• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.4
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• pp.767-783
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• 2013

This paper aims at designing a selective demodulation scheme based on Log-likelihood Ratio threshold (SDLT) instead of the conventional adaptive demodulation (ADM) scheme, by using rateless codes. The major difference is that the Log-likelihood ratio (LLR) threshold is identified as a key factor to control the demodulation rate, while the ADM uses decision region set (DRS) to adjust the bit rate. In the 16-QAM SDLT scheme, we deduce the decision regions over an additive white Gaussian channel, corresponding to the variation of LLR threshold and channel states. We also derived the equations to calculate demodulation rate and bit error rate (BER), which could be proven by simulation results. We present an adaptation strategy for SDLT, and compare it with ADM and adaptive modulation (AM). The simulation results show that our scheme not only significantly outperforms the ADM in terms of BER, but also achieves a performance as good as the AM scheme. Moreover, the proposed scheme can support much more rate patterns over a wide range of channel states.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.12-18
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• 2012

In this paper, we propose an improved analysis of transmission power of BTHP applied into the downlink multi-user (MU) multi-input multi-output (MIMO) system. On the contrary to the conventional analysis that adopts the strong interference assumption for every users in the system, the proposed analysis approximates the characteristics of the actual interference components so that provides more accurate approximation of the transmission power than that from the conventional analysis. By computer simulations, it is observed that the proposed approximation is more accurate than the conventional one, especially in the case of 4-QAM modulation.

• Journal of electromagnetic engineering and science
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• v.6 no.3
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• pp.189-195
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• 2006

In this paper, the derivation of the protection ratio for the digital microwave system with diversity is newly suggested for a basic guidance of initial planning for frequency coordination, and computational results are presented for an actual radio frequency band. The net filter discrimination has been also examined to see the effect of the adjacent channel protection ratio caused by adjacent channel interference. In addition, the protection ratios for the space or frequency diversity system are analyzed in terms of diversity improvement factors to find out an equivalent allowable noise-to-interference ratio (N/I) from degraded fade margin. According to results for 6.2 GHz system, with the space diversity of 25 m distance between antennas or the frequency diversity of ${\Delta}f/f=0.05$, under 64-QAM and 60 km at BER $10^{-6}$, the protection ratio can be greatly reduced in comparison to the non-diversity system. So, assuming that only the same protection ratio as the non-diversity system is kept, it is shown that the system with diversity may get more interference level of N/I allowing from 9.0 to - 5.9 dB or from 6.0 to - 4.3 dB for the space or frequency diversity. In consequence, it is concluded that the diversity system is more robust or tolerable for interferences or fades, which may play an important role in overcoming N/I to some extent.

• ETRI Journal
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• v.26 no.5
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• pp.375-383
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• 2004

This paper proposes a common interleaving method associated with independent channel-encoding among transmitter antenna branches in orthogonal frequency and code division multiplexing based on multiple-input multiple-output (MIMO) multiplexing to achieve an extremely high throughput such as 1 Gbps using a 100 MHz bandwidth. This paper also investigates the average packet error rate performance as a function of the average received signal energy per bit-to-background noise power spectrum density ratio $(E_b/N_0)$. We found that the loss in the required average received $E_b/N_0$ of the proposed method is only within approximately 0.3 dB in up to a 12-path Rayleigh fading channel, using 16QAM and Turbo coding with a coding rate of 5/6. We also clarify that even for a large fading correlation among antenna branches, 1 Gbps is still possible by increasing the transmission power. Therefore, the proposed method reduces the processing rate to 1/4 in the turbo decoder with only a slight loss in the required average received $E_b/N_0$.

• Journal of Satellite, Information and Communications
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• v.9 no.4
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• pp.82-86
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• 2014

In this paper, we propose a novel modulation scheme specialized in real time broadcast system using a multicopter. Since multicopters have many advantages in aerial photography, they have been widely used in broadcasting technologies. However, because of restrictions on flight time, it is difficult to utilize multicopters in real time broadcasting systems. Therefore, video transmission using multicopter is necessary for low power communication techniques in air channel environment. Performance results of the hybrid modulation in this paper are compared to that of conventional modulations with Bit Error Rate (BER) and Signal to Noise Ratio (SNR) simulations. The results also showed that proposed system is suitable for aerial photography. Experiments demonstrated the superiority of the proposed modulation scheme by showing received symbols through an USRP equipment.

• Journal of electromagnetic engineering and science
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• v.14 no.4
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• pp.393-398
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• 2014

A highly efficient dual-mode linear CMOS stacked-FET power amplifier (PA) is implemented for 3G UMTS and 4G LTE handset applications. High efficiency is achieved at a backed-off output power ($P_{out}$) below 12 dBm by employing an active-bypass amplifier, which consumes very low quiescent current and has high load-impedance. The output paths between high- and low-power modes of the PA are effectively isolated by using a bypass switch, thus no RF performance degradation occurs at high-power mode operation. The fabricated 900 MHz CMOS PA using a silicon-on-insulator (SOI) CMOS process operates with an idle current of 5.5 mA and shows power-added efficiency (PAE) of 20.5%/43.5% at $P_{out}$ = 12.4 / 28.2 dBm while maintaining an adjacent channel leakage ratio (ACLR) better than -39 dBc, using the 3GPP uplink W-CDMA signal. The PA also exhibits PAE of 35.1% and $ACLR_{E-UTRA}$ of -33 dBc at $P_{out}$ = 26.5 dBm, using the 20 MHz bandwidth 16-QAM LTE signal.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.7
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• pp.515-522
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• 2018

An orthogonal frequency division multiplexing with coded direct index modulation(OFDM-CDIM) system that can achieve higher performance and spectral efficiency than previous OFDM systems is proposed. Previous OFDM with index modulation(IM) and OFDM-IM using dual modes systems allocate additional data to indices of respective subcarriers through combining operation with high complexity and then transmit them. However, the proposed system directly allocates the mode selection information to each subcarrier without performing additional operations. Then, the system selects and transmits one symbol in the selected mode. Furthermore, only the data allocated to the index of the subcarrier is encoded, and a good performance improvement effect is obtained with a high code rate. Simulation results show quantitatively that an OFDM-CDIM system using four modes improves bit error rate performance and transmission efficiency in additive white Gaussian noise and Rayleigh fading channel environments compared with a conventional OFDM system using 4-ary quadrature amplitude modulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.6
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• pp.726-732
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• 2019

In this study, we proposed an asymmetric differential inductor to improve the linearity of differential power amplifiers. Considering the phase error between differential signals of the differential amplifier, the location of the center tap of the differential inductor was modified to minimize the error. As a result, the center tap was positioned asymmetrically inside the differential inductor. With the asymmetric differential inductor, the AM-to-AM and AM-to-PM distortions of the amplifier were suppressed. To confirm the feasibility of the inductor, we designed a 2.4 GHz differential CMOS PA for IEEE 802.11n WLAN applications with a 64-quadrature amplitude modulation (QAM), 9.6 dB peak-to-average power ratio (PAPR), and a bandwidth of 20 MHz. The designed power amplifier was fabricated using the 180-nm RF CMOS process. The measured maximum linear output power was 17 dBm, whereas EVM was 5%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9C
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• pp.771-777
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• 2010

This paper proposes a new signal detection method, called QR-OSIC with Candidates (QOC) method, for spatially multiplexed multiple input multiple output (MIMO) systems. By using the ordered successive interference cancellation (OSIC) algorithm and the maximum likelihood (ML) metric, the proposed method achieves near-ML performance without requiring a large number of candidates. Although the proposed method can be used for both hard and soft decoding systems, it is especially useful for soft decoding systems since the LLR values for all the bits can be efficiently computed without using LLR estimation. The proposed method is also suitable for VLSI implementation since it leads to fixed throughput system.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.6
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• pp.802-809
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• 2014

This paper presents a dual-mode bias modulator (BM) for complementary metal oxide semiconductor (CMOS) power amplifiers (PAs). The BM includes a hybrid buck converter and a normal buck converter for an envelope tracking (ET) mode for high output power and for an average power tracking (APT) mode for low output power, respectively. The dual-mode BM and CMOS PA are designed using a $0.18-{\mu}m$ CMOS process for the 1.75 GHz band. For the 16-QAM LTE signal with a peak-to-average power ratio of 7.3 dB and a bandwidth of 5 MHz, the PA with the ET mode exhibited a poweradded efficiency (PAE) of 39.2%, an EVM of 4.8%, a gain of 19.0 dB, and an adjacent channel leakage power ratio of -30 dBc at an average output power of 22 dBm, while the stand-alone PA has a PAE of 8% lower at the same condition. The PA with APT mode has a PAE of 21.3%, which is an improvement of 13.4% from that of the stand-alone PA at an output power of 13 dBm.