• 동력기계공학회지
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• 제17권5호
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• pp.100-111
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• 2013

Indoor real-time positioning for multiple targets is required to realize human-robot symbiosis. This study firstly presents positioning accuracy on an autonomous mobile robot controlled by 3-D coordinates that is obtained by a real-time indoor positioning system with spread spectrum (SS) ultrasonic signals communicated by code-division multiple access. Although many positioning systems have been investigated, the positioning system with the SS ultrasonic signals can measure identified multiple 3-D positions in every 70 ms with noise tolerance and error within 100 mm. This system is also robust to occlusion and environmental changes. However, thus far, the positioning errors in an autonomous mobile robot, controlled by these systems using the SS ultrasonic signals, have not been evaluated as an experimental study. Therefore, a positioning experiment for trajectory control is conducted using an autonomous mobile robot and our positioning system. The effectiveness of this positioning method for robot self-localization is shown, from this experiment, because the average control error between the target position and the robot's position at 29 mm is obtained.

• 대한전자공학회논문지TC
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• 제38권12호
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• pp.1-9
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• 2001

APON(ATM Passive Optical Network)에서, 상향 트래픽의 전송은 OLT가 ONU에게 타임슬롯을 할당하여 셀을 보내게 하는 TDMA(Time Division Multiple Access) 방식을 근간으로 한다. 상향은 스트림 모드가 아니기 때문에, 셀 동기 장치는 버스트 모드로 동작해야 한다. 또한, 하나의 광섬유에 여러 대의 ONU가 보내는 셀들 사이에서 충돌을 방지하기 위하여 셀 위상 감시기가 필요하다. 본 논문에서는 G.983.1 기반의 APON에서 상향 셀 전송을 위해 사용될 수 있는 TDMA 버스트 셀 동기장치를 FPGA(Field Programmable Gate Array)로 구현한다. 이 동기장치는 상향 데이터 복구(data recovery) 기능과 위상 감시 (Phase Monitoring)라는 두가지 주된 기능이 있다. 전자는 상향 타임슬롯의 오버헤드에서 preamble을 찾고 비트 및 셀 위상을 시스템 클럭에 정렬함으로써, OLT에서 상향 데이터와 클럭을 복구하기 위한 것이다. 후자는 상향 셀 충돌을 방지하기 위하여 인접 셀 간의 위상편차를 지속적으로 감시함으로써, 각 ONU에게 등화지연(equalization delay)을 보정할 수 있도록 정보를 제공하기 위한 것이다.

• 한국경영과학회지
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• 제29권4호
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• pp.141-157
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• 2004

In this paper, we consider broadband satellite systems using MF-TDMA(Multi-Frequency Time Division Multiple Access) scheme. First, we analyze return link, superframe structure, and QoS( Quality of Service) parameters in broadband satellite systems, and mathematically formulate the QoS-based optimal timeslot allocation problem as a nonlinear integer programming problem for broadband satellite systems with clear-sky and rain-fade satellite terminals, and multiple data classes. Next, we modify the proposed problem to solve it within in a fast time, and suggest the QoS-based optimal timeslot allocation scheme. Extensive simulation results show that the proposed scheme finds an optimal solution or a near optimal solution within 5ms at Pentium IV PC.

• International Journal of Internet, Broadcasting and Communication
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• 제11권1호
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• pp.60-68
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• 2019

In this paper, we propose the adaptive beamforming algorithm for the MIMO (Multi-Input Multi-Out)-OFDMA(Orthogonal Frequency Division Multiplexing Access)system to improve the performance. The performance of MIMO-OFDMA systems is greatly decreased in the wireless channel environment with multiusers, because the received signals are much distorted by a cochannel interference (CCI) during the space-time decoding. The proposed approach can track the DOA of each signal from the multiple antennas of the desired user without being greatly dependent on the impinging angle. And beams are directed toward the multiple transmitters of the desired user while null beams are directed toward interference directions. Therefore, we can can effectively cancel CCI and mitigate the impairment of delay spread while preserving the STC(space time code) diversity. BER performance improvement is investigated through computer simulation by applying the proposed approach to MIMO-OFDMA system in a multipath fading channel with CCI.

• 한국컴퓨터정보학회논문지
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• 제10권6호
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• pp.209-218
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• 2005

링형 광 액세스망에서 능동형 광네트워크(AON: Active Optical Network)는 DWDM(Dense Wavelength Division Multiplexing)을 이용하여 요구대역폭(BoD: Bandwidth on Demand)에 따라서 가입자에게 원활한 서비스를 제공할 수 있다. 이를 위하여 기존의 광 기가비트 이더넷 스위치에서 다수개의 파장 및 서브캐리어(Sub-Carrier) 접속을 지원하며, 특정 파장을 분기하는 WADM (Wavelength Add Drop Multiplexer)과 링의 형태로 연결된다. WADM에서 분기된 특정 파장은 가입자단에 이르러 서브캐리어별로 역다중화 되어 가입자에게 분배되므로 가입자망의 분배가 시작되는 광 기가비트 이더넷 스위치와 가입자 단말 접속 장치간의 능동적인 연결이 가능한 구조를 가진다 본 논문에서는 이러한 AON 구조에서 BoD에 따라서 달라지는 버퍼의 크기를 비교 분석하고 또한 비트의 지체시간을 서버의 처리율과 비교 분석한다. 이러한 실험을 통하여 소요 시간의 한계를 결정함으로써 가입자에게 요구 대역폭에 따른 원활한 서비스를 제공할 수 있는 네트워크의 동적 운용 프로토콜 및 효율적인 알고리즘 구현을 위한 기준을 제시한다.

• Journal of electromagnetic engineering and science
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• 제6권2호
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• pp.83-91
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• 2006

In this paper, we develop space-time(ST) Rake receivers for Time Division Synchronous Code Division Multiple Access(TD-SCDMA) base stations(BS). The beamforming of BS transforms the uplink MIMO channel space into many sub-sectors' channels to be nearly orthogonal, thus, well established 1-D Rake technology can be used to TD-SCDMA base station to construct ST Rake, which simplified the system's implementation as well as enlarged users' capacity by the beamforming. The construction and capacity of MIMO sub-sectors by multi-beamforming have been presented. The proposed ST Rake algorithm include the multi-beamforming algorithm for MIMO sub-sectors and classical 1-D Rake algorithm. The calculating formulas for interference plus noise ratio(SINR) and bit error rate(BER) have been derived. Simulations verify that the proposed ST Rake receiver for BS is effective, and the BS systems can get higher system capacity and can be of better performance than presented TD-SCDMA systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권2호
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• pp.511-527
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• 2024

This paper proposes a block-based self-organizing time-division multiple access (BSO-TDMA) protocol for very high frequency (VHF) data exchange system (VDES) in shipborne ad-hoc networks (SANETs). The BSO-TDMA reduces the collisions caused by the simultaneous transmission of automatic identification system (AIS) messages by uniformly allocating channel resources using a block-wise frame. For this purpose, the BSO-TDMA includes two functional operations: (1) frame configuration and (2) slot allocation. The first operation consists of block division and block selection. A frame is divided into multiple blocks, each consisting of fixed-size subblocks, by using the reporting interval (RI) of the ship. Then, the ship selects one of the subblocks within a block by considering the number of occupied slots for each subblock. The second operation allocates the slots within the selected subblock for transmitting AIS messages. First, one of the unoccupied slots within the selected subblock is allocated for the periodic transmission of position reports. Next, to transmit various types of AIS messages, an unoccupied slot is randomly selected from candidate slots located around the previously allocated slot. Experimental simulations are conducted to evaluate the performance of BSO-TDMA. The results show that BSO-TDMA has better performance than that of the existing SOTDMA.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.69-72
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• 2005

In this paper, pseudo noise (PN) code acquisition performance with multiple antennas in a UWB time hopping/code division multiple access system is analyzed. The closed form for the conditional probability is derived, using the Gauss-Hermite quadrature formula, when the signal with Gaussian distribution goes through the lognormal fading channel. The performance comparison of the above mentioned schemes shows that the code acquisition performance with a diversity combining technique, especially when increasing the number of antennas, is more robust than that using no diversity.

• Journal of Communications and Networks
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• 제7권3호
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• pp.284-293
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• 2005

A critical issue in applications involving networks of wireless sensors is their ability to synchronize, and mitigate the fading propagation channel effects. Especially when distributed 'slave' sensors (nodes) reach-back to communicate with the 'master' sensor (gateway), low power cooperative schemes are well motivated. Viewing each node as an antenna element in a multi-input multi-output (MIMO) multi-antenna system, we design pilot patterns to estimate the multiple carrier frequency offsets (CFO), and the multiple channels corresponding to each node-gateway link. Our novel pilot scheme consists of non-zero pilot symbols along with zeros, which separate nodes in a time division multiple access (TDMA) fashion, and lead to low complexity schemes because CFO and channel estimators per node are decoupled. The resulting training algorithm is not only suitable for wireless sensor networks, but also for synchronization and channel estimation of single- and multi-carrier MIMO systems. We investigate the performance of our estimators analytically, and with simulations.

• ETRI Journal
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• 제29권1호
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• pp.79-88
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• 2007

This paper proposes a novel concept of adjusting the hardware size in a multi-carrier code division multiple access (MC-CDMA) receiver in real time as per the channel parameters such as delay spread, signal-to-noise ratio, transmission rate, and Doppler frequency. The fast Fourier transform (FFT) or inverse FFT (IFFT) size in orthogonal frequency division multiplexing (OFDM)/MC-CDMA transceivers varies from 1024 points to 16 points. Two low-power reconfigurable radix-4 256-point FFT processor architectures are proposed that can also be dynamically configured as 64-point and 16-point as per the channel parameters to prove the concept. By tailoring the clock of the higher FFT stages for longer FFTs and switching to shorter FFTs from longer FFTs, significant power saving is achieved. In addition, two 256 sub-carrier MC-CDMA receiver architectures are proposed which can also be configured for 64 sub-carriers in real time to prove the feasibility of the concept over the whole receiver.