Subject: RE: research topics

From: George Aggelou <[email-masked]>
Date: Tue, 30 Jan 2001 20:01:47 +0000

Hello All,

With regard to adding ad hoc relaying capability onto mobile cellular
phones, you could have a look at one of my latest publications on the
topic. The article can be found in: 

Aggelou G. and Tafazolli R., "On the Relaying Capability of Next Generation
GSM Cellular Network",  to appear in IEEE Personal Communications Magazine
, Special Issue on Advances in Mobile Ad Hoc Networking, vol. 8, no 1,
February 2001.

Regards,
George A.

>Hi,
>
>Robin Poss wrote:
>>(...)
>>Second idea:
>>-------------
>>How about a "dual" mobile phone, able to switch
>>between a normal cellphone mode and an ad-hoc mode,
>>the decision to swich being based, for example, on
>>maximizing battery life, or minimizing bandwidth
>>usage? In ad-hoc mode, the phone would use a chain of
>>other phones not to reach the party called, but to
>>reach the nearest (or otherwise clerverly chosen) base
>>station.
>>(...)
>>I think "3G TR 25.924 ,Opportunity Driven Multiple
>>Access" deals with a similar idea.
>
>Let me add some information about ODMA, as proposed in 3G TR 25.924. In a
>CDMA system (which 3G is), the total power of multiple users at a receiver
>determines the noise floor after decorrelation. Therefore, power control is
>of crucial importance to all CDMA systems. ODMA aims to reduce the power per
>call by finding the optimum communication opportunity in an intelligent
>network. It is proposed to be an added feature of the UMTS-TDD mode
>(unpaired frequency band). Initial simulations by Vodaphone have shown that
>a significant increase in capacity can be obtained, mostly in environments
>with many obstacles, where shadowing from buildings can be avoided through
>multi-hopping.
>In summary, ODMA is a method to increase the capacity of a UMTS cell, not a
>proper ad hoc networking method (all calls are finally routed to the base
>station).
>
>I would like to add, Robin, that operators such as KPN are actively
>investigating the possibilities offered by ad hoc networking and that the
>scenarios you sketch are not to be rejected just because they may threaten
>our income. On the contrary, facilities to get cheap access to internet or
>communicate cheaply between devices only increases the demand on mobile data
>services...
>
>One last question, Robin, could you maybe tell us about your background?
>Which company or institution do you work for? I am always interested to
>share ideas in this field.
>
>Greetings,
>Dirk.
>
>------------------------------------------------------------------
>Dirk Groten	      	             KPN  Research		
>------------------------------------------------------------------	
>P. O. Box 421		       Tel: +31 6 53747220
>2260 AK Leidschendam	       Fax: +31 70 3326477
>The Netherlands	             E-mail: [email-masked]

* * * * * * * * * * * * * * * * * * * * * * * *
Dr. George Aggelou
UMTS Network Consultant
Cisco Systems 
4 The Square, Stockley Park, Uxbridge
Middlesex, UB11 1BN, UK
Office:  +44 (0) 20 873 44813
Mobile :+44 (0) 77 409 25900
e-mail :[email-masked]

* * * * * * * * * * * * * * * * * * * * * * * *

---

From: Raghupathy Sivakumar <[email-masked]>
Date: Tue, 30 Jan 2001 17:05:07 -0500

Hi,

In the context of the discussions that have been going on about dual-mode
networks:

We have been working on such a hybrid network model that tries to leverage the
advantages of ad-hoc networks. While we have some interesting insights into
such a hybrid model, I would like to bring your attention to some of the results
that we have observed during the course of our performance comparisons between
conventional cellular networks and  multi-hop ad-hoc networks (the results are
to appear in  ACM SIGMETRICS 2001):

Ad-hoc networks perform better in terms of raw network capacity, end-to-end
throughput, end-to-end delay, and  power consumption. The exact order of
improvement is dependent on several factors and will require a much more
involved discussion. However, a key point that our results show is that,
ad-hoc networks perform WORSE when the following metrics are considered:

1. Fairness: Although the average throughput, delay, and power-consumption
characteristics of an ad-hoc network might be better, it is very likely that
there are a good number of nodes (flows) that perform much worse than in a
similar network operating in cellular mode. While unfairness in power
consumption can potentially be addressed using a "revenue-sharing" scheme,
unfairness in throughput is less likely to be accomodated by network users.

2. Impact of mobility: While ad-hoc networks exhibit better throughput because
of more spatial-reuse, the same factor that contributes to the increase in
spatial-reuse - smaller transmission ranges - result in frequent network
partitions and route failures resulting in poor performance. This is especially
evident at vehicular speeds (15-20m/s).

3. Impact of traffic locality: While ad-hoc networks have typically been
considered in "stand-alone" network environments where sources and destinations
are within the same "network" or "cell", the same model when required to
perform over a typical Internet model wherein the mobile stations act as
clients to servers in the backbone ,  perform badly. The reason for this
performance degradation is because spatial re-use can no longer be leveraged
due to the shared space  around the base-station acting as a bottleneck.

While we have identified these problems, it is to be noted that  these are not
problems that are not surmountable. In fact, in the same paper, we do discuss a
preliminary hybrid network model that addresses some of the problems. However,
the point of our work is to identify the fact that, even from a purely
performance perspective, ad-hoc networks cannot be adopted on an "as-is" basis
to support  conventional wireless packet data in the Internet. 

Regards,
Siva

---------------------------------------------
Raghupathy Sivakumar
Assistant Professor
School of Electrical and Computer Engineering
Georgia Institute of Technology

URL: http://www.ece.gatech.edu/research/GNAN