Myung-Sun Song

HMM Based Channel Status Predictor for Cognitive Radio

Nowadays, many researchers are interested in cognitive radio (CR) technology. We can say that the CR is the extended technology of software defined radio. Both technologies seem to be similar but there is an important difference. That is a sensing and channel management function. CR always senses incumbent users (IU) (or primary users) appearing on the channel the CR has been used and the CR must evacuate from that channel for preventing IU from interferences. For this purpose, CR should include a functionality of being able to find new relevant channel to move. So, CR must evaluate the quality of empty channels. From the point of view, we propose the HMM based channel status predictor, which helps the CR evaluate the quality. We will implement a HMM channel predictor and it will predict next channel status based on past channel states.

Fully embedded LTCC spiral inductors incorporating air cavity for high Q-factor and SRF

In this paper, a new fully-embedded LTCC spiral inductor is proposed by incorporating an air cavity between the spiral and ground plane for high quality factor (Q-factor) and high self-resonant frequency (SRF). The disadvantage of fully embedded structure without an air cavity is the reduction of size efficiency in the RF system, since its structure needs a lot of layers to decrease parasitic capacitance between the spiral and ground plane for high Q-factor and SRF. The air cavity employed under the spiral reduces the shunt parasitic capacitance of the inductor, and results in high Q-factor and high SRF of the embedded inductors. The measured results of the optimized spiral inductor with the embedded air cavity show a maximum Q of 51 and SRF of 9.1 GHz, while those of the conventional spiral inductor describe a maximum Q of 43 and SRF of 8 GHz with effective inductance of 2.7 nH.

The detection and classification of the Wireless Microphone signal in the IEEE 802.22 WRAN system

For the use of the IEEE 802.22 WRAN, the spectrum sensing of the TV band is essential. In this paper, the Testbed for the signal detection and sorting algorithm and verification was proposed among the spectrum sensing algorithm about the part 74 wireless microphone (WM) signal. In case a plurality of WM signals exists within 6 MHz bandwidth, this algorithm uses the polyphase filterbank and grasps the signal absence. And by using the cyclostationary property, it has the advantage of moreover accurately knowing with the number of WM signals and frequency location.

Distributed implicit interference alignment in 802.11ac WLAN network

Recently, the demand for wireless service is highly increased because of many smart devices. Many people want to access the internet by using 802.11 WLAN network as of free service. So, a lot of APs are deployed in many places such as home, office and store. Because anyone can install the AP in any place, APs or STAs are suffered the interference between them. This interference makes whole WLAN network performance to be poor quality. The main reason existing the interference is that a huge number of AP and STA is deployed. To solve this situation, 802.11 standard has established a new study group (SG), high efficiency wireless (HEW) local area network. This SG want to enhance the area throughput which is the average throughput in a specific area. We think average throughput is mainly effected by the inter cell interference which is the interference from other APs or STAs. And average throughput is proportional to the sum rate of each node in a specific region. In this paper, we develop three different downlink interference management approach which is so called distributed interference alignment algorithms. To apply these algorithms in the 802.11 WLAN, we think there are some key points which are distributed processing between nodes, only local channel state information usage, linear processing and IA adaptation possibility for the number of general users. Our algorithms displayed in this paper are followed by above assumptions. And we show the performance comparison between our algorithms.

A fully embedded LTCC stripline parallel coupled BPF for 40 GHz BMWS application

A low-loss fully embedded bandpass filter (BPF) is proposed using low-temperature cofired ceramic (LTCC) technology with enhanced stopband characteristics for the broadband multimedia wireless system (BMWS) applications. The measured insertion loss was as small as 1.7 dB at a center frequency of 41.8 GHz, and the return loss was 10.2 dB, including the loss associated with two stripline-to-CPW transitions. This six-layer BPF showed 3-dB bandwidth of 8.4% at a center frequency of 41.8 GHz and suppressed the local oscillator (LO) signal to 20 dB at a local oscillator frequency of 38.8 GHz.

LTCC microstrip patch array antenna with WR-22 feeding structure for an integrated transceiver module

Design and fabrication of 8times8 stacked patch array antenna with the WG-to-MS transition operating at 40 GHz band based on 6 layers LTCC technology were proposed in this paper. Various measurements of reflection coefficient and gain have been presented and found to be in good agreement with the simulation results

60GHz 2×4 low temperature co-fired ceramic cavity backed array Antenna

Recently, low temperature co-fired ceramic (LTCC) technologies for low cost and small size packaging have been developed in the millimeter wave band. However, in case of designing the antenna of using LTCC substrate, its difficult to meet the bandwidth specification for broadband wireless communication such as IEEE 802.15.3c 60GHz WPAN (Wireless Personal Area Network), which needs 7GHz bandwidth (57∼64GHz), due to the high dielectric constant of LTCC substrate [1]–[2]. Furthermore the radiation efficiency of the antenna becomes reduced due to the surface wave as the height of LTCC substrate becomes increased. Previously a perfect metal cavity backed antenna fed by a coaxial cable [3], antennas using photonic bandgap substrate [4] were proposed to improve the radiation efficiency. Recently, aperture coupling antenna using soft surfaces on LTCC substrate was proposed [5], but bandwidth of the antenna was narrow.

Stacked circular patch antenna with monopole type pattern for 60GHz WPAN application

Design of stacked circular patch antenna having the omni-directional in the azimuth plane has been proposed for very short range 60 GHz WPAN application. The proposed antenna uses LTCC technology, which makes easier to integrate with a transceiver chip.

The wideband characteristics of plate antenna with elliptical cross section

In this paper, a plate antenna with elliptical cross section and ellipticity ratio is studied. The return loss of the proposed antenna and conventional antennas is investigated using the simulation package CST MW Studio ver. 3.2 and fabricated antennas. The effects of ellipticity ratio on the radiation pattern and reflection coefficients are described. The given structure can handle the average power of several hundreds of watts. The simulated results of this antenna are obtained for various values of the ellipticity ratio of elliptical cross section loaded at the input port

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.