Well, my idea was to simulate interference. You are right absolutely right, interference happens in the air so the receiver has no idea about it. But this is in real life. Since there are no signals in ns2, my idea was to calculate interference at the MAC layer which will know what are the packets (signals) that were sent at the same time on the air. So when the MAC receives more than one packet, I want to record these packets somewhere (and this will give me access to where they are coming from and going to, plus their powers), then I will apply a formula that will calculate interference between all these packets (in real life: signals). You are absolutely right, in case of one channel, this will be considered as collision IF the received packets are destined to the same receiver/. But there are two other cases, if the packet is not destined to that receiver, then I think this will be strong interference. Also, if the interfering packet belongs to a different channel (that I am willing to add after I figure out the interference) then this is will be interference depending on the correlation between the channels. Do you see my point? The first step I believe would be to capture all packets that come at the same time while I am receiving another packet. This way I can process them and decide if it is collision or strong or weak interference. I have the formula, all I need are the packets along with their powers and channels they belong to (don't care about the channels now, coz that's coming after). I am still wondering how and where in the 802.11.cc code I can capture all colliding/interfering packets and put them somewhere for processing. cheers,
On Thu, Nov 13, 2008 at 5:00 AM, Basim Javed <[EMAIL PROTECTED]> wrote: > hello Imad > > I can see ur point. > Lets talk on the issues one by one: > > The interference of one packet to an already sent packet creates collision. > right? so interference and collisions happen in the air. I dont see why it > is important that the packets should be sent to one receiver and they if > they interfere, then collision happens. I think even those nodes who are > just listening to the channel, know that collision has happened in the air, > even they were not recipients of the packet. > > Now, how does the node knows that a collision has happened.. through the > received signal power, which is lower than a threshold level (i forgot the > name). As far as I remember, the power level can be so low, that a node can > not receive a packet, or it is bit high but still not good enough to decrypt > the bits. > > What I am talking above is related to the situation of same channel (single > hop). I think multiple channels are used in neighbouring BSSs. > > About ur formula: how a receiving node can know about the power of the > signal when the packet was sent, in real situation? > > regards > basim > > > > On Wed, Nov 12, 2008 at 4:16 PM, Imad Abdeljaouad <[EMAIL PROTECTED]>wrote: > >> Thank you so much, I really need help! >> I would like to add interference support in 802.11. If my understanding is >> right, interference happens when signals send on the same channel (or >> adjacent channels, like 1 and 2 or 3 ... to 6) overlap in the medium (the >> air) and cause attenuations to each other. I think this will not be possible >> in ns2 since there are no "real" signals. So I was thinking that what I >> should do is collect the signals that arrive at the same time at the >> receiver MAC (and this is where I got collisions) and this means that these >> signals already overlapped in the air since they got to the receiver MAC at >> "the same time". >> Do you see my point? >> Once I know which siganls overlapped, I can use a formula to calculate >> interference (the fornula uses Power of the signal sent + which channel does >> it belong to, to calculate the effect of one sigan on another ). >> >> So the point is, I need to capture the packet*s* that collide while I am >> receiving another packet and for how long they collided. >> I don't know if you get my point, but please do not hesitate to ask me >> more questions! >> thank you again !!! >> >> On Wed, Nov 12, 2008 at 4:36 AM, Basim Javed <[EMAIL PROTECTED]>wrote: >> >>> hello Imad >>> >>> I want to help you, but I dont understand your definition of collision >>> and interference. Can you clarify it plz? >>> basim >>> >>> On Wed, Nov 12, 2008 at 2:55 AM, Imad Abdeljaouad <[EMAIL PROTECTED] >>> > wrote: >>> >>>> >>>> Hi Helber, >>>> Thanks for the prompt response. Actually, I am looking for the code in >>>> ns2 >>>> (source code) where we can detect collisions. I want to simulate >>>> interference, so I need to get the packets that were received at the >>>> same >>>> time on some node. I know interference happens on the physical layer, >>>> but I >>>> think it would be much more easier to implement it on the MAC in ns2. So >>>> I >>>> am actually looking the source code part that says here is another >>>> packet >>>> being transmitted while receiving another packet ( which is collision if >>>> both packets are meant for the same receiver, and interference if both >>>> packets belong to the same (or an adjacent) channel. >>>> Can you help with that ? >>>> cheers, >>>> >>>> On Tue, Nov 11, 2008 at 8:35 PM, Helber Wagner <[EMAIL PROTECTED] >>>> >wrote: >>>> >>>> > Hi, Imad. >>>> > >>>> > As far as I understood your question, you should analyze the trace >>>> file >>>> > generated >>>> > by your simulations. >>>> > >>>> > If the MAC trace is enabled in your .tcl file, it will be a row like >>>> "D >>>> > ... COL ..." >>>> > indicating the time, the node, the packet and other information about >>>> a >>>> > collision >>>> > that has been happened. >>>> > >>>> > Finally, a simple perl/awk script can retrieve this information from >>>> the >>>> > trace file. >>>> > >>>> > You can find more about mac trace in NS2 over the Internet. >>>> > >>>> > Good luck. >>>> > >>>> > --- >>>> > Helber Wagner da Silva >>>> > Federal University of Ceará - Brazil >>>> > URL: www.great.ufc.br/~helberhws<http://www.great.ufc.br/%7Ehelberhws>< >>>> http://www.great.ufc.br/%7Ehelberhws> >>>> > >>>> > >>>> > >>>> > ------------------------------ >>>> > *De:* Imad Abdeljaouad <[EMAIL PROTECTED]> >>>> > *Para:* "ns-users@isi.edu" <ns-users@ISI.EDU> >>>> > *Enviadas:* Terça-feira, 11 de Novembro de 2008 23:17:46 >>>> > *Assunto:* [ns] collisions in 802.11 or interference >>>> > >>>> > >>>> > Hello there, >>>> > I am looking for the code where collisions in 802.11 occur so that I >>>> know >>>> > which packet(s) collided and for how long they collided? this is a >>>> step in >>>> > trying to implement interference! >>>> > thank you! >>>> > >>>> > -- >>>> > best regards, >>>> > ________________________ >>>> > Imad Abdeljaouad >>>> > >>>> > ------------------------------ >>>> > Novos endereços, o Yahoo! que você conhece. Crie um email novo< >>>> http://br.rd.yahoo.com/mail/taglines/mail/*http://br.new.mail.yahoo.com/addresses>com >>>> a sua cara @ >>>> > ymail.com ou @rocketmail.com. >>>> > >>>> >>>> >>>> >>>> -- >>>> best regards, >>>> ________________________ >>>> Imad Abdeljaouad >>>> >>> >>> >> >> >> -- >> best regards, >> ________________________ >> Imad Abdeljaouad >> > > -- best regards, ________________________ Imad Abdeljaouad
