Article Technical Rating: 8 out of 10
There are numerous wireless standards at your disposal when creating a new product. Each choice has its own set of advantages and disadvantages. It really depends on your goal.
In this article we’re going to look at the three most popular short-range wireless standards including: Bluetooth Classic, Bluetooth Low-Energy (BLE), and WiFi Direct.
The Need for Speed
If high speed data transmission is the most critical requirement for your product then most likely WiFi Direct will be the best choice. Everyone has heard of WiFi, but few know of WiFi Direct. Although that is changing.
Standard WiFi requires an access point. So if you want to transfer data from one device to another it must pass through the access point.
WiFi Direct has the speed advantages of WiFi without the need for an access point. Data can be transmitted directly from one device to another just like with Bluetooth.
Table 1 – Speed Comparison
|Bluetooth Low-Energy||1 Mbps|
|Bluetooth Classic||2-3 Mbps|
WiFi Direct has a maximum data transfer speed about 10x the speed obtainable with Bluetooth Classic.
So, for example, if your product needs to stream video, especially high-definition video, you’ll need the fastest wireless connection possible. There is no way Bluetooth will be fast enough, so you’ll almost surely need to offer WiFi Direct connectivity.
At the other end of the speed spectrum is Bluetooth Low-Energy (also called Bluetooth Smart) which is about 2-3x slower than Bluetooth Classic, or 20-30x slower than WiFi Direct. It is typically used for transmitting small amounts of intermittent data, such as sensor readings (temperature, acceleration, etc.) or perhaps GPS coordinates.
When you need to constantly transmit data, such as when streaming audio, you’ll usually need to use Bluetooth Classic. Bluetooth Classic is optimized for streaming applications, versus BLE which is optimized for short, infrequent bursts of data.
However, it is possible to use BLE for streaming audio, but not at the same quality as with Bluetooth Classic. For example, Bluetooth stack provider, Searan LLC can provide you with a custom Bluetooth LE stack that allows audio streaming.
WiFi Direct has a maximum range of about 200 feet, compared to only about 50 feet typically for Bluetooth (Classic and Low-Energy). The increased range of WiFi Direct is possible because of the higher transmission power used by WiFi Direct.
The trade off is battery life and this increased transmission power will drain a small battery much faster than either Bluetooth standard.
Table 2 – Range Comparison
|Bluetooth Low-Energy||50 ft typically, but up 1,500 ft with range extender|
|Bluetooth Classic||50 ft typically, but up to 3,000 ft with range extender|
|WiFi Direct||200 ft|
But wait a minute…things aren’t always so simple. There are some exceptions. First of all, there are actually different classes of Bluetooth transmitters. Most Bluetooth products use a class 2 transmitter with a range around 50 feet as previously stated. But it’s possible to use a class 1 transmitter with a range closer to about 300 feet. But, just like with WiFi Direct, the higher transmission power comes at the cost of reduced battery life.
By using a range extender circuit (which consists mostly of a very sensitive receiver) you can increase the range with Bluetooth even further. For example, Bluetooth module provider Bluegiga offers a long-range BLE module (BLE121LR) with a range up to around 1,500 feet. They also offer a Bluetooth Classic long-range module (WT41) with a range up to 3,000 feet!
There is yet another exception. In some applications, it’s actually possible for Bluetooth (even the Low-Energy version) to transmit over a larger range than WiFi Direct while still using very little power. This is possible due to an awesome feature called mesh networking.
Normally to send data from device A to device C you must form a direct link between A and C. But with mesh networking you can instead send data from device A to device C via device B.
So if device B happens to be halfway between A and C, then A and C can be twice as far apart as normally allowed. This is because device B acts as a relay, or in many ways a signal booster. This idea can be expanded making possible a large network of interconnected, low power devices spread out over a large distance. In fact, up to 65,000 devices may be interconnected using mesh.
A leading maker of Bluetooth microchips called CSR started including mesh networking with their Bluetooth Low-Energy chips in 2014. So far they are the only chip maker to offer mesh with BLE. However, I doubt that will be the case much longer.
There is the option of having a custom Bluetooth stack developed to allow mesh networking with other chips, or with Bluetooth Classic. I know that Bluetooth stack provider Searan has the ability to add mesh networking to their Bluetooth stacks.
Power / Battery Life / Battery size
Higher speed and longer direct transmission range correlate with higher power usage and thus shorter battery life. So if battery life or battery size are important for your product then power usage becomes critical.
Bluetooth Low-Energy (BLE) is the clear winner in regards to low power usage. It was primarily developed for Internet of Things applications which many times need to run from a small, single watch battery. A BLE device can run for a year or two on a single watch battery. This is possible primarily because these types of products are designed to only transmit occasionally. For example, a BLE device may only transmit data for 1 second once per minute. This means the device is idle for 59/60 = 98.3% of the time.
If compatibility with older smart phones is critical for your product, then Bluetooth Classic may be the best choice. All smart phones support Bluetooth Classic, but only moderately newer phones support BLE and WiFi Direct.
Table 3 – Compatibility Comparison
|Bluetooth Classic||All versions||All versions|
|Bluetooth Low-Energy||Version 4.3 or later||Version 4S or later|
|WiFi Direct||Version 4.0 or later||Version 5S or later|
Best of Two Worlds: Bluetooth Dual-Mode
For some applications at times Bluetooth Classic is best choice, and at other times Bluetooth Low-Energy is the better option. For example, perhaps you prefer Bluetooth Low-Energy to conserve battery life, but you also want to allow compatibility with older smart phones.
The best solution may be Bluetooth Dual-Mode. When communicating with newer phones you could use the battery saving BLE mode, but when you need to link to older phones then you could select Classic mode. Most of the Bluetooth chip makers and module providers offer dual-mode Bluetooth solutions.
All three wireless standards offer a high level of security. However, WiFi uses 256 bit encryption versus Bluetooth (Classic and LE) use only 128 bit encryption.
In most cases Bluetooth’s level of security is sufficient, but if security is critical for your product then WiFi Direct may be the better option.
As is always the case with engineering, there are trade-offs between the various solutions. No solution is best in all applications. You need to decide which criteria is most important for your product.
This may be simple or complex. If speed is all you care about then your choice is easy. Or if battery life is your primary concern then your choice is pretty simple. But if you care about both speed and power usage equally then your choice becomes more complex.
Deciding which specifications are the most critical for your product is always a challenging aspect of product development. Welcome to the world of product development where nothing is truly simple. If it was easy, every company would be as successful as Apple.
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