string(13) "dissertations"


The PhD thesis “Hierarchical Modulation and Spatial Modulation Schemes under Generalized Fading Propagation Environments” deals with designing novel hierarchical modulation (HM) and spatial modulation (SM) schemes to improve the average bit error probability (ABEP) performance of wireless communication systems. At first, the current State of the Art considering HM is presented. HM is the most popular representative of superposition coding, hence being incorporated in many IEEE standards. Note that superposition coding aims at providing unequal error protection (UEP) to streams of different priority that are jointly transmitted. Having studied the relevant bibliography, a layered offset hierarchical modulation scheme is proposed that shifts by half a symbol period the high priority (HP) modulated stream as to the low priority (LP) one. The proposed scheme is shown to enhance the HP error performance. Finally, the application of HM in a broadcast scenario is studied aiming at maximizing the average spectral efficiency.
The PhD thesis then presents the digital signal processors (DSP) test-bed that has been implemented in the Wireless Communications Laboratory (WiCom) of the Institute of Informatics and Telecommunications, NCSR Demokritos. By employing an RF subsystem operating in the ISM band of 2.4 GHz, the test-bed is used for the wireless transmission of a gray-scale picture. It is shown that the application of hierarchical modulation enhances the depiction quality of the received image.
Considering Spatial Modulation, the PhD thesis presents the State of the Art for the spatial modulation scheme that is a promising low-complexity candidate for next generation MIMO systems. Having studied the relevant bibliography, a new framework for the ABEP performance of space shift keying (SSK) – being a subcase of SM – is developed. Specifically, a closed-form expression for the ABEP upper bound of extended generalized K (EGK) fading channels is derived based on the Hankel transform, employing integral transforms along with special functions. Special cases of EGK include generalized K (GK) and Nakagami fading, for which closed-form expressions are derived, as well. The theoretical analysis is extended to the derivation of analytical expressions concerning the coding gain and diversity gain for the considered fading environments. These expressions are finally employed to evaluate the asymptotic ABEP of SSK MIMO receivers.
The PhD thesis concludes by studying the evaluation of UEP schemes for SM systems, an open scientific area with little research contribution until today. To handle with the inadequate SSK performance under Rician fading, an hierarchical multilevel space shift keying (HMSSK) scheme is proposed, assigning the HP modulated bits to different numbers of active transmit antennas, whereas the LP stream is transmitted employing an SSK based scheme. The last issue studied in this PhD thesis is accomplishing UEP by jointly employing the spatial and signal domains for the modulation of the HP and LP streams. Taking into account specific constraints, multilevel space shift keying (MSSK) is combined with hierarchical modulation leading to the proposed multilevel spatial hierarchical modulation (MSHM) scheme.
Keywords: spatial modulation, space shift keying, hierarchical modulation, fading channels, digital signal processors, average bit error probability, average spectral efficiency.

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