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ABSTRACT: We investigate the effectiveness of cluster-based routing protocols in extending the lifetime for energy-constrained wireless sensor networks. Most routing protocol designs for wireless sensors exploit the fact that they are not communication networks in the classical meaning. They can rather be considered as distributed systems where all the different entities collaborate to perform a given task or set of tasks. This fact is used to trade per node fairness and other networking qualities for designs that are energy efficient. The networking layer is responsible for the end to end routing and delivery of data messages. Routing decisions affect the number of transmissions, the distance covered per transmission and the load placed on the intermediate nodes that participate in relaying the messages. This makes the design of energy efficient protocols in the routing layer very critical for extending the network lifetime. For these reasons, the network layer has attracted more attention than the other layers for energy-efficient designs. This study focuses on common parameters of well-known cluster based routing protocols.We use LEACH protocol as a representative to investigate their energy performance sensitivity to the number of clusters, the location of the base station and the data message size.
Innovations in Information Technology (IIT), 2011 International Conference on; 05/2011
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ABSTRACT: Multi-hop broadcast routing is a critical component in ad-hoc wireless networks. Vehicular ad-hoc network (VANET) applications for example use broadcast communications extensively. Efficient broadcast protocols are required to enable these applications. Multi-hop broadcast algorithms can roughly be classified as either topological or statistical. Statistical protocols are well-suited to applications such as VANET, because they are tolerant of rapid changes in network topology and can be designed to accommodate transmission failures due to fading and collisions. However, unlike topological protocols, statistical methods are highly stochastic in nature so it is not possible to analytically prove these algorithms will connect all nodes in the network. Instead, designers attempt to measure and minimize the probability nodes will not receive a broadcast message. Thus simulation plays an important role in the design and validation of these protocols. The key design factor in statistical protocols is the rebroadcast decision threshold curve. There are no analytical tools for creating these threshold curves, so like many stochastic systems, simulation models are required to develop them. Empirically discovering good threshold curves using simulation models requires many simulation iterations, and thus can be extremely time consuming if these iterations are slow. As a solution, this work introduces the Wireless Broadcast Design and Analysis Tool (WiBDAT), a fast and scalable high-level network simulator built from the ground up specifically for wireless broadcast. WiBDAT provides tools for quickly designing efficient statistical broadcasting protocols and evaluating their performance at a high level. WiBDAT is easy to use and extend, implements a wide variety of broadcast protocols, and provides clear results including innovative visualizations of node and transmit densities.
Wireless Communications and Networking Conference (WCNC), 2011 IEEE; 05/2011
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ABSTRACT: Multi-hop wireless broadcast is a critical component in ad-hoc wireless networks. Vehicular Ad-hoc Networks (VANET) in particular utilize broadcast as a primary communication mechanism in many applications. Such networks exhibit situations of very high node densities so it is important that the broadcast protocols used to support applications on these networks scale well to high densities. This work evaluates existing broadcast protocols in terms of this scalability using both a high-level simulation assuming an ideal medium (WiBDAT) and a standard detailed wireless simulation (JiST/SWANS). Four broadcast methods and protocols, each having been used as a forwarding node selection algorithm in VANET, are chosen for evaluation: stochastic broadcast, distance method, Advanced Adaptive Gossiping (AAG), and Multi-Point Relaying (MPR). Results show a distinct performance difference in terms of rebroadcast efficiency at high densities. Protocols using network topology information, AAG and MPR, become inefficient at high densities. Stochastic broadcast and the distance method, which use neighbor count directly to calculate retransmit thresholds, are shown to be highly adaptive to node density.
Communications and Information Technology (ICCIT), 2011 International Conference on; 05/2011
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ABSTRACT: Here we propose an analytical model of energy usage hierarchical wireless sensor network protocols such as LEACH [1]. LEACH has been used as a foundation for much of the wireless sensor network research, so results addressing the underlying nature of these systems build understanding of a wide range of existing protocols. First, we derive the probability density functions of the distance to the nearest cluster head, the distance to the nearest cluster head squared, and the expected number of nodes per cluster. These results are then applied to produce a model of the amount of average energy used per node for each data report. Using this model we give an analytic expression for the optimal cluster-head selection rate. The model is further improved to give an approximate adjustment for distortions in energy usage near the edges of the field. This final model is then compared to the simulation results presented in the original LEACH paper [1] and shown to be accurate. Sensor network protocol researchers can apply results presented here to improve performance of existing systems by making the cluster head selection rate adaptive to external factors.
High-Capacity Optical Networks and Enabling Technologies (HONET), 2010; 01/2011
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ABSTRACT: Wireless sensors are promising and revolutionary technology. The sensor devices are typically deployed in large number to form a communication network for monitoring the physical environment. These devices are battery powered and the lifetime of the device is dependent on the battery's life. Once the battery's energy is depleted, the node is considered dead and is no longer part of the network. Recharging the sensors' batteries is not feasible, and in some cases, is completely impossible. Due to their severe energy constraints and redundancy in sensed data, hierarchal architectures are usually suggested for these networks. These architectures have proven effective in extending the network life several folds. The LEACH network routing protocol is the first protocol to use clustering for energy conservation in Wireless Sensor Networks. LEACH designers observe that there is an ideal percentage of nodes that need to be cluster heads to achieve optimal energy performance. For their work and performance analysis they selected 5% as the number of cluster heads in the netwok. The majority of routing protocols for WSNs follow LEACH and use clustering for energy performance optimization. Most of these protocols have taken the 5% percentage of cluster head as their ideal working setting, without independently qualifying this assumption. In this work, we use simulation modeling to investigate the dependency of this cluster head percentage on the network node density. Our results show that this percentage is not universal for all network settings, and is indeed dependent on the density. These findings will add to the challenging task of WSNs hierarchical networking protocols design.
High-Capacity Optical Networks and Enabling Technologies (HONET), 2010; 01/2011
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ABSTRACT: Broadcast is a critical component in ad-hoc wireless networks. Some vehicular network (VANET) applications in particular use broadcast communications extensively. VANETs exhibit a wide variety of node density and distribution patterns, so broadcast protocols designed to support these applications must be adaptive to those conditions. We show that the distance method of statistical broadcast can be used to design a protocol that performs well in one-dimensional or two-dimensional uniformly distributed networks, but not both. We propose using the quadrat method of spatial analysis to characterize the distribution pattern at each node and use the resulting metric, K, as a factor in computing the statistical threshold function. The result, the Distribution-Adaptive Distance (DAD) method, is shown to exhibit a high level of reachability and efficient bandwidth utilization across a range of distribution patterns from purely linear to purely two-dimensional and sparsely distributed to densely distributed. More generally, the design methodology presented in this work provides a procedure enabling statistical broadcast protocol designers to build protocols that are adaptive to both node density and node distribution. This capability is a key prerequisite for design of practical broadcast protocols to support VANET applications.
Wireless and Mobile Computing, Networking and Communications (WiMob), 2010 IEEE 6th International Conference on; 11/2010
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ABSTRACT: Vehicular ad-hoc networks (VANETs) are an emerging important type of wireless ad-hoc network. Unlike many other types of MANETs, VANET applications such as traffic data dissemination are inherently broadcast oriented and require communication protocols to be anonymous and scalable. Simple broadcast flooding satisfies these requirements, but its performance is highly dependent on network density and may lead to the broadcast storm problem. This work is the first we are aware of to propose stochastic broadcast as a solution for VANET. Stochastic broadcast instructs nodes to rebroadcast messages according to a retransmit probability. Such a scheme is private since node identification is unnecessary, however it has an undesirable dependency on vehicle density in the same manner as simple flooding. To solve this problem, we demonstrate the link between the mathematical science of continuum percolation and stochastic broadcast. Specifically, that the critical percolation threshold in continuum percolation (¿ 4.5 expected neighbors) translates to the wireless broadcast context. Then we show that nodes can tune the performance of the broadcast system to efficient levels by adjusting the retransmit probability so the apparent density of the network approaches the critical threshold.
Consumer Communications and Networking Conference (CCNC), 2010 7th IEEE; 02/2010
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ABSTRACT: Wireless sensors are new revolutionary technology. The sensor devices are typically deployed in large numbers to form a communication network. Due to their severe energy constraints and redundancy in sensed data, hierarchal architectures are usually suggested for these networks. In this work, we propose further energy savings by optimizing the local transmission power between the node and its cluster head. The local node to cluster head transmission power is set to the minimum level that guarantees network connectivity. Often, due to close proximity of the cluster head or superior link connectivity, this local transmission power setting is still too high. We present an algorithm that optimizes the local transmission power while ensuring reliable data delivery. The performance of the protocol is evaluated using simulation. Results show significant energy savings while satisfying reliability constraint.
High-Capacity Optical Networks and Enabling Technologies (HONET), 2009 6th International Symposium on; 01/2010
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ABSTRACT: Based on the recent design trend from giant chip-vendors, multicore systems are being deployed with multilevel caches to achieve higher levels of performance. Supporting real-time applications on multicore systems becomes a great challenge as caches are power hungry and caches make the execution time predictability worse. Studies show that timing predictability can be improved using cache locking techniques. However, level-1 (L1) entire locking may not be efficient if smaller amount of instructions/data compared to the cache size is locked. An alternative choice may be way locking. For some processors, way locking is possible at level-2 (L2) cache (not permitted at L1). Even though both L1 entire locking and L2 way locking improve predictability, it is difficult to justify the performance and power trade-off between these two locking mechanisms. In this work, we simulate a multicore system with two levels of caches to explore the impact of L1 entire locking and L2 way locking on the performance, power consumption, and predictability. Simulation results using FFT, DFT, and MPEG4 algorithms show that both performance and predictability can be increased and power consumption can be decreased by using a cache locking mechanism added to a cache memory hierarchy. Results also show that for FFT and DFT, L2 way locking outperforms L1 entire locking; but for MPEG4, L1 entire locking performs better than L2 way locking.
Computer Systems and Applications, 2009. AICCSA 2009. IEEE/ACS International Conference on; 06/2009
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ABSTRACT: We propose using dynamic backoff on CSMA-type MAC layer protocols to improve message delivery reliability in wireless sensor networks. It is assumed that the MAC layer is able to determine message reliability requirements by reading a reliability data bit embedded within the message. The basic concept is to apply shorter random backoff times to important messages. This gives them the opportunity to test the availability of the communication channel more frequently, enhancing their chance of finding the medium idle. However, this technique might produce the opposite result by allowing the MAC layer to retry sending the important messages in a higher frequency. As a result important messages may reach their maximum retry limit, and get removed from the network. To counteract, we also propose giving the messages a maximum retry limit based on their type. In this setting, important messages will have a higher maximum retry limit. We developed a simulation program to validate our proposed dynamic backoff scheme. The results obtained show that under reasonable network utilization level, the latency is reduced for important messages. Under heavy network utilization conditions, the dynamic backoff scheme drops normal messages leaving the network resources available to handle the delivery of important messages.
High Capacity Optical Networks and Enabling Technologies, 2008. HONET 2008. International Symposium on; 12/2008
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ABSTRACT: A new approach to wireless network design featuring a cognitive controller stack component is presented. The controller uses system status information from the protocol components to tune the behavior of the network stack to achieve a given performance objective. A controller design strategy using a machine learning algorithm and a simulator is proposed, implemented, and tested. Results with ad-hoc wireless networks show the architecture and design strategy are capable of producing a network stack that outperforms the existing protocol stack for given performance objectives. The techniques presented give network designers the flexibility to easily tune the performance of their networks to suit their application.
Wireless Telecommunications Symposium, 2008. WTS 2008; 05/2008
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ABSTRACT: Cache memory improves performance by reducing the speed gap between the CPU and the main memory. However, the execution time becomes unpredictable due to the cache's adaptive and dynamic behavior. Real-time applications are subject to operational deadlines and predictability is considered necessary to support them. Studies show that for embedded systems, cache locking helps determine the worst case execution time (WCET) and cache-related preemption delay. In this work, we evaluate predictability of an embedded system running real-time applications by instruction cache (I-Cache) locking. We implement an algorithm that locks the blocks that may cause more cache misses, using the Heptane simulation tool. We obtain CPU utilization measures for both cache analysis (no cache locking) and I-cache locking. Experimental results show that our proposed cache locking algorithm improves predictability and performance up to 15% locking, after that, predictability may be further enhanced by sacrificing performance.
Innovations in Information Technology, 2007. IIT '07. 4th International Conference on; 12/2007
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ABSTRACT: We present a framework for cross-layer optimization in small, resource-constrained systems which require a high degree of optimization. We argue that often these systems allow for a departure from conventional network stack design principles opening up broad opportunities for optimizations. We examine these new opportunities and propose a design strategy to take advantage of them. Simulation results are presented in support of our design framework proposal and as motivation for future work in this important area.
Innovations in Information Technology, 2007. IIT '07. 4th International Conference on; 12/2007
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ABSTRACT: Wireless sensor networks consist of very large number of resource constrained nodes. Therefore, protocols and applications for wireless sensor networks need to be very scalable and efficient. To properly evaluate the performance of these networks a scalable ad-hoc wireless network simulator is needed. The JIST/SWANS is a highly scalable ad hoc wireless network simulator that has been recently developed. However, JIST/SWANS does not have an energy model or a MAC protocol for wireless sensor networks. In recent work, we developed an energy model for JiST/SWANS. This work presents our implementation of the S-MAC protocol for the JiST/SWANS simulator. The implementation is validated through simulations. Results using JiST/SWANS and NS-2 are obtained and compared for similar network scenarios.
Computer Systems and Applications, 2007. AICCSA '07. IEEE/ACS International Conference on; 06/2007
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ABSTRACT: Sensor networks consist of very large number of resource constrained nodes, and to properly evaluate the performance of these networks a scalable ad-hoc wireless network simulator is needed. The JiST/SWANS is a highly scalable wireless network simulator with reported results for a million node network. However, it lacks an energy model. This work presents the design and implementation of an energy model for the JiST/SWANS simulator, which enables it to account for the energy consumed by wireless ad hoc and sensor networks' protocols. The instrumented energy model is validated through simulation. Results using JiST/SWANS and ns-2 are obtained and compared for similar network scenarios.
Networking, 2007. ICN '07. Sixth International Conference on; 05/2007
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Computer Systems and Applications, 2006. IEEE International Conference on.; 02/2006
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ABSTRACT: The popularity of mobile/wireless embedded systems running multimedia applications is growing. MPEG4 is an important and demanding multimedia application. With improved CPU, memory subsystem deficiency is the major barrier to improving the system performance. Studies show that there is sufficient reuse of values for caching to significantly reduce the raw required memory bandwidth for video data. Decoding MPEG4 video data in software generates many times more cache-memory traffic than required. Proper understanding of the decoding algorithm and the composition of its data set is obvious to improve the performance of such a system. The focus of this paper is to enhance MPEG4 decoding performance through cache optimization of a mobile device. The architecture we simulate includes a digital signal processor (DSP) to run the decoding algorithm and a two-level cache system. Level-1 cache is split into data (D1) and instruction (I1) caches and level-2 (CL2) is a unified cache. We use Cachegrind and VisualSim simulation tools to optimize cache size, line size, associativity, and levels of caches for a wireless device decoding MPEG4 video.
Multimedia Software Engineering, 2004. Proceedings. IEEE Sixth International Symposium on; 01/2005
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ABSTRACT: Abstraction is s powerful technique for the design and implementation of complex systems. A model developed at a higher level of abstraction allows one to tackle complexity by initially hiding the details and elaborating them later. A higher level of abstraction typically has a positive effect on the simulation speed and ease of development of the model, but could affect the accuracy of the model developed. In this paper, we study the effect of model abstraction of a peripheral device developed at a higher level of abstraction using SystemC, and at the register transfer level using Verilog. The parameters compared are accuracy, simulation speed, flexibility, time to develop, code length and ease of verification. In our study to show that by raising the level of abstraction, one not only achieves better simulation speed, flexibility, ease of verification but also reduces time to develop and shorten code length. All this is achieved while being able to maintain almost the same accuracy.
VLSI, 2004. Proceedings. IEEE Computer society Annual Symposium on; 03/2004
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ABSTRACT: This paper evaluates a delta service extension to a mobile file
system cache developed in order to minimize the amount of data
transferred over wireless communications links. Network bandwidth stands
as one of the resource limitations impacting the design of mobile
computer applications. At the mobile file system service level, caching
provides resource conservation in distributed applications. This paper
proposes a delta service to enhance caching services characteristic of
mobile computer file systems. Well established mechanisms for sequence
comparison and software configuration management, file deltas have
applicability to mobile computer and distributed file system caching
environments. Study of the delta service uses trace-driven simulation
methodology incorporating traces obtained in a real world distributed
environment. A delta service model will extend the mobile computer
client cache model of various cache sizes in order to gauge the
bandwidth savings on the link obtained by the delta service
Performance, Computing and Communications, 1998. IPCCC '98., IEEE International; 03/1998
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ABSTRACT: We are on the verge of a new computing paradigm that is now widely
known as “mobile” or “nomadic” computing. The
communication capabilities of high performance portable computers is
advancing at a rapid rate with the availability of powerful wireless
communication interfaces. In this paper, we present research issues in
mobile computing and survey approaches that address these issues
Performance, Computing and Communications, 1998. IPCCC '98., IEEE International; 03/1998
