In this paper, we conduct an energy consumption analysis of a broadcast access mechanism over IEEE 802.11 networks. By assuming non-saturated conditions, we provide a statistical model of the energy consumed during one cycle period, defined as the duration between two successful broadcast transmissions. The model includes a characterization of the medium access transmission mechanism. Our results show that the broadcast protocol is a good candidate to be included in future amendments of the IEEE 802.11 standard.

Traditional location methods require specialized network infrastructure or add-on location hardware in order to estimate node positions. As an opposite approach, direction of encounter (DoE) uses standard wireless networking equipment and takes advantage of node mobility to establish static node locations. In DoE, as a mobile node enters and leaves a static node’s coverage area, it is able to discover the static node’s location with respect to its own trajectory. Mobile nodes are able to determine the position of a set of static nodes by collaborating in this discovery process. In this work, this set is called a constellation. This collaboration consists of exchanging constellation data in order to establish and improve the accuracy of the position estimates. Not only does DoE establish static node positions, but it also allows mobile users to be aware of the direction where static nodes can be found. DoE needs minimal user intervention, although fully automatic operation can be achieved if inertial sensors are available. This method can be used to develop both location-based applications and guiding procedures. By means of simulations and experiments, we carried out a performance evaluation of DoE under diverse conditions. The results show that the DoE algorithm indeed is able to estimate the static node positions without requiring additional functionality from static nodes. We believe this is an important requirement for a successful deployment of a location method.

This paper presents RegionDCF, a self-adapting media access control protocol for WLAN that seamlessly behaves as CSMA or round-robin access techniques taking advantage of the most effective properties of each access method. In contrast to preceding works in this area that focused on enhancements of each protocol, or on a mechanism that switches between them, this paper proposes a single access method able to behave both as a pure contention-based or as round-robin based protocol depending on present traffic conditions. Simulation results show that RegionDCF outperforms standard 802.11.

In this paper we propose a model to compute an upper bound for the maximum network size in mobile ad-hoc networks. Our model is based on the foundation that for a unicast route to be useful to initiate data transport, it is necessary that the time required to discover the route should be shorter than the time the route remains valid. From this model, we found that the node transmission range, mobility of nodes and number of contending nodes actually define the maximum feasible number of hops in a route, and therefore the maximum network size. Our model is derived from the combination of a route duration model, that we also derive in this paper, and a delay model for multi-hop routes extended from a single-hop delay model found in the literature. We evaluate our model numerically for different network conditions. To the best of our knowledge, this is the first time that a comparison between route discovery time and route duration is analyzed in order to establish the maximum network size in ad-hoc networks. We believe this is a fundamental scaling problem of ad-hoc networks that has not been looked at before from a mobility-delay perspective.

A reservation based medium access control (MAC) protocol has been adopted by the IEEE 802.16 standard as the basic protocol for data communication within the upstream channel. In this paper, we propose the following five new contention slot allocators (CSA) for the IEEE 802.16 MAC protocol: Forced-CSA, Variable-CSA, Multicast-CSA, Collision Free-CSA and CDMA-CSA. The new techniques dynamically fit the number of contention slots needed to solve collisions according to the current traffic load, considerably improving overall system performance. The CSAs introduced in this paper indicate that the mean access delay could be reduced up to 75% compared with the currently adopted method by the IEEE 802.16 MAC protocol, called simple-CSA. A performance evaluation of our five CSA schemes is presented and compared with previous CSA schemes, simple-CSA and IEEE 802.14-CSA. Obtained results turned out to be closer to the maximum estimated throughput than currently used methods.

Routing protocols for mobile ad hoc networks usually discover routes by flooding the entire network with control packets; this technique is known as blind flooding. This paper presents NARD, a neighbor-assisted route discovery protocol for wireless ad hoc networks. In NARD, a source node floods a limited portion of the network looking not only for the destination node, but also for routing information of other nodes (called neighbors) that were known to be near the destination node recently. Neighbor nodes can be used as anchor points where a second limited flooding takes place in search for the destination node. Because only a limited portion of the network is flooded by control packets near the source and destination nodes, NARD can significantly reduce the signaling overhead of route discovery compared with blind flooding techniques. Simulations with NS2 were undertaken to verify the validity of our approach.

An analytical model to estimate the time duration of routes formed by several intermediate nodes in MANETs is presented. Although there are works related to estimation of route duration, they only partially obtained analytical expressions. First, we approach the route duration problem by modeling a 3-node static case, source and destination (static) and one intermediate node (mobile). Then, a 3-node mobile case is analyzed. For both cases, we evaluate how long the route is valid. Finally, a K-node mobile case is presented. We conclude that the time duration of a route formed by N intermediate nodes can be accurately found from the minimum time duration of N separated 3-node routes. Simulations were developed using NS-2 to verify the proposed model. This work can be used to compute the signaling overhead during route-maintenance of routing protocols for MANETs and to adjust the maximum network size.

In this paper, we investigate the impact of variable-range transmission power control on the physical and network connectivity, on network capacity, and on power savings in wireless multihop networks. First, using previous work by Steele (1988), we show that, for a path attenuation factor a = 2, the average range of links in a planar random network of A m2having n nodes is ~aradicA/n1. We show that this average range is approximately half the range obtained when common-range transmission control is used. Combining this result and previous work by Gupta and Kumar (2000), we derive an expression for the average traffic carrying capacity of variable-range-based multihop networks. For a = 2, we show that this capacity remains constant even when more nodes are added to the network. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show that there is an optimum setting for the transmission range, not necessarily the minimum, which maximizes the capacity available to nodes in the presence of node mobility. The results presented in this paper highlight the need to design future MAC and routing protocols for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control

We study the impact of individual variable-range transmission power control on the physical and network connectivity, network capacity and power savings of wireless multihop networks such as ad hoc and sensor networks. First, using previous work by Steele (1988) and Gupta (2000) we derive an asymptotic expression for the average traffic carrying capacity of nodes in a multihop network where nodes can individually control the transmission range they use. For the case of a path attenuation factor /spl alpha/ = 2 we show that this capacity remains constant even when more nodes are added to the network. Second, we show that the ratio between the minimum transmission range levels obtained using common-range and variable-range based routing protocols is approximately 2. This is an important result because it suggests that traditional routing protocols based on common-range transmission can only achieve about half the traffic carrying capacity of variable-range power control approaches. In addition, common-range approaches consume /spl sim/ (1 $2/(2/sup /spl alpha//)) % more transmission power. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show how routing protocols based on common-range transmission power limit the capacity available to mobile nodes. The results presented in the paper highlight the need to design future wireless network protocols (e.g., routing protocols) for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control.

This paper introduces PARO, a power-aware routing optimization that helps to minimize the transmission power needed to forward packets between wireless devices in ad hoc networks. Using PARO, one or more intermediate nodes called "redirectors" elects to forward packets on behalf of source-destination pairs thus reducing the aggregate transmission power consumed by wireless devices. PARO is applicable to a number of networking environments including sensor networks, home networks and mobile ad hoc networks. In this paper, we present the detailed design of PARO and evaluate the protocol using simulation and experimentation. We show through simulation that PARO is capable of outperforming traditional broadcast-based routing protocols (e.g., MANET routing protocols) due to its power conserving point-to-point on-demand design. We discuss some initial experiences from an early implementation of the protocol in an experimental wireless testbed using off-the-shelf radio technology.

For wireless channels, interference mitigation techniques are typically applied at the packet transmission level. In this paper, we present the Havana Framework for supporting integrated adaptive-QOS that also responds to impairments over multiple time scales that are present at the flow/session level. Our framework is based on three different mechanisms that operate over distinct adaptation time scales. At the packet transmission time scale, a channel predictor determines whether to transmit a packet or not depending on the state of the wireless channel. At the packet scheduling time scale, a compensator credits and compensates flows that experience bad link quality. Over even longer time scales an adaptor regulates flows taking into account the ability of wireless applications to adapt to changes in available bandwidth and channel conditions.

A number of initiatives to add mobility to the Internet and packet data services to third generation cellular systems are being considered by emerging mobile service providers as possible candidate solutions for the delivery of IP data to mobile users. Both of these two candidates have a number of shortcomings, however. Mobile IP represents a simple and scalable global mobility solution but is not appropriate in support of fast and seamless handoff control. In contrast, third generation cellular systems offer smooth mobility support but are built on complex networking infrastructure that lacks the flexibility offered by IP-based solutions. In this paper we present an overview of cellular IP which represents a 'third way' combining the strengths of bath approaches without inheriting their weaknesses. Cellular IP combines the capability of cellular networks to provide smooth fast handoff and efficient location management of active and idle mobile users with the inherent flexibility, robustness and scalability found in IP networks.