Bluetooth v4.1: What developers need to know

Jay Tyzzer, Nordic Semiconductor -August 11, 2014

After keeping a relatively low profile after its launch as part of the Bluetooth Core Specification v4.0 (Bluetooth v4.0) in 2010, Bluetooth Smart (previously known as Bluetooth low energy) has hit the headlines.

Bluetooth Smart Ready products, which include Apple’s devices and the majority of Android-powered mobiles, are equipped with a Bluetooth v4.0/v4.1 chip that can do everything that “classic” Bluetooth technology could do but also communicate with the Bluetooth Smart chips increasingly finding their way into coin cell-powered peripherals and products like smartwatches.

In the next several years smartphone and tablets sales are forecast to surge, with analyst Statista Research, for example, estimating there will be a cumulative total of 6.1 billion mobile devices globally by 2020. Analyst IHS is a little more conservative but still predicts big numbers. The company estimates the installed base of smartphones at 1,919 million units at the end of 2013, and over the next five years projects it will grow to 5,082 million. Given Bluetooth technology’s affinity with the smartphone and tablet, and the number of companies working furiously to introduce “appcessories” the number of Bluetooth Smart devices connected to each smartphone is set to surge.

Figure 1: An appcessory teams a peripheral product such as these Scalextric slot cars with a software app on a Bluetooth Smart Ready smartphone. (Courtesy: Scalextric)

An appcessory teams a peripheral product such as a fitness sensor or toy with a software app on a Bluetooth Smart Ready smartphone, tablet- or desktop-computer. Typically powered by small batteries such as coin cells, appcessories send their data to the mobile device using the ultra low power (ULP) Bluetooth Smart chip. The host device’s app then analyses and displays the data. Many apps also make it easy to share the information via social media.

But now, among other useful new features, the latest version of Bluetooth technology, Bluetooth v4.1, introduces new capabilities that help build the foundation of technology that will eventually allow Bluetooth Smart devices to connect directly to the Internet – eliminating the need to leverage the computational power of a smartphone or tablet. (The mobile product (or other Internet-connected unit such as a Wi-Fi router) might still act as a data-forwarding device, but the increasingly powerful software that will analyze, manipulate, and share the information will reside in the cloud.)
While Bluetooth v4.1 still falls someway short of unlocking a direct Internet connection it underscores the Bluetooth Special Interest Group’s (SIG) ambition to extend the reach of Bluetooth technology. That strategy will encourage a new class of products fueling a new market sector that looks set to dwarf even that of appcessories.

A foundation for Bluetooth-over IP
From a developer’s standpoint Bluetooth v4.1 offers several advantages over the previous release. Key among these are better alignment of the quite different use cases presented by the technology’s long-standing streaming media mode, the ULP operating mode (using technology that adheres to the spec’s Low Energy Core Configuration), and Internet Protocol (IP)-connected operation.
Developers will probably consider the most important single feature introduced with Bluetooth v4.1 to be a topology that allows a device such as a smartphone to act as a Bluetooth Smart Ready hub and a Bluetooth Smart peripheral at the same time. Devices equipped with chips built to the new specification will be endowed with the ability to pass data from a sensor or smart watch to a smartphone and then on to a PC if appropriate.

Another attribute, which gives developers even greater freedom, is the ability to set up a “scatternet.” Previously, Bluetooth enabled communication by creating piconets. But its three-bit address space limited the maximum size of a piconet to eight devices––one hub and seven peripherals––which could have limited Bluetooth technology’s useability as the number of devices fitted with the technology expanded. However, now that a device can assume either hub or peripheral identities, it is possible for a hub to communicate with many more than eight devices.

Another important change for developers gives them more flexibility in maintaining communication sessions. With Bluetooth v4.0, the interval between connection “advertisements” from a Bluetooth Smart device to a Bluetooth Smart Ready device was fixed.  Unfortunately, this meant that when an activity device such as a fitness monitor was separated from the hub, the connection could be quickly abandoned and required manual restoration. Beginning with Bluetooth v4.1, the developer now sets the interval between connection advertisements that takes into account any likely use scenario for his or her end product.

However, perhaps the most notable enhancement to this version of Bluetooth technology is the one that lays the foundation of IP-connected operation (which will eventually lead to direct communication with the Internet) through the implementation of Connection-Oriented Channels in the Logical Link Control and Adaptation Protocol (L2CAP).  While L2CAP was already part of Bluetooth v4.0, it was not until the release of the latest version that L2CAP Connection-Oriented Channels became available to Bluetooth Smart and Bluetooth Smart Ready.

Within Connection-Oriented Channels is the capability to establish Dedicated Channels. Dedicated Channels have fixed numeric values associated with them. Both Connection-Oriented Channels and Dedicated Channels are a preliminary requirement for Internet Protocol version 6 (IPv6). IPv6 is the latest version of the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet and is touted as the underlying protocol for the “Internet of Things” (IoT).

In addition, Bluetooth v4.1 supports longer packet sizes, known as long maximum transmission units (MTU). Support for longer packet lengths is essential to carry IP packet data across Bluetooth Smart links.

It’s important to note that there are still many technical hurdles to overcome––and several revisions of Bluetooth technology––before Bluetooth Smart devices will be able to directly communicate with the Internet. But, in the Bluetooth SIG’s own words, “[The implementation of dedicated channels for communication in Bluetooth v4.1] is a foundation step for future support of IPv6 at the sensor level.”

The power of Bluetooth silicon
But without advanced silicon, the promise of Bluetooth’s enhanced version will come to naught. ULP Bluetooth Smart chips (technology that was introduced with Bluetooth v4.0 and which has dramatically extended the reach of Bluetooth into coin cell-powered peripheral devices) are the key to the present boom in Bluetooth technology’s popularity. Fortunately, semiconductor vendors are wasting no time in rolling out Bluetooth Smart that are fully compatible with Bluetooth v4.1.

One of the advantages of an open standard such as Bluetooth v4.1 is that it encourages a multivendor supply chain giving engineers a choice of products and fostering a competitive environment - stimulating innovation. Silicon vendors have geared up to ship billions of Bluetooth Smart chips a year that offer excellent performance and cost just a few dollars per part, with each chip is guaranteed to interoperate with all of the others.

By building on the back of the established Bluetooth technology ecosystem, and supported by manufacturers who look after the intricacies of the RF engineering, innovators ranging from commercial companies to the “maker” community can now add wireless connectivity to virtually anything, adding “smartness” to their products. And better yet, some of these Bluetooth Smart chips are capable of upgrading their software, without the consumer even being aware it’s happening.

Such over-the-air updates are routine for other wireless technologies. For example, consumers are familiar with updating apps on smartphones via the cellular network, or downloading security patches for portable computers’ operating systems via Wi-Fi. But over-the-air updating of ULP wireless chips has been anything other than routine.

However, because Bluetooth v4.1 opens a direct channel in the L2CAP layer that allows for bulk data exchange (accelerating downloads) things have become easier. Now some (but by no means all) Bluetooth Smart chips can now take advantage of this functionality to easily and rapidly upgrade their RF protocol software (“stack”), or the developer’s application code, using their own wireless links.
Nordic Semiconductor, for example, has just released its latest SoftDevice (a self-contained stack for the nRF51 Series SoCs that incorporates RF protocol software and its associated management framework) which is compliant with Bluetooth v4.1 (see Figure 2). This SoftDevice (v7.0) includes an “Over-The-Air Device Firmware Upgrade” (OTA-DFU) feature that supports wireless software upgrades.

Figure 2: Nordic Semiconductor’s latest Bluetooth Smart chip can be updated over-the-air

Over-the-air upgrades are of benefit to product developers because new features can be added to existing products and bug fixes can be implemented even when products are in the hands of consumers. Because of the unique software architecture that separates the stack from the application code, for example, Nordic chips allow the developer to upgrade one software element without any risk of corrupting the other.

But perhaps more importantly, consumers can benefit from major software upgrades that bring genuine new capabilities to their existing wireless peripheral devices. Such a capability will allow a future generation of connected devices to upgrade their software when instructed by the server residing in the cloud. There would be no need for the consumer to junk the hardware and buy a new product to take advantage of new software such as a new version of Bluetooth technology.

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