The wide use of OFDM systems in multiuser environments to overcome problem of communication over the wireless channel has gained prominence in recent years. Cross-layer Optimization technique is aimed to further improve the efficiency of this network. This chapter demonstrates that significant improvements in data traffic parameters can be achieved by applying cross-layer optimization techniques to packet switched wireless networks. This work compares the system capacity, delay time and data throughput of QoS traffic in a multiuser OFDM system using two algorithms. The first algorithm, Maximum Weighted Capacity, uses a cross-layer design to share resources and schedule traffic to users on the network, while the other algorithm (Maximum Capacity) simply allocates resources based only on the users channel quality. The results of the research shows that the delay time and data throughput of the Maximum Weighted Capacity algorithm in cross layer OFDM system is much better than that of the Maximum Capacity in simply based users channel quality system. The cost incurred for this gain is the increased complexity of the Maximum Weighted Capacity scheme.