[Tinyos-devel] RE: [Tinyos-help] shorter (cc2420/telosb) radio range in t2 compared tot1?

[Omprakash Gnawali]

I think he is talking about a shorter range and not lower
throughput. He says whenever he sends a broadcast packet, fewer nodes
receive that broadcast pkt in T2 than in T1.

- om_p

> Here's one possible explanation: the CSMA backoff changed between T1 and T2.
> 
> In T1, the CSMA backoff wasn't very fair, allowing one transmitter to
> possibly hog the channel.  The CSMA congestion and initial backoffs were
> flipped in T2, making the initial backoff longer and the congestion backoff
> shorter.  This causes less throughput but an increase in fairness.
> 
> This brings up a good point though: more energy is consumed in T2 to deliver
> the same amount of information because throughput is diminished. We should
> explore turning the radio to IDLE during CSMA backoff wait periods to see
> how that impacts energy consumption and throughput.
>  
> -David
> 
> 
> 
> -----Original Message-----
> From: tinyos-help-bounces at Millennium.Berkeley.EDU
> [mailto:tinyos-help-bounces at Millennium.Berkeley.EDU] On Behalf Of Jeongyeup
> Paek
> Sent: Tuesday, October 30, 2007 12:33 AM
> To: tinyos-help
> Subject: [Tinyos-help] shorter (cc2420/telosb) radio range in t2 compared
> tot1?
> 
> Dear all.
> 
> I am running a very simple test applications where
> 40 nodes are broadcasting packets every 10 sec,
> and a BaseStation node is listening to those packets.
> 
> And I am receiving far less packets in t2, compared to t1,
> for (what I believe to be) the same application.
> So I was wondering whether anyone had experienced
> shorter radio range in t2 compared to t1.
> 
> The exact scenario is, 40 telosb nodes,
> with & without 'CFLAGS += -DCC2420_DEF_RFPOWER=31',
> on an indoor testbed (http://enl.usc.edu/projects/tutornet/)
> where node 1~40 are sending broadcasts and node 10 is the BaseStation.
> I ran experiments several times, for several tens of minutes each time,
> and tried channel 23 and 26.
> Also, although I am new to T2, I have some experiences with T1.
> 
> In T1, I receive packets from 15~20 nodes on average.
> In T2, I receive packets from 8~12 nodes on average.
> 
> And the only guess that I can think of
> (assuming that I've done t1->t2 poring correctly)
> is shorter radio range in t2 compared to t1.... for some weird reason.
> 
> is this possible?
> 
> -- 
> Jeongyeup Paek
> Ph.D. student
> Embedded Networks Laboratory
> Department of Computer Science
> University of Southern California
> http://enl.usc.edu/~jpaek
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