Advanced Modulation and Multiplexing Techniques

Abstract

This chapter is devoted to advanced modulation and multiplexing techniques suitable for both wireless and optical communication systems. The chapter starts with signal space theory concepts applied to wireless communication systems. After the geometric representations of signals, we describe various multidimensional modulators and demodulators suitable for wireless communication applications, in particular the Euclidean distance, correlation, and matched filter-based detectors, followed by the description of frequency-shift keying (FSK). Both continuous-time (CT) and discrete-time (DT) implementations for pulse amplitude modulation schemes, suitable for wireless communications, are described as well. After that the focus is moved to multilevel schemes suitable for both wireless and optical communication applications, including M-ary PSK, star-QAM, square-QAM, and cross-QAM. Regarding the optical communications, the transmitter for M-ary PSK, star-QAM, and square/cross-QAM is described in detail. The next topic in the chapter is related to multicarrier modulation, including description multicarrier systems with both nonoverlapping and overlapping subcarriers as well as introduction of various approaches to deal with fading effects at subcarrier level. The concept of OFDM is also introduced; however, details are provided in Chap. 7. The MIMO fundamentals are then provided, including the description of key differences with respect to diversity scheme, as well as the introduction of array, diversity, and multiplexing gains. The parallel MIMO channel decomposition is briefly described. The details on MIMO signal processing are postponed for Chap. 8. In section on polarization-division multiplexing (PDM) and four-dimensional (4-D) signaling, we describe key differences between PDM and 4-D signaling and describe how both types of schemes can be implemented in both wireless and optical communications. The focused is the moved to the spatial-division multiplexing (SDM) and multidimensional signaling. We describe how SDM can be applied in wireless communications first. Then we describe how various degrees of freedom including amplitude, phase, frequency, polarization states, and spatial modes can be used to convey the information in optical domain. In the same sections, the SDM concepts for fiber-optics communications are described as well. The section concludes with SDM and multidimensional signaling concepts applied to free-space optical (FSO) communications. The next topic is devoted to the signal constellation design, including iterative polar modulation (IPM), signal constellation design for circular symmetric optical channels, energy-efficient signal constellation design, and optimum signal constellation design (OSCD). The final section of the chapter is devoted to the nonuniform signaling, in which different signal constellation points are transmitted with different probabilities.