• Journal of electromagnetic engineering and science
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• v.4 no.1
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• pp.17-22
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• 2004

In this paper, we implement an efficient MLC/PDL system for AWGN channels. In terms of the tradeoff between the hardware implementation and system performance, proposed algebra LDPC codes are optimized by the Gaussian approximation(GA) according to the rate of each level assigned by the capacity rule and chosen as the component code. System performance with Ungerboeck Partitioning(UP), Miked Partitioning(MP) and Gray Mapping(GM) of 8PSK are evaluated, respectively. Many results are presented in this paper; they can indicate that the proposed MLC/PDL system using optimized algebra LDPC codes with different code rate, capacity rule and Gray mapping(GM) can achieve the best performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4A
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• pp.502-511
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• 2000

The Gaussian Minimum Shift Keying (GMSK) modulation technique belongs to the class of nonlinear modulation technique, and it is known to be bandwidth efficient. The GMSK modulation is chosen for the digital cellular phone standard by the European Telecommunications Standards Institute (ETSI). In this paper, an efficient method for implementing all digital GMSK modulator is introduced. The proposed modulator is shown to be simple to implement as well as satisfying the required spectral shape recommended by the ETSI.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.3-10
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• 2016

To establish a network environment where multiple wireless personal area networks(WPAN) are simultaneously operating in the same area, we need to consider the effects of inter-device interference. The extent of interference effect from neighboring frequency channel interferer may be different depending on the modulation types that are used for constructing the wireless network. If a modulation scheme with high spectral side lobes is used, the spatial separation between devices plays a major role in determining the amount of interference from neighboring frequency channel interferer. In this paper, we investigate the effect of inter-device interference in the overlapped raised cosine offset quadrature-quadrature phase shift keying (ORC-$OQ^2PSK$) modulation based WPAN. By comparing the results with those of GFSK modulation based WPAN, we verify the feasibility of ORC-$OQ^2PSK$ based WPAN.

• Journal of Internet Computing and Services
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• v.9 no.1
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• pp.21-32
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• 2008

In this paper, we propose new modulation schemes using the conventional CACB (Constant Amplitude Coded Multicode Biorthogonal) modulation with constant amplitude property. Also the proposed modulation schemes supports high transmission data rate by increasing the spectral efficiency, In order to obtain the high spectral efficiency, the $Q^2$AM (Quadrature-Quadrature Amplitude Modulation) and CA-$Q^2$AM (Constant Amplitude-$Q^2$AM) are used. We explain the simplest combining modulation scheme of CACB and $Q^2$AM (i.e., CACB-$Q^2$AM). However, this modulation scheme cannot support the constant amplitude property. Hence the first CACB-CA-$Q^2$AM (or CACB-CA-$Q^2$AM I) modulation scheme is proposed for the constant amplitude property. In the modulation scheme, the redundant constant amplitude encoding (spectral efficiency decrease) is required. Therefore, the second CACB-CA-$Q^2$AM (or CACB-CA-$Q^2$AM II) modulation scheme is proposed retaining the constant amplitude and the spectral efficiency. Computer simulations show that the proposed CACB-CA-$Q^2$AM II is the efficient modulation scheme.

• Journal of Satellite, Information and Communications
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• v.7 no.1
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• pp.65-74
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• 2012

The QoS guarantee for the forward link in satellite communication networks is very important because there are a variety of packets with multiplexing. Especially, the packets are processed depending on the available bandwidth in satellite network changing the wireless channel state in accordance with weather condition. The DVB-S2 increases the transmission efficiency by applying the adaptive coding and modulation (ACM) techniques as a countermeasure of rain attenuations. However, the channel estimation algorithm is required to support the ACM techniques that select the MODCOD values depending on the feedback data transmitted by RCSTs(Return Channel via Satellite Terminal) because satellite communication networks have a long propagation delay. In this paper, we proposed the channel estimation algorithm using rain attenuation values and reference data and the packet scheduling scheme to support the QoS and fairness. As a result of performance evaluation, we showed that proposed algorithm exactly predicts the channel conditions and supports bandwidth fairness to the individual RCST and guarantees QoS for user traffics.

• 전자공학회논문지 IE
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• v.43 no.2
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• pp.80-86
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• 2006

The wireless communication based on LDPC and adaptive spatial-subcarrier coded modulation using MQAM for orthogonal frequency division multiplexing (OFDM) wireless transmission by using instantaneous channel state information and employing multiple antennas at both the transmitter and the receiver. Adaptive coded modulation is a promising idea for bandwidth-efficient transmission on time-varying, narrowband wireless channels. On power limited Additive White Gaussian Noise (AWGN) channels, low density parity check (LDPC) codes are a class of error control codes which have demonstrated impressive error correcting qualities, under some conditions performing even better than turbo codes. The paper demonstrates OFDM with LDPC and adaptive modulation applied to Multiple-Input Multiple-Output (MIMO) system. An optimization algorithm to obtain a bit and power allocation for each subcarrier assuming instantaneous channel knowledge is used. The experimental results are shown the potential of our proposed system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.11
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• pp.4419-4435
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• 2015

The use of an efficient packet scheduling scheme for a forward link in satellite communication networks is very important to support fairness for each return channel satellite terminal (RCST) and the service differentiations for user traffics. To support fairness and QoS for each RCST with service-level agreement (SLA), the Adaptive Coding and Modulation (ACM) system in a satellite hub has to process packets with considering modulation and coding (MODCOD) and packet types. Although a DVB-S2 system with ACM scheme has higher transmission efficiency, it cannot offer fairness or quality of service (QoS) to RCSTs. Because the data are transmitted with high MODCOD in regions with clear skies, while data are transmitted using low MODCOD in regions experiencing rain events. In this paper, we propose a two-step scheduling scheme offering fairness and QoS to RCSTs, while minimizing a decrease in throughput. The proposed scheme is carried out performance evaluations using a computer simulation. As results of this simulation, the proposed scheduler was shown to support bandwidth fairness to an individual RCST, and provide a level of QoS differentiation for user traffics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.3
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• pp.289-295
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• 1998

The purpose of this paper is to propose an improvement method of BER for coded 16-QAM under Rayleigh fading channel. To overcome the BER degradation due to the fading under mobile communication, we apply delay modulation technique which is efficient to get both a coding gain and approximately one-half those needed by Manchester coding on bandwidth requirements. Especially, the delay modulation scheme is insensitive to the $180^{\circ}$phase ambiquity common to NRZ-L and Manchester coding schemes. From the computer simulation, BER performance of our scheme has achieved about 3.8 dB improvement of about $10^{-4}$, compared to Manchester coded 16-QAM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.4
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• pp.519-529
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• 1993

A spectral and power efficient modulation technique, named Compact Superposed Quadrature Amplitude Modulation (Compact-SQAM), is introduced. The performance of Compact-SQAM system, in a Linearly and nonlinearly amplified single and multicarrier environment, in the presence of additive white Gaussian noise(AWGN), intersymbol interference(ISI), timing jitter and adjacent channel interference (ACI), is experimentally analyzed via computer simulation. Various channel conditions, such as channel spacing, between the main and adjacent channels and fade depth on the desired main channel, are examined. Our result shows that Compact-SQAM, and better P(e) performance that other modems using simple Butteroworth type postdetection receive filters. Especially, Compact-SQAM modem achieves higher efficiency of frequency utilization and better P(e) performance than other modems in the severly bandlimited nonlinear multicarrier channels.

• ETRI Journal
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• v.34 no.5
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• pp.649-654
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• 2012

This paper presents a novel 16-quadrature-amplitude-modulation (QAM) E-band communication system. The system can deliver 10 Gbps through eight channels with a bandwidth of 5 GHz (71-76 GHz/81-86 GHz). Each channel occupies 390 MHz and delivers 1.25 Gbps using a 16-QAM. Thus, this system can achieve a bandwidth efficiency of 3.2 bit/s/Hz. To implement the system, a driver amplifier and an RF up-/down-conversion mixer are implemented using a $0.1{\mu}m$ gallium arsenide pseudomorphic high-electron-mobility transistor (GaAs pHEMT) process. A single-IF architecture is chosen for the RF receiver. In the digital modem, 24 square root raised cosine filters and four (255, 239) Reed-Solomon forward error correction codecs are used in parallel. The modem can compensate for a carrier-frequency offset of up to 50 ppm and a symbol rate offset of up to 1 ppm. Experiment results show that the system can achieve a bit error rate of $10^{-5}$ at a signal-to-noise ratio of about 21.5 dB.