Please cite this article in press as: Shrivastava N, Trivedi A. Combined beamforming with space-time-frequency coding for MIMO–OFDM systems. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.01.013 ARTICLE IN PRESS G Model AEUE 51359 1–6 Int. J. Electron. Commun. (AEÜ) xxx (2015) xxx–xxx Contents lists available at ScienceDirect International Journal of Electronics and Communications (AEÜ) j ourna l h om epage: www.elsevier.com/locate/aeue Combined beamforming with space-time-frequency coding for MIMO–OFDM systems Neeraj Shrivastava, Aditya Trivedi Q1 ABV-Indian Institute of Information Technology and Management, Gwalior, India a r t i c l e i n f o Article history: Received 15 October 2013 Accepted 29 January 2015 Keywords: Space-time-frequency code MIMO OFDM Beamforming Diversity order a b s t r a c t Multiple antennas can be used in wireless systems to achieve good quality of service and high data rate communication. Recently, efficient space-time-frequency (STF) codes have been developed to improve the diversity gain. This paper aims at performance analysis of multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO–OFDM) system using STF Coding and random beamforming. The proposed approach which combines beamforming with STF code offers improved performance over STF in term of bit error rates (BER). It is also observed that the proposed scheme gives better performance as compared to the combined space-time block code (STBC) with beamforming. Computational complexity of the proposed scheme is also calculated. © 2015 Published by Elsevier GmbH. 1. Introduction Diversity is an effective technique to combat fading and Q2 increase the transmission reliability over wireless channels since it provides multiple independent replica of the trans- mitted signal at the receiver. The adverse effects of the wireless propagation environment can be significantly reduced by employing multiple-input multiple-output (MIMO) communica- tion systems. MIMO systems have achieved a focus of attention because it can significantly increase the spectral efficiency by exploiting the spatial degrees of freedom created by multiple antennas [1]. In wireless communications, where the channel experiences frequency selectivity, called frequency diversity, can be exploited by taking advantage of the frequency-selectivity characteristic of the channel. Both transmit diversity and orthogonal frequency- division multiplexing (OFDM) have been receiving a lot of attention and have shown great potential for the next generation wireless communication systems [2] due to its robustness to multi path fading, high spectral efficiency, and high flexibility in resource allo- cation. MIMO systems using OFDM have been actively investigated for the ever increasing demand of high data rate transmis- sion in recent or future telecommunication systems. Multiple- input multiple-output orthogonal frequency-division multiplexing E-mail addresses: neeraj@iiitm.ac.in (N. Shrivastava), atrivedi@iiitm.ac.in (A. Trivedi). (MIMO–OFDM) is used in 4G/LTE wireless communication sys- tems. This combination has the potential of meeting the stringent requirement of 4G/LTE, since MIMO can boost the capacity and diversity while OFDM can mitigate the detrimental effects due to multi path fading [3]. Many techniques have been developed to achieve the maximum diversity provided by the MIMO channel. Space-time (ST) coding exploits the spatial diversity provided by the number of transmit antennas [4]. However, frequency selective channels provide an extra diversity dimension: frequency diversity. Thus, space-time- frequency (STF) and space-frequency (SF) coding were developed to exploit the maximum diversity provided by MIMO frequency selec- tive channels [5]. In contrast to spatial multiplexing techniques, where the main objective is to provide higher bit rates compared to a single-antenna system, diversity techniques predominantly aim at an improved error performance. This is accomplished on the basis of a diversity gain and a coding gain. Indirectly, diversity techniques can also be used to enhance bit rates, when employed in conjunction with an adaptive modulation/channel coding scheme [6]. Cho et al. in [7] is proposed a new beamforming strategy for the multiuser systems which consist of N transmit antennas at the transmitter side and M ≤ N single antenna receivers end. The pro- posed scheme improves on the classical spatial division multiple accesses, and achieves the same data rates as spatial multiplexing for all users but with significantly superior performance/diversity gain. When it is compared with the Bell labs layered space-time system, its symbol rate is the same and the performance is much superior due to diversity gain. http://dx.doi.org/10.1016/j.aeue.2015.01.013 1434-8411/© 2015 Published by Elsevier GmbH. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71