Gwangzeen Ko

Channel management in IEEE 802.22 WRAN systems

Channel management policy is one of the key functions of any cognitive radio system. The channel management decision in a cognitive radio system depends on various factors such as government regulations, limitations of transmission power between communicating devices, availability of geo-location information, and the quality of various available channels. The main purpose of channel management in a cognitive radio system is to protect the incumbent users (licensed users). The first international standard based on cognitive radio technology is IEEE 802.22, Wireless Regional Area Networks, which aims at providing broadband access in rural areas by effectively utilizing the unused TV channels. This standard aims at describing both PHY and MAC layer functionalities in an infrastructure- based broadband wireless access network for communication between consumer premises equipment using a base station. This article presents the cognitive radio functionality of this standard in detail. The cognitive functionality is provided by the dynamic channel management using channel sensing, channel classification, and maintenance of channel information. Using these techniques, this standard effectively protects the incumbent users and dynamically manages the channel allocation in IEEE 802.22 WRAN systems.

An efficient quiet period management scheme for cognitive radio systems

In cognitive radio (CR) systems, the channel sensing scheme for detecting the presence of primary user directly affects the quality-of-service of CR users and primary user. In this letter, we propose a sensing scheme that consists of a series of consecutive energy detections followed by feature detection, where the energy detection time is much shorter than the feature detection time. With the proposed scheme, multiple energy detections decrease the feature detection due to false alarm and the overall channel sensing time. The performance evaluation using Markov analysis shows that the proposed scheme can heighten the maximum channel utilization of CR users, while maintaining the detection delay of primary user under a predefined value.

Self-coexistence techniques for cognitive radio LANs/PANs

Due to the license-exempt nature of the cognitive radio (CR), multiple CR networks may operate (coexist) on the same channel. In this paper, we first discuss some techniques for self-coexistence of CR local and personal area networks, where the self-coexistence means the coexistence of homogeneous CR networks using the same PHY/MAC protocol. Then, we propose a self-coexistence etiquette for the ECMA TC48-TG1 system, which is a CR personal area network specification in standardization. Simulation results show that the proposed etiquette supports effectively the self-coexistence of ECMA TC48-TG1 networks.

Protocol design for interference alignment in 802.11 WLAN interfering network

Nowadays, a huge number of WiFi devices are distributed in anywhere place. Because tremendous WLAN devices are transmitting in ISM bands, the interference problem has emerged as an important issue. The simple method to solve the interference problem is to avoid to the other vacant operating channel. However, current ISM band might be already shortage because of operating many WiFi devices. So, the researches about interference management like interference alignment (IA) which multiple nodes can simultaneously transmit in the same frequency band without interfering each other have received much attention. Most of the IA algorithms have researched to just obtain the precoding and decoding vector. To operate the IA algorithms in the real system such as 802.11 WiFi network or LTE cellular network, however, the operational procedure to function IA transceiver design is also needed. So, we propose a novel IA functional sequence protocol with our IA developed algorithm and evaluate the throughput considering protocol overhead.

Overlapping BSS interference mitigation among WLAN systems

Using OPNET simulation we evaluate performance of interference mitigation of wireless local area network (WLAN) systems by means of message exchange based approaches when basic service sets (BSSs) of WLAN systems are overlapped. To do that, we consider 802.11af systems that utilize registered location secure server (RLSS). RLSS provides channel schedule management (CSM) that enables 802.11af access points (APs) to schedule operating channel use in order to mitigate OBSS interference. We also consider 802.11af systems that take advantage of knowledge of neighbor discovery and radio environment information provided by 802.19.1 system, called 802.19.1 coexistence information service. In case of 802.11af system without 802.19.1 system, performance of OBSS interference mitigation is heavily affected by each OBSS APs radio environments based on awareness of co-channel sharing situation with harmful interference that initiates CSM. It is demonstrated that 802.19.1 coexistence information service enables 802.11af APs to facilitate the channel with negligible harmful OBSS interference.