## PERFORMANCE STUDY OF 2X2 AND 4X2 MIMO OFDM(4)

MIMO OFDM principle

The basic principle is the insertion of a guard interval, called cyclic prefix (CP), which is a copy of the last part of the OFDM symbol (Fig. 1c), and has to be long enough to accommodate the delay spread of the channel. The use of the CP turns the action of the channel on the transmitted signal from a linear convolution into a cyclic convolution, so that the resulting overall transfer function can be diagnosed through the use of an IFFT at the transmitter and an FFT at the receiver (Fig. 1b). Two signals are orthogonal if their dot product is zero. That is, two signals multiply them together and if their integral over an interval is zero, then two signals are orthogonal in that interval. This results in no interference between the carriers, allowing them to be spaced as close as theoretically possible.

Guard time and Cyclic extension

Guard Time is introduced in-order to eliminate the ISI almost completely. Making the guard time duration larger than that of the estimated delay spread in the channel, merits in the guard period when left empty, the orthogonality of the sub-carriers no longer holds, i.e., Inter-Carrier Interference (ICI). OFDM is bandwidth efficient, since the parallel sub carriers are overlapping but orthogonal to each other without causing interference. Using CP, it robust the multipath fading and insusceptible to most forms of impulse noise because of parallel transmission.

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### Representative APR 391%

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