Contributions to LTE implementation

Abstract

The third Generation Partnership Project Long Term Evolution (3GPP LTE) is one of the choices for next generation wireless networks. LTE is designed to provide a peak data rate of about 100 Mbps in Downlink and 50 Mbps in Uplink, and to ensure high mobility at speed up to 350 km/h. LTE’s objectives include a radio interface physical layer to support transmission bandwidth up to 20 MHz together with new transmission schemes and advanced multi-antenna technologies. In order to achieve its target, LTE specified a new radio interface based on Orthogonal Frequency Division Multiple Access (OFDMA) in Downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) in Uplink, which is based on OFDMA implemented by Discrete Fourier Transform (DFT) precoding, along with Multiple Input Multiple Output (MIMO) antenna processing and all services are supported on IP based architectures. This new OFDMA based air interface is utilized under Evolved UMTS terrestrial Radio Access Network (E-UTRAN) and supported with a new flatter- IP core termed as Evolved Packet Core (EPC). The principal advantage of SC-FDMA is its low Peak-to-Average Power Ratio (PAPR) of the transmitted signal. This parameter is one of the drawbacks of OFDMA. The transmitter in most radio systems uses High power Amplifier (HPA), the HPA introduce inter-modulation between subcarriers and additional interferences into the system due to its saturation, as a consequence high PAPR of OFDM systems and leads to an increased Bit Error Rate (BER) In this thesis, we analyze the PAPR characteristics for both OFDMA and SCFDMA, we investigate the most used PAPR reduction techniques and we propose new techniques in order to further reduce the PAPR by taking in consideration the signal degradation that appears usually after applying a PAPR reduction technique. A new blind estimation technique using a denoising method, based on wavelets, is also proposed in this Thesis. This technique is simpler than the non blind estimation methods, because it does not require the channel estimation and it provides a solution for estimation problem in LTE DL and UL, improving substantially the performance of both types of communication systems.