In this paper we investigate interference cancellation to faster identify tags in RFID networks. We explore how interference cancellation can be applied to ALOHA and tree-based identification schemes, its limitations, the extent of achievable improvements, and the overhead incurred to obtain effective gains. Analytical and simulation results show that for an ALOHA-based scheme interference cancellation allows us to identify nearly 23% of tags without directly interrogating them. This speeds up tag identification (over 20% faster) while producing little overhead. For a tree-based scheme nearly 50% of the tags are identified by exploiting interference cancellation, resulting in an improvement of the identification rate of over 20%. Finally, we propose an enhancement of the tree-based scheme with interference cancellation that achieves a further identification speed up of 50%.

We propose an analytical framework to study broadcasting performance in multi channel wireless networks in the presence of adversary attacks. In order to reduce the effect of such attacks on the dissemination performance we use network coding and show that it can bring significant benefits to the broadcasting process. We investigate the impact that different medium access, transmission schemes and channel conditions have on the information exchange among all nodes. We analyze such impact in terms of reception delay and robustness with respect to malicious interference generated by adversary nodes. In order to do so, we model the process of data broadcasting as a coupon collector's problem. We derive the average delay required to retrieve partial and complete information by all nodes in the network, and quantify the gains obtained when using a multi channel system. We take into account the presence of different types of adversaries and find the optimum number of channels that nodes have to access in order to minimize the data reception delay.

In this paper we propose an end-to-end algorithm, called NUM-RS, for jointly selecting link transmission rates and source rates in a multi-hop multi-rate wireless network. Prior works on rate selection, including those that explicitly account for opportunistic reception, perform rate selection on a hop-by-hop basis, attempting to maximize the throughput on each link. Our algorithm leverages the Network Utility Maximization (NUM) framework, thus providing end-to-end semantics for rate selection and proportional fairness with low overhead. By using end-to-end semantics NUM-RS considers both source rates and congestion in the vicinity of links used by a flow when selecting link rates. Our results show that NUM-RS increasingly outperforms contemporary hop-by-hop rate selection schemes as the number of hops in the flows increase. For example, 20% and 50% of 8-hop flows exhibit performance gains of at least 36% and 15%, respectively, in terms of end-to-end throughput. In some cases, gains of up to 80% can be achieved.

In this paper, we address congestion of multicast traffic in multihop wireless networks through a combination of network coding and resource reservation. Network coding reduces the number of transmissions required in multicast flows, thus allowing a network to approach its multicast capacity. In addition, it efficiently repairs errors in multicast flows by combining packets lost at different destinations. However, under conditions of extremely high congestion the repair capability of network coding is seriously degraded. In this paper, we propose cooperative channelization, in which portions of the transmission media are allocated to links that are congested at the point where network coding cannot efficiently repair loss. A health metric is proposed to allow comparison of need for channelization of different multicast links. Cooperative channelization considers the impact of channelization on overall network performance before resource reservation is triggered. Our results show that cooperative channelization improves overall network performance while being well suited for wireless networks using network coding.

Network coding has been proposed as an alternative to the conventional store-and-forward routing paradigm for data delivery in networks. When deployed in a multi-rate wireless network, network coding has to interact with rate adaptation. When multicasting packets (a requirement of network coding) in a multi-rate IEEE 802.11 wireless network, one must use care when selecting the transmission rate to use. We refer to this problem as rate selection. We analyze the performance of network coding for a small set of scenarios representative of common topologies in a network that lead to coding opportunities. Based on this analysis, we present our Network Coding aware Rate Selection (NCRS) algorithm which takes into account transmission rates used for unicast links to all multicast targets. Simulation results show that in a multi-hop wireless network, network coding with NCRS achieves up to 24% more gain over routing than network coding with other rate selection algorithms.

Network coding is increasingly being investigated as an alternative to routing to increase throughput in packet networks. Like most data transfer schemes, the effectiveness of network coding may be limited by extreme congestion. When using network coding, these congested conditions are mitigated somewhat, but may still occur. We propose a selective channelization scheme in which links that experience congestion at a level that cannot be overcome by network coding are given reserved communication resources. This method has the following benefits. First, the algorithm proposed allows network coding full opportunity to overcome congestion before performing channelization, thus reducing the number of reserved resources used. Second, when triggered, the channelization of severely congested links greatly improves the end-to-end performance of flows that traverse the channelized link. To determine the point at which channelization should be triggered, we perform a thorough analysis of potential coding gains in a network facing errors due to collisions, and determine the point at which network coding loses its effectiveness.

In typical deployments of infrastructure wireless mesh networks, mesh clients are directly connected to a mesh router. The mesh routers form a multi-hop wireless mesh backbone to provide connectivity to the Internet. In this paper, we propose and evaluate a set of distributed algorithms that enable mesh clients to form a multi-hop wireless relay network to have access to the mesh backbone. The proposed algorithms include path discovery, channel allocation, path selection, and local tuning of the resulting relay network. Results show that the performance of the relay network formed by our algorithms is very close to the optimal performance that the network can achieve.

Data generated in wireless sensor networks may not all be alike: some data may be more important than others and hence may have different delivery requirements. In this paper, we address differentiated data delivery in the presence of congestion in wireless sensor networks. We propose a class of algorithms that enforce differentiated routing based on the congested areas of a network and data priority. The basic protocol, called congestion-aware routing (CAR), discovers the congested zone of the network that exists between high-priority data sources and the data sink and, using simple forwarding rules, dedicates this portion of the network to forwarding primarily high-priority traffic. Since CAR requires some overhead for establishing the high-priority routing zone, it is unsuitable for highly mobile data sources. To accommodate these, we define MAC-enhanced CAR (MCAR), which includes MAC-layer enhancements and a protocol for forming high-priority paths on the fly for each burst of data. MCAR effectively handles the mobility of high-priority data sources, at the expense of degrading the performance of low-priority traffic. We present extensive simulation results for CAR and MCAR, and an implementation of MCAR on a 48-node testbed.

Wireless mesh networks are emerging as a means to provide ubiquitous network connectivity using various radio technologies. In this paper we propose and evaluate a set of distributed algorithms to form a multi-hop relay network to access the backbone in wireless mesh networks. The proposed algorithms include path discovery, frequency allocation, path selection, and local tuning of the resulting relay network. Our results show that the performance of the relay network formed by our algorithms is very close to the optimal performance that the network can achieve.

Many applications that make use of sensor networks require secure communication. Because asymmetric-key solutions are difficult to implement in such a resource-constrained environment, symmetric-key methods coupled with a priori key distribution schemes have been proposed to achieve the goals of data secrecy and integrity. These approaches typically assume that all nodes are similar in terms of capabilities and, hence, deploy the same number of keys in all sensors in a network to provide the aforementioned protections. In this paper, we demonstrate that a probabilistic unbalanced distribution of keys throughout the network that leverages the existence of a small percentage of more capable sensor nodes can not only provide an equal level of security, but also reduce the consequences of node compromise. To fully characterize the effects of the unbalanced key management system, we design, implement, and measure the performance of a complementary suite of key establishment protocols known as LIGER. Using their predeployed keys, nodes operating in isolation from external networks can securely and efficiently establish keys with each other. Should resources such as a backhaul link to a key distribution center (KDC) become available, networks implementing LIGER automatically incorporate and benefit from such facilities. Detailed experiments demonstrate that the unbalanced distribution in combination with the multimodal LIGER suite offers a robust and practical solution to the security needs in sensor networks

The majority of security schemes available for sensor networks assume deployment in areas without access to a wired infrastructure. More specifically, nodes in these networks are unable to leverage key distribution centers (KDCs) to assist them with key management. In networks with a heterogeneous mix of nodes, however, it is not unrealistic to assume that some more powerful nodes have at least intermittent contact with a backbone network. For instance, an air-deployed battlefield network may have to operate securely for some time until uplinked friendly forces move through the area. We therefore propose LIGER, a hybrid key management scheme for heterogeneous sensor networks that allows systems to operate in both the presence and absence of a KDC. Specifically, when no KDC is available, nodes communicate securely with each other based upon a probabilistic unbalanced method of key management. The ability to access a KDC allows nodes to probabilistically authenticate neighboring devices with which they are communicating. We also demonstrate that this scheme is robust to the compromise of both low and high capability nodes and that the same keys can be used for both modes of operation. Detailed experiments and simulations are used to show that LIGER is a highly practical solution for the current generation of sensors and the unbalanced approach can significantly reduce network initialization time.