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

Orthogonal carrier means if the first carrier frequency is f1 the second carrier will be 2xf1, the third carrier will be 3xf1, and so on. This kind of orthogonality of the carriers allows simultaneous transmission of sub-carriers in a tightly spaced bandwidth without interfering from each other because each carrier is orthogonal to each other making the result of their multiplication a zero. Normally, OFDM signals are sent via one transmitting antenna. When generated OFDM signal is transmitted through a number of antennas in order to achieve diversity or cap any gain (higher transmission rate) in MIMO-OFDM can be realized. The advantage of MIMO OFDM is less interference, diversity gain, increase data capacity, power efficiency and bandwidth gain.

Like any other communication system MIMO-OFDM system also has transmitter and receiver but the antennas are more than one both at transmit and receive end. MIMO system can be implemented in various ways, if we need to take the diversity advantage to combat fading then we need to send the same signals through various MIMO antennas and at the receiving end all the signals received by MIMO antennas will receive the same signals traveled through various path. In this case the entire received signal must pass through un-correlated channels. If we are inserted to use MIMO for capacity increase then we can send different set of data (not the same set of data like diversity MIMO) via a number of antennas and the same number of antennas will receive the signals in the receiving end. For MIMO to be efficient antenna spacing need to be done very carefully- at least half the wave length of the transmitting signal. But the limitations of MIMO-OFDM are antenna spacing must be appropriate depending on the type of channels and it has very complex transmitter and receiver.

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Figure 1. MIMO OFDM Transmitter

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Figure 2. MIMO OFDM Receiver 3. MIMO-OFDM Working

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