• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.104-116
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• 2010

With several advantages such as flexible downlink-to-uplink(DL-to-UL) ratio and flexible spectrum usage, Time Division Duplexing(TDD) is emerging as an alternate to Frequency Division Duplexing(FDD), especially in wireless broadband systems. We already have at least four different TDD systems in the industry: Time Division-Synchronous Code Division Multiple Access(TD-SCDMA), IEEE 802.16e-TDD, IEEE 802.16m-TDD, and Time Division-Long Term Evolution(TD-LTE). A disadvantage of TDD is that tight coordination such as time synchronization between adjacent operators is required to prevent interference between the adjacent TDD systems. In this paper, we investigate coexistence scenarios among the above four well-known TDD systems and calculate spectral efficiency(SE) loss in each scenario. Our findings are that SE loss can be significant if TDD ratios of the adjacent operators are considerably different. However, as long as the TDD ratios of the adjacent operators are similar, configurations in the systems permit perfect time synchronization between the two heterogeneous TDD systems, and the resulting SE loss is zero or reasonably low. We believe that the above findings and the configurations of the TDD systems recommended tominimize SE loss will be helpful for operators who deploy TDD systems in system parameter determination and cross-operator coordination.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.4
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• pp.295-301
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• 2011

A triple-band transceiver module for 2.3/2.5/3.5 GHz mobile WiMAX, IEEE 802.16e, applications is introduced. The suggested transceiver module consists of RFIC, reconfigurable/multi-resonance MIMO antenna, embedded PCB, mobile WiMAX base band, memory and channel selection front-end module. The RFIC is fabricated in $0.13{\mu}m$ RF CMOS process and has 3.5 dB noise figure(NF) of receiver and 1 dBm maximum power of transmitter with 68-pin QFN package, $8{\times}8\;mm^2$ area. The area reduction of transceiver module is achieved by using embedded PCB which decreases area by 9% of the area of transceiver module with normal PCB. The developed triple-band mobile WiMAX transceiver module is tested by performing radio conformance test(RCT) and measuring carrier to interference plus noise ratio (CINR) and received signal strength indication (RSSI) in each 2.3/2.5/3.5 GHz frequency.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.4
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• pp.876-884
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• 2014

A hardware design of LDPC decoder which is based on the improved normalized min-sum(INMS) decoding algorithm is described in this paper. The designed LDPC decoder supports 19 block lengths(576~2304) and 6 code rates(1/2, 2/3A, 2/3B, 3/4A, 3/4B, 5/6) of IEEE 802.16e mobile WiMAX standard and 3 block lengths(648, 1296, 1944) and 4 code rates(1/2, 2/3, 3/4, 5/6) of IEEE 802.11n WLAN standard. The decoding function unit(DFU) which is a main arithmetic block is implemented using sign-magnitude(SM) arithmetic and INMS decoding algorithm to optimize hardware complexity and decoding performance. The LDPC decoder synthesized using a 0.18-${\mu}m$ CMOS cell library with 100 MHz clock has 284,409 gates and RAM of 62,976 bits, and it is verified by FPGA implementation. The estimated performance depending on code rate and block length is about 82~218 Mbps at 100 MHz@1.8V.

• Electronics and Telecommunications Trends
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• v.27 no.6
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• pp.31-37
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• 2012

Hierarchical network 기술은 다양한 크기의 이동통신 셀들이 서로 중첩된 환경에서 무선 용량 증대 및 셀 커버리지 확대를 위한 차세대 통신 기술이다. 모바일 IPTV는 IPTV에 이동성이 더해진 기술로서 이동통신망을 이용하여 언제, 어디서나 고품질의 TV 및 VoD, 데이터 서비스를 제공한다. 본고에서는 IEEE 802.16 기반의 hierarchical network 및 모바일 IPTV 기술의 연구동향을 살펴보고 두 기술의 공존 가능성 측면에서의 고려 사항에 대해 기술한다.

• Information and Communications Magazine
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• v.28 no.6
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• pp.84-90
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• 2011

본 논문은 2011년 4월 IEEE SA에서 차세대 이동통신 규격으로 승인된 IEEE 802.16m의 구현에 관한 것이다. 승인된 규격은 ITU-R에서 4세대 이동통신 표준인 IMT-Advanced 표준 기술로 확정될 예정이며, 국내에서는 WiBro-Advanced, 해외에서는 Wireless MAN-Advanced 또는 WiMAX-2로 불린다. 이 규격을 기반으로 2009년부터 규격의 표준화 활동과 함께 시스템 개발을 시작하여, 2010년 12월 1차 개발을 완료하였다. 개발된 WiBro-Advanced 시스템은 ITU-R이 요구하는 4세대 이동통신의 요구사항을 만족하고 있다. 본 논문은 구현된 시스템의 핵심 기술에 대해 기술하고, 기술적인 특징들을 살펴본다.

• Environmental and Resource Economics Review
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• v.16 no.4
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• pp.781-802
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• 2007

This study estimates a demand function for municipal water in Seoul area using a Stone-Geary functional form. The Stone-Geary model offers more precise estimates for price elasticity of water demand since it explicitly separates 'basic demand' which is not influenced by the price from 'economic demand' which depends on the price. Our results show that about 84% of the total water demand is the basic demand. The results suggest that the minimum consumption range m stepwise price system should be lowered from $30m^3$ to $15m^3$ per month.

• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.275-281
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• 2006

Simple-relay aided resource allocation (SRARA) schemes are incorporated with throughput guarantee scheduling (TGS) in IEEE 802.16 type time division duplex - orthogonal frequency division multiple access (TDD-OFDMA) downlink in order to enhance service coverage, where the amount of resources for relaying at each relay is limited due to either its available power which is much smaller than base station (BS) power or the overhead required for exchanging feedback information. The performance of SRARA schemes is evaluated with schedulers such as proportional fair (PF) and TGS at 64kbps and 128kbps user throughput requirements when total MS power is set to 500mW or 1 W. For 64kbps throughput requirement level, more improvement comes from relay than scheduler design. For 128kbps case, it comse from scheduler design than relay due to the fact that simple relay can't help using strictly limited amount of resources for relaying function.

• Journal of Advanced Navigation Technology
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• v.15 no.3
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• pp.386-391
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• 2011

CRU (contiguous resource unit) composed of adjacent OFDMA subcarriers is popularly adopted for recently developed cellular communication standards, e.g. IEEE 802.16e/m. If multiple CRUs having different SNR are assigned to a mobile station, and multiple packet streams are independently transmitted by using H-ARQ transmission, an achievable data rate can be varied according to the channel allocation method of re-transmission packets and new transmission packets. In this paper, the optimum channel allocation method for the above stated problem, and several sub-optimum channel allocation methods to reduce the computational complexity of the optimum allocation method are proposed. According to the simulation results, a sub-optimum allocation method assigning a CRU having good SNR to new transmission packet shows marginal performance loss compared with optimum method, however, the computational complexity can be significantly reduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.43-51
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• 2015

Upcoming cellular networks such as LTE-advanced and IEEE 802.16m are enhanced by relay stations to support high data rate multimedia services and minimize the shadow zone with low cost. Enhancing the relay stations, however, divides the multihop cellular network into smaller microcells and the distance between microcells is closer, which intends large intra-cell and inter-cell interference. Especially the access link on downlink in the OFDMA cellular network is the throughput bottleneck due to the severe interference caused by base stations and relay stations transmitting large data to mobile stations simultaneously. In this paper, we present interference aware channel allocation algorithm to avoid severe interference on multihop cellular networks with random topology. Proposed algorithm increases SINR(signal to interference plus noise ratio) and decreases number of required control messages for channel allocation, so that increases overall throughput on the networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5B
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• pp.489-497
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• 2009

In the 3GPP LTE and IEEE 802.16m standardizations for IMT-Advanced, the efficient transmission of multicast and broadcast data is one of the important issues to improve system performance. Especially, to guarantee each user's QoS in the multicast group, H-ARQ or adaptive modulation are considered to be adoption, however, reduction of feedback overhead is one of the most important issues. In this paper, performance of the previously proposed OOK (On-Off Keying) based common ACK/NACK feedback channel is analyzed through theoretical analysis and simulation. Based on the results, system parameter optimization methods for common feedback channel are proposed. In addition, through computer simulation, it is shown that the common feedback method according to the proposed feedback parameter optimization can feedback ACK/NACK information for multicast H-ARQ transmission, more reliably than the conventional user dedicated feedback method in 3GPP LTE systems, and can reduce the feedback overhead as well.