1044  UWB Indoor Positioning Systems

1044.1 Learning Objectives

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

  • Design UWB-based indoor positioning systems with appropriate anchor placement
  • Calculate anchor density and placement for specific accuracy requirements
  • Compare TWR-based and TDoA-based system architectures
  • Evaluate commercial UWB chipsets and development platforms
  • Understand GDOP (Geometric Dilution of Precision) and its impact on accuracy

1044.2 Introduction

Designing a UWB positioning system requires careful consideration of anchor placement, ranging method, and system architecture. This chapter covers the engineering principles and practical considerations for deploying UWB infrastructure.

NoteKey Takeaway

Anchor placement is critical: Never place anchors in a line. Good geometric diversity (spread across the space, varying heights) dramatically improves position accuracy through better GDOP.

1044.3 Anchor Placement Principles

Minimum Requirements: - 2D positioning: 3 anchors (trilateration in plane) - 3D positioning: 4 anchors (trilateration in space) - Practical systems: 6-8 anchors for redundancy and coverage

Geometric Diversity Rules:

  1. Avoid Collinearity: Never place all anchors in a straight line
  2. Height Variation: For 3D, vary anchor heights (walls, ceiling)
  3. Coverage Overlap: Each point should see 4+ anchors
  4. DOP Consideration: Good geometric dilution of precision

Typical Deployment Densities:

Environment Area per Anchor Anchor Height Configuration
Office 200-300 m² 2.5-3 m (ceiling) Grid pattern
Warehouse 300-400 m² 4-8 m (high ceiling) Grid pattern
Manufacturing 150-250 m² 3-5 m (overhead) Process flow
Retail 100-200 m² 2.5-3 m Customer paths
Hospital 150-250 m² 2.5-3 m Room + corridor

1044.4 Line-of-Sight Considerations

UWB performs best with clear line-of-sight but can tolerate some obstructions:

  • Direct LOS: Best performance (10-20 cm accuracy)
  • NLOS Soft (drywall, glass): Degraded (30-50 cm accuracy)
  • NLOS Hard (metal, water): Significant error or no signal
  • Multipath: Can cause errors, mitigated by antenna design

Mitigation Strategies: - Place anchors high to maximize LOS - Use multiple anchors for redundancy - NLOS detection algorithms - Kalman filtering to smooth positions

1044.5 Worked Example: UWB Anchor Placement for Warehouse Asset Tracking

Scenario: A logistics company needs to track forklifts with 30cm accuracy in a 60m x 40m warehouse with 8-meter high ceilings and metal shelving racks.

Given:

  • Warehouse area: 2,400 m^2 (60m x 40m)
  • Ceiling height: 8 meters
  • Metal shelving racks: 6 meters tall, arranged in 4 parallel rows
  • Required accuracy: 30 cm (sub-meter for collision avoidance)
  • Tracking targets: 12 forklifts with active UWB tags
  • Budget constraint: Minimize anchor count while meeting accuracy

Steps:

  1. Calculate minimum anchor density:
    • For 30cm accuracy with TDoA, need GDOP < 2.0
    • Good GDOP requires anchor spacing of 15-20 meters
    • Area per anchor: 225-400 m²
    • Minimum anchors: 2,400 / 300 = 8 anchors (baseline)
  2. Account for shelving obstructions:
    • Metal shelves block UWB signals (20+ dB attenuation)
    • Each tracking point needs LOS to 4+ anchors
    • Add 50% redundancy for NLOS mitigation: 8 x 1.5 = 12 anchors
  3. Determine anchor positions:
    • Perimeter anchors at 15m spacing: 8 anchors at (0,0), (0,20), (0,40), (30,0), (30,40), (60,0), (60,20), (60,40)
    • Interior anchors between shelving rows: 4 anchors at (15,13), (15,27), (45,13), (45,27)
    • Total: 12 anchors
  4. Optimize anchor height:
    • Mount at 7 meters (below 8m ceiling)
    • This provides LOS over 6m shelving with 30-degree clearance angle
    • Calculation: tan(30) x 7m = 4m horizontal clearance from shelf top
  5. Verify coverage with geometry analysis:
    • Simulate GDOP across warehouse floor
    • Worst case GDOP: 1.8 (in corners between shelves)
    • Position accuracy: 15cm UERE x 1.8 GDOP = 27cm (meets 30cm requirement)

Result: Deploy 12 UWB anchors at 7-meter height achieving 27cm average positioning accuracy across the 2,400 m² warehouse floor.

Key Insight: Anchor height is critical in warehouses with tall shelving. Mounting anchors at 70-90% of ceiling height (7m in 8m space) provides clearance over obstacles while maintaining good GDOP geometry. If anchors were mounted at ceiling level (8m), the near-vertical geometry would degrade horizontal accuracy by 40%.

1044.6 System Architecture Options

UWB positioning systems can be architected in several ways depending on requirements.

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graph TB
    subgraph "Simple System (TWR)"
        S1[UWB Tag] <--> S2[UWB Anchor 1]
        S1 <--> S3[UWB Anchor 2]
        S1 <--> S4[UWB Anchor 3]
        S2 --> S5[Gateway/Controller]
        S3 --> S5
        S4 --> S5
        S5 --> S6[Location Server]
        S6 --> S7[Application]
    end

    subgraph "Enterprise System (TDoA)"
        T1[UWB Tag 1<br/>Blink only] -.-> T2[Anchor Array<br/>50+ anchors]
        T3[UWB Tag 2<br/>Blink only] -.-> T2
        T4[UWB Tag N<br/>Blink only] -.-> T2

        T2 --> T5[Time Sync<br/>Infrastructure]
        T5 --> T6[Positioning<br/>Engine<br/>Cloud/Edge]
        T6 --> T7[Real-time<br/>Location Service]
        T7 --> T8[Applications<br/>Analytics<br/>Dashboards]
    end

    style S1 fill:#E67E22,stroke:#2C3E50,stroke-width:2px,color:#fff
    style S6 fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style T6 fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff

Figure 1044.1: UWB System Architectures: Simple TWR vs Enterprise TDoA Deployments

1044.6.1 TWR-Based Architecture (Simple, Small Scale)

  1. Tags: Active devices performing ranging with anchors
  2. Anchors: Fixed positions, respond to tag polls
  3. Gateway: Collects ranging data via wired/wireless backhaul
  4. Location Server: Computes positions from ranges
  5. Application Layer: Visualization, alerts, analytics

Pros: Simple, no anchor synchronization, lower infrastructure cost Cons: Tags consume more power, scales to ~50-100 tags

1044.6.2 TDoA-Based Architecture (Complex, Large Scale)

  1. Tags: Passive beacons, only transmit blinks
  2. Anchor Network: Synchronized via wired Ethernet or GPS
  3. Positioning Engine: Centralized or distributed, performs trilateration
  4. RTLS Platform: Real-time location services, geofencing, analytics
  5. Integration Layer: APIs for third-party systems

Pros: Scales to 1000s of tags, low tag power, high update rate Cons: Complex infrastructure, anchor sync critical, higher cost

1044.6.3 Hybrid and Peer-to-Peer Modes

Modern systems often combine approaches:

  • TWR for configuration: Anchors use TWR to self-survey positions
  • TDoA for tracking: Tags use TDoA for power efficiency
  • Peer-to-peer ranging: Device-to-device ranging without infrastructure (e.g., Apple U1 chip)

1044.7 UWB vs Other Technologies

Understanding when to use UWB requires comparing it to alternative positioning technologies.

1044.7.1 Comprehensive Technology Comparison

Technology Accuracy Range Update Rate Power Infrastructure Cost Best Use Case
GPS 3-5 m Global 1 Hz High Satellites $ Outdoor navigation
Wi-Fi RSSI 3-5 m 50 m 1-10 Hz Medium Wi-Fi APs $ Room-level indoor
Wi-Fi RTT 1-2 m 50 m 1-5 Hz Medium Wi-Fi 6 APs \[ | Indoor navigation | | **BLE RSSI** | 2-3 m | 30 m | 1-10 Hz | Very Low | BLE beacons | $ | Proximity detection | | **BLE AoA** | 0.5-1 m | 30 m | 1-10 Hz | Low | BLE 5.1 anchors | \] Asset tracking
UWB 0.1-0.3 m 70 m 10-100 Hz Medium UWB anchors \[ | Precision positioning | | **Vision** | 0.01-0.1 m | 10 m | 30+ Hz | Very High | Cameras + compute | \]$ Robotics, AR/VR

1044.7.2 When to Choose UWB

UWB is ideal when: - Sub-meter accuracy is required (automotive, industrial safety) - High update rates needed (real-time tracking) - Secure ranging required (access control) - Line-of-sight is generally available - Infrastructure cost is acceptable

Consider alternatives when: - Room-level accuracy sufficient (Wi-Fi/BLE cheaper) - Outdoor use required (GPS better) - Extreme range needed (>100m) - Ultra-low cost critical (BLE beacons) - No line-of-sight available (vision-based may be better)

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graph TB
    Start[Positioning Requirement] --> Q1{Indoor or<br/>Outdoor?}

    Q1 -->|Outdoor| GPS[GPS/GNSS<br/>3-5m accuracy<br/>Global coverage]

    Q1 -->|Indoor| Q2{Required<br/>Accuracy?}

    Q2 -->|Room Level<br/>2-5m| Wi-Fi[Wi-Fi RSSI<br/>or BLE<br/>Low cost]

    Q2 -->|Sub-meter<br/>0.5-2m| Q3{Update<br/>Rate?}

    Q3 -->|Low<br/>1-5 Hz| BLE[BLE 5.1 AoA<br/>Lower cost<br/>Lower power]

    Q3 -->|High<br/>10-100 Hz| UWB1[UWB<br/>Best choice]

    Q2 -->|Centimeter<br/>0.1-0.3m| Q4{Security<br/>Critical?}

    Q4 -->|Yes| UWB2[UWB<br/>Secure ranging<br/>Relay attack<br/>protection]

    Q4 -->|No| Q5{Budget?}

    Q5 -->|High| Vision[Vision-based<br/>Camera + AI<br/>Highest accuracy]

    Q5 -->|Medium| UWB3[UWB<br/>Best balance]

    style UWB1 fill:#16A085,stroke:#2C3E50,stroke-width:3px,color:#fff
    style UWB2 fill:#16A085,stroke:#2C3E50,stroke-width:3px,color:#fff
    style UWB3 fill:#16A085,stroke:#2C3E50,stroke-width:3px,color:#fff
    style GPS fill:#E67E22,stroke:#2C3E50,stroke-width:2px,color:#fff

Figure 1044.2: Indoor Positioning Technology Selection Decision Flowchart

1044.8 Hardware Platforms

The UWB ecosystem has matured significantly with several commercial chipsets and development platforms.

1044.8.1 Commercial Chipsets

Qorvo/Decawave DW3000 Series: - Most widely deployed UWB chipset - IEEE 802.15.4z compliant - Channels 5 and 9 (6.5 GHz, 8 GHz) - ~10 cm ranging accuracy - Integrated MAC and PHY - Low power: 60 mW in active mode - Used in: Industrial tracking, automotive, consumer

NXP Trimension Family: - SR040 (automotive-grade) - SR150 (mobile/consumer) - SR100T (secure element integrated) - IEEE 802.15.4z HRP UWB - Enhanced security features - Used in: BMW digital keys, Samsung phones, Apple iPhones (rumored)

Apple U1 / U2 Chip: - Proprietary design (likely based on licensed IP) - Integrated in iPhone 11+ (U1), iPhone 15+ (U2) - Also in AirTags, HomePod mini, Apple Watch Ultra - ~50 billion potential devices - Closed ecosystem but industry-defining

STMicroelectronics SR21: - Automotive-qualified - Integrated Arm Cortex-M33 - Secure ranging with cryptography - Target: Digital car keys

1044.8.2 Development Kits and Platforms

Qorvo DWM3000EVB: - Evaluation board for DW3000 - Arduino-compatible headers - Reference TWR and TDoA firmware - ~$200 per board - Best for: Prototyping, academic research

Decawave MDEK1001: - Complete development kit (12 modules) - Pre-configured for TDoA and TWR - Android app for visualization - Out-of-box positioning demo - ~$1500 for kit - Best for: Quick proof-of-concept

Pozyx Creator: - All-in-one positioning system - Hardware + software + API - Anchors, tags, gateway included - Cloud dashboard - ~$2000+ for starter kit - Best for: Enterprise deployment, minimal development

1044.8.3 Custom PCB Integration

Key considerations when integrating UWB chips:

  • Antenna design: Critical for performance (typically PCB trace or chip antenna)
  • RF layout: Follow reference designs carefully
  • Power supply: Clean, low-noise power required
  • Crystal: High-quality oscillator for timing accuracy
  • Regulatory: FCC/CE certification required

1044.9 Summary

UWB positioning system design requires balancing accuracy requirements with infrastructure complexity and cost. Proper anchor placement with good geometric diversity is essential for achieving centimeter-level accuracy.

Key Takeaways:

  1. Anchor Placement: Avoid collinearity, vary heights for 3D, ensure 4+ anchor visibility per tracked point

  2. System Architecture: TWR for simple/small deployments, TDoA for enterprise scale

  3. Environment Matters: Line-of-sight preferred, metal and water cause significant degradation

  4. Technology Selection: UWB excels at sub-meter accuracy, high update rates, and secure ranging

  5. Commercial Options: Mature ecosystem with Qorvo DW3000, NXP Trimension, Apple U1/U2 chipsets

1044.10 What’s Next?

Now that you understand UWB positioning system design, continue to: