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Communication task/puzzle

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rednewguy

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IDEA!

i have an idea.
assume that i am in a place where i cudnt reach the tower. somewhere nearer someone "x" is there who can reach the tower. And also he is in line of sight with me.
i want to make communication with the tower via "x" so that i can originate a call or attend a call. is it possible to make communication between me and "x" without the help of tower.

thanks
 

throwaway18

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mesh networking

Please give your threads meaningful subject lines eg " relay to base station" not "IDEA!"

This is called mesh networking. There has been lots on interest in this idea in the last few years.

I'm not aware of any mesh networks between portable devices that work well. Mesh networking is more suited to connecting base stations together. There are wireless ISP such as Telabria which use rooftop access points that relay data to each other so they don't have the expense of installing a leased line to each access point.

Meshing between portable devices has many problems. Mobile telephones and digital voice radio usually transmitt and receve in different bands. The receivers only cover the frequencys used by the base stations and can't be tuned to the tx frequencys of other handsets.

If you need handsets to listen on the same band that other handset are transmitting on you have more problems with strong signals from nearby handsets causing receiver desensatization.

Battery life will be a big problem for portable devices. In a laptop you typically have a 10mW wifi transmitter and a physically large battery. In a mobile telephone you have a 1W or 2W transmitter and a tiny battery.

Wifi access points and mobile phone base stations transmitt packets every second. Your portable device knows if it is in range because it can hear the base station.
Pagers increase battery life by having the base station say "no more messages for group2, you can turn off your receiver for a few seconds to save power".
Having two handsets frequently transmitting to each other will severely reduce the battery life.

If a handset only negotiates a relay when it wants to make an outgoing call it might not be too bad. If you want the handsets to say in contact to be able to receive incoming calls then you either

a) Get the base station to get all the handsets it can contact to broadcast saying "handset 123456 can you hear me?" which kills everyones battery life

or b) Your handset has to transmit frequently.
Handset to Handset has much more path loss and nulls due to multipath reception than handset to high up base station. If you are in a basement and you cant get a connection to a base from people walking past the building with phones in their pockets you will need to renogotiate constantly as other handsets move in and out of range.

I'v seen an experiment with wifi mesh networking between a lot of people with laptops. It worked very badly but for non-fundamental reasons.
The biggest problem was that there were about fifty access points and hundreds of laptops in a field. 2.4GHz was one continuous collision as devices transmitted over each other and the usfull bandwidth was close to zero. The next problem was that when one person advertised a route between the wired LAN and the mesh network all the mesh bandwidth was taken by megabits of broadcast traffic generated by windows machines using workgroup networking (the network neighbourhood stuff is typical microsoft bugware and works very very badly with hundreds of machines in the same broadcast domain.) and arp floods.

The routing protocols such as BGM typically used for wired network work very badly when nodes have routes to lots of other nodes which are contantly coming and going and have significant packet loss on the links.

There are several software packages made specifcally for mesh networking. The guys at meshcube in Germany make some very nice little boxs with two radio's, 200MHZ processor running debian and optional power up the cat5.
 

sachinlan

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Re: IDEA!

Is this IDEA similar to Push To Talk (PTT) technology.
 

throwaway18

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IDEA!

>Is this IDEA similar to Push To Talk (PTT) technology.

No, the mobile telephone PTT feature communicates via the mobile phone base stations as normal, not direct handset to handset.
 

sachinlan

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Re: IDEA!

Thanks for the information Throwaway18.

DO u have any document or book on this technology?
 

rat_race

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Re: IDEA!

well this IDEA(..!!!!) is somehow similar to PTT technology such as TETRA. this ETSI standard supports two modes : direct mode operation (DMO) & Trunked mode operation (TMO) .in the former (DMO) hand portables can communicate with out needing any sort of infrastructure in addition to towers..!
for more details search in google for TETRA DMO...
 

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