Thesis outline

The thesis dissertation is written as follows: Chapter 1 is the current chapter, present-ing the background motivation, thesis objective along with outline.

Chapter 2, is devoted to introduce the background and the state of the art related to the different concepts to be used throughout this thesis. A very brief overview of OFDM system is provided. Then, the fundamental theory of FBMC-OQAM system is given with much emphasis on transmitter side. In that aspects such as the OQAM mapping, polyphase filtering, discrete-time representation, FBMC-OQAM modulation as matrix operation, prototype filtering, orthogonality and overlapping nature have been discussed. Non-linear aspects of PAs are studied in terms of analytical representation and conversion characteristics. Then, some memoryless models are presented. Finally, the need for mitigation of non-linear PA effects is pondered and the prevailing methods to achieve that has been discussed.

Chapter 3 deals with spectral regrowth prediction for FBMC-OQAM systems using cumulant analysis. A brief introduction of cumulants is given and the aspect of spectral prediction by cumulants is presented. Some characteristic properties of cumulants has been displayed. How a polynomial model of the PA is achieved by polynomial fitting of its conversion characteristics, is shown. Then, the usage of cumulants as a tool to derive closed-form expression for the auto-covariance function of PA output in terms of auto-covariance function of its input is putforward. Simulation results are presented to show the efficiency of using the cumulants for spectral regrowth prediction.

Chapter 1. Introduction 6

InChapter 4, different PAPR reduction techniques suggested for OFDM are discussed.

Then, a state-of-art of PAPR reduction techniques for FBMC-OQAM is presented.

FBMC-OQAM by virtue of having an overlapping signal structure cannot afford to have the conventional PAPR reduction schemes that have been effectively applied for OFDM systems. How this impacts the PAPR reduction in FBMC-OQAM systems, is clearly presented with theory and results. In this chapter, we propose three novel PAPR reduction techniques suited for FBMC-OQAM. The aspects of symbol-by-symbol ap-proach and trellis-based apap-proach are discussed. Also, their computational complexities have been derived, which can be extended to any probabilistic schemes. While, two techniques are probabilistic ones and the last one is an adding signal technique.

In Chapter 5, the co-existence capabilities of FBMC-OQAM system with Profes-sional Mobile Radio system is analyzed taking into account the implications of PA non-linearities. It is a fact that in the recent literature, the suggestion that LTE-like FBMC-OQAM system working on linear devices can coexist in PMR band, while conven-tional OFDM-based LTE system fails; is recalled. The need to take into account the RF impairments in radio communication systems, such as the non-linear nature of PAs and how they add severe hindrance in the coexistence aspect is elaborately presented. Also, in this chapter, we address this issue and show that LTE-like FBMC-OQAM system working on non-linear devices can still coexist with PMR systems. However, keeping in mind energy efficiency, the need for PAPR reduction and PA linearization is highlighted.

The analysis in this chapter has inculcated interest on the issue of PA linearization and the same is dealt in the succeeding Chapter 6.

Chapter 6 studies the PA linearization aspects. Different classes of PA linearization techniques that have been suggested for OFDM has been discussed, with much focus on digital predistortion. Then, a state-of-art of PA linearization techniques for FBMC-OQAM is presented. Similar to that of PAPR reduction, even in predistortion, the need to take into account the overlapping nature of FBMC-OQAM is putforward. The fea-sibility to view the predistortion as an adding signal technique has been presented. In this chapter, we propose a novel DPD technique suited for FBMC-OQAM. Apart from displaying the capabilities of this linearization techniques, we demonstrate that PAPR reduction before linearization shows tremendous impact on the energy efficiency and

Chapter 1. Introduction 7 diminishing the OOB spectral regrowth. An abstract idea has been pondered that both PAPR reduction and PA linearization can be combined by an adding signal operation which yields to joint optimization. It means both of these can be done at one stretch by adding a signal, which not only reduces PAPR but also linearizes the PA.

Chapter 7 draws the final conclusions by highlighting the main contributions of this dissertation. Possible future research are provided at the end.

1.5 Publications

Some publications have resulted from work contained in or related to this thesis. Below is a comprehensive list of this work:

Journals

[J1]. K. C. Bulusu, M. Renfors, J. Yli-Kaakinen, H. Shaiek, and D. Roviras, “En-hanced Multicarrier Techniques for Narrowband and Broadband PMR Systems,”Wiley Transactions on Emerging Telecommunications Technologies, May 2016.

[J2].K. C. Bulusu, H. Shaiek, and D. Roviras, “Reducing the PAPR in FBMC-OQAM Signals by Trellis-based SLM Technique,” Eurasip Journal on Advances in Signal Pro-cessing (Submitted).

Conferences

[C1]. K. C. Bulusu, H. Shaiek, and D. Roviras, “Impact of HPA Non-linearity on Coexistence of FBMC-OQAM Systems with PMR/PPDR Systems,” IEEE Vehicular Technologies Conference, May 2016.

[C2].K. C. Bulusu, H. Shaiek, and D. Roviras, “Reduction of PAPR of FBMC-OQAM Signals by Dispersive Tone Reservation Technique,”12th IEEE International Symposium on Wireless Communication Systems, Aug. 2015.

[C3]. K. C. Bulusu, H. Shaiek, and D. Roviras, “Potency of Trellis-based SLM over

Chapter 1. Introduction 8 symbol-by-symbol approach in reducing PAPR for FBMC-OQAM Signals,” IEEE In-ternational Conference on Communications, Jun. 2015.

[C4].K. C. Bulusu, H. Shaiek, and D. Roviras, “Prediction of Spectral Regrowth for FBMC-OQAM system using Cumulants,” IEEE International Conference on Wireless and Mobile Computing, Networking and Communications, pp. 402-406, Oct. 2014.

[C5]. K. C. Bulusu, H. Shaiek, D. Roviras, and R. Zayani, “PAPR Reduction for FBMC-OQAM Systems using Dispersive SLM Technique,” 11th IEEE International Symposium on Wireless Communication Systems, pp. 568-572, Aug. 2014.