Effective spectrum sharing requires a nuanced understanding of how radio activity varies not only across frequency and geography but also with altitude, an increasingly important dimension for drone networks and non-terrestrial systems. This paper presents a comprehensive survey of existing spectrum measurement studies in the sub-6 GHz range, identifying major gaps in coverage, such as limited measurements involving altitude variation, a lack of longitudinal datasets, and the absence of publicly available geotagged aerial data. To address these limitations, we conduct a multi-year spectrum monitoring campaign using an aerial platform equipped with software-defined radios (SDRs), operating in both urban and rural areas of Raleigh, NC, USA. The aerial platform enables high-resolution measurements of spectrum activity from the ground up to 300 m. We analyze occupancy patterns across licensed and unlicensed bands, including Long Term Evolution (LTE), 5G (New Radio) (NR), and Industrial, Scientific, and Medical (ISM) bands, and document year-over-year changes that reflect evolving commercial deployments and regulatory trends. We further perform an altitude-dependent analysis of spectrum occupancy and received power across the 89 MHz–6 GHz range, highlighting how three-dimensional measurement perspectives reveal usage patterns that are not observable from ground-level sensing alone. Our results demonstrate that altitude is a critical dimension for spectrum characterization and should be considered in future spectrum policy, sensing strategies, and system design. This study provides both a literature-based and measurement-based foundation for altitude-aware spectrum analytics, supported by a publicly available geotagged dataset to enable reproducible research for emerging aerial networks and non-terrestrial communication systems.

Uncrewed aerial vehicles (UAVs) have emerged as critical for various use cases, both military and civilian. This paradigm shift is poised to revolutionize various industries and aspects of modern life, from logistics and emergency services to environmental monitoring and entertainment. However, the safety of these UAVs hinges on the availability of a reliable wireless link between the UAV and the ground infrastructure for real-time communication. To effectively harness the vast potential of UAVs with safe and reliable wireless link, it is essential to model the complex air-to-ground (A2G) channel accurately. In this work, we present an open-source channel sounder built with software-defined radios (SDRs), which enables real-time measurement and characterization of the A2G channel in scenarios with mobility. Our measurement campaign conducted in a rural area provides valuable insights into the A2G channel’s characteristics, multipath effects, and channel impairments. This work provides a foundation for the development of accurate A2G channel models that can be used to optimize the design and performance of UAV communication systems.

The rapid evolution of 5G and beyond has advanced space-air-terrestrial networks, with unmanned aerial vehicles (UAVs) offering enhanced coverage, flexible configurations, and cost efficiency. However, deploying UAV-based systems presents challenges including varying propagation conditions and hardware limitations. While simulators and theoretical models have been developed, real-world experimentation is critically important to validate the research. Digital twins, virtual replicas of physical systems, enable emulation that bridge theory and practice. This paper presents our experimental results from AERPAW’s digital twin, showcasing its ability to simulate UAV communication scenarios and providing insights into system performance and reliability.

The ever-growing demand for wireless connectivity, coupled with limited spectrum resources, has resulted in spectrum congestion and interference. This research investigates the probability of occupancy in common sub-6 GHz cellular network bands based on measurements conducted in urban and rural environments. Specifically, we analyze the spectrum occupancy of various long-term evolution (LTE), 5thgeneration (5G) and Citizens Broadband Radio Service (CBRS) bands used in the United States, considering both uplink and downlink transmissions at altitudes up to 180 meters. Additionally, we explore the influence of altitude on the probability of spectrum occupancy in these bands. Our findings reveal that the probability of occupancy is generally higher in the downlink compared to the uplink. Moreover, we observe that line-of-sight (LoS) signals play a critical role in higher altitudes. These results provide insights spectrum utilization in various cellular bands across different altitudes, with implications on interference and spectrum coexistence between terrestrial networks and unmanned aerial systems (UASs) in the future.

Due to the scarcity of spectrum resources, the emergence of new technologies and ever-increasing number of wireless devices operating in the radio frequency spectrum lead to data congestion and interference. In this work, we study the effect of altitude on sub-6 GHz spectrum measurement results obtained at a Helikite flying over two distinct scenarios; i.e., urban and rural environments. Specifically, we aim at investigating the spectrum occupancy of various long-term evolution (LTE), 5thgeneration (5G) and citizens broadband radio service (CBRS) bands utilized in the United States for both uplink and downlink at altitudes up to 180 meters. Our results reveal that generally the mean value of the measured power increases as the altitude increases where the line-of-sight links with nearby base stations is more available. SigMF-compliant spectrum measurement datasets used in this paper covering all the bands between 100 MHz to 6 GHz are also provided.

Radio dynamic zones (RDZs) are geographically bounded areas where novel advanced wireless technologies can be developed, tested, and improved, without the concern of interfering to other incumbent radio technologies nearby the RDZ. In order to operate an RDZ, use of a real-time spectrum monitoring system carries critical importance. Such a monitoring system should detect out-of-zone (OoZ) signal leakage outside of the RDZ, and if the interference to nearby receivers is intolerable, the monitoring system should be capable of mitigating such interference. This can e.g. be achieved by stopping operations inside the RDZ or switching to other bands for RDZ operation. In this paper, we introduce a spectrum monitoring concept for OoZ signal leakage detection at RDZs, where sensor nodes (SNs) are installed at the boundary of an RDZ and monitor the power leakage from multiple transmitters within the RDZ. We propose a prediction algorithm that estimates the received interference at OoZ geographical locations outside of the RDZ, using the measurements obtained at sparsely located SNs at the RDZ boundary. Using computer simulations, we evaluate the performance of the proposed algorithm and study its sensitivity to SN deployment density.

The deployment at scale of Unmanned Aerial Systems have become increasingly imminent in the last few years, even as concerns regarding the dependability and predictability of their command and control channels remain fully to be addressed. The intersection of ground-to-air wireless communications, aerial networking, and trajectory control has become a research area of sharp interest. The validation of such research, beyond the theoretical/simulation stage, requires a facility that is both realistic, and admits of potentially risky or unsafe operation, while in the end guaranteeing personnel and equipment safety. The AERPAW project is an ambitious project, funded by the PAWR program of the US NSF, to create a remote accessible research platform for a research facility to enable such validation. To enable remote usage of such a testbed, yet provide the researcher with complete experimental freedom, the AERPAW facility includes a combination of architectural mechanisms that balance freedom of experimentation with regulatory compliance and safety. In this paper, we articulate the challenges and considerations of designing such mechanisms, and present the architectural features of AERPAW that attempt to realize these lofty goals.

Reliable and long-range wireless communications carry critical importance for remote identification (ID) of unmanned aerial systems (UAS). Federal Aviation Authority (FAA) in the United States has recently released rules that describe how drones can broadcast their ID and location information, without mandating a specific radio access technology. In this paper, we study LoRa as a candidate technology for drone remote ID. We first provide a brief overview of the recent FAA rules on drone remote ID released in December 2020. Subsequently, we provide preliminary results based on ray tracing and MATLAB simulations that evaluate the reliability and range of LoRa for UAS remote ID scenarios. Two different LoRa multi-user interference scenarios are considered: in one scenario, the interferer uses the same spreading factor (SF) as the desired user, while in another scenario, desired and interfering user SFs are different. Our results quantify the performance gains that may be obtained under different interference conditions, using various coding rates and SFs.

As the use of unmanned aerial vehicles (UAVs) in various commercial, civil, and military applications increases, it becomes important to study the design of aerial drone corridors that can support multiple simultaneous UAV missions. In this work, we study the placement of base stations (BSs) to serve aerial drone corridors while satisfying specific UAV mission requirements, such as the geometrical waypoints for the UAV to fly through and the minimum data rate to be supported along the mission trajectory. We develop a mathematical model of the drone corridor and propose a brute force algorithm that leverages A* search to meet the quality of service (QoS) requirements of the corridor by choosing the minimal set of BS locations from a pre-determined initial set. Using raytracing simulations, BS placement results are presented for various antenna array sizes in a dense urban region in East Manhattan. It was found that, for the scenario under consideration, a single BS equipped with an 8x8 antenna array is sufficient to satisfy the given QoS requirements of the corridor, while two BSs are required when using 4x4 antenna arrays.

To address the demands for more capacity and higher data rates, the fifth generation network (5G) technology is being developed and gradually rolled out by major cellular carriers. Millimeter wave (mmWave) systems and unmanned aerial vehicles (UAVs) are two critical enablers of 5G. To ease the integration of 5G into existing networks, it is essential to study how base stations (BSs) can be used to serve both ground and aerial users simultaneously in a mmWave network. In this work, we consider BSs equipped with two antennas- one tilted down to serve ground users and another tilted up to serve aerial users. Using ray tracing simulations, we investigate the ideal tilt of these two antennas. Our results indicate that reusing the spectrum effectively in urban environments requires an understanding of the interplay between the effects of shadowing due to buildings, ground reflections, beam orientation, BS separation, interference between the two beams, and UAV heights. Specifically, to simultaneously serve UAVs at a height of 200 m and ground users, it is desirable to use a BS equipped with one antenna tilted up at 30 degrees and another tilted down at of 10 degrees. This achieves the best compromise between the above effects for the simulation configuration considered in this paper. Further, it was observed that the aerial and ground users are, in some scenarios, actually better served by the antenna not meant for them.

New use cases for advanced wireless technologies are emerging in the unmanned aerial systems (UAS) spaces. These put pressure on technology and regulation. The way to overcome this is to gain experience and collect data while operating UAS in production environments. To this end, we introduce AERPAW: Aerial Experimentation and Research Platform for Advanced Wireless, and present an architecture for designing a large-scale community testbed in a production-like environment to enable controllable experiments with latest wireless technologies and systems. Using advanced networking and virtualization technology to manage the platform resources, users will be able to configure the testbed for running a variety of at-scale experiments for UAS localization and tracking, networking, trajectory optimization, spectrum management, and aerial-terrestrial cellular network design and optimization based on 5G and software radio technology, among others.

Unmanned aerial vehicles (UAVs) can supplement the existing ground-based heterogeneous cellular networks (Het-Nets), by replacing/supporting damaged infrastructure, providing real-time video support at the site of an emergency, offloading traffic in congested areas, extending coverage, and filling coverage gaps. In this paper, we introduce distributed algorithms that leverage UAV mobility, enhanced inter-cell interference coordination (ICIC), and cell range expansion (CRE) techniques defined in 3GPP Release-10 and 3GPP Release-11. Through Monte-Carlo simulations, we compare the system-wide 5th percentile spectral efficiency (5pSE) while optimizing the performance using a brute force algorithm, a heuristic-based sequential algorithm, and a deep Q-learning algorithm. The autonomous UAVs jointly optimize their location, ICIC parameters, and CRE to maximize 5pSE gains and minimize the outage probability. Our results show that the ICIC technique relying on a simple heuristic outperforms the ICIC technique based on deep Q-learning. Taking advantage of the multiple optimization parameters for interference coordination, the heuristic based ICIC technique can achieve 5pSE values that are reasonably close to those achieved with exhaustive brute force search techniques, at a significantly lower computational complexity.

This paper presents preliminary results for motion behavior analysis of Madagascar hissing cockroach biobots subject to stochastic and periodic neurostimulation pulses corresponding to randomly applied right and left turn, and move forward commands. We present our experimental setup and propose an unguided search strategy based stimulation profile designed for exploration of unknown environments. We study a probabilistic motion model fitted to the trajectories of biobots, perturbed from their natural motion by the stimulation pulses. Furthermore, we provide a statistical assessment of the biobotic directional response to turn commands and its correlation with stimuli profile over time. This study paves the way towards reliable control for more realistic under-rubble search and rescue applications.

Vehicle-to-vehicle channel characteristics differ significantly from those of conventional cellular channels, especially in terms of fading statistics due to varying environmental conditions, link types, vehicle types, and objects that result in complex propagation effects. Accurate modeling of the vehicular channel remains a complex challenge. In this paper, existing, common vehicular channel models (VCMs) are evaluated and compared to measurement data from the UMTRI large-scale Dedicated Short-Range Communications (DSRC) testbed involving nearly 3000 vehicles and conducted over several months around Ann Arbor, MI. While many VCMs can predict reasonably well the frequent packet error rates observed near Ann Arbor, they over-estimate inter-packet gap and under-estimate the likelihood of runs of consecutively and successfully received packets. The testbed environment shows significant fading (i.e., sub-Rayleigh) and/or shadowing effects that challenge the accuracy of traditional VCMs. Furthermore, despite 60% of the inter-vehicle paths being obstructed by items available using OpenStreetMap (OSM) geodata, a deterministic obstacle shadowing model that makes use of such geodata does not account for all shadowing effects. Evaluating vehicular channel models in terms of real-world, large-scale experiments helps researchers better understand actual behaviors and allows for the development of new and/or improved models that more accurately reflect reality.

Time synchronization is a fundamental problem in any distributed system. In particular, wireless sensor networks require scalable time synchronization for implementing distributed tasks on multiple sensor nodes. Different synchronization schemes and hardware systems are able to achieve widely different levels of synchronization accuracy. Since synchronization accuracy is very sensitive to random delays and clock rate fluctuations, we model the pairwise synchronization error as a function of random delays and clock drifts to quantitatively model synchronization performance as a function of the relevant parameters, such as the beacon interval, the number of beacons per synchronization period, and the measurement point. The synchronization error is analyzed for different state-of-the-art pairwise synchronization schemes, based on one-way sender-receiver, two-way sender-receiver, and receiver-receiver approaches, using application layer or medium access control layer timestamping. The models are validated through numerical and experimental results.

Poor Internet performance currently undermines the efficiency of hyper-responsive mobile apps such as augmented reality clients and online games, which require low-latency access to real-time backend services. While edge-assisted execution, i.e. moving entire services to the edge of an access network, helps eliminate part of the communication overhead involved, this does not scale to the number of users that share an edge infrastructure. This is due to a mismatch between the scarce availability of resources in access networks and the aggregate demand for computational power from client applications. Instead, this paper proposes a hybrid edge-assisted deployment model in which only part of a service executes on LTE edge servers. We provide insights about the conditions that must hold for such a model to be effective by investigating in simulation different deployment and application scenarios. In particular, we show that using LTE edge servers with modest capabilities, performance can improve significantly as long as at most 50% of client requests are processed at the edge. Moreover, we argue that edge servers should be installed at the core of a mobile network, rather than the mobile base station: the difference in performance is negligible, whereas the latter choice entails high deployment costs. Finally, we verify that, for the proposed model, the impact of user mobility on TCP performance is low.

The emergence of location-based applications in wireless sensor network has galvanized extensive research on localization. Nonetheless, localization remains a difficult problem due to trade-offs between accuracy, energy consumption and computing resources. Searching for a solution that is sufficiently robust to handle a variety of scenarios, we propose KickLoc, which is a fully distributed solution. KickLoc takes the reliability of distance measurements into account to mitigate errors resulting from distance measurement errors, and fuses information from all neighboring nodes to provide position estimates. We evaluated the proposed algorithms both through simulations and experiments, the results are compared with other localization schemes and the Cramer-Rao lower bound (CRLB). The results show that the proposed algorithms outperform existing solutions in most of scenarios, while requiring significantly lower resources.

To improve the performance of Massively Multiplayer Online Games (MMOGs) in mobile networks, we explore the potential benefits of an edge-assisted deployment model: part of the MMOG backend service executes closer to the end user at the edge of the LTE network. We investigate the impact on game late

Cooperative cognitive radio networks (CCRNs) incorporates cooperative communication into cognitive radio networks, in which, primary users lease their spectrum to secondary users, and in exchange, the primary users leverage secondary users as cooperative relays to enhance their own throughput. Mobile operators offload their Internet traffic to privately owned Wi-Fi access points (APs), much to the inconvenience of non-cellular users served by the APs. However, by employing the CCRN scheme, the mobile operator can lease a licensed channel to the AP, effectively doubling its capacity. In this paper, we propose an implementation of the CCRN framework applied to IEEE 802.11 WLANs. The cooperation is cast as a two-player bargaining game where the two players are the primary users (users of the mobile operator) and the secondary users (users of the AP before spectrum leasing) who bargain for either throughput share or channel access time share. The optimal resource allocation that ensures efficiency as well as fairness among users is provided by the Nash solution. Simulation results show that the users achieve higher throughput via the proposed CCRN scheme, thus providing the mobile operator (e.g., AT&T) and the private Wi-Fi provider (e.g., a Starbucks coffee shop) with incentives for cooperation.

Simulation and emulation techniques are commonly used to evaluate the performance of complex networked systems. Simulation conveniently predicts the behavior of a complex networked system while usually requiring fewer simplifying model assumptions often necessary for theoretical analysis. In contrast, emulation does not need to re-implement the target real systems, so it may improve on the implementation efficiency of simulation while maintaining much of the realism of testbeds. A hybrid approach in which simulation nodes connect to emulation hosts can be used to combine the advantages of both approaches. In this paper, we propose integrating simulation with emulation using adaptive time dilation to evaluate system performance. If a simulator schedules its events in real time and the simulation time keeps up with the real time, then the hybrid system works very well and meets its deadlines. However, a heavily-loaded simulator can introduce significant simulation delays and thereby create situations where these delays impact the accuracy of the system. Our approach uses time dilation to reduce simulation delays and thus increasing the accuracy of the integrated simulation and emulation system. Our adaptive time dilation dynamically controls the time dilation factor to avoid system overloads for both the simulation and the emulation components and to improve the execution correctness of the hybrid system.

Due to its usefulness and wide deployment, IEEE 802.11 has been the subject of numerous studies, but still lacks a complete analytical model. Hidden terminals are common in IEEE 802.11 and cause the degradation of throughput. Despite the importance of the hidden terminal problem, there have been a relatively small number of studies that consider the effect of hidden terminals on IEEE 802.11 throughput, and many are not accurate for a wide range of conditions. In this paper, we present an accurate new analytical saturation throughput model for the infrastructure case of IEEE 802.11 in the presence of hidden terminals. Simulation results show that our model is accurate in a wide variety of cases.

Multihop relaying in WiMAX networks is considered an increasingly attractive technology for providing throughput enhancement, coverage extension, or both. In this paper, we consider deploying non-transparent relay stations (RSs) that transmit on the same carrier frequency as the base station (BS) for the purpose of coverage extension. Since it is possible that the RSs and BS are transmitting/receiving simultaneously to/from the subscriber stations (SSs) during the access zone period, it is challenging to schedule resources optimally for serving SSs in a fair manner. We propose an optimal scheduling scheme that preserves fairness among active SSs, and compare its performance with two different resource allocation schemes, namely, the overlapped and orthogonal in terms of cell throughput and outage performance. Our numerical results show that proposed scheme can achieve more throughput than the orthogonal scheme, while maintaining the fairness and lower outage performance of the orthogonal one.

Multihop relaying in WiMAX networks is considered a cost effective way to extend the coverage of the base stations, increase cell capacity, or both. In this paper, we consider deploying non-transparent relay stations for coverage extension and study the issue of fairness schemes in such networks. Since there are access and relay zones in both downlink and uplink frames and simultaneous transmissions are possible in the access zone, it is challenging to schedule resources optimally for serving subscriber stations in a fair manner. We evaluate the performance of well known fairness schemes such as max-min and proportional fairness in such networks. We also propose a new scheduling scheme, named subsection fairness that can achieve better throughput than traditional fairness schemes by maximizing bandwidth utilization. Our numerical results evaluate the performance of each scheduling scheme in terms of cell throughput and fairness.

Accurate reproduction of real human movement patterns is necessary in simulations of mobile ad hoc networks in order to obtain meaningful performance results. Human activities are often socially organized, resulting in a certain level of tendency of forming groups. There exists a few mobility models that are taking this tendency into account; however, all these models require a certain level of understanding of the underlying social structure of the target scenario, which limits their application scope. In this paper we propose an N-body mobility model that tackles such social aspects from a different perspective. We extract the social information from real human movement traces, and reproduce them in the mobility model. We show that the N-body model is capable of capturing and synthesizing the group-forming tendency that matches to those observed from sample traces. Simulation results also show that N-Body models exhibit a similar pairwise heterogeneity in ad-hoc network performance as the sample traces do.

WiMAX (IEEE 802.16) has emerged as a promising radio access technology for providing high speed broadband connectivity to subscribers over large geographic regions. New enhancements allow deployments of relay stations (RSs) that can extend the coverage of the base station (BS), increase cell capacity, or both. In this paper, we focus on deploying RSs for the purpose of coverage extension. We propose a simple scheduling scheme for serving the subscriber stations (SSs) in a fair manner and evaluate the performance of WiMAX networks with relays under this scheduling scheme. Through simulation and numerical analysis, we make several fundamental observations about cost-effective coverage in such networks.

Advances in microprocessors, memory, and radio technology have enabled the emergence of embedded systems that rely on communication systems to exchange information and coordinate their activities in spatially distributed applications. However, developing embedded communication systems that satisfy specific application requirements is a challenge due to the many tradeoffs imposed by different choices of underlying protocols and their parameters. Furthermore, evaluating the correctness and performance of the design and implementation before deploying it is a nontrivial task due to the complexity of the resulting system. This article presents the design and implementation of RaPTEX, a rapid prototyping tool for embedded communication systems, especially well suited for wireless sensor networks (WSNs), consisting of three major subsystems: a toolbox, an analytical performance estimation framework, and an emulation environment. We use a hierarchical approach in the design of the toolbox to facilitate the composition of the network stack. For fast exploration of the tradeoff space at design time, we build an analytical performance estimation model for energy consumption, delay, and throughput. For realistic performance evaluation, we design and implement a hybrid, accurate, yet scalable, emulation environment. Through three use cases, we study the tradeoff space for different protocols and topologies, and highlight the benefits of using RaPTEX for designing and evaluating embedded communication systems for WSNs.

Energy efficiency of the MAC protocol is a key design factor for wireless sensor networks (WSNs). Due to the importance of the problem, a number of energy efficient MAC protocols have been developed for WSNs. Preamble-sampling based MAC protocols (e.g., B-MAC and X-MAC) have overheads due to their preambles, and are inefficient at large wakeup intervals. SCP-MAC, a very energy efficient scheduling MAC protocol, minimizes the preamble by combining preamble sampling and scheduling techniques; however, it does not prevent energy loss due to overhearing; in addition, due to its synchronization procedure, it results in increased contention and delay. In this paper, we present an energy efficient MAC protocol for WSNs that avoids overhearing and reduces contention and delay by asynchronously scheduling the wakeup time of neighboring nodes. To validate our design and analysis, we implement the proposed scheme on the MicaZ platform. Experimental results show that AS-MAC considerably reduces energy consumption, packet loss and delay when compared with SCP-MAC.

Ultra-wideband wireless (UWB) can provide the physical layer for high capacity personal area networks. When UWB is used for communication between many nodes, relatively long acquisition times are needed when dropping and re-establishing wireless links between the nodes. This paper describes the development and use of mathematical and simulation models to investigate the impact on average packet delay of dropping and reacquiring links between nodes to directly transmit packets versus simply forwarding packets through intervening nodes without breaking the established wireless links. The work presented here assumes that no specific MAC layer protocol, such as WiMedia UWB MAC, is operating. The paper describes the models, explains the selection of modeling parameters used, compares the average packet delay for a network of three simple UWB nodes, and explains the use of these results for network design engineers.

Time synchronization is a fundamental middleware service for any distributed system. Wireless sensor networks make extensive use of synchronized time in many contexts (e.g., data fusion, TDMA schedules, synchronized sleep periods, etc.). We propose a time synchronization method relevant for wireless sensor networks. The solution features minimal complexity in network bandwidth, storage as well as processing, and can achieve good accuracy. Especially relevant for sensor networks, it also provides tight, deterministic bounds on offset and clock drift. A method for synchronizing the entire network is presented. The performance of the algorithm is analyzed theoretically and validated on a realistic testbed. The results show that the proposed algorithm outperforms existing algorithms in terms of precision and resource requirements.

Recently, mobile ad hoc networks (MANETs) have evolved as an irreplaceable networking technology for situations with sparse or inexistent infrastructure. Adapting OSPFv3 to MANET environments has several advantages. The protocol has proven its maturity in the wired Internet and is now the de facto standard Intra-AS routing protocol. When used in wireless ad hoc networks with proper extensions, OSPFv3 can provide better interoperation between the ad hoc domain and the Internet. This is one of the essential requirements for any ad hoc networks (including wireless mesh networks) that require connectivity to the Internet. The main challenge is that since OSPF is highly optimized for wired-oriented environment, it needs further enhancement to be fully functional in ad hoc scenarios. The most serious obstacle is the large routing overhead associated with the frequent topology changes due to volatile wireless links and node mobility. Various overhead reduction schemes have been proposed by focusing on how to reduce hello packets, flooding nodes, or the number of adjacencies. We propose a completely different approach by taking into account the very essential characteristics of wireless ad hoc networks - namely, distance effect. We implemented the proposed scheme on a simulator that uses the real OSPFv3 as its routing module. The simulation experiments prove that the proposed scheme allows significant reduction in OSPF routing overhead at small loss of route optimality.

Awareness of the physical location for each node is required by many wireless sensor network applications. The discovery of the position can be realized utilizing range measurements including received signal strength, time of arrival, time difference of arrival and angle of arrival. In this paper, we focus on localization techniques based on angle of arrival information between neighbor nodes. We propose a new localization and orientation scheme that considers beacon information multiple hops away. The scheme is derived under the assumption of noisy angle measurements. We show that the proposed method achieves very good accuracy and precision despite inaccurate angle measurements and a small number of beacons

On a wired network, physical authentication is implicitly provided by access: if a user is able to plug a cable into a network socket, he must have cleared other security checks such as the receptionist and/or locked doors. In the case of a wireless local area network (WLAN), the signal propagation is not limited by a fixed boundary, and unauthorized access from outside the security perimeter is possible, and in many instances facile. In this paper, we present a probabilistic technique for localization of users in a WLAN. The presented technique is able to identify intruders based on their location, and thus successfully defend a "parking lot" attack. The approach relies on a probabilistic mapping from received signal strength (RSSI) to location. Calibration inside and around the security perimeter must precede the localization phase. During the localization phase, the RSSI of all the WLAN users is measured by multiple monitoring stations positioned to provide an overlapping coverage of the area (the access points needed to provide the WLAN coverage can double as monitoring stations). A Bayesian technique is used to estimate the location of the unsuspecting mobile user, and the position estimate of each user is updated with every new RSSI measurement at any of the monitoring stations. The presented approach is server-based, i.e., it works without the knowledge or cooperation of the user being tracked, thereby enabling the proposed security application, as well as location-aware services. Validation of the concepts was implemented using an experimental testbed in an office environment. The results demonstrate the ability of the proposed technique to estimate the user location to a very high degree of accuracy.

Localization is a fundamental service for many applications in wireless sensor networks. In this paper we propose a probabilistic, constraint-based approach robust to range measurement inaccuracies. The proposed approach pro- ceeds in three phases: the first phase involves modeling the uncertainties of range measurements; in the second phase, a set of probabilistic constraints are computed and combined to produce initial position estimates; in the final phase, negative constraints are used to refine the initial estimates. We evaluated the proposed approach through simulations based on real-world measurements; the results are compared with two other local- ization schemes and the Cramer-Rao lower bound. The results show that, for inaccurate range measurements, the proposed probabilistic approach performs the best and close to the optimal bound.

Ultra-wideband wireless (UWB) may provide the physical layer for high capacity personal area networks in the future. Certain characteristics of the wireless links possible using this technology give rise to properties not seen with other wireless technologies. Two such properties are long synchronization times for link establishment and the ability to change individual link capacities by choosing PN codes of different lengths. The paper formulates a novel routing problem in UWB; in particular, we investigate the impact of UWB physical layer characteristics on average network transit delay for a UWB network with a ring topology. The paper derives an expression for average network transit delay as a function of the capacity between each pair of nodes in the network. Each node is assumed to have one input and one output link resulting in a ring network topology, which guarantees access to every node. An aggregate network capacity bound for all links is assumed. A Lagrangian function is defined to obtain the optimum link capacities in order to minimize the average network delays and the resulting formula for delay is explained.

Wireless sensor networks are considered the sensing technology of the future. Large numbers of untethered sensor nodes can be used for tracking small animals and targets, environmental monitoring, enforcing security perimeters, etc. A major problem for many sensor network applications is determining the most efficient way of conserving the energy of the power source. Some networks use batteries, while others suggest different methods of gathering energy (e.g., solar cells). Regardless of the powering method, energy conservation is of prime importance for sensor networks. The best way to conserve energy is to turn the sensor nodes off; however, since an inactive sensor node is no longer part of the network, the network can become disconnected. This creates a fundamental trade-off. In this paper, we propose a deterministic, schedule-based energy conservation scheme. In the proposed approach, time-synchronized sensors form on-off schedules that enable the sensors to be awake only when necessary. The schedule establishment is fully distributed and thus appropriate for large sensor networks. The performance of the proposed approach is evaluated through the use of simulations

Wireless sensor networks have the potential to become the pervasive sensing (and actuating) technology of the future. For many applications, a large number of inexpensive sensors is preferable to a few expensive ones. The large number of sensors in a sensor network and most application scenarios preclude hand placement of the sensors. Determining the physical location of the sensors after they have been deployed is known as the problem of localization. We present a localization technique based on a single mobile beacon aware of its position (e.g. by being equipped with a GPS receiver). Sensor nodes receiving beacon packets infer proximity constraints to the mobile beacon and use them to construct and maintain position estimates. The proposed scheme is radio-frequency based, and thus no extra hardware is necessary. The accuracy (on the order of a few meters in most cases) is sufficient for most applications. An implementation is used to evaluate the performance of the proposed approach.

Recent research in sensor networks has raised issues of security for small embedded devices. Security concerns are motivated by the deployment of a large number of sensory devices in the field. Limitations in processing power, battery life, communication bandwidth and memory constrain the applicability of existing cryptography standards for small embedded devices. A mismatch between wide arithmetic for security (32 bit word operations) and embedded data bus widths (often only 8 or 16 bits) combined with lack of certain operations (e.g., multiply) in the ISA present other challenges.This paper offers two contributions. First, a survey investigating the computational requirements for e a number of common cryptographic algorithms and embedded architectures is presented. The objective of this work is to cover a wide class of commonly used encryption algorithms and to determine the impact of embedded architectures on their performance. This will help designers predict a system's performance for cryptographic tasks. Second, methods to derive the computational overhead of embedded architectures in general for encryption algorithms are developed. This allows one to project computational limitations and determine the threshold of feasible encryption schemes under a set of the constraints for an embedded architecture.Experimental measurements indicate uniform cryptographic cost for each encryption class and each architecture class and negligible impact of caches. RC4 is shown to outperform RC5 for the Atmega platform. But when message authentication is required in addition to encryption, hash or block ciphers, such as RC5, have the advantage of providing support for both authentication and encryption. The analytical model allows to assess the impact of arbitrary embedded architectures as a multi-variant function for each encryption scheme. Overall, our results are not only valuable to assess the feasibility of encryption schemes for existing embedded architectures, they also extend to assess the feasibility of encryption methods for new algorithms and architectures for sensor systems.

Time synchronization is important for any distributed system. In particular, wireless sensor networks make extensive use of synchronized time in many contexts (e.g. for data fusion, TDMA schedules, synchronized sleep periods, etc.). Existing time synchronization methods were not designed with wireless sensors in mind, and need to be extended or redesigned. Our solution centers around the development of a deterministic time synchronization method relevant for wireless sensor networks. The proposed solution features minimal complexity in network bandwidth, storage and processing and can achieve good accuracy. Highly relevant for sensor networks, it also provides tight, deterministic bounds on both the offsets and clock drifts. A method to synchronize the entire network in preparation for data fusion is presented. A real implementation of a wireless ad-hoc network is used to evaluate the performance of the proposed approach.

A new, more realistic model for the available bit rate traffic class in ATM network congestion control with explicit rate feedback is introduced and analyzed. This model is based on recent results by M.M. Ekanayake ("Robust stability of discrete time nonlinear systems", Ph.D. dissertation, Univ. Miami, Coral Gables, FL, 1999) regarding discrete time models for time-variant delays. The discrete time model takes into account the effect of time-variant buffer occupancy levels of ATM switches, thus treating the case of time-variant delays between a single congested node and the connected sources. For highly dynamic situations, such a model is crucial for a valid analysis of the resulting feedback system. The new model also handles the effects of the mismatch between the resource management cell rates and the variable bit rate controller sampling rate as well as buffer and rate nonlinearities. A brief stability study shows that an equilibrium in the buffer occupancy is impossible to achieve in the presence of time-variant forward path delays. Stability conditions for the case of time-variant delays in the return path are presented. Finally, illustrative examples are provided.