Wireless Sensor Networks BLUETOOTH LOW ENERGY Flavia Martelli [email protected] Outline • Introduction • Applications • Architecture • Topology • Controller specifications: – Physical Layer – Link Layer • Host specifications: upper layers • Products on the market 2 Introduction (1/2) Bluetooth: • Wireless technology for short-range communication • Replacement to cables connecting portable and/or fixed electronic devices • Key features: . worldwide operation . robustness . low power consumption . low cost . interoperability 3 Introduction (2/2) Bluetooth Core Specification v4.0 (adopted 30 June 2010) • Two main configurations 1. Basic Rate (BR) . Optional Enhanced Data Rate (EDR) and Alternate MAC and PHY (AMP) extensions 2. Low Energy (LE) . Lower power consumption devices operated with coin cell batteries . Lower complexity . Lower cost . Lower data rates 4 Applications (1/7) Automotive 5 Applications (2/7) Sports and fitness 6 Applications (3/7) Healthcare 7 Applications (4/7) Entertainment 8 Applications (5/7) Home automation 9 Applications (6/7) Security and proximity 10 Applications (7/7) Advertising YOU ARE HERE 11 Architecture Heart Proximity Remote Control PUID Generic Access … Rate Profile (GAP) Generic Attribute Profile (GATT) Security Manager Attribute Protocol (ATT) Protocol (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 12 Implementation modes • Single-mode (stand-alone) implementation: targeted at low power consumption and small size devices • Dual-mode implementation: extension to a classic Bluetooth radio, targeted at mobile phones and PCs Dual-mode LE single-mode device device LE single-mode device 13 Network topology • Piconet: star topology Slaves Master • Broadcast group Scanners Advertiser 14 Controller specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 15 Physical Layer (1/2) • Modulation: Gaussian Frequency Shift Keying (GFSK) . Bandwidth-bit period product: BT = 0.5 . Modulation index: 0.45 < h < 0.55 . Bit-rate: Rb = 1Mbit/s • Transmission power: -20 dBm < Ptx < + 10 dBm • Receiver sensitivity: -70 dBm [BER < 0.1%] 16 Physical Layer (2/2) • Band: ISM @ 2.4 GHz . 40 channels of 2 MHz . f = 2402 + i*2 MHz, i=0,…,39 17 PHY performance (1/2) BLUETOOTH LOW ENERGY 18 PHY performance (2/2) Normalized power spectrum [dB] 802.15.4 3 MHz 1.5 Rb Bluetooth LE 1.5 MHz 19 Controller specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 20 Link Layer: state machine Scanner Listen to Advertising packets Initiator Advertiser Listen to Advertising Tx Advertising packets packets and respond to initiate a connection Slave/Master Tx/Rx data packets 21 2480 39 2478 36 2476 35 22 2474 34 2472 33 2470 32 2468 31 2466 30 2464 29 2462 28 2460 27 2458 26 2456 25 2454 24 2452 23 2450 22 2448 21 (i = 0, 12, 39): 0, 12, (i = 2446 20 other 37 RF channels): channels): other 37 RF 2444 19 2442 18 2440 17 (the (the 2438 16 2436 15 2434 14 channels 2432 13 : 2430 12 2428 11 2426 38 2424 10 2422 9 2420 8 Layer 2418 7 2416 6 2414 5 2412 4 2410 3 Data physical channel channel physical Data communication between connected devices discovering discovering initiating devices, a connection, broadcasting data Advertising physical channel channel physical Advertising 2408 2 Link 1 2406 RF Channels are allocated into two types: 2. 1. 2404 0 37 2402 • MHz Adv Data Link Layer: events • Advertising events t • Connection events t 23 Passive scanning Scanner Advertiser Advertisement Found Channel (x) Advertisement device Channel (y) Advertisement Channel (z) Advertisement Advertisement Advertisement 24 Active scanning Scanner Advertiser Advertisement Scan Request Scan Response (name, services) Found device (name, services) 25 Broadcasting data Scanner Advertiser Advertisement (data) Found device Advertisement (data) (data) Advertisement (data) Advertisement (data) Advertisement (data) Advertisement (data) 26 Initiating a connection Initiator Advertiser Advertisement Connect Request Master Slave "poll" Channel (x) Data Communication event interval Ack "null" Channel (y) 27 Link Layer: PDU Access Preamble PDU Header PDU Payload CRC Address variable (0 – 37 1 byte 4 bytes 2 bytes 3 bytes bytes) • Error checking 01010101 or • Identifies a LL connection between 10101010 two devices • Frequency synchronization • Fixed sequence for advertising PDUs • Symbol timing estimation • Automatic gain control 28 Link Layer: advertising PDU Access Preamble PDU Header PDU Payload CRC Address variable (0 – 37 1 byte 4 bytes 2 bytes 3 bytes bytes) PDU type Res. TxAdd RxAdd Length Res. 4 bits 2 bits 1 bit 1 bit 6 bits 2 bits PDU type Packet name PDU type Packet name 0000 ADV_IND 0011 SCAN_REQ 0001 ADV_DIRECT_IND 0100 SCAN_RSP 0010 ADV_NONCONN_IND 0101 CONNECT_REQ 0110 ADV_SCAN_IND other Reserved 29 Link Layer: data PDU Access Preamble PDU Header PDU Payload CRC Address variable (0 – 37 1 byte 4 bytes 2 bytes 3 bytes bytes) LLID NESN SN MD Res. Length Res. 2 bits 1 bit 1 bit 1 bit 3 bits 5 bits 3 bit LLID Packet type 00 Reserved Logical Link Identifier: Next expected sequence More Data bit 01 LL Data PDU: continuation fragment of an L2CAP message or empty PDU data or control PDU number and sequence number: 10 LL Data PDU: start of an L2CAP• Acknowledgment message 11 LL Control PDU • Flow control 30 HCI specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 31 Host Controller Interface • The HCI provides a uniform interface method of accessing Bluetooth Controller‟s capabilities (command PHY and LL, access hardware status, control registers) • Optional implementation • Possibility of realizing separate Host and Controller interoperability of different subsystems 32 Host specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 33 L2CAP (1/2) • L2CAP provides connection-oriented and connection-less data services to upper layer protocols – Protocol multiplexing capability (not in case of LE only Controller) – Segmentation and reassembly – Per-channel flow control and retransmission 34 L2CAP (2/2) • PDU format Length CID Payload 2 bytes 2 bytes Variable (as specified in „Length‟) • 0x0004 = Attribute Protocol • 0x0005 = LE L2CAP Signaling channel • 0x0006 = Security Manager Protocol 35 Host specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 36 Attribute Protocol (1/2) • Attribute is „data‟ – Value with a meaning (UUID), permissions (read/write), that is addressable by a handle Attributes expose data on a remote device • ATT is a peer-to-peer protocol between a server and a client – Server: contains attributes, receives requests, executes, responds, can indicate values – Client: sends requests, commands, waits for responses, can confirm indications 37 Attribute Protocol (2/2) • Operations on attributes – Push: the server sends the data to the client when it changes or according to configuration – Pull: a client request the data from the server when it needs it – Set: configuring a server (actuator) – Broadcast: the server periodically broadcast the data (using LL advertising PDUs) – Get: the client requests for attributes handles and UUID to discover the services that the server offers 38 Host specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 39 Generic Attribute Profile • The GATT profile is designed to be used by an application or another profile • It defines how to use the ATT Protocol to discover, read, write and obtain indications of server attributes, as well as configuring broadcast of attributes • Attributes are grouped in services – service = collection of data and associated behaviors – characteristic = value used in a service along with properties and descriptors (how it is accessed, displayed and represented) 40 Host specification Proximity Remote Control Generic Heart PUID Rate Access … Profile (GAP) Generic Attribute Security Profile (GATT) Manager Attribute Protocol Protocol (ATT) (SMP) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface (HCI) Link Layer (LL) Physical Layer (PHY) 41 Generic Access Profile • A bluetooth profile defines the required functions and features of each layer in the Bluetooth