Qingyu Miao

Adaptive Resource Allocation in OFDMA Relay-Aided Cooperative Cellular Networks

Adaptive resource allocation to exploit multiuser diversity and spacial diversity in OFDMA relay-aided cooperative cellular networks is studied. Assuming that the BS has all the channel state information (CSI), an optimization problem for subcarrier assignment, relay selection and power allocation that maximizes downlink capacity of the system is formulated. Since the optimal solution is complex to obtain, a suboptimal solution dividing the problem into two sub-problems is proposed. Assuming equal power allocation in BS and each relay, the first sub-problem for joint subcarrier assignment and relay selection is a combinatorial optimization problem, for which an iterative algorithm derived from necessary optimality condition is proposed. Given the results from the first sub- problem, the second sub-problem for power allocation becomes a convex optimization problem and can be solved by an iterative method which optimizes the power of BS and each relay separately. Numerical results showed that two iterative algorithms can converge in reasonable steps and achieve significant improvement on system capacity due to two diversity schemes and power fully exploited.

Clustering Schemes for D2D Communications under Partial/No Network Coverage

Device-to-device (D2D) communications as an underlay to cellular networks can not only increase the system capacity and energy efficiency, but it can also enable national security and public safety (NSPS) services. A key requirement is to provide access to cellular services when the network is available and maintain local communication in the (partial) absence of the infrastructure. In this paper we propose and compare clustering schemes that are applicable for integrating D2D communications into cellular networks such that communication services can be maintained when the cellular infrastructure becomes partially dysfunctional. Our results show that there is a trade-off between coverage, energy efficiency and cluster formation delay and this trade-off can be handled by our proposed threshold-based clustering scheme.

Spatial Filter for MIMO Repeaters with First-Hop Channel State Information and End-to-End SNR

A repeater is a device that improves the rate- coverage performance of a system by amplifying and forwarding its received signal. When multiple antennas are deployed on a repeater, spatial signal processing becomes possible for better performance. In this paper we propose a spatial filter for such a multi-antenna repeater. This filter is designed based on first- hop channel state information (CSI) and end-to-end signal-to- noise ratio (SNR). The optimal filter matrix is proved to be a product of a diagonal matrix and the conjugate transpose of the left singular matrix of the first-hop channel matrix. The diagonal matrix is obtained by maximizing an upper bound of the ergodic channel capacity. Simulation results indicate that the proposed filter outperforms that without filtering in end-to-end channel capacity, especially when the number of repeater antennas is greater than that of the source antennas. As the first-hop CSI and the end-to-end SNR can be obtained without any modification of the source or the destination, a repeater with the proposed spatial filter can be easily implemented in a current system.