How Bluetooth® 5 maximizes the Bluetooth low energy connection range
With the core specification version 5.0, Bluetooth® is no longer available as a wireless protocol for personal area networks only (PAN). Three new data rates have been added to this specification, two of which are specifically tailored to increase the range of Bluetooth low energy connections. With good indoor and outdoor coverage, this upgrade makes the network easier and ideal for Internet of Things (IoT) products used in residential, building and industrial automation.
However, what is the actual range of the Bluetooth 5 wireless link? By using the new 125kbps coded physical layer (PHYsical) format, TI has previously demonstrated an outdoor range of 1.6km between two SimpleLinkTM Bluetooth low energy CC2640R2F wireless microcontroller (MCU) LaunchPadTM development kits, and this range is It is impressive. So, why don't we explicitly mention the 1.6km range of technical specifications in the CC2640R2F wireless MCU data sheet?
Hard-won microchip: The CC2640R2F wireless MCU offers several package options, including a 2.7mm x 2.7mm chip scale package (WCSP)
Unfortunately, things are often not that simple. As system developers and RF designers, we are able to clarify the parameters of the range of influence, and we can also measure these parameters in a controlled environment with reliable and repeatable results. But when using RF devices in a real environment, this "final result" from the measurements can make a significant difference. In this real environment, multiple reflections, obstacles, and interference with RF activity will form two random variables that will determine whether the user can establish a link between the two locations selected for the device. The first variable is the transmission path loss, which measures the transmit power obtained by the receiver; the second variable is the actual sensitivity level at the receiver's location. The latter depends on how much interference RF power is around the receiver. If there is no interference present, this sensitivity level is determined by the thermal background noise and will correspond to the sensitivity specified in the data sheet.
A common term used to describe the coverage of an RF system is the link budget. The link budget is the ratio or ratio between the transmit power and the sensitivity level. In a running RF link, the transmitter will transmit at a specified RF power level, and a portion of this RF power (usually very small) will be received by the receiving antenna and fed into the receiver. If this part is too small, the received power level will fall below the receiver sensitivity level and the link will also fail. Therefore, the link budget is defined as the ratio between the transmit power and the receiver sensitivity level, or is expressed as
For convenience, the link budget is usually expressed in logarithmic scale (dB). Output power and sensitivity are typically expressed as a logarithmic scale relative to 1 mW (dBm). this means
From the above equation you can clearly see two ways to increase the link budget:
· Increase output power
· Improve (reduce) receiver sensitivity level
Increasing the output power is a very simple and straightforward method, but the price to pay for it is an increase in power consumption, which can sometimes be costly and ultimately cause legal and regulatory problems. All regulatory areas limit RF emission levels and unwanted spurious emissions, both of which increase as transmit power increases.
Another option is to increase the sensitivity of the receiver when Bluetooth 5 is used to provide a 4x RF range. This is a way for the Bluetooth SIG to choose. We have also used this method to provide the longest range of Bluetooth low energy solutions with the lowest power consumption. One thing to note is that the Bluetooth Technology Alliance or any hardware vendor, including TI, does not specify the actual scope. What we have set is a theoretical ratio that is measurable based on sensitivity and measurable to the degree of improvement. If we can measure this range in a fully controlled environment, we will see the exact improvements in real-world applications. But a controlled environment is either a silencing antenna room or an external space (no other sources of radiation). Unfortunately, in terms of testing range, whether it is a kilometer long antenna room or an external space, it is not economically feasible.
In free space, doubling the range requires a fourfold increase in link budget, or an increase of 6dB. Compared to the original 1M/s Bluetooth 4.0 LE receiver that has been around since 2010, a four-fold increase in range for the new Bluetooth 5 long-range data rate means a 12dB improvement in sensitivity.
When the Bluetooth Technology Alliance defines and discusses the new coded physical layer, the best Bluetooth low energy receiver has a sensitivity rating of approximately -93dBm. This has been used as a reference for the new coding physics layer, so the new modulation and coding format will also need to adapt to the sensitivity level in the real environment, which is -105dBm. This is exactly what the new 125kbps coded physical layer can do, and it does it through a two-way approach. The biggest improvement is that the data rate is reduced to 1/8, which means that for any given power level, each bit carries eight times more energy than before. In theory, this allows the receiver to receive signals at 9 dB lower power levels, and still accumulate as much energy as before.
For the 12dB we need, we still have a 3dB gap. This last 3dB can be achieved by the encoding used. This -93dBm comparison stage (for 1Mbps) assumes a standard deviation demodulator, and each received symbol in the demodulator (1 symbol per bit) is determined to be "1" based on comparison with the previous symbols. "or "0"." This coded physical layer makes the operation of the semi-coherent receiver more convenient, with 8 symbols forming 1 bit, and the correlator can search for these known symbol sequences.
Currently, the CC2640R2F wireless MCU can provide the industry's best sensitivity level of -103dBm, which is only 2dB less than the target of -105dBm. With a +5dBm output power from the CC2640R2F device, this device offers a link budget of up to 108dBm. TI continues to expand the SimpleLink CC264x device family to provide more memory and higher security, and with these devices, we are one step closer to the 12dB goal set by the Bluetooth Technology Alliance in 2017.
The above is how to increase the sensitivity by 12dB in Bluetooth 5, and in theory, how to quadruple its range without increasing the output power compared to the first Bluetooth low-power receiver. At the same time, by adopting different technological processes, the new CC2640R2F wireless MCU has increased the 1Mbps sensitivity level from -93dBm to -97dBm, which brings its performance closer to the coherent receiver.
In a highly uncontrolled environment near TI's Oslo office in Norway, we have performed an outdoor range test using the new SimpleLink CC2640R2F wireless MCU with 125 kbps PHY, in which we are able to maintain a range of more than 1.6 km. connection.
Although the actual range will change as the environment and applications change as described earlier, the main result of this experiment is that Bluetooth 5 is bound to significantly increase the range compared to Bluetooth 4.x, which makes those exciting. New applications are possible.
Finally, it must be mentioned that power consumption remains a major concern for most Bluetooth low energy applications. The transmit power level we used in the demonstration was only +5dBm, the peak current at the time of transmission was about 9mA, and this value reached 6mA when received. Combined with the extremely low standby current consumption of the CC2640R2F device, this enables massive indoor and outdoor coverage for Bluetooth low energy applications and can be run on a button cell for years.
Technology innovation is endless when using Bluetooth low-energy connections that are powered by a small button battery and can communicate with any corner of a home, building or factory.
The Software Development Kit (SDK), which is expected to be released in the second and third quarters of 2017, supports the new Bluetooth low energy standard for the SimpleLink CC2640R2F wireless MCU. The SimpleLink CC2640R2F wireless MCU has been in mass production since early December 2016.
To get started developing your Bluetooth low energy application right away, visit:
· Access TI's SimpleLink Bluetooth Low Energy CC2640R2F Wireless MCU Product Folder.
· Order your Bluetooth low energy LaunchPad kit to get your development started quickly.
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