• Journal of Korea Multimedia Society
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• v.3 no.6
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• pp.625-632
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• 2000

This paper proposes an adaptive multislot allocation algorithm in order to achieve large system capacity and higher throughput data transmissions. The proposed system is the combination of the slow adaptive modulation system, in which the base station dynamically a signs optimum modulation parameters measuring the CNR(carrier to noise power ratio) of each transmission terminal, and the multislot allocation scheme, in which the base station flexibly allocates an appropriate number of TDMA data slots according to the instantaneous load conditions. Computer simulations confirm that the proposed system can tremendously improve average message delay characteristics in comparison with the conventional fixed slot allocation method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7A
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• pp.1028-1035
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• 1999

To increase the throughput of data transmission in burst-mode TDMA communication systems and also to get a good BER performance at the same time, it is essential to rapidly acquire the carrier while keeping the desirable tracking performance. To achieve this goal, in this paper, a new decision-directed carrier recovery algorithm is presented. The proposed scheme does not incorporate the PLL and suppress the Gaussian random process of input noise by the pre-stage low pass filter so as to get both the fast acquisition and a good performance. Through computer simulations, the performance of the scheme is analyzed with respect to the acquisition time and bit error rate. The cycle slip in the proposed scheme is seldom observed at very low SNR environment in contrast to the previous proposed one. Because of this merit, it is not required to do the differential encoding and decoding in the proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.3
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• pp.784-794
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• 1996

In this papre, the design and the fabrication of the surface mountable voltage controlled oscillator is described for local oscillator in PCS(WACS/TDMA) handset. The VCO employs two silicon bipolar transistors of $f_{gamma}$ of 4 GHz as active devices. These are asembled to form the VCO on the 4 layer PCB of the size $12{\times}10mm$which provides the strip line resonator at the third layer. The fabricated VCO shows tuning rage over 50 MHz, phase noise -100 dBc/Hz at the 100 kHz frequency offset, and 0 dBm output power with the consumption of 22 mA at 3V. It is belived that the size will be more reduced by employing 1005 chip components and that the current consumption will be improved by employing transistors of higher $f_{gamma}$.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.6
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• pp.2859-2872
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• 2019

Interference alignment (IA) has been a powerful approach to achieve the maximum degree of freedom (DoF) for K users multiple-input-multiple-output (MIMO) interference channels. However, due to the feasibility constraint, aligning all the interference signals at each receiver is impractical for large K without symbol extension. In this paper, we propose two best-effort interference alignment (BEIA) schemes that the network selects the maximum number of interfering transmitters to align their signals given the feasibility conditions when each transmitter-receiver pair has a constant number of data streams. Besides, in case of not all interfering signals aligned at each receiver, an upper bound of the average throughput is derived. Simulation results show that the proposed schemes have superiority over the traditional methods, such as time division multiple access (TDMA) and cluster IA(CIA), in low and moderate signal-to-noise ratio (SNR) region in terms of average user throughput. In addition, the proposed max-min relative interference distance alignment scheme outperforms the proposed scheme of equal interfering transmitters number alignment in terms of both average user throughput and minimum user throughput.

• Journal of IKEEE
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• v.21 no.4
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• pp.338-347
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• 2017

This paper describes the design and fabrication of a high power amplifier which is a component of TDL(Tactical Data Link) aircraft terminal. We applied high-speed frequency hopping technology, cognitive radio technology, and receive filter bank technology to efficiently use limited frequency resources with radar and other communication equipment using the same frequency band. The high-power amplifier is physically composed of a transmitter, a receiver, a mechanical part, and a cable assembly, and is designed to meet temperature characteristics and electrical characteristics such as maximum transmission distance and reception sensitivity. Modeling and simulator were used to satisfy the requirement of high power amplifier. The transmit power and the noise figure were measured at 50.02dBm and 2.682dB, respectively. It was confirmed that all the required specifications were satisfied in the electrical characteristics test and the environmental characteristic test.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.10
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• pp.4002-4014
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• 2015

ITU-R M.1842-1, as a well-known specification dedicated to maritime mobile applications, has standardized wireless transmission protocols according to the particular characteristics of a maritime communications scenario. A time division multiple access (TDMA) frame structure, along with modulation schemes to achieve a high data rate, has been described clearly in ITU-R M.1842-1. However, several specification items are still under "to be decided" status, which brings ambiguity to research works. In addition, the current version of ITU-R M.1842-1 is focused mainly on maritime transmissions in open-sea areas, where the cyclic prefix (CP) is set to zero and only 16-QAM is used in the multi-carrier (MC) system. System performance might be dramatically degraded in coastline areas due to the inter-symbol interference (ISI) caused by selective fading. This is because there is a higher probability that the signal will be reflected by obstacles in coastline areas. In this paper, we introduce the transmission resource block (TRB) dedicated to ITU-R M.1842-1 for a ship ad-hoc network (SANET), where the pilot pattern of TRB is based on the terrestrial trunked radio (TETRA). After that, we evaluated SANET performance under the maritime channel model in a coastline area. In order to avoid noise amplification and to overcome the ISI caused by selective fading, several strategies are suggested and compared in the channel estimation and equalization procedures, where the link-level simulation results finally validate our proposals.