摘要

Most people do not understand the difference between Bluetooth Low Energy and Bluetooth Basic Rate/Enhanced Data Rate. The emergence of Bluetooth 5 has further confused the landscape. This application note explains the differences and suggests ways to determine the best version for your design. A similar version of this application note originally appeared on July 18, 2019, in Electronic Design and in Microwaves & RF.

Introduction

Electronic devices equipped with wireless communication free us from the tangle of plugs and cables. Bluetooth^® wireless technology is one of the most popular protocols that enables us to send and receive data wirelessly, as its versatility allows it to be used in many applications. For example, Bluetooth wireless technology inside vehicles lets us play favorite tunes on our smartphones from the car stereo. Inside homes, Bluetooth wireless technology in smart home security systems lets us lock and unlock doors with our phones. We are also tapping into the protocol to send files between a tablet and a computer, send updates from a fitness tracker to a smartphone, and much more. Figure 1 depicts two common Bluetooth technology-enabled devices: a smartphone and a laptop.

There are a few different flavors of Bluetooth wireless technology. Some applications use Bluetooth Low Energy (Bluetooth LE, casually called BLE), while others utilize Bluetooth Basic Rate/Enhanced Data Rate (Bluetooth BR/EDR). Newer applications even have the potential to use Bluetooth 5. This application note explains the differences between Bluetooth LE and Bluetooth BR/EDR, how Bluetooth 5 promises to enhance both protocols, and ways to choose the version that is optimal for your design.

Bluetooth History

Each of the Bluetooth versions was developed by the Bluetooth Special Interest Group (Bluetooth SIG), which manages all Bluetooth protocols. When new developments are made, the Bluetooth SIG releases a new specification to introduce improvements. The timeline in Figure 2 shows the Bluetooth specifications that have been released and where Bluetooth BR, Bluetooth EDR, Bluetooth LE, and Bluetooth 5 fall within those specifications.

Bluetooth BR/EDR

Bluetooth BR, the first Bluetooth protocol developed, implements a unique method that uses Gaussian frequency shift keying (GFSK) to exchange data within the 2.4GHz ISM band. The 2.4GHz ISM band was chosen because communication is free. Unlike most frequency bands, a license is not required to operate within this band. Bluetooth BR quickly become popular because it provided a low-cost, low-power way to send and receive data wirelessly across short ranges at data rates up to 0.7Mbps.

Bluetooth 2.0 emerged a few years later and included the option for Bluetooth EDR. With Bluetooth EDR, data can be transferred 2x to 3x faster than Bluetooth BR. It uses differential quadrature phase-shift keying (QDPSK) and differential 8-level phase-shift keying (8DPSK) alongside GFSK. GFSK transmits 1 bit per symbol, while QDPSK transmits 2 bits per symbol and 8DPSK transmits 3 bits per symbol.

Bluetooth LE

Bluetooth LE was first developed by Nokia as a wireless technology called Wibree. It was designed to consume very little power, making it ideal for devices that run on small batteries. It was also developed to be very low cost and easy to configure. Wibree included many techniques similar to Bluetooth BR/EDR, including operation in the 2.4GHz ISM band, GFSK modulation, a channel scheme, and frequency hopping. Given these similarities, the Bluetooth SIG eventually adopted Wibree into its specification, releasing it as a new low-energy extension called Bluetooth Low Energy (Bluetooth LE).

Bluetooth LE first appeared in the Bluetooth 4.0 specification. Bluetooth 4.0 did not completely obsolete Bluetooth BR/EDR, but instead offered Bluetooth LE in addition to Bluetooth BR/EDR. Consumer devices with Bluetooth LE were often labeled as being Bluetooth Smart, while Bluetooth BR/EDR are labeled as Bluetooth Classic; however, these terms are no longer used. Under this specification, radios could be developed to operate as a Bluetooth BD/EDR-only radio, a Bluetooth LE-only radio, or a dual radio that supports both Bluetooth BR/EDR and Bluetooth LE.

Bluetooth 5

The Bluetooth SIG does its best to make enhancements that align with the evolution of technology, so it is no wonder that the internet of things (IoT) is driving some change. Bluetooth LE has played a big role in the growing IoT market, but the Bluetooth SIG wanted to further enhance the capabilities of Bluetooth wireless technology in IoT applications. New advancements to the original Bluetooth LE technology were released in Bluetooth 5.0, which is being called Bluetooth 5.

How Bluetooth BR/EDR and Bluetooth LE Differ

The physical layer (PHY) of the protocols is a good starting point to compare the similarities and differences between Bluetooth BR/EDR and Bluetooth LE. The PHY contains the circuity used to modulate and demodulate analog signals and turn them into digital symbols. Four areas of the PHY where Bluetooth BR/EDR and Bluetooth LE differ are the channel scheme, power consumption, latency, and throughput.

Channel Scheme

Both Bluetooth BR/EDR and Bluetooth LE communicate in the 2.4GHz ISM band, but where they differ is in the number of channels in which they divide the frequency band. Bluetooth BR/EDR divides the band into 79 channels spaced 1MHz apart. Bluetooth LE employs a simpler transmitter and receiver, so it divides the band into only 40 channels spaced 2MHz apart.

Regardless of the number of channels used, both Bluetooth BR/EDR and Bluetooth LE must address interference. The 2.4GHz ISM band is full of transmitters taking full advantage of the unlicensed band. To minimize interference, both Bluetooth BR/EDR and Bluetooth LE employ frequency hopping where the radio operates on one channel for a brief period of time before hopping to another channel to continue communication.

Bluetooth LE also adds another element to its channel scheme. Bluetooth LE reserves three channels for a Bluetooth LE radio to advertise that it wants to be discovered. The frequency of these three advertising channels were strategically chosen to avoid interference with the three most frequently used Wi-Fi channels that also operate in the 2.4GHz ISM band. Once a connection is made, the radios will continue their communication on one of the other 37 channels. Figure 3 depicts the channel scheme for Bluetooth LE and shows where the three advertising channels are located within the frequency band.

Power

Energy conservation is a key way in which Bluetooth BR/EDR and Bluetooth LE differ. Bluetooth BR/EDR uses a maximum output power of 100mW to transmit data up to ~10m–100m. These specifications worked well in the days where most devices could be charged frequently. However, as demand for products that can run off battery power for months or years without being charged increases (thanks to the IoT influence), this type of output power will no longer suffice as it would quickly drain the battery.

Bluetooth LE is ideal for these types of devices, as it reduces the energy by only turning on the transmitter and receiver when they are needed to send or receive data, with a maximum power output of only 10mW to transmit up to the same range. Bluetooth LE also sends data in short bursts of packets. When packets are not being sent, the radio sits idle, drawing little to no power.

Latency

Latency is another area where Bluetooth LE outperforms Bluetooth BR/EDR. Bluetooth BR/EDR needs approximately 100ms to be ready to send data. There is an additional 100ms latency from when data is received at the transmitter to when it is available at the receiver. This can create a fairly noticeable delay in some cases. It also leads to higher power consumption because the extra time required to send data draws more energy from the battery.

Bluetooth LE offers much lower latency, requiring only 3ms to be ready to send data. Also, the latency from when data is received at the transmitter to when it is available at the receiver is only 6ms. This allows data to be sent more quickly and also saves power.

Throughput

Where Bluetooth LE lags behind Bluetooth BR/EDR is in throughput. Both Bluetooth BR/EDR and Bluetooth LE employ GFSK, so theoretically, the maximum limit for the throughput is 1Mbps. However, factors such as protocol overhead, radio limitations, and artificial software restrictions limit the actual throughput.

In practice, Bluetooth BR can reach a throughput up to 0.7Mbps, while Bluetooth EDR can achieve a throughput of 2.1Mbps. This is sufficient for applications like streaming audio. Because Bluetooth LE sends data in short bursts to conserve power, its throughput faces additional restrictions. It can only achieve a maximum throughput of 0.27Mbps. While this throughput is not enough for streaming audio, it is more than enough to send sensor data that does not need to be transmitted constantly.

Throughput Improvements in Bluetooth 5

Bluetooth 5 uses the original low-power Bluetooth LE technology with some new enhancements. One of the biggest enhancements is the introduction of three PHYs that can be selected to improve the maximum range or throughput. Bluetooth 5 also adds enhancements that improve advertising.

The first PHY that Bluetooth 5 offers is called LE 1M. This is the same PHY used for Bluetooth LE in the Bluetooth 4.2 specification, so most of its parameters will match those shown in Table 1. LE 1M is the only PHY that is mandatory in Bluetooth 5. The other two PHYs are optional.

Bluetooth 5 integrates an LE-coded PHY as one of the optional PHYs to extend the range of communication. The coded PHY achieves longer range by introducing redundancy for some processing gain, instead of increasing the power of the transmitter. This version also has some additional redundant bits that are used to determine what the correct value of a bit should be. The coded PHY comes in two variations: S=2 and S=8. S=2 sends two symbols per bit, which decreases the throughput by a factor of two, but theoretically doubles the range. S=8 sends eight symbols per bit. This decreases the raw throughput by a factor of eight, but approximately quadruples the range. In practice, the actual range will be a little lower than the theoretical values, but this method still helps to achieve a much larger range.

Not every application is dependent on range, so Bluetooth 5 includes something for applications where throughput is more important than range. For example, it includes a data rate option called LE 2M, which doubles the raw data rate to 2Mbps. It allows for data to be sent at a maximum actual throughput of 1.4Mbps. This means that data can be transferred even faster than Bluetooth BR, but with lower power consumption.

Table 2 compares the three PHYs available in Bluetooth 5 to show how they differ in terms of raw data rate and range.

In terms of advertising, Bluetooth 5 still utilizes the same channel scheme as Bluetooth LE, but includes options for additional advertising on all 40 channels instead of just three. In Bluetooth 5, small advertising packets can be transmitted on the three advertising channels used in Bluetooth LE, but they can now point to larger advertising packets (up to 255 octets) that can be sent on the additional 37 channels. This also helps to reduce the amount of content on the three primary advertising channels. Bluetooth 5 also includes enhancements for advertising packet chaining, periodic advertising, and a lower minimum advertising interval.

Which Bluetooth Protocol Is Best for Your Application?

The differences in the PHY are key to determining which protocol best suits each application. Since Bluetooth BR/EDR compromises packet latency and power for a higher throughput rate, it is ideal for applications where throughput is a critical specification, such as streaming or sending large amounts of data. Common applications are wireless headsets (Figure 4) and point-to-point applications.

Bluetooth LE is optimal for applications that only need to send small amounts of data where the device can wake up, transmit the data it needs to, and then go back to sleep. The low power consumption of Bluetooth LE is excellent for devices that are powered from a small battery, such as a heart-rate monitor. The heart-rate monitor does not need to send data often, but it does need to run for an extended period on a battery. As more products become connected, we will likely see many new applications of Bluetooth LE.

An important consideration when choosing a Bluetooth technology-enabled device is to select an IC that supports the protocol you plan to use. You cannot buy an IC at random and assume it supports both Bluetooth BR/EDR and Bluetooth LE. As discussed, Bluetooth BR/EDR and Bluetooth LE use different PHYs, so you will need to be sure that the IC you select supports the PHY for the protocol you plan to use, or supports both PHYs if you believe both could be beneficial in your application.

Bluetooth 5, which promises extensive improvements, has begun to appear in popular technologies, including many popular smartphones. To be ready for Bluetooth 5, you'll want to be sure that you have a Bluetooth 5-compatible microcontroller that addresses the key requirements. One example is the MAX32666GWPBT, which has dual Arm^®-Cortex^®-M4 cores and separate hardware dedicated to running the Bluetooth stack. This leaves the two cores entirely free for your application. Figure 5 is a block diagram showing key features of the MAX32666GWPBT.

Another option is the MAX32665 low-power Arm Cortex-M4 with floating-point unit (FPU) microcontroller with Bluetooth 5. This microcontroller includes power management features such as a single-inductor multiple-output (SIMO) switched-mode power supply and dynamic voltage scaling to minimize power consumption, making it well suited for battery-operated systems.

Conclusion

Although all of the technologies discussed in this application note are under the realm of Bluetooth wireless technology, they truly offer different strengths and features for various types of wireless electronics. To determine the ideal version for your applications, review the differences in the PHY listed in Table 1 to see where each protocol excels. In addition, be sure to consider how Bluetooth 5 will change the industry in the next few years with its higher throughput, longer range, and extended advertising capabilities.