In this series, Nick Powers will take you through the basics of Bluetooth Low Energy (BLE) and some of the solutions offered in the space.
1. Introduction
Learn all about BLE and the architecture and versions available from key suppliers; Nordic Semiconductor, STMicroelectronics, Cypress, and Silicon Labs.
2. Physical Layer
In BLE application, it is important to understand the physical layer in order to program a more robust transmission and optimize the data rate, and hence current consumption or the amount of power used.
3. Link Layer Advertising
In BLE, information is exchanged via packets. No streaming is available. Two kind of packets are defined: advertising packets and data packets. Devices use advertising packets to find and connect to other devices or to broadcast data. Data packets are used once a connection had been made and is understandable by only two devices (master and slave). Advertising packets use channels 37, 38 and 39; channels 0 through 36 are for data packets. The link layer handles all of these packets.
4. Link Layer Connection
In the previous video, we saw how a device advertises. Once a master discovered a slave after advertising, it's time to connect. To make a connection, either the general advertising event or the direct advertising event types must be transmitted by the advertiser. Then the initiator (master) sends a connect request packet. The connection is only considered established once a packet has been acknowledged. Establishment doesn't change how the connection works, but it does change the link supervision timeout, from just 6 connections timeouts, to the value in the connection request message. This ensures that if the connection is not established quickly, it is terminated immediately.
5. Link Layer Connection Management
Let's see how a reliable connection is managed in BLE. Remember that communication between a master and a slave occurs in a connection event that uses a data channel frequency. Then, based on the frequency mapping and the hopping algorithm, it moves to the next frequency at the next connection interval.
6. HCI
HCI, or host controller interface, was designed to be the interface between the host and the controller. Hence, a physical interface is integrated in the specs, but nowadays it is not practically used as most modern BLE solutions integrate the hos and controller in a single package.
7. L2CAP
L2CAP is simply a multiplexing layer and to do this it has multiple channels. A channel is a single sequence of packets, from and to a single pair of services and a single device. Between two devices, there can be multiple channels active at the same time. L2CAP enables BLE to multiplex three different channels. It also enables segmentation and reassembly of packets that are larger than the underlying radio can deliver.
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