Wireless Communications

Ad hoc networks are a new wireless networking paradigm for mobile hosts. Unlike traditional mobile wireless networks, ad hoc networks do not rely on any fixed infrastructure. Instead, hosts rely on each other to keep the network connected. Military tactical and other security-sensitive operations are still the main applications of ad hoc networks, although there is a trend to adopt ad hoc networks for commercial uses due to their unique properties. One main challenge in the design of these networks is their vulnerability to security attacks. In this article, we study the threats on ad hoc network faces and the security goals to be achieved. We identify the new challenges and opportunities posed by this new networking environment and explore new approaches to secure its communication. In particular, we take advantage of the inherent redundancy in ad hoc networks-multiple routes between nodes-to defend routing against denial-of-service attacks. We also use replication and new cryptographic schemes, such as threshold cryptography, to build a highly secure and highly available key management service, which terms the core of our security framework.

/pdf/securing-ad-hoc-networks-3hudjv4io2.pdf

Securing ad hoc networks

http://cpham.perso.univ-pau.fr/ENSEIGNEMENT/PAU-UPPA/RESA-M2/Clustering-abasi.pdf

A survey on clustering algorithms for wireless sensor networks

A wireless network consisting of a large number of small sensors with low-power transceivers can be an effective tool for gathering data in a variety of environments. The data collected by each sensor is communicated through the network to a single processing center that uses all reported data to determine characteristics of the environment or detect an event. The communication or message passing process must be designed to conserve the limited energy resources of the sensors. Clustering sensors into groups, so that sensors communicate information only to clusterheads and then the clusterheads communicate the aggregated information to the processing center, may save energy. In this paper, we propose a distributed, randomized clustering algorithm to organize the sensors in a wireless sensor network into clusters. We then extend this algorithm to generate a hierarchy of clusterheads and observe that the energy savings increase with the number of levels in the hierarchy. Results in stochastic geometry are used to derive solutions for the values of parameters of our algorithm that minimize the total energy spent in the network when all sensors report data through the clusterheads to the processing center.

/pdf/an-energy-efficient-hierarchical-clustering-algorithm-for-574o6gyna1.pdf

An energy efficient hierarchical clustering algorithm for wireless sensor networks

An ad-hoc network of wireless static nodes is considered as it arises in a rapidly deployed, sensor-based, monitoring system. Information is generated in certain nodes and needs to reach a set of designated gateway nodes. Each node may adjust its power within a certain range that determines the set of possible one hop away neighbors. Traffic forwarding through multiple hops is employed when the intended destination is not within immediate reach. The nodes have limited initial amounts of energy that is consumed at different rates depending on the power level and the intended receiver. We propose algorithms to select the routes and the corresponding power levels such that the time until the batteries of the nodes drain-out is maximized. The algorithms are local and amenable to distributed implementation. When there is a single power level, the problem is reduced to a maximum flow problem with node capacities and the algorithms converge to the optimal solution. When there are multiple power levels then the achievable lifetime is close to the optimal (that is computed by linear programming) most of the time. It turns out that in order to maximize the lifetime, the traffic should be routed such that the energy consumption is balanced among the nodes in proportion to their energy reserves, instead of routing to minimize the absolute consumed power.

/pdf/energy-conserving-routing-in-wireless-ad-hoc-networks-3dijpovsbd.pdf

Energy conserving routing in wireless ad-hoc networks

The design of a packet radio network must reflect the operational requirements and environmental constraints to which it is subject. In this paper, we outline those features that distinguish the High Frequency (HF) Intra Task Force (ITF) Network from other packet radio networks, and we present a design concept for this network that encompasses organizational structure, waveform design, and channel access. Network survivability is achieved through the use of distributed network control and frequency hopping spread-spectrum signaling. We demonstrate how the execution of the fully distributed Linked Cluster Algorithm can enable a network to reconfigure itself when it is affected by connectivity changes such as those resulting from jamming. Additional resistance against jamming is provided by frequency hopping, which leads naturally to the use of code division mutiple access (CDMA) techniques that permit the simultaneous successful transmission by several users. Distributed algorithms that exploit CDMA properties have been developed to schedule contention-free transmissions for much of the channel access in this network. Contention-based channel access protocols can also be implemented in conjunction with the Linked Cluster network structure. The design concept presented in this paper provides a high degree of survivability and flexibility, to accommodate changing environmental conditions and user demands.

/pdf/a-design-concept-for-reliable-mobile-radio-networks-with-4yj0hqta13.pdf

A design concept for reliable mobile radio networks with frequency hopping signaling

A Distributed Algorithm for Organizing Mobile Radio Telecommunication Networks.

The authors discuss the development of a testbed, called the distributed simulation and prototyping testbed (DSPT), to model variable-connectivity radio networks. The DSPT constitutes a software environment in which distributed simulation and prototyping models of radio communication and command and control systems can easily be built. The environment consists of four separate software packages: communication simulation, communication monitor, scenario update/controller, and prototype node. These four packages work together to form a single distributed simulation and prototyping facility for communication network studies. They relieve the user from the need to consider many of the details that must be handled to implement a distributed testbed. Each package is easily extensible and can be tailored to specific networks, scenarios, monitor views, and prototyping needs. >

A distributed simulation and prototyping testbed for radio communication networks

The use of relays is known to increase the resistance of communication links to interference In a multi-user network it is necessary to establish robust management techniques that allow the users to take advantage of the relaying power a network inherently possesses In this paper we consider an Intra Task Force (ITF) Network that operates at HF We employ a network architecture that provides for the automated selection of relay nodes without the need for a central controller Under this architecture the network reorganizes itself in response to topology changes such as those that result from jamming Communication range models suitable for a jammed HF channel are presented We demonstrate that the combination of spread spectrum signaling, error correcting coding, path redundancy through frequency diversity, and adaptive relaying using automated network restructuring provide this network with a strong defense against jamming

Distributed Network Reconfiguration in Response to Jamming at HF

There are two basic types of 802.11 networks: 1) networks that operate as single "independent" basic service sets (IBSSs) and 2) networks that operate as extended service sets (ESSs), also known as infrastructure networks. Infrastructure networks have access points (APs) that may be interconnected to other APs within an ESS via a distribution system (DS) to extend the range and scalability of an infrastructure network. Also, they may have stations (STAs) that associate with a neighboring AP in order to access the DS service. On the other hand, an IBSS consists only of STAs and does not support the DS service. Protocols that enable multihop routing in IBSS networks have been proposed in the lETF's MANET working group. This paper describes an 802.11 access point that can combine with other such APs and with standard STAs to form a mobile, 802.11 ESS that is an infrastructure network, but incorporates the mobility features typical of a multihop ad hoc network. The new architecture is called a dynamic backbone subnet based on 802.11, or simply, DBS/802.11. Externally, a DBS/802.11 subnet provides network services very much like an Ethernet, which simplifies its connection to other IP networks. Both a simulation model and a Linux implementation of DBS/802.11 have been developed. We show some results from a field test scenario designed to verify the operation of the DBS/802.11 implementation using mobile nodes in a dynamic, interference prone environment.

Dennis J. Baker

Papers

A design concept for reliable mobile radio networks with frequency hopping signaling

A Distributed Algorithm for Organizing Mobile Radio Telecommunication Networks.

A distributed simulation and prototyping testbed for radio communication networks

Distributed Network Reconfiguration in Response to Jamming at HF

Mobility and routing protocols for 802.11 extended service sets