EPC gen2 can single tag can be accessed by multiple readers

[GVVIN]

two req_rn

Hi,

Can two interrogators access a single tag at the same time.??

According to Epc tag will have ability to store 2 RN16s. So if a tag receives Req_RN from two interrogators will it be able to send different RN16's.

By using different sessions and inventoried flags tag can identify different interrogators.

Is these statements correct.

Thanks
GVVIN

 

[Aya2002]

reading epc gen 2 tags

Hi friend

As I know, this is a reader collision problem. Also I know that each Tag can respond to one reader.
my friend can you eaxplain for me the abbriviations used above such as 2 RN Req_RN.

I think i can help u more but explian for me.

Thanks

 

[GVVIN]

Re: RFID TAG reading

Hi,

RN16 is the handle that the tag gives as an unique identifier for a interrogators REQ_RN command. This is the first step in inteerrogator to tag communication I guess.
I am basically an RF engineer, this area is new. We had a problem while going for certification, they told our interrogators are issuing multiple query there by resetting the flags.

my question is can 2 interrogator access single tag at the same time. I gues using SL and Flags A and B in S0 s1 s2 and s3 we can do that.

GVVIN

 

[Aya2002]

RFID TAG reading

Hi GVVIN

is your tag intellegent and active one?

if not, the tag will respond to a signal of accepted parameters.

even the tag is not active you can make it respond to multiple readers according to your design.

please tell me more and on my personal email
muntather_moto@yahoo.com

 

[FvM]

Re: RFID TAG reading

A problem with your question is, that you didn't clearly mention the particular RFID standard you're talking about. There are many, and most of it don't use RN16. It would be helpful and also a invitation for qualified answers, to use a more specific title for your question.

I'm not particular familiar to the EPC standard, your apparently referring to. But the specification contains a detailed discussion of the purpose of having multiple RN16s. As far as I understand, it's not intended for providing parallel sessions with multiple interrogators. The tag state model doesn't have respective options, I think.

 

[Aya2002]

Re: RFID TAG reading

however i can provide u with many references because i will do my PHD study on RFID

see this paper from IEEE

 

[Aya2002]

RFID TAG reading

Hi FvM

of course the tag will not process parallel sessions.

the response of the TAG will be one for the two readers so that a collision problem will appear and must be solved.

 

[GVVIN]

Hi Aya2002,

No Tags are passive.
I would like to hear more from you how a single tag can be accessed by a multiple interrogator.

Hi FvM,

My apologies. I made the post in a hurry

Yes you are right , I am referring to EPC Global gen2 standard.

As far as I understand, it's not intended for providing parallel sessions with multiple interrogators

I too think the same, But EPC standard specifies tags should support at least 2 RN sequence. Also for dense interrogator or where multiple interrogator are singulating a group of tags they can use different sessions and flags to separately address them. So had a doubt whether this can be done on the same time. Only Header/flag is different all other data remain the same in both the replies to two different interrogators.


GVVIN

Added after 15 minutes:

Also I have a query , If an interrogator using session S1 and Flag B wants to change the session , say change from S1 to s2, what is the procedure. Does a powerdown is required or it can simply issue another Req_RN command.
or
Can a tag accept two Req_RN commands and issue 2 different RN .

 

[Aya2002]

Re: EPC gen2 can single tag can be accessed by multiple read

This is a special design if you need your tag to be able to be accessed from more than one tag and of coures this is not standard as i said it is special.

now, how the tag is not passive? there are many types of tags such as passive, simiactive and active. please refere to the attached IEEE paper, you will find all the types.
-----------------------------------------------------------------------------------------------

There is growing interest in RFID systems from all commercial and government agencies such as giant retail chains like Wal-Mart and K-Mart, government agencies like the Department of Defense, and agriculture agencies like the National Live Stock Information System (NLIS) in Australia. A wide range of RFID transponders have been developed to meet the particular needs of all the potential users. Figure 1 shows the classification of RFID transponders based on their power supplies, data processing modules, programmability, reading ranges, communication protocols, and antenna configurations.



Added after 5 minutes:

4.1 Power Supply: [1]

The most important classification of RFID tags is based on their power supply requirements. RFID transponders are generally classified based on their modes of power supplies, and thus they can be defined in the following three major types:

• Active tags
• Semiactive tags
• Passive tags.
4.2.1 Active tags:[1]

Active RFID transponders have an on-board power supply in the form of a battery. An active tag uses battery power to amplify the signal and then transmit data back to the reader. Therefore, active tags do not need to use the RF carrier signal’s energy to energize the data processing section and hence have a longer reading range.

Active tags can generally be differentiated by their digital section. The digital section provides the ID code as well as embedded security protocols and encryption techniques. The data processing and protocol execution are controlled by the processor, which, in some cases, has additional coprocessors to perform the encryption and data processing instructions. Active tags have the ability to process and store more data than passive tags due to the on-board power supply and are less sensitive to the strength of the reader’s interrogation signal.

When communicating with the reader, the tag is the first entity to be engaged in data transmission. Because the presence of the reader is not necessary for data transmission from the tag, an active tag can maintain a continuous data transmission without the presence of a reader. This type of communication between the reader and the tag is known as transponder driven. Although the active transponder has an on-board power supply, additional techniques for extending the battery life with low-power consumption have been implemented in the form of sleep modes. Active tags that do not detect the interrogation zone of a reader hibernate by going into a sleep mode, and thus they do not waste power. The most significant advantage of active RFID transponders is that they are reprogrammable, and therefore, can be used on a variety of items repetitively until the battery power is exhausted.


4.2.2 Semiactive Tags: [1]
The difference between the active tag and the semiactive tag is that a semiactive tag has the provision of the on-board power supply for minor signal processing tasks but this power is not utilized for amplification of received and transmitted signals. Thus a semiactive tag consumes much less power from the on-board battery and has a longer life compared to an active tag. However, due to this budgeted power allocation that is only for the signal processing unit, semiactive tags have less reading range compared to an active tag. Therefore, the semiactive tag is an in-between approach compared to a fully active tag and a batteryless fully passive tag. When communicating with the reader, the tag must first acknowledge the interrogation signal of the reader in order to reply; this communication protocol is known as interrogator driven.

Some semiactive tags can still perform complex tasks such as data processing and encryption and can achieve reading range almost as good as active tags. These advantages are able to be exploited with the advent of very-low-powered highly efficient microprocessors available in today’s market.

4.2.3 Passive Tags: [1]

Passive Tags do not possess an on-board power supply and therefore rely only on the power emitted from the reader for both data processing and transmission. Passive tags may or may not contain an IC, memory block, or application specific IC. This means that some passive tags perform data processing, but others do not. These tags are usually in the form of electronic article surveillance (EAS) transponders commonly found in retail shops for security purposes or surface acoustic wave (SAW) tags. Most passive tags have low power consumption and low cost due to the nature of their design. Because they rely solely on the reader’s emitted energy to cull its operating energy, all passive transponders must have an RF front end, an analog circuit, and depending on their data processing techniques, a digital circuit.

The RF front end of the passive RFID tag consists of the antenna and the impedance matching circuit in order to minimize signal reflection between the antenna and transponder circuit. The analog part of the passive tag may comprise an LC tuning circuit and a rectifier. The rectifier supplies the required dc voltage to the digital circuit. The digital circuit of the RFID passive tag is completely optional and may have an IC, ASIC, or just a memory block of a few kilobits. Most passive tags have precisely designed microchips and/or ICs that contain digital logic sectors, which process data rapidly. Passive tags from Alien Technology and Intermec are shown in Figures 5 and 6. Passive RFID transponders can be made using printing techniques. There have been tremendous efforts and interests in direct printing of RFID tags on plastic, fiber, and other low-cost laminates to compete with the ultra-low-cost optical barcodes. Also, all ink-jet-deposited processes capable of creating high quality passive devices for RFID applications have been envisaged and are being developed. Due to the absence of on-board power supplies, passive RFID tags have a much shorter reading range (up to 2m). They are more vulnerable to environmental effects and have poorer or no data processing abilities at all and hence can’t be easily reprogrammed.

The advantages of passive RFID systems are low cost and low maintenance. Due to these salient features, passive tags are used in a wide range of applications such as medical, supply chain management, and wireless sensing.

figure(5)

figure 6


This is part of the attached paper please see it

 

[GVVIN]

Re: EPC gen2 can single tag can be accessed by multiple read

Thanks Aya2002,

I have been working on UHF RFID , readers and tag design
.As I said before being an RF engineer I am not much familiar with access protocol and how it works.
I need to go only by standard, as I am trying to solve an issue related to conformance test for EPC certification. particularly the flag change issue that i mentioned in my first post.

Thanks
GVVIN

 

[Aya2002]

Hi my friend:

please fell free to ask me for any IEEE papers. I will provide you all your needs

Thanks