The Performance Analyi of MIMO OFDM Sytem with Different M-QAM Modulation and Convolution Channel Coding H. S. Shwetha M.tech, Digital Communication Engineering Siddaganga Intitute of Technology Tumakuru, India Sathiha R. N Department of Telecommunication Engineering Siddaganga Intitute of Technology Tumakuru, India Abtract The MIMO-OFDM technology i under the ignificant conideration for the development of G wirele communication ytem. The combination of OFDM with MIMO deliver a ignificant performance improvement in term of many parameter like data tranmiion rate, maller bit error rate (), and increaed reliability. In thi paper, a good performance in term of low i achieved with the ue of better channel coding technique and modulation cheme. Here, OFDM with 6 QAM modulation and convolution coding with the code rate ¾ i combined with Orthogonal Space Time Block Coding (OSTBC) - a patial diverity technique which effectively reduce. Uing MATLAB/Simulink, the performance analyi i carried out by varying the MIMO antenna configuration like x, x, and x under different fading channel like Rayleigh, Rician fading channel and their effect on i examined. Keyword OFDM; MIMO; ; Convolution coding; QAM; OSTBC. I. INTRODUCTION There i ahuge demand for providing reliable high-peed wirele communication link to upport a wide range of application. Providing uch reliable link i challenging a, in a wirele environment, tranmitted ignal are received through multiple path adding detructively and cauing eriou performance degradation termed a fading. In addition, the medium i normally hared by many different uer/application leading to the poibility of ignificant interference. Further, high-peed wirele application have other challenge namely-limitation of available bandwidth, tranmit power contraint, hardware complexity and cot implication. Due to limited frequency pectrum/teady increae of new wirele application and expanion of exiting one, it may be difficult to accommodate all of them. In view of the large demand for peedy and reliable communication over wirele channel, future broadband communication ytem hould provide low complexity data proceing, higher data rate, and tronger performance. However, a broadband channel hadiadvantage liketimeelective and frequency-elective fading. To ort out thee challenge, one reliable olution i to combine two powerful technologie, namely, multiple-input multiple-output (MIMO) antenna and orthogonal frequency diviion multiplexing (OFDM) modulation []. A compared to the ingle antenna ytem, the ue of the multiple antenna at the tranmitter and receiver in wirele ytem give enhanced performance capabilitie. The multiantenna ytem- MIMO enure higher data tranmiion rate, wider coverage and higher reliability without uing additional frequency pectrum. A reliable performance can be obtained through diverity. The ame i achieved in MIMO ytem by repetition coding that end the ame information ymbol at different time lot from different tranmit antenna. Space time block coding (STBC) i a method to achieve high diverity performance which imultaneouly tranmit the ame data over different antenna at different time. Orthogonal pace time block code (OSTBC), a variant of pace time block coding ue a imple maximum likelihood decoding at the receiver enabling ignificant error rate improvement. A multicarrier modulation technique (OFDM) divide input data tream to a number of parallel ub tream and tranmitted over the individual ubcarrier that are orthogonal to each other. Hence, the wideband frequency elective channel i divided into a number of parallel narrow band ubchannel leading to flat fading. The orthogonality between the ubcarrier allow the overlapping of the ubcarrier thu preventing the interference between them. The cloe pacing of the ubcarrier enable the efficient utilization of the bandwidth. The performance of MIMO-OFDM i enhanced by uing channel coding technique. Thi MIMO OFDM ue convolution coding with the code rate ¾ under different multipath fading channel like AWGN in conjunction with Rayleigh and Rician fading channel. II. SYSTEM MODEL The modeling of the MIMO OFDM i a hown in the figure. The ytem performance in term of the bit error rate () i analyzed in MATLAB/Simulink. In thi model, the information equence i generated uing Bernoulli binary generator. The forward error correction include convolution coding, puncturing and interleaving. The output i then converted into OFDM ymbol and tranmitted over multiple antenna uing orthogonal pace time block coding technique 56
over the multipath fading channel. At the receiving end, the ignal i decoded uing OSTBC decoder and then demodulated by OFDM and QAM demodulator. The Viterbi algorithm i ued to obtain the tranmitted information equence. Fig. : Block Diagram of MIMO OFDM ytem With reference to the above block diagram, the detail regarding the ub-block are a explained below: A. Convolution Coding The main reaon for applying error correction coding in the wirele ytem i to reduce the probability of bit error. The bit error introduced by the tranmiion of the ignal over the channel i either detected or corrected by the decoder at the receiver. In the convolution encoder with the code rate ½, the input given at a rate of k bit per econd give output data bit at k bit per econd. The convolution encoder tructure ued i (7,) in octal number repreent the code generator polynomial with the contraint length of K=7.At the receiver, the decoder ue Viterbi algorithm to recover the information equence through maximum likelihood decoding. B. Puncturing Puncturing i ued to create variable code rate by removing the elected bit and retaining other depending on the puncture vector ued. The code rate of ½ i ued to obtain a ¾ code rate uing the puncture vector [00]. Thi puncture vector allow the four bit with the rd and 5 th bit removed for every ix bit tranmitted. Puncturing eliminate the redundant bit in the convolution encoding thu optimizing tranmiion bit rate. C. Interleaving To improve the performance of the coding in fading channel, coding i combined with the interleaving to overcome the effect of burt error. Interleaving help to pread burt error over many codeword o that each received codeword ha only few imultaneou bit error that can be corrected eaily.the matrix interleaver accept the input row-wie and give output bit column-wie. Then the general block interleaver will re-arrange the bit without repeating or eliminating them. D. Orthogonal Frequency Diviion Multiplexing The dicrete implementation of multicarrier modulation - Orthogonal frequency diviion multiplexing (OFDM) eliminate the inter ymbol interference (ISI) uing the cyclic prefix. The individual ubcarrier are orthogonal to each other o that the overlapping of the ubcarrier doe not caue any interference with the adjacent ubcarrier []. The input bit i modulated by uing QAM modulator wherein, the bit are converted to ymbol. The ymbol are paed through the erial to parallel converter which correpond to the QAM ymbol tranmitted over each ubcarrier. The output of erial to parallel converter i the dicrete frequency component. Thee frequency component are converted to the time domain ample by uing the IFFT on thee N ymbol. The IFFT yield the OFDM ymbol coniting of the equence x[n] of length N []. The cyclic prefix i added to the OFDM ymbol o that ISI between the data block can be eliminated. For the ubcarrier of N=6, a cyclic prefix of length 6 i added. The received ignal i paed through the channel. At the receiver the cyclic prefix i removed. The time ample are erial-parallel converted and paed through FFT. The FFT output i paed through a QAM demodulator to recover the data. The OFDM decompoe the wideband channel into a number of narrowband ub channel with different QAM ymbol ent over each ub channel []. The Fig. hown below how the implementation of OFDM ytem 57
Fig. : Block Diagram of OFDM ytem E. Space Time Block Coding (STBC) In STBC multiple copie of the ame data are tranmitted over a number of antenna.the redundancy reult in higher chance of being able to ue one or more received copie of data to correctly decode the received ignal.stbc can achieve maximal diverity gain with optimal decoding complexity for a given number of tranmit and receive antenna. The firt STBC with two tranmit antenna and one receive antenna wa dicovered by Alamouti, and i now widely known a the Alamouti code. Alamouti code ue a complex orthogonal deign and atifie the condition for complex orthogonality in both pace and time dimenion [].The code matrix i given by () C () A general cla of pace time block code called a orthogonal pace time block coding (OSTBC) can be ued to contruct the code matrix for more than two antenna ytem. For the tranmit antenna and rate ½ i given by () []: C () For a higher code rate of ¾ i given by () []: C () For the tranmit antenna and rate ½ i given by () []: C () For code rate of ¾ i given by (5) []: (5) C In MIMO OFDM, the OFDM ymbol of length N i encoded in the codeword matrix of ize N x M t, where N=Number of ub-channel plu Cyclic prefix length and M t M t =Number of tranmit antenna. 58
After paing through MIMO channel, thereceived ignal i decoded by the OSTBC decoder. The decoder ue a imple maximum likelihood decoding algorithm. The ignal received j at the receiver of whichr t i a ignal at time t at the j-th antenna i given by (6): r t j = Mt (x i t h i,j + n j i=0 t ) (6) r t j i the ignal received by the antenna at the receiver antenna j at time t; x t i i the ignal tranmitted by the tranmitter from the antenna i at time t;h i,j i the channel coefficient and n t j i the channel accepted coefficient. III. SIMULATION Fig. how the Simulink block diagram of MIMO OFDM. The information equence generated by the Bernoulli binary generator i encoded uing convolution encoder with the coding gain of ½.The ingle bit output code i combined to produce punctured code with the rate other than ½.Here, the rate ½ implementation i converted to ¾ code rate called a puncturing. The punctured code i then interleaved to make the forward error correction much more effective in overcoming the burt error. The matrix interleaver and general block interleaver i ued. The code word i mapped by QAM modulation, 6 QAM modulation i ued. The output i given to the OFDM modulator with N=6 ubcarrier and a cyclic prefix of 6 i added reulting in the OFDM ymbol. The OFDM ymbol i tranmitted over the multiple antenna uing orthogonal pace time block coding technique over the fading channel. At the receiver, the data i demodulated and decoded to recover the information equence. The bit error rate i calculated uing error rate calculation. IV. RESULTS The imulation of MIMO OFDM ytem i performed for different M-QAM level uing efficient channel coding technique under different multipath fading channel varying the number of tranmitting and receiving antenna. Fig. how the comparion of M-QAM modulation ued in the OFDM ytem. It how that a the modulation level i increaed, i increaed. 6 QAM outperform higher M-QAM level. 0 0 0-0 - 0-0 - 0-5 0-6 0 5 0 5 0 5 0 Fig. : plot of M-QAM in OFDM 8 QAM OFDM 6 QAM OFDM 56 QAM OFDM Fig. : Simulink Block Diagram of MIMO OFDM 59
Fig.5 and Fig.6 how the of MIMO OFDM ytem without channel coding for different tranmit and receive antenna. The performance of MIMO OFDM improve a tranmit and receive diverity increae. 0 0 0 - Tx Rx MIMO OFDM Tx Rx MIMO OFDM Tx Rx MIMO OFDM 0 0 0-0 - Tx Rx MIMO OFDM Tx Rx MIMO OFDM Tx Rx MIMO OFDM 0-0 - 0-0 -5 0-0 - 0-5 0 5 0 5 0 5 Fig. 5: for x, x, x 6-qam MIMO OFDM under Rayleigh fading channel 0-6 0 6 8 0 6 8 Fig. 7: of x, x, x 6-qam MIMO OFDM with convolution coding under Rayleigh channel 0 0 0 - Tx Rx MIMO OFDM Tx Rx MIMO OFDM Tx Rx MIMO OFDM 0 - Tx Rx MIMO OFDM Tx Rx MIMO OFDM Tx Rx MIMO OFDM 0-0 - 0-0 - 0-0 - 0-5 0-5 0-6 0 5 0 5 0 Fig.6: for x, x, x 6-qam MIMO OFDM under Rician fading channel Fig. 7 and Fig. 8 how the comparion of MIMO OFDM ytem with convolution coding of code rate ¾.The performance i improved with the incluion of channel coding in MIMO OFDM. When examined under Rayleigh and Rician fading channel, performance of MIMO OFDM for with/without channel coding i better under the Rayleigh fading channel. 0-6 0 6 8 0 Fig. 8: for x, x, x 6-qam MIMO OFDM with convolution coding under Rician fading channel V. CONCLUSION The performance of MIMO OFDM ytem i analyed for different M-QAM modulation with convolution channel coding by varying the number of tranmit and receive antenna. Lower modulation order and higher tranmit and receive diverity reduce bit error rate () reulting in better/improved performance. In addition to the above, the reult how that convolution coding cheme under Rayleigh multipath fading channel improve performance with le Signal-to-Noie ratio (SNR). 50
REFERENCES [] Wei Zhang, Xiang-Gen Xia &Khaled Ben Letaief, Space-time/ frequency coding for MIMO-OFDM in Next generation broadband wirele ytem IEEE Wirele Communication, 007 [] Sandeep Kaur, Gurpreet Bharti, Orthogonal frequency diviion multiplexing in wirele communication ytem: A Review International Journal of Advanced Reearch in Computer Engineering & Technology Volume, Iue, May 0. [] Andrea Goldmith, Wirele Communication Cambridge Univerity Pre 005, pp. 7-87 [] Lui Miguel Corte-Pena, MIMO Space-Time Block Coding(STBC): Simulation and reult Deign Project: Peronal and mobile communication, Georgia Tech (ECE660), April 009 5