Large Wireless networks?

  The task is to create a large (up to 10k nodes) ad-hoc wireless 
network   covering the area of several sq. km, so there is a need for 
many retransmission hops. The nodes are not moving; however the network 
should be able to reconfigure itself once a node is added or deleted. 
The communication in the network is always initiated by a single 
dedicated master. The master needs to collect the  information (~100 
bytes) from the each node once in a while, however it is desired that 
the whole network could be polled in the time of 15 minutes. Power 
consumption does matter; that rules out the 802.11x.

I am looking for the module level solution which would allow to 
implement this network with the minimum hassle. Designing the networking 
protocols is something that I would really like to avoid.

The candidate technology could be ZigBee; however I have big doubts 
about the scalability to 10k nodes. There are some proprietary and 
semi-proprietary solutions on the market; however it looks like they 
never tested it with more then 20...30 nodes.

Can you suggest a more or less proven solution for that type of application?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On Thu, 24 Apr 2008 02:39:32 GMT, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:

>
>  The task is to create a large (up to 10k nodes) ad-hoc wireless 
>network   covering the area of several sq. km, so there is a need for 
>many retransmission hops. The nodes are not moving; however the network 
>should be able to reconfigure itself once a node is added or deleted. 
>The communication in the network is always initiated by a single 
>dedicated master. The master needs to collect the  information (~100 
>bytes) from the each node once in a while, however it is desired that 
>the whole network could be polled in the time of 15 minutes. Power 
>consumption does matter; that rules out the 802.11x.

With those requirements the master can spend only 100 ms with each
slave. Assuming some timeouts and retransmissions, this is quite hard,
even if the data rate is quite low.

In practice, you will need some kind of hierarchial systems, with data
concentrators and thus different frequency channels (or CDMA
sequences).

Since the slaves are not mobile, it would help a lot (in throughput
and power consumption), if you could assign a frequency channel (and
thus a concentrator) based on the approximate geographical location.

Paul

Vladimir Vassilevsky wrote:
> 
> The task is to create a large (up to 10k nodes) ad-hoc wireless
> network   covering the area of several sq. km, so there is a need
> for many retransmission hops. The nodes are not moving; however
> the network should be able to reconfigure itself once a node is
> added or deleted. The communication in the network is always
> initiated by a single dedicated master. The master needs to
> collect the  information (~100 bytes) from the each node once in
> a while, however it is desired that the whole network could be
> polled in the time of 15 minutes. Power consumption does matter;
> that rules out the 802.11x.
> 
> I am looking for the module level solution which would allow to
> implement this network with the minimum hassle. Designing the
> networking protocols is something that I would really like to
> avoid.

While I would probably be amused by that section.  No, I am not
applying for anything.  However, you have omitted some critical
information, such as communication rate over the network, and
communication density.  From your numbers addressing requires at
least a 14 bit unsigned quantity.  Polling 10k items in 15 minutes
from a single point leaves an absolute max of 9000 / 10k ~= 1 sec
per poll.  That ignores any retransmissions needed.  Sounds like
the addresses have to be position dependant.  These are just
initial thoughts.

-- 
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: <http://cbfalconer.home.att.net>
            Try the download section.


** Posted from http://www.teranews.com **

"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> a &#4294967295;crit dans le message 
de news: EpSPj.236$506.213@newssvr27.news.prodigy.net...
>
>  The task is to create a large (up to 10k nodes) ad-hoc wireless network 
> covering the area of several sq. km, so there is a need for many 
> retransmission hops. The nodes are not moving; however the network should 
> be able to reconfigure itself once a node is added or deleted. The 
> communication in the network is always initiated by a single dedicated 
> master. The master needs to collect the  information (~100 bytes) from the 
> each node once in a while, however it is desired that the whole network 
> could be polled in the time of 15 minutes. Power consumption does matter; 
> that rules out the 802.11x.

Hi Vladimir,
We are right now developping a quite similar project. Constraints on our 
project were to get short data messages from up to 1000 moving nodes in 
"real time", meaning no longer than 20 seconds for the 1000 nodes, with low 
power consumption (around 1mA average). We quicly concluded that no standard 
protocol was applicable, and in particular not Zigbee due to the heavy 
dataflow and node count. We (unfortunatly) ended up with the design of a 
custom TDMA & FDMA protocol working in the 868MHz european ISM band, with a 
lot of cautions regarding regulatory frequency use constraints (duty cycle, 
etc). In order to reduce power the only reasonnable solution was however to 
allow the end node to initiate the communication. Design is still on going 
but that's a really interesting kind of project...
Yours,

-- 
Robert Lacoste
ALCIOM - The mixed signal experts
www.alciom.com

On Thu, 24 Apr 2008 00:53:45 -0400, CBFalconer <cbfalconer@yahoo.com>
wrote:

> Polling 10k items in 15 minutes
>from a single point leaves an absolute max of 9000 / 10k ~= 1 sec
>per poll.  That ignores any retransmissions needed.  

You must have short seconds where you live, if you managed to get 9000
into 15 minutes :-).

In any half-duplex protocol, the Rx/Tx turnaround delay is critical in
order to get a decent throughput. Any receiver with ordinary IF and a
single PLL frequency synthesizer should be avoided, since the PLL
would have to swing from the Rx local oscillator frequency to the
transmit frequency, which can take a quite long time, before the
transmission can begin. Using a zero-IF receiver or separate PLLs for
Rx and Tx would be OK.

One way to reduce the effects of Rx/Tx delays would be to use a TDMA
system, in which the master sends a common sync message and each slave
has a time slot based on the node-ID in which it has to transmit. The
distances in the OP's case are so small, that the two-way propagation
delay is only a few microseconds, so you do not have to leave large
guard bands into the slot or use some GSM style propagation delay
compensation.

In TDMA or ordinary master/slave systems, in order to reduce the slave
power consumption, the master should use a fixed poll cycle, thus the
slave receiver could be turned of for most of the polling cycle  and
be activated just slightly prior to the expected poll to this slave
(as in DVB-H).

Paul

Paul Keinanen wrote:
> CBFalconer <cbfalconer@yahoo.com> wrote:
> 
>> Polling 10k items in 15 minutes
>>
>> from a single point leaves an absolute max of 9000 / 10k ~= 1 sec
>> per poll.  That ignores any retransmissions needed.
> 
> You must have short seconds where you live, if you managed to get
> 9000 into 15 minutes :-).

Yeah, we specialize in deci-secs.  :-)

-- 
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: <http://cbfalconer.home.att.net>
            Try the download section.


** Posted from http://www.teranews.com **

Vladimir Vassilevsky wrote:
 >
 >  The task is to create a large (up to 10k nodes) ad-hoc wireless
 > network   covering the area of several sq. km, so there is a need for
 > many retransmission hops. The nodes are not moving; however the network
 > should be able to reconfigure itself once a node is added or deleted.
 > The communication in the network is always initiated by a single
 > dedicated master. The master needs to collect the  information (~100
 > bytes) from the each node once in a while, however it is desired that
 > the whole network could be polled in the time of 15 minutes. Power
 > consumption does matter; that rules out the 802.11x.
 >
 > I am looking for the module level solution which would allow to
 > implement this network with the minimum hassle. Designing the networking
 > protocols is something that I would really like to avoid.
 >
 > The candidate technology could be ZigBee; however I have big doubts
 > about the scalability to 10k nodes. There are some proprietary and
 > semi-proprietary solutions on the market; however it looks like they
 > never tested it with more then 20...30 nodes.
 >
 > Can you suggest a more or less proven solution for that type of
 > application?
 >
 >
 > Vladimir Vassilevsky
 > DSP and Mixed Signal Design Consultant
 > http://www.abvolt.com


Consider trying http://www.inovonics.com/

They may have an off-the-shelf answer.   I don't work for them or 
represent them in any way.  I am not overly familiar with their offerings.

I used one of their products to implement a custom solution years ago. 
Their product was solid and easy to use.

Cheers,
Jody

Un bel giorno Vladimir Vassilevsky digit�:

> Power consumption does matter

Define "matter". :)
If something near to 30 mW is acceptable, the easiest and ready-to-go
solution is to use some RF chip with embedded packet handling, for example
the Nordic chips (nRF24L01, or nRF24LU1 if costs requirements are tight and
an 8051 MCU is enough).

Scalability doesn't look to be a problem, if you have a point-multipoint
architecture (a single master). IIRC the entire send-acknowlesge sequence
of nRF24L01's proprietary protocol needs something in the range 1-10 ms,
depending on how many retransmissions you set.

-- 
emboliaschizoide.splinder.com

Vladimir Vassilevsky wrote:

>  The task is to create a large (up to 10k nodes) ad-hoc wireless 
> network   covering the area of several sq. km, so there is a need for 
> many retransmission hops. 

That, and considerable transmission strength even for individual hops. 
10k nodes spread over several km^2 means you're looking at over 20 
meters average node distance --- each node has several 100 m^2 to itself!

> The communication in the network is always initiated by a single 
> dedicated master. 

That's a bad idea, I think.  It doubles the network's latency for no 
positive effect.

> The master needs to collect the  information (~100 
> bytes) from the each node once in a while, however it is desired that 
> the whole network could be polled in the time of 15 minutes.

So the master needs 1 Mbyte/s of bandwidth --- so will the individual 
nodes, because any of them may have to be able to bridge large parts of 
the master's throughput.  That runs seriously afoul of this requirement:

> Power consumption does matter; that rules out the 802.11x.

Well, you'll need a good part of its bandwidth, more than its (reliable) 
distance, and way more than its capacity in terms of number of nodes in 
the net.  In other words, you're trying to put to shame an entire 
industry that is putting a lot of time and money into out-performing 
each other on all these aspects.  Good luck --- you'll need it

Un bel giorno dalai lamah digit�:

>> covering the area of several sq. km, so there is a need for 
>> many retransmission hops

Ooops, I didn't notice the multiple hops thing. It's much easier if you can
install a big and high antenna on the master station so that you can
separately contact every client. "Several square kilometers" could mean a
maximum distance of 2-3 km from the master station; I think that it's a lot
easier to find a way to reach that range obeying the ITU/FCC/etc rules on
tx power, rather than building a complex mesh network with 10k clients
based on a trivial, lightweight protocol.
Using the 868/900 MHz ISM band instead of the 2.4 GHz band could help.

-- 
emboliaschizoide.splinder.com