We investigate the following fundamental question-how fast can information
     be collected from a wireless sensor network organized as tree? To address
     this, we explore and evaluate a number of different techniques using
     realistic simulation models under the many-to-one communication paradigm
     known as convergecast. We first consider time scheduling on a single
     frequency channel with the aim of minimizing the number of time slots
     required (schedule length) to complete a convergecast. Next, we combine
     scheduling with transmission power control to mitigate the effects of
     interference, and show that while power control helps in reducing the
     schedule length under a single frequency, scheduling transmissions using
     multiple frequencies is more efficient. We give lower bounds on the schedule
     length when interference is completely eliminated, and propose algorithms
     that achieve these bounds. We also evaluate the performance of various
     channel assignment methods and find empirically that for moderate size
     networks of about 100 nodes, the use of multifrequency scheduling can
     suffice to eliminate most of the interference. Then, the data collection rate
     no longer remains limited by interference but by the topology of the routing
     tree. To this end, we construct degree-constrained spanning trees and
     capacitated minimal spanning trees, and show significant improvement in
     scheduling performance over different deployment densities. Lastly, we
     evaluate the impact of different interference and channel models on the
     schedule length.


  This paper addresses the problem of delivering data packets for highly dynamic
  mobile ad hoc networks in a reliable and timely manner. Most existing ad hoc
  routing protocols are susceptible to node mobility, especially for large-scale
  networks. Driven by this issue, we propose an efficient Position-based
  Opportunistic Routing (POR) protocol which takes advantage of the stateless
  property of geographic routing and the broadcast nature of wireless medium.
  When a data packet is sent out, some of the neighbor nodes that have
  overheard the transmission will serve as forwarding candidates, and take turn to
  forward the packet if it is not relayed by the specific best forwarder within a
  certain period of time. By utilizing such in-the-air backup, communication is

maintained without being interrupted. The additional latency incurred by local
route recovery is greatly reduced and the duplicate relaying caused by packet
reroute is also decreased. In the case of communication hole, a Virtual
Destination-based Void Handling (VDVH) scheme is further proposed to work
together with POR. Both theoretical analysis and simulation results show that
POR achieves excellent performance even under high node mobility with
acceptable overhead and the new void handling scheme also works well.

3. ERROR REDUCTION             IN     MULTIPLE-ACCESS         SYSTEMS        BY

   In wireless multiple-access systems, CSMA/CA cannot eliminate packet
   collision completely, especially in the presence of hidden terminals. To
   address the problem, ZigZag decoding was proposed to resolve collisions. In
   this paper, we characterise the probability of decoding failure (due to rank
   deficiency) for a given transmission overhead. We then propose a new
   technique called message wrapping to further reduce the probability of
   decoding error. Our analytical and numerical results both show that errors
   can be significantly reduced by message wrapping.

4. Energy-Efficient Cooperative Video Distribution with Statistical QoS
   Provisions over Wireless Networks

   For real-time video broadcast where multiple users are interested in the
   same content, mobile-to-mobile cooperation can be utilized to improve
   delivery efficiency and reduce network utilization. Under such cooperation,
   however, real-time video transmission requires end-to-end delay bounds. Due
   to the inherently stochastic nature of wireless fading channels,
   deterministic delay bounds are prohibitively difficult to guarantee. For a
   scalable video structure, an alternative is to provide statistical guarantees
   using the concept of effective capacity/bandwidth by deriving quality of
   service exponents for each video layer. Using this concept, we formulate the
   resource allocation problem for general multihop multicast network flows
   and derive the optimal solution that minimizes the total energy consumption
   while guaranteeing a statistical end-to-end delay bound on each network

      path. A method is described to compute the optimal resource allocation at
      each node in a distributed fashion. Furthermore, we propose low complexity
      approximation algorithms for energy-efficient flow selection from the set
      of directed acyclic graphs forming the candidate network flows. The flow
      selection and resource allocation process is adapted for each video frame
      according to the channel conditions on the network links. Considering
      different network topologies, results demonstrate that the proposed
      resource allocation and flow selection algorithms provide notable
      performance gains with small optimality gaps at a low computational cost.


Trust is an important aspect of mobile adhoc networks (MANETs). It enables
entities to cope with uncertainty and uncontrollability caused by the free will of
others. Trust computations and management are highly challenging issues in
MANETs due to computational complexity constraints, and the independent
movement of component nodes. This prevents the direct application of techniques
suited for other networks. In MANETs, an untrustworthy node can wreak
considerable damage and adversely affect the quality and reliability of data.
Therefore, analyzing the trust level of a node has a positive influence on the
confidence with which an entity conducts transactions with that node. In this work
we present a detailed survey on various trust computing approaches that are geared
towards MANETs. We highlight the summary and comparisons of these approaches.
In addition, we analyze various works on trust dynamics including trust propagation,
prediction and aggregation algorithms, the influence of network dynamics on trust
dynamics and the impact of trust on security services.


      Broadcasting is a fundamental operation in wireless networks and plays an
      important role in the communication protocol design. In multihop wireless
      networks, however, interference at a node due to simultaneous transmissions
      from its neighbors makes it non-trivial to design a minimum-latency
      broadcast algorithm, which is known to be NP-complete. We present a simple
      12-approximation algorithm for the one-to-all broadcast problem that

  improves all previously known guarantees for this problem. We then consider
  the all-to-all broadcast problem where each node sends its own message to
  all other nodes. For the all-to-all broadcast problem, we present two
  algorithms with approximation ratios of 20 and 34, improving the best result
  available in the literature. Finally, we report experimental evaluation of our
  algorithms. Our studies indicate that our algorithms perform much better in
  practice than the worst-case guarantees provided in the theoretical analysis
  and achieve up to 37% performance improvement over existing schemes.

7. EXACT FORMULAE FOR RESILIENCE                       IN    RANDOM        KEY
  As wireless sensor networks are often deployed in adverse or hostile
  environments, key management schemes are required for sensor nodes. The
  random key predistribution (RKP) scheme is a probabilistic key management
  scheme where each node is preloaded with a subset of keys that are
  randomly selected from a pool of keys. If a pair of neighbor nodes have a
  common key, it can be used to establish a secure link between the nodes. The
  q-composite RKP scheme requires that a pair of neighbor nodes have at least
  q common keys for a secure link. In this article, we show that the previous
  security analysis (i.e., resilience against node capture) of the q-composite
  RKP scheme is inaccurate and present new formulae for resilience in the RKP
  scheme and the q-composite RKP scheme.


  WiFi interface is known to be a primary energy consumer in mobile devices,
  and idle listening (IL) is the dominant source of energy consumption in WiFi.
  Most existing protocols, such as the 802.11 power-saving mode (PSM),
  attempt to reduce the time spent in IL by sleep scheduling. However,
  through an extensive analysis of real-world traffic, we found more than 60
  percent of energy is consumed in IL, even with PSM enabled. To remedy this
  problem, we propose Energy-Minimizing idle Listening (E-MiLi) that reduces
  the power consumption in IL, given that the time spent in IL has already
  been optimized by sleep scheduling. Observing that radio power consumption
  decreases proportionally to its clock rate, E-MiLi adaptively downclocks the
  radio during IL, and reverts to full clock rate when an incoming packet is
  detected or a packet has to be transmitted. E-MiLi incorporates sampling
  rate invariant detection, ensuring accurate packet detection and address
  filtering even when the receiver's sampling clock rate is much lower than the

      signal bandwidth. Further, it employs an opportunistic downclocking
      mechanism to optimize the efficiency of switching clock rate, based on a
      simple interface to existing MAC-layer scheduling protocols. We have
      implemented E-MiLi on the USRP software radio platform. Our experimental
      evaluation shows that E-MiLi can detect packets with close to 100 percent
      accuracy even with downclocking by a factor of 16. When integrated with
      802.11, E-MiLi can reduce energy consumption by around 44 percent for 92
      percent of users in real-world wireless networks.

9. Bandwidth Recycling in IEEE 802.16 Networks

IEEE 802.16 standard was designed to support the bandwidth demanding
applications with quality of service (QoS). Bandwidth is reserved for each
application to ensure the QoS. For variable bit rate (VBR) applications, however, it
is difficult for the subscriber stations (SSs) to predict the amount of incoming
data. To ensure the QoS guaranteed services, the SS may reserve bandwidth more
than the amount of its transmitting data. As a result, the reserved bandwidth may
not be fully utilized all the time. In this paper, we propose a scheme, named
Bandwidth Recycling, to recycle the unused bandwidth without changing the
existing bandwidth reservation. The idea of our scheme is to allow other SSs to
utilize the unused bandwidth when it is available. Thus, not only the same QoS
guaranteed services can be provided but also the system throughput can be
improved. Mathematical analysis and simulation are used to evaluate the proposed
scheme. Simulation and analysis results confirm that our proposed scheme can
recycle 35 percent of unused bandwidth on average. By analyzing factors affecting
the recycling performance, three scheduling algorithms are proposed to improve
the overall throughput. The simulation results show that our proposed algorithm can
further improve the overall throughput by 40 percent when the network is in the
steady state.



In a mobile ad hoc network, the mobility and resource constraints of mobile nodes
may lead to network partitioning or performance degradation. Several data

replication techniques have been proposed to minimize performance degradation.
Most of them assume that all mobile nodes collaborate fully in terms of sharing
their memory space. In reality, however, some nodes may selfishly decide only to
cooperate partially, or not at all, with other nodes. These selfish nodes could then
reduce the overall data accessibility in the network. In this paper, we examine the
impact of selfish nodes in a mobile ad hoc network from the perspective of replica
allocation. We term this selfish replica allocation. In particular, we develop a selfish
node detection algorithm that considers partial selfishness and novel replica
allocation techniques to properly cope with selfish replica allocation. The conducted
simulations demonstrate the proposed approach outperforms traditional
cooperative replica allocation techniques in terms of data accessibility,
communication cost, and average query delay.



Throughput capacity in mobile ad hoc networks has been studied extensively under
many different mobility models. However, most previous research assumes global
mobility, and the results show that a constant per-node throughput can be achieved
at the cost of very high delay. Thus, we are having a very big gap here, i.e., either
low throughput and low delay in static networks or high throughput and high delay in
mobile networks. In this paper, employing a practical restricted random mobility
model, we try to fill this gap. Specifically, we assume that a network of unit area
with n nodes is evenly divided into cells with an area of n -2α, each of which is
further evenly divided into squares with an area of n-2β(0≤ α ≤ β ≤1/2). All nodes can
only move inside the cell which they are initially distributed in, and at the beginning
of each time slot, every node moves from its current square to a uniformly chosen
point in a uniformly chosen adjacent square. By proposing a new multihop relay
scheme, we present smooth trade-offs between throughput and delay by controlling
nodes' mobility. We also consider a network of area nγ (0 ≤ γ ≤ 1) and find that
network size does not affect the results obtained before.

12.Local Broadcast Algorithms in Wireless Ad Hoc Networks: Reducing
the Number of Transmissions

There are two main approaches, static and dynamic, to broadcast algorithms in
wireless ad hoc networks. In the static approach, local algorithms determine the
status (forwarding/nonforwarding) of each node proactively based on local topology
information and a globally known priority function. In this paper, we first show that
local broadcast algorithms based on the static approach cannot achieve a good
approximation factor to the optimum solution (an NP-hard problem). However, we
show that a constant approximation factor is achievable if (relative) position
information is available. In the dynamic approach, local algorithms determine the
status of each node "on-the-fly” based on local topology information and broadcast
state information. Using the dynamic approach, it was recently shown that local
broadcast algorithms can achieve a constant approximation factor to the optimum
solution when (approximate) position information is available. However, using
position information can simplify the problem. Also, in some applications it may not
be practical to have position information. Therefore, we wish to know whether local
broadcast algorithms based on the dynamic approach can achieve a constant
approximation factor without using position information. We answer this question in
the positive-we design a local broadcast algorithm in which the status of each node
is decided "on-the-fly” and prove that the algorithm can achieve both full delivery
and a constant approximation to the optimum solution.

13.FESCIM: Fair, Efficient, and Secure                     Cooperation    Incentive
Mechanism for Multihop Cellular Networks

In multihop cellular networks, the mobile nodes usually relay others' packets for
enhancing the network performance and deployment. However, selfish nodes usually
do not cooperate but make use of the cooperative nodes to relay their packets,
which has a negative effect on the network fairness and performance. In this
paper, we propose a fair and efficient incentive mechanism to stimulate the node
cooperation. Our mechanism applies a fair charging policy by charging the source
and destination nodes when both of them benefit from the communication. To
implement this charging policy efficiently, hashing operations are used in the ACK
packets to reduce the number of public-key-cryptography operations. Moreover,
reducing the overhead of the payment checks is essential for the efficient
implementation of the incentive mechanism due to the large number of payment
transactions. Instead of generating a check per message, a small-size check can be
generated per route, and a check submission scheme is proposed to reduce the
number of submitted checks and protect against collusion attacks. Extensive
analysis and simulations demonstrate that our mechanism can secure the payment

and significantly reduce the checks' overhead, and the fair charging policy can be
implemented almost computationally free by using hashing operations.

14.Acknowledgment-Based Broadcast Protocol for Reliable and Efficient
Data Dissemination in Vehicular Ad Hoc Networks

We propose a broadcast algorithm suitable for a wide range of vehicular scenarios,
which only employs local information acquired via periodic beacon messages,
containing acknowledgments of the circulated broadcast messages. Each vehicle
decides whether it belongs to a connected dominating set (CDS). Vehicles in the
CDS use a shorter waiting period before possible retransmission. At time-out
expiration, a vehicle retransmits if it is aware of at least one neighbor in need of
the message. To address intermittent connectivity and appearance of new
neighbors, the evaluation timer can be restarted. Our algorithm resolves
propagation at road intersections without any need to even recognize intersections.
It is inherently adaptable to different mobility regimes, without the need to
classify network or vehicle speeds. In a thorough simulation-based performance
evaluation, our algorithm is shown to provide higher reliability and message
efficiency than existing approaches for nonsafety applications.

15.Characterizing the Security Implications of Third-Party Emergency
Alert Systems over Cellular Text Messaging Services

Cellular text messaging services are increasingly being relied upon to disseminate
critical information during emergencies. Accordingly, a wide range of organizations
including colleges and universities now partner with third-party providers that
promise to improve physical security by rapidly delivering such messages.
Unfortunately, these products do not work as advertised due to limitations of
cellular infrastructure and therefore provide a false sense of security to their
users. In this paper, we perform the first extensive investigation and
characterization of the limitations of an Emergency Alert System (EAS) using text
messages as a security incident response mechanism. We show emergency alert
systems built on text messaging not only can meet the 10 minute delivery
requirement mandated by the WARN Act, but also potentially cause other voice and
SMS traffic to be blocked at rates upward of 80 percent. We then show that our
results are representative of reality by comparing them to a number of documented
but not previously understood failures. Finally, we analyze a targeted messaging

mechanism as a means of efficiently using currently deployed infrastructure and
third-party EAS. In so doing, we demonstrate that this increasingly deployed
security infrastructure does not achieve its stated requirements for large

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