Theory and System Simulation of the WiMAX

Abstract

OFDM transmission is a multicarrier modulation scheme unsing orthogonal subcarriers, thus increasing the spectral eciency.OFDM has developed into a popular scheme for wideband digital communication systems, such as WiMAX. WiMAX is one of the competitive systems of the 4G wireless networks, and comprises two standards: 802.16-2004 for xed access and 802.16e for mobile access. 802.16e is a scalable extension of 802.16-2004 supporting mobility and MIMO among others. Both standards support the 256-OFDM transmission technique, which uses 256 orthogonal subcarriers. An important feature is obtained when OFDM is used in combination cyclic prefix: this mitigates the ISI between consecutive OFDM symbols, and fakes a circular convolution with the channel. The latter property can also be used to more easily combat ICI, i.e. channel equalization. An OFDM system targeting the OFDM parameters of 802.16-2004 has been implemented and simulated in Matlab. This illustrates the various system aspects and the signal degradation caused by transmission over a two-ray channel. In addition, the capacity of this transmission scheme over various Rice fading two-ray channels has been estimated in another simulation, identifying the increase in average capacity caused by multipath reception. This is a result of increased overall received energy compared to the at time-invariant channel.