Reader Modes (RF Modes) Made Easy

What are Reader Modes (RF 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. 

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 Speedway RAIN RFID Reader Modes

Impinj's Speedway 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:

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 Speedway reader:

1. Read rates for each of the reader modes were compared by continuously reading 20 tags placed 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. 

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

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.

  

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.

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.

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 Impinj ItemTest software 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 Impinj xPortal RAIN RFID gateways and Impinj xSpan RAIN RFID gateways work best when selecting a reader mode which tolerates interference since the antenna beams are pointed toward each other.

Terms Used

• Dense reader environment - an RF environment in which reader antenna or gateway transmissions have a lot of overlap, producing a noisy environment that requires more robust signal modulation.
• Dense Reader Mode (DRM) - A category of RF Modes in which readers are configured to minimize out-of-band interference with other readers and tags, enabling many readers to operate in the same physical location.
• Coverage area - The amount of area in front of an antenna or gateway where a tag can be read a high percentage of the time
• Field of view -  The area near or typically in front of an antenna where the tags can be read
• Read range -  the maximum distance from a reader antenna a tag can still be read reliably.
  
  

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Reader and Gateway Compatibility

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

 (* Note: the implementation of mode 1002 on R120 and R220 differs from the other Impinj readers/gateways; this implementation on R120 & R220 will yield slower read rates than their counterparts)