Quadrature Spatial Modulation Orthogonal Frequency Division Multiplexing

This paper investigates the application of quadrature spatial modulation (QSM) to orthogonal frequency division multiplexing (OFDM). In comparison to spatial modulation OFDM (SM-OFDM), the proposed QSM-OFDM achieves an enhanced spectral efficiency by decomposing the amplitude and/or phase modulated signal into its real and imaginary components as the transmitted symbols. The index/indices of the activated transmit antenna(s) are employed to convey additional information. These symbols are transmitted orthogonally to eliminate inter-channel interference with little trade-off in synchronization. The average bit error probability for QSM-OFDM and other schemes, including the SM-OFDM, conventional multiple-input multiple-output (MIMO-OFDM), maximal-ratio combining single-input multiple-output (MRC-OFDM), vertical Bell Laboratories layered space-time architecture (VBLAST-OFDM) and Alamouti-OFDM systems are demonstrated using Monte Carlo simulation. The expressions for the receiver computational complexities in terms of the number of real operations are further derived. QSM-OFDM yields a significant signal-to-noise ratio gain of  dB with little trade-off in computational complexity over SM-OFDM, while substantial gains greater than  dB are evident, when compared to other systems

Index modulation for next-generation wireless networks.

Doctoral Degree, University of KwaZulu- Natal, Durban.The desirability of high throughput and superior system performance for multimedia services requires schemes that can achieve high spectral efficiency. However, this imposes high system/hardware complexity due to the large number of antennas required at the transmitter. This led to the development of several innovative multiple-input multiple-output (MIMO) techniques in the research community, such as generalized spatial modulation (GSM). GSM is a spatial modulation (SM) based scheme, which employs transmit antenna combinations coupled with identical symbols to convey additional information. This made the use of multiple transmit antennas possible in index modulation, improving the setback/limitation of hardware complexity experienced in the conventional MIMO and SM schemes. Furthermore, in the literature, an improved spectral efficient quadrature spatial modulation (QSM) based scheme termed generalized quadrature spatial modulation (GQSM) is proposed. In GQSM, the antennas at the transmitter are divided into groups and a unique symbol is employed across multi-active transmit antenna groups. Hence, GQSM requires less transmit antennas to achieve a high data rate when compared to its counterparts. However, GQSM requires multiple radio frequency (RF) chains, considering unique symbols are employed in each transmit antenna group. This motivates us to investigate single-symbol GQSM (SS-GQSM), which employs identical symbols across each group requiring a single RF chain. Recently, the application of RF mirrors termed media-based modulation (MBM) was introduced to the research community as a technique to enhance the spectral efficiency at a reduced hardware complexity. This motivates us to investigate MBM with single-symbol GSM to enhance its error performance and to mitigate the drawback of the requirement of multiple RF chains. In addition, link adaptation has been stated in literature as a technique, which can enhance the performance of a single-input multiple-output (SIMO)/MIMO scheme. MBM achieves a high data rate coupled with enhanced system performance. However, to the author's best knowledge, link adaptation has not been investigated with MBM. This motivates us to propose an adaptive algorithm that employs different candidate transmission modes to enhance the reliability of the SIMO system. The proposed scheme is called adaptive SIMOMBM (ASIMOMBM). Lately, two-way cooperative relaying has been proven as a spectral efficient relaying system. This technique employs two or more source nodes, which transmit information to the relay node simultaneously. Considering the advantages of GQSM stated earlier, this motivates us to investigate two-way decode-and-forward relaying for the GQSM scheme to improve the error performance of the conventional GQSM system

Transmit antenna selection algorithms for quadrature spatial modulation.

Master of Science in Electronic Engineering. University of KwaZulu-Natal, Durban 2016.The use of multiple-input multiple-output (MIMO) systems has become increasingly popular due to the demand for high data rate transmissions. One such attractive MIMO system is spatial modulation (SM). SM is an ideal candidate for high data rate transmission as it is able to achieve a high spectral efficiency, whilst maintaining a relatively low receiver complexity. SM completely avoids inter-channel interference and the need for inter-antenna synchronisation. Furthermore, SM requires the existence of only one radio frequency chain. However, the need to increase the spectral efficiency achieved by SM is a topic which continues to garner interest. Quadrature spatial modulation (QSM) was introduced as an innovative SM-based MIMO system. QSM maintains the aforementioned advantages of SM, whilst further increasing the spectral efficiency of SM. However, similar to SM, the need to improve the reliability (error performance) of QSM still exists. One such strategy is the application of a closed-loop technique, such as transmit antenna selection (TAS). In this dissertation, Euclidean distance-based antenna selection for QSM (EDAS-QSM) is proposed. A substantial improvement in the average error performance is demonstrated. However, this is at the expense of a relatively high computational complexity. To address this, we formulate an algorithm in the form of reduced-complexity Euclidean distance-based antenna selection for QSM (RCEDAS-QSM) that is used for the computation of EDAS-QSM. RCEDAS-QSM yields a significant reduction in the computational complexity, whilst preserving the error performance. To further address computational complexity, four sub-optimal, low-complexity, TAS schemes for QSM are investigated, viz. capacity optimised antenna selection for QSM (COASQSM), TAS for QSM based on amplitude and antenna correlation (TAS-A-C-QSM), lowcomplexity TAS for QSM based on amplitude and antenna correlation using the splitting technique (LCTAS-A-C-QSM) and TAS based on amplitude, antenna correlation and Euclidean distance for QSM (A-C-ED-QSM). Amongst the sub-optimal algorithms, A-C-ED-QSM provides superior error performance. While the computational complexity of A-C-ED-QSM is higher than the other sub-optimal, lowcomplexity schemes, there is a significant reduction in the computational complexity compared to the optimal RCEDAS-QSM. However, this is at the expense of error performance. Hence, clearly a trade-off exists between error performance and computational complexity, and is investigated in detail in this dissertation

Index modulation for next generation wireless communications.

Doctoral Degree. University of KwaZulu-Natal, Durban.A multicarrier index modulation technique in the form of quadrature spatial modulation (QSM) orthogonal frequency division multiplexing (QSM-OFDM) is proposed, in which transmit antenna indices are employed to transmit additional bits. Monte Carlo simulation results demonstrates a 5 dB gain in signal-to-noise ratio (SNR) over other OFDM schemes. Furthermore, an analysis of the receiver computational complexity is presented. A low-complexity near-ML detector for space-time block coded (STBC) spatial modulation (STBC-SM) with cyclic structure (STBC-CSM), which demonstrate near-ML error performance and yields significant reduction in computational complexity is proposed. In addition, the union-bound theoretical framework to quantify the average bit-error probability (ABEP) of STBC-CSM is formulated and validates the Monte Carlo simulation results. The application of media-based modulation (MBM), to STBC-SM and STBC-CSM employing radio frequency (RF) mirrors, in the form of MBSTBC-SM and MBSTBC-CSM is proposed to improve the error performance. Numerical results of the proposed schemes demonstrate significant improvement in error performance when compared with STBC-CSM and STBC-SM. In addition, the analytical framework of the union-bound on the ABEP of MBSTBC-SM and MBSTBC-CSM for the ML detector is formulated and agrees well with Monte Carlo simulations. Furthermore, a low-complexity near-ML detector for MBSTBC-SM and MBSTBC-CSM is proposed, and achieves a near-ML error performance. Monte Carlo simulation results demonstrate a trade-off between the error performance and the resolution of the detector that is employed. Finally, the application of MBM, an index modulated system to spatial modulation, in the form of spatial MBM (SMBM) is investigated. SMBM employs RF mirrors located around the transmit antenna units to create distinct channel paths to the receiver. This thesis presents an easy to evaluate theoretical bound for the error performance of SMBM, which is validated by Monte Carlo simulation results. Lastly, two low-complexity suboptimal mirror activation pattern (MAP) optimization techniques are proposed, which improve the error performance of SMBM significantly