• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.5 s.108
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• pp.408-415
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• 2006

This paper suggests an improved system-level model of RF power amplifiers(PAs) including memory effects, and validates the suggested model by analyzing the power spectral density of the output signal with a predistortion linearizer. The original three-box(Wiener-Hammerstein) model uses input and output filters to capture RF frequency response of PAs. The adjacent spectral regrowth that occurs in three-box model can be perfectly removed by Hammerstein structure predistorter. However, the predistorter based on Hammerstein structure achieves limited performance in real PA applications due to other memory effects except RF frequency response. The spectrum of the output signal can be predicted accurately using the suggested model that changes a memoryless block in a three-box model with a memory polynomial. The proposed model accurately predicts the output spectrum density of PA with Hammerstein structure predistorter with less than 2 dB errors over ${\pm}30$ MHz adjacent channel ranges for IEEE 802.11 g WLAN signal.

• Journal of Digital Convergence
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• v.10 no.3
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• pp.265-271
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• 2012

This paper proposes a communication distance performance evaluation method for mobility of service robots equipped with a Wi-Fi module. Service robots have function of mobile communication system according to classified services and utilize a (preferred) communication method, wireless lan(IEEE802.11 a/b/gin) communication method of ISM band(2.4GHz and 5.8GHz). For evaluating degradation performance of wireless data for the service robot's mobility. We measured and presented reference vectors obtained by utilizing a distance attenuation correlation method in the real world environment. To evaluate performance of the proposed method, path loss of reference vectors was assigned to the Azimuth 301W and then transmission rate and the transmit throughput of the test sample were measured by the Chariot. The proposed measurement method is necessary for securing wireless LAN communication distance for mobility of mobile smart device and service robots. In addition, if the proposed measurement method os adopted, It would be expected that mobile smart device vendors would utilize the method as an effective wireless LAN mobility communication distance performance evaluation method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.3 s.357
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• pp.92-97
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• 2007

Switching mode amplifiers have been studied widely for use at microwave frequency range, and the class E amplifier which is a type of switching mode amplifier offers very high efficiency approaching 100%. In this paper, 2.4GHz microwave class E amplifier with 66% power added efficiency (PAE) and 17.6dBm output has been linearized for use at wireless LAN transmitter, and digital predistortion technique with look up table is applied. With -3dBm input power of wireless LAN, measured output spectrum can meet the required IEEE 802.11g standard spectrum mask, and the digital predistortion output spectrum has been improved by 5dB of ACPR at 20MHz offset from center frequency.

• ETRI Journal
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• v.31 no.5
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• pp.601-603
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• 2009

This letter presents a high performance 2.4 GHz two-stage power amplifier (PA) operating in the temperature range from $-30^{\circ}C$ to $+85^{\circ}C$ for IEEE 802.11g, wireless local area network application. It is implemented in InGaP/GaAs hetero-junction bipolar transistor technology and has a bias circuit employing a temperature compensation technique for error vector magnitude (EVM) performance. The technique uses a resistor made with a base layer of HBT. The design improves EVM performance in cold temperatures by increasing current. The implemented PA has a dynamic EVM of less than 4%, a gain of over 26 dB, and a current less than 130 mA below the output power of 19 dBm across the temperature range from $-30^{\circ}C$ to $+85^{\circ}C$.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2787-2794
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• 2011

A mesh node, a component of a mesh network, is connected with the network by dynamic routing using routing protocol and collects the information of adjacent or connected mesh nodes for its self-management and settings. Also, it relays packets between the mesh nodes and provides AP(Access Point) with its corresponding functions based on IEEE 802.11 a/b/g for clients' access to the network. In this paper, the study focused on the design and performance tests of Wireless Mesh Network(WMN) which is applied to the wireless communication network for the CBTC(Communications Based Train Control) system. The WMN was established on a K-AGT test-line (Kyeongsan city, Gyeongsangbuk-do), and to verify the applicability, its operation and performances are checked by measuring the data throughput, delay latency, quality measurements such as transmission loss, radio interference and path recovery and setup between the on-board and wayside.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.1131-1132
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• 2008

In this paper, we developed UHF RFID R/W system using AT91SAM7S256(ARM chip), UHF RFID R/W module (WJ7090) and wireless LAN(IEEE 802.11.a/b). And we developed a transmission/receiving packet which is send to UHF R/W module in AT91SAM7S256. In order to show the usefulness of UHF RFID R/W system, we executed a performance test. The developed UHF RFID R/W system shows better performance for reading of RFID tag and data transmission through wireless LAN.

• Journal of information and communication convergence engineering
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• v.8 no.6
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• pp.635-639
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• 2010

A multi-resonance antenna for wireless communications is reported. By using double inverted-L strips, the antenna demonstrated compact size (15 mm ${\times}$ 14 mm) including the ground, multi-band operation for IEEE 802.11 a/b/g/p applications, and wide bandwidth of 1.7 GHz at 5 GHz band. Good radiation features of omni-directional patterns and 1.98 and 2.29 dBi peak antenna gains for the lower and upper bands, respectively, have been achieved.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.3
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• pp.174-181
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• 2004

In this paper, we review the four receiver architectures and four methods for multi-standard receiver design. Propose reconfigurable RF block can be used for both low-IF and direct conversion architecture. Also, using reconfigurable mixer method, it can be operated at $2{\sim}6$ GHz range for multi-standard receiver. It consists of wideband mixer, filter, and automatic gain control amplifier and to get wide-band operation, $2{\sim}6$ GHz, wide-band mixer use flexible input matching method. Besides, to design multi-standard receiver, LNA bank that support each standard is necessary and it has good performance to compensate the performance of wide-band mixer. Finally, we design and simulate proposed reconfigurable RF block and to prove that it has acceptable performances for various wireless standards, the LNA bank that supports both IEEE 802.11a/b/g and WCDMA is also designed and simulated with it.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11B
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• pp.1272-1282
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• 2009

This paper consists of two parts: the protocol for tag-to-tag mesh network and the implementation of dual-radio RFID system. Recently, RFID has been adopted in ports or warehouse, being attached to containers and palettes for loading/unloading automation. However, the RFID system has encountered one problem - some tags cannot receive any command from reader intermittently due to signal interference by containers or field equipments (e. g. cranes and yard tractors). This area where reader signal cannot reach is called dead-zone. The proposed method for solving the dead-zone problem is as follows. A zone which can be communicated directly between readers and tags communicates in 433MHz frequency band in compliance with ISO/IEC 18000-7 standard. On the other hand, dead-zone communicates in 2.4GHz frequency band by using tag-to-tag mesh network in compliance with IEEE 802.15.4 standard. The proposed method can not only save much cost to install additional readers but also help resolve the dead-zone problem. Furthermore, it can provide the easier, faster, and more economical network infrastructure.

• The Journal of Engineering Research
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• v.7 no.1
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• pp.53-60
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• 2005

Community Wireless Networks define the next generation wireless services. Multimedia usages for financial services over community Wireless LAN (WLAN) based mesh networks require link stability. Several new services are being proposed for multimedia over WLANs. Portable Internet Services are implemented by several wireless carriers to proliferate their customer base. However, these services are still expensive and require a central telecom/wireless carrier whose monopoly and preference defines the availability of new services. Our research project identifies the usage of these critical services in public places over the financial services backbone architecture to provide efficient easy-to-use and economical services to their customers and merchants without being dependent on the central wireless carrier. The user connects to the network using his regular WLAN NIC using the Mesh Router/Bridge interconnectivity and obtains the needed multimedia and financial services from the ATM-AP Gateway, In our proposed scenario, the ATN AP-MR use AODV protocol and MR-MC is based on 802.11g/a/b IEEE standard. We use multi path routing protocols for reducing the congestion over a particular route. We demonstrate the results of our simulations and test-bed outcome to evaluate link failure rate and oversubscription factors to eliminate network congestion and non-availability of the critical financial services.