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IoT Architecture, WSN & Wireless Protocols (Smart Sensing & IoT) Solved Questions & Notes (2026) - Apex Rankers

Smart Sensing, IoT & Autonomous Systems > Smart Sensing & IoT > IoT Architecture, WSN & Wireless Protocols

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IoT Architecture, WSN & Wireless Protocols

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Q. 1 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
In the 3-tier IoT architecture, which layer is responsible for data acquisition from physical transducers and edge actuation?
A
Perception / Sensing Layer
✓ Correct
B
Network / Transport Layer
C
Application / Presentation Layer
D
Business / Analytics Layer
💡 Step-by-Step Explanation & Concept Rationale
The Perception Layer consists of physical sensors (temperature, seismic, water level), actuators, and RFID/barcode tags that interact directly with the physical environment.
Q. 2 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is the primary physical layer modulation technique used by LoRa (Long Range) wireless technology?
A
Chirp Spread Spectrum (CSS) modulation
✓ Correct
B
Orthogonal Frequency Division Multiplexing (OFDM)
C
Binary Phase Shift Keying (BPSK)
D
Frequency Hopping Spread Spectrum (FHSS) only
💡 Step-by-Step Explanation & Concept Rationale
LoRa utilizes Chirp Spread Spectrum (CSS), where data is encoded using linear chirps (up-chirps and down-chirps) to provide exceptional resistance to multipath fading and Doppler shifts.
Q. 3 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
In LoRaWAN networks, what is 'Spreading Factor' (SF7 to SF12), and what is the trade-off of using higher spreading factors (e.g. SF12)?
A
Higher SF increases link budget and communication range (higher sensitivity) at the expense of lower data rates and longer time-on-air (higher battery consumption)
✓ Correct
B
Higher SF increases data rate but reduces transmission range
C
Higher SF consumes less battery power and sends data faster
D
Higher SF eliminates the need for gateways
💡 Step-by-Step Explanation & Concept Rationale
SF12 provides up to ~15-20 km range and -137 dBm sensitivity, but transmits at only ~250 bps, increasing airtime and battery usage.
Q. 4 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
Which LoRaWAN Device Class is designed for ultra-low power battery operation where the node only opens two short receive windows (RX1 and RX2) immediately after uplink transmission?
A
Class A (All / Battery Powered End-devices)
✓ Correct
B
Class B (Beacon / Synchronized receive slots)
C
Class C (Continuous / Mains powered listen mode)
D
Class D (Direct device-to-device mode)
💡 Step-by-Step Explanation & Concept Rationale
Class A is the most energy-efficient mode because the radio transceiver remains in deep sleep mode until the sensor wakes up to transmit an uplink packet.
Q. 5 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is the difference between LoRaWAN Class B and Class C devices?
A
Class B opens scheduled receive windows synchronized by gateway beacons; Class C keeps its receiver continuously open except when transmitting
✓ Correct
B
Class B is for satellites; Class C is for mobile phones
C
Class B operates on 5 GHz; Class C operates on 2.4 GHz
D
Class B has zero latency; Class C has 10 second delay
💡 Step-by-Step Explanation & Concept Rationale
Class C devices offer lowest downlink latency because they listen constantly, but require continuous mains electrical power.
Q. 6 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What transport layer protocol does MQTT (Message Queuing Telemetry Transport) operate on top of, and what is its default unencrypted TCP port?
A
TCP (Transmission Control Protocol); Port 1883
✓ Correct
B
UDP (User Datagram Protocol); Port 53
C
HTTP; Port 80
D
SCTP; Port 443
💡 Step-by-Step Explanation & Concept Rationale
MQTT is a lightweight publish-subscribe messaging protocol that runs over reliable TCP connection on Port 1883 (or TLS Port 8883).
Q. 7 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
In MQTT messaging, what does 'QoS Level 1' (At least once) guarantee?
A
The message is guaranteed to arrive at the broker/subscriber at least once, with delivery confirmed via PUBACK packet, though duplicates may occur
✓ Correct
B
The message is delivered at most once with no acknowledgment (fire and forget)
C
The message is delivered exactly once using a 4-way handshake (PUBLISH, PUBREC, PUBREL, PUBCOMP)
D
The message is dropped if bandwidth drops below 1 Mbps
💡 Step-by-Step Explanation & Concept Rationale
QoS 0 is 'At most once', QoS 1 is 'At least once' (PUBACK), and QoS 2 is 'Exactly once' (4-step handshake).
Q. 8 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
In MQTT protocol, what is the 'Last Will and Testament' (LWT) feature used for in disaster telemetry?
A
A pre-configured message stored on the broker that is automatically published to subscribers if the sensor node ungracefully disconnects or suffers sudden power failure
✓ Correct
B
A legal document signed by the sensor manufacturer
C
A message sent right before a planned software update
D
An encryption key for securing data
💡 Step-by-Step Explanation & Concept Rationale
LWT allows central disaster management servers (NEOC) to instantly detect when a river flood sensor has been destroyed or swept away by floodwaters.
Q. 9 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is CoAP (Constrained Application Protocol), and how does its transport layer architecture differ from MQTT?
A
CoAP is a RESTful request/response protocol (GET, POST, PUT, DELETE) running over UDP (Port 5683) with minimal 4-byte header overhead for resource-constrained microcontrollers
✓ Correct
B
CoAP runs over TCP only with 100-byte headers
C
CoAP uses publish-subscribe architecture over WebSockets
D
CoAP is a video streaming protocol
💡 Step-by-Step Explanation & Concept Rationale
CoAP brings web architecture (URIs and REST methods) to microcontrollers over UDP, avoiding TCP connection establishment overhead.
Q. 10 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is 'Confirmable Message' (CON) in CoAP protocol?
A
A message that requires an explicit Acknowledgment (ACK) packet from the receiver, providing reliable transport over connectionless UDP with exponential backoff retransmission
✓ Correct
B
A message encrypted with a password
C
A broadcast message sent to all devices
D
A message confirming user identity
💡 Step-by-Step Explanation & Concept Rationale
CoAP CON messages implement lightweight reliability on top of UDP without incurring the continuous state overhead of TCP.
Q. 11 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is 'NB-IoT' (Narrowband IoT / LTE Cat-NB1/NB2) standardized by 3GPP?
A
A cellular LPWAN standard that operates in a narrow 180 kHz carrier bandwidth, offering deep indoor penetration (+20 dB link budget over GSM) and 10+ year battery life
✓ Correct
B
A high-speed 5G broadband service for 4K video streaming
C
A satellite TV broadcasting standard
D
A short-range Bluetooth replacement
💡 Step-by-Step Explanation & Concept Rationale
NB-IoT reuses existing cellular base station infrastructure, providing nationwide cellular connectivity for smart utility meters and flood warning stations.
Q. 12 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What are the three deployment modes supported by NB-IoT in cellular spectrum?
A
Stand-Alone (in dedicated GSM carriers), Guard-Band (in LTE carrier guard bands), and In-Band (within standard LTE resource blocks)
✓ Correct
B
Indoor, Outdoor, and Underground
C
Morning, Afternoon, and Night mode
D
Low power, Medium power, and Maximum power
💡 Step-by-Step Explanation & Concept Rationale
NB-IoT's flexible 180 kHz spectrum allocation allows cellular operators to deploy IoT coverage inside existing 4G LTE bandwidth.
Q. 13 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is 'LTE-M' (eMTC / LTE Cat-M1) compared to NB-IoT?
A
LTE-M offers higher data rates (~1 Mbps), lower latency, voice support (VoLTE), and full cell-to-cell mobility handover, whereas NB-IoT is optimized for stationary, low-throughput sensors
✓ Correct
B
LTE-M operates without cellular towers
C
LTE-M has shorter battery life than Wi-Fi
D
There is no difference between them
💡 Step-by-Step Explanation & Concept Rationale
LTE-M is preferred for mobile emergency vehicle telemetry and wearable personnel trackers that require seamless cell handover and voice communication.
Q. 14 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is '6LoWPAN' (IPv6 over Low-Power Wireless Personal Area Networks)?
A
An adaptation layer protocol (RFC 4944) that enables 128-bit IPv6 packets to be transmitted over constrained 127-byte IEEE 802.15.4 wireless frame links via header compression and fragmentation
✓ Correct
B
A 6-port local area network switch
C
A power supply standard for microcontrollers
D
A wireless protocol for 6-rotor drones
💡 Step-by-Step Explanation & Concept Rationale
6LoWPAN compresses bulky 40-byte IPv6 headers down to as little as 2-4 bytes, giving every individual sensor node its own native routable IP address.
Q. 15 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is 'RPL' (Routing Protocol for Low-Power and Lossy Networks)?
A
A distance-vector routing protocol that builds a Destination-Oriented Directed Acyclic Graph (DODAG) rooted at the gateway to route packets across multi-hop WSN mesh networks
✓ Correct
B
A programming language for microcontrollers
C
A radio power amplifier circuit
D
A file format for saving sensor logs
💡 Step-by-Step Explanation & Concept Rationale
RPL is the standard routing protocol for 6LoWPAN mesh sensor networks deployed across large disaster zones.
Q. 16 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
In IEEE 802.15.4 standard (the foundation of Zigbee and Thread), what are the frequency bands and maximum data rates?
A
2.4 GHz ISM band (up to 250 kbps), and sub-GHz bands: 868 MHz Europe (20 kbps) and 915 MHz North America (40 kbps)
✓ Correct
B
5.8 GHz band with 1 Gbps data rate
C
FM radio band (88-108 MHz) with 10 bps
D
Satellite Ku-band with 100 Mbps
💡 Step-by-Step Explanation & Concept Rationale
IEEE 802.15.4 defines low-rate physical and MAC layer specifications for low-power wireless personal area networks.
Q. 17 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is 'Zigbee' network topology model?
A
A self-healing, multi-hop mesh network consisting of a single Coordinator (ZC), multiple Routers (ZR), and End Devices (ZED) that sleep periodically
✓ Correct
B
A single star topology with no repeaters
C
A point-to-point physical cable connection
D
A ring topology requiring fiber optic cables
💡 Step-by-Step Explanation & Concept Rationale
Zigbee mesh topology allows sensor readings to hop across dozens of intermediate nodes to reach a central disaster gateway beyond single-hop radio range.
Q. 18 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is 'Thread' protocol in IoT smart building and emergency sensing?
A
An open, IPv6-based, low-power mesh networking technology built on IEEE 802.15.4 and 6LoWPAN, featuring no single point of failure and native IP routing
✓ Correct
B
A multi-threaded software compiler
C
A physical sewing thread used in wearables
D
A brand of Wi-Fi router
💡 Step-by-Step Explanation & Concept Rationale
Unlike Zigbee which requires application-layer translation bridges, Thread routes IPv6 packets end-to-end directly to cloud servers.
Q. 19 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is 'BLE Mesh' (Bluetooth Low Energy Mesh)?
A
A flood-based multi-hop mesh networking standard running over Bluetooth 4.0/5.0 advertising channels, allowing thousands of BLE nodes to communicate without central routers
✓ Correct
B
A wireless headset for playing music
C
A Bluetooth file transfer software
D
A technique for charging batteries wirelessly
💡 Step-by-Step Explanation & Concept Rationale
BLE Mesh uses managed flooding to propagate emergency evacuation beacon alerts and building sensor alerts across entire facilities.
Q. 20 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is '5G mMTC' (massive Machine-Type Communications)?
A
A 5G ITU-R service category engineered to support high connection densities of up to 1 million IoT devices per square kilometer (1,000,000 devices/km²) with ultra-low power consumption
✓ Correct
B
5G enhanced Mobile Broadband for smartphones
C
Ultra-Reliable Low-Latency Communication for remote surgery
D
A military satellite radar protocol
💡 Step-by-Step Explanation & Concept Rationale
5G mMTC handles the astronomical density of environmental, seismic, and municipal smart sensors deployed in smart disaster-resilient cities.
Q. 21 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is 'CSMA/CA' (Carrier Sense Multiple Access with Collision Avoidance) in wireless sensor MAC protocols?
A
A contention-based channel access method where nodes listen to the radio frequency channel (Clear Channel Assessment) before transmitting, using random backoff if busy to avoid collisions
✓ Correct
B
A method where nodes transmit continuously at maximum power
C
A schedule where each node has a fixed assigned time slot
D
A technique for encrypting radio packets
💡 Step-by-Step Explanation & Concept Rationale
CSMA/CA avoids collision destruction of wireless packets when hundreds of independent sensors attempt to broadcast simultaneously.
Q. 22 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is 'Duty Cycling' in Wireless Sensor Networks (WSN)?
A
The fraction of time a sensor node radio remains active (listening/transmitting) compared to its sleep time (e.g. 1% duty cycle = active 10ms, sleep 990ms) to achieve multi-year battery life
✓ Correct
B
The warranty life cycle of a sensor in months
C
The work hours of a maintenance technician
D
The voltage variation of a solar panel
💡 Step-by-Step Explanation & Concept Rationale
Aggressive duty cycling (<1% active radio time) is the primary technique that allows battery-powered flood and seismic sensors to operate unattended for 5-10 years.
Q. 23 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is 'Energy Harvesting' in autonomous disaster sensor nodes?
A
Capturing ambient environmental energy (solar photovoltaic, thermoelectric gradients, piezoelectric vibration, RF energy) to continuously recharge internal supercapacitors/batteries
✓ Correct
B
Harvesting crops during agricultural seasons
C
Burning wood to generate heat in winter
D
Storing food rations in an emergency shelter
💡 Step-by-Step Explanation & Concept Rationale
Solar and vibrational energy harvesting allows environmental monitoring stations on remote mountain slopes to operate indefinitely without battery replacement.
Q. 24 Smart Sensing & IoT
Difficulty: Hard (1 Mark)
What is 'Time Slotted Channel Hopping' (TSCH / IEEE 802.15.4e)?
A
A deterministic MAC protocol combining time division multiple access (TDMA) with pseudo-random frequency hopping across 16 channels to achieve 99.999% industrial wireless reliability
✓ Correct
B
Hopping across Wi-Fi networks in a coffee shop
C
Changing TV channels with a remote control
D
A software tool for syncing calendar appointments
💡 Step-by-Step Explanation & Concept Rationale
TSCH eliminates multi-path fading and external RF interference, providing carrier-grade wireless reliability in metal-heavy industrial and refinery disaster zones.
Q. 25 Smart Sensing & IoT
Difficulty: Medium (1 Mark)
What is 'RSSI' (Received Signal Strength Indicator) and 'SNR' (Signal-to-Noise Ratio) in wireless link quality assessment?
A
RSSI measures total received RF power in dBm (typically -30 dBm strong to -120 dBm weak); SNR measures the ratio of true signal power to background noise floor (positive dB is cleaner)
✓ Correct
B
RSSI measures battery voltage; SNR measures temperature
C
RSSI measures download speed; SNR measures upload speed
D
There is no difference between them
💡 Step-by-Step Explanation & Concept Rationale
In LoRa and wireless networks, an RSSI of -80 dBm with SNR of +8 dB indicates a strong, pristine link; -125 dBm with SNR of -15 dB indicates extreme edge of reception.
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