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durga ch
durga ch • Oct 14, 2008

Inter block interference

1.could any one brief me with inter block interference??
Consider the case of OFDM, where a block of bits are sent on a subcarrier..when we talk about multi path fading.. the channel ideally should be acting a filter at t=0, allowing only the data stream at that specific instance.but since no ideal channels, we will be having channels impulses at various instances and due to multi path fading the data bit xi which already passed thorugh the direct path at t=i instancem reoccurs at some other interval of t.say tk.
so at the time instance 'k'., we as well have the bit coming from the direct path which is xk,and the bit coming from a second path x1( first bit comes in after a time delay of xk-1 bits).
thus resulting in our output to be:
yk=h0.xk + hk.xi
can any one explain me if yk,xk,xi are block of bits instead of one single bit as in intersignal interference how is the behaviour??
I got totally lost and confused!!!

2.I would also want to know, the definition of 'tap' when you talk about 'n-tap' channel
durga ch
durga ch • Oct 15, 2008

This is what I could find out about inter-block interference.

As the issue raised is w.r.t OFDM, I would be presenting in that perspective.
the OFDM frequency is furhter divided into 64 subcarrirers and each carrier carries a chunk of data.

this chunk of data is called a block of data.

in time domain due to multi path fading, the (i-1)th block transmitted in the previous itme slot , follows a different path in the same channel and reaches the reciever along with the ith block at the current time slot, thus leading to a interference.there would also be a time delay in the second time packet being recieved.

to avoid IBI, cyclic prefix is added to the block of signal such that the value of cyclic prefix is always greater than IBI.

in cyclic prefix , the last l bits are padded to the start of the block and l value is such that l-1 is the maximum channel vector.
sad_engineer • Nov 8, 2012
can anyone tell me the definition of IBI...?

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