Subject: [6lowpan] Regarding coexistence with 802.11n

From: "Mustafa Hasan" <[email-masked]>
Date: Fri, 4 Jul 2008 09:04:43 -0700

Dear 6lowpaner,

I need little help regarding the coexistence issue of ISM Band with
other ISM, especially with the 802.11n, 802.11b.

I want to know what are the factor is going to save the 802.15.4
fighting with others frequency.

Thanks in Advance...

Regards

M. Hasan
_______________________________________________
6lowpan mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/6lowpan

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From: Geoff Mulligan <[email-masked]>
Date: Mon, 07 Jul 2008 09:30:38 -0600

Appendix E of the 802.15.4 standard goes into detail on co-existence.

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From: "Adams Jon" <[email-masked]>
Date: Mon, 14 Jul 2008 17:54:29 -0700

Good afternoon, Hasan (and Geoff)

Appendix e does discuss a number of mitigation factors designed into
802.15.4 to improve its ability to coexist with other 802 as well as a
narrow class of known interferers. Two important features are the
non-alignment of of 802.11 channels with that of 802.15.4 channels in
the 2400MHz band. This in theory allows an 802.15.4 station to operate
away from a given 802.11 station in the immediate vicinity and even
provides (in many regulatory domains) a few 15.4 channels that are
completely clear of 802.11 channels. The other is the temporal agility
of the 15.4 radio and the brevity of conversations (low duty cycle)- the
fact that clear channel assessment and an entire 802.15.4 conversation
(data transmission and acknowledgement) can occur in a few milliseconds.
This means that 802.15.4 transceivers can take advantage of small gaps
in conversations taking place between 802.11 equipment, the off times
for consumer microwave ovens, etc. 

There is a real issue with 802.11n in 40MHz channels, one that was not
perceived long ago. As it is described right now, the expectation by a
number of 802.11 voters is to allow 2 channels of non-overlapping
40MHz-wide operation in the US 2400-2483.5MHz band (and likely in other
regions/countries as well). If there is agreement on this, there will be
locations (likely many) where both 40MHz channels are occupied and used
intensively. With two heavily loaded 11n channels and a number of hidden
transmitters, it may prove difficult for 802.15.4 stations to compete
successfully as there will be NO clear channels and only the temporal
agility of the 15.4 radio gives it a chance to communicate.

Sincerely, Jon
 
Jon Adams
Business Development, Wireless Connectivity Operation
Freescale Semiconductor
2100 E Elliot Rd MD EL 542
Tempe, AZ 85284
+1 480.628.6686 mobile
+1 480.413.3439 office
[email-masked]

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Geoff Mulligan
Sent: Monday, July 07, 2008 8:31 AM
To: Mustafa Hasan
Cc: [email-masked]
Subject: Re: [6lowpan] Regarding coexistence with 802.11n

---

From: "Mustafa Hasan" <[email-masked]>
Date: Tue, 15 Jul 2008 06:08:01 -0700

Dear Jon & Geoff,

Thank you very much for such a nice and detail mail.... It helped me a
lot. I want to add few comments regarding this issues, after my little
research in this field.

1. Even thr are some free channels available for different region, but
still creating problem for IEEE802.15.4 traffic. Actually, high power
of wifi is killing ieee802.15.4 traffic (testbed results).

2. The current research on this issue is interestingly biased, some
are saying its not a big problem (e.g ZigBee Alliance) and others
(e.g. Z-Wave Alliance) are saying its a big issue.

3. Distance between ieee802.15.4 and ieee802.11x is a big problem in
this case. If I summarize all the research efforts (ieee802.19
coexistence assurance documents, white paper(ZigBee, Z-Wave) and many
research papers), its not possible that 15.4 & 11x stay together in a
distance of <2 meters (even tried with offset 20MHz).

4. thr are many potential application require this distance to be in
few centimeters. May be some technique in upper layers can give little
bit reliability... but is it enough???

I am looking for some help, comments and suggestion, how coexistence
problem can be solved for very short distance scenario...

Thank you.......

Regards

M. Hasan

---

From: "Christian Herzog" <[email-masked]>
Date: Tue, 15 Jul 2008 10:44:21 -0500

> From: [email-masked] 
> [mailto:[email-masked]] On Behalf Of Mustafa Hasan
> Sent: Tuesday, July 15, 2008 8:08 AM
> To: Adams Jon; [email-masked]
> Cc: [email-masked]

The 802 family of standards has some modicum of coexistence "built-in"
as Jon suggested - our experience is that a serious interference
source are non-802 devices including various FHSS devices that pay
little to no heed to whatever else is in the band.  The often have no
coexistence considerations and blatantly use the band as if they were
the only device in town.

Some of these devices are getting smarter though (but for their own
selfish reasons).  Various first generation 2.4GHz cordless phones
used to horrible spectrum users by using the entire 2.4GHz band with
little regard for anything else.  They seem to be taking some steps
now to segment the band and avoid Wi-Fi sized areas now; probably not
to help Wi-Fi but to make themselves work better by avoiding sections
of the band that don't work well for *them*.

> distance of <2 meters (even tried with offset 20MHz).

Our practical experience is 2 meters is plenty in most situations,
even 1 meter is enough but getting riskier.

A lot of the vendor/organization white papers seem incredibly biased
to me and upon reading them, I basically get the idea that the network
running right on my desk couldn't possibly work (and might even kill
me ;) when clearly it is working.

> problem can be solved for very short distance scenario...

For a few centimeters, this problem may very well be unsolvable (at
reasonable cost/effort).  The only way the upper layers can
accommodate something as brutal as this is through coordination and
knowing that the radio will effectively be "blinded" at specific
times.  For uncoordinated networks, this isn't really practical.

At centimeter distances, *everything* can act like an antenna and it
is very easy to saturate a radio receiver which effectively blinds it
from receiving anything - as you pointed out, even significant
frequency separation isn't enough when things are closely located;
there is just so far to run in a relatively small band.

Even closely located *receivers* can interfere with each other even if
they never transmit; we have had to use shielding between closely
colocated receivers in some multi-receiver designs to prevent them
from interfering with each other.  In simple terms, if it oscillates,
it radiates and something either sensitive enough or close enough will
get effected by such radiation possibly to the point of incorrect
operation.

Few centimeter separation of transmitters is a difficult problem to
solve and would likely be out of scope of this effort.

--
Christian Herzog           Software Technologies Group, Inc.
mailto:[email-masked]         http://www.stg.com
+1 (708) 547-0110 x225     FAX +1 (708) 547-0783

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From: "Benjamin A. Rolfe" <[email-masked]>
Date: Tue, 15 Jul 2008 08:57:31 -0700

Jon gives an excellent summary of the current situation. I'll elaborate 
slightly on a few points....

> perceived long ago.

This issue was raised quite some time ago. That is one reason it has become 
a bit contentious now.  'nuff said...

> As it is described right now, the expectation by a

Additionally, the usage models and applications discussed by TGn raise 
concernes of near 100% occupation in time as well as frequency. Systems such 
as Bluetooth and 802.15.4 depend on other services leaving some time to 
squeak in, as well.  There is a perception that 11n may completely fill the 
band in frequency and in time, which presents much greater conflict than 
with the typical usage models of today.  The most common usage of  802.11g 
today is connecting to the internet, which usually involves a bottleneck of 
6MBps or less between the user and the internet. Thus actually air duty 
cycle for the most common 11g usage scenarios leaves a lot of room in time 
for other services.  Thus explanations offered by TGn based on similarity of 
channel bonding to having multiple 11g APs in the same space have been less 
than reassuring.  I think this is significant.

Another factor is that while operating under the same rules, it is likely 
802.15.4 nodes will be operating at much lower effective transmit power than 
11n (due to focus on low power, low cost implementation).

Alas, the same factors that make 802.15.4 unlikely to interfere with, and 
likely to "lose" contention with an 11n system, also make 15.4 neighbors 
harder for other services such as 11n to detect.

-Ben

---

From: "Adams Jon" <[email-masked]>
Date: Tue, 15 Jul 2008 10:34:58 -0700

-----Original Message-----
From: Mustafa Hasan [mailto:[email-masked]] 
Sent: Tuesday, July 15, 2008 6:08 AM
To: Adams Jon; [email-masked]
Cc: [email-masked]
Subject: Re: [6lowpan] Regarding coexistence with 802.11n

>2. The current research on this issue is interestingly biased, some are
saying its not a big
>problem (e.g ZigBee Alliance) and others (e.g. Z-Wave Alliance) are
saying its a big issue.

<ADAMS> Beware of wild claims %^). At least in the US, the 902MHz band
has enjoyed a huge resurgence of uses as well as a strengthening of
licensed uses. As many do not realize, the 902-928MHz band has some
licensed users including location services and amateur radio, in
addition to a huge and growing amount of license-free users. 

For the license-free users, it's the location and monitoring services
(LMS) though, that is most concerning from a usability point of view.
Back in the early 1990's, before the price of GPS receivers dropped much
below US$1k, several companies in the US were able to get licenses to
occupy 6MHz wide channels in the 902MHz band with fairly high power
mountaintop or towertop radios. The object was to provide trilateration
services to mobile receivers in delivery trucks, theft recovery services
for automobiles, etc. Well, the price of GPS dropped more quickly than
LMS, and the companies went silent, the licenses pretty much worthless.
In the last few years, there has been a LOT of lobbying of the FCC to
repurpose these licenses to allow the licensees to do pretty much
whatever they want with their frequencies, including wireless broadband,
etc. This is a great concern as they are not subject to the power
limitations of Part 15 and in fact at least one licensee wants to exact
some significant restrictions on 900MHz Part 15 devices.

Wireless broadband internet service providers have discovered the
excellent propagation and penetration of 902MHz. It is now common to
find, especially in suburban or rural areas, wireless ISPs delivering
broadband in the 902MHz band, in 5, 10 and even 20MHz bandwidths. The
legal limit there is +36dBm EIRP as well.

Lastly, one significant and continually growing use of the 902MHz band
is wireless metering for electric, gas and water meters. My house has a
900MHz wireless gas meter that blurps out a packet every minute or so.
In dense housing areas the aggregation can be impressive. US railroads
have deployed 900MHz readers for RFID tags that are on about 80% of the
railcar fleet (about 8M railcars) and those readers transmit essentially
a CW carrier at a +44dBm level for several minutes while the train
passes the reader. RFID readers in stores and commercial establishments
are increasingly using 900MHz for illuminating tags using similar power
levels.

Amateur radio is making greater use of the 902MHz band (they're a
primary licensed user). While it's FM narrow-band comms for the most
part (but there is digital QPSK and GMSK as well), the EIRP is typically
in the +43 to +50dBm range for mobile, portable and tower/mountaintop.

The 900MHz band is no panacea. The users there are often digitally
modulated, with power levels from Part 15 levels (+36dBm EIRP) and up. A
truly obsolete technology (narrow-band FSK, traditionally 9600 baud,
with some usage now at 40k baud, single RF channel) like Z-Wave cannot
compete with any of the above uses. Not only is Z-Wave exceedingly slow
and inaccurate in assessing the availability of the channel, its packets
are 40-80ms long, and it isn't detected by the digitally modulated
systems out there, so they punch holes in the packet. FSK requires a
significant SNR (10-15dB) to demodulate successfully, so any
interference can threaten its link performance. The sole Z-Wave
908.42MHz frequency happens to be in the middle of the mobile transmit
side for ham radio, so the ham down the street can saturate a Z-Wave
receiver without even knowing. It's no wonder that the new Z-Wave 401
chip is purported to support the 2.4GHz band.

Now, all of this doesn't mean that somehow the 2.4GHz band is much
better - like Christian and Ben remind us, there's plenty of uses in the
2.4GHz band that aren't too worried about who else is out there.
However, both in-lab extreme testing, real-world testing, and anecdotal
evidence show that 15.4, 802.11, microwave ovens, Bluetooth and cordless
phones aren't necessarily incompatible. Witness the success of 15.4
systems and demonstrations in huge conference arenas like CES in the US,
where the density and average power level of 802.11g systems (nodes on
nearly every channel, even though that doesn't make much sense due to
overlap) conspire only to generally increase latency of the 15.4 system
by a few milliseconds at worst. Our 15.4 systems here at work behave
well even with our very high usage and density of 802.11g systems. Use
of 15.4 systems is most successful for low-duty cycle (<1%), moderate
latency (10ms) uses. As Ben points out, there is significant concern by
many that 802.11n has the potential to not play very fair with the
channel, and make life difficult for the rest of us. This is a good
reason for those of those with voting rights in 802.11 to stand up and
fight against this threat to the 2.4GHz band.
</ADAMS>

Sincerely, Jon
 
Jon Adams

---

From: "Benjamin A. Rolfe" <[email-masked]>
Date: Tue, 15 Jul 2008 10:57:29 -0700

1 meter is *probably* a safe assumption for coexistence of 802.11 and 
802.15.4 in most use cases.
It is definitely *not* a good assumption for 802.11 and BT.   These already 
are collocated in the same deice (phone, PDA, laptop) and require 
simultaneous operation. One reason it works is both are operating at fairly 
low duty cycle today and so there is the opportunity for good luck.  Some 
cleverness, some luck ;-).
-Ben

----- Original Message ----- 
From: "Christian Herzog" <[email-masked]>
To: "'Mustafa Hasan'" <[email-masked]>; "'Adams Jon'" 
<[email-masked]>; <[email-masked]>
Cc: <[email-masked]>
Sent: Tuesday, July 15, 2008 8:44 AM
Subject: Re: [6lowpan] Regarding coexistence with 802.11n

---

From: Carsten Bormann <[email-masked]>
Date: Tue, 15 Jul 2008 21:24:22 +0200

Jon,

this was really useful background material, especially for those of us  
living in GSM 900 land (where 870 to 960 MHz are taken for various  
variants of GSM).

Modern usage models for home WiFi are indeed likely to use much higher  
duty cycles (consider Apple's Time Capsule product, which might do a  
full backup for multiple hours, mostly limited by the bitrate  
achievable over the radio).  Apart from the fact that .11n has  
revitalized 5 GHz usage, the only hope may be that neither the backup  
software nor the MAC is not good enough to go up to 100 %.

However, I'm a bit uneasy with the following part:

> 802.11n has the potential to not play very fair with the

The .11n cat has been out of the bag for slightly more than a year now  
(http://www.wi-fi.org/pressroom_overview.php?newsid=694 -- 325  
approved products, more than half of the WiFi chipsets now); IEEE  
politics won't stop that.
More importantly, I don't think we should use IETF lists for  
attempting to kindle tensions between IEEE groups.

Gruesse, Carsten
(typing this from an IEEE 802.11n laptop to an IEEE 802.11n base  
station which both won't care whether a formal standard exists)