237 Multi-Hop Ad Hoc: Real-World Applications

237.1 Learning Objectives

By the end of this chapter, you will be able to:

Analyze Real-World Deployments: Examine multi-hop IoT systems in disaster rescue, agriculture, and archaeology
Design Relay Placement: Calculate optimal relay node positions for coverage and hop count constraints
Compare Network Architectures: Evaluate ad hoc vs infrastructure networks for specific use cases
Plan Deployment Strategies: Create cost-effective multi-hop IoT network designs
Calculate Energy Requirements: Determine node battery capacity and relay burden distribution

237.2 Prerequisites

Before diving into this chapter, you should be familiar with:

Multi-Hop Core Concepts: Understanding of ad hoc networks, hop count trade-offs, and energy distribution patterns

237.3 Real-World Ad Hoc IoT Deployments

237.3.1 Disaster Rescue Operations

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graph TB
    subgraph Rescue["Rescue Team Equipment"]
        R1["Team Alpha<br/>Portable Node"]
        R2["Team Beta<br/>Portable Node"]
        R3["Team Gamma<br/>Portable Node"]
    end

    subgraph Drones["Aerial Relay Network"]
        D1["Drone 1<br/>High Altitude"]
        D2["Drone 2<br/>High Altitude"]
    end

    subgraph Victims["Victim Signals"]
        V1["Smartphone<br/>Distress Signal"]
        V2["Wearable<br/>Vital Signs"]
    end

    subgraph Command["Command Center"]
        CC["Mobile<br/>Command Post"]
    end

    V1 --> R1
    V2 --> R2
    R1 --> D1
    R2 --> D1
    R3 --> D2
    D1 --> CC
    D2 --> CC

    style V1 fill:#E74C3C,color:#fff
    style V2 fill:#E74C3C,color:#fff
    style R1 fill:#16A085,color:#fff
    style R2 fill:#16A085,color:#fff
    style R3 fill:#16A085,color:#fff
    style D1 fill:#E67E22,color:#fff
    style D2 fill:#E67E22,color:#fff
    style CC fill:#2C3E50,color:#fff

Figure 237.1: Disaster Rescue Operations: Emergency Multi-Hop Communication Network with drone relays

Scenario:

Earthquake destroys cellular infrastructure
Rescue teams carry portable IoT nodes
Victims’ smartphones/wearables transmit distress signals
Drones provide aerial relay nodes
Network self-organizes as teams move through rubble
Real-time victim location and vital signs relayed to command center

Requirements:

Rapid deployment (no time for infrastructure setup)
Resilience to node failures
Support for mobile nodes
Low power consumption (battery-operated)

237.3.2 Agricultural Monitoring Network

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graph TB
    subgraph Zone1["Field Zone A (Corn)"]
        S1["Soil Sensor<br/>Moisture: 45%"]
        S2["Soil Sensor<br/>Moisture: 38%"]
    end

    subgraph Zone2["Field Zone B (Wheat)"]
        S3["Soil Sensor<br/>Temp: 22C"]
        S4["Weather Station"]
    end

    subgraph Path["Farm Road Relay Line"]
        R1["Solar Relay 1"]
        R2["Solar Relay 2"]
    end

    subgraph Farm["Farmhouse"]
        GW["Gateway<br/>LoRa + Cellular"]
        Dashboard["Farmer<br/>Dashboard"]
    end

    S1 --> R1
    S2 --> R1
    S3 --> R2
    S4 --> R2
    R1 --> GW
    R2 --> R1
    GW --> Dashboard

    style Zone1 fill:#16A085,stroke:#2C3E50,color:#fff
    style Zone2 fill:#16A085,stroke:#2C3E50,color:#fff
    style Path fill:#E67E22,stroke:#2C3E50,color:#fff
    style Farm fill:#2C3E50,stroke:#16A085,color:#fff

Figure 237.2: Agricultural Mesh Network: Field sensors in multiple zones relay through solar-powered nodes along farm roads to reach the gateway. This topology adapts to seasonal crop rotation and equipment movement.

Scenario:

Large farm with hundreds of hectares
Sensors deployed across multiple field sections
No cellular coverage in remote areas
Sensors form mesh to relay data to farmhouse gateway
Dynamic routing adapts to:
- Seasonal node deployments
- Battery failures
- Weather-induced link quality changes
- Moving agricultural equipment (temporary obstacles)

Benefits:

Cost-effective (no infrastructure deployment)
Scalable (add nodes anywhere)
Resilient (multiple paths to gateway)
Flexible topology (adapt to crop rotation)

237.3.3 Archaeological Site Monitoring

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graph TB
    subgraph Site["Excavation Site"]
        direction LR
        Struct["Structural<br/>Strain Gauges"]
        Env["Environment<br/>Temp/Humidity"]
        Sec["Security<br/>Camera Traps"]
    end

    subgraph Solar["Solar Relay Ring"]
        R1["Relay A<br/>Solar + Battery"]
        R2["Relay B<br/>Solar + Battery"]
        R3["Relay C<br/>Solar + Battery"]
    end

    subgraph Station["Research Station"]
        GW["Gateway<br/>Satellite Uplink"]
        Storage["Local<br/>Data Logger"]
    end

    Struct --> R1
    Env --> R1
    Sec --> R2
    R1 --> R3
    R2 --> R3
    R3 --> GW
    GW --> Storage

    style Site fill:#16A085,stroke:#2C3E50,color:#fff
    style Solar fill:#E67E22,stroke:#2C3E50,color:#fff
    style Station fill:#2C3E50,stroke:#16A085,color:#fff

Figure 237.3: Archaeological Site Network: Sensors monitor ruins with solar-powered relays forming an expandable ring around the excavation perimeter. Network topology evolves as new areas are uncovered, with satellite uplink for remote sites without cellular coverage.

Scenario:

Remote archaeological site without power/connectivity
Structural health monitoring of exposed ruins
Environmental sensors tracking preservation conditions
Security monitoring for artifact protection
Nodes battery-powered with solar charging
Network topology changes as excavation progresses

Challenges:

Ultra-low power requirements (solar-charged batteries)
Harsh environmental conditions
Variable node density as sites expand
Need for multi-year deployment without maintenance

237.4 Ad Hoc vs Infrastructure Networks

Table 237.1: Ad Hoc vs Infrastructure Network Comparison

Feature	Ad Hoc Networks	Infrastructure Networks
Topology	Dynamic mesh	Fixed star/tree
Setup	Self-organizing	Requires planning/installation
Cost	Low (no infrastructure)	High (APs, cabling, power)
Scalability	Organic growth	Requires infrastructure expansion
Reliability	Resilient (multi-path)	Single point of failure (AP)
Range	Extended via multi-hop	Limited by AP coverage
Routing	Distributed protocols	Centralized (AP-based)
Power	Battery-constrained	Infrastructure-powered APs
Mobility	High node mobility	Fixed infrastructure
Best For	Temporary, remote, mobile	Permanent, high-density, high-bandwidth

237.5 Smart Agriculture Case Study

Scenario: 500-acre farm in rural Iowa needs soil moisture monitoring across 200 sensor nodes.

Challenge: No cellular coverage, Wi-Fi range limited to 100m, budget constraints prohibit infrastructure.

Solution Architecture:

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graph TB
    subgraph Field["Field Sensors (200 nodes)"]
        S1[Soil Sensor 1<br/>200m from gateway]
        S2[Soil Sensor 2<br/>400m from gateway]
        S3[Soil Sensor 3<br/>600m from gateway]
    end

    subgraph Relay["Relay Nodes (Strategic)"]
        R1[Relay at 200m]
        R2[Relay at 400m]
    end

    Gateway[Gateway<br/>Farmhouse<br/>LTE Backhaul]
    Cloud[Cloud Platform<br/>Analytics]

    S1 -->|1 hop, direct| Gateway
    S2 -->|2 hops| R1 --> Gateway
    S3 -->|3 hops| R2 --> R1

    Gateway -->|LTE| Cloud

    style S1 fill:#16A085,stroke:#2C3E50,color:#fff
    style S2 fill:#16A085,stroke:#2C3E50,color:#fff
    style S3 fill:#16A085,stroke:#2C3E50,color:#fff
    style R1 fill:#E67E22,stroke:#2C3E50,color:#fff
    style R2 fill:#E67E22,stroke:#2C3E50,color:#fff
    style Gateway fill:#2C3E50,stroke:#16A085,color:#fff
    style Cloud fill:#7F8C8D,stroke:#2C3E50,color:#fff

Figure 237.4: Smart Agriculture Deployment: 500-Acre Farm with Strategic Relay Nodes

Implementation Details:

Component	Specification	Cost	Rationale
Field Sensors	ESP32 + soil moisture probe, 915 MHz LoRa	$25 x 200 = $5,000	Battery-powered, 2-year life, 2km range per hop
Relay Nodes	Solar-powered repeaters, always-on	$150 x 15 = $2,250	Strategic placement every 200m along field perimeter
Gateway	Raspberry Pi + LTE modem + LoRa concentrator	$200	Aggregates data, cellular backhaul to cloud
Monthly Cost	LTE data plan	$30/month	1 GB sufficient for daily sensor updates
Total Investment		$7,450	vs. $50K+ for cellular module per sensor

Performance Metrics (6 months operation):

Average hop count: 2.3 hops per message
Packet delivery rate: 97.8% (baseline: 95% target)
Energy efficiency: Sensors last 18 months on 2x AA batteries (90% duty cycle sleep mode)
Latency: 3.2 seconds average from sensor reading to cloud (acceptable for daily irrigation decisions)
Network resilience: 2 relay node failures caused zero data loss (automatic rerouting)

Key Lessons:

Strategic relay placement more important than total relay count - 15 well-placed nodes cover 500 acres
Heterogeneous network: Different node types (sensor, relay, gateway) optimize cost vs. capability
Duty cycling critical: Sensors transmit 1 reading per hour, sleep otherwise - battery life extended from 3 months to 18 months
Packet loss acceptable: Missing 2-3% of readings has no impact on irrigation decisions (daily aggregates used)

237.6 Worked Example: Relay Node Placement for Coverage

Worked Example: Relay Node Placement for Coverage

Scenario: A warehouse needs temperature monitoring across a 300m x 200m floor. Design relay placement to ensure 2-hop maximum path length to gateway.

Given:

Warehouse dimensions: 300m x 200m
Gateway location: Corner (0, 0)
Sensor radio range: 100m (circular coverage)
Target: All sensors reach gateway in 2 hops or less
Grid sensor deployment: 50m spacing

Steps:

Calculate coverage requirements:
- 2-hop coverage from gateway: 100m (hop 1) + 100m (hop 2) = 200m radius
- Farthest point: diagonal corner at sqrt(300^2 + 200^2) = 361m
- 361m > 200m -> Single gateway insufficient for 2-hop coverage
Determine relay positions:
- Relay needed at ~150m from gateway to extend coverage
- Optimal position: Along diagonal toward far corner
- Relay at (150, 100): Covers nodes from 50m to 250m along diagonal
Verify coverage with relay:
- Gateway covers: (0,0) to (100,100) direct
- Relay covers: (100,50) to (250,200) via gateway
- Far corner (300, 200): Distance to relay = sqrt(150^2 + 100^2) = 180m (within range for 2 hops via relay)
Calculate total deployment:
- Grid sensors: (300/50 + 1) x (200/50 + 1) = 7 x 5 = 35 sensors
- Relay nodes: 1 (strategic placement)
- Maximum hops: 2 (gateway <- relay <- far sensor)

Result: One relay at (150, 100) extends gateway coverage to entire warehouse with 2-hop maximum.

Key Insight: Strategic relay placement multiplies coverage area. Placing relays along the diagonal maximizes reach. For a rectangular area, relays at 60-70% of the maximum dimension along the diagonal typically optimize 2-hop coverage. Each additional relay extends coverage by one radio range in the placement direction.

237.7 Worked Example: Hop Count vs Energy Trade-off Analysis

Worked Example: Hop Count vs Energy Trade-off Analysis

Scenario: A vineyard deploys soil moisture sensors that must reach a gateway 800m away. Compare direct single-hop transmission versus multi-hop relay.

Given:

Distance to gateway: 800m
Single-hop radio: 1W transmit power, 1km range
Multi-hop radio: 50mW transmit power, 200m range
Message size: 100 bytes
Transmission energy: P x t (power x time)
Transmission time: 10ms per message at either power level
Path loss model: Energy proportional to d^2 (power required grows with distance squared)

Steps:

Calculate single-hop energy:
- Distance: 800m
- Power needed: 1W (to reach 1km, covering 800m with margin)
- Energy per transmission: 1W x 10ms = 10 mJ
- Total network energy: 10 mJ (only source transmits)
Calculate multi-hop energy:
- Hops needed: 800m / 200m = 4 hops
- Power per hop: 50mW (200m range)
- Energy per hop: 50mW x 10ms = 0.5 mJ
- Total network energy: 4 hops x 0.5 mJ = 2 mJ
Compare approaches:
- Single-hop: 10 mJ (source only)
- Multi-hop: 2 mJ (distributed across 4 nodes)
- Energy savings: 80% with multi-hop
Consider relay energy burden:
- Source: 0.5 mJ (transmit own data)
- Relay 1: 0.5 mJ receive + 0.5 mJ transmit = 1 mJ
- Relay 2-3: 1 mJ each
- Source energy: 0.5 mJ vs 10 mJ = 95% savings for source

Result: Multi-hop uses 80% less total network energy and 95% less source energy, at cost of involving 3 additional relay nodes.

Key Insight: Multi-hop dramatically reduces source energy consumption but creates the “funnel effect” - relay nodes near the gateway handle all traffic. Plan for this by placing mains-powered or larger-battery nodes near gateways.

237.8 Visual Reference Gallery

Visual: Multi-Hop Communication Path

Modern visualization of multi-hop communication path showing source node transmitting through intermediate relay nodes to reach destination beyond single-hop radio range, illustrating how hop count and path selection affect latency and reliability

Multi-hop relay network extending coverage

Visual: Relay Node Architecture

Modern diagram of relay node architecture showing receive chain, packet buffer, forwarding logic, and transmit chain, with power management for duty cycling and routing table for next-hop selection

Relay node design in wireless sensor networks

Visual: Ad Hoc Routing Protocols

Modern visualization classifying ad hoc routing protocols into proactive like DSDV and OLSR maintaining tables continuously, reactive like DSR and AODV discovering routes on demand, and hybrid like ZRP combining both approaches

Classification of ad hoc routing protocols

237.9 Summary

This chapter covered real-world multi-hop IoT applications:

Disaster Rescue: Self-organizing networks with drone relays for emergency communication when infrastructure is destroyed
Agricultural Monitoring: Cost-effective sensor meshes covering hundreds of hectares with organic scalability and seasonal adaptability
Archaeological Sites: Ultra-low power deployments for multi-year monitoring in remote locations without maintenance access
Network Comparison: Ad hoc networks excel in temporary, remote, and mobile scenarios; infrastructure networks suit permanent high-bandwidth deployments
Case Study: Smart agriculture deployment showing 200 sensors, 15 relays, $7,450 total cost vs. $50K+ for per-device cellular
Relay Placement: Strategic positioning along diagonals maximizes 2-hop coverage; 60-70% of maximum dimension is optimal
Energy Analysis: Multi-hop can save 80% network energy but creates funnel effect requiring heterogeneous battery sizing

237.10 What’s Next

Complete your multi-hop learning with Multi-Hop Assessment for knowledge checks, common pitfalls, and additional worked examples to test your understanding.