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Implementing Directionality Feature

Directional intelligence is the ability to discern whether a tagged object is coming or going, that is entering or leaving a room, crossing a choke point or even entering a trailer from a given dock door. There are two methods to accomplish this; 1) single read zone using dwell feature or 2) two read zones on each side of threshold.


Method 1: Single Read Zone using Dwell

This is a less complex approach but it has limitations. A read zone (aka Portal) is deployed with sufficient antennas to read all the tagged objects going through that doorway or choke point. When a tagged object passes through that read zone and TagNet changes its location state from A to B, the dwell period gives it time to move away from the read zone before it is evaluated again for another inventory move (i.e returning back through same doorway e.g. B to A).  The dwell time should be long enough to allow the object to move away from the portal read zone, but not too long that if it is brought back in the reverse direction it will be not be ignored.  Below are examples of single zone Man door Portals.




This approach can be defeated if the person transporting the asset turns around and reenters same doorway before the dwell time expires, thus the asset will not be considered for another move. Also, if the asset remains stationary at the read zone longer than the dwell period, TagNet will move it back into the room location (or whatever the IMOVE rules are setup for). This can Ping-Pong the asset's location indefinitely and when it starts moving again its calculated inventory location (which side of the threshold) may not be correct.  Additionally this creates a confusing transaction history that makes it difficult to bread-crumb the movement of that asset or object.


Method 2: Dual Read Zones

This approach requires more planning and hardware resources, however it is more accurate than Method 1 as it is self-correcting if a tag reverses direction and there are no considerations as to how long an asset can dwell anywhere between the two read zones. This logic can be implemented a number of ways based on your use case:


1.If a single reader is managing all the read points (antennas) as depicted in the schematic D1 below, then this would be classified as a basic configuration. The antennas in each zone would be named the same so as to enable Net Change feature as a group, and there would be IMOVE rules setup for each antenna.  During each read cycle, a given tag will only register on the antenna where it is seen the strongest thus this assists greatly in determining which side of the threshold (or zone) it is on.

2.If read points are being managed by multiple readers, a different logic is deployed as it cannot be determined by a single reader which antenna is seeing the tag the strongest (e.g. the winner) and thus which side of the Zone the tag is on. This logic is designed when deploying multiple zones whereas each read point in the zone (such as inside perimeter of a room) could be managed by different readers such as a choke point In example D2, In this scenario Zone A is managed from Reader R1 and Zone B is managed from Reader R2. So in this case you don't have the advantage of the strongest antenna wins because read points are spread over multiple physical readers.  Refer to the RFDDTAG binding that details out how this is setup.

3.Regardless of either method 1 or 2 above, the two read zones need be a reasonable distance from each other so there is an RF 'Quiet Zone' between the two (typically 3-4 ft. minimum on each side of the threshold). The greater the distance the more accurate the directionality will be. TagNet is making very rapid calculations based on the RSSI to determine which read zone is seeing the tag the strongest and that becomes the 'winning' side... at that point the appropriate IMOVE rules are executed to change the inventory state (e.g. In or Out of room).

4.Not all doorways will be ideal for antenna placement, there may obstructions on walls such as light switches or fire alarms the prohibits placement in the desired location. How the tagged object is transported through the doorway is important, is it hand carried where the person's body can obstruct the RF signal or are they on an open cart where the tag is always exposed to the Antennas?

5.You must test, test and further test all the transport scenarios to determine what level of readability can be achieved. The results may dictate reorienting or adding more antennas, or possibly stipulating workflow changes to employees on how to handle/transport those tagged objects through RFID doorways (aka 'Portals').

6.Note that directional accuracy will suffer if the object is simply missed (not scanned) on either side of the doorway during passage. Ensure that your antenna selection & orientation is optimized for this use case and your  tag selection is the best suited for your object/substrate using the largest Inlay possible. Refer to the topic on Calibrating a Read Zone.

7.If using the Smart Reader Client (SRC) consider the speed of your network to determine if very short read event cycles (< 1 second) can be posted fast enough for TagNet Server to change inventory state of an asset before it reaches the next read zone. Otherwise the Dual Read Zone method may not be a good option. The timing (speed) of asset movement between read zones is important, if this duration is less then that time it takes for server to process payloads then then directional accuracy can become inconsistent.



Use Case D1 below


Use Case D2 below


Note: Ideally you would have gone through a Phase I implementation with Stratum guiding the way and the correct antennas and tags have been chosen and implemented. This is the important starting point so that calibration can have an impact and you are not fighting against a bad foundation. This may seem simple but there are many antennas out there such as linear, circular and specialty so refer to the RFID 101 section to ensure you are clear about the terminology and what options are available for passive UHF equipment. 



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