Subject: Wireless Sensor Net works Subject Code: PECS5407 th Semester: 8 Applicable Branch (es): CSE, IT Question Code: F356 Year of Examination: 2014 Exam Type: (Special/Regular): Regular 1.a) What is the necessity of time synchronization in distributed wireless sensor networks. Answer: Distributed wireless sensor networks need time synchronization for a number of good reasons such as time-stamping measurements, in-network signal processing, localization, cooperative communication, medium-access, sleep scheduling, and coordinated actuation. b) What is ETX matrix? Answer: The ETX matrix is suitable for robust routing in a wireless network. This metric minimizes the expected number of total transmissions on a path. The expected number of transmissions required for successful delivery of a packet on the link is: 1 ETX d f .dr Where d f is the packet reception rate (probability of successful delivery) on a link in the forward direction, and d r is the probability that the corresponding ACK is received in the reverse direction. c) What is preamble sampling? Answer: In preamble sampling or low-power listening, the receivers periodically wake-up to sense the channel. If no activity is found, they go back to sleep. If a node wishes to transmit, it sends a preamble signal prior to packet transmission. Upon detecting such a preamble, the receiving node will change to a fully active receive mode.
d) What are the state of information required for energy efficient robust routing? Answer: Information routing in wireless sensor networks can be made robust and energyefficient by taking into account a number of state information available locally within the network such as Link quality, Link distance, Residual energy, Location information and Mobility information. e) Define and differentiate between coverage and connectivity.
Answer: The network must be deployed keeping in mind two main objectives: coverage and connectivity. Coverage pertains to the application-specific quality of information obtained from the environment by the networked sensor devices. Connectivity pertains to the network topology over which information routing can take place. f) What is voronoi Tessellation? Answer: A Voronoi tessellation separates the field into separate cells, one for each node, such that all points within each cell are closer to that node than to any other. While the maximal breach path is not unique, it can be shown that at least one maximal breach path must follow Voronoi edges, because they provide points of maximal distance from a set of nodes. g) Differentiate between Uniform Random vs Square Grid Deployment Model. Answer: The uniform random deployment approach is appealing for futuristic applications of a large scale. However, many small–medium-scale WSNs are likely to be deployed in a structured manner (e.g. Square Grid) via careful hand placement of network nodes. In both cases, the cost and availability of equipment will often be a significant constraint. Uniform random deployment is more challenging in some respects, since there is no way to configure a priori the exact location of each device. Additional post-deployment self-configuration mechanisms are therefore required to obtain the desired coverage and connectivity. h) What is Fading Channel? Answer: A fading channel is a communication channel comprising fading. In wireless systems, fading may either be due to multipath propagation, referred to as multipath induced fading, or due to shadowing from obstacles affecting the wave propagation, sometimes referred to as shadow fading. i) What are the different empirical measurements needed in a RADAR technique?
Answer: The different empirical measurements needed in a RADAR technique are the signal strength statistics (mean, variance, median) from different reference transmitters at various locations. j) What do you mean by Monotone property in geometric random theory? Answer: A monotonically increasing property is any graph property that continues to hold if additional edges are added to a graph that already has the property. A graph property is called monotone if the property or its inverse is monotonically increasing. Nearly all graph properties of interest from a networking perspective, such as K-connectivity, Hamiltonicity, K-colorability, etc., are monotone. 2. a) What are the different types of topologies present in WSN? Answer: The WSN can be configured into several different topologies such as Single-hop star, Multi-hop mesh and grid and Two-tier hierarchical cluster. Single-hop star The simplest WSN topology is the single-hop star, where every node in this topology communicates its measurements directly to the gateway. Wherever feasible, this approach can significantly simplify design, as the networking concerns are reduced to a minimum. However, the limitation of this topology is its poor scalability and robustness properties. For instance, in larger areas, nodes that are distant from the gateway will have poor-quality wireless links. Multi-hop mesh and grid For larger areas and networks, multi-hop routing is necessary. Depending on how they are placed, the nodes could form an arbitrary mesh graph or they could form a more structured communication graph such as the 2D grid. Two-tier hierarchical cluster Perhaps the most compelling architecture for WSN is a deployment architecture where multiple nodes within each local region report to different cluster-heads. There are a number of ways in which such a hierarchical architecture may be implemented. This approach becomes particularly attractive in heterogeneous settings when the cluster-head nodes are more powerful