• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.276.2-278
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• 2000

In a recent years, a number of approaches have been studied, including passive, active, and hybrid mode-locking of semi-conductor lasers for short pulse generation and research has been devoted to achieve low timing-jitter operation since the timing jitter is unfavorable for system applications. Among the methods of mode locking, passive mode locking does not need external rf drives, and therefore the operation and fabrication procedures are simplified. In spite of these attractive advantages of passive mode-locked laser, it has critical drawbacks such as large timing jitter and the difficulty in synchronization with external circuits. Their inherent large timing jitter value was shown to be suppressed to certain levels by means of hybrid mode-locking technique$^{(1)}$ , where the saturable absorber section was modulated by an external signal with the cavity round trip frequency. Furthermore, the subharmonic mode-locking (SHML) technique alleviates the restrictions of high speed driving electronics. It has been demonstrated experimentally$^{(1)}$ that the hybrid subharmonic mode-locking technique has lead to significant reduction of the timing jitter. (omitted)

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.659-665
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• 2008

If ranging processes are not frequent in an uplink OFDMA system, the timing synchronization between base and mobile stations may not be maintained. Especially in the case of infrequent random accesses in a large cell, timing offsets can be considerable and the destroyed orthogonality of OFDMA signals may result in the degraded performance. This paper proposes a novel random access scheme for uplink OFDMA systems, which support the orthogonality of OFDMA signals with timing offsets by allowing a random access OFDMA symbol shorter than a normal one. In order to make uplink OFDMA systems robust to timing offsets, the proposed scheme inserts a zero-padding region in an OFDMA symbol.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.336-340
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• 2003

The frame synchronization should be acquired before performing other data-aided receiving algorithms, such as data-aided channel equalizing, beam-forming and phase, symbol timing, and frequency synchronizing, since all of them are using preamble or training sequence to estimate the amount of error from the received signal. In this paper, we present a new frame synchronization scheme for underwater ultrasonic image burst transmission system, which computes the correlation between received symbol sequence and one CAZAC sequence, composed of the latter half of the first CAZAC sequence of preamble and the first half of the second CAZAC sequence of preamble and then compares a threshold value. If the correlation value is bigger than the threshold value, the frame detector determines that the frame synchronization is achieved at that sample.

• The KIPS Transactions:PartC
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• v.18C no.1
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• pp.15-22
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• 2011

Usually time synchronization is performed after routing tree is constructed. This thesis proposes a time synchronization algorithm combined with single-flooding routing tree construction algorithm in a single path. TSRA (Time Synchronization Routing Algorithm) uses routing packets to construct a routing tree. Two types of time information are added to the routing packet: one is the packet receiving time, and the other is the packet sending time. Time offset and transmission time-delay between parent node and child node could be retrieved from the added time information using LTS (Lightweight Time Synchronization) algorithm. Then parent node sends the time offset and transmission time to children nodes and children nodes can synchronize their time to the parent node time along the routing tree. The performance of proposed algorithm is compared to the TPSN (Timing-sync Protocol for Sensor Networks) which is known to have high accuracy using NS2 simulation tool. The simulation result shows that the accuracy of time synchronization is comparable to TPSN, the synchronization time of all sensor nodes is faster than TPSN, and the energy consumption is less than TPSN.

• Proceedings of the KIEE Conference
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• 2008.04a
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• pp.159-160
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• 2008

Initial Ranging Detection and Synchronization is suggested for IEEE 802.16e OFDMA Systems. However ranging is vulnerable to the channel selectivity and other user's interference at low SNR. This paper presents enhanced ranging scheme that improves ranging detection process using the combine multiple FFT blocks and cope with channel selectivity and other user's interference at low SNR. Based on the ranging detection timing offset is calculated for synchronization.

• IEMEK Journal of Embedded Systems and Applications
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• v.14 no.6
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• pp.339-346
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• 2019

Multi-axis servo systems are widely used in various fields such as industiral systems for improving production efficiency, robotics and complex systems where many mechanical devices and sensor systems are connected. Such a servo system requires that the servo control technique to realize the synchronization of the drive shaft in the steady state and transient conditions and to control so as to follow the target track in order to improve product precision and production efficiency. In addition, embedded type hardware is required for smooth control of the entire multi-axis system. Therefore, this paper uses hardware based on FPGA which is widely used in digital signal processing field and various control system because hardware design change is easy and parallel processing is possible. In addition, Labview based servo motor control program was studied that can control the servo motor by ensuring the performance and flexibility of the FPGA and follow the target trajectory according to various speed processing and accurate timing synchronization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1477-1486
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• 1997

Conventioally the decoding methods and the design of coset codes for burst synchronization and error detection have been based on the concept that slips occuring to the right or to the left with respect to a reference timing are corrected. In this paper we newly approach to the design of coset codes relying on the condition that only a single code word can exists in an observation interval, which provides an extentended view on the conventional approach. A theorem concerning the condition is presented. A combined burst synchronization and error detection system with maximum slip correction capability have been devised based on the theorem and a detection method is falsely accepted in the presented of channel errors. The false acceptance probabilities of the system are derived and its performance is analyzed through computer computation using the derived results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.516-522
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• 2010

In this paper, the carrier frequency offset estimator is proposed for the China multimedia mobile broadcasting (CMMB). The fractional carrier frequency offset is estimated by utilizing the cyclic prefix in each CMMB symbol. In addition, the integer carrier frequency offset can be estimated with the synchronization signal in every CMMB frame. The proposed estimator is the most suitable for the frame structure of CMMB. It shows a prominent performance even in timing offset and multipath conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.10C
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• pp.951-962
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• 2002

A DMT transceiver recovers the sampling time from reserved sub-carriers, the pilots. Since the pilots are available after the FFT, the symbol synchronization must be done before sample synchronization. In DMT VDSL system, symbol synchronization is handled separately from sample synchronization, although the two processes are intimately related. The DMT symbol itself contains sufficient information, the cyclic extension, for symbol synchronization. Using only the sign bit of received signal, the Maximum Likelihood Estimation solution is derived. The Tx windowing in the transmitter of DMT VDSL system results in the blurring of MLE peaks. We propose the weighted summing MLE method using the sign bit which produces the clearly sharp top of MLE peaks. The stability of symbol synchronization is improved significantly by averaging over a few symbols. This paper presents the study of the original MLE and the weighted summing MLE using sign bit. A clock difference between transmitter and receiver destroys the oahogonality of the carriers. Therefore, a receiver using asynchronous sampling must perform timing correction in the discrete-time domain. We introduce an efficient digital sample synchronization method which is based on temporal and frequency domain digital signal processing.

• Journal of Advanced Navigation Technology
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• v.13 no.3
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• pp.337-343
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• 2009

In this paper, we proposed a burst mode symbol timing recovery unit that is applicable to the VDL Mode-2 using D8PSK modulation. A method that IIR loop filter is used to minimize symbol timing error is hard to apply to burst mode because its convergence time is long. That is, the fast convergence property is important. In this paper, the proposed method takes one sample which has maximum symbol power after the initial synchronization has been achieved by using preambles. The main principle of operation is that the unit moves one sample clock to advance or retard according to symbol power. We verify that the proposed method is operated well in ${\pm}100$ ppm or greater through the test results between Australia ADS Corp. transmitter and the designed receiver.