Optimizing Tag Throughput Using ReaderMode


There are many parameters which can be set in an EPC GEN 2 - compliant reader in order to optimize throughput; these can include: data rates, modulation type (both reader-to-tag and tag-to-reader), bit encoding, pulse widths and other air protocol particulars. It is beyond the scope of this posting to get into details of each of these but you can get an overview here.

In fact there are over 128 combinations of settings on a typical EPC GEN 2 reader when you factor in all the variables; imagine trying to decide which ones to use when installing an RFID system and then having to change it every time the RF environment or reader requirements change! This is why Impinj offers a number of preset modes selected by Impinj system engineering to provide the best performance. The Speedway reader firmware (known as "Octane") supports several pre-configured Gen2 modes. In addition, Octane supports four mode settings that provide automatic control over the Gen2 Mode.

This posting will describe some more detail regarding reader mode settings, what are the key differences between them and how to select and set the appropriate mode for your deployment.



The chart below describes the static, pre-configured Gen 2 reader modes.


A couple of important things to note regarding reader mode settings:
1. Not all modes are available on all reader models or in all regions.
2. As a rule, there is an inverse relationship between data rate and sensitivity/interference tolerance. Higher data rates generate, and are more susceptible to, interference whereas lower data rates cause less interference and are more tolerant of it.

The second point above explains why a user may not (and most likely should not) always select "Max Throughput" mode. The name of this mode is a bit misleading, while it will support the highest data rate of any of the settings, it will not necessarily yield the best throughput or actual tag read rate due to interference and tag collisions.

The term "Environment" in this case refers to the number of deployed GEN 2 readers, or other sources of interference, within the operating environment (defined by the EPC GEN2 standard as within a 1km radius of the reader). If most of the channels are occupied by active readers (for example, more than 25 readers operating in the 50 available channels in North America), then this is said to be a "Dense-Interrogator Operating Environment". If less than this, it is defined as a "Multiple-interrogator Operating Environment". Some regions do not allow for any mode of operation other than Dense-interrogator due to the limited available spectrum (and thus number of channels).

In Dense-interrogator mode, the reader transmits using settings which will generate less interference but will not support the highest data rates.

When deploying the Impinj Speedway RAIN RFID readers and/or gateways in a region which offers the choice of either of these environments, be sure to do a thorough site survey to ensure the operating environment will support settings other than Dense-interrogator mode. Please note that, in order to be effective, all deployed readers must be set to Dense-interrogator mode if necessary. If even one reader in a Dense-interrogator environment is set for Multiple-interrogator, it will generate interference which will negatively impact the throughput of all other readers in the environment.



In addition to the reader modes shown in the chart above, the Impinj reader offers mode setting whereby the reader adjusts automatically and dynamically according to the environment and measured throughput. This mode is designated AutoSet (LLRP mode index '1000').

This graph below illustrates how the AutoSet mode automatically adapts for the environment.

Note: 'DRM' means Dense Reader Mode



Besides AutoSet (1000), Impinj reader offers four other AutoSet reader modes as shown in the table below:

 Index  Reader Mode Name  Description
1002  AutoSet Static  Default mode. Configures the reader to choose the best Gen2  link parameters for the environment where the tags population is relatively static, and attempts to search for the weakest tag.
1003  AutoSet Static Fast  This is an adaptation of AutoSet Static mode for good RF environments.
1004  AutoSet Static DRM  This is an adaptation of AutoSet Static mode for difficult RF environments.
1005  AutoSet Custom  Reserved for future use.



The reader mode on the Impinj reader can be configured using a few different interfaces. One of these is the Impinj ItemTest tool.

The second method is to use the Impinj Octane SDK. If programming in C#, use the enum ReaderMode in the Settings class as shown below.

The third option is to use the Low Level Reader Protocol (LLRP) implementation known as LTK. The LTK parameter "C1G2RFControl" in the Set_Reader_Config message sets the reader mode as shown below (see LTK Programmer's Guide for details).



The AutoSet Static (1002) is the default reader mode on the Impinj readers and/or gateways and, in most cases, is the best option. If greater throughput/tag read rate is required then it's suggested to work up through the options in this order: AutoSet Static Fast, AutoSet Static DRM, MaxMiller (where available), DRM8, DRM4 and Hybrid; select the first mode that provides an increase in throughput versus AutoSet. In very few instances is MaxThroughput recommended (i.e. anechoic chamber reading only a few tags).

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