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IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com

IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com

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  • 1. Kumar Mausam, Sanjay Kumar Sharma / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.659-663 Performance Evaluation of Orthogonal Space-Time Block Codes in MIMO Wireless Communications Kumar Mausam Sanjay Kumar Sharma Department of Electronics and Communication Department of Electronics and Communication Engg. Engg., Mewar University Krishna Institute of Engg. And Technology Chittorgarh (Rajasthan), India Ghaziabad (U.P.), India Abstract— With the integration of voice, Internet new dimensions in communications. People can be and multimedia applications in next generation reached at any time and at any place. Presently, the wireless mobile communication, the demand for wireless communication research community and reliable high data rate and quality of service is industry are exploring standards for the fourth growing at a very rapid pace. The increasing generation (4G) of mobile communication. There are requirements on the service quality and data flow many drawbacks in the wireless communication in wireless mobile communication system call for environments, such as multipath fading, Doppler new approaches to improve the bandwidth frequency shifting and channel change. In order to efficiency and reliability of the systems. Recently, ensure the stable transmission, many useful MIMO systems with multiple antenna elements at technologies have been provided. The research both link ends have received great attention for community has generated a number of promising future wireless communications systems as they solutions for significant improvements in system provide high data rates by exploiting the spatial performance. Wireless communication is highly domain under the constraints of limited challenging due to the complex, time varying bandwidth and transmit power and thus have propagation medium. If we consider a wireless link capabilities to improve the overall system with one transmitter and one receiver, the transmitted performance. In MIMO wireless mobile signal that is launched into wireless environment communications, space-time block coding (STBC) arrives at the receiver along a number of diverse is an attractive approach to achieve high bit rate paths, referred to as multi-paths. These paths occur and reliable transmission over fading channels. from scattering and rejection of radiated energy from Space-Time Block Coding (STBC) exploits objects like buildings, hills, trees etc. and each path transmit diversity and high reliability. Although has a different and time-varying delay, angle of STBC has full diversity gain but no coding gain. arrival, and signal amplitude. Because of this, the Usually, STBCs are of two types i.e. Orthogonal received signal can vary as a function of frequency, Space-Time Block Codes (OSTBCs) and Non- time and space. These variations are referred to as Orthogonal Space-Time Block Codes fading and cause deterioration of the system quality (NOSTBCs). This paper presents the bit error [1,2]. Therefore, wireless systems must be designed rate performance evaluation of orthogonal space- to mitigate fading and interference to guarantee a time block codes with multiple transmit antennas reliable communication. in wireless mobile communication systems with A successful method to improve reliable the help of computer simulation. The research communication over a wireless link is to use multiple study shows that combined use of multiple antennas at the transmitter and at the receiver. transmit antennas and Orthogonal Space-Time Multiple antennas play an important role in Block Codes (OSTBCs) results in the significant improving radio communications. Multiple antenna overall system performance without any extra systems have the potential of achieving high rate data signal processing. access and increased capacity of mobile services. MIMO stands for multiple-input multiple-output and Keywords— Space time block codes, Diversity, means multiple antennas at both link ends of a MIMO systems, Bit Error Rate (BER) and Multipath communication system, i.e., at the transmit and at the fading, Rayleigh fading channels, Orthogonal Space- receive side. The multiple-antennas at the transmitter Time Block Codes. and/or at the receiver in a wireless communication can improve the system performance substantially.I. INTRODUCTION The idea behind MIMO is that the transmit antennas In modern times, communication at one end and the receive antennas at the other end technologies have become a very vital part of human are ―connected and combined‖ in such a way that the life. Wireless communication systems have opened quality (the bit error rate (BER), or the data rate) for 659 | P a g e
  • 2. Kumar Mausam, Sanjay Kumar Sharma / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.each user is improved. The core idea in MIMO their number of inputs and outputs. The simplesttransmission is space-time signal processing in which configuration is a single antenna at both sides of thesignal processing in time is complemented by signal wireless link, denoted as single-input/single outputprocessing in the spatial dimension by using multiple, (SISO) system. Using multiple antennas on one orspatially distributed antennas at both link ends [3,4]. both sides of the communication link are denoted asIn case of multiple antennas at both link ends, multiple input/multiple output (MIMO) systems [14].utilization of diversity requires a combination of the The difference between a SISO system and a MIMOreceive and transmit diversity. The diversity order is system with Nt transmit antennas and Nr receivebounded by the product of the number of antennas is the way of mapping the single stream oftransmit and receive antennas [5,6]. data symbols to Nt streams of symbols and the The key feature of all diversity methods is to corresponding inverse operation at the receiver side.provide a low bit error rate. Usually, the system Systems with multiple antennas on the receive sideperformance with diversity techniques depends on only are called single input/multiple output (SIMO)signal replicas combined at the receiver end to systems and systems with multiple antennas at theincrease the value of signal to noise ratio. Basically, transmitter side and a single antenna at the receiverthere are four main types of signal combining side are called multiple input/single output (MISO)techniques at the receiver. These are: selection systems [15].combining, switched combining, equal-gain combin- The MIMO system is the most general and includesing and maximum ratio combining (MRC). More SISO, MISO, and SIMO systems as special cases. Toinformation about combining techniques can be transmit information over a single wireless link,found in [7, 8]. Because of the enormous capacity different transmission and reception approaches canincrease MIMO systems offer, such systems gained a be applied. Which one of them should be usedlot of interest in mobile communication research depends on the knowledge of the instantaneous[9,10]. Several transmission schemes have been MIMO channel parameters at the transmitter side.proposed that utilize the MIMO channel in differentways, e.g., spatial multiplexing, space-time coding orbeam forming. Space-time coding (STC), introducedfirst by Tarokh at el. [11], is a promising methodwhere the number of the transmitted code symbolsper time slot are equal to the number of transmitantennas. These code symbols are generated by the Transmitter Receiverspace-time encoder in such a way that diversity gain,coding gain, as well as high spectral efficiency are (Tx) (Rx)achieved. There are various coding methods as space-timetrellis codes (STTC), space-time block codes(STBC), space-time turbo trellis codes and layered Fig. 1 A Basic MIMO Communicationspace-time codes [13]. This paper explains the Systemconcept of orthogonal space-time block coding in a III. SPACE TIME BLOCK CODESsystematic way. The paper provides an overview ofOSTBCs design principles and performance. In this (STBCs) Space-time coding is a technique thatpaper, we investigate and analyze the bit error rate promises greatly improved performance in wireless(BER) performance of orthogonal space-time block networks by using multiple antennas at thecodes in MIMO wireless communication systems transmitter and receiver. Space-Time Codes (STCs)with the help of computer simulation. are widely used in cellular communications as well The rest of the paper is organized as follows. In as in wireless local area networks. Space-timesection 2, we present structure of a basic wireless coding (STC) is performed in both spatial andMIMO system. Various space-time block codes temporal domain, which introduce redundancy(STBC) have been introduced in section 3. In section between those signals that are transmitted from4, we have introduced the concept of OSTBCs. In different antennas at different time instants. With thesection 5, we have formulated the simulation help of space-time coding (STC), transmit diversityenvironments and simulation results are presented to and antenna gain can be achieved over spatiallysee the performance and we conclude the paper with uncoded systems without any loss of bandwidth.some remarks in section 6. Thus, space-time coding (STC) focuses on II. A BASIC MIMO improving the system performance by using a fewCOMMUNICATION SYSTEM extra transmit antennas. Usually, the design of STC Wireless systems consisting of a transmitter, leads to finding transmit matrices, which can satisfya radio channel and a receiver are categorized by a particular optimality criterion. While designing 660 | P a g e
  • 3. Kumar Mausam, Sanjay Kumar Sharma / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.STC, we have to trade-off between three main order equal to NtNr. Orthogonal STBCs haveaspects. These are a simple decoding scheme, received considerable attention in recent open loopminimizing the bit error rate (BER), and maximizing multiple input multiple output (MIMO) wirelessthe information rate or data rate. For small values of mobile communication systems because they allowtotal diversity and slow fading channels, the low complexity maximum likelihood decoding anddiversity and the coding gain must be maximized by guarantee full diversity [13]. The main drawback ofchoosing an appropriate code having the largest OSTBCs is the fact that for more than two transmitdeterminant of the distance matrix. antennas and complex-valued signals, OSTBCs onlyFor fast fading channels, a code with the largest exist for code rates smaller than one symbol per timeminimum symbol-wise Hamming distance and the slot. An OSTBC is a linear space-time block code Slargest product distance must be chosen. Basically that has the following unitary property:there are two different space-time coding methods. NThese are space-time trellis codes (STTCs) andspace-time block codes (STBCs). STTC has been SH  | sn |2 I S ...(1) n 1introduced in [3]. This is a coding technique that The i-th row of S corresponds to the symbolsyields full diversity and sufficient coding gain at the transmitted from the i-th transmit antenna in Ncost of a quite high decoding complexity. To avoid transmission periods, while the j-th column of Sthis drawback, STBCs have been proposed by represents the symbols transmitted simultaneouslyAlamouti [12]. Alamouti code yields full diversity through nt transmit antennas at time j. According toand full data rate in case of two transmit antennas.The special feature of this scheme is that the signal equation (1) the columns of the transmission matrix Svectors transmitted over the two transmit antennas are orthogonal to each other. That means that in eachare orthogonal to each other. This scheme can be block, the signal sequences from any two transmitgeneralized to an arbitrary number of transmit antennas are orthogonal. The orthogonality enablesantennas with the help of orthogonal design us to achieve full transmit diversity and at the sameprinciples. time, it allows the receiver by means of simple MRCThe generalized schemes are referred to as space- to decouple the signals transmitted from differenttime block codes. Thus, in brief, space–time block antennas and consequently, it allows a simple MLcoding is a technique used in wireless decoding.communications to transmit multiple copies of a data A. Few illustrations of OSTBCsstream across a number of antennas and to exploit 1. OSTBC with a rate of 1/2 symbol per timethe various received versions of the data to improve slotthe reliability of data-transfer. The fact that the For any arbitrary complex signaltransmitted signal must traverse a potentially constellation, there are OSTBCs that can achieve adifficult environment with scattering, reflection, rate of 1/2 for any given number of Nt transmitrefraction and so on and may then be further antennas. For example, the code matrices S3 and S4corrupted by thermal noise in the receiver means that are OSTBCs for three and four transmit antennas,some of the received copies of the data will be respectively and they have the rate 1/2 [3]. With thebetter than others. This redundancy results in a code matrix S3, four complex symbols are taken at ahigher chance of being able to use one or more of time and transmitted via three transmit antennas inthe received copies to correctly decode the received eight time slots. Thus, the symbol rate is 1/2. Withsignal. In fact, space–time coding combines all the the code matrix S4, four symbols are taken at a timecopies of the received signal in an optimal way to and transmitted via four transmit antennas in eightextract as much information from each of them as time slots, resulting in a transmission rate of 1/2 aspossible.Thus, the essential feature of STBCs is the well.provision of full diversity with extremely lowencoder/decoder complexity.  s1 s2 s3  s s1  s4 IV. ORTHOGONAL SPACE-TIME  2 BLOCK CODES (OSTBCs)   s3 s4 s1    The pioneering work of Alamouti has been   s4  s3 s2 a basis to create OSTBCs for more than two transmit S3=  s* * s2 s3  * ...(2)antennas. First of all, Tarokh studied the error  1 performance associated with unitary signal matrices.   s* * s1  s4  *Orthogonal STBCs are an important subclass of  2    s* * s4 s1  *linear STBCs that guarantee that the ML detection of  3 different symbols {sn} is decoupled and at the same   s4  *  s3 * s2  * time the transmission scheme achieves a diversity 661 | P a g e
  • 4. Kumar Mausam, Sanjay Kumar Sharma / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.  s1 s2 s3 s4  antennas, the 16-QAM constellation and the codes s s1  s4 s3  S3 from equation (4) and S  from equation (5),   2  4   s3 s4 s1  s2  respectively, are utilized.   The total transmission rate in each case is 6- s  s3 s2 s1  S4=  *4 s . ..(3) bits/second. It may be observed that at the BER of  1 * s2 * s3 s4  *  10–2, the rate 3/4 16-QAM code S  provides about 9   s* * s1  s4 * s3  * 4  2  dB gain over the use of an uncoded 4-PSK data   s* * s4 * s1  s2  * transmission. For higher SNR values, the code S   3  4   s4  *  s3 * * s2 s1  *  for four transmit antennas provides about 6 dB gain at BER = 10–3 over use of the Alamouti code. Figure2. OSTBC with a rate of 3/4 3 illustrates bit error rate (BER) for OSTBCs using The following code matrices S3 and S4 are two, three, and four transmit antennas together withcomplex generalized designs for OSTBC with rate an uncoded 8-PSK transmission. The transmission3/4 for three and four transmit antennas, respectively using two transmit antennas employs the 8-PSK[3]. constellation and the Alamouti code. For three and four transmit antennas, the 16-QAM constellation and the codes S3 and S4, respectively, are used. Since  s3  S3 and S4 are rate 1/2 codes, the total transmission  s1 s2  rate in each case is 4 bits/second. It may be observed  2   * s3  that at the BER of 10–3 the rate 1/2 16-QAM code S4   s2 * s1  gives about 8 dB gain over the use of an uncoded 4-  2  PSK data transmission and at BER = 10–4 about 2 dB S 3 =  s*  * s3 * *  (4) ( s1  s1  s2  s2 ) over the codes with two and three transmit antennas.  3  From simulation results, it may be observed that with  2 2 2  increase in the number of transmit antennas; a  * *  significant performance gain can be achieved. One  s3 s* ( s2  s2  s1  s1 )  *   3  very important feature of OSTBCs is that if we   2 2 2   increase the number of transmit antennas, the decoding complexity is not significantly increased,  s3 s3  due to the fact that only linear processing is required  s1 s2  for decoding.  2 2   * *  100 s3 s3 s2 s1   uncoded Tx = 2, Rx = 1  2 2  –1 × Tx = 3, Rx = 1  s* s* (  s  s*  s  s* ) (  s  s *  s  s * )  10S =  3 4 3 1 1 2 2 2 2 1 1  (5) Tx = 4, Rx = 1  2 2 2 2  Bit Error Rate (BER)  * *  10 –2  s3 s3 (s2  s2  s1  s1 ) (s1  s1  s2  s2 )  * * * *     2  2 2 2   10–3 ×Obviously, some transmitted signal samples arescaled linear combinations of the original symbols. 10–4 ×V. SIMULATION RESULTS This section provides simulation results forthe codes given above. In figure 2 and figure 3, we 10–5have drawn the bit error rate (BER) curves against 5 10 15 20 25 SNR (dB)SNR values for the Nt x 1 configuration withRayleigh channel coefficients using OSTBCs. Here, Fig. 2. BER performance for OSTBCs of 6we consider two special cases. Figure 2 shows bit bits/channel using (Nt × 1) configurationerror rate (BER) for OSTBCs for an uncoded 4-PSKand for the OSTBCs using two; three, and fourtransmit antennas. The transmission using twotransmit antennas makes use of 4-PSK constellationand the Alamouti code. For three and four transmit 662 | P a g e
  • 5. Kumar Mausam, Sanjay Kumar Sharma / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp. 0 10 REFERENCES uncoded [1] I.E. Telatar, ―Capacity of Multi-Antenna Tx = 2, Rx = 1 Gaussian Channels‖, AT&T Bell Labs, 1995. × Tx = 3, Rx = 1 [2] G. J. Foschini, M. J. Gans, "On Limits of 10–1 Wireless Communications in Fading Tx = 4, Rx = 1 Environments when Using Multiple Antennas",Bit Error Rate (BER) × Wireless Personal Communications, vol. 6, pp. –2 311-335, March 1998. 10 [3] V. Tarokh, N. Seshadri, A. R. Calderbank, × "Space-Time Codes for High Data Rate Wireless Communication: Performance Criterion and 10–3 Code Construction", IEEE Trans. Inform. Theory, vol. 44, no. 2, pp. 744-765, March 1998. [4] Z. Liu, G. B. Giannakis, S. Zhou, B. Muquet, × ―Space-time coding for boradband wireless –4 10 communications‖, Wireless Communications and Mobile Computing, vol. 1, no. 1. pp. 35-53, Jan. 2001. J. H. Winters, ―On the capacity of radio 10–5 × [5] 5 10 20 15 25 30 35 communication systems with diversity in a SNR (dB) Rayleigh fading environment‖, IEEE Journal on Selected Areas in Communications, pp. 871- Fig. 3. BER performance for OSTBCs of 4 bits/channel 878, June 1987. using (Nt × 1) configuration [6] A. Wittneben, ―A new bandwidth efficient transmit antenna modulation diversity scheme VI. CONCLUSIONS for linear digital modulation‖, IEEE Int. This paper presents the bit error rate Conference on Com., vol. 3, pp. 1630 - 1634, performance evaluation of orthogonal space-time Geneva, May 1993. block codes with multiple transmit antennas in [7] V. Tarokh, N. Seshadri, A. R. Calderbank, wireless mobile communication systems with the ―Combined Array Processing and Space-Time Coding‖, IEEE Trans. Inform. Theory, vol. 45, help of computer simulation. We plot the bit error no. 5, pp. 1121 - 1128, May 1999. rate (BER) versus SNR for the Nt x 1 configuration [8] A. Hottinen, O. Tirkkonen, R. Wichman, ―Multi- with Rayleigh channel coefficients using OSTBCs. Antenna Transceiver Techniques for 3G and Be- From simulation results, it may be observed that yond‖, John Wiley and Son Ltd. 2003. increasing the number of transmit antennas yields [9] M. K. Simon, M.-S. Alouini, Digital reasonable performance gain. One of the most Communication over Fading Channel: A Unified Approach to Performance Analysis, John Wiley illustrative features of OSTBCs is that increasing the & Sohn, 2000. number of transmit antennas does not increase the [10] T. S. Rappapot, Wireless Communications: decoding complexity significantly. This happens due Principles and Practice, Prentice Hall, 1996. to the fact that we need only linear processing for [11] M. Rupp, H. Weinrichter, G. Gritsch, decoding. Simulation results show that full ―Approximate ML Detection for MIMO transmission rate is more important at very low SNR Systems with Very Low Complexity‖, values and high BERs, whereas full diversity is the ICASSPO04, Montreal, Canada, pp. 809-812, right choice for high SNR values and low BERs. May 2004. This is due to the fact that the slope of the [12] S.M. Alamouti, A Simple transmit diversity technique for wireless communication, IEEE J. performance curve at high SNR is determined by the Select. Areas Commun., vol.16, no. 8, pp diversity order. Note that the receiver of the full 1451-1458, Oct. 1998. diversity OSTBC can decode the symbols one by [13] Hao Zhang and T. Aaron Gulliver, ―Capacity one. This means that the decoding complexity of the and Error Probability analysis for Orthogonal full diversity orthogonal codes is lower, although Space Time Block Codes over fading channels‖, OSTBCs have a very low decoding complexity IEEE Transaction on Wireless Communications compared to the decoding of Space-Time Trellis ,vol.4, No. 2, pp. 808-819, March 2005. Codes. The encoding complexity of the system is [14] A. Hottinen et al., ―Industrial embrace of smart low for both types of OSTBCs. Thus, the research antennas MIMO,‖ IEEE Wireless Commun, Mag., August 2006. study shows that combined use of multiple transmit [15] E. Biglieri et al.,‖Diversity,interference antennas and Orthogonal Space-Time Block Codes cancellation and spatial multiplexing in MIMO (OSTBCs) results in the significant overall system mobile WiMAX systems‖, to appear in IEEE performance without ant extra signal processing. WiMAX’07,2007. 663 | P a g e

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