• Journal of Advanced Navigation Technology
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• v.12 no.6
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• pp.567-573
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• 2008

According to the ICAO's Global Air Navigation Plan for CNS/ATM - Communications, Navigation, and Surveillance - systems, employing digital technologies, including satellite systems together with various levels of automation, are to be applied in support of a seamless global air traffic management system. For the future navigation, the focus of future implementation efforts can be placed entirely on an expected gradual migration toward GNSS-based navigation, Korea has been considered various options for airspace GNSS augmentation system: GBAS, SBAS and GRAS. This paper discusses current status and future trend of GNSS airspace navigation systems, and presents the results of possible augmentation options and scenarios to analyze system availabilities which could lead to the conclusion of the best program for Korea. The results showed that Korea could have sufficient availabilities from en-route to CAT-I approach with ABAS and GBAS. The study was in cooperated with MITRE, an American research company.

• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.87-93
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• 2001

As a new type of a linear decorrelating receiver, the Pseudo-Decorrelator was presented for asynchronous code division multiple access systems by the author. In this paper, the concept of the Pseudo-Decorrelator is extended to derive a receiver for WCDMA uplink systems over an additive white Gaussian noise channel. Starting with the analysis of the multiple access components of the decision statistics, a non-square cross-correlation matrix for each bit is obtained. This cross-correlation matrix is then inverted, and the inverted matrix is applied to the decision statistics obtained from a conventional receiver. In this receiver, the detection process can be started after the first three consecutive bits are received. Simulation results are presented for K-user systems over an additive white Gaussian noise channel under the circumstances in which synchronization errors, including time delay errors and carrier phase errors exist. It is shown that the proposed receiver performs better than a conventional receiver and parallel interference canceller.

• Journal of Advanced Navigation Technology
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• v.21 no.5
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• pp.428-434
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• 2017

In recent years, owing to the growing user demand for the two-way internet service based on the mobile global broadband communications, a new type of satellite terminal has been developed, known as ESIM(Earth Station in Motion). This service was required by Resolution 158(WRC-15) to study on the coexistence with the co-primary FS(Fixed Service) in 27.5-29.5 GHz as a FSS(Fixed Satellite Service) uplink. In this paper, the average received power on ESIM within -10 dB of beam width of FS and its outage probability was analyzed theoretically and also simulated to account for the azimuth angle with uniform distribution. From the results, it can be concluded that this theoretical analysis is very useful to analyze the interference from ESIM into FS based on the statistical and probabilistic method. Therefore, it is necessary to control the azimuth angle due to a moving terminal as well as the inclination angle of moving path, the operation hours, and the speed of ESIM to protect the co-primary FS.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.543-550
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• 2002

This paper proposes the dynamic slot allocation method for real-time VBR (rt-VBR) services in wireless ATM networks. The proposed method is characterized by a contention-based mechanism of the reservation request, a contention-free polling scheme for transferring the dynamic parameters. The base station scheduler allocates a dynamic parameter minislot to the wireless terminal for transferring the residual lifetime and the number of requesting slots as the dynamic parameters. The scheduling algorithm uses a priority scheme based on the maximum cell transfer delay parameter. Based on the received dynamic parameters, the scheduler allocates the uplink slots to the wireless terminal with the most stringent delay requirement. The simulation results show that the proposed method guarantee the delay constraint of rt-VBR services along with its cell loss rate significantly reduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7A
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• pp.569-580
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• 2012

In this paper, an enhanced initial ranging algorithm for large-cell coverage fixed wireless communication system is proposed. In typical wireless communication system such as WiBro, because a round-trip delay between a transmitter and a receiver is within one OFDM (Orthogonal Frequency Division Multiplexing) symbol duration, a frequency-domain differential correlation method is generally used. However, the conventional method cannot be applied due to an increase of a maximum time delay in large-cell system. In case of an accumulative differential method, estimation errors can occur because of frequent sign transitions. In this paper, therefore, we propose an algorithm which can estimate a total timing offset in a ranging channel structure for 15 km cell. The proposed method can improve performance by sign comparison based sign error correction rule between the estimated values and using a weighting scheme based on channel correlation, the number of accumulations, and the noise reduction effect in normalization process. Also, it can estimate the integer timing offset of symbol duration by comparing peak-powers after compensating for the fractional timing offset of symbol duration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4A
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• pp.291-301
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• 2009

In this paper, the effect of ISI(Inter-Symbol Interference) and ICI(Inter-Carrier Interference) due to time difference of arrival on OFDMA-based mobile multi-hop relay (MMR) systems is analyzed. Analyses are performed for the ISI caused by the previous OFDMA symbol transmitted from neighboring macro or relay cell as well as the ISI caused by the next OFDMA symbol transmitted from neighboring macro or relay cell. Then, an effective SINR(Signal to Interference plus Noise Ratio) estimation method and a path selection method considering time difference of arrival are proposed to minimize the effect of ISI and ICI. It is shown by simulation that the performance degradation caused by time difference of arrival can be significantly mitigated when the proposed path selection method is applied to the uplink of OFDMA-based MMR systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.992-1003
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• 2007

In this paper, a channel estimation technique based on pilot tones, which does not degrade channel estimation performance even with the existence of symbol timing offset (STO) in OFDM systems, is proposed. The proposed technique performs channel estimation by interpolating channels with respect to amplitude and phase with a minimum computational complexity, differently from the conventional interpolation techniques. The proposed technique requires neither the estimation of fine STO in advance nor trigonometric operation for phase interpolation, signifying a significant reduction in computational complexity. Since the performance of the proposed technique does not depend on the STO present in OFDM systems. It can be directly applied to the following areas in OFDM-based communication system: elimination of fine STO estimation step in the synchronization procedure, elimination of STO estimation step in multiuser uplink, and channel estimation in multi-hop relay system. It is verified by computer simulation that the proposed technique can improve the performance of channel estimation significantly in the presence of STOs, compared with previous channel estimation techniques based on pilot tones.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.1
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• pp.9-14
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• 2003

APON, the subscriber network using bus or tree topology, requires MAC protocol, because it shares the uplink channel for many subscribers to transmit data to OLT. Although various MAC schemes, which consider each QoS characteristics of traffic are proposed considering transmission characteristics of ATM traffic class, existing schemes reduce the network efficiency by increasing transmission overhead in frame. In this paper, we propose new MAC scheme, which shows similar performance as those of existing schemes but does not increase transmission overhead. To prevent increasing transmission overhead, the proposed scheme encodes the information about each cell information of traffic of the local queue in RAU transmitted periodically from ONU to OLT Thus, the proposed MAC scheme shows similar performance as those of existing ones and increases efficiency of entire network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.8
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• pp.2797-2820
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• 2015

In order to accommodate huge number of antennas in a limited antenna size, a large scale antenna array is expected to have a three dimensional (3D) array structure. By using the Active Antenna Systems (AAS), the weights of the antenna elements arranged vertically could be configured adaptively. Then, a degree of freedom (DOF) in the vertical plane is provided for system design. So the three-dimension MIMO (3D MIMO) could be realized to solve the actual implementation problem of the massive MIMO. However, in 3D massive MIMO systems, the pilot contamination problem studied in 2D massive MIMO systems and the inter-cell interference as well as inter-vertical sector interference in 3D MIMO systems with vertical sectorization exist simultaneously, when the number of antenna is not large enough. This paper investigates the interference management towards the above challenges in 3D massive MIMO systems. Here, vertical sectorization based on vertical beamforming is included in the concerned systems. Firstly, a cooperative joint vertical beams adjustment and pilot assignment scheme is developed to improve the channel estimation precision of the uplink with pilots being reused across the vertical sectors. Secondly, a downlink interference coordination scheme by jointly controlling weight vectors and power of vertical beams is proposed, where the estimated channel state information is used in the optimization modelling, and the performance loss induced by pilot contamination could be compensated in some degree. Simulation results show that the proposed joint optimization algorithm with controllable vertical beams' weight vectors outperforms the method combining downtilts adjustment and power allocation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.2 no.2
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• pp.63-81
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• 2008

WiMAX has been introduced as a competitive alternative for metropolitan broadband wireless access technologies. It is connection oriented and it can provide very high data rates, large service coverage, and flexible quality of services (QoS). Due to the large number of connections and flexible QoS supported by WiMAX, the uplink access in WiMAX networks is very challenging since the medium access control (MAC) protocol must efficiently manage the bandwidth and related channel allocations. In this paper, we propose and investigate a cost-effective WiMAX bandwidth management scheme, named the WiMAX partial sharing scheme (WPSS), in order to provide good QoS while achieving better bandwidth utilization and network throughput. The proposed bandwidth management scheme is compared with a simple but inefficient scheme, named the WiMAX complete sharing scheme (WCPS). A maximum entropy (ME) based analytical model (MEAM) is proposed for the performance evaluation of the two bandwidth management schemes. The reason for using MEAM for the performance evaluation is that MEAM can efficiently model a large-scale system in which the number of stations or connections is generally very high, while the traditional simulation and analytical (e.g., Markov models) approaches cannot perform well due to the high computation complexity. We model the bandwidth management scheme as a queuing network model (QNM) that consists of interacting multiclass queues for different service classes. Closed form expressions for the state and blocking probability distributions are derived for those schemes. Simulation results verify the MEAM numerical results and show that WPSS can significantly improve the network’s performance compared to WCPS.