Orthogonal Frequency Division Multiple Access (OFDMA) is the basis for several emerging wireless systems, such as 802.16e (WiMAX) or 3GPP Long Term Evolution (LTE). In OFDMA, different users are multiplexed in time and frequency. In the 802.16e Adaptive Modulation and Coding (AMC) downlink, the data bursts for a particular terminal have a rectangular shape and need to be placed in the two-dimensional time/frequency plane. The position and shape of the rectangles is arbitrary, and it is the task of the frame packer to pack the frame efficiently, wasting as little space as possible. In this paper, we treat the frame packing problem as a strip-packing problem. We solve this combinatorial optimization problem by developing a suitable representation for a genetic algorithm. This algorithm can reach within 5% of the theoretical lower bound for the packing efficiency.