R-3 Repository :: Browsing by Author "Johnson, David B."

Browsing by Author "Johnson, David B."

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A dynamic distributed transmission power control MAC protocol for mobile ad hoc networks
(2003) Dhar, Aditya; Johnson, David B.
Ad hoc networking involves multihop, peer-to-peer communication between a group of wireless mobile nodes in a network with a dynamically changing topology. Achieving energy-efficient communication in such a network is more challenging than in cellular net works due to the absence of a centralized access point that can administer power control. For example, the commonly used MAC protocol for ad hoc networks, the IEEE 802.11 MAC protocol, uses a fixed power for all packet transmissions, for reasons of simplicity and to maintain the correct operation of its collision avoidance mechanism. In this thesis, I propose a distributed power-control based MAC protocol for ad hoc networks that uses variable transmission power for the control (RTS, CTS) packets and the minimum required transmission power for the DATA and ACK packets. The proposed solution, called PACA (Power-controlled Access with Collision Avoidance), improves both energy consumption and throughput, by reducing the energy used for most packet transmissions and by allowing simultaneous transmissions by different nodes, depending on the location of the respective receivers. PACA also improves the fairness among contending flows, in terms of the channel access time-share. I perform an extensive set of ns -2 simulations to study the impact of factors such as offered load, topology, number of flows, and node mobility on the performance of the proposed protocol and compare it to the IEEE 802.11 MAC protocol. The performance improvements are more pronounced in clustered networks with localized source-destination pairs because they utilize the available spectral reuse more efficiently.
A minimum-cost-neighbor multicast routing protocol for mobile wireless ad hoc networks
(2010) Amiri, Keyvan; Johnson, David B.
MiCoN (Minimum-Cost Neighbor) is a new on-demand multicast routing protocol for mobile wireless ad hoc networks. Multicast routing in MiCoN is based on a new multi-route unicast routing protocol for maintaining routes between the network nodes and all group receivers. This routing is guaranteed to be loop-free even in the presence of dropped packets in the wireless network. MiCoN packet forwarding is based on a new local approximation of the optimal multicast tree, achieved by modeling multicasting as a Facility-Location-Problem. Evaluated in ns-2 simulations. MiCoN outperforms ADMR, the previously best performing on-demand multicast routing protocol for mobile ad hoc networks. To support this evaluation, I have also developed a new simulation model for sparse movement scenarios in ad hoc networks. MiCoN achieves better performance than ADMR, in terms of its packet delivery ratio, latency, and overhead in dense scenarios, and substantially outperforms ADMR on these metrics in sparse networks.
An adaptive sensor network architecture for multi-scale communication
(2006) PalChaudhuri, Santashil; Johnson, David B.
Sensor networking has emerged as a promising tool for monitoring and actuating the devices of the physical world, employing self-organizing networks of battery-powered wireless sensors that can sense, process, and communicate. Such networks can be rapidly deployed at low cost, enabling large-scale, on-demand monitoring and tracking over a wide area. Energy is the most crucial and scarce resource for such networks. However, since sensor network applications generally exhibit specific limited behaviors, there is both a need and an opportunity for adapting the network architecture to match the application in order to optimize resource utilization. Many applications-such as large-scale collaborative sensing, distributed signal processing, and distributed data assimilation-require sensor data to be available at multiple resolutions, or allow fidelity to be traded-off for energy efficiency. In this thesis, I develop an adaptive cross-layered sensor network architecture that enables multi-scale collaboration and communication. Analyzing the unique characteristics of sensor networks, I identify cross-layering and adaptability to applications as the primary design principles needed to build three closely coupled-protocols: (1) a self-organizing adaptive hierarchical data service for multi-scale communication, together with communication primitives to simplify application design; (2) a medium scheduling protocol tailored for this hierarchical data service, to take advantage of the communication and routing characteristics to achieve close to optimal latency and energy usage; and (3) an adaptive clock synchronization service, which provides an analytical framework for mapping clock synchronization requirements to actual protocol parameters, to provide required synchronization. I have analyzed as well as simulated the performance of these protocols to show optimized energy utilization.
An Architecture for Distributed Wavelet Analysis and Processing in Sensor Networks
(2006-04-01) Wagner, Raymond; Baraniuk, Richard G.; Du, Shu; Johnson, David B.; Cohen, Albert
Distributed wavelet processing within sensor networks holds promise for reducing communication energy and wireless bandwidth usage at sensor nodes. Local collaboration among nodes de-correlates measurements, yielding a sparser data set with significant values at far fewer nodes. Sparsity can then be leveraged for subsequent processing such as measurement compression, de-noising, and query routing. A number of factors complicate realizing such a transform in real-world deployments, including irregular spatial placement of nodes and a potentially prohibitive energy cost associated with calculating the transform in-network. In this paper, we address these concerns head-on; our contributions are fourfold. First, we propose a simple interpolatory wavelet transform for irregular sampling grids. Second, using ns-2 simulations of network traffic generated by the transform, we establish for a variety of network configurations break-even points in network size beyond which multiscale data processing provides energy savings. Distributed lossy compression of network measurements provides a representative application for this study. Third, we develop a new protocol for extracting approximations given only a vague notion of source statistics and analyze its energy savings over a more intuitive but naive approach. Finally, we extend the 2-dimensional (2-D) spatial irregular grid transform to a 3-D spatio-temporal transform, demonstrating the substantial gain of distributed 3-D compression over repeated 2-D compression.
Coordination and Interference in 802.11 Networks: Inference, Analysis and Mitigation
(2013-09-16) Magistretti, Eugenio; Knightly, Edward W.; Gurewitz, Omer; Johnson, David B.; Sabharwal, Ashutosh
In the last decade, 802.11 wireless devices data-rates have increased by three orders of magnitude, while communications experiencing low throughput are still largely present. Such throughput loss is a fundamental problem of wireless networking that is difficult to diagnose and amend. My research addresses two key causes of throughput loss: MAC layer protocol overhead and destructive link interference. First, I design WiFi-Nano reducing the channel access overhead by an order of magnitude leveraging an innovative speculative technique to transmit preambles. This new concept is based on simultaneous preamble transmission and detection via a self-interference cancellation design, and paves the way to the realization of the collision detection paradigm in wireless networks. Next, I propose 802.11ec (Encoded Control), the first 802.11-based protocol that eliminates the overhead of control packets. Instead, 802.11ec coordinates node transmissions via a set of predefined pseudo-noise codewords, resulting in the dramatic increase of throughput and communication robustness. Finally, I design MIDAS, a model-driven network management tool that alleviates low throughput wireless links identifying key corrective actions. MIDAS' key contribution is to reveal the fundamental role of node transmission coordination in characterizing destructive interference. I implement WiFi-Nano, 802.11ec, and MIDAS using a combination of WARP FPGA-based radio boards, custom emulation platforms, and network simulators. The results obtained show that WiFi-Nano increases the network throughput by up to 100%, 802.11ec improves network access fairness by up to 90%, and MIDAS identifies corrective actions with a prediction error as low as 20%.
Design and Evaluation of Primitives for Passive Link Assessment and Route Selection in Static Wireless Networks
(2012-09-05) Miskovic, Stanislav; Knightly, Edward W.; Johnson, David B.; Sabharwal, Ashutosh
Communication in wireless networks elementally comprises of packet exchanges over individual wireless links and routes formed by these links. To this end, two problems are fundamental: assessment of link quality and identification of the least-cost (optimal) routes. However, little is known about achieving these goals without incurring additional overhead to IEEE 802.11 networks. In this thesis, I design and experimentally evaluate two frameworks that enable individual 802.11 nodes to characterize their wireless links and routes by employing only local and passively collected information. First, I enable 802.11 nodes to assess their links by characterizing packet delivery failures and failure causes. The key problem is that nodes cannot individually observe many factors that affect the packet delivery at both ends of their links and in both directions of 802.11 communication. To this end, instead of relying on the assistance of other nodes, I design the first practical framework that extrapolates the missing information locally from the nodes' overhearing, the observable causal relationships of 802.11 operation and characterization of the corrupted and undecodable packets. The proposed framework employs only packet-level information generally reported by commodity 802.11 wireless cards. Next, I design and evaluate routing primitives that enable individual nodes to suppress their poor route selections. I refer to a route selection as poor whenever the employed routing protocol fails to establish the existing least-cost path according to an employed routing metric. This thesis shows that an entire family of the state-of-the art on-demand distance-vector routing protocols, including the standards-proposed protocol for IEEE 802.11s mesh networks, suffers from frequent and long-term poor selections having arbitrary path costs. Consequently, such selections generally induce severe throughput degradations for network users. To address this problem, I design mechanisms that identify optimal paths locally by employing only the information readily available to the affected nodes. The proposed mechanisms largely suppress occurrence of inferior routes. Even when such routes are selected their durations are reduced by several orders of magnitude, often to sub-second time scales. My work has implications on several key areas of wireless networking: It removes systematic failures from wireless routing and serves as a source of information for a wide range of protocols including the protocols for network management and diagnostics.
Design and Performance of PRAN: A System for Physical Implementation ofAd Hoc Network Routing Protocols
(2005-02-28) Du, Shu; Johnson, David B.; PalChaudhuri, Santashil; Saha, Amit Kumar; To, Khoa
Simulation and physical implementation are both valuable tools in evaluating ad hoc network routing protocols, but neither alone is sufficient. In this paper, we present the design and performance of PRAN, a new system for implementation of ad hoc network routing protocols that merges these two types of evaluation tools. PRAN (Physical Realization of Ad Hoc Networks) allows existing simulation models of ad hoc network routing protocols to be used—without modification—to create a physical implementation of the same protocol. We have evaluated the simplicity and portability of our approach across multiple protocols and multiple operating systems through example implementations in PRAN of the DSR and AODV routing protocols in FreeBSD and Linux using the existing, unmodified ns-2 simulation models. We illustrate the ability of the resulting protocol implementations to handle real, demanding applications by describing a demonstration with this DSR implementation transmitting real-time video over a multi hop mobile ad hoc network; the demonstration features mobile robots being remotely operated based on the video stream transmitted over the network. We also present a detailed performance evaluation of PRAN to show the feasibility of our architecture.
Design of Adaptive Overlays for Multi-scale Communication in Sensor Networks
(2005-06-01) PalChaudhuri, Santashil; Kumar, Rajnish; Baraniuk, Richard G.; Johnson, David B.; Digital Signal Processing (http://dsp.rice.edu/)
In wireless sensor networks, energy and communication bandwidth are precious resources. Traditionally, layering has been used as a design principle for network stacks; hence routing protocols assume no knowledge of the application behavior in the sensor node. In resource-constrained sensor-nodes, there is simultaneously a need and an opportunity to optimize the protocol to match the application. In this paper, we design a network architecture that efficiently supports multi-scale communication and collaboration among sensors. The architecture complements the previously proposed Abstract Regions architecture for local communication and collaboration. We design a self-organizing hierarchical overlay that scales to a large number of sensors and enables multi-resolution collaboration. We design effective Network Programming Interfaces to simplify the development of applications on top of the architecture; these interfaces are efficiently implemented in the network layer. The overlay hierarchy can adapt to match the collaboration requirements of the application and data both temporally and spatially. We present an initial evaluation of our design under simulation to show that it leads to reduced communication overhead, thereby saving energy.We are currently building our architecture in the TinyOS environment to demonstrate its effectiveness.
Efficient duty cycle MAC protocols for dynamic traffic loads in wireless sensor networks
(2009) Sun, Yanjun; Johnson, David B.
Idle listening is one of the most significant causes of energy consumption in wireless sensor networks (WSNs), and many protocols have been proposed based on duty cycling to reduce this cost. These protocols, either synchronous or asynchronous, are mainly optimized for light traffic loads. A WSN, however, could often experience bursty and high traffic loads, as may happen for example with broadcast or convergecast traffic. In this thesis, I design and evaluate a new synchronous protocol, DW-MAC (Demand Wakeup MAC), and a new asynchronous protocol, RI-MAC (Receiver Initiated MAC), that are both efficient under dynamic traffic loads, including light or heavy loads. I also design and evaluate ADB (Asynchronous Duty-cycle Broadcasting), a new protocol for efficient multihop broadcasting in WSNs using asynchronous duty cycling. DW-MAC introduces a new low-overhead scheduling algorithm that allows nodes to wake up on demand during the Sleep period of an operational cycle and ensures that data transmissions do not collide at their intended receivers; this demand wakeup adaptively increases effective channel capacity as traffic load increases. RI-MAC, instead, uses receiver-initiated transmissions, in which each transmitter passively waits until its intended receiver wakes up and transmits a beacon frame; this technique minimizes the time a sender and its intended receiver occupy the wireless medium to find a rendezvous time for exchanging data. ADB is integrated with RI-MAC to exploit information only available at this layer; rather than treating the data transmission from a node to all of its neighbors as the basic unit of progress for the multihop broadcast. ADB dynamically optimizes the broadcast at the level of transmission to each individual neighbor of a node as the neighbors asynchronously wakeup, avoiding redundant transmissions and transmissions over poor links, and allowing a transmitter to go to sleep as early as possible. In detailed simulation of all three protocols using ns-2, they each substantially outperform earlier competing protocols in terms of reduced energy and latency and increased packet delivery ratio. I also implemented RI-MAC and ADB in a testbed of MICAz motes using TinyOS and further demonstrate the significant performance improvements made over prior protocols.
Energy saving and partition bridging using directional antennas in mobile ad hoc networks
(2003) Saha, Amit Kumar; Johnson, David B.
In this thesis, I present the design and evaluation of new techniques for using directional antennas to save energy and to bridge network partitions in a mobile ad hoc network. This thesis advocates close but simple collaboration between the routing layer and the Medium Access Control (MAC) layer and shows through simulations, the effectiveness of this design by modifying the Dynamic Source Routing (DSR) protocol, an on-demand ad hoc network routing protocol based on source routing. First, in order to save energy, Route Requests and data packets are transmitted directionally. Extensive simulations show that without affecting the behavior of the routing protocol noticeably, energy savings of up to 75% is achieved. Second, in order to bridge network partitions, the routing protocol is modified to use the ability of a directional antenna to transmit directionally over longer distance as compared to an omnidirectional antenna, both antennas using the same power. Again, through simulations, the protocol is shown to be able to bridge network partitions. Also, when no partitions are present, the protocol is otherwise equivalent to the version without the partition bridging modifications.
Evaluating Multihop Mobile Wireless Networks with Controllable Node Sparsity or Density
(2015-12-04) Amiri, Keyvan; Johnson, David B.; Baraniuk, Richard G.; Jermaine, Christopher
Simulation is the most widely used tool for evaluating the performance of multihop mobile wireless networks, yet such simulation has so far been limited due to the lack of sufficient wireless mobility models for creating a wide range of different types of network scenarios of mobile nodes moving about for use in protocol simulation. For example, the very commonly used Random Waypoint mobility model can only effectively be used in scenarios with relatively high node density, as attempting to generate sparser scenarios (e.g., trying the same number of nodes in larger and larger spaces) results in scenarios in which the network is frequently or always partitioned, with no possible multihop wireless path between many different pairs of nodes. In this thesis, I present the design and evaluation of the Random Controlled Sparse (RCS) mobility model, a new dynamic, tunable mobility model that can be controlled to generate a wide range of mobile scenarios with varying levels of node sparsity or density while avoiding network partitions. The model requires only a small set of parameters to define the desired behavior of the scenarios being generated. In generating a scenario, RCS itself internally operates as a separate discrete event simulator, utilizing highly efficient graph and computational geometry algorithms to control the desired sparse behavior and manage the constraints between the motions of different nodes. To further improve the performance and scalability of the model, I have also parallelized certain key parts of the scenario generation in the model. To show the performance of the model in generating scenarios, I have evaluated the running time of the model across wide range of number of nodes and node densities. I also present an evaluation of the scenarios generated, in terms of metrics such as the average number of neighbors of a node and the average minimum possible path length (hop count) existing between each pair of nodes, demonstrating the range of scenarios that RCS is able to produce. To show the usefulness of the model in revealing protocol behavior, I show the performance of DSDV, a common multihop wireless ad hoc network routing protocol, across a wide range of sparse and dense network scenarios. These results demonstrate that different degrees of node sparsity or density sometimes have surprising effects on protocol performance. Simulations such as these, revealing these types of results, have not generally been possible before due to the lack of suitable mobility models. Finally, to more fully show the use of the RCS model in evaluating real protocols, I present the design and evaluation of LAMP, the Local-Approximation Multicast Protocol, a new on-demand multicast routing protocol I have designed for mobile wireless ad hoc networks that delivers high performance in both sparse as well as dense scenarios. LAMP maintains high performance by utilizing link-layer unicast transmissions, based on a new algorithm in which each node computes a local approximation of the globally optimal multicast forwarding tree to the receivers. LAMP also introduces a new distributed protocol optimization known as anticipatory forwarding, to further improve both overhead and packet delivery latency when this local approximation deviates from the globally optimal tree. I have evaluated LAMP through detailed ns-2 simulations using scenarios from the RCS model as well as the Random Waypoint model, and compared it with ODMRP and ADMR, two existing on-demand multicasting protocols that have previously been shown to perform well.
High-Performance Communication Protocols for Asynchronous Duty-Cycling Wireless Networks
(2013-11-07) Tang, Lei; Johnson, David B.; Ng, T. S. Eugene; Knightly, Edward W.
Duty cycling is a technique for saving energy in resource-limited wireless networks such as sensor networks. With duty cycling, each node periodically switches between active and sleeping states, for example being active for only 1 to 10 percent of the time. Wireless duty-cycling networks face many challenges such as maintaining high energy efficiency, efficient packet delivery under dynamic channel conditions, and effective route discovery. This thesis presents a series of protocols to address these challenges. The first part of this thesis presents a new single-channel energy-efficient MAC protocol, called the Predictive-Wakeup MAC (PW-MAC). The key idea behind PW-MAC is to allow each node to wake up asynchronously at randomized times, while enabling senders to predict receiver wakeup times to save energy. Extending the randomized predictive wakeup mechanism of PW-MAC, the second part of this thesis presents a new multichannel energy-efficient MAC protocol, called the Efficient-Multichannel MAC (EM-MAC). EM-MAC enables each node to dynamically optimize the selection of wireless channels it utilizes based on the channel conditions it senses. By adapting to changing channel conditions, EM-MAC achieves high packet delivery performance. EM-MAC also achieves high energy efficiency through its predictive multichannel wakeup mechanism. Although duty cycling saves energy, I found that, in asynchronous duty-cycling networks, existing on-demand routing protocols tend to discover routes much worse than the optimal routes. The last part of this thesis presents four optimization techniques to improve the routes discovered in such networks. These optimizations are fully distributed and work on different route metrics, such as hop-count and ETX. Implemented in TinyOS on a testbed of MICAz sensor nodes, PW-MAC achieved the lowest energy consumption and delivery latency among the single-channel protocols, while EM-MAC significantly outperformed all other protocols tested. EM-MAC maintained the lowest duty cycles, the lowest packet delivery latency, and 100% packet delivery ratio across all experiments, including those with concurrent multihop traffic flows, and those with heavy ZigBee and Wi-Fi interference. Finally, in simulations on the ns-2 network simulator, compared with the conventional on-demand route discovery, the presented route discovery optimizations substantially improved the routes discovered in asynchronous duty-cycling networks.
Interference-aware protocol enhancements for ad hoc wireless networks
(2006) Sun, Yanjun; Johnson, David B.
An ad hoc network is an autonomous system of wireless mobile nodes, in which each node forwards packets for other nodes so that nodes out of direct wireless transmission range can communicate. In on-demand routing protocols for ad hoc networks, we find that existing schemes mistakenly may decide that a link is broken when it is not, especially when either endpoint node of the link experiences heavy interference. Moreover, a route claimed to be available may contain broken links due to the presence of stale routing information. We develop interference-aware enhancements both at the MAC layer and at the routing layer to address these problems. Simulation results show that our proposed enhancements reduce the problem dramatically and in turn increase the performance and efficiency of the routing protocol. In our simulations, total network throughput improved by up to 38% with DSR and by up to 13% with AODV.
Location-aided routing in intermittently connected networks
(2005) To, Khoa Anh; Johnson, David B.
One of the difficulties in achieving pervasive deployment of mobile ad hoc network routing protocols is their strong assumption regarding node connectivity. Many realistic networking scenarios fail to meet this assumption, as nodes often form wireless clusters that are only intermittently connected with each other. In this work, I introduce Oriole, a routing protocol for mobile communications in intermittently connected networks. My design of Oriole explores node location information (for instance, through GPS) and realistic node mobility for achieving efficient packet delivery. I evaluate the protocol in terms of packet delivery latency, network overhead, and memory requirements at each node, using realistic simulations of the Rice University campus topography. I show that packet delivery latency of Oriole is comparable to that of Epidemic Routing and an omniscient routing protocol, with Oriole imposing an order of magnitude (over 30 times) less per-node network and memory overhead than Epidemic Routing.
Mobile Access and Network-Coding in Diverse-Band Wireless Networks: Design and Evaluation
(2013-06-05) Giannoulis, Anastasios; Knightly, Edward W.; Johnson, David B.; Sabharwal, Ashutosh
Wireless networks increasingly utilize diverse spectral bands, which exhibit vast differences in transmission range, bandwidth and available airtime. While tremendous efforts have been devoted to enable efficient mobile access of single-band networks and increase their throughput, e.g., via network coding, such single-band solutions are unfortunately oblivious to the diversity and abundance of the available spectral bands. In this thesis, I present and evaluate novel schemes for mobile access and for throughput increase using network coding, schemes that are designed for diverse-band wireless networks, i.e., networks operating in multiple diverse bands. Specifically, I introduce the first scheme designed for mobile clients to evaluate and select both APs and spectral bands in diverse-band networks. The fundamental problem is that the potentially vast number of spectrum and AP options may render scanning prohibitive. Thus, my key technique is for clients to infer the critical metrics of channel quality and available airtime for their current location and bands using limited measurements collected in other bands and at other locations. I evaluate my scheme via experiments and emulations, which are enabled by a four-band testbed that I deploy. A key finding is that under a diverse set of operating conditions, mobile clients can accurately predict their performance without a direct measurement at their current location and spectral bands. Moreover, I introduce the first band selection schemes designed for diverse-band networks exploiting overheard packets to enable network coding. The main problem is that band selections in such networks are challenged by conflicting factors affecting throughput: while the number of overhearing nodes generally increases with decreasing frequency, channel width and spatial reuse unfortunately decrease. Thus, the key technique of the proposed schemes is to jointly incorporate coding gains, channel width and spatial reuse in band selections. I evaluate these schemes via simulations employing a physical-layer model driven by measurements collected using the deployed four-band testbed. An important finding is that the proposed schemes can outperform coding-oblivious spectrum access in terms of throughput, as their band selection enables more coding opportunities. My work has two key implications. First, it can significantly improve throughput performance in networks enabled by today’s unlicensed spectrum and by the billion-dollar industry of white-space networking. Second, I anticipate that this thesis will highly impact future research, as I open new research areas in a domain that has attracted such tremendous commercial and research interest.
Network Stack Architecture for Future Sensors
(2005-01-26) Johnson, David B.; Kumar, Rajnish; PalChaudhuri, Santashil; Ramachandran, Umakishore
With wireless ad hoc sensor networks, there is simultaneously a need and an opportunity to optimize the protocol stack behavior to match the sensor-based applications. A general-purpose internet stack is neither appropriate nor sufficient to meet the needs of such applications. Motivated by this observation, we pose two related questions: (a) What is an appropriate layering of the protocol stack for future sensor networks? (b) How do we make the network stack tunable to a specific sensor application? We present the design of a new protocol stack, and we qualitatively argue that the new stack is more suitable to meet the demands of sensor network applications than traditional stacks.
Physical Implementation of Synchronous Duty-Cycling MAC Protocols: Experiences and Evaluation
(2013-07-24) Xiao, Wei-Cheng; Johnson, David B.; Knightly, Edward W.; Ng, T. S. Eugene
Energy consumption and network latency are important issues in wireless sensor networks. The mechanism duty cycling is generally used in wireless sensor networks for avoiding energy consumption due to idle listening. Duty cycling, however, also introduces additional latency in communication among sensors. Some protocols have been proposed to work in wireless sensor networks with duty cycling, such as S-MAC and DW-MAC. Those protocols also tried to make efficient channel utilization and to mitigate the chance of packet collision and the network latency increase resulting from collision. DW-MAC was also designed to tolerate bursty and high traffic loads without increasing energy consumption, by spreading packet transmission and node wakeup times during a cycle. Some performance comparison between S-MAC and DW-MAC has been done in previous work; however, this comparison was performed in the ns-2 simulator only. In the real world, there are further issues not considered or discussed in the simulation, and some of those issues contribute significant influences to the MAC protocol performance. In this work, I implemented both S-MAC and DW-MAC physically on MICAz sensor motes and compared their performance through experiments. Through my implementation, experiments, and performance evaluation, hardware properties and issues that were not addressed in the previous work are presented, and their impacts on the performance are shown and discussed. I also simulated S-MAC and DW-MAC on ns-2 to give a mutual validation of the experimental results and my interpretation of the results. The experiences of physical implementations presented in this work can contribute new information and insights for helping in future MAC protocol design and implementation in wireless sensor networks.
Power mode scheduling for ad hoc network routing
(2002) PalChaudhuri, Santashil; Johnson, David B.
An ad hoc network is a group of mobile wireless nodes that cooperatively form a network among themselves without any fixed infrastructure. Each node in the ad hoc network forwards packets for other nodes, to allow nodes not within direct wireless transmission range to communicate, using a routing protocol. Increasingly, power consumption within ad hoc networks is becoming a core issue for these low-power mobile devices. This thesis focuses on a novel approach for energy conservation within the ad hoc network routing protocol. I develop and evaluate two types of mechanisms for reducing this power consumption by the routing protocol in the network. The routing protocol uses information from packets received promiscuously to improve routing performance. The first part of this work is a strategy for reducing this use of promiscuous mode intelligently, thereby saving energy but retaining all the benefits of being in promiscuous mode. In addition, a wireless network interface in sleep mode expends an order of magnitude less power than in idle mode, but no packets can be sent or received while in sleep mode. In the second part of this work, I propose two probabilistic algorithms for scheduling transition from idle mode to sleep mode. Performance evaluation of these strategies shows significant reduction in power usage, with only a slight decrease in performance.
Probabilistic Clock Synchronization Service in Sensor Networks
(2003-04-16) Johnson, David B.; PalChaudhuri, Santashil; Saha, Amit
Recent advances in technology have made low cost, low power wireless sensors a reality. Clock synchronization is an important service in any distributed system, including sensor network systems. Applications of clock synchronization in sensor networks include data integration in sensors, sensor reading fusion, TDMA medium access scheduling, and power mode energy saving. However, for a number of reasons, standard clock synchronization protocols are unsuitable for direct application in sensor networks. In this paper, we describe a probabilistic service for clock synchronization that is based on the Reference Broadcast Synchronization protocol. In particular, we use the higher precision of receiver-to-receiver synchronization, as described in Reference Broadcast Synchronization protocol. We extend this deterministic protocol to provide a probabilistic bound on the accuracy of the clock synchronization service, allowing for a tradeoff between accuracy and resource requirement. We derive expressions to convert service specifications (maximum clock synchronization error and confidence probability) to actual protocol parameters(minimum number of messages and synchronization overhead). We also extend this protocol for maintaining clock synchronization in a multi hop network.
Robustness and Optimality in CSMA Wireless Networks
(2013-06-04) Nardelli, Bruno; Knightly, Edward W.; Sabharwal, Ashutosh; Johnson, David B.
In today's widely diffused CSMA wireless networks, problems of coordination in the access to the channel by multiple transmitters can lead to unfair situations where some of the flows receive much of the network throughput while others suffer from poor performance. As a solution to this problem, recent theoretical studies have proposed distributed CSMA adaptation protocols that, under certain assumptions, maximize a network utility function, yielding high throughput fairly distributed among flows. The main idea in the operation of such protocols, referred to as Optimal CSMA, is to adapt the contention aggressiveness of a flow as a function of its queue length, without the need of any information exchange among nodes. Thus, their operation is distributed, and does not introduce additional control overhead to CSMA operation. However, we show that such an approach is fragile, and can suffer high performance degradation under conditions of frequent occurrence, namely; asymmetric channels, heterogeneous traffic, and packet collisions. In this work, we address the main sources of performance degradation in Optimal CSMA to design a distributed protocol for proportional-fair throughput maximization robust to such conditions. First, we generalize Optimal CSMA models to incorporate individual per-link modulation and coding rates. With our generalized network optimization model, we derive distributed algorithms that maximize utility under arbitrary channel capacities. Second, we propose a novel structure that can be used in the place of queues to provide optimal CSMA adaptation. As such a structure does not use traffic backlog to operate, the resulting adaptation is optimal for the set of active flows under general traffic arrival patterns. Third, we propose a robustness function compatible with the optimization approach, which maintains high medium access rates to maximize performance in low contention scenarios, yet reduces medium access to avoid collisions as the network contention increases. Finally, we validate our design by evaluating its performance against state-of-the-art protocols for distributed CSMA optimization under critical scenarios combining the three aforementioned sources of performance degradation, observing vast gains in network logarithmic utility across a wide-range of network operating conditions.

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