Wireless Network (EC-803 (A)) - Unit 5 Short Notes

UNIT 5: ADVANCED WIRELESS NETWORKS AND EMERGING TECHNOLOGIES

1. Wireless Channel Fundamentals and Medium Access

1.1 Characteristics of the Wireless Medium

• Shared Medium: Multiple nodes contend for the same frequency spectrum.

• 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 arrive at the receiver via multiple paths (reflection, diffraction, scattering), causing constructive/destructive interference (fading).

• 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.

• Limited Bandwidth: Spectrum is a scarce, regulated resource.

• Noise & Interference: Susceptible to thermal noise, co-channel interference (CCI), and adjacent-channel interference (ACI).

[!TIP] Exam Focus: Be prepared to explain how multipath causes flat fading (signal bandwidth < channel coherence bandwidth) vs. frequency-selective fading (signal bandwidth > coherence bandwidth).

1.2 Multipath Propagation and Doppler Effect

• Multipath: Causes Inter-Symbol Interference (ISI). The time dispersion is characterized by delay spread ($$\displaystyle \tau_{rms} $$). If symbol duration $$\displaystyle T_s < \tau_{rms} $$, ISI occurs.

• Doppler Effect: Causes time-varying channel (fast fading). Coherence time ($$\displaystyle T_c $$) is the time over which channel impulse response is invariant. If $$\displaystyle T_s > T_c $$, the channel changes within a symbol.

• Key Parameters: Coherence Bandwidth ($$\displaystyle B_c $$), Coherence Time ($$\displaystyle T_c $$), Doppler Spread ($$\displaystyle f_d $$).

1.3 Medium Access Control (MAC) Challenges in Wireless Environments

• Hidden Terminal Problem: Node A cannot sense transmission from B to C, so A may transmit to B, causing collision at B.

• Exposed Terminal Problem: Node B is transmitting to A. Node C (near B, far from A) defers transmission to D (near A), even though C's transmission would not collide at A. This reduces spatial reuse.

• Resource Allocation: Need to allocate scarce bandwidth efficiently among users with varying QoS needs.

• Power Control: To manage interference and extend battery life.

1.4 Exposed Terminal Problem and Mitigation Techniques

• Problem: As defined above. Leads to underutilization of network capacity.

• Mitigation:

  • RTS/CTS (Request-to-Send/Clear-to-Send): A virtual carrier sensing mechanism. Before data transmission, sender sends RTS; receiver replies with CTS if clear. Nodes hearing CTS defer. This partially solves hidden terminal but can exacerbate exposed terminal if RTS/CTS range is large.

  • Directional Antennas: Transmit/receive in specific directions, reducing the area where nodes are "exposed".

  • Power Control: Transmit with minimum required power, reducing the exposed area.

1.5 CSMA/CA in Wireless vs. CSMA/CD in Wired Networks

2. Cellular Network Standards and Architectures

2.1 Evolution from GSM to UMTS

2.2 UMTS Network Architecture (Components & Interactions)

• UE (User Equipment): Mobile device (phone, modem).

• UTRAN (UMTS Terrestrial RAN):

  • Node B: Base Station (BS). Handles radio transmission/reception.

  • RNC (Radio Network Controller): Manages radio resources, handovers, connects Node Bs to core.

• Core Network (CN):

  • MSC/VLR (Mobile Switching Center / Visitor Location Register): Circuit-switched domain. Handles voice calls, mobility management (VLR stores visiting UE info).

  • SGSN (Serving GPRS Support Node): Packet-switched domain. Tracks UE location, authenticates, manages PDP contexts.

  • GGSN (Gateway GPRS Support Node): Gateway to external PDNs (Internet). Assigns IP addresses, tunnels packets.

• Interaction (Data Session): UE ↔ Node B (Uu interface) ↔ RNC (Iub) ↔ SGSN (Iu-PS) ↔ GGSN (Gn/Gp) ↔ Internet. MSC/VLR involved for voice (Iu-CS).

2.3 3GPP Standards: Role, Objectives, and Principles in LTE/LTE-A

• Role: 3rd Generation Partnership Project. Global collaboration (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC) to develop technical specifications for mobile systems (GSM, UMTS, LTE, 5G NR).

• Objectives for LTE/LTE-A:

  1. High data rates (DL: 100 Mbps, UL: 50 Mbps for LTE; 1 Gbps+ for LTE-A).

  2. Reduced latency (<10 ms).

  3. Simplified architecture (All-IP, flat network).

  4. Improved spectral efficiency.

  5. Seamless mobility.

• Principles: OFDMA (downlink), SC-FDMA (uplink), MIMO, flat IP architecture (E-UTRAN + EPC).

2.4 E-UTRAN (Evolved UTRAN) Architecture

• Key Principle: Simplified, flat architecture. RNC is removed.

• Components:

  • eNodeB (eNB): Single node performs all RNC + Node B functions. Handles radio resource management, scheduling, HARQ, connectivity to MME/S-GW.

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

  • S-GW (Serving Gateway): User plane. Local mobility anchor, packet routing/forwarding, lawful interception.

  • P-GW (PDN Gateway): User plane. Connectivity to external PDNs, IP address allocation, policy enforcement, charging.

• Roles:

  • Mobility: MME tracks UE, coordinates handovers between eNBs. S-GW anchors user plane during handover.

  • Resource Management: eNB does dynamic, per-subband scheduling (every 1 ms TTI). Uses CQI reports from UE.

2.5 IEEE 802.16 (WiMAX): Mobile vs. Fixed Standard

• Fixed WiMAX (802.16-2004): Point-to-multipoint, stationary CPE. Uses OFDM (256/2048-point). No support for handover.

• Mobile WiMAX (802.16e-2005): Key Enhancements for Mobility:

  1. OFDMA: Scalable OFDMA (SOFDMA) for different channel bandwidths (1.25-20 MHz).

  2. Fast Scheduling & HARQ: To combat fast fading.

  3. MIMO Support: For diversity and multiplexing.

  4. Power Saving Modes: To conserve battery.

  5. Seamless Handover: Hard handover (break-before-make) with predictive scanning. Supports macro-diversity (BSs transmit same data to UE).

  6. Security: Enhanced PKM (Privacy Key Management) with AES.

3. Wireless Local and Personal Area Networks

3.1 IEEE 802.11 WLAN Protocol Architecture

• PHY Layer: Defines modulation (DSSS, OFDM), channelization, data rates.

  • Legacy (a/b/g): 2.4 GHz (b/g) / 5 GHz (a). DSSS (b), OFDM (a/g).

  • Modern (n/ac/ax): MIMO-OFDM, channel bonding (40/80/160 MHz), higher modulation (256-QAM).

• MAC Layer (Common): DCF (Distributed Coordination Function) - mandatory, contention-based (CSMA/CA). PCF (Point Coordination Function) - optional, contention-free (AP polls).

• Management Layer: MLME (MAC Layer Management Entity) & PLME (PHY Layer Management Entity). Handles association, authentication, synchronization, power management.

3.2 MAC Layer Functions in IEEE 802.11

• DCF (Core Mechanism):

  1. DIFS (DCF Inter-Frame Space): Shorter than PIFS. Used by contending stations.

  2. Random Backoff: $$\displaystyle Backoff~Time = Random(0, CW-1) \times Slot~Time $$. CW (Contention Window) starts at $$\displaystyle CW_{min} $$ (31), doubles on collision up to $$\displaystyle CW_{max} $$ (1023).

  3. NAV (Network Allocation Vector): Virtual carrier sense. Set from Duration field in RTS/CTS/Data/ACK.

  4. ACK Frame: Required after successful data reception.

• PCF: AP acts as point coordinator. Uses PIFS (shorter than DIFS) to gain priority. Polls stations in a list.

• Frame Formats: Management (Beacon, Auth, Assoc), Control (RTS, CTS, ACK, PS-Poll), Data.

• Association: Station scans channels → finds AP → exchanges Authentication/Association Request/Response → joins BSS. AP assigns AID (Association ID).

3.3 HIPERLAN vs. IEEE 802.11

3.4 IEEE 802.15 WPAN Family

• 802.15.1: Bluetooth (low-cost, short-range, low-power, ad-hoc).

• 802.15.3: High-Rate WPAN (for multimedia, >20 Mbps). Replaced by 802.15.3c (mmWave).

• 802.15.4: Low-Rate WPAN (LR-WPAN). Basis for Zigbee, WirelessHART, ISA100.11a. Very low power, low data rate (250 kbps max), large network capacity.

• 802.15.6: Body Area Networks (BAN) for medical/non-medical applications.

• 802.15.7: Visible Light Communication (VLC).

3.5 Bluetooth Technology: Piconet vs. Scatternet

3.6 Interface and Coexistence between IEEE 802.11 and Bluetooth

• Problem: Both operate in 2.4 GHz ISM band. 802.11 (Wi-Fi) uses OFDM with 20/22 MHz channels; Bluetooth uses FHSS (1 MHz hops). Mutual interference causes performance degradation.

• Coexistence Mechanisms:

  1. Time-Division Multiplexing (TDM): Schedule Wi-Fi and BT transmissions in non-overlapping time slots (requires coordination).

  2. Adaptive Frequency Hopping (AFH): Bluetooth avoids channels occupied by a strong, continuous 802.11 signal (detected via RSSI scan).

  3. Packet Scheduling: Prioritize time-sensitive traffic.

  4. Physical Separation: Use 5 GHz band for 802.11a/n/ac (no overlap with BT).

  5. Power Control: Reduce transmit power to limit interference footprint.

3.7 WiMAX Overview

• Standard: IEEE 802.16 (Fixed: 2004, Mobile: 2005e, Advanced: 802.16m).

• Goal: "Last-mile" broadband wireless access (MAN technology).

• Key Features:

  • OFDMA (Scalable: 1.25-20 MHz).

  • TDD/FDD operation.

  • MIMO support (802.16e/m).

  • QoS Classes: UGS, rtPS, nrtPS, BE.

  • Mesh Mode: Optional multi-hop.

• Architecture: SS (Subscriber Station) ↔ BS (Base Station) ↔ ASN (Access Service Network) ↔ CSN (Connectivity Service Network) ↔ IP Core.

• Status: Largely superseded by LTE, but used for fixed wireless access in some regions.

4. Advanced Physical Layer Techniques

4.1 SISO vs. MIMO Systems

4.2 Advantages of MIMO over SISO

1. Spatial Multiplexing (SM): Send independent data streams from $$\displaystyle N_t $$ antennas. Increases data rate linearly with $$\displaystyle \min(N_t, N_r) $$. Requires good channel knowledge at receiver (and optionally transmitter).

2. Diversity Gain: Transmit/receive same signal over multiple paths (e.g., Alamouti code). Increases reliability, reduces BER. Achieves full diversity order $$\displaystyle N_t N_r $$.

3. Array Gain (Beamforming): Focus energy in a direction using multiple antennas. Increases SNR at receiver, extending coverage.

4.3 MIMO Application in LTE Networks

• Downlink (eNB to UE): MU-MIMO (Multi-User MIMO). eNB with 4+ antennas serves multiple UEs simultaneously on same time-frequency resource using precoding. Increases cell throughput.

• Uplink (UE to eNB): Single-User MIMO (if UE has multiple antennas). Less common due to UE cost/power.

• Benefits in LTE:

  • Spectral Efficiency: SM boosts peak rates.

  • Coverage: Beamforming improves cell-edge performance.

  • Reliability: Diversity combats fading.

4.4 OFDM Principles

• Core Idea: Split high-rate data stream into N parallel low-rate subcarriers that are orthogonal.

• Orthogonality: Subcarrier spacing $$\displaystyle \Delta f = 1/T_s $$, where $$\displaystyle T_s $$ is symbol duration. Allows spectra to overlap without ICI.

• Transmitter:

  1. Serial-to-Parallel converter.

  2. IFFT (maps N frequency-domain symbols to N time-domain samples).

  3. Add Cyclic Prefix (CP) (copy last $$\displaystyle N_{cp} $$ samples to front). Converts linear convolution to circular, making channel appear flat per subcarrier. CP length > channel delay spread.

  4. DAC & RF upconversion.

• Receiver:

  1. RF downconversion & ADC.

  2. Remove CP.

  3. FFT (recovers parallel subcarriers).

  4. Channel estimation & equalization (1-tap per subcarrier).

  5. Parallel-to-Serial converter.

• Advantages: Robust to ISI (via CP), efficient FFT implementation, flexible spectrum shaping.

• Disadvantages: High PAPR (Peak-to-Average Power Ratio), sensitivity to frequency offset.

4.5 OFDM-MIMO

• Combination: Use MIMO antenna arrays with OFDM modulation.

• How it Addresses Challenges:

  1. Channel Variability (Fast Fading): OFDM converts wideband frequency-selective channel into many narrowband flat-fading subcarriers. MIMO (diversity/SM) operates independently on each subcarrier.

  2. Inter-Symbol Interference (ISI): OFDM's CP eliminates ISI between OFDM symbols. MIMO processing (e.g., zero-forcing, MMSE) is done per subcarrier on the flat-fading MIMO channel matrix $\mathbf{H}(k)$ for subcarrier $k$.

• Implementation: MIMO-OFDM is the de facto standard for modern systems (LTE, Wi-Fi 4/5/6, 5G NR). Transmitter: Encode data → map to spatial streams → OFDM modulate per antenna. Receiver: OFDM demod per antenna → MIMO detection (e.g., V-BLAST, Alamouti) → decode.

5. Wireless Sensor Networks (WSN)

5.1 WSN Architecture and Node Components

• Architecture: Star, Tree, or Mesh. Typically many Sensor Nodes → Sink/Base Station → Gateway → Remote Management Station.

• Sensor Node Components:

  1. Sensing Unit: Transducer (temperature, light, vibration, etc.).

  2. Processing Unit: Microcontroller (low-power, e.g., ARM Cortex-M, AVR).

  3. Communication Unit: Radio transceiver (e.g., 802.15.4, BLE). Often half-duplex.

  4. Power Unit: Battery (often non-rechargeable) + power management.

  5. Memory: Small RAM/Flash for code & data.

  6. Optional: Mobilizer, GPS, ADC/DAC.

5.2 Topology Management in WSNs

• Definition: Control of network connectivity and node roles (e.g., cluster head, relay) to meet application goals.

• Importance:

  • Energy Efficiency: Reduces redundant transmissions. Enables sleep scheduling.

  • Network Longevity: Balances energy consumption (e.g., rotating cluster heads in LEACH).

  • Robustness: Maintains connectivity despite node failures.

  • Scalability: Manages large number of nodes.

  • Coverage & Connectivity: Ensures area is monitored and network is connected.

5.3 Routing Protocols in WSNs

5.4 Security in WSNs

• Challenges:

  • Resource Constraints: Limited CPU, memory, energy → heavy crypto (RSA) infeasible.

  • Deployment: Often unattended, physical capture easy.

  • Ad-hoc Nature: No fixed infrastructure.

  • Scalability: Security must scale to thousands of nodes.

• Techniques:

  • Confidentiality: Symmetric-key crypto (AES, TEA). Lightweight ciphers (SPECK, SIMON). Key management (pre-distribution, LEAP+).

  • Integrity: Message Authentication Codes (MACs) like CBC-MAC, HMAC. Prevents tampering.

  • Authenticity: Symmetric-key based (shared key). Asymmetric (ECC) for bootstrapping.

  • Availability: Tamper-resistant hardware, redundancy, secure routing against DoS (e.g., in Directed Diffusion).

  • Key Management: Random Key Pre-distribution (Eschenauer-Gligor scheme). $k$-random: each node gets $k$ keys from pool. Two neighbors share a key with probability $p$.

5.5 Underwater Wireless Sensor Networks (UWSNs)

• Architecture: Sensor nodes (anchored/mobile) → Underwater Gateways (surface buoy) → Surface Station → On-shore base station. May use AUVs (Autonomous Underwater Vehicles).

• Main Applications:

  • Environmental monitoring (temperature, pollution).

  • Oceanographic data collection.

  • Disaster prevention (tsunami, oil spill).

  • Military (surveillance, mine detection).

  • Navigation (AUV localization).

• Unique Challenges:

  • High Path Loss & Attenuation: Especially at high frequencies. Acoustic is primary (low bandwidth, high delay).

  • Long & Variable Propagation Delay: ~1.5 sec/km. 3D mobility (currents).

  • Limited Bandwidth: Acoustic channel bandwidth ~10-100 kHz.

  • High Bit Error Rate: Multi-path, Doppler, noise.

  • Node Cost & Maintenance: Deployment/recovery difficult.

  • Energy: Battery replacement impossible. Very low-power design needed.

5.6 Applications and Use Cases of WSNs

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

• Industrial: Machine monitoring, structural health (bridge, building), inventory tracking.

• Health: Patient monitoring, drug administration, implantable sensors.

• Military: Enemy tracking, battlefield surveillance, NBC (Nuclear, Biological, Chemical) detection.

• Smart Home/Building: HVAC control, lighting, security.

• Urban: Traffic monitoring, smart parking, waste management.

5.7 Coverage and Placement Strategies for Sensor Nodes

• Coverage Types:

  • Area Coverage: Entire region must be monitored.

  • Point Coverage: Specific points of interest.

  • Barrier Coverage: Detect intruders crossing a perimeter.

• Placement Strategies:

  1. Deterministic (Planned): Pre-deployed in grid/pattern. Maximizes coverage with minimum nodes. Used in controlled environments (factories, farms).

  2. Random: Dropped from aircraft/scattered. Requires redundancy to ensure coverage despite gaps. Coverage problem: Calculate probability a point is covered by ≥1 node. k-coverage: Point covered by ≥k nodes.

  3. Self-Organization: Nodes adjust transmit power or sleep schedule after deployment to optimize coverage/connectivity (e.g., GAF - Geographic Adaptive Fidelity).

6. Mobility and Transport Layer Protocols

6.1 Mobility Management

• Concepts:

  • Location Tracking: Knowing where a Mobile Node (MN) is (home vs. visited network).

  • Handoff (Handover): Transfer of an ongoing session from one access point/base station to another as MN moves. Types: Layer 2 (link-layer) vs. Layer 3 (network-layer); hard (break-before-make) vs. soft (make-before-break).

• Significance: Enables seamless communication while mobile. Maintains session continuity (TCP connections), QoS, and location transparency.

6.2 Mobile IP

• Goal: Allow MN to use its permanent Home Address (HoA) while visiting foreign networks. Session continuity.

• Components:

  • Home Agent (HA): Router in MN's home network. Intercepts packets destined to HoA. Tunnels them to Care-of Address (CoA).

  • Foreign Agent (FA): Router in visited network. Provides CoA (often its own address) to MN. May decapsulate tunneled packets.

  • Care-of Address (CoA): Temporary IP address of MN in visited network. Can be FA-CoA (FA's address) or Co-located CoA (MN's own address on foreign link).

  • Mobile Node (MN): Registers its CoA with HA (via FA or directly). Uses triangular routing: CN → HA → tunnel → MN.

• Data Forwarding Process:

  1. CN sends packet to MN's HoA.

  2. HA intercepts (proxy ARP), tunnels packet to MN's CoA (encapsulation: IP-in-IP, GRE, or minimal encapsulation).

  3. FA (if present) decapsulates, delivers to MN.

  4. MN sends packets directly to CN (source address = HoA).

• Optimizations:

  • Route Optimization (RFC 4725): MN sends its CoA to CN in binding updates. CN can directly tunnel packets to CoA, bypassing HA ("shortcut"). Reduces latency, avoids HA bottleneck.

  • Reverse Tunneling: MN's packets tunneled back to HA to avoid ingress filtering (if CN expects packets from HoA's network).

  • IPv6 Mobile IP (MIPv6): Simpler, no FA needed. MN obtains CoA via stateless/stateful autoconf. Uses binding updates to HA and CNs.

[!TIP] Exam Scenario: "Japanese and German meet on Hawaii, both run Mobile IP." → They are in each other's foreign networks. They can use route optimization to send packets directly to each other's CoA (obtained via binding updates), avoiding their respective Home Agents in Japan/Germany.

6.3 Mobile TCP (Adaptations for Wireless)

• Problems with Standard TCP:

  • Packet Loss ≠ Congestion: Wireless losses (fading, interference) trigger TCP's congestion control (cwnd reduction) unnecessarily → throughput collapse.

  • High Latency & Variability: Long RTTs cause spurious timeouts, poor RTT estimation.

  • Handoffs: Disruptive, cause packet loss/timeouts.

• Mobile TCP Approaches:

  1. Split Connection (Indirect TCP - I-TCP): Break TCP connection at mobile host's foreign agent. Separate connections: CN ↔ FA (wired, stable) & FA ↔ MH (wireless). FA does local retransmissions. Pros: Isolates wireless losses. Cons: Breaks end-to-end semantics, FA is single point of failure.

  2. Snooping TCP: FA snoops on ACKs between CN and MH. Buffers data, performs local retransmissions to MH. Maintains single TCP connection. Cons: FA must parse TCP segments.

  3. Mobile TCP (M-TCP): Uses shallow headers in wireless link. FA notifies MH's HA of connection state. HA does retransmissions for wireless losses. MH's TCP connection is suspended (cwnd=0) during disconnection.

  4. TCP Feedback (F-TCP): Explicit feedback from FA/MH to CN about wireless losses (e.g., using ECN bits or new TCP option).

  5. Link Layer Retransmissions: Most common practical solution. RLC/MAC layer provides reliable delivery over wireless link (e.g., 802.11 ARQ, RLC in UMTS/LTE). Hides wireless errors from TCP. Trade-off: Increased latency if retransmissions are slow.

6.4 TCP Variants for Wireless/Mobile Environments

6.5 Congestion Window Management

• Principle: TCP sender maintains Congestion Window (cwnd) limiting unacknowledged data in flight. Slow Start (SS) and Congestion Avoidance (CA).

  • SS: $$\displaystyle cwnd \leftarrow cwnd + 1 $$ MSS per ACK (exponential growth). Until $cwnd \geq ssthresh$.

  • CA: $$\displaystyle cwnd \leftarrow cwnd + 1 $$ MSS per RTT (linear growth: $$\displaystyle cwnd \leftarrow cwnd + \frac{1}{cwnd} $$ per ACK).

• On Loss (3 dupACKs): $$\displaystyle ssthresh \leftarrow cwnd/2 $$, $$\displaystyle cwnd \leftarrow ssthresh + 3 $$ (Fast Recovery), then $$\displaystyle cwnd \leftarrow ssthresh $$ after new ACK.

• On Timeout: $$\displaystyle ssthresh \leftarrow cwnd/2 $$, $$\displaystyle cwnd \leftarrow 1 $$ MSS (SS).

• Practical Consequences in Wireless:

  • Spurious Timeout: Wireless loss → cwnd → 1 → terrible throughput. Solution: Use RTT-based (Vegas) or explicit notification (Eifel, F-TCP).

  • Frequent Handoffs: Cause packet loss/timeouts → repeated SS → low throughput. Solution: Link layer recovery, M-TCP, or TCP proxies.

  • Large BDP (Bandwidth-Delay Product): Wireless links often have high delay (satellite, UWSN). Need large cwnd. Standard TCP may be slow to open window. Solution: Window scaling (RFC 1323), Large Initial Window.

7. Internet of Things (IoT)

7.1 IoT Architecture (Layered View)

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

|   Application Layer |  (Smart Apps, Analytics, UI)

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

|   Middleware Layer  |  (IoT Platforms: ThingWorx, AWS IoT, Azure IoT Hub)

|                     |  - Device Management

|                     |  - Data Processing/Storage

|                     |  - API Management

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

|   Network Layer     |  (Communication: LPWAN, WLAN, WPAN, Cellular)

|                     |  - Routing, Addressing (IPv6/6LoWPAN)

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

|   Perception Layer  |  (Physical Devices: Sensors, Actuators, Tags)

|                     |  - Data Acquisition

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

• Key Components: Things (sensors/actuators), Gateway (protocol translation, edge processing), Network (wired/wireless), Cloud/Platform (data storage, analytics, device mgmt), Applications (end-user services).

7.2 Main Design Principles and Required Capabilities

• Design Principles:

  1. Interoperability: Standards-based (e.g., IETF, IEEE, oneM2M).

  2. Scalability: Support billions of devices.

  3. Security & Privacy: By design (authentication, encryption, secure boot).

  4. Energy Efficiency: Long battery life (years) → low-power protocols, duty cycling.

  5. Modularity: Loose coupling, plug-and-play.

  6. Data-Centric: Focus on data collection, processing, and actions.

• Required Capabilities:

  • Unique Identification: (e.g., IPv6 address, EPC).

  • Sensing & Actuation.

  • Communication: Diverse, low-power.

  • Computation: Edge/cloud processing.

  • Security: Mutual authentication, data integrity.

  • Manageability: Remote provisioning, monitoring, updates.

7.3 Emerging IoT Standards and Protocols (for Networking Engineers)

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

  • LoRaWAN: Long Range, star-of-stars. Adaptive data rate, very low power. Unlicensed band.

  • NB-IoT (Narrowband IoT): Cellular (LTE-based). Licensed band, operator-managed. Better coverage, QoS.

  • Sigfox: Ultra-narrowband, very long range, low throughput. Global network.

• Short-Range:

  • Bluetooth Low Energy (BLE 5.x): Mesh networking, high throughput (2 Mbps), longer range.

  • Zigbee 3.0 / Thread: Based on 802.15.4. IP-enabled (6LoWPAN), mesh. Thread for smart home.

  • Wi-Fi HaLow (802.11ah): Sub-1 GHz Wi-Fi. Longer range, lower power than traditional Wi-Fi.

• IoT Protocols:

  • Application Layer: MQTT (lightweight pub/sub), CoAP (RESTful for constrained devices), HTTP/2.

  • Network/Transport: 6LoWPAN (IPv6 over 802.15.4), RPL (IPv6 Routing Protocol for LLNs).

  • Device Management: LwM2M (Lightweight M2M).

7.4 Sensor Body Area Network (BAN) Case Study

• Definition: Network of wearable/implantable sensors on/near human body for health/fitness monitoring.

• Implementation Example:

  • Sensors: ECG (heart rate), SpO2 (blood oxygen), temperature, accelerometer (activity), glucose monitor.

  • Hub: Smartphone or dedicated BAN coordinator (e.g., using BLE or 802.15.6). Aggregates data.

  • Communication: IEEE 802.15.6 standard for short-range, low-power, safe for human body. Uses ultra-wideband (UWB) or narrowband in ISM bands. BLE is dominant commercially.

  • Data Flow: Sensors → Hub (via BAN) → Smartphone App → Cloud (via Wi-Fi/Cellular) → Doctor's portal.

  • Challenges: Battery life (months/years), miniaturization, biocompatibility, security (medical data privacy), reliability (life-critical).

  • Applications: Remote patient monitoring, elderly care, sports/fitness tracking, chronic disease management.

8. Specialized and Cross-Cutting Topics

8.1 Wireless ATM (Asynchronous Transfer Mode)

• Goal: Extend ATM's QoS guarantees (CBR, VBR, ABR) to wireless links. Enable high-speed data transmission with guaranteed service levels.

• Architecture:

  • Mobile Terminal (MT).

  • Base Station (BS): Terminates wireless link, connects to fixed ATM network.

  • Mobile ATM Switch (M-ATM): In the wired core. Handles mobility (handoffs).

  • Home & Foreign Agents: For mobility management (similar to Mobile IP).

• How it Enables High-Speed: Uses small, fixed-size 53-byte cells. Enables hard QoS via traffic contracts and scheduling in switches. Suitable for integrated services (voice, video, data).

• Research Challenges:

  1. Wireless Error Handling: High BER → need FEC, ARQ at wireless link layer without violating ATM cell timing.

  2. Handoff Latency & Cell Loss: Seamless handoff with zero cell loss is hard.

  3. Resource Allocation: Dynamic bandwidth allocation for mobile users with varying channel conditions.

  4. Interworking with IP: ATM's complexity vs. IP's simplicity. Largely overtaken by IP-based QoS (DiffServ, IntServ) and cellular packet-switched (UMTS PS, LTE).

8.2 GPS and GAGAN

• GPS (Global Positioning System): US-owned satellite-based navigation system. Provides global positioning, navigation, timing.

  • Segments: Space (satellites), Control (ground stations), User (receivers).

  • Limitations: Selective Availability (SA) was a deliberate error (disabled in 2000). Still has errors: atmospheric (ionospheric, tropospheric), multipath, satellite geometry (PDOP).

• GAGAN (GPS Aided GEO Augmented Navigation):

  • Purpose: Satellite-Based Augmentation System (SBAS) for Indian region. Improve GPS accuracy, integrity, availability for civil aviation (CAT-I/II/III approaches).

  • How it Works:

    1. Ground Segment: Indian Reference Stations (INRES) monitor GPS satellites. Indian Master Control Centre (INMCC) generates correction messages.

    2. Geostationary Satellite (GSAT): Broadcasts augmentation signals (corrections for satellite orbit/clock, ionospheric delay, integrity alerts).

    3. User Segment: Aircraft/vehicle receiver uses both GPS and GAGAN signals.

  • Benefits: Accuracy: ~1-3 m horizontal. Integrity: Alerts user within 6 sec if satellite faulty. Availability: Especially in challenging terrain (Himalayas, oceans).

8.3 Network Layer Comparison: IPv4 vs. IPv6 Addressing

8.4 Transport Layer Comparison: TCP vs. UDP

8.5 Security Considerations Across Wireless Technologies

• Common Threats: Eavesdropping (passive), message modification (active), masquerading (spoofing), replay attacks, denial-of-service (jamming, exhaustion), node capture (WSN).

• General Principles:

  1. Confidentiality: Encryption (AES-CCM, AES-GCM for 802.11; lightweight ciphers for WSN). Avoid WEP (broken). Use WPA2/WPA3.

  2. Integrity & Authenticity: Message Authentication Codes (MACs). HMAC-SHA1/256, CBC-MAC. Prevents tampering and spoofing.

  3. Access Control: Authentication (802.1X/EAP for WLAN; pre-shared keys for WPAN). Strong mutual authentication.

  4. Key Management: Crucial & hard. Pre-distribution (WSN), PKI (large networks), key exchange (Diffie-Hellman, ECDH).

  5. Availability: Anti-jamming (FHSS, DSSS), intrusion detection, redundancy.

  6. Privacy: Anonymity (MAC address randomization in BLE/Wi-Fi), data minimization.

• Technology-Specific:

  • WLAN (802.11): WPA2/WPA3 (AES-CCMP), 802.1X/EAP for enterprise. WPS vulnerability.

  • Cellular (LTE/5G): Strong mutual authentication (AKA), network slicing security, subscriber privacy (SUCI).

  • WSN/IoT: Lightweight crypto (SPECK, SIMON, ECC), hardware security modules (HSMs) for root of trust, secure boot.

  • Bluetooth: Secure Simple Pairing (SSP) with Elliptic Curve Diffie-Hellman (ECDH). Just Works mode is vulnerable to MITM. LE Secure Connections is stronger.