BLE ARCHITECTURE (CONTROLLER)

THE BLE ARCHITECTURE

Three main block of BLE architecture

1. Application : The application uses the host software to build use cases
2. Host : A software that manages how two or more devices communicate
3. Controller : A physical device that can transmit and receive radio signals

Each block is made of layers

Layers of BLE architecture

Controller

1. The Physical layer (PHY) is the radio hardware used for communication
2. BLE operates in the 2.4GHz ISM band
3. The spectrum is segmented into 40RF channels, each separated by 20MHz
4. 3 out of the 40 channels are called Primary advertising channels
5. The other 37 channels are used for secondary advertising and for data transfer during connections
6. The radio uses a technique called frequency hopping spread spectrum(FHSS)

?This technique minimizes the effect of any radio interference potentially present in 2.4GHz spectrum across any single channel

1. In BLE 4.0 4.1 and 4.2 the data rate is fixed at 1Mbps
2. The physical layer in these versions is therefore called 1M PHY
3. In BLE 5, two new physical layers were introduced?

???????- 2Mbps PHY : This provides? 2x speed of earlier BLE version

???????- Coded PHY : This provides a longer range compared to BLE version

1. The modulation used to encode the bitstream is Gaussian frequency shift keying (GFSK)

?? This is the same modulation used by bluetooth classic and some proprietary wireless protocols

Direct test mode?

1. This layer is used for performing RF tests during manufacturing and for certifications

Link layer

1. This layer is responsible for advertising, scanning and creating/ maintaining the connection
2. Also responsible for ensuring packets are structured properly
3. The link layer interface with the physical layer and provides the higher layers a means to talk to the radio through HCI layer
4. The link layer defines the following roles:

1.? Advertiser :? A device sending advertising packets

2. Scanner : a device scanning for advertising packets

3. Master : a device that initiates and manages a connection

4. Slave : a device that accepts a connection request

1. The link layer manages the following states:

1 . Standby : default state radio does not transmit or receive any data

2. Advertising : devices sends out advertising packets

3. Scanning:? devices scans for devices that are advertising

4. Initiating : scanning device decides to establish a connection with advertising device

5. Connected : device has established a link with another device

1. Packet

1.. Labelled piece of data transmitted by one device and received by one or more other devices

Packet types

1. Advertising packets : for finding and connecting to other devices
2. Data packets : for sending/receiving data once a connection is made

Preamble : first 8 bit transmitted

Acesss addresses : 32 bits in size, which is of two types 1 advertising access address and data access address

Header : content of header depends on whether packet is advertising or data packet

Data(payload) : user data to be sent

CRC : checks for errors, calculated over the header length and payload fields