Woojin Ahn's research while affiliated with Korea National University of Transportation and other places

The demand for high-data-rate and time-sensitive applications, such as 4k/8k video streaming and real-time augmented reality (AR), virtual reality (VR), and gaming, has increased significantly. Addressing the inefficiency of distributed channel access and the fairness problem between uplink and downlink flows is crucial for the development of wireless local area network (WLAN) technologies. In this study, we propose a novel transmission scheme for IEEE 802.11be networks that addresses the fairness problem and improves the system throughput. Utilizing the concept of multi-AP coordinated OFDMA introduced in the 7th-generation WLAN IEEE 802.11be, the proposed transmission scheme allows an AP to share a granted transmission opportunity (TXOP) with nearby APs. A mathematically analysis of the throughput performance of the proposed schemes was performed using a Markov chain model. The simulation results verify that the scheme effectively improves the downlink fairness and the system throughput. Combined with the advanced multiuser (MU) features of IEEE 802.11ax, such as TUA, MU cascading sequence, and MU EDCA, the proposed scheme not only enhances downlink AP transmission, but also guarantees improved control over the medium. The scheme is carefully designed to be fully compatible with conventional IEEE 802.11 protocols, and is thus potentially universal.

In this paper, a novel channel access scheme, Distributed Triggered Access (DTA), is proposed for distributed V2V Basic Safety Message (BSM) dissemination in future platooning environment. To meet the stringent delay requirements of platooning communications, the proposed scheme is designed to use Wireless Local Area Network (WLAN) multi-user channel access in a distributed manner. The proposed scheme leverages advanced Medium Access Control (MAC) layer features, such as Triggered Uplink Access and Multi-user Request-To-Send (RTS), introduced in the 6th generation mainstream WLAN standard, IEEE 802.11ax, based upon a conceptual Physical (PHY) layer frame structure for IEEE 802.11bd, the successor of IEEE 802.11p. The proposed scheme is analyzed by mathematical model and simulations from transmission delay and successful transmission rate perspective. The mathematical model includes a Markov chain analysis that models the Enhanced Distributed Channel Access (EDCA) backoff procedure of DTA considering the effect of resumed backoff procedure with empty buffer caused by triggered access. Also, a Markov arrival/General service distribution/1 service channel (M/G/1) queuing model is provided to analyze the transmission delay of a BSM under unsaturated traffic condition. The extensive simulation results corroborate that DTA effectively improves the transmission success rate and reduces the average BSM collecting delay in a highly congested environment.

As Intelligent Transport System (ITS) applications are diversified and amount of ITS data increases, high throughput and reliability are required in next-generation V2X communications. In order to meet such increased throughput and reliability requirements, IEEE 802.11bd, the next-generation V2X communication standard, has commenced standard development. One of the main features of IEEE 802.11bd is a 20-MHz bandwidth transmission. In this paper, a novel wide-bandwidth channel access scheme in next-generation Wireless Local Area Network (WLAN)-based vehicular communications is proposed. The proposed scheme is designed to provide fairness with other ITS devices and channel efficiency considering adjacent channel interference. By using the proposed scheme, through extensive simulations, it is verified that, while satisfying the fairness requirement with other ITS devices, the channel access delay of wide-bandwidth packet transmission can be optimized.

This paper proposes a novel and energy efficient Internet of Things (IoT) communication scheme for next generation Wireless Local Area Network (WLAN). There are a couple of crucial requirements among unique IoT requirements: a large number of communication devices must be supported, and they must have low power consumption. Since sensor-type IoT devices, which are expected to be one of the major types of IoT devices, normally generate uplink traffic rather than downlink traffic, an energy efficient multiuser uplink transmission scheme is a crucial feature of IoT communication. In the next generation WLAN, IEEE 802.11ax, Orthogonal Frequency Division Multiple Access (OFDMA) is adopted to support a greater number of devices. However, uplink OFDMA procedures that consider the unique IoT requirements have not been fully considered in the next generation WLANs. A random access-based WLAN uplink OFDMA transmission scheme is proposed in this paper, and analytical modeling of the proposed scheme is provided. The proposed random access-based WLAN uplink OFDMA transmission scheme is able to dynamically adjust the number of contending users by uniquely applying congestion status in a very simple and distributed manner. Our numerical analysis and extensive simulation corroborate the fact that the proposed scheme is able to support a greater number of IoT devices with less power consumption.

As a possible standardization of wireless local area network (WLAN), IEEE 802.11 LRLP is under discussion in order to support long range and low power (LRLP) communication for internet of things (IoT) including drones and many other IoT devices. In this paper, an efficient adaptive resource unit allocation scheme for uplink multiuser transmission in IEEE 802.11 LRLP networks is proposed. In the proposed scheme, which adopts OFDMA random access based transmission scheme of IEEE 802.11ax, in order to enhance the efficiency of the slotted OFDMA random access, access point (AP) traces the history of the sizes of successfully transmitted uplink data, and adjusts the sizes of resource units for the next uplink multiuser transmission adaptively. Our simulation results corroborate that the proposed scheme significantly improves the system throughput.

In this paper a novel access scheme for uplink multiuser transmission based on IEEE 802.11ax random access in in-aircraft wireless sensor networks is proposed. The proposed scheme provides an efficient access control mechanism with three divisions of OFDMA backoff counter (OBO): access, deferring, dropping, which controls the number of potential uplink transmission stations. The proposed scheme can be used efficiently in in-aircraft wireless sensor network where a large number of sensors need to be supported. By using the proposed scheme, since in-aircraft sensors attempt channel access using the proposed differentiated OBO parameters, the number of stations exceeds the access capacity can be efficiently controlled. This paper also provides the mathematical analysis of the proposed scheme, regarding the optimal parameters. According to the performance analysis, the proposed scheme is able to efficiently control the access behavior of wireless sensors in the network.

In order to minimize packet error rate in extremely dynamic vehicular networks, a novel vehicle to vehicle (V2V) mobile content transmission scheme that jointly employs random network coding and shuffling/scattering techniques is proposed in this paper. The proposed scheme consists of 3 steps: Step 1-The original mobile content data consisting of several packets is encoded to generate encoded blocks using random network coding for efficient error recovery. Step 2-The encoded blocks are shuffled for averaging the error rate among the encoded blocks. Step 3-The shuffled blocks are scattered at different vehicle locations to overcome the estimation error of optimum transmission location. Applying the proposed scheme in vehicular networks can yield error free transmission with high efficiency. Our simulation results corroborate that the proposed scheme significantly improves the packet error rate performance in high mobility environments. Thanks to the flexibility of network coding, the proposed scheme can be designed as a separate module in the physical layer of various wireless access technologies.

In this paper, we propose a novel V2V transmission scheme, namely S3-RNC (Shuffled Scattered Symbol-level Random Network Coding), for Mobile Content Distribution (MCD) between communication pairs traveling on opposite directions. To cope with the Doppler Effect caused by extremely high relative velocity, symbol-level random network coding (RNC) with shuffling (interleaving) and scattering is used in our proposed scheme. As the second step, receivers, moving together as a cluster, cooperatively relay their received S3-RNC coded blocks, in order to maximize the probability of successful decoding. Our simulation results show that S3-RNC improves throughput performance significantly in high mobility environment. By utilizing S3-RNC, consumer vehicular communication devices are able to provide a lot of useful information to vehicular users.