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Location Mode with Multiple xArrays [Developer Note]

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Overview

Besides providing greater RF coverage, installing multiple xArrays is an excellent way to increase location accuracy.  By applying a simple weighted averaging calculation on tags read by multiple xArrays, you may achieve a more accurate tag location coordinate. This support article will illustrate how a weighted average calculation from multiple xArrays will improve location accuracy.

Example – Weighted Average Calculation

To understand how using a weighted average calculation provides more accurate coordinates, consider the following: We have 2 xArrays reading a tag that is above the level defined by the Height CM parameter.  The Height CM parameter defines the average tag height plane below the xArrays. Because the tag is above the average tag height plane, xArray1 will project the location too far to the right and xArray 2 will project a location too far to the left as shown by the blue arrows.  The error of these projections is canceled out when taking the average of the calculated locations from xArray1 and xArray2’s location calculations.

WeightedXArrayAverage.png

For more information, please review the xArray/xSpan Deployment Guide.

Code Examples

You may download code examples for Octane SDK, in .NET and Java that implement the weighted average calculations. The code may also be extracted and integrated into your own building structure.

Program Output

The example is designed to output the weighted average calculations and other diagnostics about the installation.

For each tag read, the following comma delimited data is produced:

  • EPC– The tag’s Electronic product code
  • Confidence– The confidence in location, based on the read count. The higher the read count, the higher the confidence.
  • #xArrays– The number of xArray used to calculate the x, y coordinate.
  • x,y – The x, y weighted average coordinate in centimeters
  • Jitter– The distance in centimeters between the more recent coordinate with the previous coordinate calculation. Less jitter is better especially when the tag is not moving.

After the run has completed, the following averages are provided:

  • Average confidence– The average confidence value of every tag read during the test run
  • Average number of xArrays– The overlap of xArray reads in deployment (e.g. 1.5 means 50% overlap).
  • Average jitter- There is always some jitter, and there is typically more jitter in a high multipath environment. Under 100 cm jitter is preferable. For more information, see the Support Article on Location Mode in a Multipath Environment.

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Impinj (NASDAQ: PI) wirelessly connects billions of everyday items such as apparel, medical supplies, and automobile parts to consumer and business applications such as inventory management, patient safety, and asset tracking. The Impinj platform uses RAIN RFID, delivering information about items to the digital world and enabling the Internet of Things.