Spectrally Efficient Transmission Strategies for MIMO Optical Wireless Communications

  • Shimaa A. Naser

Student thesis: Doctoral Thesis

Abstract

The exponential growth of connected devices and emergence of the Internet-of- Everything (IoE), enabling ubiquitous connectivity among billions of people and machines, have been the major driving forces towards the evolution of innovative wireless technologies. The aim of this is to ultimately support a plethora of new services, including enhanced mobile broadband and ultra-reliable and low-latency communications. Achieving this is rather vital since while the demand for new IoE services, e.g., extended reality, autonomous driving and tactile internet continues to grow, it is necessary for future wireless networks to operate with considerably high reliability, low latency, and increased data rates. In this context, the notion of visible light communication (VLC), a form of optical wireless communication (OWC), has emerged as a promising energy efficient and green wireless technology for massive connectivity of users with increased quality-of-service (QoS) requirements, such as high data rates. Despite its advantages, VLC suffers from several drawbacks that limit its performance capabilities. For example, the limited modulation bandwidth and peak optical power of the light emitting diodes (LEDs) and the positive and real-valued nature of the signals are considered the main obstacles towards realizing the full potential of VLC systems. In this research, we propose three different techniques to enable high data-rate in- door VLC systems. In specific, the first part of the thesis proposes space time coded spatial modulation (STBC-SM) scheme for indoor VLC systems. To this end, we develop a comprehensive frame work for the design and analysis of the pro- posed scheme for any number of transmitting LEDs and any Mary constellation size. Then,tofurtherenhancetheachievabletransmissiondatarate,weintegratea quasi-orthogonal STBC(QOSTBC)with SM, since relaxing the orthogonality condition ofOSTBCpotentiallyprovidesahighercodingrate.Finally,toevaluatethe performanceoftheconsideredscheme,wederiveatightandtractableupperbound for thecorrespondingbiterrorrateandcomparetheobtainedresultswithrecent benchmark multiple-input multiple-output(MIMO)modulation schemes. Then, in the second contribution, we propose an enhanced SM-based scheme for in- door VLC systems referred to as amplitude, phase, and quadrant (APQ)-SM. This scheme enhances the achievable throughput of conventional SM schemes by trans- Abstract mitting higher order complex modulation symbol, which is decomposed into three different parts. These part scarry the amplitude, phase, and quadrant components of the complex symbol, which are then represented by unipolar pulse amplitude modulation symbols. Superposition coding is exploited to allocate a fraction of the total power to each part before they are all multiplexed and transmitted simultaneously, exploiting the entire available band width. Furthermore, since the performance of the proposed modulation scheme is sensitive to the power allocation factors, we formulate anaveragesymbolerrorrateminimizationproblemandproposeasub-optimal, yet, alow complexity solution using success iveconvex approximation (SCA). In the third contribution, we propose rates plitting multiple access (RSMA) yet, a low complexity solution using successive convex approximation (SCA). In the third contribution, we propose rate splitting multiple access (RSMA) as a promising scheme to enhance the achievable throughput for broadcast VLC sys- tems. In specific, we develop a comprehensive framework for the precoding design and rate-splitting for RSMA in multi-cell MIMO VLC networks. Since cell-edge users in multi-cell configurations suffer from high interference from both the same cell and adjacent cells, advanced precoding strategies for the common and private messages are required to efficiently mitigate the incurred interference. Hence, in order to alleviate the effect of the interference, we propose three different coordi- nation/cooperation strategies to efficiently design the precoders for RSMA signals in cellular configuration. Optimum rate-splitting and transmit precoders for differ- ent coordination/cooperation strategies are evaluated through formulating spectral efficiency maximization problems. The formulated problems are shown to be non- convex, were efficient sub-optimal solutions are found through integrating semidefi- nite relaxation and SCA.
Date of AwardMay 2022
Original languageAmerican English

Keywords

  • MIMO
  • RSMA
  • SDMA
  • spatial modulation
  • STBC
  • visible light communication.

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