CHANNEL ESTIMATION OF WIMAX OFDM SYSTEM BASED ON PILOT SYMBOL ARRANGEMENT

• Main Author: SANJAYA PICESA (NIM 13203058), ROSA
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/11333
• Institution: Institut Teknologi Bandung

<p align="justify">In this final project, a channel estimation scheme for IEEE 802.16-2004 Worldwide Interoperability for Microwave Access-Orthogonal Frequency Division Multiplexing (WiMAX OFDM) system is investigated due to frequency selective and multipath fading channel condition, which limits the data rate. A channel estimation scheme is investigated in the case that the channel impulse response is longer than the cyclic prefix (CP). This channel estimation scheme is kind of a coherent detection that is transmitting some pilot symbols as a reference symbol. The channel estimation technique is based on pilot symbols arrangement. The arrangement is performed by sending the reference symbols at every subcarrier frequency of WiMAX OFDM system periodically with a specific period, this kind of arrangement is called comb type or transmitting the reference symbols pilots at subcarrier frequency of WiMAX OFDM system periodically, in which all of subcarrier symbols is used as pilots, this kind of arrangement is called block type. These pilots are generated by Pseudo Random Binary Sequence (PRBS).<p align="justify"><p>Block type channel estimation is performed by measuring the estimate BER performance based on the number of pilot subcarrier frequency and the data subcarrier frequency ratio, while comb type channel estimation is performed by measuring the estimate BER performance based on the number of pilot and data symbols ratio. The simulation results show that increasing the number of pilot subcarriers and pilot symbols will decrease the BER performance. This shows that there is loss of SNR when adding the number of pilot subcarriers and pilot symbols. The channel estimation is evaluated with linear estimation method, MSE estimator and time or frequency domain interpolation technique. Estimation is also observed to show the Doppler frequency effect on fading Rayleigh channel. The Doppler shift due to the spread of transmitting and receiving frequency is also affect the BER performance.<p align="justify"><p>Channel estimation is kind of important thing for the communication system with the channel affect by multipath fading, with this estimation results, the channel condition will be known so a channel predictor can be used to give a feedback for the WiMAX transmitter to determine what the suitable modulation scheme level for the next transmitting data information. Choosing the suitable modulation scheme level will increase the system performance. In the simulation, the performance of each modulation scheme (BPSK, QPSK, 16QAM and 64QAM) that is applied to the WiMAX OFDM system is compared. Simulation results show that BPSK modulation gives best estimate BER performance on the AWGN and Rayleigh fading channel.