Subject: RE: [Rfid] Reader Deployments (was: Rfid Digest, Vol 6, Issue 9)

From: "David Husak" <[email-masked]>
Date: Thu, 24 Mar 2005 07:42:09 -0500

Margaret, Marshall, RFID:

There's a lot here to comment on, so I will paraphrase the quotes from
Margaret's last message:

>           ... In EPC1 (the protocol with which I am most familiar) 
> the bit rate from the reader to the tag ranges from ~20 bits per 
> second up to ~75 bits per second, and the return bit rate from the 
> tag to the reader is twice that -- ~40 bits per second to ~150 bits 
> per second...

It may be obvious to everyone, but for those that are not as familiar
with the Auto-ID (it was never adopted as an EPCglobal spec) Class 1
protocol, Margaret omitted a 'k' in front of the word 'bits' in all of
the foregoing. See
http://www.epcglobalinc.org/standards_technology/Secure/v1.0/UHF-class1.
pdf

> The EPC Gen2 protocol supports higher bit rates, but I believe that 
> the maximum bit rates are still in the low 100's of bits per second.

The EPCglobal Gen2 maximum bit-rate is 640kbps. And, reasonable models
have shown singulation rates in excess of 1600 tags/sec.  I'll also
point out that there are RFID technologies coming to market (over the
next 18 months or so), in particular those employing wide- or
ultra-wideband technologies (as opposed to the narrowband UHF approach
that we're talking about here) that will have r-t and t-r bit-rates many
times faster than that.

> We have yet to see final tags for this protocol (it is still in the 
> early stages of development) ...

While it's true that we won't see production-quantity, general
availability of Gen2 tags 'til 2H05, let's be abundantly clear -- the
Gen2 protocol was ratified by EPCglobal last December, as was the
completion of the necessary interoperability testing. 

The Gen2 air protocol has been extensively modeled and incorporates a
great deal of learning form the Auto-ID C0 and C1 experience. Tag
models, emulators, prototypes and engineering samples exist today, and
I'd assert that there is high confidence among the companies, large and
small, that plan to play in that space, regarding the performance
capabilities of the tags they are bringing to market.

>                                       ... around a location on a 
> conveyor belt, or across the opening to a pick bay, for instance). 
> This is a nice arrangement...

It certainly is! These are well-understood, practical examples of
instrumenting a variety of so-called choke-points that turn out to be
common features in retail and consumer packaged goods (CPG) distribution
and supply chain applications for RFID*. 

However, many equally-important RFID applications do not have the
convenience of easily-enforceable choke-points and instead require the
instrumentation of more open, volumetric, spaces. These applications
should be supported as well. More on this topic, below.

*(It's probably worth pointing out that the Auto-ID Center and EPCglobal
were created of, by and for the retail and CPG industry. One result of
this is that a lot of the existing application analysis, documentation,
early results, and lore are from this particular space. The process of
collecting requirements for RFID applications in other vertical markets
has begun, so hopefully this dialogue will eventually be a little less
parochial.)

> Some of the "smart antenna" devices ...

For those not as familiar with the terminology, a "smart antenna" is,
indeed, a term used (sometimes pejoratively) to describe a reader with
one antenna, generally integrated into the reader packaging itself. For
example, see http://www.awid.com/product/mpr-2010an/mpr-2010an.htm ,
which  is also, interestingly enough, PoE-powered.

If we look (not very far) ahead, there _will_ be a time when the silicon
$-content of the reader (processor, memory, RF guts) diminishes in
relation to the packaging and antennae and RF cabling and
connectorization costs and power requirements of multi-antenna readers,
especially as integrated, mixed-signal reader silicon solutions come to
market. 

At this point the economics of making readers will tilt strongly toward
the "smart antenna" model, with substantial benefit to the RFID user
marketplace (read: lower prices, standardization, interchangeability,
repeatability. That pesky "invisible hand.")

It is essential that the spectrum of devices from the hi-function
"robo-reader" to the lowly "smart antenna" be accommodated in the
architecture, protocols and recommendations that this group supplies.
Both have and will continue to have application for years to come.

> The problem comes in when you have multiple active readers...  

Thanks for a very cogent statement of one of the problems at hand.

> This is a fundamental limit of the technology, and it is not 
> substantially changed by EPC Gen2 or any other RFID protocols that I 
> have heard discussed.

Au contraire! The Gen2 UHF specification supplies an array of features
and controls to address precisely these problems -- including control of
forward and return baud rate, backscatter modulation frequency, three
different reader transmit mask options, read session control, et. al. 

One of the principal motivations of the SLRRP definition is to provide
well-defined access to these knobs and dials (for Gen2 and for other air
protocols) so that these features can be exercised as intelligently and
dynamically as necessary to maximize overall system performance in the
broadest possible range of applications and environments.

>                                                 ... there is no 
> real advantage (in the number of readers that will be active at one 
> time, or in the number of tags that will be read) to installing 
> readers in a much denser deployments than I have described above.

There are, in fact, a number of very real advantages to incrementally
denser deployment of readers, including reducing polarization
sensitivity, increasing penetration in dense tag environments, and the
ability to provision redundant read-points, to name a few.

> In general, there is no known application to filling the volumetric 
> space of an entire facility with RF...

You had asked in a previous message if anyone had any other data points
regarding dense reader deployments. While I share Marshall's skepticism
about designing-to-anecdote, since you asked, I'll offer up the
following: 

Several months ago I was meeting with the RFID planning group at a very
prominent (non-consumer goods) manufacturing company. They were/are
planning on deploying a very ambitious system over the course of the
next 2-3 years. They had studied available reader specs and had
determined that they needed -- I am not making this up -- 20,000+
readers in each of several facilities they were planning on
instrumenting. The reason was that they needed to more-or-less
seamlessly cover several large, volumetric spaces in several very large
buildings.

I dutifully spent the next hour explaining how, in contrast to the
(over-)simplified 'read-range' metrics typically quoted from reader
tear-sheets, reader and tag interactions may destructively interfere,
which would create a complex set of challenges in their application --
in order to develop an comprehensive understanding of the system-level
and reader-level capabilities they would require, (and hopefully get the
reader count down to a slightly more manageable number:). 

>                                     ...and the human dwell time and 
> tissue heating regulations (CE, OSHA, etc.) in various regions make 
> it _highly_ unlikely that this will ever be legal.  

Ensuring compliance with regulatory and safety requirements stands
side-by-side with application data and performance requirements which
all need to be reliably, concurrently satisfied in the operation of the
system. Obviously, if you just tossed a thousand readers into a metal
building, plugged them in, turned them on, and let them free-wheel...
well, nothing good is going to happen, that's for sure.

So, where does this all lead? I guess I'll quote Margaret one more time:

> If we are going to write a protocol to manage RFID readers, I want 
> us to make a protocol that is well-suited to the nature of RFID 
> readers.. 

Me, too, and hopefully I shed some light on what the length and breadth
of the "nature of RFID" might be. This group, the Internet community,
and the RFID community alike will be ill-served if we restrict our
understanding to what one particular flavor of the technology can
presently accomplish in one particular application.

Dave Husak
Reva Systems

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---

From: Margaret Wasserman <[email-masked]>
Date: Thu, 24 Mar 2005 10:00:16 -0500

>http://www.epcglobalinc.org/standards_technology/Secure/v1.0/UHF-class1.

Yes.  I am so used to thinking of these numbers in terms of 
milliseconds that I failed to convert properly when discussing bits 
per second.  My apologies.

Margaret