Wireless Network (EC-803 (A)) - Unit 4 Short Notes

UNIT 4: WIRELESS NETWORKS (EC-803(A))

1.0 FOUNDATIONAL WIRELESS CONCEPTS & CHALLENGES

Characteristics of the Wireless Medium

• Broadcast Nature: Signals propagate in all directions, making eavesdropping and interference easier.

• Limited & Shared Spectrum: Radio frequencies are a scarce, regulated resource, requiring efficient sharing (e.g., via MAC protocols).

• High Path Loss: Signal strength decays rapidly with distance (often proportional to $$\displaystyle d^n $$, where $n$ is the path loss exponent, typically 2-6).

• Multipath Propagation: Signals reach the receiver via multiple paths (reflection, diffraction, scattering), causing constructive/destructive interference.

• Doppler Shift: Frequency shift due to relative motion between transmitter and receiver ($$\displaystyle f_d = \frac{v}{\lambda} f_c $$), where $v$ is relative velocity, $\lambda$ wavelength, $$\displaystyle f_c $$ carrier frequency.

Effects of Multipath Propagation and Doppler Shift

Fundamental Challenges

• Interference: From other users (co-channel, adjacent channel) and environmental noise.

• Fading: Signal strength variations due to multipath and mobility. Types: Flat fading (narrowband), Frequency-selective fading (wideband).

• Limited Resources: Constrained bandwidth and power at mobile devices.

[!TIP] Exam Focus: Be prepared to define multipath, Doppler shift, and explain how they lead to ISI and fading. Contrast flat vs. frequency-selective fading.

2.0 CELLULAR MOBILE STANDARDS (2G/3G/4G/5G) & ARCHITECTURES

Evolution from GSM to UMTS (3G)

UMTS Network Architecture

Key Components & Interfaces:

Interaction Flow (Data): UE ↔ Node B (Uu) ↔ RNC (Iub) ↔ SGSN (Iu) ↔ GGSN ↔ Internet.

LTE / LTE-Advanced (4G) & E-UTRAN Architecture

• Core Philosophy: Flat, All-IP Network. Eliminates circuit-switched domain. Reduces latency.

• E-UTRAN Components:

  • eNodeB (evolved Node B): Single node combines Node B + RNC functions. Handles scheduling, radio resource control (RRC), mobility management (handover). Directly connects to MME (control plane) and S-GW (user plane) via S1 interface.

  • MME (Mobility Management Entity): Control plane. Handles authentication, bearer management, idle mode tracking.

  • S-GW (Serving Gateway): User plane. Local mobility anchor, routes/forwards user data packets.

  • P-GW (Packet Data Network Gateway): User plane. Interface to external PDNs (Internet). IP address allocation, policy enforcement.

• Architecture: Two-tier hierarchy (eNodeBs directly connected to EPC - Evolved Packet Core). No RNC.

Role of 3GPP (3rd Generation Partnership Project)

• Objective: Develop and maintain technical specifications for mobile telecommunications systems (GSM, UMTS, LTE, 5G NR).

• Principles: Global interoperability, backward compatibility, technology neutrality, fair licensing.

• Impact: Standardizes air interfaces (UTRA, E-UTRA), core networks (CN), and service/system aspects. Ensures devices/networks from different vendors work together globally. Drives evolution from 2G to 5G.

[!TIP] Exam Focus: Know the UMTS components and their interfaces (Uu, Iub, Iu). Contrast E-UTRAN's flat architecture (eNodeB, MME, S-GW, P-GW) with legacy 3G's RNC-based hierarchy. Understand 3GPP's role as a standards body.

3.0 WIRELESS LOCAL AREA NETWORKS (WLAN) & MEDIUM ACCESS

IEEE 802.11 WLAN Protocol Architecture

+-----------------------------------+

|     Management Sublayer (MLME)    |  <-- Handles scanning, authentication, association.

+-----------------------------------+

|         MAC Sublayer (MAC)        |  <-- CSMA/CA, fragmentation, encryption.

+-----------------------------------+

| Physical Layer Convergence (PLCP) |  <-- Preamble, header, rate adaptation.

+-----------------------------------+

|        Physical Medium (PMD)      |  <-- Modulation (DSSS, OFDM), RF.

+-----------------------------------+

• PHY Layer: Defines modulation (DSSS, OFDM), data rates, frequency bands (2.4 GHz, 5 GHz).

• MAC Management Sublayer (MLME): Manages association, authentication, power management.

IEEE 802.11 MAC Layer Functions

• CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance):

  1. Sense medium (CCA - Clear Channel Assessment).

  2. If idle for DIFS, transmit. If busy, defer and backoff (random counter).

  3. ACK frame required for unicast data (reliability).

• Coordination Functions:

  • DCF (Distributed Coordination Function): Mandatory, contention-based (uses CSMA/CA).

  • PCF (Point Coordination Function): Optional, contention-free (AP polls stations). Rarely used.

• Frame Exchange: Data → ACK (after SIFS). RTS → CTS → Data → ACK (optional, for large frames/hidden nodes).

Medium Access Problems & Mitigation

[!TIP] Exam Focus: CSMA/CA steps are crucial. Draw and explain hidden vs. exposed terminal problems with diagrams. Contrast with CSMA/CD.

4.0 WIRELESS PERSONAL AREA NETWORKS (WPAN) & TECHNOLOGIES

Bluetooth Technology

• Piconet Topology:

  • 1 Master, up to 7 Active Slaves. Master controls clock, hopping sequence, and polled access.

  • Parked/Sniff/Hold modes for power saving (more than 7 devices).

• Scatternet Formation:

  • A device (bridge) can be a Master in one piconet and a Slave in another.

  • Enables inter-piconet communication but increases complexity and overhead.

• Comparison: Piconet vs. Scatternet

  | Feature | Piconet | Scatternet | | :--- | :--- | :--- | | Topology | Single star (1 master, ≤7 slaves). | Multiple interconnected piconets. | | Scalability | Limited to ~8 active devices. | Higher (via bridges), but complex. | | Coverage | ~10 m (Class 2). | Extended via bridges. | | Device Role | Fixed (Master/Slave). | Dynamic (device can be master in one, slave in another). | | Interaction | Simple, synchronized by master. | Complex, requires time-division across hopping sequences. |

• Frequency Hopping: FHSS across 79 (or 40) 1-MHz channels in 2.4 GHz ISM band. Hopping rate ~1600 hops/sec. Provides resilience to interference and eavesdropping.

• Protocol Stack: Includes L2CAP (logical link), RFCOMM (serial port emulation), SDP (service discovery).

IEEE 802.15 WPAN Family

• 802.15.1: Bluetooth (adopted).

• 802.15.4: Basis for Zigbee, WirelessHART, 6LoWPAN. Defines PHY/MAC for low-rate, low-power devices.

  • Topologies: Star, Peer-to-Peer, Cluster-Tree, Mesh.

  • Data Rates: 250 kbps (2.4 GHz), 40 kbps (915 MHz), 20 kbps (868 MHz).

Zigbee Technology

• Architecture: Based on 802.15.4. Adds Network (NWK) and Application (APL) layers.

• Features: Very low power, long battery life (months/years), large network size (>65,000 nodes), self-healing mesh, low data rate (250 kbps).

• Applications: Home automation, industrial control, sensor networks, smart metering.

Interoperability: Interface between 802.11 (WLAN) and Bluetooth (WPAN)

• Coexistence Challenge: Both operate in 2.4 GHz ISM band → interference.

• Solutions:

  1. Frequency Hopping (Bluetooth) vs. DSSS/OFDM (Wi-Fi): FHSS inherently hops over narrowband interferers.

  2. Adaptive Frequency Hopping (AFH): Bluetooth detects and avoids Wi-Fi channels in use.

  3. Time Division: Coordinate active periods (e.g., Wi-Fi AP schedules Bluetooth traffic).

  4. Packet Scheduling: Prioritize time-sensitive traffic.

  5. Physical Separation: Use 5 GHz Wi-Fi band (802.11a/n/ac) to avoid overlap.

[!TIP] Exam Focus: Bluetooth piconet/scatternet differences are a common 7-mark question. Zigbee's key features (mesh, low power) and 802.11/Bluetooth coexistence techniques are short-note favorites.

5.0 WIRELESS BROADBAND ACCESS (MAN/WAN)

WiMAX (Worldwide Interoperability for Microwave Access)

• IEEE 802.16 Standards:

  • 802.16-2004 (Fixed WiMAX): Fixed stations, licensed bands (2-11 GHz). Uses OFDMA (downlink), TDMA (uplink). Point-to-Multipoint.

  • 802.16e-2005 (Mobile WiMAX): Supports mobility (handovers) up to vehicular speeds. Adds MIMO-OFDMA, scalable OFDMA (bandwidth scalable from 1.25 to 20 MHz).

• Key Features: Broadband (up to 1 Gbps theoretical), long range (up to 50 km), QoS classes (UGS, rtPS, nrtPS, BE), secure.

• Architecture: SS (Subscriber Station) ↔ BS (Base Station) ↔ ASN (Access Service Network) ↔ CSN (Connectivity Service Network). Similar to cellular (eNodeB/EPC concept).

Wireless ATM (Asynchronous Transfer Mode)

• Concept: Extend ATM's QoS guarantees (CBR, VBR, ABR) and cell-switching efficiency to wireless links.

• Architecture: Mobile hosts communicate via Mobile Termination (MT) to Base Station (BS). BS connects to Wireless Access Controller (WAC), which interfaces with Fixed ATM Network. WAC handles handoffs, location management, and radio resource management.

• Biggest Research Challenges:

  1. High Bit Error Rates (BER): Wireless links are error-prone → need robust FEC, ARQ.

  2. Limited Bandwidth & Variable Capacity: Radio spectrum scarce, channel capacity fluctuates (fading).

  3. Mobility & Handoff: Seamless handoff with QoS preservation across ATM switches is complex.

  4. Power Constraints: Mobile devices have limited battery.

  5. Location Management: Efficient paging and location updates.

[!TIP] Exam Focus: Contrast Fixed vs. Mobile WiMAX (key: mobility support, MIMO, scalable OFDMA). For Wireless ATM, focus on the architectural components (MT, BS, WAC) and list the top 3-4 research challenges.

6.0 ADVANCED ANTENNA & MULTIPLEXING TECHNIQUES

SISO vs. MIMO Systems

OFDM (Orthogonal Frequency Division Multiplexing)

• Principle of Orthogonality: Subcarriers are spaced such that the peak of one aligns with the null of others → no ICI (Inter-Carrier Interference) even with overlapping spectra. Spacing $$\displaystyle \Delta f = 1/T_s $$, where $$\displaystyle T_s $$ is symbol duration.

• Handling ISI: By using a longer symbol duration ($$\displaystyle T_s $$) and inserting a Cyclic Prefix (CP) (copy of end of symbol prepended), the channel appears "circular" → single-tap equalization per subcarrier. CP length > channel delay spread.

• Transmitter Block Diagram:

  Serial Data → Serial-to-Parallel → QAM/Mapper → IFFT → Add CP → Parallel-to-Serial → DAC → RF → Channel.

• Receiver Block Diagram:

  RF → ADC → Remove CP → FFT → Channel Estimation/Equalization → Demapper → Parallel-to-Serial → Data.

OFDM-MIMO Integration

• How it Addresses Challenges:

  1. Channel Variability (Fading): MIMO provides spatial diversity (e.g., Alamouti code) to combat fading across antennas. OFDM converts wideband frequency-selective channel into many flat-fading subchannels.

  2. ISI: OFDM's CP inherently combats ISI within each subcarrier. MIMO spatial processing further mitigates residual effects.

• Benefits in Modern Standards (LTE, Wi-Fi):

  • Spatial Multiplexing Gain: Transmit multiple independent data streams on same OFDM subcarriers across different antennas → spectral efficiency boost.

  • Diversity Gain: Improved link reliability.

  • Beamforming: Directional transmission on OFDM subcarriers → better SNR, coverage.

  • Standard Implementation: LTE uses OFDMA (downlink) & SC-FDMA (uplink) with MIMO. Wi-Fi (802.11n/ac/ax) uses OFDM with MIMO.

[!TIP] Exam Focus: Draw OFDM Tx/Rx block diagrams. Explain orthogonality and CP's role against ISI. For OFDM-MIMO, state how MIMO adds spatial dimension to OFDM's frequency diversity/multiplexing. MIMO capacity formula is a key differentiator from SISO.

7.0 WIRELESS SENSOR NETWORKS (WSNs) & UNDERWATER WSNs

WSN Fundamentals & Architecture

• Sensor Node Components:

  • Sensing: Transducer (temperature, light, vibration).

  • Processing: Microcontroller/CPU.

  • Communication: Transceiver (radio, often IEEE 802.15.4/Zigbee).

  • Power: Battery (often irreplaceable), energy harvesting.

  • Memory & ADC.

• Network Architecture:

  • Star: All nodes talk to central sink. Simple, but sink is single point of failure.

  • Tree (Cluster-Tree): Hierarchical. Cluster Heads aggregate data. More scalable.

  • Mesh: Multi-hop, peer-to-peer. Most robust, self-healing, but complex.

• Deployment & Coverage: Often dense, random deployment (aerial scattering, artillery). Coverage = area monitored. Placement affects connectivity, redundancy, and energy consumption.

WSN Topology Management

• Importance: Directly impacts network lifetime (energy efficiency), connectivity (data delivery), robustness (node/link failures), and coverage.

• Activities: Sleep scheduling (duty cycling), clustering (LEACH, TEEN), node activation/deactivation to maintain coverage/connectivity while saving energy.

WSN Routing Protocols Classification

Security in WSNs

• Specific Challenges: Resource constraints (CPU, memory, energy), uncontrolled deployment (vulnerable to physical capture), ad-hoc nature (no central authority), cooperative medium (easy eavesdropping).

• Techniques:

  • Confidentiality: Symmetric key crypto (AES), lightweight ciphers (Skipjack, PRESENT). Key management is critical.

  • Integrity: Message Authentication Codes (MACs) like CBC-MAC.

  • Authenticity: Pre-deployed keys, pairwise keys between nodes, public-key (rare, expensive like ECC).

  • Attacks Defended: Eavesdropping, message replay, node capture (tamper-resistant hardware), Sybil, wormhole.

Applications of WSNs

• Environmental: Forest fire detection, precision agriculture, habitat monitoring.

• Military: Intrusion detection, battlefield surveillance, target tracking.

• Healthcare: Patient monitoring, drug administration.

• Smart Homes/Buildings: HVAC control, lighting, security.

• Industrial: Process monitoring, structural health monitoring.

Underwater Wireless Sensor Networks (UWSNs)

• Unique Architecture & Challenges:

  • Acoustic Communication: Primary medium (RF attenuates rapidly). High propagation delay (1500 m/s vs. 3e8 m/s for RF) → very high latency.

  • Node Mobility: Water currents cause 3D mobility → topology changes, localization hard.

  • Limited Bandwidth: Narrow bandwidth (tens of kbps), high path loss.

  • Energy: Battery replacement extremely difficult. Energy harvesting (currents, thermal) challenging.

  • Multipath & Doppler: Severe due to surface/bottom reflection and moving nodes/water.

• Main Applications:

  • Oceanography: Data collection (temperature, salinity, currents).

  • Disaster Prevention: Tsunami/earthquake early warning (seismic, pressure sensors).

  • Military: Harbor security, mine detection, submarine communication.

  • Aquaculture: Fish farm monitoring.

[!TIP] Exam Focus: WSN Routing: Contrast Proactive vs. Reactive with examples. UWSN Challenges: Always list acoustic comms, high delay, node mobility, energy. WSN Security: Link challenges to specific techniques (e.g., key management for resource constraints).

8.0 MOBILITY MANAGEMENT & TRANSPORT LAYER PROTOCOLS

Mobile IP (Internet Protocol)

• Core Concepts:

  • Home Agent (HA): Router in MN's home network. Stores Care-of Address (CoA) and tunnels packets to it.

  • Foreign Agent (FA): Router in visited network. Provides CoA (often its own address) and registration service.

  • Mobile Node (MN): Host that changes point of attachment.

  • Care-of Address (CoA): Temporary IP address in visited network. Foreign Agent CoA (FA's address) or Co-located CoA (temporary address obtained by MN).

• Data Forwarding Process (Away from Home):

  1. Registration: MN sends Agent Advertisement/ Solicitation → discovers FA/HA. MN registers its CoA with HA (via FA if present).

  2. Correspondent Node (CN) → MN: CN sends packet to MN's Home Address. HA intercepts (proxy ARP), tunnels packet to MN's CoA (encapsulation: original IP in new IP header).

  3. MN → CN: MN uses reverse tunneling (optional) or sends directly (if CN supports route optimization). Direct route often causes ** Triangular Routing** (HA detour).

• Optimizations (Route Optimization):

  • Binding Updates: MN sends its current CoA directly to CN (bypassing HA for data path).

  • CN caches CoA → sends packets directly to MN's CoA.

  • Eliminates Triangular Routing, reduces latency, saves HA resources.

  • Requires CN to be Mobile IP aware.

TCP for Mobile/Wireless Networks

• Limitations of Traditional TCP:

  • Congestion vs. Loss Confusion: TCP interprets all packet loss as congestion → reduces congestion window ($cwnd$) aggressively. In wireless, loss often due to fading, interference, handoffs → unnecessary $cwnd$ reduction → throughput collapse.

  • High RTT & Variability: Wireless links have high and variable delay → TCP's RTT estimation and timeout (RTO) become inaccurate.

  • Handoffs: Temporary loss of connectivity during handoff → spurious timeout → $cwnd$ set to 1 (slow start).

• TCP Variants & Enhancements:

  | Variant | Key Mechanism | Wireless Adaptation | | :--- | :--- | :--- | | Indirect TCP (I-TCP) | Split connection at Mobile Host's FA. Two separate TCP connections: CN↔FA (wired) & FA↔MN (wireless). | Shields wired TCP from wireless errors. FA does local retransmissions over wireless link. Disrupts end-to-end semantics. | | TCP Tahoe | On 3 duplicate ACKs or timeout: $$\displaystyle cwnd \leftarrow 1 $$ (slow start). | Too aggressive for wireless loss. | | TCP Reno | Fast Retransmit + Fast Recovery on 3 dupACKs: $$\displaystyle cwnd \leftarrow cwnd/2 $$, $$\displaystyle ssthresh \leftarrow cwnd/2 $$. | Better than Tahoe, but still halves $cwnd$ on wireless loss. | | TCP New-Reno | Improved Fast Recovery (partial ACKs). | More robust than Reno in presence of multiple losses per window. | | TCP Vegas | Delay-based congestion detection. Measures RTT vs. expected. Increases $cwnd$ only if RTT is low. | Proactive, avoids congestion. Less sensitive to wireless loss (if delay stable). Performance degrades if delay varies for other reasons. | | Mobile TCP (M-TCP) | Split connection but maintains end-to-end semantics. FA snoops ACKs, suppresses ACKs to CN during wireless disconnection → CN's $cwnd$ stays large. | Maintains high $cwnd$ during wireless outages. Requires FA modification. |

Congestion Window Management

• Principle: TCP uses Additive Increase, Multiplicative Decrease (AIMD). $cwnd$ increases by 1 MSS per RTT (in congestion avoidance) and halves on congestion signal (3 dupACKs/timeout).

• Practical Consequences in Wireless:

  • Unnecessary $cwnd$ Reduction: Wireless loss → $cwnd$ halves → throughput drops drastically.

  • Slow Recovery: After wireless link recovers, TCP slowly ramps up $cwnd$ (slow start/congestion avoidance) → underutilizes available bandwidth.

  • Solution: Split connection protocols (I-TCP, M-TCP) or differentiated loss detection (e.g., using link-layer feedback) to distinguish wireless loss from congestion.

[!TIP] Exam Focus: Mobile IP: Draw the triangular routing problem and explain route optimization. TCP: Contrast I-TCP (split) vs. end-to-end variants (Reno, Vegas). Explain why traditional TCP fails (loss confusion) and how Vegas (delay-based) is an alternative.

9.0 INTERNET OF THINGS (IoT) ARCHITECTURE & STANDARDS

IoT System Architecture

+-------------------+     +-------------------+     +-------------------+

|   Perception      |     |    Network        |     |   Application     |
|   Layer           |---->|    Layer          |---->|   Layer           |
| (Sensors, Actuators,|     | (Gateway,        |     | (Smart Apps,     |
|  RFID, Embedded)  |     |  IoT Network,    |     |  Analytics,      |
|                   |     |  Internet)       |     |  Cloud)          |

+-------------------+     +-------------------+     +-------------------+

                              ^

                              |

                         +-------------------+

                         |    Middleware     |
| (Data Processing, |
|  Abstraction,    |
|  Security,       |
|  Management)     |

                         +-------------------+

• Perception Layer: Physical devices sensing/actuating (sensors, actuators, RFID tags, embedded systems).

• Network Layer: Connects devices to network. Includes gateways (protocol translation), IoT-specific networks (LPWAN: LoRaWAN, NB-IoT; WPAN: Zigbee, BLE), and the Internet.

• Middleware/Service Layer: Provides data processing, storage, device management, security services, abstraction for applications. Often cloud-based.

• Application Layer: Domain-specific applications (smart city, smart home, industrial IoT, e-health).

IoT Design Principles & Required Capabilities

• Scalability: Must support billions of devices.

• Interoperability: Heterogeneous devices/networks must communicate (standard protocols like MQTT, CoAP, HTTP/2).

• Security & Privacy: Device authentication, data encryption, secure boot, privacy-preserving data aggregation.

• Power Efficiency: Many devices battery-powered → low-power operation (sleep modes, efficient protocols).

• Connectivity: Support for various ranges (PAN, LAN, WAN, LPWAN).

• Data Management: Handling massive, often unstructured, data streams (big data, edge computing).

Emerging IoT Standards for Networking Engineers

• LPWAN (Low-Power Wide-Area Network):

  • LoRaWAN: Long Range, low power, unlicensed bands. Star-of-stars topology.

  • NB-IoT (Narrowband IoT): Cellular-based (LTE), licensed spectrum, better coverage/power than GSM.

  • Sigfox: Ultra-narrowband, very long range, very low data rate.

• Short-Range:

  • Bluetooth 5 / BLE (Bluetooth Low Energy): Mesh networking support.

  • Zigbee 3.0 / Thread: IP-based, secure, mesh (for home/industry).

• Communication Protocols:

  • MQTT (Message Queuing Telemetry Transport): Lightweight publish/subscribe.

  • CoAP (Constrained Application Protocol): RESTful for constrained devices (like HTTP for IoT).

  • 6LoWPAN: IPv6 over low-power WPANs (e.g., over 802.15.4).

[!TIP] Exam Focus: Draw the 4-layer IoT architecture (Perception, Network, Middleware, Application). List key design principles (scalability, security, power). Name 2-3 LPWAN standards (LoRaWAN, NB-IoT) and 1-2 application protocols (MQTT, CoAP).

10.0 SPECIALIZED TOPICS & SHORT NOTE SUBJECTS

GPS-Aided GEO Augmented Navigation (GAGAN)

• Purpose: Satellite-Based Augmentation System (SBAS) for Indian Regional Navigation Satellite System (IRNSS) and GPS.

• Role in GNSS: Provides differential corrections and integrity information to improve GPS/IRNSS accuracy, integrity, and availability for civil aviation (Cat I/II/III operations) and other users.

• How it works: Geostationary satellites broadcast correction messages (from ground reference stations) to user receivers. Corrects errors due to satellite orbit/clock drift, ionospheric delays.

IPv4 vs. IPv6 Addressing Comparison

Sensor Body Area Network (BAN) Case Study

• Architecture:

  • In-body/On-body Sensors: ECG, EEG, temperature, glucose, motion sensors.

  • BAN Hub/Coordinator: Wearable device (smartwatch, belt) aggregates data via short-range radio (BLE, Zigbee, 802.15.6).

  • Gateway: Hub connects to WLAN/Cellular to send data to Healthcare Cloud/Server.

• Healthcare Applications:

  • Remote Patient Monitoring: Chronic disease management (diabetes, heart disease).

  • Elderly Care: Fall detection, activity monitoring.

  • Fitness & Wellness: Activity trackers, sleep monitoring.

  • Clinical Trials: Continuous, real-world data collection.

• Challenges: Ultra-low power, biocompatibility, reliable data transmission in dynamic body environment, security/privacy of sensitive health data, regulatory compliance (FDA, CE).

IEEE 802.16 Mobile (WiMAX) vs. Fixed Standard

• Key Enhancements for Mobility Support (802.16e vs. 802.16-2004):

  1. MIMO-OFDMA: Supports spatial multiplexing and diversity for mobile channels.

  2. Scalable OFDMA: Bandwidth scalable (1.25–20 MHz) to support different channel conditions and regulatory domains.

  3. Advanced Handover: Fast and seamless handovers (hard/soft) between base stations. Supports macro-diversity (simultaneous connection to multiple BSs).

  4. Power Saving Modes: Sleep Mode and Idle Mode to conserve battery in mobile devices.

  5. Enhanced Security: More robust key management and encryption for mobile environment.

  6. QoS Classes: Refined for real-time applications ( VoIP, video) during mobility.

  7. Support for Vehicular Speeds: Up to 120 km/h (fixed: stationary/ pedestrian).

[!TIP] Exam Focus: For short notes (3-4m), structure as: Definition → Key Features → Applications/Impact. For GAGAN, state it's an SBAS for aviation. For IPv4/IPv6, use a comparison table. For Sensor BAN, describe architecture → apps → challenges. For WiMAX Mobile vs Fixed, list 3-4 key mobility enhancements.

END OF UNIT 4 NOTES
Aligned with RGPV EC-803(A) past paper trends (2022-2025). Focus on definitions, diagrams (conceptual), comparisons, and process explanations.