Internet of Things Amr El Mougy Alaa Gohar

Independent BLE sensors Layers of the IoT Applications Middleware Processing Layer High-end computational devices Internet Aggregation Layer RFID reader M2M comm. Smartphone Gateways Sensing Layer Wireless Sensor Networks Independent BLE sensors Human emotions

Sensors Other Peripherals Sensor Node Battery Board Microcontroller Communication Module Sensors

The Sensing Layer Sources of different types of information Available sensors can detect a wide range of parameters and are connected to a wireless transceiver Expected to be deployed in 10s of billions by 2020 These “sensor nodes” are typically required to remain operational for long durations (months or even years) They are also small in size and thus have limited processing, memory, and energy capabilities ZigBee BLE RFID

Radio Frequency Identification (RFID) A system that consists of a tag that stores a limited amount of information (few KB) and a reader that obtains this information Fast, low cost, unique identification of items Uses RF which does not require line of sight (key advantage over barcode) Other advantages over barcode: Stores more data Can be read from longer distances

Types of Tags Passive: No battery, draws power from RF Very small storage (~1KB) Small reading range (few metres) Very cheap Typically write-once/read-many times Tag remains readable for a long time, often exceeds product lifetime Active: Small battery Bigger storage (few hundred KBs) Longer range (few hundred metres) Not cheap Typically re-writable Larger size Tag expires when battery dies

Automatic checkout at the grocery store RFID Applications Automatic checkout at the grocery store Library management Access control Supply chain

Communication Process RFID sends activation command that powers nearby tags Tags respond with their data Some material (metal, plastic, cardboard) can have negative effects on the RF signal

Collision Problems Reader collision Multiple readers try to read the same tag at the same time Tag cannot differentiate between readers’ signals and cannot respond The challenge is that tags are very simple  no collision avoidance protocols can be implemented on them Solution: implement protocols at the reader. Ex: Readers can have different frequencies or work in different time slots. Alternatively, readers send beacons to announce their intention to transmit

Collision Problems Tag collision Multiple tags receive the activation signal and respond Reader receives reports from multiple tags  all readings are lost Challenge is that tags are quite simple and cannot have protocols Solution  hardware modification The solutions general force tags to not transmit whenever they hear the reader Transmissions can be probabilistic or selective

Sensor Networks

Network Topologies

The Wireless Signal A wireless signal is affected by three factors: Attenuation due to distance Shadowing due to large objects Multipath fading due to small objects

Sensor Technology BLE ZigBee WiFi ANT RF4CE IrDA Range 10m 200m 300m Throughput 1 Mbps 255 kbps 100 Mbps 60 kbps 1 Gbps Delay 2.5 ms 20 ms 1.5 ms ~0 25 ms Power efficiency 0.153 μW/bit 186 μW/bit 0.00525 μW/bit 0.71 12 Power consumption 12.5 mA 40 mA 116 mA 17 mA 10 mA Comments No sleep cycle Which one is more suitable for direct user interaction?

Applications No longer true

Bluetooth Bluetooth is the brand name for the family of standards known as 802.15.1 It was designed initially to replace wired cables The name comes from the former king of Denmark who unified his country Standard Data Rate Spectrum Range Comments V1.0 and v1.0B Not successful, had many flaws V1.1 (2002) Fixed many of the errors of the previous versions V1.2 (2005) 1 Mbps 2.4 GHz 1m, 10m, 100m V2.0 (2004), V2.1 (2007) + EDR 3 Mbps V3.0 + HS (2009) 24 Mbps WiFi links are used for data communication V4.0 BLE (2011) 1~2 Mbps Very low power consumption V5.0 (2016) 2 Mbps 4x range Higher message capacity

Logos

Traditional Bluetooth Traditional Bluetooth is connection oriented. When a device is connected, a link is maintained, even if there is no data flowing. Sniff modes allow devices to sleep, reducing power consumption to give months of battery life. Peak transmit current is typically around 25mA. Even though it has been independently shown to be lower power than other radio standards, it is still not low enough power for coin cells and energy harvesting applications

Traditional Bluetooth Architecture Communication uses Master – Slave architecture Time is divided into slots and the master controls who transmits in each slot A set of one master and its slaves is called a Piconet No direct communication between slaves Two or more joined Piconets is called a Scatternet Parked Slaves Master Active Slaves

Connected State - Transmission Modes Asynchronous Connection-Less (ACL) mode One ACL can exist between any two devices Even slots are for master transmissions and odd slots are for slave Synchronous Connection-Oriented (SCO) mode Reserved channel bandwidth and slots between master and slaves A master can support up to 3 SCO links A slave can support 3 SCOs from one master or 2 SCOs from different masters No retransmissions Used for voice communications

Transmission modes

Bluetooth High Speed Connections are established using Bluetooth Data is transferred using WiFi channels Backward compatible with other Bluetooth devices Consumers benefit from the way they use Bluetooth while benefiting from high speed WiFi connections

Bluetooth Low Energy A new radio, new protocol stack, new profile architecture It’s designed to run from coin cells It is a radio standard for a new decade, enabling the Internet of Things Features: Mostly new PHY New advertising mechanism, for ease of discovery & connection Asynchronous connection-less MAC: used for low latency, fast transactions (e.g. 3ms from start to finish) New Generic Attribute Profile to simplify devices and the software that uses them. Asynchronous Client / Server architecture Designed to be LOWEST cost and EASY to implement

Bluetooth Low Energy For Bluetooth low energy, data throughput is not a meaningful parameter. It does not support streaming. It has a data rate of 1Mbps, but is not optimised for file transfer. It is designed for sending small chunks of data (exposing state). It’s good at small, discrete data transfers. Data can triggered by local events. Data can be read at any time by a client. Interface model is very simple (GATT) Generic Gateways (optimized for the IoT): Devices that support BLE Gateway functionality provide a transparent pipe from a device to an IP address. Middleware at the IP address can access the device directly as if it were a collector talking to it locally. The Gateway device plays no part other than in acting as a pipe.

Protocol Stack Low Complexity 1 packet format 2 PDU types – depending on Advertising / Data Channel 7 Advertising PDU Types 7 Link Layer Control Procedures Useful Features Adaptive Frequency Hopping Low Power Acknowledgement Very Fast Connections Devices can advertise for a variety of reasons: To broadcast promiscuously To transmit signed data to a previously bonded device To advertise their presence to a device wanting to connect To reconnect asynchronously due to a local event

The ATT Protocol A Bluetooth packet is called an attribute. The ATT protocol defines the attributes Each attribute is defined using three fields: 16-bit handle: a sequence number of the attribute Universally unique ID (UUID): an identifier specified by the application or GATT A value: the content of the packet. Can be of any length (Beacons specify 31 bytes) ATT features include searching for all attributes with the same UUID and getting all attributes within a specific range of handles ATT is client-server

The GATT Protocol GATT defines how ATT attributes are grouped together to provide meaningful services This is done by specifying a range of handles that belong to the same UUID (ex: all handles belonging to UUID 0x2816 are temperature readings GATT is also able to specify characteristics for the readings (ex: all readings with UUID 0x2816 are temperature with unit Celsius and were taken on 9 Feb 2016). These are read only parameters

The GAP Protocol GAP is about interoperability. It defines how different devices are going to implement specific functions Thus, the GAP profiles specify how nodes will operate (discover, connect, etc.) to serve a particular application It defines the topology of the BLE network

Roles Broadcaster (advertiser): Broadcast advertisements Observer (scanner): Listen for advertisements. Can connect to an advertiser. Central (master): Communicates with the device in slave role, defining timings and transmissions. Peripheral (slave): A device connected to a master. Can have only one master at the same time.

Active States

GAP States A Broadcaster cannot enter the Scanning state. An Observer cannot enter the Advertising State.

Scanning State The way to detect other Bluetooth nodes is to scan looking for slave messages (called advertisements). Some parameters should be configured to allow scanning in the desired way. Some functions have been implemented to easily scan for other devices, defining time, number of devices to discover, etc. Parameters must be configured before doing a scan. The parameters are defined inside the General Access Profile (GAP) of the module. It is not possible to change scanning parameters while scanning, so the user must stop scanning before making any change. General Access Profile mode: There are three possible states regarding visibility of BLE devices, so the scan can filter the devices by this state. The possible choices are: Limited discoverable: Discover only slaves which have the limited discoverable mode enabled. Generic discoverable: Discover slaves which have limited discoverable mode or generic discoverable mode enabled. Observation: Discover all devices (default).

Scanning State Parameters to be defined include: scan interval, scan window, and passive/active scanning: In passive scanning, the BLE module just listens to other node advertisements. When one of these advertisements is detected, the module reports the discovered device. Normally, the advertisement contains information like discoverability and connectability modes, TX power level, MAC address of the node (called advertiser) or application data. On the other hand, in active scanning the module will request more information once an advertisement is received, and the advertiser will answer with information like friendly name and supported profiles. The advertisement packets are configurable as is described in next sections. In addition, BLE has an option to accept advertisements only from specific nodes (called the whitelist) The transmission power can be set to one of 16 ranges BLE, like many other standards, provides RSSI measurements. The higher the RSSI, the stronger the received signal Can be used for indoor localization

Advertising State Advertising is a process used for BLE modules to send data to other BLE devices. This data is packed in advertisements, which are modifiable by the user, so they represent an easy way of sending data without the need of connecting first. The advertisements contain information about address of the advertiser, discoverability and connectability modes, TX power level, application data, etc. They can be built according to the Bluetooth standard or customized by the user to send its own data. Configuring advertisements: Visibility - GAP discoverable modes This specifies who can see the advertisements of the BLE module Non discoverable: Device is not advertising Limited discoverable: Device will be visible using limited discoverable scanning mode General discoverable: Device will be visible using general discoverable scanning mode

Advertising State Configuring advertisements: Connectability - GAP connectivity modes A flag inside the advertisements states who can connect to this node Non connectable: Device is not connectable by others Direct connectable: Device can be connected by only one node Indirect connectable: Device can be connected by any node Configuring advertisements: Responses to scan requests Defines an advertisement policy to specify if the module will respond to scan requests and allow connections All: Responds to scan requests from any master, allows connection from any master. WhiteList scan: Responds to scan requests from whitelist only, allows connection from any master. WhiteList connect: Responds to scan requests from any master, allows connection from whitelist only. WhiteList all: Respond to scan requests from whitelist only, allows connection from whitelist only. Time between advertisements is configurable Maximum size of advertisement is 31 bytes Custom payload can be defined, but if compatibility with BLE is required, a specific format must be used Advertisements can be normal (when state is anything but non-discoverable) or a scan response