laim that their algorithm significantly increases the number of nonreal-time services without compromising much cell throughput. Despite many authors having presented solutions implementing QoS scheduling to trans- mit data over a wireless channel, few have combined algorithms guaranteeing QoS while making efficient use of channel resources. The following section discusses the efforts made in this direction. Chapter 7 Wireless scheduling and Quality of Service optimization techniques 247 Combined Quality of Service and opportunistic schedulers Certain authors attempt to combine a QoS-approach to scheduling, while attempting to achieve efficient use of spectrum. A combination of adjacent subcarrier allocation and fair scheduling is presented by Ergen et al.41 The authors admit that although an optimal solution to the problem is unlikely to be implementable in real time, their suboptimal solution allocates data fairly and converges close to meeting the optimal QoS criteria per symbol. It is, however, limited by the characteristic problem of not knowing CSI between the transmitter and receiver. Wu and Negi also attempt to combine multiuser diversity and efficient QoS support over fading channels. 42 The authors claim a substantial increase in channel capacity, but only when delay requirements are not very tight. Recently, Khattab and Elsayed have presented a scheduling scheme based on the EDD algorithm that exploits multiuser diversity and can provide statistical guarantees on delays. The scheme achieves high throughput and exhibits good fairness performance with respect to throughput and deadline violations. The tests and simulations performed were on a 1.25 MHz CDMA channel, but such algorithm could be very useful for scheduling real-time traffic if adaptable to an OFDMA network. A recent paper from Farrokhi et al. combines QoS scheduling and the efficient use of channel resources. 44 This builds on a previously submitted paper by the same authors. 45 proposes to allocate specific subcarriers to specific users, th