• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.2
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• pp.153-160
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• 2017

Recently, the demand has continued to increase for higher data rates and improved multimedia services through wireless internet access. In order to increase the data rate and link reliability, 3GPP LTE/A and IEEE 802.16e/m WiMAX systems incorporate MIMO transmission schemes. Since the hardware complexity increases with the number of transmit data streams and mobile devices have limited physical dimensions, an multiple input multiple output (MIMO) ystem with two antennas at both the transmitter and the receiver ($2{\times}2$) is considered to be a possible solution for mobile devices. In this paper, a low-complexity soft output MIMO symbol detector based on Modified-SQRD is proposed for mobile devices with two transmit and two receive antennas.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.667-670
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• 2004

In this paper, we have presented the improved IF transceiver architecture and the implementation and experimental results on re-configurable transceiver based on digital IF for multiple wideband OFDM/TDD base stations for high-speed portable internet-service in which is issued Korea. The implemented IF transceiver has been designed to support multiple frequency allocations and multiple standards by only modifying the programmable software not its hardware like as the software-defined-radio concept. Also, the digital complex quadrature modulation technique has been used for the digital IF transmitter, which is able to combine multiple frequency bands in digital processing block not RF block and to reject the image frequency signals. And the bandpass sampling technique has been used for the digital IF receiver to reduce the sampling rate of ADC. This paper has shown the experiment results on the frequency response and constellation on the base-station implemented using the modified IEEE 802.16a/e physical layer channel structure based on OFDM/TDD.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.4
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• pp.65-72
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• 2009

In this paper, we propose a proxy-based fast handover scheme to improve a performance in the mobile WiMAX network using PMIPv6 for supporting the network-layer mobility. In our proposed scheme, we define three link-layer messages and one network-layer message to reduce the handover latency, and propose a buffering mechanism to minimize packet loss and solve out-of-sequence problem. A performance evaluation indicates that the proposed scheme works more efficiently than PMIPv6 in terms of the handover latency and packet loss.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.10
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• pp.989-995
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• 2006

This paper shows that the OFDM(Orthogonal Frequency Division Multiplex) system is robust to multipath than CDMA (Code Division Multiple Access) system and it has a strong possibility to be utilized as a supplementing wireless location system for the forthcoming portable internet network. The OFDM system based on IEEE 802.16e is a wireless TDD (Time Division Duplex) OFDMA (Orthogonal Frequency Division Multiple Access) system providing portable internet services in 2.3 GHz frequency band and is scheduled in service in Korea starting in 2006. In this paper, multipath error is calculated using a two-ray model and compared with that of a CDMA system which is following IS-95. The OFDM system shows a maximum multipath error of 3 m while a CDMA system shows a maximum multipath error of 61 m. For this simulation, an early-late technique is used. This technique is usually used to match synchronization of signal in DLL(Delay Lock Loop).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.7
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• pp.1-8
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• 2008

Low Density Parity Check codes(LDPC) are recently focused on communication systems due to its good performance. The standard of WiBro has also included LDPC codes as a channel coding. The weak point of implementation for LDPC encoder is that conventional binary Matrix Vector Multiplier has many clock cycles which limit throughput. In this paper, we propose semi-parallel architecture by using cyclic shift registers and exclusive-OR without conventional Matrix Vector Multipliers over the standard parity check matrices with Circulant Permutation Matrices(CPM). Furthermore, multi-rate encoder is designed by using proposed architecture. Our encoder with multi-rate for IEEE 802.16e LDPC has lower clock cycles and higher throughput.

• Journal of Communications and Networks
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• v.9 no.2
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• pp.118-127
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• 2007

We propose a link adaptation and selection method for the links constituting an orthogonal frequency division multiplexing (OFDM) based wireless relay network. The proposed link adaptation and selection method selects the forwarding, modulation, and channel coding schemes providing the highest end-to-end throughput and decides whether to use the relay or not. The link adaptation and selection is done for each sub-channel based on instantaneous signal to interference plus noise ratio (SINR) conditions in the source-to-destination, source-to-relay and relay-to-destination links. The considered forwarding schemes are amplify and forward (AF) and simple adaptive decode and forward (DF). Efficient adaptive modulation and coding decision rules are provided for various relaying schemes. The proposed end-to-end link adaptation and selection method ensures that the end-to-end throughput is always larger than or equal to that of transmissions without relay and non-adaptive relayed transmissions. Our evaluations show that over the region where relaying improves the end-to-end throughput, the DF scheme provides significant throughput gain over the AF scheme provided that the error propagation is avoided via error detection techniques. We provide a frame structure to enable the proposed link adaptation and selection method for orthogonal frequency division multiple access (OFDMA)-time division duplex relay networks based on the IEEE 802.16e standard.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.547-550
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• 2006

휴대 인터넷은 이동 중에도 무선으로 고속의 데이터 송수신이 가능한 통신 서비스로서 우리나라에서는 WiBro(Wireless Broadband)라고 명명되어 2006년 6월 상용 서비스를 시작하였다. 한국 정보 통신 기술협회(TTA)와 IEEE802.16e 표준에서 제시된 휴대인터넷 서비스는 기본적으로 기지국과 단말을 기반으로 한 CDMA통신 시스템과 유사한 셀룰러 망 구조를 가지고 있다. 와이브로에서 모든 RAS(Radio Access Station)는 매 5msec마다 프레임을 전송하고, 이 프레임의 앞 단에는 Preamble이 위치하고 있어 기지국과 단말의 Synchronization을 가능케 해준다. 각 RAS는 서로 다른 Preamble을 사용하므로 단말은 Preamble detection을 통해 기지국을 구분할 수 있다. 본 논문에서는 휴대인터넷을 이용한 무선측위의 해상도 및 가청성을 현장실험을 통하여 분석한다. 현재 상용화 되어 사용중인Wibro 신호를 기저대역으로 낮추고 이 신호를 디지타이저를 사용하여 20MHz의 샘플링 주파수로 수집한다. 5msec 주기의 Wibro프레임 중에서 Preamble을 Correlation detection 기법을 사용하여 기지국과 단말 사이의 relative delay를 측정하여 기지국들과 단말 사이의 거리의 차를 구한다. 거리측정치를 이용하여 Wibro 망에서의 무선측위 추정치를 구하고 해상도와 정확도 및 가청성 등의 Wibro의 측위성능을 분석한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.29-35
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• 2010

The cooperative transmission between sectors in next generation communications standards, e.g., 3GPP LTE-Advanced and IEEE 802.16m, has become an important research issue. Hence methods to decide the optimal antenna tilting angle in cooperative transmission between sectors are needed. This paper proposes methods to decide the optimal antenna tilting angle in cases of non-cooperative and cooperative transmissions between sectors. The proposed methods use an objective function that maximizes the cell average log rate or the cell average rate for users distributed uniformly within the radius of the sector. Also, the objective function which maximizes the cell average rate determined by adaptive modulation and coding (AMC) used in actual cellular systems is considered. When the cell average rate becomes the objective function, the system rate efficiency increases significantly for both cooperative and non-cooperative transmission. When the cell average log rate and the AMC rate become the objective functions, an optimal antenna tilting decision method which effectively increases the efficiency of cell boundary users is discussed.

• The KIPS Transactions:PartC
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• v.12C no.6 s.102
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• pp.799-808
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• 2005

This paper proposes low latency handover procedure for seamless connectivity and QoS support between wired (e.g. Ethernet) and wireless (e.g. WLAN, WiBro(802.16-compatible), CDMA) networks by the mobile-assisted and server-initiated handover strategy. It is assumed that the server decides the best target network considering network status and user preferences. In this algorithm a mobile terminal associates with the wireless link decided at the server In advance and receives CoA as well. When handover occurs without the prediction in wired networks, the server performs fast binding update using physical handover trigger through the MIH(media independent handover) function. As a result, a mobile terminal does not need to perform L2 and L3 handover during handover so that this procedure decreases handover latency and loss.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.12
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• pp.45-52
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• 2005

This paper proposes low latency handover procedure for seamless connectivity and QoS support between wired (e.g. Ethernet) and wireless (e.g. WLAN, WiBro(802.16-compatible), CDMA) networks by the mobile-assisted and server-initiated handover strategy. It is assumed that the server decides the best target network considering network status and user preferences. In this procedure, a mobile terminal associates with the wireless link decided at the server in advance and receives CoA as well. When handover occurs without the prediction in wired networks, the server performs fast binding update using physical handover trigger through the MIH (media independent handover) function. As a result, a mobile terminal does not need to perform L2 and L3 handover during handover so that this procedure decreases handover latency and loss.