EVALUASI KINERJA OFDMA DENGAN MODULASI ADAPTIF PADA KANAL DOWNLINK

Abstract

Orthogonal Frequency Division Multiple Access (OFDMA) is a multiple access method is prepared to apply to wireless networks-4th generation. By leveraging OFDM technology (Orthogonal Frequency Division Multiplexing), a wide channel can be divided into several narrow subkanal, each of which can be used to transmit data in parallel. OFDMA develop, so that a channel can be shared by several users. If the entire OFDM subcarrier is used only by one user, the OFDMA subcarrier is allocated in such a way as to the number of users. In this final task, investigated the use of subcarrier allocation technique multiakses FDMA systems used in OFDM. And the use of adaptive modulation in OFDMA systems. In the simulation, compared the use of techniques multiakses Block and Interleaved FDMA, the use of adaptive modulation and fixed modulation, and influences the use of channel coding in OFDMA adaptive modulation. Adaptive modulation is used depends on the feedback provided in accordance with the existing channel conditions or in accordance with the received SNR value. The mechanism allows the sending retransmissions of corrupted data back but reduce performance. Adaptive modulation technique is expected to reduce retransmissions by changing the level of modulation (BPSK, QPSK, 16QAM, and 64QAM), the target BER is used in adaptive modulation is 10-2 and 10-3, the use of channel coding in wireless communication system also serves to reduce retransmissions by providing bits redundancies that will improve system performance. Channel coding is used convolutional code and transmission channel used is AWGN. Simulation results show that the subcarrier block allocation techniques and Interleaved FDMA on the AWGN channel did not show differences signifikan BER value.Dengan adaptive modulation system can be optimum in improving datarate the condition of the channel. The use of convolutional coding to show significant performance, the difference in SNR for treshold BER 10-3 for BPSK, QPSK, 16QAM, and 64QAM, respectively ± 4dB, 2dB, 3dB, and 3dB. Keywords: OFDMA, Adaptive Modulation, Convolutional code, AWGN, BER, SNR