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

Improved Spatial Modulation Techniques for Wireless Communications

Transmission and reception methods with multiple antennas have been demonstrated to be very useful in providing high data rates and improving reliability in wireless communications. In particular, spatial modulation (SM) has recently emerged as an attractive transmission method for multiple-antennas systems due to its better energy efficiency and lower system complexity. This thesis is concerned with developing transmission techniques to improve the spectral efficiency of SM where antenna/subcarrier index involves in conveying information bits. In the first part of the thesis, new transmission techniques are developed for SM over frequency-flat fading channels. The first proposed scheme is based on a high-rate space-time block code instead of using the classical Alamouti STBC, which helps to increase the spectral efficiency and achieve a transmit diversity order of two. A simplified maximum likelihood detection is also developed for this proposed scheme. Analysis of coding gains and simulation results demonstrate that the proposed scheme outperforms previously-proposed SM schemes at high data transmission rates. Then, a new space-shift keying (SSK) modulation scheme is proposed which requires a smaller number of transmit antennas than that required in the bi-space shift keying (BiSSK). Such a proposed SSK-based scheme is obtained by multiplexing two in-phase and quadrature generalized SSK streams and optimizing the carrier signals transmitted by the activated antennas. Performance of the proposed scheme is compared with other SSK-based schemes via minimum Euclidean distance analysis and computer simulation. The third scheme proposed in this part is an improved version of quadrature SM (QSM). The main feature of this proposed scheme is to send a second constellation symbol over the in-phase and quadrature antenna dimensions. A significant performance advantage of the proposed scheme is realized at the cost of a slight increase in the number of radio-frequency (RF) chains. Performance comparisons with the most recent SM schemes confirm the advantage of the proposed scheme. The last contribution of the first part is an optimal constellation design for QSM to minimize the average probability of error. It is shown that, the error performance of QSM not only depends on the Euclidean distances between the amplitude phase modulation (APM) symbols and the energies of APM symbols, but also on the in-phase and quadrature components of the QSM symbols. The analysis of the union bound of the average error probability reveals that at a very large number of transmit antennas, the optimal constellations for QSM converge to a quadrature phase shift keying (QPSK) constellation. Simulation results demonstrate the performance superiority of the obtained constellations over other modulation schemes. In the second part of the thesis, the applications of SM in frequency-selective fading channels are studied. First, a new transmission scheme that employs SM for each group of subcarriers in orthogonal frequency-division multiplexing (OFDM) transmission is investigated. Specifically, OFDM symbols in each group are passed through a precoder to maximize the diversity and coding gains, while SM is applied in each group to convey more information bits by antenna indices. Performance analysis and simulation results are carried out to demonstrate the superiority of the proposed scheme over a previously-proposed combination of SM and OFDM. Next, the performance of OFDM based on index modulation and a flexible version of OFDM, knows as OFDM with multiple constellations, is compared for both case of "no precoding'' and "with precoding'' of data symbols. It is shown that the precoded OFDM with multiple constellations outperforms precoded-IM based OFDM systems over frequency-selective fading channels. The last part of the thesis investigates a multiuser downlink transmission system based on in-phase and quadrature space-shift keying modulation and precoding to reduce the minimum number of transmit antennas while keeping the complexity of the receiver low. In addition to the maximum likelihood (ML) detection, the low complexity zero forcing (ZF) receiver is also studied. Theoretical upper bounds for the error probabilities of both ML and ZF receivers are obtained and corroborated with simulation results

Μελέτη,Σχεδίαση και Υλοποίηση Συστήματος Ασύρματων Οπτικών Επικοινωνιών Ορατού Φάσματος με Χρήση Χωρικής Διαμόρφωσης

H Χωρική διαμόρφωση (SM) είναι μια τεχνική μετάδοσης που εφαρμόζεται σε συστήματα πολλαπλών εισόδων - πολλαπλών εξόδων (MIMO), όπου όμως μόνο μια κεραία εκπομπής είναι ενεργή κάθε φορά, προσφέροντας μια αύξηση στη φασματική απόκριση ίση με τον λογάριθμο με βάση δύο του αριθμού των κεραιών εκπομπής. Η ενεργοποίηση μόνο μίας κεραίας σε κάθε χρονική στιγμή, μειώνει το μέσο Ρυθμό Σφαλμάτων Bit (Bit Error Rate (ABER)), οι παρεμβολές του καναλιού αποφεύγονται, ενώ ταυτόχρονα μειώνεται η πολυπλοκότητα του υλικού και η κατανάλωση ενέργειας. Ο σκοπός της παρούσας διπλωματικής εργασίας, είναι να εξεταστεί η χωρική διαμόρφωση για ένα σύστημα επικοινωνιών ορατού φωτός. Αρχικά, παρουσιάζεται η βασική θεωρία πίσω από τις τεχνολογίες Επικοινωνιών Ορατού Φωτός (Visible Light Communications –VLC), ακολουθούν βασικές έννοιες της θεωρίας συστημάτων Πολλαπλών Εισόδων – Πολλαπλών Εξόδων (MIMO) και της Οπτικής Χωρικής Διαμόρφωσης (Optical SM). Σε πρακτικό επίπεδο, εξετάζεται η απλούστερη εφαρμογή της Χωρικής Διαμόρφωσης, Space Shift Keying (SSK), και μελετάται η απόδοση ενός τέτοιου συστήματος. Τέλος, παρουσιάζεται αναλυτικά μια πρόταση πρακτικής πειραματικής υλοποίησης ενός συστήματος στηριζόμενου στην τεχνική SSK, και παρατίθεται και η πρακτική υλοποίηση του πομπού του ανωτέρω συστήματος.Summary Spatial modulation (SM) is a transmission technique applicable in multiple–input multiple–output (MIMO) systems, where only one transmit antenna is active at a time, offering an increase in the spectral efficiency equal to the base two logarithm of the number of transmit antennas. The activation of only one antenna at each time instance reduces the average bit error ratio (ABER) as interchannel interference (ICI) is avoided, as well as hardware complexity, and power consumption. Thus, in this thesis, SM is considered for an optical MIMO system, where the signals are transmitted through light emitting diodes (LEDs) and the receivers are photodiodes (PDs). At first the basic theory behind VLC is presented, followed by the theory of Multiple Input – Multiple Output (MIMO) Systems and Optical SM. In practical level, the simplest implementation of SM is considered, namely Space Shift Keying (SSK), and the performance of such a system is investigated. Finally, a design proposal for practical implementation of an SSK system is presented, as well as the practical implementation of the transmitter of the aforementioned system

Soft-output detection for transit antenna index modulation-based schemes.

Master of Sciences in Electronic Engineering. University of KwaZulu-Natal, Durban 2016.Abstract available in PDF file

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 radio communications.

Masters Degree. University of KwaZulu- Natal, Durban.Man’s insatiable desire for swift and more efficient internet service, a wide range of connectivity and increased data rate of transmission necessitated the need for further research to improve the efficiency of the existing systems. The development and evolution of the next-generation communication systems can be ascribed to the multiple-input multiple-output (MIMO) techniques implemented. The fundamental founding block of the MIMO systems is the spatial modulation (SM) which interestingly was able to attain high spectral efficiency as the receiver maintained significantly lower complexity. However, even with the feat achieved by the SM scheme, there was still a need improve on the performance of the SM scheme which meant an increase in the spectral efficiency was required, this prompted further research and a new scheme was introduced. The quadrature SM (QSM) scheme was introduced to better the performance of the conventional SM. QSM retains all the good benefits the SM scheme offers, while still enhancing the spectral efficiency and improving overall throughput. However, the demand for increased reliability, i.e., improving the QSM scheme’s error performance led to a new scheme being introduced. Space-time QSM (ST-QSM) improves the QSM scheme’s error performance by achieving second-order diversity gain for QSM. This scheme combines both the spatial dimension and diversity to the QSM scheme, bringing about a new and improved scheme. In this dissertation, a scheme was introduced to fix the high computational complexity (CC) that affects MIMO systems transmitting at high data rates. Signal orthogonal projection (OP) was employed to decrease the CC of the space-time block coded spatial modulation (STBC-SM). The proposed scheme is called STBC-SM-OP and its results were investigated by comparing it with the STBC-SM with maximum likelihood detection (STBC-SM-ML). The proposed STBC-SM-OP scheme’s error performance matched that of STBC-SM-ML tightly down to low BER whilst maintaining a low CC

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