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

Space shift keying modulation for MIMO channels

In this thesis, we analyze modulation techniques that exploit multiple antennas in wireless communication. We first study the so-called spatial modulation (SM) technique for MIMO channels. Since the original SM detector is based on an ad hoc design, and only functions under some artificial assumptions about the channel, we derive the optimal detector for SM. The new detector performs significantly better than the original ({598} 4 dB gain), and we support our results by deriving a closed form expression for the average bit error probability. As well, we show that SM with the optimal detector achieves better performance gains ({598}1.5 - 3 dB) over popular multiple antenna systems. We then introduce space shift keying (SSK), a new modulation scheme based on the SM concept. SSK exploits fading in multiple input multiple output (MIMO) channels to provide better performance over conventional amplitude/phase modulation (APM) techniques. In SSK, only the antenna indices, and not the symbols themselves, relay information. This absence of symbol information eliminates the transceiver elements necessary for APM transmission and detection (such as coherent detectors). As well, the simplicity involved in modulation reduces detection complexity compared to that of SM, while achieving almost identical performance gains. Throughout the thesis, we illustrate SSK's strength by studying its interaction with the fading channel, and obtain tight upper bounds on bit error probability. To improve performance, adaptive forms of SSK are also presented, including a symbol design technique, and an antenna selection scheme. We also illustrate SSK's performance under channel estimation error, and spatial correlation. Analytical and simulation results show performance gains over APM systems (3 dB at a bit error rate of 10 -5 ), making SSK an interesting candidate for wireless applications. We then present SSK coded modulation (SSK-CM) to integrate coding for practical wireless systems. In particular, we present a bit interleaved CM (BICM) system using iterative decoding. We illustrate SSK-CM capacity improvements over APM, and derive upper bounds on SSK-CM's performance. We also analytically present SSK's coded diversity advantage over APM, where significant performance gains are observed (up to 9 dB), motivating SSK-CM's integration in future wireless standard

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