| Strategies to improve network capacities of ad-hoc relay, power control, and orthogonal frequency division multiple access (OFDMA) systems are proposed. First, we examine how the node density can be reduced by cooperative actions of nodes in ad-hoc networks in multi-hop routing. This results from the greater channel capacity of the broadcast, multiple access and multiple-input multiple-output (MIMO) channel compared to the point-to-point channel for the individual links making up the paths. We simulate the effects of cooperative actions in various channel conditions under very optimistic assumptions to establish upper limits on the benefits of cooperation. In some circumstances, node density can be reduced by up to 80% although lesser gains are more typical. Second, we have devised a cooperative power control algorithm and proved that the cooperation enhances the convergence speed. The cooperative links predict the future interference state as reliably as possible with the shared information. This brings a significant improvement in the convergence speed. It is proved by the eigenvalue analysis that not all the cross-link gains in a cooperative group have to be identified and shared; using any of them reduces the maximum modulus eigenvalue of the matrix updating power vector. Finally, we proposed an efficient dynamic resource allocation algorithm for real time traffic in uplink OFDMA systems. In contrast to the conventional algorithms performing computations for each subcarrier, the proposed algorithm performs computations for each user. Since the number of users who do not meet their quality-of-service (QoS) requirements is usually very small in practical situations, the proposed algorithm results in a large reduction in the complexity. In addition to the complexity reduction, the proposed algorithm outperforms the conventional algorithms for real time traffic. |
