Optimal Guard Time Length Determination for Mobile WiMAX over Multipath Fading Channel

摘要

Guard time length (GT) is one of the key OFDM parameters. It is implemented as Cyclic Prefix (CP) to completely alleviate Intersymbol Interference (ISI) and to preserve orthogonality among OFDM subcarriers as long as the guard time length is sufficiently greater than channel delay spread. Conventional OFDM system uses a large GT length to tolerate worst case channel condition irrespective of its current state. This technique, however, degrades the overall spectral efficiency as well as consumes transmitter energy proportional to the length of the guard time. In this paper, we determine the optimal guard time length for mobile WiMAX system over ITU-R M.1225 multipath fading channel. The results show that the optimum values of the GT approximately dependant on the maximum delay spread.