We present the DECODE technique to determine whether a set of transmitters are co-moving, i.e., moving together in close proxim- ity. Co-movement information can find use in applications ranging from inventory tracking, to social network sensing, and to optimizing mobile device localization. The positioning errors from indoor RSS based localization systems tend to be too large making it difficult to detect whether two devices are moving together based on the inter-device distances. DECODE achieves accurate co-movement detection by exploiting the correlations in positioning errors over time. DECODE can not only be implemented in the position space but also in the signal space where a correlation in shadow fading due to objects blocking the path between the transmitter and receiver exists. This technique requires no changes in or cooperation from the tracked devices other than sporadic trans- mission of packets. Using experiments from an office environment, we show that DECODE can achieve near perfect co-movement detection at walking-speed mobility using correlation coefficients computed over approximately 60-second time intervals. We further show that DECODE is generic and could accomplish detection for mixed mobile transmitters of different technologies (IEEE 802.11b/g and IEEE 802.15.4), and our results are not very sensitive to the frequency at which transmitters communicate.

OMF was originally developed for the (stationary) ORBIT wireless testbed at WINLAB, Rutgers University. Through active development and extensions at NICTA, it has now evolved into an independent framework, which supports heterogenous wired or wireless resources. OMF is one of the candidates currently being evaluated as potential testbed frameworks by both GENI2 and FIRE3 funded testbed initiatives, such as Onelab4. OMF is currently deployed and used on different testbeds in Australia, USA, and Europe.This demonstration showcases OMF's current capabilities with an experiment demonstrating a common investigative life cycle.

This work investigates the lower bounds of wireless localization accuracy using signal strength on commodity hardware. Our work relies on trace-driven analysis using an extensive indoor experimental infrastructure. First, we report the best experimental accuracy, twice the best prior reported accuracy for any localization system. We experimentally show that adding more and more resources (e.g., training points or landmarks) beyond a certain limit, can degrade the localization performance for lateration-based algorithms, and that it could only be improved further by 'cleaning' the data. However, matching algorithms are more robust to poor quality RSS measurements. We next compare with a theoretical lower bound using standard Cramer Rao Bound (CRB) analysis for unbiased estimators, which is frequently used to provide bounds on localization precision. Because many localization algorithms are based on different mathematical foundations, we apply a diverse set of existing algorithms to our packet traces and found that the variance of the localization errors from these algorithms are smaller than the variance bound established by the CRB. Finally, we found that there exists a wide discrepancy from what free-space models predict in the signal to distance function even in an environment with limited shadowing and multipath, thereby imposing a fundamental limit on the achievable localization accuracy indoors.

This paper presents an experimental study on the spectrum coexistence problems between multi-radio platforms in dense-radio physical world environments. Computing and communication devices such as laptops and cellular phones with multiple radios including WiFi, Bluetooth, UWB, WiMax and Zigbee in a small conference room face significant interference problems. A realistic small office/home office (SOHO) scenario with 10-25 multi-radio platforms is mapped onto the ORBIT radio grid testbed, and system throughput results are obtained experimentally, demonstrating significant degradation due to inter-platform interference. The CSCC (Common Spectrum Coordination Channel) protocol proposed in earlier work is used as the basis for implementing a set of distributed spectrum coexistence algorithms intended to improve system performance. Detailed results from ORBIT testbed experiments are given for the proposed CSCC-based distributed spectrum coordination algorithms. The results show significant performance gains due to CSCC coordination, typically achieving 2x improvement in system throughput for WiFi/Bluetooth dual radio scenarios.

In this paper, we report on our experimental study of the effects of inter-cell interference on IEEE 802.11 performance. Due to growing use of wireless LANs (WLANs) in residential areas and settings supporting flash crowds, chaotic unplanned deployments are becoming the norm rather than an exception. Environments in which these WLANs are deployed, have many nearby access points and stations on the same channel, either due to lack of coordination or insufficient available channels. Thus, inter-cell interference is common but not well-understood. According to conventional wisdom, the efficiency of an IEEE 802.11 network is determined by the number of active clients. However, we find that with a typical TCP-dominant workload, cumulative system throughput is characterized by the number of actively interfering access points rather than the number of clients. We verify that due to TCP flow control, the number of backlogged stations in such a network equals twice the number of active access points. Thus, a single access point network proves very robust even with over one hundred clients, while multiple interfering access points lead to a significant increase in collisions that reduces throughput and affects media traffic. Only two congested interfering cells prevent high quality VoIP calls. Based on these findings, we suggest a practical contention window adaptation technique using information on the number of nearby access points rather than clients. We also point out the need for collision-resilient rate adaptation in such a setting. Together these techniques can largely recover the 50% loss in cumulative throughput in a setting with four strongly interfering access points.

We present the DECODE technique to determine from a remote receiver whether two transmitters are co-moving, that is moving together in close proximity. Co-movement information can find use in applications ranging from inventory tracking and social network sensing, to optimizing mobile device localization. DECODE detects co-moving transmitters by identifying correlations in communication signal strength due to shadow fading. Unlike localization systems, it can operate using measurements from only a single receiver. It requires no changes in or cooperation from the tracked devices other than sporadic transmission of packets. Using experiments from an office environment, we show that DECODE can achieve near perfect co-movement detection at walking-speed mobility using correlation coefficients computed over approximately 60s time intervals. We further show that DECODE could accomplish detection for mixed mobile transmitters of different technologies (IEEE 802.11b/g and IEEE 802.15.4) and our results are not very sensitive to the frequency at which transmitters communicate.

This article presents an integrated admission control and routing mechanism for multi-rate wireless mesh networks. Admission control depends on precise estimates of available bandwidth at involved nodes and the bandwidth consumption required by a new flow. Estimating these parameters in wireless networks is challenging due to the shared and open nature of the wireless channel. Existing available bandwidth estimation techniques do not accurately consider interference from neighboring nodes and flow bandwidth requirement estimates or act overly conservative, restricting opportunities for parallel transmission due to spatial reuse. We propose the DCSPT method for available bandwidth estimation, based on dual carrier sensing with parallel transmission awareness. We also introduce a packet probing-based available bandwidth estimation method, suitable for legacy device implementations, and verify it experimentally. These techniques are integrated in an admission control mechanism designed for a hop-by-hop routing protocol (LUNAR), enabling alternate route identification when shortest paths are congested. Our protocol uses temporal accounting to enable bandwidth estimation across links using different bit-rates. Simulation results demonstrate that our admission control mechanism can effectively control the traffic load while considering parallel transmission opportunities, leading to cumulative system throughput improvements up to 80% compared to more conservative approaches. We further show that additional gains in system throughput come without significant cost in terms of packet delivery ratio or end-to-end delay and discuss our implementation experience on the ORBIT wireless research testbed.

In this paper, we present a systematic experimental study of the effect of inter-cell interference on IEEE 802.11 performance. With increasing penetration of WiFi into residential areas and usage in ad hoc conference settings, chaotic unplanned deployments are becoming the norm rather than an exception. These networks often operate many nearby access points and stations on the same channel, either due to lack of coordination or insufficient available channels. Thus, inter-cell interference is common but not well-understood. According to conventional wisdom, the efficiency of an 802.11 network is determined by the number of active clients. Surprisingly, we find that with a typical TCP-dominant workload, cumulative system throughput is characterized by the number of interfering access points rather than the number of clients. We find that due to TCP flow control, the number of backlogged stations in such a network equals twice the number of access points. Thus, a single access point network proved very robust even with over one hundred clients. Multiple interfering access points, however, lead to an increase in collisions that reduces throughput and affects volume of traffic in the network.

We analyze the feasibility of boostrapping a location service through geocoded postal addresses rather than the common wardriving technique. A location service that contains the MAC addresses and geographic position of wireless LAN access points enables positioning services for WLAN devices and location-aware networking protocols. This work thus compares the accuracy of access point position estimates obtained based on RF signal strengths readings (wardriving) with the accuracy of the geocoded postal address. The results show similar accuracy for geocoding in comparison to typical wardriving studies, with significantly reduced effort if postal addresses of access point positions are known.

Evaluating available bandwidth estimation methods requires a malleable MAC protocol implementation, precise MAC layer packet timing measurements, and the ability to create control topologies in laboratory setups so that not all nodes are within communication range. To address these challenges, we have exploited IEEE 802.11e-derived features to obtain more control over the MAC layer operation of off-the-shelf radios and implemented a measurement-system that uses CPU timestamp counter and radio hardware timestamps to monitor MAC activity with microsecond resolution. In addition to presenting performance of our available bandwidth estimation method using packet probes, we also discuss solutions and open issues to provide useful information for other testbed cross-layer protocol evaluations, which are likely to face similar challenges.

The ability of properly covering the terrain under investigation and collecting measurements from redundantly sensed portions of the terrain are two important objectives for monitoring applications using wireless sensor networks. Here, a new architectural view of information retrieval for XML compliant environmental monitoring applications is introduced. The sensor network is constructed to satisfy the requirements of monitoring applications and maintained as long as the application has queries to be run on the sensor nodes. Mobile clients of the architecture (drivers), such as human beings or autonomous robots, navigate within the sensing environment and build up sensor node trees in order to effectively disseminate queries and collect the results. In the paper, viable methods are proposed for query service binding, query driven sensor network topology construction and end-to-end event delivery on dynamically maintained return paths. Simulation results considering the reliability and coverage performance of the proposed approach are provided to evaluate the new schemes.

An open source Internet application, Student Transcript and Registration System (STARS), used by Yeditepe University, Faculty of Engineering and Architecture is introduced in this paper. This system provides Internet services for university members, such as course registration and grade follow up for students, entering grades and advising for faculty staff and furthermore, it provides services for academic and administrative units to enter and view information via Intranet. STARS is an interactive, user friendly, flexible, open to integration and easy to maintain product, using latest technologies.

Mobile Ad Hoc Networks (MANET) are composed of moving wireless communication capable computers usually deployed for the purpose of temporal information exchange in cases where coverage of infrastructured networks is not available. Considering the fragile environment of MANET, simple and application aware communication approaches must be preferred in favor of complex and general purpose cascaded stack of protocols. These approaches must serve the applications need for access to services available on other hosts, addressing the announcement, discovery, binding and utilization of those services. In this thesis, dynamic access to named non-interactive services in ad hoc networks is studied and a simple cross layer protocol is designed for service discovery and routing. The algorithms of the proposed protocol are implemented in a wireless network simulation software, GloMoSim, for the purpose of algorithm veri cation and performance evaluation. Some representative applications and scenarios designed out of these applications using the simulation software extensions for the new protocol are also implemented. The results from these experiments have shown that a service aware slim protocol stack implementation is possible for non-interactive service access in mobile ad hoc networks. The advantages of having service awareness in the network layer are also emphasized. Content of the thesis includes the necessary motivation and background for MANET, proposed communication infrastructure, designed mechanisms, simulation implementation details, experiment and results.

This paper introduces an architectural approach to ser vice access in an environment where no established infra stucture at any level exists. Mobile clients invoke services by their descriptive names and a temporary multihop net work is dynamically formed between the client and the host offering a service instance. The proposed protocol stack supports dynamically optimized routing to named services. The elements of the architecture for adapting clients and services to a highly varying topology are explained and the algorithms are given in pseudo code like notation using a service model specified in XML.

Dynamic service discovery and late binding to the most appropriate network service will be the key characteristics of future ad hoc networks. In adhoc networks, the nodes are mobile and the multihop environment does not rely on an existing communication infrastructure. Mobile nodes dynamically establish routes among themselves to form a network “on the fly”. “Appropriateness” of a service is a system-specific definition associated with the current state; such as “the nearest accesible” or “the least loaded”. These environments require a resource discovery model based on expressive and descriptive service definitions for binding. In this paper, we present a service discovery protocol based on a node mobility and service definition model formally specified in eXtensible Markup Language (XML). The protocol employs a session-based approach to service access whereas the discovery algorithm returns both the service location and the route information for late binding. Initial thoughts on the simulation model that will be used for the validation and performance analysis are also given.