Protocol Structure

The BLE Stack

┌─────────────────────────┐
│      Application        │
├─────────────────────────┤
│         GAP            │  Generic Access Profile
├─────────────────────────┤
│         GATT           │  Generic Attribute Profile
├─────────────────────────┤
│         ATT            │  Attribute Protocol
├─────────────────────────┤
│         L2CAP          │  Logical Link Control
├─────────────────────────┤
│         HCI            │  Host Controller Interface
├─────────────────────────┤
│     Link Layer         │
├─────────────────────────┤
│     Physical Layer     │  2.4 GHz Radio
└─────────────────────────┘

BLE Roles

Peripheral (Slave)

• Advertises presence
• Accepts connections
• Offers services (GATT Server)
• Example: Fitness band, beacon

Central (Master)

• Scans for peripherals
• Initiates connections
• Consumes services (GATT Client)
• Example: Smartphone, gateway

Advertising

Channels: 37, 38, 39 (avoids WiFi interference)

Types:

• Connectable: Allows connection
• Non-connectable: Broadcast only
• Scannable: Responds to scan request

BLE Data Model

GATT Structure

Profile - Collection of services for a use-case Service - Logical grouping of characteristics Characteristic - Data unit with properties Descriptor - Metadata for characteristic

Example: Heart Rate Profile

Heart Rate Service (UUID: 0x180D)
├── Heart Rate Measurement (0x2A37)
│   ├── Properties: Notify
│   └── CCCD Descriptor (enable notifications)
├── Body Sensor Location (0x2A38)
│   └── Properties: Read
└── Heart Rate Control Point (0x2A39)
    └── Properties: Write

Standard Services (SIG)

Common:

• Battery Service (0x180F)
• Device Information (0x180A)
• Heart Rate (0x180D)
• Environmental Sensing (0x181A)

Custom Services:

• Own 128-bit UUID
• Custom characteristic definition
• Documentation for integration

Selecting the BLE Chip

Popular Options

Nordic nRF52 Series

• nRF52832: BLE 5.0, ARM Cortex-M4
• nRF52840: BLE 5.0, USB, Zigbee capable
• nRF52833: Direction finding
• Advantage: Excellent SDK, large community

Dialog DA1469x

• Ultra-low power
• Integrated audio codec
• Display controller
• Use: Premium wearables

Texas Instruments CC26xx

• Multi-protocol (BLE, Zigbee, Thread)
• Sensor controller for wake-up
• Use: Industrial, smart home

Silicon Labs EFR32

• BLE + Zigbee + Thread
• Gecko SDK
• Use: Multi-protocol IoT

Module vs Chip

Module (e.g., nRF52 Raytac MDBT42Q)

• Integrated antenna
• Certifications included (FCC, CE)
• Rapid time-to-market
• Premium cost

Chip (e.g., nRF52832 QFN)

• Design flexibility
• Optimized cost at volume
• Requires certification
• PCB with RF knowledge

Maximum Battery Autonomy

Low-Power Principles

Minimize Wake Time

• Process as fast as possible
• Sleep immediately after task
• Avoid polling, use interrupts

Reduce TX Power

• Adjust based on RSSI
• +4dBm vs 0dBm = 40% more current
• Short distance = reduced power

Optimize Advertising

• Larger interval = lower consumption
• 1000ms interval vs 100ms = 10x savings
• Balance: Discovery latency vs battery

Connection Parameters

Connection Interval

• Range: 7.5ms - 4s
• Trade-off: Latency vs consumption
• Negotiation with central

Slave Latency

• Skip connection events if nothing to send
• Major consumption reduction

Supervision Timeout

• Timeout for disconnect detection
• Too small = false reconnections

Typical nRF52 Consumption

• TX (+4dBm): 5.3mA
• RX: 5.4mA
• CPU active: 3mA
• System ON, RAM retention: 1.5µA
• System OFF: 0.3µA

Software Implementation

SDKs and Stacks

Nordic nRF Connect SDK (Zephyr based)

• Modern, cross-platform
• Bluetooth Host + Controller
• Thread, Zigbee support
• Open source

Nordic SoftDevice (legacy)

• Binary blob for controller
• Stable and tested API
• Still used in production

Zephyr RTOS

• Integrated Bluetooth stack
• Multi-vendor support
• Configurable and modular

Development Flow

1. GATT Definition

BT_GATT_SERVICE_DEFINE(my_service,
    BT_GATT_PRIMARY_SERVICE(&my_uuid),
    BT_GATT_CHARACTERISTIC(&char_uuid,
        BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY,
        BT_GATT_PERM_READ,
        read_cb, NULL, &value),
    BT_GATT_CCC(ccc_cfg_changed, BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),
);

2. Advertising Setup

static const struct bt_data ad[] = {
    BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR),
    BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, sizeof(DEVICE_NAME) - 1),
};

bt_le_adv_start(BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL, 0);

Communication Protection

Security Levels

Mode 1 (Encryption)

• Level 1: No security
• Level 2: Unauthenticated encryption (Just Works)
• Level 3: Authenticated encryption (PIN, OOB)
• Level 4: Authenticated LE Secure Connections

Mode 2 (Signing)

• Data signing without encryption
• Use: Authenticated broadcast

Pairing Methods

Just Works

• Zero user interaction
• Vulnerable to MITM
• Use: Devices without display/input

Passkey Entry

• 6-digit PIN
• MITM protection
• Requires display or input

Numeric Comparison

• Both devices display number
• User confirms match
• Most secure for devices with display

Out of Band (OOB)

• Key exchange through other channel (NFC, QR)
• Very secure
• Implementation complexity

Security Best Practices

• Enable bonding for trusted devices
• Use LE Secure Connections (BLE 4.2+)
• Implement app-level encryption for sensitive data
• Periodic key rotation

Implementation Validation

Development Tools

nRF Connect App (iOS/Android)

• Device scanning
• Connect and explore GATT
• Read/Write/Subscribe characteristics
• Log for debugging

Wireshark + nRF Sniffer

• Over-the-air packet capture
• Detailed protocol analysis
• Debug pairing issues

Nordic Power Profiler Kit

• Real-time consumption measurement
• Resolution: µA
• Correlation with software events

Testing Checklist

Functional:

• Advertising visible
• Stable connection
• All characteristics functional
• Notifications working
• Reconnect after disconnect

Interoperability:

• iOS (various versions)
• Android (various phones)
• Other centrals (gateways)

Power:

• Advertising consumption
• Idle connection consumption
• Active transfer consumption
• Sleep current

Range:

• Maximum distance in open field
• Performance through obstacles

Road to Market

Bluetooth SIG Certification

Required for:

• Bluetooth logo use
• Guaranteed interoperability
• Access to major markets

Process:

1. Register as SIG member
2. Qualification (QDID) for stack used
3. Declaration (final product)
4. Listing on bluetooth.com

Costs:

• Membership: $2,500 - $35,000/year (based on revenue)
• Declaration: $0-8,000 (based on membership level)

Radio Certifications

CE (Europe)

• RED (Radio Equipment Directive)
• EMC and radio testing
• Self-declaration (with test report)

FCC (USA)

• Part 15 for ISM band
• Unique FCC ID
• Testing at accredited lab

IC (Canada), MIC (Japan), etc.

• Similar requirements
• Required for export

Using Certified Module

Major Advantage:

• Radio certifications included
• Reduces time-to-market
• Lower cost than own certification

Conditions:

• Follow design guidelines (antenna, impedance)
• Don't modify RF parameters
• Include IDs in documentation

BLE for Your Product

Bluetooth Low Energy is the ideal choice for low-power wireless devices. With the right hardware and firmware, you can achieve years of autonomy on a coin cell battery.

Success Factors

• Right Hardware - Choose chip/module for your application
• Optimized Stack - Mature, production-tested SDK
• Power Design - Optimization from start, not at end
• Rigorous Testing - Interoperability and consumption
• Certification - Plan from design phase

Torcip BLE Services

Hardware Development:

• PCB design with RF
• Antenna selection and matching
• Production optimization

Firmware Development:

• Nordic nRF52/53 specialist
• Custom GATT profiles
• OTA updates
• Power optimization

Production:

• Assembly and testing
• Programming and provisioning
• Certification support

Completed Projects:

• Fitness wristbands
• Indoor positioning beacons
• Wireless industrial sensors
• Medical wearables

Contact us for a discussion about your BLE project and receive free technical consulting.