Seungyeob Chae

Interference mitigation and D2D parameter estimation for distributed‐control D2D underlay systems

Although centralised-control schemes for device-to-device (D2D) underlay communications can produce satisfactory results by efficiently managing the interference between cellular and D2D transmissions, they can become prohibitively complicated and may require a large amount of feedbacks from devices, because it is important to handle the inter-cell interference as well as the intra-cell interference. Such a burden can be alleviated by a distributed-control mechanism, in which a base station performs the resource management of its cellular devices and each D2D device selects its own resource without a small-scale control of the cellular network. This paper addresses interference issues in distributed-control D2D underlay systems and presents an interference mitigation technique based on frequency spreading, in order to meet the target outage probability. This paper also proposes a simple estimation scheme, which can be used for the mode selection and the determination of D2D transmission parameters. Copyright

Optimization Framework and Parameter Determination for Proximity-Based Device Discovery in D2D Communication Systems

One of the most important processes in device-to-device communications of cellular devices is that of discovery, which determines the proximity of devices. When a discovery process is performed, there are several parameters to determine, including the discovery range, the discovery period, and the modulation and coding scheme of the discovery messages. In this paper, we address the relationships between these parameters and describe an optimization framework to determine them. In the proposed procedure, it is important to first optimize the discovery rate, which is defined as the number of discoverable devices per unit time. Once the discovery rate is maximized, the discovery period can be determined accordingly based on the device density and the target discovery range. Since the discovery rate is not affected by many of discovery parameters such as the discovery range, the device density, and the discovery period, it can be used as a performance metric for comparing discovery schemes with different discovery ranges or different discovery periods.

System level simulation for 5G cellular communication systems

In 5G cellular communication systems, a new type of simulation methodology may be required due to the emergence of new services and applications, new environments and requirements, new performance indicators, and increased need for accurate end-to-end performance measurements of systems including wired and wireless sections. In this paper, we address the characteristics of 5G simulations compared with 4G simulations especially focusing on system level simulation. Considering the characteristics of 5G simulations, the requirements for 5G simulators can be derived. In order to fulfill the requirements, a system level simulator is currently being developed and some selected features of the simulator are presented.

Relay location considering in-band emission for OFDMA-based D2D overlay systems

In device-to-device (D2D) communication systems, orthogonal frequency division multiple access (OFDMA) is widely used to secure the communication coverage and maintain the similarity with cellular systems. In order to avoid severe interference between cellular and D2D systems, one can use overlay schemes, where D2D devices use dedicated sub-channels of uplink OFDMA resources. However, sub-channels in OFDMA systems are not completely orthogonal and there is still some interference between sub-channels due to in-band emission. There are many advantages of D2D communications and the advantages can be enjoyed even for not-very-close devices by using D2D relays. In this paper, we discuss the optimal relay location taking care of in-band emission for OFDMA-based D2D overlay systems.

Coded random access with multiple coverage classes for massive machine type communication

One of the major requirements for next generation mobile or wireless communication systems is to efficiently support a large number of machine type communication (MTC) devices for internet-of-things (IoT) applications. For IoT services, a base station needs to receive packets with very low receive sensitivity since many MTC devices are placed inside buildings or underground while the transmission power of MTC devices is usually low. In order to maintain a wide coverage area, MTC devices with very bad channel conditions need to transmit with low data rates, i.e., with long packet lengths compared to others in good conditions. In this paper, we discuss the performance improvement of random access using a coded random access technique when MTC devices use different packet lengths according to their channel conditions.

Orthogonal data repetition patterns for massive connectivity

One of the main requirements in the next generation wireless and mobile communication system is supporting a huge number of machine type communication (MTC) devices efficiently. MTC devices may be placed in indoor or underground environments, where the signal is hard to reach. In order to maintain a proper communication range, devices with bad channel conditions may use very low data rates using data repetitions. However, the performance of devices with long packet lengths may be degraded due to increased collisions with other short packets. In this paper, we propose random access schemes using orthogonal data repetition patterns to reduce the collision probability of devices with bad channel conditions.