Design and Implementation of Modulation and Detection Strategies for Spatial Modulation MIMO Systems

Abstract

It is well known that MIMO communication systems possess higher spectral efficiency when compared with SISO systems. A novel MIMO technique that tried to combine the advantages of multiple antenna communication while simultaneously conserving energy was proposed by Mesleh [Mesleh et al. (2008)]. This technique uses only one active antenna out of the available multiple antennas to communicate information. The advantage of this scheme is that the active antenna index is also used to communicate information and only a single RF chain is required at the transmitter. Since certain symbols are conveyed by means of the antenna index, they need not be physically radiated. This has the effect of increasing spectral efficiency while reducing the power consumed by the transmitting circuits. A study of relevant litreature shows that the performance of all SM schemes deteriorate under Spatially Correlated (SC) fading channel conditions. To combat the impact of SC, Trellis Coded Spatial Modulation (TCSM) was introduced by [Mesleh et al. (2010)]. In TCSM, the impact of correlation on the performance of SM is reduced by segregating antennas into subsets. This offers maximum spatial separation between the antennas within the same set, though a minimum of four transmit antennas are needed to make the subsets. In this thesis, we have developed and synthesized modulation schemes which are capable of delivering good BER performance under uncorrelated as well as correlated channel conditions. Our primary concern is on practical hand held devices which exhibit spatial correlation quite often. We have designed a scheme called Redesigned Spatial Modulation (ReSM) which can be employed under spatially correlated channel conditions (Chapter-3). This scheme exhibits significant advantage over TCSM and other SM schemes in terms of ABER performance improvement. An experimental setup was established in order to realize the working of the proposed ReSM scheme for indoor environment and a comparative study over SM scheme was performed. The observed results clearly indicate the superiority of ReSM over SM ischemes. In the next chapter (Chapter-4), we have attempted to design SM schemes with an underlying Space Time Block Code (STBC). This is motivated by the desire to further improve the integrity of information transfer. A study of relevant literature lead us to explore the class of codes bearing good rank distance properties. We converged on the class of n-length cyclic codes over GF(qm) which have good rank distance properties. We have synthesized several Non Orthogonal Space Time Block Codes for MIMO systems. These schemes ahieve high rate, are spectrally efficient and can serve as alternatives to traditional STBC schemes. The improvement achieved in terms of ABER by the use of these Non Orthogonal STBCs is explored in Chapter-4. In the following chapters, different aspects of varied Spatial Modulation schemes have been explored. The BER performance of various SM schemes in the presence and absence of channel state information in MIMO environments for various fading channels has been determined. We have employed a high rate spectrally efficient modulation scheme, designated as Double Spatial Modulation (DSM) which yields a performance that is superior to all known variants of SM under these conditions. The performance of DSM under conditions of non-uniform phase distribution which is associated with several real world channel scenarios (Nakagami-m) have been simulated and synthesized in Chapter-5. In Chapter-6, we have synthesized SM schemes which preseve spectral efficiency while being compatible with the requirements of LTE-Advanced and 5G systems employing MIMO architecture with single and Multistream configurations. This is achieved through the use of non-uniform constellations derived from multiplicative groups of Gaussian and Eisenstein integers. In the last part of our work, the advantages of a Multistream Spatial Modulation (MSM) scheme has been explored. The simulation results show that, MSM scheme can yield impressive SNR gains in all possible uncorrelated fading environments. This encouraged us to formulate, a new design employing MSM under conditions of high spatial correlation. The observed results reveal that the proposed Multistream Spatial Modulation scheme yields performance improvement of the order ∼ 2.5 dB over all iiconventional Multistream SM schemes in SC channels. In summary, the focus of the thesis has been on the design of uncoded and codes SM schemes which have high spectral efficiency, moderate decoding complexity and BER performance that is superior to known SM constructions, over various channel fading models in the presence and absence of Channel State Information. Further, the SM systems designed and described in the thesis have employed the notions of non-uniform constellation design and the effect of Multistream configurations. Every design was formulated keeping in mind the adaptation to the latest communication setup and standards. We have also proposed certain extensions to this body of work which can bring about further improvements to the integrity of information transfer while conserving resources such as spectrum and energy.