Performance evaluation of subcarrier mapping techniques for multiuser in presence of Doppler in LTE uplink.

摘要

Orthogonal Frequency Division Multiplexing (OFDM) is an advanced 3G/4G scheme which achieves high data rate and combats multipath fading. However, OFDM systems suffer from nonlinear peak to average power ratio (PAPR) and Carrier Frequency Offsets (CFO). These two factors lead to degraded performance and thereby reducing the system efficiency. In order to reduce the PAPR, the Single Carrier Frequency Division Multiple Access (SCFDMA) in the Long Term Evolution (LTE) uplink was developed. In this thesis, the Bit Error Rate (BER) and PAPR for Localized Frequency Division Multiple Access (LFDMA), Modified Hybrid Frequency Division Multiple Access (MHFDMA) and Zero Interleaved Frequency Division Multiple Access (IFDMA) in the presence of multipath fading and Doppler have been evaluated and compared. The MHFDMA has been designed using the LFDMA and IFDMA subcarrier mapping techniques in SCFDMA. The multiuser SCFDMA system is simulated using different number of subcarriers and modulation schemes. In terms of PAPR, IFDMA gives a lower value compared to the MHFDMA and LFDMA but its implementation is complex for the base station. The LFDMA gives a higher PAPR value compared to the IFDMA and MHFDMA, but it gives a lower value compared to the conventional OFDM systems. The implementation complexity of LFDMA is very low. The MHFDMA gives a PAPR in between LFDMA and IFDMA with the implementation complexity also in between LFDMA and IFDMA. However, it extracts the multiuser diversity and frequency diversity of both the schemes. The system is simulated for four users and 1024 subcarriers, with each user accessing 256 subcarriers, in the presence of Doppler and multipath Rayleigh fading channel. The BER performance for all the three subcarrier mapping techniques was the same in no Doppler case and different percentage Doppler cases. The BER performance degraded as the constellation size in the modulation increased.