Woon-Young Yeo

Channel Availability Analysis of Spectrum Handoff in Cognitive Radio Networks

In this letter, steady-state analyses of spectrum handoff delay and channel availability are presented when spectrum handoff is used in a cognitive radio network. The effects of spectrum sensing time, data transmission time, and state transition rates of primary user signals are studied. Numerical results show that executing spectrum handoff results in higher channel availability than not executing spectrum handoff. However, this benefit of spectrum handoff decreases as the data transmission time or the state transition rates of primary user signals increase.

A New Precoding Scheme for Constructive Superposition of Interfering Signals in Multiuser MIMO Systems

In a multiuser multiple-input-multiple-output system, handling inherent co-channel interference has been a major problem for reliable transmission. Most previous closed-form linear precoding schemes are based on channel inversion (CI). Several extended studies have attempted to retain power gain from already existing interference, instead of nulling it while still based on CI. However, there has not been a study on manipulating the interference to maximize the gain. In this letter, we propose a new precoding scheme for a base station to manipulate both a desired signal and interfering signals such that the desired signal can be superimposed with the interfering signals. In our approach, a Jacobian-based algorithm is applied to improve the performance. Simulation results demonstrate that the proposed scheme achieves improved robustness. Furthermore, we show that robustness becomes stronger with an increasing number of co-scheduled users in the phase-shift keying-based systems.

A coherent data filtering method for large scale RF fingerprint Wi-Fi Positioning Systems

The rapid growth of mobile communication and the proliferation of smart phones have drawn significant attention to location-based services (LBS). The Wi-Fi positioning system (WPS) is a newly attractive method as a widely applicable positioning technique in LBS. In WPS, the received signal strength indication (RSSI) data of all Wi-Fi access points (APs) are measured, and stored in a huge database, as a form of radio fingerprint map. Because of the millions of APs in urban areas, radio fingerprint data are seriously contaminated. Therefore, we present a coherent filtering method for radio fingerprint data. All fingerprints used in the developed test bed are harvested from actual radio fingerprint measurements taken throughout Seoul, Korea. This demonstrates the practical usefulness of the proposed methodology.

Efficient anti-collision algorithm using variable length ID in RFID systems

The RFID tags are used for low cost and convenient object identification. For the fast tag identification, the anti-collision algorithm is used. A new algorithm to identify RFID tags using a shortened ID instead of a long original tag ID is proposed. The proposed method changes the length of the shortened ID adaptively according to the number of unidentified tags. The proposed algorithm shows better performance compared to previous anti-collision algorithms in terms of average transmitted bits per one tag identification.

A Design of Irregular Grid Map for Large-Scale Wi-Fi LAN Fingerprint Positioning Systems

The rapid growth of mobile communication and the proliferation of smartphones have drawn significant attention to location-based services (LBSs). One of the most important factors in the vitalization of LBSs is the accurate position estimation of a mobile device. The Wi-Fi positioning system (WPS) is a new positioning method that measures received signal strength indication (RSSI) data from all Wi-Fi access points (APs) and stores them in a large database as a form of radio fingerprint map. Because of the millions of APs in urban areas, radio fingerprints are seriously contaminated and confused. Moreover, the algorithmic advances for positioning face computational limitation. Therefore, we present a novel irregular grid structure and data analytics for efficient fingerprint map management. The usefulness of the proposed methodology is presented using the actual radio fingerprint measurements taken throughout Seoul, Korea.

New rate control scheme BSased on adaptive RateLimit for 1xEV-DO reverse link traffic channels

cdma2000 UEV-130 standard has a distributed rate control scheme on a reverse link. In this paper, we propose an adaptive rate control scheme based on the control of Rate Limit, which is a maximum possible data rate in the reverse link. From numerical and simulation results, it is shown that our proposed scheme achieves significant capacity gain in reverse link compared to 1xEV-D0 rate control scheme.

Cell coverage estimation by radio fingerprint data analytics

We develop a novel cell coverage estimation method based on radio fingerprints collected from practical wireless service systems. A large size radio fingerprint map that shows cell identifiers and signal strength measurements on grid segmentation is built for effective estimation of cell coverage. An essential part of cell coverage estimation is radio fingerprint data cleansing and compensation. Based on this proposed iterative fingerprint data analysis method, we detect the proper cell borderline for each cell site. By the proposed method, we can efficiently estimate the cell coverage of each cell site without difficult manual field measurements. Moreover, mobile service providers can economically plan network configuration and manage subscribers using these advances in cell coverage estimation.

A Framework-Based Approach for Fault-Tolerant Service Robots

Recently the component-based approach has become a major trend in intelligent service robot development due to its reusability and productivity. The framework in a component-based system should provide essential services for application components. However, to our knowledge the existing robot frameworks do not yet support fault tolerance service. Moreover, it is often believed that faults can be handled only at the application level. In this paper, by extending the robot framework with the fault tolerance function, we argue that the framework-based fault tolerance approach is feasible and even has many benefits, including that: 1) the system integrators can build fault tolerance applications from non-fault-aware components; 2) the constraints of the components and the operating environment can be considered at the time of integration, which – cannot be anticipated eaily at the time of component development; 3) consistency in system reliability can be obtained even in spite of diverse application component sources. In the proposed construction, we build XML rule files defining the rules for probing and determining the fault conditions of each component, contamination cases from a faulty component, and the possible recovery and safety methods. The rule files are established by a system integrator and the fault manager in the framework controls the fault tolerance process according to the rules. We demonstrate that the fault-tolerant framework can incorporate widely accepted fault tolerance techniques. The effectiveness and real-time performance of the framework-based approach and its techniques are examined by testing an autonomous mobile robot in typical fault scenarios.

Comments on “Low-Complexity Power Allocation for Energy Efficiency Maximization in DAS” and a Novel Algorithm for Energy Efficiency Maximization in DAS

In a recent letter, Wu et al. proposed a low complexity algorithm for maximizing the energy efficiency in distributed antenna systems (DAS). The complexity is shown to be reduced due to decrease in the number of Lambert function calculations. In this letter, we highlight a few mistakes in the proof of Theorem 1 of the Wu et al. letter. Further, we show that the proposed algorithm in the Wu et al. letter cannot achieve optimal power allocation for energy maximization if the number of optimal antennas for a particular user is greater than 1. Finally, we propose a new algorithm to find the optimal power allocation to maximize the energy efficiency in DAS.

Traffic management of high-speed CDMA systems based on load prediction

The cdma2000 1xEV-DO system has a probabilistic rate control on the reverse link, but a simple up/down command from the base station may make the reverse link unstable. In this paper, we propose and analyze an enhanced rate control that minimizes the traffic overload on the reverse link by predicting the noise rise and defining a new command for stable operation. It is shown that the proposed rate control has a much higher revere-link throughput than the conventional schemes.