This paper describes the nyquist filter based technique to reduce the peak to average power ratio (PAPR) in multiple input multiple output Orthogonal Frequency Division Multiplication (MIMO-OFDM) systems. OFDM-MIMO system faces one of the main problems regarding PAPR of a transmitted signal. In present paper a nyquist filter along with conventional selected mapping (SLM) and alternative multiseqence (AMS) techniques are used for reducing the PAPR. The nyquist filter reduces the peak power of

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... transmitted signal and this may cause the reduction in PAPR. The simulated results are compared with conventional SLM and AMS techniques. Proposed nyquist filter based technique shows the lesser PAPR than the conventional SLM and AMS techniques. Coding and simulation has been done in Matlab 7.6. I. Introduction Multiple-input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) system have drawn significant interests due to its potential in achieving high data rate and providing reliable performance of diversity and spatial multiplexing. However, MIMO-OFDM system suffers from high peak-toaverage power ratio (PAPR) [1]. In MIMO-OFDM wireless system, independent OFDM signals are simultaneously transmitted from multiple-transmit antennas to multiple-receive antennas. Due to these multiple signals, PAPR problem occurs [2] . Recently, various algorithms of PAPR reduction have been proposed for OFDM system. There is a novel sub block linear combination scheme for peak-to-average power ratio reduction in OFDM system [3] . The key idea two novel methods is to divide an OFDM block into several subblocks, and iteratively generate the linear combination of these subblocks with low PAPR. One efficient technique for PAPR reduction is using low complexity partial transmitted sequence to construct of OFDM signals without side information [4] . In this scheme at the receiver, by utilizing the natural diversity of phase constellation for different blocks, the detector can successfully recover the original signal without side information. A nonlinear distributed companding scheme efficiently reduces PAPR with low Bit Error Rate. Therefore in [5] the novel scheme that transforms the OFDM signals into a trapezium distribution. The uniformly distributed companding scheme is a special case for PAPR reduction. In [6] a constellation reshaping method to reduce the PAPR of OFDM signals without side information. A reshaped quadrature amplitude modulation (R-QAM) constellation is generated, then, the inherent diversity of the R-QAM constellation with different phase rotation factors could be exploited at the receiver. Clipping and filtering also effects the PAPR , crest factor and the power spectral density of the signal. However, clipping time domain signals causes out-of-band spectral regrowth and in band distortion. But the iterative clipping and filtering (ICF) procedure may be the simplest technique to approach a specified PAPR threshold in the processed OFDM symbols [7] [8] . In [9] a PAPR analysis reduction of space-time block-coded (STBC) MIMO-OFDM system for a 4G networks has been done. In [10] a modified selective mapping (SLM) technique for PAPR reduction of coded OFDM signal. In this technique, the phase sequence, this is used to lower the PAPR of the data block, in the check symbols of the coded OFDM data block. Both PAPR reductions from the SLM technique as well as error performance improvement from the channel coding with no loss in data rate from the transmission of side information. In [10] [11] there is review and analysis different OFDM PAPR reduction techniques are given which is based on computational complexity, bandwidth expansion, spectral spillage and performance. These factors play an important role and effects PAPR of the signal. In another technique PAPR can be reduced by using precoding technique [12] . In this technique the precoding has been done at the transmitter end. In [13] interleaving method is used for PAPR reduction. This method is also termed as adaptive symbol selection method .Multiple OFDM symbols are created by bit interleaving of input sequences and then the symbol with the lowest PAPR is selected at the receiver. Adaptive flipping of parity bits can also effect the PAPR of the OFDM signal [14] . In this method the PAPR ratio of the turbo coded OFDM signal is reduced with adaptive flipping of the phase of parity carriers. Dummy sequence insertion is also a PAPR reduction method shown in [15] . In this method the complementary sequence and the combination of the correlation sequence