In recently decades, the Orthogonal Frequency Division Multiplexing (OFDM) Scheme have made very wide part in telecommunication industries, as it is adopted for all of its robust nature through which it eliminates the frequency selective fading which is obtain due to the conversation of channels to the flat fading sub-channels. OFDM scheme is of technology in which we can use multicarrier modulation technique and it can be implemented using the Fast Fourier Transforms (FFT) or the Inverse Fast Fourier Transforms. OFDM is a promising technique because it gives high data rate transmission and thus it is adopted by many of the telecommunications transmission systems such as high bit rate digital subscriber lines (HDSL), digital video broadcasting (DVB), asymmetric digital subscriber lines (ADSL), long term evolution (LTE), wireless local area network (Wireless LAN), and digital audio broadcasting (DAB).
12Multiple Input and Multiple Output is a multiple antenna using system at both of the receiving and the sending sides, combining both MIMO and OFDM can improve the spectral efficiency for the system beyond 1Gbps , the use OFDM(Orthogonal frequency division multiplexing) in mimo which gives separate space-time codes for each set of channels, MIMO-OFDM is used in wideband transmission to eliminate Inter-symbol Interference and for enhance system capacity. The main reason for using OFDM in the MIMO is that the OFDM modulates the frequency selective MIMO channels into the parallel frequency MIMO channel. Which means that the OFDM in MIMO provide the chennal equalization simple, with each channel subs-carrier is identified as matrix to invert it at the receiving end.11 Well planned MIMO-OFDM systems are based on the Fast Fourier transforms algorithms and on some encoding technqiues, for example; Alamouti Space Time Block coding (STBC), Vertical Bell-Labs layered Space Time Block code (VBLASTSTBC), and the Golden Space Time Trellis Code (GSTTC).
OFDM is used in many of the telecommunications technologies like Worldwide Interoperability for Microwave Access (WIMAX), Wireless Fidelity (WIFI), Long Term Evolution (LTE) and Digital Video Broadcasting (DVB). The use of MIMO-OFDM gives next generation a high data rate with very low disturbing profile system and it is the future of telecommunication world.12OFDM provides user with a group of the subcarriers, with these 1000s of subcarrier to the user, they get a small part of carrier. In the LTE systems the users are mainly allowed with one or many users depending on there requirement. Such as in 4G systems the carriers spacing is 15 KHz. And by using 1-10 MHz possible numbers of carriers provided to the user are 666.
And if the users are given 6 subcarriers, then we can approximately place 85 users, so the users are provided with the numbers of subcarrier is depend upon the bandwidth and the peed needed.14Results of some field taken from are given below:- 1. In 2*2 MIMO Antenna technology, highest data rate in 14· Down Link: 170 Mbps· UpLink : 56 Mbps (16 QAM) 2. In 4*4 MIMO Antenna technology, highest data rate in 14· Downlink: 325 Mbps 3. In Radio Access 14· Down Link: OFDM· Up Link : SC- FDMA