radio Implementation
A cross-layer scheme, namely ALOHA With Collision Resolution (ALOHA-CR), is
proposed for high throughput wireless communications in a cellular scenario.
Transmissions occur in a time-slotted ALOHA-type fashion but with an important
difference: simultaneous transmissions of two users can be successful. If more
than two users transmit in the same slot the collision cannot be resolved and
retransmission is required. If only one user transmits, the transmitted packet
is recovered with some probability, depending on the state of the channel. If
two users transmit the collision is resolved and the packets are recovered by
first over-sampling the collision signal and then exploiting independent
information about the two users that is contained in the signal polyphase
components. The ALOHA-CR throughput is derived under the infinite backlog
assumption and also under the assumption of finite backlog. The contention
probability is determined under these two assumptions in order to maximize the
network throughput and maintain stability. Queuing delay analysis for network
users is also conducted. The performance of ALOHA-CR is demonstrated on the
Wireless Open Access Research Platform (WARP) test-bed containing five software
defined radio nodes. Analysis and test-bed results indicate that ALOHA-CR leads
to significant increase in throughput and reduction of service delays
A Comprehensive Analysis of Literature Reported Mac and Phy Enhancements of Zigbee and its Alliances
Wireless communication is one of the most required technologies by the common man. The strength of this technology is rigorously progressing towards several novel directions in establishing personal wireless networks mounted over on low power consuming systems. The cutting-edge communication technologies like bluetooth, WIFI and ZigBee significantly play a prime role to cater the basic needs of any individual. ZigBee is one such evolutionary technology steadily getting its popularity in establishing personal wireless networks which is built on small and low-power digital radios. Zigbee defines the physical and MAC layers built on IEEE standard. This paper presents a comprehensive survey of literature reported MAC and PHY enhancements of ZigBee and its contemporary technologies with respect to performance, power consumption, scheduling, resource management and timing and address binding. The work also discusses on the areas of ZigBee MAC and PHY towards their design for specific applications
Entrepreneurship in the Netherlands; SMEs and International co-operation
This is the seventh edition of the series 'Entrepreneurship in the Netherlands'. The series started in 1997 and is a joint publication of the Netherlands Ministry of Economic Affairs and EIM Business & Policy Research. This edition deals with international cooperation of SMEs. The first Chapter by EIM describes characteristics of international cooperation: why, how and with what type of effects? Thereafter staff members of the Ministry sketch the aims and the ambition of policy instruments in the field. As practical illustrations three enterprises haven been portrayed. In addition to authors from EIM and the Ministry of Economic Affairs, three staff members working on internationalisation and entrepreneurship at the Nottingham University Business school in UK, reflect on the issues covered in this publication by presenting and commenting on ten myths that surround the internationalisation of smaller private firms.
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