Hyukjun Oh

Towards reliable OSGi framework and applications

Upcoming ubiquitous computing systems are required to operate in dynamic, diverse, unverified, and unpredictable operating environment. The OSGi (Open Service Gateway initiative) framework employs the service-oriented approach and the java classloader architecture for the runtime service deployment, that are well suited to the dynamic environment envisioned for home networking and ubiquitous computing. However, the current OSGi framework does not provide full reliability measures, especially for failure conditions such as network, device, and application failures. This paper analyzes software reliability issues in OSGi framework and proposes a proxy-based reliable extensions. The design concept is implemented and partly tested on an open source OSGi platform, Oscar, for the smart home residential gateway test-bed.

A precisely gain controlled RF front end for T-DMB tuner ICs

A precisely gain controlled RF front end is developed for T-DMB tuner IC applications. A precise RF gain control with 50dB dynamic range is achieved in RF VGA by employing a capacitive ladder type attenuator. The proposed method enables us to design and analyze very fine gain step VGA concretely. Implemented in 0.13µm CMOS, the tuner RF front end consumes 9.7mA at 1.2V supply. Measured results are NF < 1.5dB at the maximum gain and the accurate 1dB gain step is obtained.

28 GHz RF transceiver module for 5G beam-forming system

This paper presents a 28 GHz RF transceiver module for 5G beam-forming system. EM simulation supports precise module design at quasi-millimeter wave frequency. The receiver employs heterodyne architecture and IR filter is composed on PCB board. The gain and NF of receiver are 25.5 dB and 6.5 dB, respectively. The gain and P1dB of transmitter are 10.5 dB and 5.6 dBm. The RF module is also inter-operated with USRP-2942R based BB modem and 4×8 array antenna. The measured EVM at −90 dBm is −12 dBc.

Propagation Prediction for LTE Small Cells with Antenna Beam Tilt

This paper proposes some modifications of the COST 231 Walfisch-Ikegami (WI) model to reflect the information related to building and terrain heights of practical environments. Based on the modified WI model, a dual slope propagation model is developed for small cells with electrical and mechanical tilt. To validate the proposed model, propagation measurements are performed in a metropolitan area using commercially deployed small cells. We suggest a procedure to compute the path loss from measurement data considering transmit antenna beam patterns, and determine the break point for the proposed dual slope model using measurement results. Finally, the proposed model is compared through data analysis with conventional propagation prediction models in terms of root mean square deviation (RMSD).

Time synchronization for M-WiMAX femtocells using IEEE 802.11 based wireless backhaul

In this paper, we propose a new time synchronization method for femtocells connected to the core network through IEEE 802.11 based wireless link. In the proposed method, the time information is transmitted to a femtocell via the wireless backhaul using modified IEEE 802.11 beacon frames, and a least squared based estimation method is used to reduce the timing jitter at the femtocell. Through simulations, it is shown that the femtocells using the proposed algorithm satisfy the time accuracy specification for M-WiMAX.

XMAS: An eXtraordinary Memory Allocation Scheme for Resource-Constrained Sensor Operating Systems

The wireless sensor networks are sensing, computing and communication infrastructures that allow us to monitor, instrument, observe, and respond to phenomena in the harsh environment. Sensor operating systems that run on tiny sensor nodes are the key to the performance of the distributed computing environment for the wireless sensor networks. Therefore, sensor operating systems should be able to operate efficiently in terms of energy consumption and resource management. In this paper, we present XMAS to improve the time and space efficiency of memory management for the sensor operating systems. XMAS was implemented on Nano-Qplus which is a multi-threading sensor operating system. Our experimental results show that the XMAS performs efficiently in both time and space compared with existing memory allocation mechanisms.

An intelligent power management scheme for wireless embedded systems using channel state feedbacks

In this paper, an intelligent power management scheme for embedded systems with wireless applications is proposed to reduce the power consumption of the overall system. The proposed method is based on the feedback of the extreme channel state indicator that is designed to detect the extremely bad channel condition. The considerable power reduction is achieved by turning off modules within the embedded system related to the information transmissions under such an unreliable channel condition. A simple extreme channel state detector is also proposed.

Radio Propagation Model Considering Antenna Beam Tilt with Application to Small Cells

Antenna beam tilting techniques are commonly used to deploy small cells with reduced coverage compared than macrocells. This paper proposes a new statistical propagation model for small cells with electrical and mechanical antenna tilt. The proposed model combines the dual slope path loss model with the departure angle spread model for considering antenna beam tilt. The proposed departure angle spread model introduces a new parameter reflecting the azimuth spread of departure (ASD) angles in order to account for the change of transmit antenna gain by electrical and mechanical tilt. Through this approach, the antenna gain for each ray is separately computed by considering the transmit antenna beam pattern as well as the antenna beam tilt. We perform field tests to measure the receive signal power in the downlink of commercial Long-Term Evolution small cells with antenna tilt. Based on the measurement data, we find the statistically optimal ASD parameter using a grid search and calculate the antenna gain for each ray. Also, the overall transmit antenna gain is obtained by averaging antenna gains for multiple rays. To assess the accuracy of the proposed model, the estimation error is evaluated by comparing the measured receive signal power with the estimated value using a propagation model, and the performance of the proposed propagation model is compared with those of existing path loss models in terms of root mean square error deviation. Then, it is shown that the proposed model provides more accurate propagation estimation for small cells than existing models.

Autonomous traffic management for CDMA-based real-time services in in-building environments

The CDMA-based IS-856 standard provides high-speed wireless Internet connectivity to mobile subscribers and is well suited for the packet data applications. The IS-856 access point can be used as a small base station designed for in-building environments to improve the in-building signal coverage and quality. The standard has an autonomous traffic management algorithm for the reverse-link transmission. In order to support delay-sensitive real-time services, it is essential to guarantee the minimum data rate over the air interface. In this paper, it is pointed out that some data rates in IS-856 are not suitable for the real-time voice services and they need to be avoided during the traffic management. In the proposed schemes, the original traffic management is improved by suppressing the excessive fluctuations of traffic load and by restricting the operation range of data rates. The analysis results show that the proposed schemes can improve the reverse-link performance and effectively support real-time services at the same time.

Performance Analysis of Forward Link Transmit Power Control during Soft Handoff in Mobile Cellular Systems

Forward link performance during a soft handoff for two conditions is evaluated. We showed quantitatively that the performance of the combined signal from two base stations is better than of a signal from each of two base stations as diversity combining. We also showed that the use of diversity combining at the mobile allowed the call to be maintained at a sufficiently low Eb/No value.