• Kelly Liu

Guide to Bluetooth 5, 5.1, and 5.2

Updated: Sep 13

In the past decade, the development of Bluetooth Low Energy (BLE) has been crucial to the adoption of wireless personal area network (WPAN) technologies. BLE is pertinent in various applications, ranging from healthcare to security industries. At Allosense, we develop "always connected” sensors and asset trackers; the “always connected” aspect means that our products utilize satellite, cellular, and mesh communication. The new BLE protocol stack provides unique features for enabling localized networking and location finding across multiple low-powered devices. Most recently, Bluetooth 5, 5.1, and 5.2 have been important advances to BLE. Before diving into the specifics of those developments, we need to understand the basis of BLE. The main features discussed in this article include BLE throughput improvements, location finding, and new enhancements.

Bluetooth Low Energy was first introduced as the Bluetooth 4.0. BLE presents low power consumption as the most important feature in this technology. Low power consumption allows for applications to run on small batteries for up to 4-5 years typically. The life of the battery is flexible because BLE is intended to only operate during an initiated connection and remains in sleep mode otherwise. This application only requires a few milliseconds to connect and transfer data since the data rates are around 1 Mbps. A faster transfer rate allows the device to return to sleep mode sooner. Furthermore, BLE is vital for applications that require transmitting small amounts of data periodically because of the ability to do so for multiple years on the same battery. This technology is able to operate within the 2.4 gigahertz ISM (Industrial, Scientific, and Medical) band. Machine to Machine (M2M) and Internet of Things (IoT) devices that use Bluetooth Low Energy include blood pressure monitors and proximity sensors. Overall, BLE is different from the original Bluetooth standards (including Basic Data Rate and Enhanced Data Rate) due to its optimal low data transfer in applications, ability to run on a longer battery life, and use of cheaper wireless components.

The expansion of Bluetooth Low Energy resulted in Bluetooth 5, 5.1, and 5.2. Bluetooth 5 increased the data transfer speed to 2 megabits per second (Mbps), implemented a long-range mode for enhanced sensitivity at 500 kilobits per second (kbps) and 125 kbps, and decreased power consumption between 15% to 50%. The higher data transfer speed decreases the connection time needed to transfer data, the update provides the choice of either operating in a longer range or operating with more speed, and power consumption allows longer usage. Additionally, Bluetooth 5 added two new PHY (Physical Layer) variants on top of the existing PHY: Low Energy 1 mega symbol per second (LE 1M), Low Energy 2 mega symbol per second (LE 2M), and Low Energy Coded (LE Coded). LE 1M, used in Bluetooth 4.0, is a mandatory support in Bluetooth 5 that uses Gaussian Frequency-Shift Keying (GFSK). GFSK uses a Gaussian filter on Frequency-Shift Keying modulation to restrict signal emissions to a narrow spectral band. The 1M stands for 1 mega symbol per second. Each symbol represents a bit, meaning that 1M also stands for 1 Mbps.

On the other hand, LE 2M is a newly optional feature that allows the PHY to operate at a faster data rate of 2 Mbps, which is double of LE 1M PHY, and provides a high frequency deviation to lessen the inter-symbol interference. The faster data rate allows for quicker transmit rates and a reduction in power consumption. Inter-symbol interference is a distortion of signals and not wanted because the noise results in a less reliable communication. The third feature is LE Coded PHY; this new component quadruples the range in comparison to the Bluetooth 4.0 without increasing the transmission power that is required. Finally, Bluetooth 5 offers advertising extensions that are eight times the previous capacity, allowing for an improvement in the broadcasting capability. Advertising defines how a Bluetooth device announces its availability to connect to other nearby Bluetooth devices. The changes made in advertising allow for the broadcasting of larger amounts of data in connectionless circumstances. Bluetooth 5 also introduces periodic and deterministic advertising, which allows for scanners to synchronize the scanning for available packets with respect to the schedule of an advertising device. Packets are small amounts of data sent over a network that includes user data and control information. Periodic implies that packets broadcast to devices at a fixed interval, which means that more than one device can dial in on the periodic advertising. Deterministic means that no randomness will be found in the future output and that the same initial conditions will always result in the same output. This introduction allows for a more power efficient way to scan for packets compared to the previous inability to perform synchronized scanning.

The following update, Bluetooth 5.1, revealed new direction-finding features that allowed devices to pinpoint the physical location of objects, which greatly improved indoor positioning. The system uses a set of phased-array antennas on the receivers. The two new methods for determining direction are Angle of Arrival (AoA) and Angle of Departure (AoD). Angle of Arrival, seen in Figure 1, operates with a transmitter and a receiver.

Figure 1. Angle of Arrival method

The transmitter broadcasts a signal with a single antenna, and the receiver, like a locator, has multiple antennas to receive the signal in an array. Once the transmitted signal crosses the array of antennas, the receiver is able to see a signal phase difference since each antenna in the array will experience the signal at different distances from the transmitter. Thus, the receiver can simultaneously take the In-Phase and Quadrature-Phase (IQ) data samples of the signal and shift to an active antenna in the array in order to yield accurate coordinate points. AoA has the benefits of simplicity and use of low-cost tags as the transmitter; the downside of AoA is the requirement for complex locator units that are required to be mounted with an unobstructed view. Some examples of AoA technology include asset tracing in a warehouse and identifying the location of staff in a defined facility.

Angle of Departure, seen in Figure 2, also operates with a transmitter and a receiver.

Figure 2. Angle of Departure method

However, the transmitter has multiple antennas arranged in an array, and the receiver has a singular antenna. The transmitter sends multiple signals using the antennas to the receiver. The receiver takes IQ data samples to calculate the relative location of the transmitter. This method is more complicated than AoA due to the hardware and software of the complex tags; on the other hand, AoD uses a simpler locator device. An example of AoD is wayfinding in larger spaces. Wayfinding is an information system that guides the user through a complex environment and can be presented in the form of indoor maps, building directories, and mobile applications.

Finally, Bluetooth 5.1 also offers improved advertising beyond the advancements seen in Bluetooth 5. Bluetooth 5.1 has the ability to randomize the advertising channel index. This feature allows devices to select channels at random. By doing so, the probability that two Bluetooth devices will interfere with each other on the same channel to advertise their readiness to connect will decrease. Previously, Bluetooth 5 required available devices to cycle through channels 37, 38, and 39 in an exact order. Devices operating with connectionless communication in busy radio environments experience improved reliability, and devices conserve battery power.

The latest update, Bluetooth 5.2, provides three key features: Isochronous Channels (ISOC), Low Energy Power Control (LEPC), and Enhanced Attribute Protocol (EATT). First, ISOC supports the implementation of Low Energy (LE) Audio. LE Audio aims to provide high quality and low power while supporting synchronized audio streams. The low power aspect of this new technology is essential for Bluetooth hearing aids. Low power allows a single charge to last the user longer, and manufacturers can develop smaller and more compact devices. ISOC helps implement LE Audio in BLE devices through the ability to synchronize time-sensitive data streams across multiple receivers. ISOC also supports connection-oriented and broadcast communication. Connection-oriented communication is when a connection must be established before transferring data, and the data is received in the same order sent. Broadcast, or connectionless, communication is when packet switching networks are used to deliver individual data units without the need for a fixed order of delivery. The ISO interval defines the time duration of when events occur, and ISO can typically range between 5 milliseconds to 4 seconds in 1.25 millisecond intervals. Lastly, ISOC supports data retransmissions to ensure that unacknowledged packets are acknowledged, meaning that all sets of data sent over the network are recognized.

The second feature is Low Energy Power Control (LEPC). LEPC allows for the receiver to request a change in the transmit power level for associated devices. The transmitter has the ability to adjust their own power level and inform associated devices. The dynamic control the receiver exhibits affects the Received Signal Strength Indicator (RSSI). The RSSI is desired to be within an optimal range for the purpose of approximating the distance between the transmitter and the receiver. For instance, LEPC can be seen when the receiver asks the associated device to increase the transmit power if the RSSI becomes relatively low. This feature is beneficial because of improvement in quality control of the signal, decline of the error rates seen at the receiver, and the enhancement of the ability for signals to coexist in the 2.4 GHz frequency range.

The final update presented in Bluetooth 5.2 is the Enhanced Attribute Protocol (EATT). EATT, an improvement upon the existing Attribute Protocol (ATT) feature, allows the performance of concurrent ATT transactions between the client and a server. EATT permits L2CAP-packets and ATT Maximum-Transmission-Unit (MTU) to interleave. L2CAP-packets stand for logical link control and adaptation protocol, and these packets enable higher layer protocols and lower layer links to multiplex. This update provides multiple applications the ability to concurrently use the Bluetooth LE stack and potentially reduce latency. Different applications will end up running in parallel and not blocking each other. Lastly, EATT is more beneficial than ATT because this feature requires the connection between BLE devices to be encrypted for security. ATT did not offer encryption.

In conclusion, Bluetooth Low Energy development has played an essential role for technology within the past decade. Based on the evidence, Bluetooth 5.1 seems to have the most crucial update. By providing Angle of Arrival and Angle of Departure as methods for determining direction, real time location capabilities have significantly improved. Furthermore, because the Internet of Things continues to expand on larger scales, knowing the location of assets allows for a reduction of costs and for companies to become more efficient. These features allowed for Allosense to develop up to date “always connected” asset trackers with the purpose of reducing waste.

Disclaimer/Side note:

This article does not lay out an exhaustive list of all of the features offered by Bluetooth Low Energy and the recent versions. However, this article does contain a summary of the important features that are offered. Besides from the references, additional resources can be found on Bluetooth’s official website and ScienceDirect.



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About the Author:

Kelly Liu is in the engineering division of Allosense, Inc. She works with the firmware team and vendors for evaluating Bluetooth capabilities.