International Journal of Computer Applications (0975 – 8887) Volume 98– No.17, July 20143 1 A Study on Recent Advancements in MIMO-FBMC Systems Bidyalaxmi Devi Tensubam Post Graduate Scholar DIT University ECE Department Nongmaithem Lalleima Chanu Post Graduate Scholar DIT University ECE Department Sonika Singh, Ph.D Associate Professor DIT University ECE Department ABSTRACT Multicarrier (MC) techniques when combined with Multiple Input Multiple Output (MIMO) technology increases the throughput and QOS of the system. OFDM with its unique capability of converting the frequency selective channel into a set of frequency flat channel have proved to be one of the best multicarrier technique that can be applied to MIMO channels. However, OFDM suffers from Bandwidth loss due to the addition of cyclic prefix. Filter bank multicarrier (FBMC) modulation system on the other hand, is highly bandwidth efficient but its application to MIMO channels is still a subject of study to various researchers for the past decade. So far, only FMT based FBMC system offers same flexibility as OFDM in adopting MIMO techniques. This paper presents the various advancements or methods proposed to enhance the flexibility of FBMC systems (FMT,CMT,OFDM-OQAM) while adopting MIMO techniques mainly highlighting the ISI and ICI mitigation methods through improved decoding techniques, equalization schemes and modified FBMC schemes. Keywords MC, MIMO, FBMC, OFDM, OFDM-OQAM, QAM, FMT, CMT. 1. INTRODUCTION Multicarreir modulation(MCM) techniques are the potential candidates taken into consideration to meet the growing demands of high data rate users. This demand can be more efficiently dealt with the combination of multicarrier techniques and MIMO technology, which uses multiple antennas at transmission and reception to boost the system performance without the requirement of additional bandwidth. This combination provides both efficiency and Quality of service(QOS) to the system. One of the best MC techniques that can be jointly used with MIMO technology is OFDM. In OFDM, the fading at the subcarrier level is modelled flat which which facilitates the implementation of MIMO concept. However OFDM suffers from some serious drawbacks such as poor stopband attenuation, which necessitates tight synchronization and the need of a cyclic prefix to deal with the channel impulse response which accounts to the reduced bandwidth efficiency[1]. FBMC, an alternative MC technique with a better spectral localization overcomes the drawbacks of OFDM and offers several advantages such as increased spectral efficiency through the removal of cyclic prefix, lower spectral leakage, reduced sensitivity to doppler effects and also much relaxed synchronization requirements[2]. However, it turns out that, while the application of OFDM to MIMO channels is a straightforward task, direct application of FBMC to MIMO channels is a nontrivial task. Recently various studies have been done on the various FBMC systems namely Filtered Multitone (FMT), Cosine Modulated Multitone (CMT), Staggered Modulated Multitone (SMT) or OFDM-OQAM and many improvements have been proposed for all the systems with respect to their applications to MIMO channels. In FMT, the subcarriers do not overlap as it follows the conventional method of Frequency Division Multiplexing (FDM) and its application to MIMO channels is straightforward and can offer the same flexibility as OFDM in adopting MIMO techniques as the channel can be approximated by a flat gain over each subcarrier band. However, FMT suffers from bandwidth loss due to the guard bands employed. Whereas in CMT and SMT, the subcarrier overlap and offset QAM (OQAM) modulation is used, which preserves bandwidth. OQAM has the potential to outperform QAM modulation, however its main drawback is the inter symbol interference (ISI) and inter carrier interference (ICI) terms associated with the received data symbol received at the receiver. This paper presents the study of various methods introduced by various researchers which contributes in the extension of MIMO architectures to FBMC. 2. MIMO FBMC-OQAM MODEL A MIMO FBMC-OQAM system with Transmit antennas and Receive antennas is considered [3] and the corresponding block diagram is shown in Fig.1. At the M- subchannel synthesis bank of the FBMC-OQAM transmitter, the discrete time baseband signal that corresponds to the transmit antenna can be expressed as- = Here, = is the output of the OQAM modulator for the subchannel at the transmit antenna and denotes the set of active subchannels. The transmitted symbols are assumed to be uncorrelated in space, time and frequency. The signals , for i=1,2,….., , are then transmitted through a frequency selective MIMO channel which is assumed to be time invariant over the duration of a transmitted FBMC-OQAM frame. The multipath impulse response of the tap is given by