Subject: [manet] Tx Range on Contention

From: "S.Sivavakeesar" <[email-masked]>
Date: Sun, 20 Mar 2005 14:43:17 -0000

Dear All :
 
I am sure some of you guys who deal with Tx power/range control in MANETcan answer my question. Considering IEEE 802.11 a/b/g  DCF based operation as the underlying MAC, can we assume that increase of Tx range would result in reduced contention for a given MANET having a constant load and node-density. If I refine my question, does Tx range have any impact on MAC-level contention - surely yes, but how ?. I am currently reading a paper, in which it is stated that under heavy loaded condition, increasing the Tx range would increase the overall throughput - Is it true ? As per my understanding, inccreasing the Tx range would result in increased contention, and hence lead to reduced throughput. Can any one clarify this for me please.
 
Thanks in advance for your invaluable time.
 
Cheers
 
Siva
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From: Hasan Raza <[email-masked]>
Date: Mon, 21 Mar 2005 00:57:23 +0530 (IST)

> under heavy loaded condition, increasing the Tx range would increase the
> overall throughput - Is it true ? As per my understanding, inccreasing
> the Tx range would result in increased contention, and hence lead to
> reduced throughput.

If you are talking about adjusting the tx power for each individual tx-rx
pair (link), then it might be true. More number of links can be packed in
the network by adjusting the power of the links. An incoming link might
not be able to join the network (due to lower SIR at receiver)  unless the
transmitter increases its power. However, increasing the power must be in
a controlled fashion such that other links' SIR is not deteriorated below
the required threshold.

Regards.
Hasan

On Sun, 20 Mar 2005, S.Sivavakeesar wrote:

> Dear All :
>
> I am sure some of you guys who deal with Tx power/range control in MANETcan answer my question.
> Considering IEEE 802.11 a/b/g  DCF based operation as the underlying MAC, can we assume that
> increase of Tx range would result in reduced contention for a given  MANET having a constant
> load and node-density. If I refine my question, does Tx range have any impact on MAC-level
> contention - surely yes, but how ?. I am currently reading a paper, in which it is stated that
> under heavy loaded condition, increasing the Tx range would increase the overall throughput -
> Is it true ? As per my understanding, inccreasing the Tx range would result in increased
> contention, and hence lead to reduced throughput. Can any one clarify this for me please.
>

---

From: [email-masked]
Date: Mon, 21 Mar 2005 11:13:12 +0100 (CET)

Dear Sivavakeesar ;==),

 You can find a detail on how common-range and varaiable transmission
range techniques (IEEE 802.11 as well as most CSMA MAC protocols use a
common-range transmission and are not flexible enough to exploit the
spectral reuse of the network) impact a number of system performance
metrics such as the connectivity, capacity and powerconserving properties
of wireless ad hoc networls in this paper:

"A Case for variable-Range Transmission Power Control in Wireless Ad Hoc
Networks" infocom 2004.

Regards

Hakim

> Dear All :
>
> I am sure some of you guys who deal with Tx power/range control in
> MANETcan answer my question. Considering IEEE 802.11 a/b/g  DCF based
> operation as the underlying MAC, can we assume that increase of Tx range
> would result in reduced contention for a given MANET having a constant
> load and node-density. If I refine my question, does Tx range have any
> impact on MAC-level contention - surely yes, but how ?. I am currently
> reading a paper, in which it is stated that under heavy loaded condition,
> increasing the Tx range would increase the overall throughput - Is it true
> ? As per my understanding, inccreasing the Tx range would result in
> increased contention, and hence lead to reduced throughput. Can any one
> clarify this for me please.
>

---

From: Christian de Waal <[email-masked]>
Date: Tue, 22 Mar 2005 08:56:08 +0100

Dear Siva, dear MANET list,

I believe the paper you mention is the paper by Park and Sivakumar, 
"Load-sensitive tx power control...".

We have looked closely at the influence of transmission power control on 
the throughput both from a high-level point of view as well as using 
ns-2 simulations, because we found it quite peculiar that on the one 
hand, there is work indicating that unnecessarily high tx powers should 
result in a reduced spatial reuse and thus in reduced throughput, 
whereas on the other hand, there is work presenting simulation results 
showing that increasing tx power also increases throughput (e.g. the 
Park/Sivakumar paper).

The solution is that it actually depends on the size of the network 
which of the above is true: The more stations the network consists of, 
the more can be gained by reducing the tx powers / increasing spatial 
reuse, as we explain in [1]. The reason Park and Sivakumar find that 
increasing tx power unconditionally increases the throughput is that 
their scenarios have no more than 100 nodes. In [2], we show that the 
situation for networks with 500 nodes is different. (Actually, Park and 
Sivakumar also note that things might be different for larger networks 
in another paper [3], but they disregard networks with more than 100 
nodes as "untypical MANET scenarios".)

I hope this helps to clarify the seemingly contradictory statements on 
this issue found in the literature.

Best regards,
Christian de Waal

[1] Michael Gerharz, Christian de Waal, Matthias Frank, Peter Martini, 
"Influence Of Transmission Power Control On The Transport Capacity of 
Wireless Multihop Networks", Proc. of the 15th IEEE International 
Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 
Barcelona, Spain, September 2004, 
http://web.informatik.uni-bonn.de/IV/Mitarbeiter/dewaal/pimrc04.html

[2] Michael Gerharz, Christian de Waal, Peter Martini, Paul James, "A 
Cooperative Nearest Neighbours Topology Control Algorithm for Wireless 
Ad Hoc Networks", Telecommunication Systems, Vol. 28, No. 3-4, pp. 
317-331, March 2005, 
http://www.springerlink.com/openurl.asp?genre=article&issn=1018-4864&volume=28&issue=3&spage=317

[3] Seung-Jong Park, Raghupathy Sivakumar, "Quantitative Analysis of 
Transmission Power Control in Wireless Ad-hoc Networks", Proc. 31st 
International Conference on Parallel Processing Workshops (ICPP 
Workshops), pp. 56-63, August 2002

S.Sivavakeesar wrote:
> ------------------------------------------------------------------------
> 

-- 
____________________________________________________________________
Christian de Waal

University of Bonn                            Phone: +49 228 73-4548
Institute of Computer Science IV                Fax: +49 228 73-4571
Roemerstr. 164                         E-mail: [email-masked]
53117 Bonn, Germany                    http://www.cs.uni-bonn.de/IV/