Subject: Re: [manet] Tx Range on Contention

From: Huixian <[email-masked]>
Date: Mon, 21 Mar 2005 08:30:56 +0800

Hi Siva,

There are a few factors to take into consideration, when evaluating the 
effects of the Tx range on throughput. Some of these factors include 
node mobility, node density and traffic load.

Having a higher Tx range will tend to increase the contention at the MAC 
layer, lead to higher probability of collisions and reduce the spatial 
reuse of the channel. However, higher Tx range will also lead to shorter 
path lengths and therefore, less frequent link breakages.

I think you need to consider the above mentioned factors when evaluating 
the effects of adjusting the Tx power on throughput. In general,  
increasing the Tx power (and hence the range) will tend to increase the 
throughput during high node mobility. If you increase your node density 
gradually, you will find that your throughput starts to drop due to the 
increased contention and decreased spatial reuse.

Hope this helps!

regards
Hwee-Xian Tan
School of Computing
National University of Singapore

>Today's Topics:
>
>   1. Tx Range on Contention (S.Sivavakeesar)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Sun, 20 Mar 2005 14:43:17 -0000
>From: "S.Sivavakeesar" <[email-masked]>
>Subject: [manet] Tx Range on Contention
>To: manet <[email-masked]>
>Message-ID:
>	<[email-masked]>
>Content-Type: text/plain; charset="iso-8859-1"
>
>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: "S.Sivavakeesar" <[email-masked]>
Date: Mon, 21 Mar 2005 09:24:09 -0000

Dear Huixian :
 
Thanks for your mail. I think it is better for me to put my question in a different way. Given a static MANET having a constant traffic load, node-density, and terrain-range, what happens to the throughput if we change the tx range only. ie. I need a graph of throughput V tx range. Can you say something about the pattern of this graph (every thing is unchanged except the tx range) ?
 
Thanks in advance for your invaluable time
 
Cheers
 
Siva

 

Date: Mon, 21 Mar 2005 08:30:56 +0800
From: Huixian <[email-masked]>
Subject: Re: [manet] Tx Range on Contention
To: [email-masked]
Message-ID: <[email-masked]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hi Siva,

Hope this helps!

regards
Hwee-Xian Tan
School of Computing

---

From: Dr John P Mullen <[email-masked]>
Date: Mon, 21 Mar 2005 20:46:28 -0700 (MST)

Hi Siva,

As Tan pointed out, it depends.  As transmit range is increased,  
throughput could either increase or decrease, depending on the nature 
of the load, etc.  

However, it is more likely to decrease throughput in a situation in 
which  many node pairs are communicating with each other.

If I double power, terrain permitting, I can double range and decrease 
the number of links required to complete a transmission, but this will 
not help paths that are already one hop long.  On the other hand, 
although I double my range, I more than quadruple the area over which I 
might interfere with other traffic.  This occurs because 1) while range 
is linear, interference involves area and 2) at LOS frequencies and 
moderate bit rates, the maximum interference range is significantly 
greater than the maximum communications range. So, in most cases, I 
would ecpect such a tactic to  cause more problems than it solves.

John Mullen

S.Sivavakeesar wrote:

>Dear Huixian :
> 
>Thanks for your mail. I think it is better for me to put my question in 
a different way. Given a static MANET having a constant traffic load, 
node-density, and terrain-range, what happens to the throughput if we 
change the tx range only. ie. I need a graph of throughput V tx range. 
Can you say something about the pattern of this graph (every thing is 
unchanged except the tx range) ?
>National University of Singapore

------------------------------------------------------------------------

---

From: "S.Sivavakeesar" <[email-masked]>
Date: Tue, 22 Mar 2005 10:11:49 -0000

Dear Christian :
 
Thanks for your information. Although the classification of MANETs into typical and generic MANETs is ok to a certain extent, any proposed algorithm/protocol should be robust and work in any environment. The authors argument that their proposed method works only in one environment but not in the other is not reasonable. In this regard, the authors can't simply make a general statement that increasing the Tx Range (for all nodes at the same time) would bring in improvement in terms of contention delay and throughput.
 
Cheers
 
Siva

________________________________

From: Christian de Waal [mailto:[email-masked]]
Sent: Tue 3/22/2005 7:56 AM
To: Sivavakeesar S Mr (PG/R - CCSR)
Cc: [email-masked]
Subject: Re: [manet] Tx Range on Contention

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

--
____________________________________________________________________
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/