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ABSTRACT
Multiple transmit and receive can be used to form multiple input multiple-output (MIMO) channels
to increase the capacity and data rate.MIMO has brought a major breakthrough in the field of wireless communication. Using MIMO system ensure the probability of information to be higher at the receivers side with less error rate. Modelling of MIMO has been done under various fading channels and for various modulation schemes. Comparison has evaluated that shows MIMO has better performance under Rayleigh channel.
INTRODUCTION
The technique of cooperative communication has achieved world wide popularity in this world .It has acquired the world wide popularity in communication system engineering. The performance of the communication system is studied on the basis of BER evaluation and the determination of probability of output. The orthogonal technique using MIMO has become quite popular among the user. Here the input waveform is encoded using Bernoulli waveform generator. It will have frame based output which is given as an input to the convolution encoder. The function of convolution encoder is to give a convolution of input bit with the set code. The code is pre defined by the user. And it can be formulated using the convolution formula. This output of convolution encoder is making to pass through a mapped or punctured. Here few of the bit are masked which means that some of the bits are secured for the consumer use. This is now made to pass through a MIMO parser, which basically splits the masked bit of the consumer into two interleave. The two interleave scans the two incoming bit streams in their own way. Then came the insert pilot. The function of the block is to insert the plot of the generated curve obtain from the interleave. After that we will take the inverse Fourier transform of the generated waveform. This is followed by the extraction of bit streams using decoder. The techniques used here is orthogonal frequency division multiplexing. In the technique we take the auto correlation of two input waveform if it is found to be zero then it shows that it has zero similarities with the generated output. On the other hand if the product of two input waveform found to be one it means that the waveform resembles itself hundred percent or completely.
MIMO is used for virtual communication deploying the need of physical antenna. Earlier in order to transmit data or to established any communication between the two distant point sources. We require number of physical antenna which consumes lot of space and energy. This disadvantage of physical antenna is overcome by the invention of co-operative communication. It utilized the protocol of mutual agreements of nodes which will act as an antenna when in idle condition. This not only overcame the limitation of space consumption but also prove the lowering down the cost to the major extents.
OSTBC AND OFDM SYSTEM
OSTBC IN MIMO
MIMO is used for virtual communication deploying the need of physical antenna. Earlier in order to transmit data or to established any communication between the two distant point sources. We require number of physical antenna which consumes lot of space and energy. This disadvantage of physical antenna is overcome by the invention of co-operative communication. It utilized the protocol of mutual agreements of nodes which will act as an antenna when in idle condition. This not only overcome the limitation of space consumption but also prove the lowering down the cost to the major extents.
WHAT IS OFDM
OFDM stands for orthogonal frequency division multiplexing technique. We are using this technique because it has worldwide popularity among the consumers but have also proved to be useful in the field of communication and engineering. it has gained popularity in the field of telecommunication . The concept of ofdm is actually evolved and based on the spreading of data streams for a number of users over a communication channel. It is considered as a technique which has a number of carriers and a number of tones and a technique having the Fourier transform usage too. Here the carriers are split into number of sub bands of frequency so that there will be no interference and also there won’t be any noise in the output stream. In this technique the signal stream is divided into the respective streams so that the codes are orthogonal in nature.
The concept of orthogonality is used here. In this case the code to be encoded are orthogonal to one another so that there will not be any interference in the reaccepted codes. This technique is proved to be useful not only for the noise reduction purpose but is also considered to be reliable.
COOPERATIVE COMMUNICATION
Types of MIMO
• MIMO involves a number of blocks like Space Time Transmit Diversity block (STTD), Spatial Multiplexing block (SM) and Uplink Collaborative block for MIMO.
• block of Space Time Transmit Diversity (STTD) - The repetitive number of signal are made to pass through number of antenna, which actually increases the power capacity in the transmitting channel. This enhances the Signal Noise Ratio (SNR) for the purpose of better performance.
• Spatial Multiplexing block (SM) - SM transports the data of cpe to the respective blocks and thus increasing the capacity of the links to twice or to four times and output. This actually results in higher capacity when the conditions are supporting to the required scenario.
• Uplink Collaborative block for MIMO Link –it makes use of Leverages conventional device and single Power Amplifier (PA) at device. Two MIMO systems could collectively transmit on the same side.
Cooperative Communication FOR MIMO
INTRODUCTION:
The technique of cooperative communication has achieved world wide popularity in this world .It has acquired the world wide popularity in communication system engineering. The performance of the communication system is studied on the basis of BER evaluation and the determination of probability of output. The orthogonal technique using MIMO has become quiet popular among the user. Here the input waveform is encoded using Bernoulli waveform generator. it will have frame based output which is given as an input to the convolution encoder. the function of convolution encoder is to give a convolution of input bit with the set code. The code is pre defined by the user. And it can be formulated using the convolution formula. This output of convolution encoder is making to pass through a mapped or punctured. Here few of the bit are masked which means that some of the bits are secured for the consumer use. This is now made to pass through a MIMO parser, which basically splits the masked bit of the consumer into two interleave. The two interleave scans the two incoming bit streams in their own way. Then came the insert pilot. The function of the block is to insert the plot of the generated curve obtain from the interleave. After that we will take the inverse Fourier transform of the generated waveform. This is followed by the extraction of bit streams using decoder. The techniques used here is orthogonal frequency division multiplexing. In the technique we take the auto correlation of two input waveform if it is found to be zero then it shows that it has zero similarities with the generated output. On the other hand if the product of two input waveform found to be one it means that the waveform resembles itself hundred percent or completely.
Outage Probability:
Lower Bound Equation in Case of Nakagami-m
(1)
P_out=1-e^(-γ_th/γ ̅_(`1) ) τ(m,(mγ_th)/τ(m) )
Where τ(., .) is incomplete gamma function
CO-OPERATIVE SYSTEM PROTOCOLS:
In wireless communication ,Cooperative Communication protocols are categorized in 3 forms namely :
1. Amplify and Forward
2. Detect and Forward
3. Coded Cooperation
Amplify and Forward cooperative protocol transmission is the simplest and practically usable protocol. It has easier implementation but a major drawback is associated with it i.e. along with the signal amplification perpendicular noise amplification appears with that, which is unwanted. This problem is overcome by decode and forward relaying as this relaying scheme inherently eliminates the perpendicular noise. In coded cooperation, two mobile devices affiliate with one another to collectively transmit the data. They use their resources collectively to achieve this. Since, the data is accepted through independent fading paths spatial diversity is achieved.
4*4 MIMO
Description
MIMO is used for multiple input multiple output purpose. here we make use of virtual antennas which will not consume any space and will also reduce to the cost. the 4*4 MIMO system actually has 4 virtual transmitter and 4 virtual receiver. these trams miter and receiver will agree on a certain protocol for a fixed amount of time. In idle case they will transmit and receiver depending upon the situation. MIMO system has attended word wide popularity among the consumer using co-operative communication. here we make use of OFDM technique which will split the codes on the basis of frequency band and thus reducing the error rate to minimum and outage probability to maximum. we can obtain maximum throughput in this case.
The Transmitter
The transmitter has convolutional encoder having frame based outputs, MIMO carries a block named parser and IFFT which have their respective functions. The bits which are reuired to be encoded are used here for giving an input to the encoder having a 1/3 convolution block encoder, which is then input and trunk, and as a whole is fed to the output side. The ROM_Imaginary (ROM Imaginary ) part , and a ROM Real combined to forms 64 QAM mapper.
MIMO Parser: The Imaginary and Real image are applied as an input to the MIMO parser as In 1 and In 2 respectively. The sole aim was basically to divide the one stream input data.
Block of Ofdm : The first Imaginary part is applied . After that Real part i.e. the primary first output and third block outputs of MIMO system parser1 were given to their respective blocks. IFFT transforms the signal into time domain of 64 size QAM. The output is given at the output node of ofdm_out.
Receiving Sub system
In receiving sub system outputs which are taken from the four streams from the output stream is applied to the output side it has the capacity of removing unnecessary occurring of an error like noise distortion, fluctuation accruing in the output signal waveform..
MIMO Deparser
At the transmitter side, working at this system begins by initiation of the signal is divided whereas at the receiver side it is made to split into imaginary and real parts using the decoder output. These two real and imaginary parts are decode and then made to pass through the detector and the output waveform is then obtained from this extraction of data streams.
Demodulator block and Decoder block
The real part of rom and imaginary part of ROM were used to input to the demodulator respectively. For 64 QAM demodulator ,a matlab code can be generated and is given out at Dout.
SIMULATION
The Simulink block diagram of MIMO OFDM is shown as below. The information sequence that is generated by the Bernoulli binary generator is encoded using convolution encoder with the coding gain of ½.The single bit output codes is combined to produce punctured codes with the rate other than ½ and hence punctured as 1/3 . The rate ½ implementation is changed to ¾ code rate called as puncturing. The punctured code is then interleaved to make the forward error correction much more effective in overcoming the burst errors. The matrix interleaved and general block interleave is used. The code word is mapped by QAM modulation. The output is given to the OFDM modulator with N=64 subcarriers and a cyclic prefix of 16 is added resulting in the OFDM symbol. The OFDM symbols is transmitted over the multiple antennas using orthogonal space time block coding technique over fading channel. On the receiver side of the MIMO system, the data is demodulated to extract the information sequence.
VI. RESULTS
The simulation of MIMO OFDM system is performed for various modulation schemes such as QAM levels,BPSK using efficient channel coding technique under different multipath fading channels varying the number of transmitting and receiving antennas. BER comparison and outage probability of QAM . It shows that as the modulation level is increased, BER is increased. 64 QAM outperforms higher 64-QAM levels. Fig1 shows relation of outage probability with average SNR for various modulation schemes.
Fig2 shows comparison three modulation schemes for different schemes like 64QAM ,BPSK and QPSK under nakagami channel. Fig 3 shows comparison of channels for BPSK.Fig4 shows outage capacity for Nakagami channel.fig 5 shows comparison of various channels for 64QAM
CONCLUSION
The performance of MIMO OFDM system with cooperative communication is analyzed for 64-QAM modulation with convolution channel coding by varying that is increasing or decreasing the number of antennas. Modulation order is lower and higher transmit and receive diversity reduces bit error rate (BER) resulting in better/improved performance. In addition to the above, the results show that convolution coding scheme under Rayleigh multipath fading channel improves performance with less Signal-to-Noise ratio (SNR) with better throughput and improved quality of signal.The bit error rate for the 64QAM is found to be 0.0001006 and that for BPSK it was found to be 0.00256 under Rayleigh fading channel.Thus Rayleigh channel is found to be better than any other fading channel.
VIII. FUTURE SCOPE
In this study, different problems of OFDM system have been considered and suitable solutions have been provided. As it is known that research is regarded as a process having no ending process, a new beginning is always awaiting. Hence , there are a list of things to be considered for future usage. Some of them are:
(a) Channel can be estimated using this principle .
(b) Extending the algorithm of timing offset estimation for channel estimation in OFDM system.
© The timing offset and frequency offset estimator can be utilized for MIMO OFDM system.
(d) The closed form expression of Bit Error Rate can be derived for OFDM system with proposed PAPR reduction method.
(e) The windowing method of ICI reduction.