MULTIPATH MITIGATION
CAPABILITY OF OFDM
OFDM Stands
for Orthogonal Frequency Division Multiplexing . High spectrum efficiency of
OFDM is already explained in earlier blogs ( Please refer to blog Wi-Max
Technology).
Here I will
explain about the multipath mitigation capability of OFDM.
In OFDM the
frequency band available is multiplexed to multiple sub-bands.
And the data
is transmitted in parallel over the multiple sub-bands for the longer period of
time.
Now when the
data is being transmitted serially ( Non
– OFDM ) and it is taking multiple paths
( 2 paths in this example ) one is direct path and through reflection from any
reflecting surface.
Lets say we
have to transmit 1 0 1 0 and each bit will be transmitted for ta
period of time now initially the transmitter will transmit bit 0 for ta period
of time the bit 0 will be received in minimum time from direct path by the time
0 is received from shortest path the it will still be on the way on longer path
after time ta collapses transmitter will start transmit bit 1 now 1 will be received
by the receiver in shortest time from shortest path and it will also receive
earlier bit 0 which was travelling through longer path so here the interference
has occurred.
Now when the
data is transmitted parallel ( OFDM ) The data which we were earlier
transmitting serially will transmitted parallel and each bit will be
transmitted for the longer period of time here the time period of each bit will
become 4ta .
In this
since each data stream is transmitted for a longer period of time so even if
the time ta collapses same data will be travelling through the direct path and
reflective path so interference will not occur.
