Best Practices for Air Interface Load Management

In some deployment environments, the air interface loads are very heavy because of the high number of devices sending Bluetooth® signals (e.g. mobile phones and displays). In these cases, some adjustments might be needed to the Quuppa system settings to make sure that it is working optimally. This document describes the best known practices for running the Quuppa system in heavily congested environments such as large exhibition centers, shopping malls, retail stores and some manufacturing sites.

Please note that the following Quuppa recommendations are subject to change based on new findings. If you have any questions, please contact us via the Quuppa Forum.

Minimum System Requirements

To implement the following best practices, you will need:

  • Quuppa Positioning Engine (QPE) version 6.0 or newer

  • Quuppa Site Planner (QSP) version 6.0 or newer

  • Locator firmware version 11.00x or newer

Checking the Air Interface Load Status

First things first, you will need to identify whether air interface congestion is challenging your system performance. You can use the QPE Web Console to do so, by checking that the following indicators do not surpass maximum recommendations.

Air Interface Load Indicator

The Air Interface Load Indicator (i.e. the syncs ps (age) column in the Locator Details table) shows how much air interface traffic a specific Locator is picking up (including both Quuppa traffic and all other Bluetooth traffic).

As the air interface is typically the scarce resource in any wireless communication system, it is important to start the system performance analysis by ensuring that the wireless link is healthy. A level of about 300-350 syncs per second is typically a good indication of heavy congestion. However, this level should always be compared to the number of Direction Finding (DF) packets received per second (shown in the DF pps column) to get a better understanding of the level of congestion. For example, if the system is only picking up 200 packets per second but receiving 0 DF packets, even though there are tags or other devices transmitting DF packets in the monitored area, this could already indicate congestion issues.

RSSI Locator Count

The RSSI Locator Count (an optional field in the Get Tag Data API) reports how many Locators are receiving data from a specific tag, at any given time.

For example, assuming a well-deployed system with good coverage, Locators that are further away from a tag do not typically contribute to the positioning of that tag. In retail stores and exhibition centers it is typically enough to have a maximum of 2-5 Locators receiving packets from the same tag at any given moment. Having more than 10-20 Locators receiving packets from the same tag at the same time typically indicates an unnecessary use of capacity in already congested areas.

Managing Heavy Air Interface Loads

If you have identified challenges to system performance caused by air interface congestion, then you can try the following tips to improve performance. In some cases, you may need to use a combination of these to achieve the best results.

Use the Proprietary Mode

Quuppa tags (or other Quuppa Compatible and Approved devices) can operate on a non-standard Bluetooth advertisement channel and the Quuppa system can be configured to operate in a so-called proprietary mode. In the proprietary mode, standard Bluetooth radio traffic cannot interfere with the Quuppa Tags as the tags use frequency channels at the edges of the 2.4GHz ISM band.

Quuppa always recommends using the proprietary channel whenever possible.

For more information, see the Edit Operation Channel section of the Quuppa Site Planner User Manual.

Reduce Locator Sensitivity

By default, Quuppa Locators are set to their maximum sensitivity level to provide maximum range, i.e. they can detect radio packets transmitted from far away. In highly congested areas, Locator Sensitivity can be turned down to reduce system congestion.

This is similar to reducing the base station cells in wireless cellular communication to better allocate resources to the users close by. The Locator Sensitivity feature can be used to adjust the required signal strength (Rx sensitivity tuning) for radio packets received by specific Locators. This means that tags need to be physically closer (see wireless link budget for more info) to the Locator for their packets to be received by the Locators.

Quuppa recommends on site testing, as the optimal sensitivity level is case-specific. However as a benchmark, lowering the Locator Sensitivity to -9 dBm or -12 dBm is often a good level for highly congested exhibition centers.

For more information, see the Edit Locator Sensitivity section of the Quuppa Site Planner User Manual.

Increase Tag Tx Power

The Quuppa tag Tx power (i.e. the transmission power) can be adjusted in the QSP. In cases where Locators are losing a lot of packets due to congestion, it might be helpful to increase the Tx power, even to the maximum. Doing so is particularly effective especially when used together with reducing the Locator Sensitivity.

For more information, see the Edit Tag Tx Power section of the Quuppa Site Planner User Manual.

Place Locators Closer Together

In heavily congested areas, it can help to mount the Locators closer together than usual. In cellular communication, if the amount of radio traffic increases, the mobile cells are made smaller to increase capacity. Similarly for the Quuppa system, the Locator Sensitivity can be turned down to reduce the size of the coverage area of a single Locator, but then it is important to remember to mount Locators closer together to ensure continuous and uniform coverage of the tracking area.

Always test your coverage level by using the QSP's coverage estimate tool, as well as estimate the tracking performance using the Quuppa System Simulator (QSS).

Optimise Locator Data Scan Mode Settings

By default, Quuppa Locators are set to scan for Data Packet in addition to Direction Finding packets. However, in some cases it may make sense to optimise the project so that some Locators don't scan for data packets at all.

In such cases, you can use the QSP's Scan Mode settings to define Locators that will not scan for Data Packets, reducing their processing load.

Even in cases where you need both types of data, you typically don't need all of the Locators to scan for both types of packet. So you can optimise processing load by selecting just a few Locators to scan for the Data Packets as well, while the others focus only on Direction Finding packets.

For more information, see the Edit Locator Scan Mode section.

Change the Transmit Rate of the Tags

The QPE uses the reported Tx rate to tune some of its internal parameters, that are used for positioning a tracked object. The faster the Tx rate reported by the tag, the faster the QPE assumes the tag is moving and based on this assumption, it uses a shorter time window to collect data from Locators to minimize positioning lag. However, in very congested environments, where many packets are lost, the QPE may not get enough data to compute the position of the tracked object. This may lead to unreliable positioning data.

In these cases, Quuppa recommends that the tag transmit rate is adjusted to balance the impact of the air interference. This means that the effective transmit rate of the tag can be set to be higher than the reported tag Tx rate (value within the DF radio packet); i.e. the phone transmits faster than what it reports to the QPE. For example, if a phone is being used for tag emulation, the tag can be set to transmit at a rate of 5-9 Hz even though the reported Tx rate us only 2 Hz.

As a general rule, if you are tracking an object that is moving at walking speed, you should report to the QPE a maximum tag Tx rate of 2 Hz to get a roughly 1.5 second window for data collection with an average latency of some 750 ms.

Note: Please note that testing in your deployment environment is essential for finding the optimal settings for your use case. All of the numbers presented in this document are general guidelines.