Subject: Re: [Fwd: Re: [manet] Power Saving in 802.11]

From: Jean Lorchat <[email-masked]>
Date: Tue, 04 Nov 2003 11:09:32 +0100

Hi Peter & Justin,

If you want some in-depth measurements and models, you can also consider the following
reports (especially for TX power differences) :

http://www.tkn.tu-berlin.de/publications/papers/tr_01_007.pdf
and
http://www.tkn.tu-berlin.de/publications/papers/networking2002_withcover.pdf

Jean

> Hi Peter,
> 
>> Thanks for the info. I really appreaciate this.
>> However, it is questionable whether the model is close to the reality.
>> In some other paper, in the receiving mode and idle mode, the node
>> spends the same amount of energy approximately no matter whether it
>> actually receives the data or not.
> 
> 
> If you consider Feeny's measurements.
> Idle power : 843mW , Receive power : 967mW , Transmit power : 1327mW.
> 
> The model could probably be adapted to encorporate these values 
> including idle
> time etc.  However, Im pretty sure Feeny's paper has some linear models of
> consumption, does it not? I also think that differences between idle, 
> receive
> and transmit power consumption are important when one considers the total
> number of packets sent and received by all nodes. Thus I think the validity
> of the model really depends on how you intend to use and interpret the
> results.
> 
> One more point, since I know you are looking at power saving schemes for ad
> hoc networks. Perhaps you should look at something along the lines of
> Activity Scheduling as described in:
> 
> J. Shaikh, J. Solano, I. Stojmenovic and J. Wu, New metrics for 
> dominating set
> based energy efficient activity scheduling in ad hoc networks, Proc. WLN
> Workshop at IEEE Conf. on Local Computer Networks, Bonn, Germany, Oct. 
> 20-24,
> 2003.
> 
> It would be very interesting to find out the differences between idle, 
> receive
> and transmit in newer 802.11 cards.
> 
>> Furthermore, it does not model the fact that for a sent packet every
>> node around the sending station in a certain range will  ``hear'' the
>> packet thus will consume energy.
> 
> 
> Yes it does. If you want to model the energy consumed by a broadcast, then
> every node upon receiving a k-bit frame should adjust its available 
> energy by
> E_rx(k). Likewise the transmitting node should adjust its remaining 
> energy by
> E_tx(k,d). It just does not account for idle energy over time.
> 
> cheerio,
> Justin
> 

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---

From: Justin Lipman <[email-masked]>
Date: Tue, 4 Nov 2003 21:52:19 +1100

Jean,

Thats excellent! Thankyou!

From your conclusion (quick read), it would seem that the first order radio 
model I quoted is reasonably accurate in terms of reception and transmission?

Cheers,
Justin

-- 
PhD Candidate
Telecommunications & Information Technology Research Institute
School of Computer, Electrical & Telecommunications Engineering
University of Wollongong, Australia 
http://www.titr.uow.edu.au/~justin

On Tue, 4 Nov 2003 09:09 pm, Jean Lorchat wrote:
> Hi Peter & Justin,
>
> If you want some in-depth measurements and models, you can also consider
> the following reports (especially for TX power differences) :
>
> > time etc.  However, Im pretty sure Feeny's paper has some linear models
> > of consumption, does it not? I also think that differences between idle,
> > receive
> > number of packets sent and received by all nodes. Thus I think the
> > validity of the model really depends on how you intend to use and
> > interpret the results.
> >
> > One more point, since I know you are looking at power saving schemes for
> > ad hoc networks. Perhaps you should look at something along the lines of
> > Yes it does. If you want to model the energy consumed by a broadcast,
> > then every node upon receiving a k-bit frame should adjust its available
> > energy by

---

From: Jean Lorchat <[email-masked]>
Date: Tue, 04 Nov 2003 14:30:24 +0100

Hi Justin,

> model I quoted is reasonably accurate in terms of reception and transmission?

Although these are not my conclusions (I'm not the author), that's what it seems.
However, I think that John is right when he states that we should differenciate
so-called idle mode corresponding to "discarding a packet not intended to us" and
real sleep mode that 802.11 hardware is capable of (namely PSP in infrastructures).
But knowing this, you must also have a way to use it in adhoc mode (and I don't know
whether adhoc PSP is a good solution for manets...) ? or do you mean MAC modifications ?

Jean

---

From: Peter Pham <[email-masked]>
Date: Thu, 06 Nov 2003 12:29:06 +1030

Hi

I am really interested in the time switch between the ``sleep'' state to 
other state.

By the spec, the turn around time between Tx and Rx must be less than 
5micro sec. However it does not state this. I guess it should be in 
order of few microsec right ?

Although, it is easily modelled in ns2 or Glomosim, is it feasible in 
practice ?...What I mean is is that possible we can control the NIC card 
as that easy ?. For example, can we change the Tx power as any level as 
we wish at anytime. Can we set the card to sleep mode and turn it back 
on at anytime as we wish.

Is there anyone has any info on this...I appreciate some ``real'' 
knowledge on this.

Cheers
Peter Pham

Jean Lorchat wrote:

> Hi Justin,
>
>> From your conclusion (quick read), it would seem that the first order 
>> radio model I quoted is reasonably accurate in terms of reception and 
>> transmission?
>
>

---

From: "dholmer" <[email-masked]>
Date: Thu, 6 Nov 2003 19:03:08 -0500

The turnaround time from Tx to Rx cited in the 802.11 spec deals with a
somewhat different area than the power saving state transitions. A while
back I downloaded a document from Intersil called "PRISM Power
Management Modes" (application note AN9665) that was dated February
1997. This document details the power saving states of the original
PRISM chipset, current consumption, and most interestingly the time
needed to transition between these states. What I hadn't known before
reading this document, was that there isn't just one "sleep" mode, but a
number of different levels of power saving modes. Each mode corresponds
to deactivating a larger and larger fraction of the radio hardware. The
result of this is that "deeper" sleep modes consume less power, but take
more time to wake up from because more hardware must be reinitialized
and stabilized. Here is a basic summery of the operating modes they
described:

       Mode           Current  Recovery Time
Transmit (continuous)  488mA          NA
Receive  (continuous)  287mA          NA
Power Saving Mode 1    190mA        1 us
Power Saving Mode 2     70mA       25 us
Power Saving Mode 3     60mA     2000 us (2 ms)
Power Saving Mode 4     30mA     5000 us (5 ms)

Going from an active mode to a power saving mode takes essentially zero
time, but the time till fully active from a given power saving mode
takes the time listed in the table above. The wakeup process seems to
transition up through the power states, with some brief (10us) power
spikes when transitions are made. In other words, if you are in power
saving mode 4 (consuming 30mA) and are scheduled to be active at time T,
you begin by transitioning to power saving mode 3 at T minus 5000 us.
After a brief power spike, you'll be consuming 60 mA until T minus 2000
us when you transition to power saving mode 2. After another brief power
spike you consume 70 mA until T minus 25 us when you go to power saving
mode 1. Then you consume 190 mA until T minus 1 us when you make the
final transition to active mode. A graphical representation of this is
shown at the end of the document.

It seems that as long as we are setting sleep times for >5ms then the
turn on time isn't going to be much of a problem in actual
implementations. Obviously these numbers will be different for cards
with different chipsets, but the order of magnitude in timing should
probably be the same.

Now for your other question on how feasible is it to control the power
saving state of an actual NIC card. I haven't had that much experience
with attempting that yet. The real question is if that functionality is
available at the driver level, or if it is only a firmware controlled
feature. A quick search through the Linux open source orinoco driver
(which actually supports many types of cards) yielded no promising leads
for manual power control. However many options for enabling the default
802.11 PSM and tweaking its parameters were available. In a pinch, it
may be possible to switch the card in and out of PSM with very long
beacon intervals, but some in depth experimentation would be necessary
to test this out.

David Holmer

PS I had trouble locating a link to the Intersil application note. If it
has been removed, people can email me directly for a copy.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Peter Pham
Sent: Wednesday, November 05, 2003 8:59 PM
To: Jean Lorchat; MANET
Subject: Re: [Fwd: Re: [manet] Power Saving in 802.11]

Hi

other state.

Cheers
Peter Pham

> so-called idle mode corresponding to "discarding a packet not intended

> to us" and

---

From: [email-masked]
Date: Fri, 7 Nov 2003 07:33:10 +0100

Hi all !
> Power Saving Mode 4     30mA     5000 us (5 ms)

very interesting...
> (which actually supports many types of cards) yielded no promising leads
However, there are cards with no firmware and almost open-source driver that
look very promising, using Atheros chipset. See the madwifi project
http://www.sourceforge.net/projects/madwifi. 

> beacon intervals, but some in depth experimentation would be necessary
I think that this should work for adhoc, although an answer may be needed to the
PS mode frame by the IBSS master depending on the firmware, not sure of this one
though. As you said, experimentation needed...

Jean

---

From: Miguel Sanchez <[email-masked]>
Date: Thu, 13 Nov 2003 15:43:34 +0100

Hi,

You may want to look for tech specs of Aironet Cisco 340 and 350 series
adapters.
I think 340 allow 4 power levels and 350 six different power levels,
software selectable. I haven't researched how long does a power change
to become effective though.

I think this paper
[http://black1.csl.uiuc.edu/~prkumar/ps_files/compow.pdf] uses these
cards to adapt transmission power level.  They did a real implementation
using Linux. I guess the paper will give you some of the details my
answer is lacking.

Best regards,

Miguel Sánchez
Polytechnic University of Valencia, Spain

dholmer wrote:

>...