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Reader Modes Made Easy

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What are Reader Modes?

Reader modes define the over-the-air data transmission between the reader antenna and tag/endpoint. Different reader modes allow the user to set the balance between read rate and resistance to interference that best suits the needs of their use case, by changing the modulation scheme that encodes the data. The more modulations used to encode each bit, the more resistant the data transmission is to interference from other readers or devices in the area that happen to share the same frequency. To illustrate how signals are modulated to encode binary data, 3 examples are included below, sending the same information with different levels of modulation. 

modulation.png

Note: Miller (M) sets the number of modulations used to encode each bit. Higher Miller means more modulations per bit, which generally requires more transmission time, but produces a more robust signal.

Impinj Reader Modes

Impinj's readers and gateways offer a pre-defined set of reader modes with their own advantages. The table below shows the pre-defined reader modes and their key features:

Mode

Name
Type
Encoding
Notes
0 Max Throughput Standard FM0 Fastest data rate, but most susceptible to interference
1 Hybrid Standard Miller 2  
2 Dense Reader M4 Standard Miller 4  
3 Dense Reader M8 Standard Miller 8 Most interference tolerant of the standard modes.
4 Max Miller Standard Miller 4 Higher read rate with tolerance for multiple readers in the area
5 Dense Reader M4 Two Standard Miller 4
  • Higher read rate with tolerance for multiple readers in the area
  • Faster forward link than mode 2
1000 AutoSet Dense Reader Impinj Various
  • Listens to RF environment before selecting reader mode 1 to 5
  • Patented by Impinj
1002 AutoSet Dense Reader Deep Scan Impinj Various
  • Combination of faster modes and slower Dense Reader Modes (DRMs)
  • Maximizes the number of unique tag reads
1003 AutoSet Static Fast Impinj Various
  • Combination of faster modes only
  • Higher read rate with some tolerance for multiple readers in the area
1004 AutoSet Static Dense Reader Impinj Various Combination of DRMs only

Read Rate vs Sensitivity

To illustrate the trade-offs between read rate (tag reads/second) and sensitivity (robustness of the communications link), we performed the following tests with a FCC based Impinj reader:

  1. Read rates for each of the reader modes were compared by continuously reading 20 tags paced in front of one reader antenna.  Notice from the "Read Rate Example" barchart below, a difference of about 10 X in read rate between the slowest (mode 8 & 1002) and fasted modes (mode 0).
  2. In the Sensitivity Test shown in the lower barchart, a test was run to see which reader mode was able to read the greatest number of unique tags from a large, densely packed, difficult to read tag population. This test showed about a 2 dB difference between the most sensitive (mode 1002) and least sensitive (mode 0).   This 2 dB difference translates to a 26% difference in read range. 

Example.png

A more sensitive reader mode will result in a larger coverage area.  In the ceiling mounted xArray test illustrated below, the most sensitive reader mode increases the coverage area by over 40% over the least sensitive modes.

Mode 0:  Max Throughput
Mode 1002: AutoSet Dense Reader Deep Scan

left.png

right.png

 

Recommendations by Operating Mode

The recommended reader mode will vary based on the operating mode the reader is running - i.e. Inventory Mode, Location Mode or Direction Mode.

Inventory Mode

Inventory mode, the most common mode used by RAIN RFID applications, is available on all Impinj reader/gateway models. A reader typically only needs to read a tag once when running inventory mode. For this reason, high read rates are often not necessary.

Models: R120, R220, R420, R640, R660, and R680

Recommendations:

  • For use cases with a static tag population, take advantage of Mode 1002 with its high unique tag reads.
  • If the reader is operating in a noisy RF Environment, select a slower (Dense Reader) mode.
  • Use cases with dynamic moving tags can utilize faster reader modes when there is a risk of missing tags that are briefly in the field of view.
Mode
Why choose?

1002

(Starting Point)

  • Static tag population
  • Want highest number of unique tags
  • Low to medium interference environment
  • Slow read rate adaquate
1000
  • Dynamic tag population (moving tags)
  • Periodically noisy RF environment
  • Medium read rate allowed
0
  • Dynamic tag population (moving tags)
  • Low interference
  • Need fastest read rate possible
3 or 1004
  • High interference environment
  • Regions with a limited number of frequency bands
1, 4, or 1003
  • Low to medium interfere and faster read rate
  • Dynamic tag population


Location Mode

Picking the reader mode with the highest read rate will deliver the most accurate tag location calculations. The more times the xArray reads a tag in Location Mode, the greater the sample size that the algorithm can use to determine an accurate (x,y) tag location.

Model: Impinj xArray R680 ONLY

Recommendations:

  • When multiple xArrays are running location mode, there will be some interference because of beam overlap. In this case, you may need to choose a more interference tolerant reader mode to achieve the highest read rates.
Mode(s)
Why choose?

1003 (Starting point)

  • High read rate, good with shorter compute windows
  • Low interference environment
  • Better in reflective environments
  • Good starting point with multiple xArray
4 (FCC) or 5 (ETSI)
  • Good choice for larger/dense xArray deployments
1002
  • Need the highest unique tag read rates possible
  • Slow read rate, longer compute window required
  • Bad in reflective environments
0
  • Low interference environment ONLY
  • Ideal when tracking moving tags
  • Good starting point in a single xArray deployment
1004
  • Extremely high interference environment
  • Narrow band region (ex. ETSI)

 

Direction Mode

Direction modes maximizes the accuracy of identifying the direction of a tags motion by reading tags as often as possible as they travel past the gateway. High Performance reader modes will track a greater number of tags with accuracy.

Model: xSpan R660 and xArray R680 ONLY

Recommendations:

  • To insure the highest accuracy, limit the number of tags in the field of view at any one time.
  • Unless high sensitivity mode is required to read your tags, use high performance.
Mode(s)
Why choose?

High Performance (Starting point)

  • Easier to reach tags
  • Low interference environment
  • Up to 50 tags in the field of View
High Sensitivity
  • Harder to reach tags
  • Dense reader environment
  • Up to 20 tags in the field of view

 

Other Recommendations

  • Perform a site survey by using a spectrum analysis of the noise and interference level in the RAIN RFID spectrum.
  • Testing is always the best way to determine the reader mode that best works for your use case. Use ItemTest to evaluate the performance of different reader modes.  Look at at tag read rates and the number of unique tags read.
  • Portal applications with side by side mounted xPortals and xSpan work best when selecting a reader mode which tolerates interference since the antenna beams are pointed toward each other.

Terms Used

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Reader and Gateway Compatibility

The supported reader mode is dependent on the region and Impinj reader/gateway model.

Mode Index
Mode Name
Regions

R120

1port

R220

2port

R420

4port

R640

xPortal

R660

xSpan

R680

xArray

0 Max Throughput All     Y Y Y Y
1 Hybrid Mode(M=2) All     Y Y Y Y
2 Dense Reader (M=4) All Y Y Y Y Y Y
3 Dense Reader (M=8) All Y Y Y Y Y Y
4 Max Miller (M=4) Not supported by regions supporting mode 5.     Y Y Y Y
5 Dense Reader (M=4) 2 ETSI, China, India, Japan, Korea, and So. Africa Y Y Y Y Y Y
1000 AutoSet Dense Reader All Y Y Y Y Y Y
1002 AutoSet Dense Reader Deep Scan All     Y Y Y Y
1003 AutoSet Static Fast All     Y Y Y Y
1004 AutoSet Static Dense Reader All     Y Y Y Y

 


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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.