• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2391-2396
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• 2010

The power-controlled six-port element that can control the local oscillator signal power and receiving RF signal power was designed and implemented in this paper. The direct conversion six-port element configuration was proposed, which provides the constant six-port output power by controlling the six-port input power with various signal strength. The direct conversion six-port element protects the power detector element of six-port receiver from the saturation status and compensates the transmission performance degradation. For implementation of power-controlled six-port element, the power-controlled six-port element including the power controller was analyzed. The implemented power-controlled six-port element shows the power control capability of 36 dB and gain imbalance of about 1.6 dB, phase imbalance of about $4^{\circ}$ in the frequency range of 1.69 GHz. The measured results show the good performance as direct conversion front-end element.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.5
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• pp.1071-1077
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• 2010

The six-port phase correlator using lumped elements was designed and fabricated in this paper, also the receiving performance of L-band direct conversion receiver using lumped six-port phase correlator element was analyzed. The proposed L-band lumped six-port phase correlator element was composed of a resistive power divider and the twist-wire coaxial cables. The proposed lumped six-port structure provides the small-sized configuration and wide-band characteristics. The performance of the L-band lumped direct conversion receiver structure was measured under the conditions of 1.69 GHz frequency for LO-CW signal and RF-QPSK signal, which are input signals for the lumped six-port phase correlator element. The direct conversion receiving structure using the proposed lumped six-port phase correlator element can recovered the good digital I/Q signal.

• Journal of Broadcast Engineering
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• v.21 no.5
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• pp.803-815
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• 2016

In this paper, we design a direct radio frequency (RF) sampling receiver for multiband GNSS signals and demonstrate its performance. The direct RF sampling is a technique that does not use an analog mixer, but samples the passband signal directly, and all receiver processes are done in digital domain, whereas the conventional intermediate frequency (IF) receiver samples the IF band signals. In contrast to the IF sampling receiver, the RF sampling receiver is less complex in hardware, reconfigurable, and simultaneously converts multiband signals to digital signals with an analog-to-digital (AD) converter. The reconfigurability and simultaneous reception are very important in military applications where rapid change to other system is needed when a system is jammed by an enemy. For simultaneous reception of multiband signals, the sampling frequency should be selected with caution by considering the carrier frequencies, bandwidths, desired intermediate frequencies, and guard bands. In this paper, we select a sampling frequency and design a direct RF sampling receiver to receive multiband global navigation satellite system (GNSS) signals such as GPS L1, GLONASS G1 and G2 signals. The receiver is implemented with a commercial AD converter and software. The receiver performance is demonstrated by receiving the real signals.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.222-225
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• 2003

본 논문에서는 six port 를 사용한 실시간 디지털 직접 변환 수신기를 소개하고 실제 six port 구조를 이용해 구현된 직접 변환 수신기의 성능을 분석한다. 제안한 알고리즘은 송신단과 수신단의 위상 오류를 보정하고 랜덤한 채널 잡음 환경에서도 성능의 저하가 크지 않다. 다음으로는 위상 오류 추정 방법을 사용하여 수신기에서의 성능 향상을 컴퓨터 시뮬레이션을 통해서 살펴보았다.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.2
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• pp.18-26
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• 2015

In this paper, we studied the method for analyzing and estimating the parameters that induce I/Q imbalance in the repeater using direct conversion RF. In repeater, amplitude, phase, and filter mismatch are generated in the receiving-end which converts RF signal to baseband signal. And amplitude and phase mismatch are generated in the transmitting-end which converts baseband signal to RF signal. Accordingly, we modeled the parameters that cause I/Q imbalance in the structure of the repeater in order, and proposed a feedback test structure from the transmitting-end to the receiving-end for estimating the corresponding parameters. By comparing the test transmitting signal and received signal, it is possible to estimate the I/Q imbalance parameters which occurred from mixed components of real and imaginary part. And it was confirmed that I/Q imbalance phenomenon has been properly compensated with estimated parameters at the direct conversion RF repeater.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1397-1398
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• 2008

본 논문에서는 BPSK 수신을 위한 덧셈(sum) 방식의 4-port 직접 변환 수신기를 제안하고, 국부 발진기(LO) 전력의 크기에 대한 수신기의 성능을 분석하였다. 수신 성능 분석에는 열잡음, 전력 검출기의 산탄(shot) 잡음, LO의 위상 잡음을 고려하였다. 수신 성능 분석 결과 최적의 신호대 잡음비를 보이는 최적의 LO 전력이 존재할 수 있음을 보였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.11
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• pp.2267-2272
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• 2009

The six-port direct conversion receiver front-end that is comprised of a carrier recovery and a phase shifter, which gets the same structure with six-port phase correlator using the multi-layer coupled line, was designed and fabricated in this paper. The six-port element that is comprised of the power divider and the hybrid coupler is designed by multi-layer coupled line structure. The multi-coupled structure is utilized as the basic structure in receiver phase correlator, carrier recovery circuit and phase shifter. The receiver front-end with the same multi-layer coupled line structure for the receiver elements shows the simple structure and no difficulty in integration. The fabricated multi-layer coupled six-port receiver front-end re-generates the carrier signal with a constant phase and demodulates the PSK transmission signal.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.6 s.324
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• pp.1-7
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• 2004

The development of direct receiver techniques is expected to be a solution for future wideband or multi-band wireless systems based on software defined radio. In this Paper, we study the regeneration of I and Q signals for the SDR based direct conversion receiver, so that we can handle a wide bandwidth and maintain maximal flexibility in system utilization. After modeling the basic system considering the real wireless communication environment, and studying the impact of imperfect phase imbalance on the performance of a direct conversion receiver, we propose a suboptimal I and Q signal regeneration algorithm for the system. The proposed algerian regenerates I and Q signals using a real time early-late compensator which effectively estimates phase imbalances and gives feedback in a directreceiver. The proposed algorithm is shown to mitigate the impact of AWGN and improves performance especially at low SNR channel condition. According to the computer simulation, the BER performance of the proposed system is at least about 4 dB better than conventional systems under $45{\~}55$ degrees random phase errors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.730-735
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• 2004

This paper describes what brings about DC offset and the impact or the DC offset on the performance or direct-conversion mobile receiver in WCDMA system. The performance degradation of $E_{b}/N_{o}$ due to the DC offset is presented through simulation result. Direct-conversion RF Transceiver which has the function of DC offset control is implemented and then applied to the WCDMA test-bed for the performance evaluation. The receiver performance degradation of $E_{c}/I_{o}$ is evaluated and analyzed by varying DC offset value. The practical test showed the minimum requirement of DC offset value to meet system performance.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.3
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• pp.41-49
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• 2003

본 고에서는 휴대 이동단말 시스템의 복합다기능화 및 단말기내 적용되는 주파수 변조 방식의 변화에 따른 핵심부품으로서 표면탄성파필터의 요구 성능의 변화 및 그에 따른 대응방향에 대해서 설명하고 있다. 현재 전세계적으로 널리 보급되고 있는 코드분할다중접속방식(CDMA)의 이동단말기에서는 수퍼헤테로다인 변복조방식의 적용에 따라 표면탄성파 소자로서 듀플렉서, 송신 RF 필터, 수신 RF 필터 및 수신 IF 필터 등이 적용되어 왔다. 하지만 최근 들어 RF 대역에서 기저대역으로 신호의 직접변환(Direct Conversion)이 가능한 Chipset의 보급과 더불어 급속히 Zero-IF화가 추진되고 있으며, 그에 따라 RE 필터부의 고성능화가 요구되고 있다. Zero-IF Chipset은 신호대 잡음비를 크게 하기 위해서 수신 RE 필터에 있어서 Balance 구동을 기본으로 하고 있으며, 듀플렉서에 있어서는 통과대역의 저손실화, 저지대역의 고감쇠화 및 송수신간 높은 격리도를 요구하고 있다. 본 고에서는 이러한 요구사항을 만족시킬 수 있는 표면탄성파 필터의 구현 원리와 향후 동향에 대해 논의하였다.