12,055 research outputs found
Optimal Timer Based Selection Schemes
Timer-based mechanisms are often used to help a given (sink) node select the
best helper node among many available nodes. Specifically, a node transmits a
packet when its timer expires, and the timer value is a monotone non-increasing
function of its local suitability metric. The best node is selected
successfully if no other node's timer expires within a 'vulnerability' window
after its timer expiry, and so long as the sink can hear the available nodes.
In this paper, we show that the optimal metric-to-timer mapping that (i)
maximizes the probability of success or (ii) minimizes the average selection
time subject to a minimum constraint on the probability of success, maps the
metric into a set of discrete timer values. We specify, in closed-form, the
optimal scheme as a function of the maximum selection duration, the
vulnerability window, and the number of nodes. An asymptotic characterization
of the optimal scheme turns out to be elegant and insightful. For any
probability distribution function of the metric, the optimal scheme is
scalable, distributed, and performs much better than the popular inverse metric
timer mapping. It even compares favorably with splitting-based selection, when
the latter's feedback overhead is accounted for.Comment: 21 pages, 6 figures, 1 table, submitted to IEEE Transactions on
Communications, uses stackrel.st
Relay Selection with Network Coding in Two-Way Relay Channels
In this paper, we consider the design of joint network coding (NC)and relay
selection (RS) in two-way relay channels. In the proposed schemes, two users
first sequentially broadcast their respective information to all the relays. We
propose two RS schemes, a single relay selection with NC and a dual relay
selection with NC. For both schemes, the selected relay(s) perform NC on the
received signals sent from the two users and forward them to both users. The
proposed schemes are analyzed and the exact bit error rate (BER) expressions
are derived and verified through Monte Carlo simulations. It is shown that the
dual relay selection with NC outperforms other considered relay selection
schemes in two-way relay channels. The results also reveal that the proposed NC
relay selection schemes provide a selection gain compared to a NC scheme with
no relay selection, and a network coding gain relative to a conventional relay
selection scheme with no NC.Comment: 11 pages, 5 figure
Topology Construction in RPL Networks over Beacon-Enabled 802.15.4
In this paper, we propose a new scheme that allows coupling beacon-enabled
IEEE 802.15.4 with the RPL routing protocol while keeping full compliance with
both standards. We provide a means for RPL to pass the routing information to
Layer 2 before the 802.15.4 topology is created by encapsulating RPL DIO
messages in beacon frames. The scheme takes advantage of 802.15.4 command
frames to solicit RPL DIO messages. The effect of the command frames is to
reset the Trickle timer that governs sending DIO messages. We provide a
detailed analysis of the overhead incurred by the proposed scheme to understand
topology construction costs. We have evaluated the scheme using Contiki and the
instruction-level Cooja simulator and compared our results against the most
common scheme used for dissemination of the upper-layer information in
beacon-enabled PANs. The results show energy savings during the topology
construction phase and in the steady state
Design and analysis of a beacon-less routing protocol for large volume content dissemination in vehicular ad hoc networks
Largevolumecontentdisseminationispursuedbythegrowingnumberofhighquality applications for Vehicular Ad hoc NETworks(VANETs), e.g., the live road surveillance service and the video-based overtaking assistant service. For the highly dynamical vehicular network topology, beacon-less routing protocols have been proven to be efficient in achieving a balance between the system performance and the control overhead. However, to the authors’ best knowledge, the routing design for large volume content has not been well considered in the previous work, which will introduce new challenges, e.g., the enhanced connectivity requirement for a radio link. In this paper, a link Lifetime-aware Beacon-less Routing Protocol (LBRP) is designed for large volume content delivery in VANETs. Each vehicle makes the forwarding decision based on the message header information and its current state, including the speed and position information. A semi-Markov process analytical model is proposed to evaluate the expected delay in constructing one routing path for LBRP. Simulations show that the proposed LBRP scheme outperforms the traditional dissemination protocols in providing a low end-to-end delay. The analytical model is shown to exhibit a good match on the delay estimation with Monte Carlo simulations, as well
DMT Optimal On-Demand Relaying for Mesh Networks
This paper presents a new cooperative MAC (Medium Access Control) protocol called BRIAF (Best Relay based Incremental Amplify-and-Forward). The proposed protocol presents two features: on-demand relaying and selection of the best relay terminal. “On-demand relaying” means that a cooperative transmission is implemented between a source terminal and a destination terminal only when the destination terminal fails in decoding the data transmitted by the source terminal. This feature maximizes the spatial multiplexing gain r of the transmission. “Selection of the best relay terminal” means that a selection of the best relay among a set of (m-1) relay candidates is implemented when a cooperative transmission is needed. This feature maximizes the diversity order d(r) of the transmission. Hence, an optimal DMT (Diversity Multiplexing Tradeoff) curve is achieved with a diversity order d(r) = m(1-r) for 0 ≤ r ≤ 1
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