BER Analysis of OFDM with Different Modulation Techniques

摘要

A common problem found in high-speed communication is inter-symbol interference (ISI). ISI occurs when a transmission interferes with itself and the receiver cannot decode the transmission correctly. For example, in a wireless communication system, the signal reflects off large objects such as mountains or buildings and the receiver sees more than one copy of the signal. In communication terminology, this is called multipath. Since the indirect paths take more time to travel to the receiver, the delayed copies of the signal interfere with the direct signal, causing ISI [16].rnThis paper focuses on orthogonal frequency division multiplexing (OFDM) simulation and implementation, as well as compare the output result of binary phase shift keying (BPSK) and quaternary phase shift keying (QPSK) modulation technique with OFDM.rnOFDM is especially suitable for high-speed communication due to its resistance to ISI. As communication systems increase their information transfer speed, the time for each transmission necessarily becomes shorter. Since the delay time caused by multipath remains constant, ISI becomes a limitation in high-data-rate communication. OFDM avoids this problem by sending many low-speed transmissions simultaneously.rnFigure 1 shows two ways to transmit the same four pieces of binary data. Suppose that this transmission takes four seconds. Then, each piece of data in the left picture has a duration of one second. On the other hand, OFDM would send the four pieces simultaneously, as shown on the right. In this case, each piece of data has a duration of four seconds. This longer duration leads to fewer problems with ISI. Another reason to consider OFDM is low-complexity implementation for high-speed systems compared to traditional single-carrier techniques [16].