IOSR Journal of Electronics and Communication Engineering (IOSR-JECE) e-ISSN: 2278-2834,p- ISSN: 2278-8735 PP 30-36 www.iosrjournals.org International Conference on Future Technology in Engineering – ICFTE’16 30 | Page College of Engineering Perumon Test bed for Selecting Optimum Sequences for Preamble Structures in MIMO OFDM Suma Sekhar 1 , Sakuntala S.Pillai 2 1 (Department of Electronics and Communication, LBS Institute of Technology for Women, Poojappura, Thiruvananthapuram, India) 2 (Senior Member, IEEE, Department of Electronics and Communication, Mar Baselios College of Engineering & Technology, Trivandrum, India) Abstract: The main challenge faced during the implementation of Multiple Input Multiple Output(MIMO) Orthogonal Frequency Division Multiplexing (OFDM)System is that it is subjected to impairments of frequency and timing offsets which causes performance degradation of the system. Preamble based offset estimation techniques are equipped with mathematical sequences in the header of each OFDM frame. To ensure accurate estimation of offsets, selection of apt sequence is crucial. The sequences with high autocorrelation properties and low autocorrelation side lobes are preferred. A test bed for analyzing the correlation properties and side lobe level of the sequence is developed and discussed in this paper. Keywords: MIMO OFDM, Timing Metric, Schmidl and Cox algorithm, Minn’s Algorithm, Gold, Kasami, Barker, GCL. I. Introduction The high bandwidth requirements in the new generation data transmission applications are increasing day by day and demanding efficient exploitation of frequency spectrum. The data throughput can be improved significantly without additional bandwidth or transmit power by placing multiple antenna elements both on transmitter or receiver, the technology referred to as Multiple Input Multiple Output (MIMO). Increased spectral efficiency through spatial multiplexing, improved link reliability through antenna diversity and high capacity are the main attractions of MIMO. Sufficient robustness to radio channel impairments can be provided by selecting Orthogonal Frequency Division Multiplexing modulation (OFDM) scheme. OFDM is a multicarrier system where the modulation is attained through Inverse Fast Fourier Transform and simultaneous transmission of data through closely packed orthogonal carriers is allowed utilizing parallel processing techniques. Dividing the available spectrum into several orthogonal subchannels whose bandwidth is less than coherence bandwidth of the channel, a frequency selective fading channel can be converted into a collection of flat fading subchannels. Combining the advantages of both the above technologies, MIMO OFDM systems increases data rate as well as improve quality of service against fading which is one of the main challenges in wireless communication. The benefits of MIMO OFDM strongly depend on perfect synchronization and all the transceiver systems based on OFDM/MIMO OFDM are highly sensitive to timing and frequency offsets. It is required that receiver must be synchronized to both the time frame and the transmitted frequency. But in the case of all practical wireless communication systems, frequency and timing offsets are created due to discrepancies between transmitter and receiver oscillators and Doppler shifts introduced by nonlinear channels. The destructive effects caused by the offsets are reduction in signal amplitude and the introduction of inter carrier interference (ICI) caused by loss of orthogonality between subcarriers. As the presence of these offsets degrades the system performance in a non- graceful way, the estimation and correction of offsets in MIMO OFDM have been a topic of active research since last decade. Different approaches for offset estimation [1-4] include data-aided synchronization which uses preambles before OFDM signals, blind synchronization methods which exploit the inherent characteristics in OFDM signals like redundancy in the cyclic prefix and semi blind synchronization that includes pilot symbols in addition to cyclic prefix. This paper considers offset estimation using repeated training sequence for comparing the performance of different mathematical sequences because of its accuracy and reduced complexity in estimating the errors. Even though the other two techniques are easier to apply and save bandwidth they achieve the target at the expense of added complexity and degraded performance. This paper is organized as follows. Section II describes the system model of MIMO OFDM. The offset estimation methods in OFDM and conventional methods like Schmidl and Cox Algorithm and Minn’s algorithm are reviewed in Section III. Different mathematical sequences used in offset estimation are briefly introduced in