• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.1
• /
• pp.145-152
• /
• 2009

IEEE 802.16e standard, a kind of WMAN standard, was established to support data services with cheaper cost to mobile users than traditional mobile communications system and wireless LAN system can do. In this paper, we propose an uplink QoS packet-scheduler for VoIP service which can be installed in IEEE 802.16 system and evaluate its performance with NS-2 network simulator. The proposed QoS packet-scheduler consists of three procedures: determining scheduler interval, determining the amount of resource assignment, and deciding which mobile station the base station should serve first among multiple mobile stations. According to numerical results, the proposed QoS packet-scheduler can provide more increased system capacity by 220% than UGS service scheme does and by 25 % than ertPS service scheme does.

• Communications for Statistical Applications and Methods
• /
• v.10 no.1
• /
• pp.61-77
• /
• 2003

Due to the wide expansion of the internet, people can freely get information what they want with lesser efforts. However without adequate forms or rules to follow, it is getting more and more difficult to get necessary information. Because of seemingly chaotic status of the current web environment, it is sometimes called "Dizzy web" The user should wander from page to page to get necessary information. Therefore we need to construct system which properly recommends appropriate information for general user. The representative research field for this system is called Recommendation System(RS), The collaborative recommendation system is one of the RS. It was known to perform better than the other systems. When we perform the web user modeling or other web-mining tasks, the continuous feedback data is very important and frequently used. In this paper, we propose a collaborative recommendation system which can deal with the continuous feedback data and tried to construct the web page prediction system. We use a sojourn time of a user as continuous feedback data and combine the traditional model-based algorithm framework with the Support Vector Regression technique. In our experiments, we show the accuracy of our system and the computing time of page prediction compared with Pearson's correlation algorithm.algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.7C
• /
• pp.688-695
• /
• 2003

In this paper, the parallel sub-filter searching structure to be adapted that divides a filter into several sub filters and the parameter decision technique to control adaptive parameters with power of received signal in the code acquisition system using adaptive filter are proposed. The numerical results for the system probabilities are derived that the code acquisition system using parallel sub-filter searching structure is statistically analyzed. Also, characteristic of the parameters in adaptive code acquisition system is analyzed by simulations and the parameter decision technique through SNRc estimation is explained. The system with parallel sub-filter searching structure outperforms by 1∼l.5 dB for 16 taps, 5∼6 dB for 64 taps. And the system with parameter decision technique works efficiently with the reasonable degree of degradation about 1 ∼2.5dB for 16 and 32 taps.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.10A
• /
• pp.1123-1130
• /
• 2004

This paper proposes the fast OVSF code generation method using the multi-stage spreading scheme based on the single code indexing scheme. The conventional OVSF indexing scheme based on the code-tree structure uses two numbers as the codeword indices, the layer number and the code number of the corresponding layer. However, the single code index number implicitly includes the information of the spreading factor as well as the code number. Since the binary representation of the single code indices shows the pattern of the codeword, the orthogonality between two different codewords can be determined by comparing their code indices instead of much longer codewords. The above useful property also makes the codeword can be generated directly kom its single code index. In this paper, the multi-stage spreading scheme is applied to generate the long code by spreading two shorter codewords with the appropriate code indices. The proposed fast code generation algorithm is designed for 3GPP UMTS systems and verified by the simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.1
• /
• pp.33-39
• /
• 2002

In mobile communication systems, there are areas where signal coverage is not adequately accomplished by base stations. These areas may be underground parking zones, underground stores, tunnels, and insides of buildings, etc. In these areas, repeaters are broadly used as an economical solution. However, the capacity is decreased as the number of repeaters increases because the noise power that flows to a base station in the reverse link is proportional to the number of repeaters. The reduction of capacity in the reverse link is no longer negligible in the case that several tens or hundreds repeaters are connected to a base station. In this paper, we propose c repeater that is switched off automatically when there is no active user within its coverage. With the switching repeater, we can reduce the unnecessary noise level enhancement when there is no active user within the repeaters coverage. The reverse link capacity of a DS/CDMA system with AOS repeater is analyzed mathematically and compared with that without switching repeater. From the numerical results, noticeable improvement with the switching repeaters is shown.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.46 no.3
• /
• pp.75-85
• /
• 2009

This work proposes a 13b 100MS/s 0.13um CMOS ADC for 3G communication systems such as two-carrier W-CDMA applications simultaneously requiring high resolution, low power, and small size at high speed. The proposed ADC employs a four-step pipeline architecture to optimize power consumption and chip area at the target resolution and sampling rate. Area-efficient high-speed high-resolution gate-bootstrapping circuits are implemented at the sampling switches of the input SHA to maintain signal linearity over the Nyquist rate even at a 1.0V supply operation. The cascode compensation technique on a low-impedance path implemented in the two-stage amplifiers of the SHA and MDAC simultaneously achieves the required operation speed and phase margin with more reduced power consumption than the Miller compensation technique. Low-glitch dynamic latches in sub-ranging flash ADCs reduce kickback-noise referred to the differential input stage of the comparator by isolating the input stage from output nodes to improve system accuracy. The proposed low-noise current and voltage references based on triple negative T.C. circuits are employed on chip with optional off-chip reference voltages. The prototype ADC in a 0.13um 1P8M CMOS technology demonstrates the measured DNL and INL within 0.70LSB and 1.79LSB, respectively. The ADC shows a maximum SNDR of 64.5dB and a maximum SFDR of 78.0dB at 100MS/s, respectively. The ABC with an active die area of $1.22mm^2$ consumes 42.0mW at 100MS/s and a 1.2V supply, corresponding to a FOM of 0.31pJ/conv-step.

• Korean Journal of Optics and Photonics
• /
• v.13 no.2
• /
• pp.146-150
• /
• 2002

1.55${\mu}{\textrm}{m}$ PnpN optical thyristor as a smart optical switch has potential applications in advanced optical communication systems. PnpP optical thyristors operating at 1.55${\mu}{\textrm}{m}$ are proposed and fabricated for the first time. In the optical thyristors, we employ InGaAs/InP multiple quantum well (MQW) for the active n- and p-layers. The thyristors show sufficiently nonlinear s-shape I-V characteristics and spontaneous emission. In the OFF-state, the device has a high-impedance up to switching voltage of 4.03(V). On the other hand, it has low-impedance and emits spontaneous light as a light-emitting diode in the ON-state voltage of 1.77(V), and switching voltage is changed under several light input conditions. It can be used as a header processor in optical asynchronous transfer mode (ATM), as a hard limiter in optical code division multiple access (CDMA) and as a wavelength converter in optical WDM systems.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.49 no.8
• /
• pp.1-11
• /
• 2012

The multi-code spread spectrum communication system, which spreads data bit stream by multiplexing orthogonal codes, can transmit data in high rate. However it needs the high-cost good linear amplifier because of the multi-level output signal. In order to overcome this drawback several systems making the amplitude of output signal constant with Walsh codes have been proposed. Recently constant amplitude pre-coded multi-code spread spectrum systems using extended m-sequence have been proposed. In this paper we consider an extended m-sequence based constant amplitude multi-code spread spectrum system with code set partitioning. By grouping the orthogonal codes into 4 subsets, not only is the computational complexity of the transceiver reduced but BER performance also improves. It has been shown that parity checking on four detected codes at the receiver can correct code detection error and result in BER performance enhancement. In this paper we propose a improved parity check receiver. We carried out computer simulation to verify feasibility of the proposed algorithm.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.5 no.5
• /
• pp.908-915
• /
• 2001

In this paper, it is analyzed theoretically that the performance degradation, caused by carrier frequency offset, in an OFDM/M-ary PSK system. Then, when Turbo coding is adopted to an OFDM/M-ary PSK system, the degree of performance enhancement is evaluated. Finally, the maximum frequency offset is calculated to satisfy the BER performance required in a Turbo coded OFDM/M-ary PSK system. As results of analysis, it is shown that the more the number of M-ary is, the worse the BER performance is. Moreover, 7dB, 9dB, and 17dB of $E_b/N_o$ are required in QPSK, 8PSK and 16PSK systems, respectively in order to satisfy the error performance, $BER=10^{-3}$ for voice communication. If $E_b/N_o$ are 10㏈ and 15㏈, the frequency offset should be below 0.05 and 0.075, respectively, for voice communication. When Turbo coding is adopted to an OFDM/M-ary PSK system, the less the number of M-ary is, the greater the performance enhancement of Turbo coding is. If the number of a M-ary system of the system is below 16, it is found that required $E_b/N_o$ is about 8dB to satisfy $BER=10^{-5}$ Moreover, in the system the Turbo coding scheme, voice communication is available with greatly low$E_b/N_o$, and 8dB of $E_b/N_o$ is enough for data communication regardless of the permission range of frequency offset.

• Journal of KIISE:Computing Practices and Letters
• /
• v.15 no.11
• /
• pp.846-850
• /
• 2009

Recently, wireless sensor networks have found their way into a wide variety of applications and systems with vastly varying requirements and characteristics such as environmental monitoring, smart spaces, medical applications, and precision agriculture. The sensor nodes are battery powered. Therefore, the energy is the most precious resource of a wireless sensor network since periodically replacing the battery of the nodes in large scale deployments is infeasible. Energy efficient mechanisms for gathering sensor readings are indispensable to prolong the lifetime of a sensor network as long as possible. There are two energy-efficient approaches to prolong the network lifetime in sensor networks. One is the compression scheme to reduce the size of sensor readings. When the communication conflict is occurred between two sensor nodes, the sender must try to retransmit its reading. The other is the MAC protocol to prevent the communication conflict. In this paper, we propose a novel approaches to reduce the size of the sensor readings in the MAC layer. The proposed scheme compresses sensor readings by allocating the time slots of the TDMA schedule to them dynamically. We also present a mathematical model to predict latency from collecting the sensor readings as the compression ratio is changed. In the simulation result, our proposed scheme reduces the communication cost by about 52% over the existing scheme.