As one of the techniques beyond 3G, because of the effective performance of high spectrum utilization and anti-fading for frequency selecting and adopted multi-carrier modulation technique that meets the requirement of the explosive traffic capacity, Orthogonal Frequency Division Multiplexing (OFDM) has carried great weight in wireless communications. This paper expounds OFDM technical characteristics and performs computer simulation on the OFDM system based on Inverse Fast Fourier Transform (IFFT) by means MATLAB. During the course of simulation, comparison between OFDM and traditional single-carrier technology is performed. The simulation results have great significance for research and applications in the field.
TopTechnique Principle
The essential technical principle is to divides one high speed data flow into plurality of low speed data flows. And the low-speed data flows are modulated by orthogonal frequency and transmit data simultaneously, thus wide band becomes narrow bands, and consequently, the problem of selective fading can be solved. In addition, if adding a delayed protection to generated OFDM signal, intersymbol interference can be figured out (Gong & Jia, 2002; IEEE Computer Society, 1999). The modulation principle in OFDM system is seen in Figure 2.
Figure 2. OFDM modulation principle
After the modulating of MQAM, MPSK or DPSK, etc., taking advantage of sub-carrier orthogonality, the original signal is demodulated. The principle is seen in Figure 3.
Figure 3. OFDM demodulation principle
One OFDM symbol includes signals which are combined by multiple modulated sub-carriers, and each sub-carrier can be modulated by PSK or QAM symbol. If N indicates the number of sub-channel, T indicates OFDM symbol density, di (i=0, 1, 2, …, N-1) indicates data symbol distributed to each sub-channel, and fc indicates the carrier frequency of the No. 0, rect(t)=1, |t|≤T/2, the original OFDM symbol can be indicated as following:
(2)
or
OFDM output signal is described by equivalent baseband symbol:
(3)