A study of impact of inband signalling and realistic channel knowledge for an example dynamic OFDM–FDMA system

Dynamically assigning sub‐carriers of o rthogonal f requency d ivision m ultiplexing (OFDM) systems to multiple different terminals in a cell has been shown to be beneficial in terms of different transmission metrics. The success of such a scheme, however depends on the ability of the access point to inform terminals of their newest sub‐carrier assignments as well as on the accuracy of the channel state information used to generate new assignments. It is not clear whether the overhead required to implement these two functions consumes all of the potential performance increase possible by dynamically assigning sub‐carriers. In this paper, a specific MAC structure is selected enabling the operation of a dynamic OFDM system, incorporating a signalling scheme for dynamically assigned sub‐carriers. Based on this structure, we study the overhead required for a dynamic sub‐carrier scheme; a static variant that serves as a comparison case. We investigate the performance difference of these two schemes for various scenarios where at first signalling and then realistic channel knowledge is added to the system model. Average throughput and goodput per terminal serve as figures of merit; the number of terminals in the cell, the transmission power per sub‐carrier, the delay spread and the movement speed of the terminals are varied. We find that a realistic overhead model decreases the performance of both static and dynamic schemes such that the overall ratio favours in all cases except for higher speeds the dynamic rather than the static scheme especially in realistic system environments. Copyright © 2005 AEIT.