Subject: [manet] adhoc wearable electronics

From: dgp <[email-masked]>
Date: Wed, 25 Oct 2006 23:20:35 -0700 (PDT)

hi,
i have application of ad hoc network for mobile (human) nodes with wearable sensors, USB ports(full duplex), camera (simplex), audio (full duplex), control channel (full duplex), etc total comes out to 10Mbytes/sec if all channels exist at a node. 
the base stations at each area act to allocate spectrum to node's requsting chanels and act as data collector for higher data rate fiber ring which can be tapped at any point in the building using a plug in at defined points by a high end application and security login.
i need following discussion for group to make.
1. algorithm for allocation of spectrum (different data rate channel, like audio needs kbytes/sec and camera Mbytes/sec etc) by base station to channels: i read base station's spectrum is divided into slots which can be combined to make high data rate channel but still has a problem as low data rate channels need only low end  spectrum to have efficient use. if base stations operate like cellular cells at different center freq. then the base stations should have different low spectrum bands. then i dont understand the use of spectrum by modern cellular networks which also need only duplex audio channel which can be 10kbytes/sec or so. since there is no multiplexing between node and base station, the channel is one to one. then why the stations are said to operate at Mhz etc etc.
2) i need to find out that the protocols including the frequency at which i want to transmit can be tested on paper by some means. guidance in this will be very much appreciated.
thank you. 

D'Jay

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From: "Xu (Kevin) Su" <[email-masked]>
Date: Thu, 26 Oct 2006 20:38:11 -0500 (CDT)

Hi everyone,

I am doing small experiments using 3 wireless routers. Each router is set
to ad hoc mode. They are placed almost along a line, as follows:
   R1 -------------  R2 ------- R3
The distance between R1 and R2 is larger than the distance between R2 and
R3.

One router is sending 4000 packets (size: 500 bytes) to another router
over UDP with rate 200 kbps. All routers record the total number of
packets received or overheard.

I did two experiments:
case (1):  R1 is sending packets to R3
  R3 receives 3844 packets, R2 overhears 3389 packets.
case (2):  R1 is sending packets to R2
  R2 receives 3940 packets, R3 overhears 2700 packets.

In both cases, R1 uses static route (add a static route to R3 or R2 in the
routing table using command "route add").

I am confused about the results from case (1). why the number of packets
R2 overheard (3389) is less than that R3 received (3844) since R2 is
located between R1 and R3? If R2 can overhear R1's transmission, it should
at least heard the packets received by R3.

In case (2), when R1 sent packets to R2 instead, R3 overheard much
less packets than the number of packets received by R3 in case (1).

I tried mutliple times, and got similar results. Can anyone explain it?
Any comments are welcome.

Thanks,
Kevin

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From: Hwee-Xian Tan <[email-masked]>
Date: Fri, 27 Oct 2006 13:53:58 +0800

Hi Kevin,

I think you need to provide more details such as the transmission range, 
sensing range and actual distance between the nodes before we can make 
more conclusions. For example, is R3 directly connected to R1, or does 
R1 route to R3 via R2?

In case 1, it is possible that R2 overhears less packets than R3 if: (i) 
R3 is within the transmission range of R1; and (ii) R2 attempts to 
forward packets that it overhears to R3, resulting in collisions when R1 
is sending packets.

In case 2, R3 would definitely overhear less packets than it received in 
case 1 if this is a multi-hop scenario (i.e. packets from R1 are 
forwarded to R3 using multi-hops in case 1).

-- 
Hwee-Xian Tan
Department of Computer Science
School of Computing
National University of Singapore
http://www.comp.nus.edu.sg/~tanhweex