Orthogonal Frequency Division Multiplexing (OFDM)

In broadband wireless system, the signal energy is scattered and reflected from objects in the environment, components of the signal arriving at the receiver are spread out over a longer period of time than is desirable. The challenge is then to provide a high-performance reliable data link that can operate with the restricted receiver power levels, severe channel fading due to multipath reflections and interfering energy from other devices nearby. With OFDM, it is possible to use a differential coding/differential detection either in the time or frequency domain depending on the condition of transmission channels with the adoption of DQPSK as a method of subcarrier modulation. This paper proposes an approximate derivation method of the bit error rate (BER) in DQPSK/OFDM system over frequency non-selective Nakagmai-Rice and Rayleigh fading channels. The validity of this equation is confirmed from the fact that the BER derived from this approximate equation coincides with that from the computer simulation, even when the system parameters, for example Doppler frequency, Rician parameter and so on, are varied. This paper will also review where OFDM is applicable and future applications.