• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.8
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• pp.1789-1798
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• 2012

IEEE 802.15.4a standard can provide a variety of location-based services for ZigBee or wireless network applications by adapting the time-of-arrival (TOA) ranging technique. The non-line-of-sight (NLOS) condition is the critical problem in the IEEE 802.15.4a networks, and it can significantly degrade the performance of the TOA-based localization. To enhance the location accuracy due to the NLOS problem, this paper proposes an energy-efficient low complexity localization algorithm. The proposed approach performs the ranging with the multicast method, which can reduce the message overhead due to packet exchanges. By limiting the search region for the location of the node, the proposed approach can enhance the location accuracy. Experimental results show that the proposed algorithm outperforms previous algorithms in terms of the energy consumption and the localization accuracy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1143-1149
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• 2006

In this paper, the modified iterative decoding algorithm[8] by partitioning check nodes is applied to low-density parity-check(LDPC) codes in IEEE 802.16e standards, which gives us the improvement for convergence speed of decoding. Also, the new method of check node partitioning which is suitable for decoding of the LDPC codes in IEEE 802.16e system is proposed. The improvement of convergence speed in decoding reduces the number of iterations and thus the computational complexity of the decoder. The decoding method by partitioning check nodes can be applied to the LDPC codes whose decoder cannot be implemented in the fully parallel processing as an efficient sequential processing method. The modified iterative decoding method of LDPC codes using the proposed check node partitioning method can be used to implement the practical decoder in the wireless communication systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4B
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• pp.319-328
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• 2009

IEEE 802.16e standard defines different Sleep Mode Operations according to kind of services which aims at saving energy for MS efficiently. The previous study of Sleep Mode Operation is limited for single service environment, real sleep interval is decreased because different Sleep Mode Operations are applied at once when MS is on multi service. The proposed Enhanced Sleep Mode Operation increasing real sleep interval of this paper guarantees QoS(Quality of Services) which is same as standard, minimizes energy consumption when different Sleep Mode Operations are applied at once. Therefore Enhanced Sleep Mode Operation of this paper will be useful in case of increase battery life time as well as guaranteeing QoS for MS in IEEE 802.16 system.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.5
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• pp.31-40
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• 2010

This paper describes a LDPC decoder for IEEE 802.11n wireless LAN standard. The designed processor supports parity check matrix for block length of 1,944 and code rate of 1/2 in IEEE 802.11n standard. To reduce hardware complexity, the min-sum algorithm and layered decoding architecture are adopted. A novel memory reduction technique suitable for min-sum algorithm was devised, and our design reduces memory size to 25% of conventional method. The LDPC decoder processor synthesized with a $0.35-{\mu}m$ CMOS cell library has 200,400 gates and memory of 19,400 bits, and the estimated throughput is about 135 Mbps at 80 MHz@2.5v. The designed processor is verified by FPGA implementation and BER evaluation to validate the usefulness as a LDPC decoder.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.3
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• pp.22-33
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• 2014

As a standard of WMNs, IEEE 802.11s supports two kinds of MAC algorithm: a mandatory EDCA used by IEEE 802.11e and an optional MCCA. While EDCA classifies traffic according to four Access Categories (AC) and offer differentiated service using a classified priority, MCCA can guarantee the specific bandwidth of users with a TDMA-style bandwidth reservation scheme between mesh routers. In case that a flow is VBR traffic of a multimedia application, MCCA has disadvantage that the reserved bandwidth does not be used entirely, though it guarantees required bandwidth of users and fairness using bandwidth reservation with neighbors' node. In this paper, we showed a problem that is wastes the reserved bandwidth when MCCA is enabled and proposed a new scheduling algorithm to prevent waste of bandwidth and to improve network utilization effectively, named Resource Sharing Round Robin (RSRR) scheduling. Finally we showed simulation results that performance of a proposed RSRR is better than the legacy MCCA through NS-2 simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.3 s.333
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• pp.39-44
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• 2005

The OFDM modulation and transmission block have been modeled in order to analyse the relationship between the 2.4GHz power amplifier distortion and output ACPR for the IEEE 802.11g wireless LAN. The nonlinear characteristic of the power amplifier has been modeled as AM-to-AM and AM-to-PM using the behavioral model, and the output spectrum is analysed with the phase distortion variation. Also, amplifier back-off value from P1dB to satisfy the required IEEE 802.11g standard spectrum mask s been simulated with modeled phase distortion, and the simulation data have been compared to the measured result by using the pre-distortion technique.

• Journal of the Korea Society for Simulation
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• v.21 no.2
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• pp.51-58
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• 2012

In IEEE 802.16j MMR protocol, two modes about usage of RS are proposed; one is transparent mode to enhance data throughput and the other is non-transparent mode to extend coverage. In this paper, we focus on non-transparent mode and find that the mode can also improve data throughput. Therefore, we analyze data throughput on various RS topology and their extended coverage area by simulation in IEEE 802.16j non-transparent mode. We also compare the simulation results with the single MR-BS system of which coverage is extended by higher transmission power. From the comparisons of simulation results, we see that higher throughput can be obtained in the proposed non-transparent mode.

• Journal of the Korea Society for Simulation
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• v.23 no.4
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• pp.65-74
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• 2014

IEEE 802.11n standard has introduced the new schemes in MAC and PHY layers to improve network throughput. Frame aggregation and Block ACK are mainly defined to increase the efficiency of the MAC layer. There exists still problem in IEEE 802.11n. When block ACK request and/or response frames are missing or received in error, the sender does not know the status (success/failure) of each frame in the aggregated large frame and retransmits all the frames. This can cause a lower network performance. To solve this problem, we propose a new effective scheme, called reduced retransmission of MPDUs (RRM) scheme. In the proposed scheme, when a sender does not receive a block ACK response frame, it just transmits a next data frame and requests a block ACK. Therefore, it can retransmits the erroneous frames. Performance of the proposed scheme is investigated by simulation. Our results show that the proposed scheme is very effective and improves the performance under a wide range of channel error conditions.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.1 s.343
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• pp.49-56
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• 2006

This paper describes the design and the verification of IEEE 802.15.4 LR-WPAN 2.4GHz Physical layer for Ubiquitous Sensor Network(USN). We designed the Carrier Frequency Offset(CFO) compensation satisfied the frequency tolerance of IEEE 802.15.4 LR-WPAN and the adaptive matched filter that re-setting of the threshold for the symbol synchronization of the various USN environment. The multiplications is reduced 1/16 by this method each other at i, q phases and has 0.5dB performance improvement in detection probability. Proposed baseband system is designed with verilog HDL and implemented using FPGA prototype board.

• Journal of IKEEE
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• v.19 no.1
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• pp.45-51
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• 2015

Recently, as WPAN (Wireless Personal Area Network) becomes the necessary feature in IoT (Internet of Things) devices, the importance of data security also hugely increases. In this paper, we present the low-complexity 128-bit AES-$CCM^*$ hardware IP for IEEE 802.15.4 standard. For low-cost and low-power implementation which is essentially required in IoT devices, we propose two optimization methods. First, the folded AES(Advanced Encryption Standard) processing core with 8-bit datapath is presented where composite field arithmetic is adopted for reduced hardware complexity. In addition, to support $CCM^*$ mode defined in IEEE 802.15.4, we propose the mode-toggling architecture which requires less hardware resources and processing time. With the proposed methods, the gate count of the proposed AES-$CCM^*$ IP can be lowered up to 57% compared to the conventional architecture.