Kyung Kyoon Bae

Applying Radio Environment Maps to Cognitive Wireless Regional Area Networks

The IEEE 802.22 wireless regional area network (WRAN) is the first worldwide commercial application of cognitive radio (CR) networks refarming the TV broadcast bands. According to US FCCs recent public notice, WRAN products are scheduled to be available for the market by February, 2009. This paper first presents a brief review of the IEEE 802.22 WRAN standardization, and then introduces the radio environment map (REM) as an innovative cost-efficient approach to developing and managing WRAN systems. REMs can provide powerful infrastructure support to the functionality of the WRAN cognitive engine (CE). The data model of the REM is presented together with an extensive discussion on how to exploit the REM for a variety of applications in WRAN systems, focusing on the REM-enabled case- and knowledge-based learning algorithms (REM-CKL) for WRAN CEs. Furthermore, REM-based radio scenario-driven testing (REM-SDT) is also presented as a viable approach to evaluating the performance of CEs. Future research topics are discussed in the final section.

In-building wideband multipath characteristics at 2.5 and 60 GHz

This paper contains measured data for 2.5 and 60 GHz in-building partition loss. Path loss measurements were recorded using a broadband sliding correlator channel sounder which recorded over 39000 power delay profiles (PDP) in 22 separate locations in a modern office building. Transmitters and receivers were separated by distances ranging from 3.5 to 27.4 meters, and were separated by a variety of obstructions, in order to emulate future single-cell-per-room wireless networks. These measurements may aid in the development of future in-building wireless networks in the unlicensed 2.4 GHz and 60 GHz bands.

Development of Radio Environment Map Enabled Case- and Knowledge-Based Learning Algorithms for IEEE 802.22 WRAN Cognitive Engines

The IEEE 802.22 wireless regional area network (WRAN) is the first worldwide commercial application of cognitive radio (CR) networks in unlicensed television broadcast bands. With the intent of efficiently occupying under-utilized spectrum, the network must be cognizant of spectrum available for secondary use and vacate channels as primary users are present. According to FCCs recent public notice, WRAN products are anticipated to be available for the market by February, 2009. This paper first presents a generic architecture for WRAN cognitive engines (CE), and details the design of a CE leveraging the radio environment map database and case-and knowledge-based learning algorithms (REM-CKL). Furthermore, the performance of REM-CKL CE has been evaluated under various radio scenarios and compared to search-based optimizers, including a genetic algorithm (GA). The simulated results show that the WRAN CE can make significantly faster adaptations and achieve near-optimal utility by synergistically leveraging REM-CKL and a local search (LS). Insights into REM-CKL, GA, and LS CE have been gained through the WRAN CE testbed development and preliminary testing.

Globally optimal transmitter placement for indoor wireless communication systems

A global optimization technique is applied to solve the optimal transmitter placement problem for indoor wireless systems. An efficient pattern search algorithm - DIviding RECTangles (DIRECT) of Jones et al.- has been connected to a parallel three-dimensional radio propagation ray tracing modeler running on a 200-node Beowulf cluster of Linux workstations. Surrogate functions for a parallel wideband code-division multiple-access (WCDMA) simulator were used to estimate the system performance for the global optimization algorithm. Power coverage and bit-error rate are considered as two different criteria for optimizing locations of a specified number of transmitters across the feasible region of the design space. This paper briefly describes the underlying radio propagation and WCDMA simulations and focuses on the design issues of the optimization loop.

Overhead Analysis for Radio Environment Mapenabled Cognitive Radio Networks

This paper presents a novel and general approach to cognitive radio (CR) networking based on the Radio Environment Map (REM). REM is envisioned to be an integrated database that consists of comprehensive multi-domain information for CR, such as geographical features, available services, spectral regulations, locations and activities of radio devices, policies, and past experiences. Disseminating and sharing REM information offers a proper vehicle of CR network support, which can be exploited by cognitive engine (CE) for most cognitive functionalities such as situation awareness, reasoning, learning, planning and decision support. Tradeoffs have to be made between the performance gain and the cost of overhead. This paper focuses on analyzing the overhead associated with REM dissemination under various scenarios. With analytical models and network simulations, it is shown that the overhead of REM dissemination can be significantly reduced by extending the optimized link state routing protocol (OLSR). Application-specific ad hoc methods have also been proposed and can be employed to further reduce the overhead. Simulations are presented, comparing the overhead of REM dissemination for different network size, topology, node density and mobility. Preliminary results show that the speed of wireless nodes has little impact to the load of overhead if the REM dissemination rate is fixed. The size of REM information element is estimated for the emerging cognitive wireless regional area networks (IEEE 802.22 WRAN).

S/sup 4/W: globally optimized design of wireless communication systems

In this paper, a global optimization technique is applied to solve the optimal transmitter placement problem for indoor wireless systems. An efficient pattern, search algorithm--DIRECT (DIviding RECTangles) of Jones, Perttunen, and Stuckman (1993)--has been connected to a parallel 3D radio propagation ray tracing modeler running on a 200-node Beowulf cluster of Linux workstations. Surrogate functions for a parallel WCDMA (wideband code division multiple access) simulator were used to estimate the system performance for the global optimization algorithm. Power coverage and BER (bit error rate) are considered as two different criteria for optimizing locations of a specified number of transmitters across the feasible region of the design space. This paper briefly describes the underlying radio propagation and WCDMA simulations and focuses on the design issues of the optimization loop.

Impact of transmit diversity at handsets on the reverse link DS/CDMA system capacity

This article investigates the impact of antenna diversity implementation at both mobile handsets and basestations on the reverse link DS/CDMA capacity in a myriad of fading environments. Our numerical results reveal that transmit diversity implementation at mobile handsets is most beneficial in indoor propagation channels (since only a few significant resolvable multipaths are available) with low order antenna diversity at the base-station and in harsh fading environments.

BSML: A binding schema markup language for data interchange in problem solving environments

We describe a binding schema markup language (BSML) for describing data interchange between scientific codes. Such a facility is an important constituent of scientific problem solving environments (PSEs). BSML is designed to integrate with a PSE or application composition system that views model specification and execution as a problem of managing semistructured data. The data interchange problem is addressed by three techniques for processing semistructured data: validation, binding, and conversion. We present BSML and describe its application to a PSE for wireless communications system design.

WCDMA STTD performance analysis with transmitter location optimization in indoor systems using ray-tracing technique

This paper presents the performance of space-time block coding based transmit diversity (STTD) in WCDMA on correlated fading channels and on unbalanced transmitted power. Then, based on the performance, transmitter location optimization in indoor environments is considered. Results indicate that the effective diversity order is retained even when high cross correlation exists and power imbalance exists between signals from different antennas. Also, a global optimization algorithm with the help of a ray tracer can find transmitter locations which are optimal (global optimum) in the sense of power coverage or overall BER in the area of interest.

Transmit and Receive Diversity in the Uplink of DS/CDMA Cellular Systems

This paper investigates the efficacy of MIMO implementations with adaptive spatial diversity in the uplink of direct spread/code division multiple access (DS/CDMA) cellular systems. Analytical framework to analyze both system capacity and coverage is developed based on the evaluation of outage probability of signal-to-interference ratio (SIR). It is shown that MIMO implementations can significantly improves the system performances; however, transmit diversity and receive diversity shows different system performances contrary to their link level bit error rate (BER) performances.