Analysis and evaluation of OFDM in LTE network

Abstract

Orthogonality of OFDM is a dominant solution to achieve a reliable fast speed data rates. OFDM is implemented according to the concept of dividing the available bandwidth into sub-streams, and that is accomplished by splitting the data stream into parallel data sub-streams. In OFDM a various set of orthogonal narrow sub-carriers are transmitted in parallel and they overlap orthogonally. OFDM provides a high data rates across frequency selective channels including multipath fading, phase noise and frequency offset. OFDM changes the selectivity of multipath channel frequency into a more stable channel with flat fading characteristics, and therefore, minimize inter-symbol-interference ISI. Although it is highly sensitive to synchronization errors, it is simplifying the process of equalization at receiver. Multiple input multiple output MIMO-OFDM is implemented within OFDM systems which uses multiple antennas to rise the throughput without maximizing the power of transmitter or receiver. OFDM is configured within LTE Long Term Evolution as down-link air-interface. Despite the fact that OFDM system achieves many advantages, it is facing serious issues. Particularly, PAPR peak to average power ratio, which is considered as a problematic drawback [1]. PAPR occurs due to highly variated fluctuations in transmitted signal that leads to the requirement of having linearity of high power amplifiers HPA. Frequency offset is another problem encountering OFDM systems which is caused by Doppler shift frequency. The main purpose of this thesis is studying an OFDM system mathematically and proposing a Matlab simulation demonstrates each of the components of the OFDM system, analyze and evaluate its performance with respect to the bit error ratio BER using quadrature amplitude modulation QAM. The simulation is modeled under different environmental conditions such as Rayleigh fading and AWGN additive white Gaussian noise. After that, many proposed techniques are analyzed and simulated to reduce PAPR, frequency offset, channel estimation, synchronization and phase noise effects from the received signal. Finally, OFDM system optimization can be achieved by applying techniques that give better results within the system. Simulations and analysis are studied with consideration of using LTE as the technology that is using the OFDM modulation.