What is Near-Far Effect in wireless communications??

[akmirror]

near far effect

I was going through Adjacent Channel Interference where i found out the term near far effect. What does that mean? please suggest me....

Regards

 

[samir67]

near-far effect

See this link

en.wikipedia.org/wiki/Near-far_problem

 

[Communications_Engineer]

near far effect in cdma

near far effect is a problem in CDMA as the PSD is no longer constant since MS near the BS seems to have more power than the one away from it (the one away would lose its power via path loss)

And you since CDMA is really Power division mulitple access (only using it as analogy), this is a big problem and we need power control to mitigate it



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[akmirror]

near far effect cdma

Thanks for helping me out. Can you please tell me about near far effect in respect to GSM

 

[mowgli]

near and far effect

GSM is less sensitive to the near far effect because it uses Time and Frequency division duplexing: every MS has its own channel and time slot assigned to it by the BS to transmit/Receive during the uplink/downlink.
In CDMA more users share the same bandwidth at the same time: every user encode its transmission with a unique spreading code chosen between those belonging to an orthogonal set, so the BS is capable to separate users from the interference resulting from the sum of all MS transmitting at that time by multiplying the received signal by the code assigned to the user of interest.
This is possible if the TX power of all MS is controlled in a way that at BS end each user is received "more or less with the same power" and the resulting multi-user interference is kept below a threshold that is managed by the processing gain.
But if for some reason a user (Near user) is transmitting with an uncontrolled power its stronger signal will mask the weakest signals (Far users) and BS is no more capable to demodulate them correctly (some times in literature you could find references to pirate terminal to describe the behaviour of MS operating with uncontrolled power loop).
For this reason in CDMA cellular systems power control loop of MS is more accurate than in GSM systems and is implemented in cooperation with BS using a dedicated channel.

Regards
Mowgli

 

[akmirror]

near-far effect

Thanks MOWGLI...

It really helped me understand near far effect.
Regards...