Non-linear equalizer techniques for 5G NR mobile communications systems

• Autor(a) principal: Gonçalves, Pedro José da Silva
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33940
• topic: 5G NR numerology; OFDM; Uplink; DFT-s-OFDM; TDL-channels; Frequency equalizers; IB-DFE; BER

Due to the increase of data rates, users and the pressure made by the telecommunication market, new technologies have emerged to supply their necessities. 5G New Radio (NR) appears then, offering higher data rates, better spectral efficiency and lower latency when compared to the previous mobile networks technologies. With the increase of devices with wireless connections, interference problems appears causing a reducing in the system performance. In the last years, orthogonal frequency division multiplexing (OFDM) was a modulation technique that provided more efficient transmissions. However, the main disadvantage of this technique, is its higher peak-to-average ratio (PAPR), motivating then the search for more promising modeling techniques. So, one advantage that 5G offers is the possibility of using techniques in the uplink (UL) like the discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-s-OFDM). Comparing with OFDM, the advantage of this transmission technique is its lower (PAPR), being then less sensitive to non-linear distortions caused by the power amplifier (PA). This type of techniques are important for the overall system performance, as they can handle transmission channels experiencing strong frequency selectivity while still providing transmissions with high data rates. DFT-s-OFDM performance can be improved using non-linear equalizers in the frequency domain. One example of these equalizers is the iterative block decision-feedback equalizer (IB-DFE). In this dissertation we implement and evaluate single and multi-user nonlinear equalizers based on IB-DFE approach for DFT-s-OFDM 5G NR systems. It is considered two main different scenarios:single-user and multi-user cases. In the first one, the data of each each user is transmitted by different set of carriers and therefore there is no multi-user interference and the equalizer only needs to deal with inter-symbol interference (ISI). In the second case, the same set of carries are allocated to the several users, with the base station equipped with multiple antennas and the user terminal with a single antenna. Therefore the equalizer must deals with both intersymbol- interference and multi-user interference (MUI). The nonlinear equalizers are designed for different number of antennas at the receiver terminal in order to exploit the space diversity and increase the Signal-to-Noise Ratio (SNR) and consequently reduce the Bit Error Rate (BER). The implemented single/multi-user equalizers are evaluated under several TDL channel models and for different numerologies defined in the 5G NR.