• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.2
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• pp.363-371
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• 2013

This paper describes a multi-standard LDPC decoder which 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. To minimize hardware complexity, it adopts a block-serial (partially parallel) architecture based on the layered decoding scheme. A DFU(decoding function unit) based on sign-magnitude arithmetic is used for hardware reduction. The designed LDPC decoder is verified by FPGA implementation, and synthesized with a 0.13-${\mu}m$ CMOS cell library. It has 312,000 gates and 70,000 bits RAM. The estimated throughput is about 79~210 Mbps at 100 MHz@1.8v.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.1
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• pp.82-91
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• 2009

Routing (or path selection) is one of the key issues of multi-hop relay networks such as the IEEE 802.16j. Moreover, the allocation of appropriate resource such as bandwidth should not only be made in accordance with the paths selected, but the utilization of radio resource of an entire cell should also be maximized. Due to this interdependency between the problems of resource allocation and routing, it is desired these two problems are addressed simultaneously. In this paper, we propose a joint resource allocation and routing scheme for an OFDMA-based multi-hop cellular system. This scheme uses a polynomial time heuristic algorithm called Multi-Dimensional Multi-choice Knapsack Problem (MMKP) in order to find an approximate solution maximizing the total downlink throughput. In the simulation results, we show that the proposed scheme finds a sub-optimal solution which is superior to a link quality-based routing scheme, but slightly worse than the optimal solution.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.85-94
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• 2006

Simple-relay aided resource allocation (SRARA) schemes are incorporated with throughput guarantee scheduling (TGS) in IEEE 802.16 type TDD-OFDMA downlink to enhance service coverage, where the amount of resources at each relay is limited due to either its available power which is much smaller than base station (BS) power or the required overhead The performance of SRARA schemes is evaluated with both proportional fair (PF) and TGS schedulers at 64 kbps and 128 kbps user throughput requirements. For SRARA with RSs of relatively lower power, a scheme putting total power into only one subchannel shows larger coverage than when both subchnnels are used in a manner of equal power allocation, while the RS with evenly power-allocated two subchannels could provide larger coverage gain for a relatively higher power. In a lower target (64kbps), more improvement comes from relay scheme rather than scheduler design. For a relatively higher level (128 kbps), it comes from scheduler design rather than relay.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.3
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• pp.51-57
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• 2010

A dual-mode direct conversion receiver is developed in $0.13\;{\mu}m$ RF CMOS process for IEEE 802.11n based wireless LAN and IEEE 802.16e based mobile WiMAX application. The RF receiver covers the frequency band between 2.3 and 2.7 GHz. Three-step gain control is realized in LNA by using current steering technique. Current bleeding technique is applied to the down-conversion mixer in order to lower the flicker noise. A frequency divide-by-2 circuit is included in the receiver for LO I/Q differential signal generation. The receiver consumes 56 mA at 1.4 V supply voltage including all LO buffers. Measured results show a power gain of 32 dB, a noise figure of 4.8 dB, a output $P_{1dB}$ of +6 dBm over the entire band.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.498-504
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• 2008

In this paper, an efficient hardware platform for the digital signal processing for OFDM Communication systems is presented. The hardware platform consists of a single FPGA, two DSPs with 8000 MIPS of maximum at 1 GHz clock, 2-channel ADC and DAC supporting maximum 125 MHz sampling rate, and flexible data bus architecture, so that a wide variety of baseband signal processing algorithms for practical OFDM communication systems may be implemented and tested. The IEEE 802.16 software modem is also presented in order to verify the effectiveness and usefulness of the designed platform.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.154-160
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• 2005

Microwave Otters are essential device in modem wireless systems. A compact dimension BPF(Band-pass Filter) for IEEE 802.11a WLAN service is realized using LTCC multi-layer process. To extrude 2-stage band-pass equivalent circuit, band-pass and J-inverter transform applied to Chebyshev low-pass prototype filter. Because parallel L-C resonator is complicate and hard to control the inductor characteristics in high frequency, the shorted $\lambda/4$ stripline is selected for the resonator structure. The passive element is located in the different layers connected by conventional via structure and isolated by inner GND. The dimension of fabricated stacked band-pass filter which is composed of six layers, is $2.51\times2.27\times1.02\;mm^3$. The measured filter characteristics show the insertion loss of -2.25 dB, half-power bandwidth of 220 MHz, attenuation at 5.7 GHz of -32.25 dB and group delay of 0.9 ns at 5.25 GHz.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.3
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• pp.395-400
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• 2021

In this paper, the wideband patch antenna is simulated and manufactured for the wireless LAN of 5GHz band that is defined in IEEE 802.11a. In the 802.11a, 200 channels of 675MHz are defined. Therefore, the bandwidth is needed more than 12.3%. For the wideband characteristics, low dielectric constant is realized with the multi-layer of 2 teflon substrates and the air dielectric layer and the feeding method of the coupled-line is used. Optimized wideband patch antenna is simulated with the return loss of 38.99dB at the center frequency of 5.43GHz and the bandwidth of 12.9%. The gain of manufactured patch antenna is 4.38, 4.52, and 5.12dBi at the channel number of 46, 56, and 153, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.9
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• pp.47-54
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• 2004

The previous works for WLAN system based on OFDM is mainly individual study for independent frequency offset or symbol synchronization. In this paper, the performance of IEEE 802.11a WLAN(Wireless Local Area Network) system in the realistic indoor multipath channel models is analyzed with frequency offset compensation and channel estimation methods. For the performance analysis of the WLAN system indoor Rayleigh multipath channels are adopted, and the BER(Bit Error Rate) of WLAN system is calculated with y2 code-rate 16-QAM based on standard specification. From the simulation results, the difference of required Eb/No for BER of 10-3 is 1-2dB between the channel estimation and frequency offset compensation, and perfect channel estimation and no frequency offset.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.6
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• pp.159-164
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• 2016

This paper proposes an improved superframe structure with one : N situation of the network as a target for efficiency battery and communication performance used in the existing standard IEEE 702.15.4 MAC layer. The proposed superframe transforms and adds a two structures. First, we add the proposed scheduling interval after the arrival of the beacon. Second, we change to a structure in which one of the contention access period is divided into two. The contention access period and the contention-free access period of active portion are divided according to the LQI value of the device. Through this system-level simulation written by $c{^+^+}$, as a results show that the battery consumption and transmission performance has been increased.

• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.44-51
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• 2002

This paper describes the performance evaluation and analysis of an Orthogonal Frequency-Division Multiplexing (OFDM) system having the least Inter Symbol Interference (ISI) in a multi-path fading channel environment. Wireless Local Area Network (W-LAN) in accordance with IEEE 802.11a and IEEE 802.11b provides high-speed transmission to universities, businesses and other various places. In addition, service providers can offer a public W-LAN service on restricted areas such as a subway. The proliferation of W-LAN has led to greater W-LAN service demands, but problems are also on the rise in offering a good W-LAN service. In particular, urban areas with high radio wave interference and many buildings are vulnerable to deteriorated QoS including disconnected data and errors. For example, when high-speed data is transmitted in such areas, the relatively high frequency generates ISI between Access Points (AP) and Mobile Terminals (such as a notebook computer), leading to a frequency selective fading channel environment. Consequently, it is difficult to expect a goodW-LAN service. The simulation proves that the OFDM system enables W-LAN to implement QoS in high-speed data transmission in a multi-path fading channel environment. The enhanced OFDM performance with 52 sub-carriers is verified via data modulation methods such as BPSK, QPSK and 16QAM based on IEEE 802.11a and punched convolutional codes with code rate of 1/2 and 3/4 and constraint length of 7. Especially, the simulation finds that the OFDM system has better performance and there is no data disconnection even in a mobile environment by applying a single tap equalizer and a decision feedback equalizer to a mobile channel environment with heavy fading influence. Given the above result, the OFDM system is an ideal solution to guarantee QoS of the W-LAN service in a high-speed mobile environment.