Quuppa Tag Design Principles

The Quuppa Intelligent Locating System™ is able to track any Bluetooth® device from Bluetooth 4.0 onwards, including but not limited to Quuppa's own reference tags and Quuppa Approved Partner Tags. When developing Quuppa trackable tags, it is important to apply certain design principles to the tag design, to ensure that they can provide good performance when used together with the Quuppa system. The aim of this document is to take a deep-dive into the details of these design principles.

Table of Contents

1. How to Make Bluetooth Devices Quuppa Trackable?

2. Quuppa Native Tags vs Quuppa Emulation Tags

3. Firmware & State Machine Logic

4. Antenna

5. Accelerometer & Other Components

6. Proprietary (Edge) Bluetooth Channels

7. Mechanical Design

1. How to Make Bluetooth Devices Quuppa Trackable?

Any Bluetooth device from Bluetooth 4.0 onwards can be made Quuppa trackable by enabling the device to advertise Quuppa Profiles. There are effectively specific advertisement payloads, or Direction Finding packets, that make the device "visible" to the Quuppa Locators.

Note: The Quuppa Profiles are just enablers for tracking, and do not affect the tracking accuracy or general performance of the device itself.

2. Quuppa Native Tags vs Quuppa Emulation Tags

Quuppa Native Firmware

Quuppa licenses natively compatible Quuppa Firmware Libraries (currently available for Nordic nRF52832/833/840) to its Tag Partners. These firmware libraries natively support all of the features that work seamlessly together with Quuppa Locators, Quuppa Site Planner (QSP), Quuppa Positioning Engine (QPE) and other proprietary software tools. This firmware carries a perpetual license and is currently available for Nordic Semiconductor's nRF52832, nRF52833, and nRF52840 models.

Emulation Specifications

To track devices equipped with radios other than those mentioned above, Quuppa has created a Tag Emulation Specification. This specification enables device manufacturers to program their devices to advertise Direction Finding packets (uplink), send data packets (uplink), and use backchannel functionalities (downlink) to command tag. In addition, Quuppa offers sample source code for a reference mobile app, both for Android and iOS, to make them trackable.

Typically, emulation is the only feasible option if the device has additional radios (e.g. Wi-Fi, LoRa, etc) or if the Bluetooth radio is also used for other purposes in addition to Quuppa tracking. While the Quuppa Firmware is optimised for the Quuppa system, it is good to remember that well-designed emulation tags can also provide good positioning performance. There are many factors that affect the tracking performance of a tag (e.g. the antenna, state machine and accelerometer), which will be explored in the next sections.

3. Firmware & State Machine Logic

State Machine Makes Systems Scalable

Quuppa's Tag Firmware (Library) implements State Machine Logic, i.e. the tag's brain that controls how it operates. The state machine has several important functions, but first and foremost it listens to the accelerometer data to control tag's advertisement on one hand to save battery for that given tag, and on the other hand to decrease unnecessary Bluetooth congestion in environments with tens of thousands of tags (e.g. warehouse).

Tags with Quuppa Firmware have a state machine built-in, but for the emulation tags, the manufacturer has to develop their own firmware and state machine logic. This state machine logic may well be either simpler or more complicated than what has been implemented in the Quuppa Firmware. In asset tracking use cases with high volumes of tags residing in the same environment, it's important that state machines command static tags to lower their transmit intervals to minimize unnecessary radio noise.

Emulation Pro Support from Silicon Vendors

In addition to the options presented above, there is a third option. Quuppa is working with several Silicon Vendors who have implemented the Quuppa Emulation Specification (including Direction Finding and data packets as well as backchannel functionality) and support for proprietary channels (2403 MHz, 2481 MHz). Furthermore, these selected vendors have also implemented the state machine, and pre-defined tag profiles (asset tag, people tag, etc) to be leveraged by the manufactures. The implementation is shared via the respective vendors' developer portal (as is), and they typically come with some source code samples. To shorten developers go-to-market times, some of the vendors share their tag reference designs with the BOMs and related design files.

4. Antenna

Positioning Accuracy and Confidence Start With Good Antenna Design

The tag's antenna is one of the most important hardware components for achieving optimal performance together with the Quuppa system.

Quuppa's positioning methodology is based on Angle-of-Arrival (AoA), meaning that the Quuppa Locators measure the direction of the radio signal received from a tag. This is why it is crucial that the radiation pattern of the antenna is as omnidirectional as possible and that there are no significant (i.e. no deep nor wide) nulls.

Printed IFA for Omnidirectional Radiation

Quuppa recommends using a PCB antenna, e.g. a printed IFA antenna. Changing the thickness of or the material used for the PCB will require a redesign of the antenna dimensions or matching circuit. Some high relative permittivity enclosure materials also require a redesign.

Note: Tag Partners are granted access to Quuppa's QT1-1 design files which they can use as a reference for designing their own tags.

The use of a ceramic chip antenna is not recommended as they produce radiation patterns with significant nulls. However, if a ceramic chip antenna is the only option, antennas with the shortest electrical length should be avoided.

Note: It's unlikely that a tag with ceramic chip antenna will fulfil Quuppa's certification requirements.

Good Total Efficiency Helps

Quuppa tags can operate within the whole 2.4 GHz ISM band: from 2401 MHz up to 2481 MHz, with 1 MHz spacing. The antenna and matching circuitry should be designed so that the antenna performance is good throughout the band. We recommend using a 50 ohm matching plane for easier measurement of the antenna matching.

While a Quuppa tag benefits from good total efficiency of the antenna, it is secondary to antenna radiation. The target for total efficiency (includes both the matching loss and the radiation efficiency) for the whole frequency range is better than -5dB.

As always, you also need to take the antenna placement into consideration and make sure you design it properly, also taking into account keep-out areas on the PCB, ground plate, enclosure etc.

Simulate Before Production

It's highly recommended to model and simulate the antenna performance before production. It is important for catching any design challenges early. It is also equally important to simulate and measure the efficiency and radiation pattern of the final antenna design inside the intended enclosure, instead of only in free space, as the enclosure can also affect antenna performance. The matching (reflection coefficient) should be measured first, before any efficiency and radiation pattern measurements are taken.

Challenges With Non-Optimal Antenna Design

Omni-directionality for Positioning Accuracy and Confidence

The tag is a small and simple radio transmitting device. It's fairly easy to manufacture, and there are plenty of reference designs available online. However, when creating a tag for an AoA positioning system, antenna design is critical for the overall system performance.

In Quuppa's case, Locators are like cameras, in that they take small radio images of radio signals that they see. From these images, the Locator measures the azimuth and elevation angles and the QPE converts those into x-, y-, and z-coordinates. If the strongest radio signals that Locators receive are not coming directly from the tag (but from a reflection), it can cause a significant reduction in the positioning performance of the system. This typically happens when the antenna does not radiate to all directions with the same power, but the radiated power is weaker to specific direction. The picture below shows the difference between omnidirectional antenna-radiation patterns of the correctly positioned black tag, and the green tag with a deep and wide null in radiation pattern towards the Locator, resulting in its wrongly computed position visualised as a red dot in the picture.

5. Accelerometer & Other Components

An Accelerometer is a Must

As mentioned above, the accelerometer has a crucial role not just from an individual tags perspective but also from overall system performance perspective. For Quuppa, having an accelerometer is a mandatory requirement.

Beyond the system logic, an accelerometer also has a key role in several use cases (e.g. man-down, impact detection, movement analysis). Tag manufacturers have the freedom to choose the accelerometer that they want to use, they just have to write the drivers for themselves. The Quuppa Firmware has readily written drivers for ST LIS2DH.

Sensors as Use Case Enablers

Quuppa tags also typically have other sensors and actuators, such as a push button and an LED indicator, to address and complement a variety of use cases. Another interesting and new sensor to be highlighted here is a barometer / pressure sensor. It captures the atmospheric pressure from a tag, allowing Quuppa to define its relative height (z-axis).

Different sensors and actuators consume different amounts of energy. Having a vibrator motor or buzzer that can be commanded with the backchannel (downlink) via the Locators enables fantastic use cases, but they also tend to be very power hungry and hence require some smart design choices from the manufacturer's side.

6. Quuppa Proprietary Channels

Interference Tolerance on Non-Standard Channels

The Quuppa System is able to track a tag on the standard Bluetooth advertising channels, as well as at the edges of the 2.4GHz ISM band. Tags with Quuppa Tag Firmware (and upcoming Emulation Pro) allow a proprietary operation mode for tracking Quuppa Compatible Tags using the Quuppa proprietary channels (2401 MHz, 2403 MHz, 2481 MHz). The benefit of this is that these proprietary channels are free from other standard wireless systems, including WiFi, and Bluetooth.

Using the proprietary channels becomes especially important in environments where fast location update rates are required and/or Bluetooth channels are crowded, such as sport stadiums and exhibitions (i.e. areas where large numbers of people carry smartphones and headsets).

Radio Certifications Compliance is the Vendors' Responsibility

From a tag manufacturer's point of view, it is important to acknowledge that when a tag operates on the proprietary channels, the tag's radio certifications must also cover the use of said channels. It's worth noting that there are some country-to-country differences and limitations to operations on different radio frequencies. It is the manufacturer's responsibility to ensure that tag complies with the rules and regulations of the geographical markets where the tags are used in and sold to.

7. Mechanical Design

The saying "form follows function" also holds true in asset tracking tags. The sensors and actuators are defined by use cases that the tag is used for. In the same manner, the type of the tracked entity (i.e. a person, pallet, vehicle, or small asset) sets requirements for the tags size, shape, robustness and its suitable mounting mechanisms. Most enclosure and mechanics design choices are fairly logical and follow common sense.

In the Quuppa Certification process, we test the mechanical functionalities (e.g. buttons, plugs, locking systems, hinges etc) so that they work as specified by the manufacturer. We also evaluate the materials and surface quality (i.e. visual quality), shape of the product (e.g. no sharp edges, pinch points etc), wearing endurance of the product and check that it should not make any unusual noises when pressing or twisting.

By no means the list is exhaustive, but the use case, usage environment, the customer, or even related regulations and other requirements may impose material, functional, size, or other qualities that a tag has to fulfill. These requirements are at manufacturer's and/or user's responsibility.