OPTIONS TO INCREASE BLUETOOTH RANGE

Due to today’s environmental challenges in commercial, industrial, and even residential settings, many of our customers ask us how to increase the range of their Bluetooth solution. With multiple networks present, long distances to achieve, obstacles to overcome, walls to penetrate…achieving long range Bluetooth performance can be difficult. We advise that an in-depth systems approach be taken to deal with extending Bluetooth range, as each application, product, and network has different needs and requirements. However, there are some main methods to improve Bluetooth communication and CEL highlights them here.

1. ANTENNA

Unfortunately, this is often overlooked or an afterthought in many designs. However, it can be one of the most critical elements to achieving long range Bluetooth performance. Optimizing your antenna for efficiency and radiation pattern (Omni or Directional) can have a significant impact on your range. CEL strives for its antennas to be >80% efficient and omnidirectional. We confirm efficiency by measuring and comparing the conducted vs. radiated power. Additionally, we measure and plot the radiation pattern and look for areas of weak or no signal strength; we’re seeking a uniform radiation pattern in all directions, as most of our customers cannot guarantee the installation and antenna orientation in the field. To give you maximum antenna performance, the antenna needs to be looked at from both the Tx and Rx side; it’s not always possible to control both sides if one of them is a 3rd party device, like a mobile phone or tablet. Using the Friis equation, below is a range calculation showing the achievable distance between two sets of antennas, each with different gain.

Antenna distance comparison table 1 when environment exponent is 2.7

2.TRANSMITTER AMPLIFICATION

Increasing your output power with an amplifier is one of the best options there is to extending your Bluetooth range. Yes, it may consume more power, but it has better power efficiencies than S2 and S8 CODED PHY options. Additionally, it may help you avoid a more expensive repeater, which as a result, your total installed costs will be lower. Finally, if you can achieve a Pt-Pt connection versus say a MESH network, you’ll have improved latency and throughput, and a far less complex network to develop, install, and provision. Below is a calculation on how your range improves with a stronger Bluetooth transmitter.

Antenna distance comparison table 2 when environment exponent is 2.7

3.LEVERAGE A REPEATER

Typically, utilizing a repeater is less than ideal, as it adds cost, provisioning complexity, and security factors need to be considered. However, installing a repeater might be one of the quickest and easiest solutions to extending Bluetooth range, when you have very few options to reach certain devices. Strong considerations need to be made about location, who’s installing it, if the physical network will change, Etc.

4.MOVING TO A CODED PHY

Bluetooth 5 gave us LE Long Range or CODED PHY. The technique here is to deliver a more robust coding scheme (using Froward Error Correction gave us S2 and S8 coding schemes) at the expense of throughput and increased power consumption compared to other PHYs. Coded S2 and S8 give us a data rate of 500kbps and 125kbps respectively. In theory, range can be increased by 4X. CEL’s internal testing on its BT modules at 1Mbps, and even comparing it to the Friis Equation (range calculator), show that only the S8/125kbps has much of a range advantage.  See our 1Mbps comparison to a competitor’s solution using the S2 Coded PHY(500kbps) below. However, if throughput and power efficiency are not a concern, the S8 coding scheme is the one to consider. Also, keep in mind that both communicating devices need to support CODED PHY…your smart device may not.

Test Scenario

  • CEL's CBT250 module @1Mbps PHY
  • Competitor module @500kbps PHY (S=2 Coded PHY)
  • Tx power is the same for each calculation
  • CEL-PCB trace antenna, Competitor-Ceramic chip antenna

Results/Takeaway

  • Same range despite competitor increasing its Rx sensitivity (reducing it's data rate)
  • CEL's antenna performance compensated for its higher data rate
Bluetooth Communication Range Graph showing range based on Tx Power

5.MESH NETWORK

If your system and application is such that you can support a Bluetooth MESH Network, then allowing other devices to assist in extending the range of communication and ensuring your message gets to the final destination is a good option. There’s also an added element of reliability due to the ability of the message to take more than one path to get to its destination. However, this is the most complex and challenging of the possible solutions to extend your Bluetooth range. For one, there are multiple device types to deal with…relay nodes, friend nodes, low-power nodes, proxy node. Also, if any of these are battery powered, this further complicates the provisioning and management of the system. It’s also a more expensive solution. If you can overcome the network complexities and technical issues, as well as afford the higher costs, this is a reliable method to extend Bluetooth range.

6.PROPER DESIGN

Following implementation and integration guidelines is critical. It’s amazing the types of issues we have come across and resolved…from detuning the antenna with metallic paint on the housing, enclosing the radio in essentially a Faraday cage, placing a battery directly under the antenna, reducing/eliminating the impact of EMI generating devices, not accommodating any antenna keep-out or proper spacing, improper grounding, Etc. CEL provides specific guidance on the ground plane size and dimensions, as well as proper vias. The antenna keep-out, overhang, or spacing to your host and other boards is also critical to achieving long range performance. Finally, having maximum air gap distance to your housing is also essential. CEL is more than happy to provide front-end design support, make recommendations, do schematic reviews…to assist in optimizing the design. Also, CEL has invested heavily in simulation software, where we can run ‘what if’ tests to get an idea of what the Bluetooth range will look like in a given design and enclosure.

7.TEST IT, FIX IT, REPEAT

CEL has several tests that it likes to perform to verify companies are achieving maximum Bluetooth range. The first is Total Radiated Power testing; we compare the performance of the end-product to the TRP of the module. If we see deficiencies, we advise on implementation changes to the host board, module location/orientation, enclosure, or all. Next, we suggest that companies perform a PER test. Finally, we recommend and can assist with network or field testing.

Applicable Modules