Download or read book Wireless Networks Model and Optimization Based Approaches to Clock Synchronization Random Access MAC and Video Streaming written by Nikolaos M. Freris and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We, via a model and optimization-based approach, address three issues related to wireless networks: clock synchronization, medium access control (MAC) and scalable video streaming. In Chapter 2 we develop, study and simulate a new model-based distributed network clock synchronization protocol. In a network of clocks, a given node is taken as reference and is associated with the time evolution t. We introduce and analyze a stochastic model for clocks, in which the relative speedup of a clock with respect to the reference node, called the skew, is characterized by an exponential transformation of an Orstein-Uhlenbeck process. We study the properties of our model, namely moment and sample path properties of the stochastic processes, and calculate its Allan variance. We show how our model can be used to translate the time of a clock to another clock's units. We study the problem of synchronizing clocks in a network, which amounts to estimating the instantaneous relative skews and relative offsets, i.e., the differences in the clock readouts, by exchange of time-stamped packets between pairs of nodes in the network. Based on a stochastic model for delays, we derive a scheme for obtaining relative skew measurements in a communication link by sending two time-stamped packets from node i to node j in order to obtain a noisy measurement of their relative skew. We develop an algorithm for filtering relative skew measurements across a link (i,j) in order to estimate the logarithm of the relative skew. We study the properties of the algorithms and provide theoretical guarantees on their performance. We also develop an online, centralized, model-based, asynchronous skew estimation algorithm for optimal filtering of the time-stamps in the entire network, as well as an efficient distributed suboptimal scheme which demonstrates near-optimal performance in simulations. Furthermore, we study some implementation issues, and present a scheme for pairwise relative offset estimation given skew estimates. We use the distributed asynchronous algorithm to obtain nodal offset estimates from relative offset estimates. We combine our findings into developing a new protocol for clock synchronization, namely the Model-Based Clock Synchronization Protocol (MBCSP). We present a comparative simulation study of its performance versus the leading scheme by Solis et al. (2006); the results show that MBCSP performs better in terms of skew, offset and delay estimation. Finally, we have performed trace-driven simulation based on time-stamps obtained from Berkeley motes. Our scheme outperforms that of Solis et al. by 45%, where we used the accuracy in predicting the receipt time-stamp at the sender as the clock synchronization metric. In Chapter 3, we study random access based MAC in the framework of network utility maximization (NUM). There has been much recent interest in protocol design for wireless networks based on maximizing a network utility function. A significant advance is the observation that a decomposition of the Lagrangian suggests an approach where transmissions are scheduled to minimize back-pressure. However, a satisfactory MAC protocol that can realize such a scheduling algorithm is notably missing, and we develop one potential scheme. We present a candidate random access MAC protocol that extends an existing algorithm by Gupta and Stolyar (2006) in calculating the access probabilities. We also consider the online adaptation of access probabilities using local information about queue lengths and active links. We provide OPNET simulation results to compare the performance of our scheme with the leading schemes. We estimate the capacity region of our scheme by simulation for various topologies and multiple flows. Our simulation studies indicate that our extension in conjunction with an implementation of back-pressure significantly outperforms the slotted-time algorithm of Gupta and Stolyar (2006). In Chapter 4, we present performance bounds for random access based MAC using carrier-sense multiple access (CSMA). In recent work, it was shown that a distributed CSMA-based MAC protocol is throughput-optimal which, in turn, implies that the class of controlled distributed random access MAC protocols can support the entire capacity region. It is challenging to study the performance of such schemes in terms of mean delays and compare it with some known results on the performance of centralized scheduling. We modify the model of Jiang and Walrand (2008) to obtain Markov chain models that incorporate the queue lengths as well as the information about the independent set, for single-hop networks. We show that the delay of the new models yields an upper bound on the delay of the original models. We derive upper and lower bounds on the mean total delay at the steady-state, and show that these bounds coincide with those for max-weight scheduling. Finally, we develop a method of deriving upper and lower bounds for random-access schemes by using linear programs (LPs). We present an optimization program for minimizing the upper bounds. In Chapter 5, we consider multihomed scalable video streaming systems where each video is concurrently transmitted over several access networks to a client. The problem is to determine which video packets of a video stream to transmit, and associate each video packet with an access network, so that the video quality at the client is maximized under measured network conditions. We present a network model and a video distortion model to capture the network conditions and video distortion characteristics, respectively. We develop a mathematical formulation to find the streaming strategy for maximizing the average video quality at the client. While the formulation can be optimally solved using exhaustive search or dynamic programming, doing so takes a prohibitively long time, and is not practical for real-time video streaming servers. In order to efficiently solve the problem in real time, we propose several suboptimal convex problems along with two heuristic algorithms. We conduct extensive trace-driven simulations to evaluate the algorithms using real network conditions and actual scalable video streams. We compare our algorithms against the rate control algorithms defined in the Datagram Congestion Control Protocol (DCCP) standard. The simulation results show that our algorithms significantly outperform current systems while being TCP-friendly. For example, compared to DCCP, our algorithms achieve at least 10 dB quality improvement and result in up to 83% packet delivery delay reduction. Finally, we study the trade-off between efficiency and optimality: One of the heuristic algorithms runs faster and is suitable for large-scale streaming systems, while the other one achieves better video quality and is more appropriate for smaller streaming servers. The convex programming approach demonstrates a good trade-off between running time and performance.

Download or read book Throughput Optimization in Multi hop Wireless Networks with Random Access written by Md. Forkan Uddin and published by . This book was released on 2011 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research investigates cross-layer design in multi-hop wireless networks with random access. Due to the complexity of the problem, we study cross-layer design with a simple slotted ALOHA medium access control (MAC) protocol without considering any network dynamics.

Download or read book Energy Efficient Scheduling under Delay Constraints for Wireless Networks written by Randal Berry and published by Morgan & Claypool Publishers. This book was released on 2012-10-01 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: Packet delay and energy consumption are important considerations in wireless and sensor networks as these metrics directly affect the quality of service of the application and the resource consumption of the network; especially, for a rapidly growing class of real-time applications that impose strict restrictions on packet delays. Dynamic rate control is a novel technique for adapting the transmission rate of wireless devices, almost in real-time, to opportunistically exploit time-varying channel conditions as well as changing traffic patterns. Since power consumption is not a linear function of the rate and varies significantly with the channel conditions, adapting the rate has significant benefits in minimizing energy consumption. These benefits have prompted significant research in developing algorithms for achieving optimal rate adaptation while satisfying quality of service requirements. In this book, we provide a comprehensive study of dynamic rate control for energy minimization under packet delay constraints. We present several formulations and approaches adopted in the literature ranging from discrete-time formulations and dynamic programming based solutions to continuous-time approaches utilizing ideas from network calculus and stochastic optimal control theory. The goal of this book is to expose the reader to the important problem of wireless data transmission with delay constraints and to the rich set of tools developed in recent years to address it. Table of Contents: Introduction / Transmission Rate Adaptation under Deadline Constraints / Average Delay Constraints

Download or read book Modeling and Optimization of Wireless Local Area Networks MAC Protocols written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As wireless local area network (WLAN) technology is gaining popularity, performance analysis and optimization of it becomes more important. However, as compared to wired LAN, wireless channels are error-prone. Most of the existing work on the performance analysis of IEEE 802.11 distributed coordination function (DCF) assumes saturated traffic and ideal channel condition. In this dissertation, DCF is analyzed under a general traffic load and variable channel condition. A more realistic and comprehensive model is proposed to optimize the performance of DCF in both ideal and error-prone channels. Many factors, such as the number of contending nodes, the traffic load, contention window, packet overhead and channel condition, which affect the performance of a wireless network have been incorporated. It is shown that under error-prone environment, a trade-off exists between the desire to reduce the ratio of overhead in the data packet by adopting a larger packet size, and the need to reduce the packet error rate by using a smaller packet length. Based on our analytical model, both the optimal packet size and the optimal minimum contention window are determined under various traffic loads and channel conditions. It is also observed that, in error-prone environments, optimal packet size has more significant improvement on the performance than optimal contention window. Our analytical model is validated via simulations using ns-2. We provide a novel approach to model the different channel conditions incurred by different nodes. This work has applications in performance optimization by establishing tradeoffs between transmission error rate and transmission power, modulation, coding scheme, packet size. A better approach of modeling the wireless channel is considered. A Markov chain with alternating good and bad states is adopted to model the bursty characteristics of wireless channel errors. Furthermore, we introduce an analytical model to investigate the energy efficiency of 802.11 DCF. Our future work will extend existing work to further performance enhancement for 802.11 DCF. Also we plan to apply our work in 802.11 to UWB (Ultra-wideband) since CSMA/CA is defined for UMB MAC protocol. To solve the new research challenge of UWB, we will consider a new channel model and channel estimation approach.

Download or read book Topics on Ad Hoc Wireless Network Design written by Hazer Inaltekin and published by . This book was released on 2006 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scheduling and Congestion Control for Wireless Internet written by Xin Wang and published by Springer Science & Business Media. This book was released on 2013-07-30 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: This brief proposes that the keys to internet cross-layer optimization are the development of non-standard implicit primal-dual solvers for underlying optimization problems, and design of jointly optimal network protocols as decomposition of such solvers. Relying on this novel design-space oriented approach, the author develops joint TCP congestion control and wireless-link scheduling schemes for wireless applications over Internet with centralized and distributed (multi-hop) wireless links. Different from the existing solutions, the proposed schemes can be asynchronously implemented without message passing among network nodes; thus they are readily deployed with current infrastructure. Moreover, global convergence/stability of the proposed schemes to optimal equilibrium is established using the Lyapunov method in the network fluid model. Simulation results are provided to evaluate the proposed schemes in practical networks.

Download or read book Performance Enhancement for Wireless Networks written by Zhe Yang and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Wireless networks become more and more important in modern information systems as the last mile/meter solutions, thanks to the flexibility of mobile access to facilitate Internet access anytime, anywhere. Given the limited resources, e.g., spectrum and energy supplies, to meet the ever increasing demand for wireless data services, new approaches are beckoned to enhance the spectrum and energy efficiency. We investigate this problem from three important aspects, digital modulation, clock synchronization and concurrent transmission scheduling. The contributions of this dissertation are four-fold. First, we employ the cross-layer design to explore the spatial diversity and broadcast nature of wireless links and propose a novel network modulation scheme that can superpose the information bits of different priorities into one symbol. It offers a new dimension to improve the network throughput since we can flexibly configure the transmission according to the channels among transceivers. Moreover, it is compatible with the main-stream hardware and we just need a software upgrade to implement the idea. Second, we propose modulation schemes based on hexagonal tiling, which is known to be the most compact way of two-dimensional regular tiling. In order to fully utilize the advantage of hexagonal constellation, we employ the non-binary error control coding since the number of constellation points of hexagonal constellation is not necessarily to be an integer power-of-two. The feasibility of these new modulation schemes is verified by the prototype system based on the software defined radio platform USRP2 and GNU Radio. Third, to facilitate a wide range of wireless communications technologies and protocols, clock synchronization among several wireless devices is a fundamental requirement. We investigated this problem by tracing to the source of clock desynchronization, which is the clock skew. However, as shown by measurement results, the clock skew is not constant and related to the working temperature. We propose a novel clock skew estimation algorithm that can leverage the temperature information to accurately estimate the clock skew. Based on the estimation results, we propose a clock synchronization scheme that can directly remove the clock skew according to the working temperature. Fourth, the traditional time-sharing based scheduling schemes usually schedule one transmission within certain area. The emerging broadband wireless devices can dynamically adjust the transmitted data rate according to the received signal to interference and noise ratio (SINR). Allowing concurrent transmissions may be more efficient, while optimal scheduling problem for concurrent transmissions is an NP-hard problem. We propose simple yet effective heuristic algorithms that can significantly improve the system throughput with moderate computational complexity.

Download or read book MAC Protocols Design and a Cross layered QoS Framework for Next Generation Wireless Networks written by Essaïd Sabir and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present dissertation deals with the problem of under-utilization of collision channels and other related problems in wireless networks. It deals with the design of random access protocols for wireless systems and provides a mathematical framework for performance evaluation of multihop based heterogeneous wireless networks. This thesis is divided into three parts. In the first part, we propose new versions of slotted aloha incorporating power control, priority and hierarchy. Our simulations were important to understand the behaviour of such a system and the real impact of involved parameters (transmit power, transmit rate, arrival rate, hierarchy order). Both team problem (common objective function is maximized) and game problem (each user maximizes its own objective) were discussed. Introducing hierarchy seems to provide many promising improvement without/or with a low amount of external information. We also proposed two distributed algorithms to learn the desired throughput. Next, we developed in the second part an analytical Framework to evaluate performances of multihop based heterogeneous Wireless networks. We built a cross-layer model and derived expression of stability, end-to-end throughput and end-to-end delay. Furthermore, we provided an accurate approximation for the distribution of end-to-end delay in multihop ad hoc networks (operating with slotted aloha protocol). As a direct application, we highlighted how streaming and conversational flows could be supported in this class of ubiquitous networks. The third part of this thesis is devoted to understanding and modelling of IEEE 802.11e DCF/EDCF-operated multihop ad hoc networks. We indeed built a complete and simple APPLICATION/NETWORK/MAC/PHY cross-layered model with finite retries per packet per flow. We analyzed the stability of forwarding queues and derived expression of end-to-end throughput. We finally proposed a Fountain code-based MAC layer to improve the throughput/fairness over the network.

Download or read book Clock synchronization in distributed systems a comparison written by Harald Bachner and published by GRIN Verlag. This book was released on 2007-03-01 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bachelor Thesis from the year 2007 in the subject Computer Science - Technical Computer Science, grade: 1,0, University of Applied Sciences Technikum Vienna (Informations- und Kommunikationssysteme), language: English, abstract: Clock synchronization is a necessary and critical part in most distributed systems. For many years NTP was the state-of-the-art way of synchronizing computer clocks distributed in space. However, as recent advances in miniaturization lead to the construction of smaller, more powerful and less power consuming computers, embedded devices, sensors and actuators, the need for more precise time synchronization grew. This work thus sets out to compare selected approaches to clock synchronization in distributed systems. The well known Global Positioning System is disseminating accurate time and frequency information from the International Institutes that keep the time, NTP can still do the same, but at different levels of accuracy as well as cost. Clock synchronization protocols like IEEE1588 or TTP and bus architectures like FlexRay evolved from the need to further propagate the timing information within small networks and therefore staying within the specified limits of preciseness.

Download or read book Packets with Deadlines written by I-Hong Hou and published by Springer. This book was released on 2013-06-13 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the explosive increase in the number of mobile devices and applications, it is anticipated that wireless traffic will increase exponentially in the coming years. Moreover, future wireless networks all carry a wide variety of flows, such as video streaming, online gaming, and VoIP, which have various quality of service (QoS) requirements. Therefore, a new mechanism that can provide satisfactory performance to the complete variety of all kinds of flows, in a coherent and unified framework, is needed. In this book, we introduce a framework for real-time wireless networks. This consists of a model that jointly addresses several practical concerns for real-time wireless networks, including per-packet delay bounds, throughput requirements, and heterogeneity of wireless channels. We detail how this framework can be employed to address a wide range of problems, including admission control, packet scheduling, and utility maximization. Table of Contents: Preface / Introduction / A Study of the Base Case / Admission Control / Scheduling Policies / Utility Maximization without Rate Adaptation / Utility Maximization with Rate Adaptation / Systems with Both Real-Time Flows and Non-Real-Time Flows / Broadcasting and Network Coding / Bibliography / Authors' Biographies

Download or read book Optimising Video Streaming Over Multi hop Wireless Networks written by Yuwei Xu and published by . This book was released on 2013 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Exploiting Wireless Broadcast Property to Improve Performance of Distributed Algorithms and Mac Protocols in Wireless Networks written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Resource Allocation for Scalable Video Transmission Over Next generation Wireless Networks written by Mohammud Zubeir Bocus and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Advancements in broadband wireless networks and video compression tech- nologies have led to a tremendous increase in the demand for wireless multimedia services over recent years. Popular wireless transmission techniques enabling en- hanced throughput include orthogonal frequency division multiplexing (OFDM) while the recent video coding standard, namely the H.264/ AYC, enables up to twice the compression efficiency to be attained relative to previous video com- pression techniques. Regardless of these developments, the highly dynamic and unpredictable nature of wireless channels, along with the requirements for main- taining the quality of service (Q08) and seamless video playback for all users, impose severe constraints on the design of wireless multimedia systems. A video coding technique that has been developed for such environments is the scalable video coding (8YC), which allows parts of the encoded bitstream to be discarded in response to a drop in the channel quality. However, state-of-the-art resource allocation techniques for SYC transmission over the wireless medium suffer from high computational complexity. Low-complexity, sub-optimal alternatives, on the other hand, are not always adequate. Given the sparse nature of spectrum resources, and the paradigm shift in spectrum access with the advent of cognitive radio systems, it is evident that sub-optimal algorithms having large optimality gaps are not desired. In fact, such approaches would be in contradiction to the definition of spectrum efficient, cognitive radio systems. In this thesis, resource allocation schemes for the transmission of H.264 SYC over wireless networks are investigated. In particular, OFDM systems are consid- ered, including OFDM-based cognitive radio networks. Cross-layer optimisation techniques for fine grain scalable (FGS) video sequences are analysed. Although the problem is initially non-convex and has non-polynomial-time (NP) complex- ity, low complexity techniques are derived that lead to solutions very close to the optimal. Resource allocation schemes for coarse grain scalable (CGS) and medium grain scalable (MGS) sequences over OFDM-based cognitive systems are also investigated. As opposed to FGS, CGS/MGS do not allow an encoded bitstream to be truncated at random bit location. Consequently, new methods are derived that focus on this particular type of video coding. The presence of multiple antennas at the cognitive transmitter and their effect on the aggregate visual quality of all secondary users are also discussed. Furthermore, a joint call admission control (CAC) and resource allocation for the transmission of CGS and MGS video sequences over orthogonal frequency division multiple access (OFDMA) are analysed. This scheme considers the sce- narios where the available channel resources are not enough to support the video data of all users. Finally, rate-adaptation techniques for scalable video transmission over wire- less networks are presented. Rate-adaptation refers to the methods by which the encoding parameters of the video coding are adapted in response to the chan- nel conditions. Interestingly, it is shown that under a given channel condition, increasing the granularity of a scalable sequence lead to diminishing returns in terms of the rate achieved. Moreover, the transmission of scalable sequences over cognitive radio networks where perfect channel knowledge is not available is investigated. The effect of the granularity of the bitstream on the interference observed by incumbent users is also presented. It is shown that the probability of exceeding the interference threshold can be significantly reduced by proper specification of the video encoding parameters.

Download or read book Optimal Random Access Protocols for Wireless Networks written by Man Hon Cheung and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Clock Synchronization and Dominating Set Construction in Ad Hoc Wireless Networks written by Dong Zhou and published by . This book was released on 2005 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Ad Hoc wireless networks have been gaining importance in the communication world for the past decade. Wireless network extends the access to the network by removing the restriction of physical wires. Ad hoc network further improves the network coverage and availability to places without infrastructure support. Clock synchronization and dominating set are two of the fundamental issues in the wireless ad hoc networks. They are important for the correctness and/or performance of many protocols and applications. We focus on IEEE 802.11 wireless ad hoc networks in this dissertation due to the wide deployments of 802.11 networks. The theories and practices are definitely extensible to other types of ad hoc networks. IEEE 802.11 wireless network depends heavily on the distribution of timing information to all the stations in the network. Clock synchronization is important for frequency hopping, power saving and wireless medium reservation. We review the Timing Synchronization Function (TSF) of Ad Hoc mode defined in the 802.11 standard. It is well-known that the 802.11 TSF is not scalable. We carefully analyze the root causes of the scalability problem and design new schemes to overcome the problem. Our new schemes show great improvement over the 802.11 TSF and other solutions in the fields. Our solutions have nice characteristics: scalable, accurate, bounded and adaptive to station mobility. We are able to control the maximum clock differences under 25 micro seconds and 50 micro seconds in single hop and multihop networks respectively. The performance improvement is at least 200% or more compared with the current solutions. Dominating set has been widely used in multihop ad hoc networks (MANET) by numerous routing, broadcast and collision avoidance protocols. The problem to construct a minimum sized dominating set is known to be NP-hard. We propose a protocol that is simple, distributed, inexpensive, and adaptive to station mobility. We show that our protocol can construct dominating set using 35% to 60% less nodes than other distributed dominating set protocols. We study and address two of the fundamental and difficult problems in ad hoc wireless networks. Our solutions show significant improvements over the current solutions. Our work provides solid foundations to other important problems: routing, power saving, frequency hopping, media access scheduling, and broadcast storm mitigation.

Download or read book Wireless Network Design written by Jeff Kennington and published by Springer Science & Business Media. This book was released on 2010-11-10 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book surveys state-of-the-art optimization modeling for design, analysis, and management of wireless networks, such as cellular and wireless local area networks (LANs), and the services they deliver. The past two decades have seen a tremendous growth in the deployment and use of wireless networks. The current-generation wireless systems can provide mobile users with high-speed data services at rates substantially higher than those of the previous generation. As a result, the demand for mobile information services with high reliability, fast response times, and ubiquitous connectivity continues to increase rapidly. The optimization of system performance has become critically important both in terms of practical utility and commercial viability, and presents a rich area for research. In the editors' previous work on traditional wired networks, we have observed that designing low cost, survivable telecommunication networks involves extremely complicated processes. Commercial products available to help with this task typically have been based on simulation and/or proprietary heuristics. As demonstrated in this book, however, mathematical programming deserves a prominent place in the designer's toolkit. Convenient modeling languages and powerful optimization solvers have greatly facilitated the implementation of mathematical programming theory into the practice of commercial network design. These points are equally relevant and applicable in today’s world of wireless network technology and design. But there are new issues as well: many wireless network design decisions, such as routing and facility/element location, must be dealt with in innovative ways that are unique and distinct from wired (fiber optic) networks. The book specifically treats the recent research and the use of modeling languages and network optimization techniques that are playing particularly important and distinctive roles in the wireless domain.

Download or read book Efficient Schemes for Improving the Performance of Clock Synchronization Protocols in Wireless Sensor Networks Using TDMA Based MAC Protocols written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Clock synchronization in a wireless sensor network (WSN) is essential as it provides a consistent and a coherent time frame for all the nodes across the network. Typically, clock synchronization is achieved by message passing using carrier sense multiple access (CSMA) for media access. The nodes try to synchronize with each other, by sending synchronization request messages. If many nodes try to send messages simultaneously, contention-based schemes cannot efficiently avoid collisions which results in message losses and affects the synchronization accuracy. Since the nodes in a WSN have limited energy, it is required that the energy consumed by the clock synchronization protocols is as minimum as possible. This can be achieved by reducing the duration for which the clock synchronization protocols execute. Synchronous clock synchronization protocols in WSNs execute the clock synchronization process at each node, roughly during the same real-time interval, called synchronization phase. The duration when there is no synchronization activity is called the synchronization interval. Synchronization phases are divided into synchronization rounds. The energy consumed by these protocols depends on the duration of the synchronization phase and how frequently the synchronization phase is executed. Hence, to minimize the energy consumption by each node, the duration of synchronization phase should be as small as possible. Due to different drift rates of the clocks, the synchronization phases at different nodes drift apart and special techniques are required to keep them in sync. An existing protocol, called improved weighted-average based clock synchronization (IWICS) uses a pullback technique to achieve this. If a message from (i + 1)th synchronization round is received by a node still executing the ith synchronization round, the receiving node reduces its next synchronization interval to ensure greater overlap in the synchronization rounds. The reduction in overlap is a gradu