• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.11
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• pp.2465-2473
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• 2011

This paper describes a circuit-level optimization of DFU(decoding function unit) for LDPC decoder which is used in wireless communication systems including WiMAX and WLAN. A new design of DFU based on sign-magnitude arithmetic instead of two's complement arithmetic is proposed, resulting in 18% reduction of gate count for 96 DFUs array used in mobile WiMAX LDPC decoder. A multi-mode LDPC decoder for mobile WiMAX standard is designed using the proposed DFU. The LDPC decoder synthesized using a 0.18-${\mu}m$ CMOS cell library with 50 MHz clock has 268,870 gates and 71,424 bits RAM, and it is verified by FPGA implementation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.2
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• pp.119-126
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• 2011

In this paper, we expect that the IEEE 802.15.4a, which is based on CSS, will be used a lot without getting help from other systems or sensors and will make it possible to measure the distance between radio chips in sensor network field, where the location information of the standard have to be based upon. But, the error rate will be high, so we will correct the location of the tag, which will be received by anchor. The technology of location correction we offer is reducing the error rate through calculating the distance from Compensation Tag, and after that, unite the Toa method with the Fingerprint method and adapt them to location correction technology, calculate the location's estimate, and finally abstract the best suited location estimate for Compensation Tag. At last, we offer developing systems as indoor systems of CSS, which pursue the location between nodes, and a thesis about indoor systems and making their accuracy higher.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1248-1253
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• 2010

In this paper, the compensation algorithm for localization using the concept of equivalent distance rate(AEDR) in order to compensate ranging error in the SDS-TWR(Symmetric Double-Sided Two-Way Ranging) is proposed and the performance of the proposed algorithm is analyzed by the localization experiments. The ranging error of the SDS-TWR in the distance between mobile node and beacon node is measured to average 1m~8m by ranging experiments. But it is confirmed that the performance of the localization by the AEDR is better than that of the SDS-TWR 4 times in university auditorium and corridor, and the localization error of above 3~10m is reduced to average 2m and that of below 3m is reduced to average 1m respectively. It is concluded that the AEDR is superior to the NLOS(Non Line Of Sight) than LOS(Line Of Sight) in performance of ranging compensation for localization, and the AEDR is more helpful to localization systems practically considering the environment of sensor networks is under NLOS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.8
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• pp.623-631
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• 2013

Wireless LAN (WLAN) interface is one of the major sources drastically depleting the battery power of mobile devices such as smartphones and tablets. Most commercial mobile devices employ a power saving technique putting their WLAN interface into a sleep state when there is no network traffic, and thereby, save the battery power. However, since an access point (AP) just transmits the packet(s) received from a server to the corresponding mobile device immediately, it may cause a problem that the mobile device constantly remains in an awake state so that its battery power is rapidly drained. In this paper, we point out this problem and propose a new scheme that can save the mobile device's battery power with an adaptive packet scheduling at the AP side. From the experimental results based on a testbed, we found that the proposed scheme outperforms existing schemes over 50% in terms of power saving.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.7
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• pp.775-782
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• 2016

In this paper, we presented the paper-based reconfigurable frequency selective surface(FSS) for transmitting or blocking the wireless LAN signal in indoor environments. The proposed reconfigurable FSS are designed on coated paper using a printing of conductive ink and conductive adhesive for PIN diode, which provides ON/OFF of the reconfigurable FSS for passing or blocking the 5GHz signal. The reconfigurable FSS attached on the wall can pass or block the incident wireless signal as the received signal strength in indoor. To provide the validity of the proposed FSS, we fabricated the reconfigurable FSS on the paper and confirmed the very similar results between simulations and measurements. From the measured results of the proposed spectrum control system, we know that the proposed reconfigurable FSS can block about 20dB at 5.745GHz~5.805GHz.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.2
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• pp.103-114
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• 2007

The existing handover authentication schemes have authentication delay and overhead of the authentication server since they have been separately studied handover authentication at the link layer and the network layer. This paper proposes a handover authentication scheme initiated by Mobile Node on FMIPv6 based mobile access networks. The main idea of the paper is to generate a session key at the mobile node side, and transfer it to the next Access Router through the authentication server. Also, the scheme has a hierarchical key management at access router. There are two advantages of the scheme. First, the generated session key can be utilized for protecting the binding update messages and also for access authentication. Second, hierarchical key management at the access router reduced the handover delay time. The security aspects on the against PFS, PBS, and DoS attack of proposed scheme are discussed.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.1
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• pp.51-61
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• 2010

Koinonia system is designed to fully utilize the advantage of Binary CDMA so as to guarantee QoS in wireless networks. In this paper, we propose the new network structure based on this system and refer to it as BLAN(Binary CDMA LAN). Although BLAN is similar structure to IEEE 802.11 WLAN, it will ensure the fast handover and QoS. We also propose the AKA(Authentication and Key Agreement) protocol and Reauthentication protocol to be used for communication in BLAN. These protocols are securely and efficiently designed using the user identity module to support the more powerful authentication. Hence, BLAN, including the proposed protocols, will support the high mobility and security. In conclusion, we expect that BLAN can be applied to future infrastructure on special environment, and it can be helpful showing the new network model which alternate WLAN.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.3
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• pp.75-81
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• 2015

This paper proposed the new eight-parallel MDC FFT processor using the eight-parallel MDC architecture and the efficient scheduling scheme. The proposed FFT processor supports the 256-point FFT based on the modified radix-$2^6$ FFT algorithm. The proposed scheduling scheme can reduce the number of complex multipliers from eight to six without increasing delay buffers and computation cycles. Moreover, the proposed FFT processor can be used in OFDM systems required high throughput and low hardware complexity. The proposed FFT processor has been designed and implemented with a 90nm CMOS technology. The experimental result shows that the area of the proposed FFT processor is $0.27mm^2$. Furthermore, the proposed eight-parallel MDC FFT processor can achieve the throughput rate up to 2.7 GSample/s at 388MHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.2
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• pp.165-171
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• 2013

WAVE(Wireless Access in Vehicular Environments) is a representative V2V communication protocol and its standards of MAC and PHY parts except for security were published. In order to control traffic flow and ensure driver's safety using V2V communication, various projects are conducting. In particular, safety application has been researched. Therefore, in this paper, we designed the safety application algorithm, which informs a driver of the dangerous status when driver tries to turn left in an intersection and we also implemented the algorithm. Proposed algorithm configures a model for a host vehicle and a vehicle coming in opposite lane and in case that there is collision hazard it provides warning message to driver by using HMI. In order to evaluate the proposed algorithm's performance, we configured the test bed using test vehicles and we tested the algorithm on proving ground with the composed test scenarios. As test results, our system showed excellent performance. If the infrastructures for V2I communications are constructed, we will optimize our system more precisely and stably.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.476-483
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• 2016

Super Wi-Fi is a Wi-Fi-like service exploiting TV white space (WS) which is expected to achieve larger coverage than today's Wi-Fi thanks to its superior propagation characteristics. Super Wi-Fi has been materialized as an international standard, IEEE 802.11af, targeting indoor and outdoor applications, and is undergoing worldwide field tests. This paper demonstrates the true potential of indoor Super Wi-Fi, by experimentally comparing the signal propagation characteristics of Super Wi-Fi and Wi-Fi in the same indoor environment. Specifically, we measured the wall and floor attenuation factors and the path-loss distribution at 770MHz, 2.401 GHz, and 5.540 GHz, and predicted the downlink capacity of Wi-Fi and Super Wi-Fi. The experimental results have revealed that TVWS signals can penetrate up to two floors above and below, whereas Wi-Fi signals experience significant path loss even through a single floor. It has been also shown that Super Wi-Fi mitigates shaded regions of Wi-Fi by providing almost-homogeneous data rates within its coverage, performs comparable to Wi-Fi utilizing less bandwidth, and always achieves better spectral efficiency than Wi-Fi. The observed phenomena imply that Super Wi-Fi is suitable for indoor applications and has the potential of extending horizontal and vertical coverage of today's Wi-Fi.