| 摘要 |
<p>To ensure that the performance of an OFDM system is adequate, it is necessary to provide a guard space between symbols so that the effects of mutual interference between adjacent symbols is avoided. In a conventional OFDM system the length of this guard space must be equal to, or greater than, the maximum delay spread in the system. Bearing in mind that under some conditions the delay spread in a mobile system may be large, while under other conditions the delay spread may be low, the use of a fixed guard space corresponding to the longest delay spread, imposes an overhead on the transmission capacity of a communications channel. This conflict between channel traffic capacity and the need for long guard spaces between symbols can be overcome by using a variable length guard space, i.e. a guard space of variable duration. A receiver is able to instruct a transmitter to increase the duration of the guard space if the system performance is degraded.</p> |
