Analysis of downlink capacity for an OFDM based cellular system

In this paper, we investigate the capacity performance of downlink transmission for an orthogonal frequency division multiplexing (OFDM) based cellular system. Three resource allocation schemes are examined for a multi-user cellular system by evaluating their channel capacity bound averages. The first scheme is random subchannel allocation with equal probabilities, the second scheme is subchannel allocation with equal overall capacities, and the third scheme is adaptive subchannel allocation among active users. Analytical and numerical methods are combined to study the capacity performance of these three resource allocation schemes for both 1-cell and 3-cell frequency reuse plans (FRPs). Results show that the 1-cell FRP exhibits a higher average capacity than the 3-cell FRP for the three resource allocation schemes in almost all conditions when the total available bandwidth is fixed. Furthermore, the adaptive subchannel allocation scheme offers a significant capacity improvement for both the FRPs.