From its inception as a simple tool for wireless headsets to its current role as the backbone of the sprawling Internet of Things (IoT), Bluetooth technology has undergone a remarkable evolution. Each new version of Bluetooth has pushed the boundaries of wireless connectivity, offering enhancements that have paved the way for new devices and applications.Each iteration of Bluetooth has not only responded to the demands of the time but also anticipated the needs of the future, consistently revolutionizing the way our devices communicate and interact. As we look to the horizon, Bluetooth continues to evolve, promising to deliver more seamless connectivity and innovative applications that will further integrate technology into the fabric of our daily lives.

Let's follow the versions in the order they were released. The table first gives the whole picture. Then each section explains what one version added. Where it helps, a section also works out the numbers behind the headline claim, such as a data rate or a range. The last section covers the versions after 5.2, up to Core Specification v6.2.

• How do the Bluetooth versions compare in one table ?
• Bluetooth 1.0
• Bluetooth 2.0 + EDR
• Bluetooth 3.0 + HS
• Bluetooth 4.0
• Bluetooth 4.1 and 4.2
• Bluetooth 5.0
• Bluetooth 5.1
• Bluetooth 5.2
• What came after Bluetooth 5.2 ?
• Reference

How do the Bluetooth versions compare in one table ?

Before we go through the versions one by one, let's put them side by side. Each version kept the older modes and added new ones. So the table reads as a list of additions, not as a list of replacements. It gives the main feature, the approximate range, the transmit power and the data rate of each version.

The timeline below marks five generations with their years. V1 in 1999 is Basic Rate (BR). V2 in 2004 adds Enhanced Data Rate (EDR), with 3 times the transmission speed. V3 in 2009 adds High Speed (HS) through a Wi-Fi channel. V4 in 2010 adds Low Energy (LE), and V5 in 2016 is optimized for IoT, with Mesh following in 2017.

Image Source : A Survey on Bluetooth 5.0 and Mesh: New Milestones of IoT

In the table, the Data Rate column is the gross air rate of the fastest mode in that version. It is not the throughput an application sees. The Transmission Power column is the range of maximum output power that the power classes of that version allow, so one device sits at one point in that range. The version numbers in the first column link to the section for that version.

• Every version keeps the older modes : A dual-mode 5.2 device still supports BR/EDR, and every LE device still supports the LE 1M PHY. So the peer with the older version sets the common rate.
• The Data Rate column is a gross air rate : The application throughput is lower, because of packet headers, the return packet and the gaps between packets. The Bluetooth 1.0 and the Bluetooth 4.1 and 4.2 sections work out the real numbers.
• The BR/EDR power classes did not change from 1.0 to 3.0 : The same three classes, from 1 mW to 100 mW, apply to every BR/EDR version. The Bluetooth 1.0 section lists them.
• The table stops at 5.2 : Versions 5.3 to 6.2 are not in the table. The last section lists what they added.

Bluetooth 1.0

The journey began with Bluetooth 1.0, a pioneering technology that introduced us to the concept of a wireless personal area network. Despite its limitations in speed and range, it was a revelation, cutting the cords that tethered our devices.

Let's look at what that first radio actually did, because every later version still carries it as Basic Rate (BR). The radio hops over 79 RF channels at f = 2402 + k MHz, with k = 0 to 78, so the channels are 1 MHz apart. Time is divided into slots of 625 microseconds. In the Connection state the radio hops at up to 1600 hops per second, which is one hop per slot, because 1 s / 625 microseconds = 1600. The modulation is GFSK at 1 Msym/s, and that gives the gross air rate of 1 Mb/s in the table above.

The gross rate is not what an application sees. A packet also carries an access code, a header and a CRC, and the Central and the Peripheral take turns on the slots. The largest Basic Rate packet, DH5, carries up to 339 bytes of user payload in 5 slots. If the other side answers with a 1-slot packet, one cycle takes 6 slots, which is 3.75 ms. So the rate is 339 x 8 bits / 3.75 ms = 723.2 kb/s. If both sides send DH5 packets, one cycle takes 10 slots, and the rate in each direction drops to 433.9 kb/s. These are the asymmetric and symmetric maximum rates of DH5 in the ACL packet table of the Baseband Specification.

Bluetooth 1.2 then added several features that the later sections take for granted. Its main additions were faster connection, adaptive frequency hopping (AFH), extended SCO (eSCO) links, enhanced error detection and flow control, and enhanced synchronization capability. AFH matters most in practice. It lets a connection avoid the RF channels that Wi-Fi or other interferers keep busy, so the adapted hopping sequence may use fewer than 79 channels.

The transmit power in the version table comes from three power classes, and they are the same for every BR/EDR version. A class 1 device must also be able to reduce its power to 4 dBm or less.

• Basic Rate is 1 Mb/s on air and about 723 kb/s at best for an application : Packet overhead and the return slot make the difference, so always check which of the two a quoted rate means.
• The 625 microsecond slot is the clock of BR/EDR : The hop rate, the packet lengths of 1, 3 and 5 slots and the throughput numbers all follow from it.
• AFH arrived in Bluetooth 1.2, not in 2.0 : It is a key coexistence mechanism for Bluetooth and Wi-Fi in the 2.4 GHz band.

Bluetooth 2.0 + EDR

Significant improvements in data transfer rates arrived with Bluetooth 2.0 + EDR (Enhanced Data Rate), making wireless audio and file sharing more practical and enjoyable. Bluetooth 2.1 added simplicity and security to pairing, a feature we now take for granted.

• Enhanced Data Rate (EDR): The most significant feature introduced with Bluetooth 2.0 + EDR was the Enhanced Data Rate capability, which allowed for data transfer rates of up to 3 Megabits per second (Mbps), a notable increase from the 1 Mbps of the previous Bluetooth 1.2 standard. This was achieved by using a different modulation scheme that could carry more data in the same amount of radio waves.
• Modulation Scheme: EDR uses a phase shift keying (PSK) modulation scheme instead of the Gaussian Frequency Shift Keying (GFSK) used by the original Bluetooth. Specifically, it employs π/4-DQPSK (Differential Quadrature Phase Shift Keying) for 2 Mbps and 8-DPSK (Differential 8 Phase Shift Keying) for 3 Mbps data rates.
• Packet Structure: To facilitate higher data rates, EDR introduces a new packet structure. These packets carry more data in each transmission, reducing overhead and increasing efficiency.
• Adaptive Modulation: Bluetooth 2.0 + EDR can switch between the basic rate (BR) modulation and EDR modulation schemes adaptively. This is dependent on the quality of the radio link. If the connection is good, it can use 8-DPSK to achieve the highest data rate. If the connection is less stable, it can fall back to π/4-DQPSK or even GFSK to maintain a stable connection, albeit at lower data rates.
• Backward Compatibility: Bluetooth 2.0 + EDR maintained backward compatibility with earlier versions, ensuring that new devices could still connect with older devices, albeit at the older devices' lower data transfer rates.
• Lower Power Consumption: Despite the higher data rates, Bluetooth 2.0 + EDR was designed to consume less power than its predecessors, making it more suitable for battery-operated devices like mobile phones and portable media players.
• Improved Interference Handling: This version also improved the performance in environments with interference from other wireless signals by including Adaptive Frequency Hopping (AFH), which Bluetooth 1.2 had introduced and which helped Bluetooth devices avoid busy frequencies in the 2.4 GHz band that is also used by Wi-Fi and other RF devices.
• Enhanced Voice and Audio Quality: With the higher data rates, audio and voice transmission quality was improved, which benefited wireless headsets, car kits, and stereo audio streaming applications.
• Enhanced Security: Security enhancements were also introduced, although more significant security features like Secure Simple Pairing were added in the subsequent version, Bluetooth 2.1.

Let's check the EDR gain with the same slot arithmetic as in the Bluetooth 1.0 section. The symbol rate stays at 1 Msym/s. Only the bits per symbol change, from 1 with GFSK to 2 with π/4-DQPSK and 3 with 8DPSK. So the gross air rate becomes 2 Mb/s and 3 Mb/s. The largest EDR packet, 3-DH5, carries up to 1021 bytes in 5 slots. With a 1-slot return packet, the rate is 1021 x 8 bits / 3.75 ms = 2178.1 kb/s. That is about three times the 723.2 kb/s of DH5, which matches the 3x transmission speed in the timeline at the top of the page.

Bluetooth 2.1 + EDR followed. Its main additions were Secure Simple Pairing, Extended Inquiry Response, Sniff Subrating, Encryption Pause and Resume, Erroneous Data Reporting and Security Mode 4. Secure Simple Pairing is the one users notice, because it replaced the PIN code entry of older pairing.

• EDR raises the bits per symbol, not the symbols per second : The 1 Msym/s rate and the 625 microsecond slot stay, so EDR fits into the same piconet timing as Basic Rate.
• 3-DH5 gives about 2.18 Mb/s to an application at best : This is the ceiling for file transfer and audio streaming over BR/EDR.
• Sniff Subrating and Secure Simple Pairing belong to 2.1 : The 3.0 + HS section lists both, but they were introduced one version earlier.

Bluetooth 3.0 + HS

The arrival of Bluetooth 3.0 + HS (High Speed) was marked by even faster data transmission, leveraging Wi-Fi to facilitate rapid file transfers. This enhancement allowed for more robust wireless applications that required higher throughput. Bluetooth 3.0 + HS (High Speed) introduced a significant advancement in Bluetooth technology, especially at the physical layer, by incorporating an Alternate MAC/PHY (AMP) feature that allowed it to utilize Wi-Fi (802.11) for data transmission, providing much higher data transfer rates than previously possible with Bluetooth alone

• High-Speed Data Transfer:
• 802.11 Protocol Adaptation Layer (PAL): Bluetooth 3.0 + HS uses the 802.11 Protocol Adaptation Layer, allowing Bluetooth profiles to operate over an 802.11 link. This layer acts as a bridge, enabling Bluetooth connections to leverage Wi-Fi for high-speed data transfer when needed.
• Data Rate: By utilizing Wi-Fi, Bluetooth 3.0 + HS can achieve data transfer rates up to 24 Mbps, significantly higher than the 3 Mbps limit of Bluetooth 2.0 + EDR.
• Seamless Transition:
• Generic Alternate MAC/PHY (AMP): The inclusion of AMP allowed Bluetooth devices to dynamically switch between the standard Bluetooth radio (BR/EDR) and an alternate MAC/PHY for data transfers, such as Wi-Fi, depending on the requirements of the application and the quality of the connection.
• AMP Manager Protocol: This protocol manages the discovery of AMPs and controls the switching between the standard Bluetooth controller and any available AMPs, ensuring a smooth transition and optimal use of the high-speed physical layer.
• Physical Layer Operation:
• Utilization of Wi-Fi: For the physical layer transmission, Bluetooth 3.0 + HS devices use the existing Wi-Fi hardware when available, bypassing the Bluetooth radio's lower data rates. This method is particularly beneficial for transferring large files or streaming high-definition video content.
• Compatibility and Coexistence: Despite leveraging Wi-Fi for high-speed data transfer, Bluetooth 3.0 + HS maintains backward compatibility with earlier Bluetooth versions for basic rate operations and device discovery. It also ensures coexistence mechanisms to manage the radio spectrum efficiently when both Bluetooth and Wi-Fi are active.
• Enhanced Power Control:
• Improved Power Saving: Bluetooth 3.0 introduces enhanced power control methods to minimize power consumption during high-speed data transfers, making it suitable for battery-operated devices.
• Enhanced L2CAP
• Logical Link Control and Adaptation Protocol (L2CAP): Bluetooth 3.0 introduced enhancements to L2CAP, which is responsible for multiplexing data between different higher layer protocols. Enhanced retransmission mode (ERTM) and streaming mode (SM) were introduced for more efficient data transfer, providing better quality of service (QoS) management.
• Enhanced Power Saving
• Sniff Subrating: This feature significantly increases the battery life of devices in low-power mode. By reducing the frequency of active communication between Bluetooth devices in a paired but idle state, it allows devices like mice and keyboards to consume less power, extending their battery life.
• Security Enhancements
• Secure Simple Pairing (SSP): While introduced in Bluetooth 2.1, SSP in Bluetooth 3.0 continued to offer a more secure pairing process using Elliptic Curve Diffie-Hellman (ECDH) for key exchange, providing better protection against eavesdropping and man-in-the-middle attacks.
• Enhanced Data Rate (EDR)
• Continued Support for EDR: Bluetooth 3.0 maintained support for Enhanced Data Rate (EDR) from Bluetooth 2.0 + EDR, allowing devices not leveraging HS to still enjoy faster data transmission rates than the original Bluetooth speeds.
• Generic Alternate MAC/PHY (AMP)
• AMP Controllers: The introduction of Generic AMP Controllers facilitated the management of alternate MAC/PHYs like 802.11, enabling the device to switch between them for optimal data transmission rates. This is managed at higher protocol layers, making the transition seamless to applications.
• Enhanced Synchronization
• Unicast Connectionless Data (UCD): Bluetooth 3.0 introduced UCD for sending unicast data to a single remote device over the connectionless L2CAP channel, without first opening a connection-oriented L2CAP channel. The same connectionless channel had already carried broadcast data from the Central to all members of the piconet.
• Enhanced User Experience
• User-Friendly Device Discovery: Improvements in device discovery and pairing processes made it easier for users to connect devices quickly and securely, enhancing the user experience.

Two points about this version are worth keeping in mind. First, Sniff Subrating and Secure Simple Pairing in the list above came with 2.1 + EDR, and 3.0 + HS carried them forward. Second, the High Speed path did not last. Bluetooth 5.3 removed the Alternative MAC/PHY, the AMP Manager protocol (A2MP), the L2CAP enhancements for AMP and the 802.11 PAL from the Core Specification. A removed feature is no longer recommended, but a product can still implement it against an older specification version that contains it. So a current Bluetooth device reaches its highest rates with EDR or the LE 2M PHY, not with an 802.11 link.

• The 24 Mbps of 3.0 + HS came from 802.11, not from the Bluetooth radio : Bluetooth set up and controlled the link, and the Wi-Fi radio carried the data.
• AMP is gone from the current specification : Bluetooth 5.3 removed it, so treat HS as a historical feature.
• ERTM and Streaming Mode survived : These L2CAP modes came with 3.0 + HS and are still part of L2CAP today.

Bluetooth 4.0

Bluetooth 4.0 introduced Bluetooth Low Energy (BLE), a game-changer for power conservation. It opened the door to a wave of low-power devices, from fitness trackers to smart home appliances, all running on tiny batteries for extended periods.

• Bluetooth Low Energy (BLE): The hallmark of Bluetooth 4.0 is the introduction of Bluetooth Low Energy (BLE), designed for very low power consumption. BLE operates in the same 2.4 GHz ISM band as classic Bluetooth but with significant differences in the physical layer:
• Modulation: BLE uses Gaussian Frequency-Shift Keying (GFSK) modulation, similar to classic Bluetooth, but it's optimized for low power consumption.
• Channels: BLE operates on 40 2-MHz channels, compared to the 79 1-MHz channels used by classic Bluetooth. This includes 3 advertising channels for device discovery and 37 data channels.
• Data Rate: Offers a data rate of up to 1 Mbps, which is efficient for the types of small, periodic data packets typical in BLE applications.
• Range: BLE extends the possible range up to 100 meters under optimal conditions, depending on the power class of the devices.
• Energy Efficiency: BLE's protocol stack is designed for low energy use, with features like quick connection and disconnection, shorter packets, and simplified operations that minimize power consumption.
• Dual-Mode Devices: Bluetooth 4.0 supports dual-mode devices that can simultaneously support both classic Bluetooth and Bluetooth Low Energy. This ensures compatibility with a broader range of devices.
• GATT Protocol: At the heart of BLE's non-PHY layer is the Generic Attribute Profile (GATT), which defines the way that two Bluetooth Low Energy devices transfer data back and forth using concepts called Services and Characteristics. This structure is optimized for low power consumption and efficient data transfer.
• Security: Bluetooth 4.0 introduced improved security features, including AES-128 CCM encryption for secure data transmission, enhancing the protection against eavesdropping and data tampering.
• LE Privacy 1.2: Added later, in Bluetooth 4.2 as Link Layer privacy, this feature prevents tracking of BLE devices through random address changes, enhancing user privacy.
• LE Secure Connections: An enhancement in Bluetooth 4.2, but relevant for BLE devices, introduced features like Elliptic Curve Diffie Hellman (ECDH) for public key cryptography, providing better security for BLE connections.

NOTE : How to achieve Low Energy Consumption

The mechanism that Bluetooth Low Energy (BLE) utilizes to achieve low energy consumption revolves around several core principles and technological innovations designed specifically to minimize power usage.

• Efficient Connection Intervals: BLE devices can adjust their connection intervals flexibly. This means they can choose to communicate at low frequencies, only connecting at specified intervals (ranging from milliseconds to seconds) to exchange data and then returning to a sleep mode. This significantly reduces power consumption compared to being constantly connected.
• Short Data Packets: BLE uses short data packets that are quick to transmit. The small packet size means that the radio can be turned off more quickly compared to transmitting larger amounts of data, reducing the time the device spends in high-energy-consuming modes.
• Simplified Protocol Stack: BLE has a simplified protocol stack compared to classic Bluetooth, with fewer layers and a more straightforward structure. This reduces the processing power needed for data transmission, thus conserving energy.
• Adaptive Frequency Hopping: BLE incorporates an adaptive frequency hopping spread spectrum (AFHSS) technology that improves interference avoidance with other wireless signals in the 2.4 GHz ISM band. By efficiently managing the communication channels, devices can maintain connections with less power and minimize the likelihood of having to retransmit data due to interference.
• Duty Cycling: BLE devices are designed to spend most of their time in sleep or standby modes and only wake up for brief periods to perform actions. This duty cycling significantly reduces power consumption, allowing devices to operate for years on a single small battery in some cases.
• Low Energy Radio: The BLE radio operates at a lower power compared to the classic Bluetooth radio. The design and operation of the BLE radio are optimized for short bursts of data transmission, contributing to its low energy profile.
• Automated Power Management: BLE devices can automatically manage their power states and transition between these states based on their activity and connection status. This ensures that the device is only using more power when necessary and conserving energy at all other times.
• LE Privacy and Security Features: BLE includes privacy features like random address generation and secure connections with low energy overhead. These features are designed to provide security without significantly impacting battery life.

Bluetooth 4.1 and 4.2

The subsequent versions, Bluetooth 4.1 and 4.2, brought incremental upgrades in efficiency and IoT capabilities, with 4.2 specifically increasing the capacity for IoT devices with Internet connectivity. Neither version changed the LE PHY. The gains came from the Link Layer and the host, such as LE connection-oriented channels in 4.1 and longer packets and stronger pairing in 4.2. The longer packets have the largest effect on throughput, so the end of this section works that out.

• Bluetooth 4.1:
• Enhanced Coexistence
• Improved Coexistence with LTE: Bluetooth 4.1 introduced mechanisms to reduce interference with LTE signals, improving the performance of both Bluetooth and LTE networks when operated simultaneously. This was particularly important in smartphones and tablets that use both technologies.
• Better Connectivity
• Reconnection Times: Devices can reconnect automatically and faster when they are in range, without user intervention, improving the user experience.
• Connection Flexibility: It allowed devices to act as both a Bluetooth Smart peripheral and a Bluetooth Smart Ready hub at the same time. This means a device can be a data collection point (like collecting information from a heart rate monitor) while also being connected to a smartphone.
• Developer Benefits
• Developer Control: Gave developers more control over creating and maintaining Bluetooth connections by allowing them to hand-pick the parameters that define connection intervals, timeouts, and more.
• Bluetooth 4.2:
• Building upon the foundations laid by Bluetooth 4.1, Bluetooth 4.2 introduced significant improvements, particularly in security, data transfer, and IoT capabilities. Here are the notable enhancements:
• Increased Privacy and Security
• LE Secure Connections: Introduced LE Secure Connections that offer stronger encryption for data transfer, based on the Federal Information Processing Standard (FIPS) Public Key Cryptography Algorithms, enhancing security for BLE devices.
• Privacy Features: Improved privacy features prevent tracking of devices through Bluetooth addresses without compromising the functionality of location-based services.
• Internet Connectivity
• Internet Protocol Support Profile (IPSP): Bluetooth 4.2 added support for the Internet Protocol Support Profile, enabling BLE devices to access the Internet directly via IPv6/6LoWPAN. This was a significant step forward for the IoT, allowing devices to send and receive data over the Internet without requiring an intermediary smartphone or PC.
• Enhanced Data Transfer
• Data Packet Length Extension: Increased the maximum data packet length that can be transferred, allowing for faster data transfers and improved efficiency of data exchange, which is beneficial for both application data throughput and OTA (Over-The-Air) firmware updates.
• Improved Efficiency
• Low Power IP (L2CAP) Connection-Oriented Channels: This feature, added to LE in Bluetooth 4.1 and used by IPSP in 4.2, provided dedicated channels for data transmission, reducing latency and increasing data transfer efficiency between devices.

Let's work out what the Data Packet Length Extension buys. An LE packet on the LE 1M PHY has a 1-byte preamble, a 4-byte Access Address, a 2-byte PDU header, the payload and a 3-byte CRC. On the LE 2M PHY the preamble is 2 bytes. Before 4.2 the payload was at most 27 bytes, and from 4.2 it can be up to 251 bytes. In the best case the Central sends one full packet and the Peripheral answers with an empty packet. Each packet is followed by the inter frame space T_IFS of 150 microseconds. The table below adds up the air time of this exchange and divides the payload by it. The LE 2M row belongs to Bluetooth 5.0, and it is here for comparison.

The payload here is the Link Layer payload, so the L2CAP and ATT headers still come out of it. Encryption adds a 4-byte MIC to each packet, and real connection events leave gaps. So a real application sees less than these numbers. Even so, the ratio is clear. The longer packet raises the best case on the LE 1M PHY by about 2.5 times. This is because the fixed cost of the headers, the empty reply and two T_IFS gaps is shared by more payload bytes.

• 4.1 and 4.2 changed the protocol, not the radio : The LE 1M PHY and its 1 Mb/s gross rate stayed the only LE PHY until 5.0.
• Data Length Extension is the throughput feature of 4.2 : Going from 27 to 251 bytes raises the best-case Link Layer rate from about 320 kb/s to about 814 kb/s.
• LE Secure Connections uses ECDH for pairing : The key agreement no longer depends on a short secret, so a passive listener on the pairing cannot derive the key.

Bluetooth 5.0

Bluetooth 5.0 marked a significant leap forward with increased range, speed, and broadcasting capacity, making connections more reliable and extending the possibilities for Bluetooth in commercial and industrial environments.  The extended range capability is particularly beneficial for IoT applications that require long-range sensor data collection or control over large areas, such as agricultural sensors, outdoor lighting control, and asset tracking in large facilities. It enables the deployment of Bluetooth in applications previously considered out of reach for the technology, expanding its use cases significantly.

• Increased Range and Speed: Bluetooth 5.0 introduced two new PHYs for LE: the LE 2M PHY and the LE Coded PHY. The LE 2M PHY doubled the data rate to 2 Mbps compared to Bluetooth 4.2, allowing for faster data transfer. The LE Coded PHY, on the other hand, provided options for significantly increasing the range of BLE connections (up to 4 times in certain conditions) at reduced data rates, which is ideal for IoT applications requiring long-range communication. These options give developers the flexibility to prioritize between speed and range when developing Bluetooth applications, depending on the specific requirements of their application.
• Improved Channel Efficiency:The introduction of these new PHYs also meant improved efficiency in channel utilization, reducing the likelihood of interference in congested RF environments and enhancing the reliability of Bluetooth connections.
• Increased Broadcasting Capacity:Bluetooth 5.0 expanded the data broadcasting capacity by increasing the packet length and adding support for more data in advertising packets. This improvement is particularly beneficial for BLE beaconing applications, where devices broadcast information like location or identification to nearby devices without establishing a connection.
• Slot Availability Mask (SAM):SAM is a feature that improves coexistence with other wireless technologies by indicating periods when the Bluetooth device will not be using the wireless spectrum, allowing other technologies (such as Wi-Fi) to use it more effectively.
• Improved Energy Efficiency:Despite the increased data rate and range, Bluetooth 5.0 includes features designed to maintain and improve energy efficiency, making it suitable for devices powered by small batteries.
• Enhanced Security:Continuing the trend of its predecessors, Bluetooth 5.0 includes further enhancements to security features, ensuring secure communication between devices.
• LE Advertising Extensions:These extensions allow for more efficient use of advertising channels and greater data throughput for advertising operations, which is critical for IoT applications that rely on broadcasting small amounts of data over large areas.
• Integration with IoT:With its increased range, speed, and broadcasting capacity, Bluetooth 5.0 is well-suited for IoT applications, allowing for the deployment of Bluetooth in smart city projects, industrial environments, and more complex connected devices ecosystems.

NOTE : How to achieve the extended range ?

The key mechanism to achieve extended range in Bluetooth 5.0 is the introduction of the LE Coded PHY (Physical Layer). This feature allows for significantly increased communication range between Bluetooth devices, crucial for applications where devices need to communicate over greater distances, such as in smart buildings or outdoor tracking. The LE Coded PHY with its coding schemes for increased redundancy and improved error correction is the key mechanism behind the extended range capabilities of Bluetooth 5.0, making it a versatile choice for a wide array of long-range, low-power wireless applications. The LE Coded PHY can extend the range of Bluetooth Low Energy communications up to four times compared to the 1M PHY used in Bluetooth 4.x. In real-world conditions, this can mean a reliable communication range of several hundred meters, depending on factors like environmental conditions, device antenna design, and interference.

• LE Coded PHY Overview
• Coding Schemes: LE Coded PHY utilizes two coding schemes to extend range:
• S=2 Coding: Doubles the redundancy of the transmitted data, providing a modest increase in range with a moderate decrease in data rate.
• S=8 Coding: Increases the redundancy eightfold, offering a maximum increase in range at a lower data rate. This coding is designed for scenarios where long-range communication is prioritized over data transmission speed.
• Mechanism for Extended Range
• Increased Redundancy: By adding redundancy to the data being transmitted, LE Coded PHY enhances the receiver's ability to correctly interpret signals received at very low power levels. This redundancy compensates for signal degradation over distance or through obstacles, making it possible for devices to maintain a connection even when far apart or in challenging RF environments.
• Improved Error Correction: The added redundancy also improves error correction capabilities, allowing devices to correct for more errors that might occur during transmission. This means that data can be reliably sent and received over greater distances without needing retransmissions, which is crucial for maintaining low energy consumption.
• Adaptive Configurations: Bluetooth 5.0 devices can dynamically choose between the standard 1M PHY, 2M PHY for faster data rates, and LE Coded PHY for extended range during operation. This flexibility allows devices to adapt to their environment and application requirements, optimizing for either speed or range as needed.

Let's check the "up to 4 times" range against the receiver requirements. The LE Coded PHY carries the payload at 125 kb/s with S=8 coding or 500 kb/s with S=2 coding, against 1 Mb/s for LE 1M. The receiver sensitivity must be -70 dBm or better on the uncoded PHYs, -75 dBm with S=2 and -82 dBm with S=8. So S=8 gains 12 dB of link budget. In free space the path loss grows by 20 log₁₀(d), so 12 dB is a distance factor of 10^12/20 = 3.98. That is the factor of 4. The 5 dB of S=2 gives a factor of 1.78.

The LE 2M PHY works the other way. It doubles the symbol rate to 2 Msym/s, so a 251-byte packet takes about half the air time. With the arithmetic of the Bluetooth 4.1 and 4.2 section, the best-case Link Layer rate rises from 813.6 kb/s to 1442.5 kb/s. The gain is less than 2 times, because the two T_IFS gaps of 150 microseconds do not shrink. Advertising grew as well. A legacy advertisement carries at most 31 bytes of data. With LE Advertising Extensions, one advertising PDU payload can be up to 255 bytes, and the host data can be up to 1650 bytes across a chain of PDUs.

Two more 5.0 features are missing from the list above: LE Channel Selection Algorithm #2 and High Duty Cycle Non-Connectable Advertising. Bluetooth 5.0 also removed the Park State of BR/EDR.

• Range and rate are one trade-off : S=8 buys 12 dB of sensitivity for an 8 times lower rate. LE 2M buys speed with the same sensitivity requirement as LE 1M.
• The 4 times range assumes free space : Indoors the path loss grows faster than 20 log₁₀(d), so the same 12 dB buys less distance.
• Extended advertising moves the large data off the primary channels : The primary advertising channels carry only a short pointer, and the data follows on a secondary channel.

Bluetooth 5.1

With Bluetooth 5.1, 'direction finding' became possible, enabling location services with pinpoint accuracy, which has been instrumental in navigation and tracking systems. This feature significantly enhances the capability of Bluetooth technology in terms of precise positioning and tracking, making it highly valuable for a wide range of applications. The enhancements brought by Bluetooth 5.1, especially in direction finding, have significantly broadened the scope of Bluetooth technology applications. The ability to pinpoint the exact location of devices has vast implications for IoT deployments, smart buildings, retail environments, and security applications, allowing for more interactive and precise services.

In short, Bluetooth 5.1 has set a new standard for location services in wireless technology, combining the low power consumption and wide adoption of Bluetooth with the precision required for next-generation positioning and tracking systems.

• Direction Finding
• Angle of Arrival (AoA) and Angle of Departure (AoD):
• The cornerstone of Bluetooth 5.1's direction finding is the introduction of the Angle of Arrival (AoA) and Angle of Departure (AoD) methodologies. These allow devices to determine the direction from which a signal is being sent, enabling the calculation of the device's precise location.
• AoA requires the receiving device to have an array of antennas and measures the difference in the signal's phase at each antenna to calculate the angle.
• AoD involves the transmitting device sending signals from multiple antennas with known geometrical spacing, allowing the receiving device to calculate the signal's angle based on the phase differences it samples.
• Enhanced Location Services
• Precision: With the introduction of direction finding, Bluetooth 5.1 can achieve centimeter-level location accuracy, a significant improvement over previous versions, which were limited to meter-level precision.
• Application Scenarios: This high level of precision opens up new possibilities for Bluetooth applications, including indoor navigation systems, asset tracking, item finding solutions, and enhanced automation in industrial environments.
• Non-PHY Enhancements
• Randomized Advertising Channel Indexing: Bluetooth 5.1 introduced changes to advertising channel indexing, which helps in reducing the likelihood of collision and interference on the 2.4 GHz band, thus improving the reliability of Bluetooth communications in dense environments.
• GATT Caching Enhancements: Improvements were made to the way Bluetooth devices cache GATT information, which speeds up the connection establishment process between devices that have previously communicated. This is particularly useful for devices that frequently connect and disconnect, reducing the time needed to re-establish connections.
• Periodic Advertising Sync Transfer: Bluetooth 5.1 allows the transfer of periodic advertising synchronization information from one device to another, enabling better coordination and planning of communication sessions between devices. This feature is useful in scenarios where a central device needs to manage multiple connections efficiently.

Let's look at what the receiver actually measures. For direction finding, the packet carries a Constant Tone Extension (CTE) after the CRC. The CTE is 16 to 160 microseconds long, in steps of 8 microseconds. It starts with a 4 microsecond guard period and an 8 microsecond reference period. After that, switch slots and sample slots of 1 or 2 microseconds alternate. For AoA the receiver switches between its antennas and takes IQ samples. For AoD the transmitter switches between its antennas, and the receiver samples with one antenna.

The angle follows from the phase difference between two antennas. The path to the far antenna is longer by d sin(θ), where d is the antenna spacing and θ is the angle from broadside. So the phase difference is Δφ = 2π d sin(θ) / λ. At 2.44 GHz the wavelength λ is 12.3 cm, and a spacing of λ/2 is 6.1 cm. A measured phase difference of 90 deg then gives sin(θ) = 0.5, so θ = 30 deg. A spacing of λ/2 or less keeps the answer unique, because the phase difference then stays within +/-180 deg.

• Direction finding measures phase, not arrival time : A path difference of 6.1 cm is only 0.2 ns, so the receiver reads it as a phase shift of the CTE.
• AoA puts the antenna array in the receiver, and AoD puts it in the transmitter : AoA suits a fixed locator that tracks tags. AoD suits a phone that finds its own direction from fixed beacons.
• One angle is not a position : A position needs angles from two or more locators, or an angle combined with a distance estimate.

Bluetooth 5.2

Next, Bluetooth 5.2 continues to optimize for audio with the introduction of LE Audio, which allows for multi-stream audio and brings new functionalities like Audio Sharing and improvements in hearing aids. LE Audio is not just an incremental upgrade; it's a comprehensive overhaul of Bluetooth audio, introducing new features that enhance the way we use audio devices and interact with sound. The introduction of Bluetooth 5.2 and LE Audio marks a significant milestone in wireless audio technology, setting new standards for audio quality, efficiency, and functionality. It paves the way for innovative uses of audio in both personal and public spaces, making it more accessible and enjoyable. Additionally, the advancements in LE Audio are expected to greatly benefit the development and functionality of hearing aids, providing better connectivity, audio quality, and battery life for users.

In short, Bluetooth 5.2 and its LE Audio specification represent a forward leap in Bluetooth technology, offering enhanced audio experiences, improved power efficiency, and new functionalities that expand the role of Bluetooth in our daily lives and the broader IoT ecosystem.

• LE Audio
• Introduction of the LC3 Codec: At the heart of LE Audio is the Low Complexity Communications Codec (LC3). This new audio codec offers significant improvements in audio quality even at lower data rates compared to the classic SBC codec used in classic Bluetooth audio. This means better sound quality for less power, extending battery life in devices like earbuds and hearing aids.
• Multi-Stream Audio: LE Audio introduces the ability to handle multiple audio streams between devices. This allows for a single source device (like a smartphone) to stream audio to multiple sink devices (like two separate earbuds) simultaneously, ensuring perfect audio synchronization between them. This is a marked improvement over previous implementations that often had to share a single stream, leading to issues with synchronization and stereo imaging.
• Audio Sharing: One of the most consumer-friendly features of LE Audio is Broadcast Audio, allowing audio streams to be broadcasted to an unlimited number of receivers. This opens up new possibilities for public audio sharing in places like gyms, cinemas, or conference centers and private sharing among friends and family.
• Enhancements Beyond Audio
• Isochronous Channels: Bluetooth 5.2 introduces isochronous channels, enabling synchronized data streams with defined latency. This is crucial for ensuring that audio data can be transmitted at regular intervals, which is necessary for both high-quality audio experiences and reliable performance in applications that require precise timing, such as real-time control systems.
• Enhanced Attribute Protocol (EATT): The Enhanced Attribute Protocol improves the efficiency and performance of data transfers, particularly in devices that use multiple applications simultaneously. EATT allows for multiple transactions to occur in parallel, reducing latency and improving the overall responsiveness of devices.
• Power Efficiency: With the introduction of LE Audio and the LC3 codec, Bluetooth 5.2 devices can deliver high-quality audio experiences while consuming less power, significantly enhancing the battery life of devices like wireless earbuds, hearing aids, and other wearable audio devices.
• Improved Reliability and Performance in Challenging Environments: Bluetooth 5.2 includes updates that improve the reliability and performance of Bluetooth communications in environments where there is significant wireless interference, such as in busy urban areas or crowded events.

One point helps when reading about LE Audio. The Core Specification v5.2 added three features: LE Isochronous Channels, the Enhanced Attribute Protocol (EATT) and LE Power Control. LC3, multi-stream audio and broadcast audio sharing are defined in separate LE Audio specifications that run on top of the isochronous channels. So a controller that supports 5.2 gives the transport, and LE Audio needs the host profiles as well. LE Power Control is missing from the list above. It lets two connected devices ask each other to change the transmit power, so neither side transmits more power than the link needs.

• Isochronous channels are the core of LE Audio : They deliver data with a fixed timing, which audio needs and which an ACL connection does not provide.
• Connected and broadcast streams use the same idea : Connected isochronous streams serve earbuds, and broadcast isochronous streams serve any number of listeners.

What came after Bluetooth 5.2 ?

Bluetooth did not stop at 5.2, and several later features matter for the IoT use cases on this page. The Core Specification is now at v6.2. None of the later versions raised the 2 Mb/s peak rate of LE. Instead they refined advertising, connection control, security and ranging. The table below lists the new and removed features of each version, with the names that the change history of the Core Specification uses.

A few of these features link back to earlier sections. Connection Subrating is the Link Layer feature of LE Enhanced Connection Update in 5.3. It lets a connection use only every Nth connection event, and it can switch back to the full rate without a new connection update. That extends the low-power ideas of the Bluetooth 4.0 section. Periodic Advertising with Responses in 5.4 lets one advertiser exchange data with many devices without a connection to each of them. Electronic shelf labels are the typical use case.

Channel Sounding in 6.0 measures distance with phase-based ranging and round-trip time measurements. So it complements the angle from the direction finding of 5.1. Shorter Connection Intervals in 6.2 goes below the classic grid of 1.25 ms. For this, the Link Layer also expresses the connection interval in units of 125 microseconds.

• The later versions refine LE rather than speed it up : The peak rate stayed at 2 Mb/s, and the work moved to advertising, power, security and ranging.
• Removals are rare but real : Park State went in 5.0, Unit keys in 5.1, and AMP with the 802.11 PAL in 5.3.
• Distance and angle together give a position : Channel Sounding measures distance and direction finding measures angle, so one locator can place a device with both.

Reference

• Evolution of Bluetooth - COPPERPOD (2022)
• The Evolution of Bluetooth® to Becoming a Low-Power Protocol - Telink (2022)
• Bluetooth Technology: What Has Changed Over The Years - JAYCON (2023)
• A little history of Bluetooth - Android Authority (2023)
• A Survey on Bluetooth 5.0 and Mesh: New Milestones of IoT - Research Gate
• Bluetooth Core Specification v6.2 Vol 1 Part C - Bluetooth SIG : Core Specification Change History
• Bluetooth Core Specification v6.2 Vol 2 Part A - Bluetooth SIG : Radio Specification, BR/EDR
• Bluetooth Core Specification v6.2 Vol 2 Part B - Bluetooth SIG : Baseband Specification
• Bluetooth Core Specification v6.2 Vol 3 Part A - Bluetooth SIG : Logical Link Control and Adaptation Protocol Specification
• Bluetooth Core Specification v6.2 Vol 6 Part A - Bluetooth SIG : Physical Layer Specification, LE
• Bluetooth Core Specification v6.2 Vol 6 Part B - Bluetooth SIG : Link Layer Specification