| Description |
The fifth generation of cellular networks is going to radically change the current wireless networks paradigm and provide novel services ranging from broadband data connection to machine to machine communications. Many different elements of the wireless networks have to be upgraded to fulfill the expectations and requirements of 5G. One of the challenging aspects of 5G networks design is finding a suitable waveform for its physical layer. The currently used waveform, Orthogonal Frequency Division Multiplexing (OFDM), has some serious limitations and fails to provide the expected performance of 5G. Therefore, there is active research to find a suitable waveform for 5G and beyond. In this dissertation, we study three major candidate waveforms of 5G; Generalized Frequency Division Multiplexing (GFDM), windowed circular filterbank multicarrier offset QAM (C-FBMC), and Orthogonal Time-Frequency Space (OTFS). We present GFDM and C-FBMC waveforms and describe novel efficient transceiver implementations where we compare their computational complexity and showthat the GFDMreceiver has a very high implementation complexity. Moreover, we compare Bit Error Rate (BER) performance of both waveforms and show that C-FBMC outperforms GFDM. Thus, we conclude C-FBMC outperforms GFDM by providing a lower complexity and superior BER performance. In addition, we derive equations that quantify out-of-band (OOB) emissions and multiuser interference (MUI) of the C-FBMC waveform when utilized in an asynchronous scenario. We show how different OOB suppression methods result in an improved MUI performance. We show that our analysis can also be applied to GFDM. We present a detailed information theoretic analysis of filterbank multicarrier offset QAM waveform (FBMC-OQAM) and show that the conventional FBMC-OQAM receivers incur a marginal performance loss when they discard imaginary interference of matched filter output. We attribute this marginal performance loss to the ramp-up and ramp-down portions of an FBMC-OQAM signal, noting that the circular version of FBMC-OQAM, that is, C-FBMC, does not suffer from this information loss. Furthermore, we present a capacity analysis of C-FBMC from a signal processing perspective and prove that regardless of statistics of wireless channel and additive noise, real and imaginary parts of the matched filter output of a C-FBMC receiver are related though an orthonormal transformation. Thus, they both carry the same information content and utilization of an imaginary part in the detection process cannot improve the receiver performance. Finally, we present a novel vectorized formulation for a MIMO OFDM-based OTFS setup that streamlines analysis of OTFS systems. We use this formulation to derive ergodic capacity of OFDM-based OTFS waveform and prove that both OFDM and OFDM-based OTFS have the same ergodic capacity under a time varying channel. iv |
