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Question 1: (25 Points)
Indicate whether true or false for the following;
In AODV, route discovery packets can travel in the network forever?

External synchronization may use GPS as reference clock to achieve synchronization of the clocks in a network
RBS with the pair-wise synchronization is a bad choice approach when compared to TPSN when synchronization messages experience send and access delays with high variance
In distance vector routing , every node maintains a list of distances for each
possible destination, including a neighbor
Hierarchical routing protocols can reduce the energy and communication overheads for sensor nodes
The depth of the synchronization tree in centralized LTS should be large

Anchor based localization refers to the use of measurements of the distances between nodes
Two way ToA does not need clock synchronization

With collaborative multi-lateration process , the localization error is accumulative
DMAC (Data Gathering MAC) protocol is optimized for sensor networks that send data from the sensor nodes upward to the root of a data gathering tree
Energy waste from collisions is more in contention MAC protocols than in scheduled MAC protocols
Perimeter Routing in WSN require knowledge of global topology for path construction
In WSN more hops in the route increase latency but improve energy efficiency for the whole network
YMAC uses multiple channels to increase throughput

RIMAC protocol has the sender (instead of the) receiver in control over the timing of transmissions
With respect to WSN MACs, fairness is more important than collision avoidance.
Power considerations make channel utilization a crucial, if not the most important attribute of a WSN MAC.
A major problem with “Routing on a Curve” is that each node must know the location of all nodes along the routing path.
A major disadvantage of perimeter routing in WSN is that path construction requires knowledge of the global topology.
When routing a packet in a WSN, more hops increase delay, but the advantage is that it increases energy efficiency for the WSN as a whole.
The hamming distance for two data sequences v1 = 011011 v2 = 110001 is three >
LEACH protocol considers the available energy on each node when performing cluster election process
Flooding routing do addresses the implosion problem in WSN
Energy waste from collisions is more in contention MAC protocols than in scheduled MAC.
SPIN family of protocols disadvantage is that it introduces a significant amount of control overhead.

Question 2: (15 Points)

(a) (4 points) Three nodes A, B, and C are known to be positioned at locations (0, 0), (6, 0), and (3, -8), respectively. Node D is estimated to be a distance of 5 from A, a distance of 5 from B, and 4 from C. Determine the location of D using trilateration.

(c) (3 points) Suppose 3 nodes: A (100, 100), B (50, 50), C (80, 70). And the distances between a sensor S and those 3 nodes are: S-A = 25, S-B = 20, S-C = 20. Calculate the sensor’s location based on multi-lateration theory.

(d) (2 points) A wireless sensor network is deployed in a remote nature reserve. There is little to no interference from other networks, and the overall traffic volume is low, but unpredictable: each node takes sensor readings at random times and sends them to its nearest gateway. Each sensor reading contains only a few bytes of data, and the data is not delay-sensitive. The network is very dense, i.e. a large number of nodes within range of each other, however it is uncommon for multiple nodes to take sensor readings at the same time. Which MAC protocol would you choose for this network and why?
A) contention based protocol e.g. Pure ALOHA
B) Time-division multiple access (TDMA)

Question 3: (7 Points)

A Wireless sensor Network designers generally attempt to deploy sensor nodes that don’t have single points of failure, and to have a WSN topologies that employ redundancy are of much interest.
(a) . (2 points ) Sketch an example of a WSN with six-node topology in which the failure of a single link does not disconnect the entire network (that is, any node can still reach any other node).
(b) (3 points ). Sketch an example of a WSN with six-node topology in which the failure of any single link cannot disconnect the entire network, but the failure of some single node does disconnect it.
( C) . ( 2 points ) Sketch an example of a WSN with six-node network in which the failure of any single node cannot disconnect the entire network, but the failure of some single link does disconnect it.
Hint: Not all the cases above may have a feasible example. If not state that this requirement is not possible

Question 4: (15 Points)
Match each WSN term number to its corresponding label of characteristic or type . (Not all options are used.)

Item number WSN term Match characteristic Label
1 Data centric routing
A node in A WSN A
2 Disadvantages of ZMAC establishes and maintains routing tables before it is actually needed. B
3 Flooding routing problems addressed by Gossiping routing reduces the probability for collisions and thereby increasing the throughput. C
4 Through Duty cycling in WSN
reduce the duty cycles , where nodes using the same sleep wake schedule belong to the same cluster. D
5 Use of RSSI in WSN focus is on the data generated by sensors and not the sensors IDs E
6 Directed Diffusion It uses an active period that adapts to traffic density, not fixed size listening period F
7 Application optimized for the use of DMAC protocol removes the nondeterministic
synchronization errors caused by sender G
8 Mote 8-A It requires an explicit setup phase, consuming both time and energy. And add to the traffic overheads. H
9 SMAC uses virtual clusters to Static WSN that rely
On converge cast communications, upward to the root of a data gathering tree. & WSN where the traffic rates are known and stable. I
10 Proactive Routing protocol
devices are awake for brief periods of time and sleep otherwise. J
11 Disadvantages of the TRAMA nodes request data by sending interests for data which are disseminated throughout the network and gradients are established to direct sensor data back to the originator K
12 The shortcoming of SMAC that TMAC address are the implosion challenges as it uses a probabilistic approach to decide whether to forward data or not L
13 RBS uses broadcast messages to a set of receivers

is a link quality indicator in WSN & used to construct node links   M

14 Main disadvantage of TDoA and AoA

 Limited scaling beyond its initial frame slots  N

15 Main disadvantage of TDMA MAC protocol of WSN
communication may experience larger latencies O
16 Advantages of the TRAMA requires extra hardware ( radios and an array of antennas), which may be infeasible for low cost and low power sensor networks P

Question 5: (10 Points)

(a) (2 points) In the above figure, A is transmitting to B. During the same transmission, C decides to transmit to D. B and C are within the range of each other.
(i) Will C ever be able to transmit to D at the same time ?

(b) ( 2 points) Describe the solution by showing all message exchanges based on RTS/CLS (NAV) , CSMA/CA MAC protocol .

(c) (3 points)Calculate the maximum precision that can be obtained for a WSN , If the maximum errors of the network node ranges between 2 to 6 seconds when the network nodes are synchronized to an external reference clock time

(d ) (3 points) Consider two senor nodes in a WSN with each node maximum clock deviation from real time is 500 μs per second . If the node clocks to be synchronized in their clocks such that their relative offset does not exceed 1 s What is the necessary re-synchronization interval ?

Question 6: (8 Points)

(a) ( 4 points) In the figure below, nodes can communicate directly with their immediate neighbour only. If DST is interested in the data SRC senses, how can the data reach DST using:
a. The SPIN protocol?
b. The Directed Diffusion protocol?

(b) ( 4 points) Two nodes A and B do not know their own positions, but they can hear beacons in
their proximities. Node A can hear beacons located at X (4, 2) and Y (2, 5). Node B can
hear beacons located at (2, 5) and Z (3, 7). All nodes have a radio range of 2 units. See figures
(a) Are either (3, 3.5) or (3, 4.5) possible locations for node A?
(b) Are either (2, 6) or (4, 5) possible locations for node B?

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