BER Performance of MIMO-OFDM System using STTC

Transcription

1 International Journal of Sientifi Researh Publiations, Volume 3, Issue, February 3 ISS BER Performane of MIMO-OFDM System using STTC K.Vidhya *, K.R.Shankarkumar ** * APECE, Sri Ramakrishna Engineering College, Coimbatore-, vidhyasre@gmail.om ** ProfessorECE, Sri Ramakrishna Engineering College, Coimbatore-, shanwire@gmail.om Abstrat- This aer rovides the hannel arameter estimation bit error rate erformane for multile-inut multile-outut (MIMO) orthogonal frequeny division multilexing (OFDM) system in new transmission sheme. Channel estimation arameter bit error rate alulation for x MIMO OFDM system is erformed. This new transmission sheme is used in symmetri hannels suh as the link between two transmit antennas two reeive antennas in the system. Channel arameters are estimated with the hel of ilot data. These are send by the reeiver to the transmitter. The roosed x MIMO hannel model rovides good erformane omared to onventional MIMO OFDM system model. Mat lab software is used to simulate the results in this aer. I. ITRODUCTIO igh data rate wireless ommuniation links with transmission rates nearing Gigabitseond, in whih hannel aaity is ahieved[]. MIMO OFDM system model rovides high seed links that offer good quality of servie, this will minimize the robability of error. Real life issues are minimize omlexity ost of imlementation of roosed system, minimize the transmission ower required bwidth used. MIMO is known to boost hannel aaity[]. OFDM system is b width effiient, robust to multiath fading, easy to imlement by using IFFT FFT algorithm flexible in resoure alloation. It onverts a frequeny seletive hannel into a arallel olletion of frequeny flat sub hannels[3]. It imroves multiath fading issues. It redues the effet of inter symbol interferene. In OFDM system, transmitter side initially the high serial data rate inut with samling time T s is modulated using any digital modulation tehniques to give digital symbols. ext the modulated serial data is onverted to low rate arallel data stream using serial to arallel onverter. Due to this arallel onversion, the effetive symbol duration is inreased to T= MT s. To mitigate the effet of ISI, yli refix is used. In Channel the transmitted signal x(t) travels though wireless hannel through multiath in various tyes of environments (indoor, outdoor, stati mobile)thus the signal y(t) undergo distortion, sattering, refletion addition of noise. These henomenon ultimately haraterizes the hannel mathematially in terms of delay sread fading oeffiients of the hannel whih are treated as rom variables. In reeiver side yli refix is arried out from the reeived signal first. After CP removal the signal is demodulated using FFT, whih onverts the time domain signal to frequeny domain signal. MIMO enoding, suh as Alamouti Sae Time Blok oding (STBC), the Vertial Bell-Labs layered Sae Time Blok ode (VBLASTSTBC), Sae-Time Trellis Code ( STTC)[4] In this aer, hannel arameter estimation bit error rate erformane of MIMO OFDM systems is roosed. The no of reeiving antennas inreases, bit error rate will be redues signifiantly for the symmetri hannel. The rinial of this aer is based on hannel oding whih make use of the estimated hannel arameters extrated from a ilot signal transmitted by the destination reeiver. The aer is desribed as follows. In setion II, the onventional MIMO-OFDM system is desribed. In setion III, the new transmission model is resented. In setion IV, the hannel matrix bit error rate erformanes of the roosed transmission sheme are analyzed via simulations, a omarative study with the onventional MIMO-OFDM system using sae time trellis ode (STTC) enoder is also desribed. Finally, onlusions are drawn in setion V. II. COVETIOAL MIMO-OFDM SSTEM The onventional MIMO-OFDM system is shown in figure. The roosed system onsists of transmit reeive antennas. In transmitter side initially mas the sequene of bits in eah satial stream to onstellation oints. Then it is enoded in to digital form. A ilot sequene is inserted used for the hannel estimation. Then, a yli refix is inserted in front of the OFDM symbol at the last ste of OFDM modulation blok. The time length of the yli refix should be greater than the maximum delay sread of the hannel[5]. The urose of adding yli refix is to guard the OFDM symbol against Inter Symbol Interferene (ISI), hene, this yli refix is alled the guard interval of the OFDM symbols. The MIMO oding an use several enoders suh as STBC, STTC oding. In this aer, the onventional MIMO-OFDM system is imlemented using STTC with two transmit two reeive antennas[6]. Figure.Conventional MIMO-OFDM system model

2 International Journal of Sientifi Researh Publiations, Volume 3, Issue, February 3 ISS III. EW TRASMISSIO MODEL The new transmission model is suitable for symmetri hannels, suh as the transmission between two transmit antennas two reeive antennas. The roosed MIMO-OFDM model is shown in the following figure. Where: are the orthogonal transmitted ilot signals from the transmit antenna T T resetively. are the reeived ilot signals on the reeive antenna R R resetively. are the reeived information at time slot on reeive antenna R R resetively. ij is the hannel from j th transmit antenna Tj to i th antenna Ri with i j {,}. reeive are the noise omonents on reeive antenna R R resetively. Figure. Proosed MIMO-OFDM system model for symmetri hannel. In this new MIMO-OFDM model, the hannel arameters are estimated from a ilot data transmitted by the reeiver side[7]. These estimated arameters are used by a seial hannel oding blok to adat the transmitter signal to the diverse hannel imairments variations[8]. To redue the system omlexity we have removed the ilot insert, the ilot extration, the MIMO enoder the MIMO deoder from the onventional MIMO-OFDM sheme[9]. The hannel oding is based on the hannel arameters, this hannel in our ase is between two transmit antennas two reeive antennas, it an be modeled as shown in the figure. First, the reeiver send a ilot signal to the transmitter, whih an exressed as follows :.... () are the noise at time slot on the reeive antenna R R resetively. Let us also define the ilot reeived signal the matrix hannel the ilot transmitted signal the noise vetor as follows resetively. as By using the above notations, equation () an be rewritten. () Using the transmitted ilot signal the reeived ilot signal, the hannel arameters are estimated as following ˆ Figure 3. x hannel model

3 International Journal of Sientifi Researh Publiations, Volume 3, Issue, February 3 3 ISS The term beause the ilots are hosen to be orthogonal signals. then In addition, if the ilot signal ower is (3) (4) >> Similarly, all hannel arameters ij an be easily deduted ˆ ˆ ˆ......, if if if By ombining results obtained from equations (3), (5), (6) (7), a more omat exression an be easily written ˆ ˆ ˆ ˆ.[ ]. (5) (6) (7) (8) ˆ ˆ ˆ ˆ ˆ then () Moreover, equation (9) an be further rewritten as follows. Where, P P (.( )).A A. () (9) If simlified () Finally, the hannel an be easily estimated using the following exression A. A A...(.(.( ) ) ) (3) (4) (5) Consequently, the hannel oding rinial an be easily imlemented by just multilying the original transmitted signal with the inverse of the estimated hannel to extrat the oded signal given by ˆ.. (6) The reeived signal of the seond time slot is given by the following equation (7)..... (7) (8). (9)

4 Bit Error Rate International Journal of Sientifi Researh Publiations, Volume 3, Issue, February 3 4 ISS The advantage of this hannel oding is that there is no need to erform the hannel estimation MIMO enoding at the reeiver, beause going through the hannel the reeived signal beomes -... ˆ () So we an diretly demodulate the reeived signal to find the estimation of the original transmitted symbol. IV. SIMULATIO RESULTS The new transmission MIMO-OFDM system is simulated using arameters shown in Table. These arameters are based on transmission between two transmit two reeive antennas. Table. Simulation Parameters Parameters Seifiations System x MIMO-OFDM o of Subarrier 64 Modulation QAM Delay Sread 5 Size of DFTIDFT 64 MIMO enoder STTC (Tx Rx) In this aer we are interested in omaring the roosed sheme with the onventional MIMO- OFDM system in the ase of symmetri hannel based on STTC oding []. This simulation onsiders the transmission between two transmit reeive antennas. The hannel arameters are used for the hannel oding in the new transmission sheme[]. Figure 4 shows the variation of BER as a funtion of SR. This system has better erformanes than the onventional MIMO-OFDM system. Besides the erformane of this sheme, its omlexity is low there are no needs of omliate MIMO enoder or hannel estimation at the reeiver side. In addition, to the simlifiation of the onventional MIMO-OFDM system, bwidth effiieny an be highly inreased Bit Bit Error Error Rate Rate with with BPSK QAM Modulation Modulation Tx=,Rx= Tx=,Rx=, MRC Tx=, Rx=, Alamouti Proessed (Tx=, Rx=, Alamouti) Ebo, db Figure 4. Bit Error R ate as funtion of Signal to oise Ratio Table shows the values of BER orresonding SR The roosed sheme has better erformanes than the onventional MIMO-OFDM system when the number of antennas inreases. Table. SR Vs BER values for MIMO OFDM System Eb o BER Tx Rx Tx Rx Tx Rx Tx Rx e e e e e e e e e e e e -5.5e e -6.94e e e -4.95e -6.73e e e -4.78e e e e e e e e e e -7.87e e e e e e e -8.87e -7.97e -8 Table 3 shows the hannel arameter values for x hannel model for only five subarriers. Table 3. Channel Matrix of x Channel Model V. COCLUSIO This aer rovides hannel arameter estimation bit error rate erformane for multile-inut multile-outut (MIMO) orthogonal frequeny division multilexing (OFDM) systems in new transmission sheme. This system is based on hannel oding using estimated hannel arameters from a transmitted ilot data at the reeiver end. Simulation results onfirm the high erformane the low omlexity of the

5 International Journal of Sientifi Researh Publiations, Volume 3, Issue, February 3 5 ISS roosed transmission sheme when omared to the onventional MIMO OFDM system using STTC Coding. REFERECES [] e (Geoffrey) Li, ambirajan Seshadri Sirikiat Ariyavisitakul, "Channel Estimation for OFDM Systems with Transmitter Diversity in Mobile Wireless Channels", IEEE Journal on Seleted Areas in Communiations, Vol. 7, o. 3, , Marh 999. [] e (Geoffrey) Li, Jak. Winters elson R. Sollenberger, "MIMO- OFDM for Wireless Communiations: Signal Detetion with Enhaned Channel Estimation", IEEE Transations on Communiations, Vol. 5, o. 9, , Se. [3] M.P. Chitra S.K. Srivatsa, "BER Analysis of Coded Unoded MIMO-OFDM System in Wireless Communiation", Indian Journal of Comuter Siene Engineering, Vol., o. 4, , De. [4] eetu Sood, Ajay K Sharma Moin Uddin, "On Channel Estimation of OFDM-BPSK -QPSK over akagami-m Fading Channels", An International Journal (SPIJ), Vol. 4, ,. [5] A. Omri, R. Bouallegue, R. amila M. asna, "Channel Estimation for LTE Ulink System by Peretron eural etwork", International Journal of Wireless & Mobile etworks, Vol., o. 3, , Aug. [6] Imad Barhumi, Geert Leus Mar Moonen, "Otimal Training Design for MIMO OFDM Systems in Mobile Wireless Channels", IEEE Transations on Signal Proessing, Vol. 5, o. 6, , June 3. [7] Marello Cierone, Osvaldo Simeone Umberto Sagnolini, "Channel Estimation for MIMO-OFDM Systems by Modal AnalysisFiltering", IEEE Transations on Communiations, Vol. 54, o.,. 6-74, ov 6. [8] Berna Ozbek Reyat ilmaz, "The Adative Channel Estimation for STBC-OFDM Systems", Journal of Eletrial & Eletronis Engineering, Vol. 5, o., , 5. [9] Prasanta Kumar Pradhan, Oliver Fausty, Sarat Kumar Patra Beng Koon Chua, "Channel Estimation Algorithms for OFDM Systems",International Conferene on Eletronis Systems, ational Institute of Tehnology, India, Jan. [] e (Geoffrey) Li, Leonard J. Cimini elson R. Sollenberger, "Robust Channel Estimation for OFDM Systems with Raid Disersive Fading Channels", IEEE Transations on Communiations, Vol. 46, o. 7,. 9-95, July 998. [] Omri R.Bouallegue, ew Transmission Sheme for MIMO OFDM Syatem International Journal of ext Generation etworks Vol. 3 o., Marh AUTORS First Author K.Vidhya obtained her Bahelor s degree in Eletronis Communiation Engineering from University of Madras. Then she obtained her Master s degree in Communiation Systems from Anna University Chennai ursuing PhD in wireless ommuniation in Anna University, Chennai. She is a Assistant Professor at the Faulty of Eletronis Communiation Engineering, Sri Ramakrishna Engineering College, Coimbatore. er seializations inlude Wireless Communiation, Wireless networks. er urrent researh interests are hannel estimation on OFDM Systems. She is a member of ISTE, IETE. Seond Author Dr.K.R.Shankar Kumar reeived the B.E. degree in Eletronis Communiation Engineering from the Coimbatore Institute of Tehnology, Coimbatore in 997, M.E. degree in Eletronis from the Madras Institute of Tehnology, Chennai, in 999, the Ph.D. degree in CDMA Systems from the Indian Institute of Siene, Bangalore in 4. e is urrently Professor in the Deartment of Eletronis Communiation Engineering at Sri Ramakrishna Engineering College, Coimbatore. is seializations are Mathematis Wireless Communiation. is urrent researh interests are MIMO systems, Transeiver Design. e is a member of IEEE, ISTE, IETE.