Exposed terminal problem

February 21, 2010 at 02:06:51
Specs: N/A
if a station hears no response to an overheard
RTS, then it may assume that the intended
recipient of the RTS is either down or out of
range. An example is shown in figure 4.
Station X is within range of Y, but not Z. When
Y sends traffic to Z, X will hear Y’s RTS
packets but not Z’s CTS responses. X may
therefore transmit on the channel without fear
of interfering with Y’s data transmissions to Z
even though it can hear them. In this case
MACA allows a transmission to proceed when
ordinary CSMA would prevent it unnecessarily,
thus relieving the exposed terminal problem.

Since X can hear the transmission from Y to Z,
Y can also hear the transmission from X to
another station. X and Y are inside the
communication ranges of each other. When
they send data to their receivers respectively,
don't the signals interfere each other in the
middle of each sender and receiver? The
following figure illustrates the scenario.

A capital letter stands for a station.
n stands for the border of the communication
range of station N.
The communication range of a station is the
width of 6 characters.


As shown in the figure,
(1)X cannot hear z.
(2)X can hear y.
(3)Y can hear x.
(4)Since all signals go through the same
channel, x and y collide between the right x
and the left y so that W and Z receive corrupt

Does radio communication work as (4)? Or, is
a signal corrupt for a receiver only when there
is another signal in the same channel at the
same time?

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February 21, 2010 at 04:35:57

I see that you posted your coursework question on at least two other sites:

The answer is of course 42.


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February 21, 2010 at 07:54:11
re: is a signal corrupt for a receiver only when there is another signal in the same channel at the same time?

Another way to attack this issue is to prevent more than one signal from being in the same channel at the same time.

At the front end of your channel receiver, install a MSPF or "Multiple Signal Prevention Filter".

Information on MSPF's can be found here.

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