Hyunseok Ryu

Collision-aware resource access in LTE-based device-to-device communication systems

In the Long Term Evolution (LTE) based device-to-device (D2D) communication systems, there are two resource access modes, i.e., eNB scheduled and random access. The eNB scheduled resource access gives flexibility to eNB with additional signalling overhead. The random access scheme is simple without the eNB control but has the drawback of data collision. In this paper, we propose a collision-aware random access scheme for the D2D communications. The proposed scheme utilizes the feature that there are many unused resources in the data transmission period and all user equipments (UEs) have full information about the resource usage. Before data transmission, the UEs send the resource reservation messages in the unused resource to inform others about the selected resources to be used in the next period. By this means, the D2D UEs can detect the resource reservation messages from each other, and hence can try to select different resources to avoid collision. The performance of the proposed scheme is analyzed and evaluated by simulations. Our results shown that the proposed scheme outperforms the random access scheme by a wide margin in terms of data collision probability.

Performance comparison of resource allocation schemes for D2D communications

It is generally accepted that centralized resource allocation can achieve better performance than distributed resource allocation in terms of system optimization at the cost of signaling overhead. However, it may be not true in D2D broadcast communication, especially when any closed-loop feedback on PHY, MAC, RLC, or PDCP layer is not allowed. In this paper, we provide performance comparison between centralized and distributed resource allocation schemes in an outside network coverage scenario, according to evaluation methodology and simulation environment agreed in current 3GPP RAN1 D2D standardization. Based on our system level simulation results, it is shown that distributed resource allocation using an implicit coordination (e.g., energy sensing) can achieve better performance than centralized resource allocation schemes under consideration, especially when the frequency resource granularity is small. Therefore, distributed resource allocation in D2D broadcast communication can be the baseline approach for Public Safety in outside network coverage.

Distributed iterative scheduling for D2D communications

In this paper, we propose the novel distributed iterative scheduling (DIS) method where each device determines its own resources by exchanging resource assignment and resource demand information with neighboring devices. Higher spatial reuse gain as well as fairness can be achieved by resource conflict resolution based on signal-to-interference ratio at receiver device and channel-state dependent resource assignment in a synchronous and iterative manner. It is shown that the proposed scheme can provide the large number of concurrent links and high system throughput. With our simulation results, DIS can be a useful means as enabling efficient Device-to-Device (D2D) communications as compared to conventional WiFi system.