• Title/Summary/Keyword: OFDM Communication

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The Efficient Detection Algorithm of Various CR signals using Channel Bonding in TV White Space (TV White Space에서 채널 본딩된 다양한 CR 시스템의 효율적인 검출 알고리즘)

  • Lim, Sun-Min;Jung, Hoi-Yoon;Jeong, Byung-Jang
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.5A
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    • pp.536-542
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    • 2011
  • For efficient utilization of spectrum resources in TV white space after DTV transition, FCC allowed usage of the spectrum for CR system. The CR system is required to cognize channel usage state for utilizing the unused spectrum in TV white space which coexists various primary and secondary systems. In the meantime, as a demand for high throughput communication had been increased recently, CR systems also consider to adopt channel bonding technology, thus spectrum sensing for channel bonded system is essentially required. In this paper, we propose a novel spectrum sensing algorithm for channel bonding system using a single channel receiver. For IEEE 802.l1af signal, the proposed algorithm provide detection probability of 90% with false alarm probability 10% at SNR -18dB for single channel system and at SNR -7dB for 8 channel bonded system, respectively. Utilizing the proposed scheme, we can detect channel bonded signal using only a single receiver, therefore system overhead for spectrum sensing can be reduced significantly.

Guard Interval Extension for Individual Users in Uplink OFDMA Mobile Communication Systems (상향링크 OFDMA 이동통신 시스템에서의 개별 사용자의 보호구간 확장)

  • Rim, Min-Joong;Lim, Dae-Woon;Jeong, Byung-Jang;Noh, Tae-Gyun
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.5A
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    • pp.417-425
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    • 2007
  • While the cyclic prefix lengths of downlink OFDMA(Orthogonal Frequency Division Multiple Access) systems are determined based on the maximum delay spreads encountered in cellular environments, the guard interval of uplink OFDMA systems should consider the timing offsets of uplink signals as well as the delay spread lengths. Especially in the cases of initial accesses, handovers, and considerable time elapsed without data transmissions between base and mobile stations in a large cell, uplink timing offsets can be large and a very long guard interval length may be required. In order to keep the small size of the cyclic prefix in uplink OFDMA systems, the systems require a method of extending the guard intervals for users with large timing offsets without affecting the cyclic prefix length of the system. This paper proposes a method extending the guard intervals of individual users in uplink OFDMA systems.

A RF MEMS Transmitter Based on Flexible Printed Circuit Boards (연성 인쇄 회로 기판을 이용한 초고주파 MEMS 송신기 연구)

  • Myoung, Seong-Sik;Kim, Seon-Il;Jung, Joo-Yong;Yook, Jong-Gwan
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.19 no.1
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    • pp.61-70
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    • 2008
  • This paper presents the flexible MEMS transmitter based on flexible printed circuit board or FPCB, which can be transformed to arbitrary shape. The FPCB is suitable to fabricate light weight and small size modules with the help of its thin thickness. Moreover a module based on FPCB can be attached on the arbitrary curved surface due to its flexible enough to be lolled up like paper. In this paper, the flexible MEMS transmitter integrated on FPCB for a short-distance sensor network which is based on orthogonal frequency division multiplexing(OFDM) communication system is proposed. The active device of the proposed flexible MEMS transmitter is fabricated on InGaP/GaAs HBT process which has been used for power amplifier design to take advantages of high linear and high efficient characteristics. Moreover, the passive devices such as the filter and signal lines are integrated and fabricated on the FPCB board. The performance of the fabricated flexible MEMS transmitter is analyzed with EVM characteristics of the output signal.

A Analysis on wireless performance of unified data transmission in a subway and railway (18GHz 차지상간통합데이터전송 시스템의 지하 및 지상구간 무선특성 분석)

  • Jeong, Sang-Guk;An, Tae-Ki;Kim, Baek-Hyun;Choi, Gab-Bong
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.13 no.6
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    • pp.1083-1090
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    • 2009
  • In 18GHz using unified data transmission in a subway and railway, Influence of the multipath fading is big and an arrival range of the micro wave takes the influence greatly according to the transmit angle and receive angle because it not diffracted. This thesis analyzed microwave property underground tunnel and ground railway at unified data transmission in subway and railway. Antenna gain of directional antenna many used unified transmission in an subway and railway, is used 15dBi and 10dBi in simulation. Transmitter's property is compared underground tunnel to ground railway about curved railway of R=100, R=200, R=400. Specification of transmitter is used sample unified transmission system in subway and railway of KRRI(korea railroad research Institute). Transmitter's power is 20dBm and Reciever's sensitivity is -90dBm. According to result of simulation.

A Study on the Postprocessing of Channel Estimates in LTE System (LTE 시스템 채널 추정치의 후처리 기법 연구)

  • Yoo, Kyung-Yul
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.60 no.1
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    • pp.205-213
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    • 2011
  • The Long Term Evolution (LTE) system is designed to provide a high quality data service for fast moving mobile users. It is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the training samples which are systematically built within the transmitting data. Either a preamble or a lattice type is used for the distribution of training samples and the latter suits better for the multipath fading channel environment whose channel frequency response (CFR) fluctuates rapidly with time. In the lattice-type structure, the estimation of the CFR makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in time-and in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. All interpolation schemes should rely on the pilot estimates only, and thus, their performances are bounded by the quality of pilot estimates. However, the additive noise give rise to high fluctuation on the pilot estimates, especially in a communication environment with low signal-to-noise ratio. These high fluctuations could be monitored in the alternating high values of the first forward differences (FFD) between pilot estimates. In this paper, we analyzed statistically those FFD values and propose a postprocessing algorithm to suppress high fluctuations in the noisy pilot estimates. The proposed method is based on a localized adaptive moving-average filtering. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification. It is shown that the mean-squared error (MSE) between the actual CFR and pilot estimates could be reduced up to 68% from the noisy pilot estimates.

Unified DC Offset Cancellation and I/Q Regeneration with Carrier Phase Recovery in Five-Port Junction based Direct Receivers (Five-port 접합을 이용한 RF 수신기를 위한 동시 DC 오프셋 제거와 I/Q 신호 재생 알고리즘)

  • Park, Hyung-Chul;Lim, Hyung-Sun;Yu, Jong-Won
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.44 no.6 s.360
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    • pp.64-70
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    • 2007
  • This paper presents a novel unified DC offset cancellation and I/Q regeneration for five-port junction based direct receivers. It utilizes the symmetry characteristics of the single-frequency continuous-wave (CW) signal, making it possible that the proposed method can be used regardless of carrier phase offset. The proposed method eliminates the additional DC offset cancellation and reduces the I/Q regeneration parameter estimation time. Since the proposed method employs a single-frequency CW signal independent of the modulation scheme, five-port junction based direct receivers can be used for the demodulation of orthogonal frequency-division multiplexing and continuous phase modulation as well as phase shift-keying.

A Synchronous Digital Duplexing Technique for Wireless Transmission in Indoor Environments (옥내 환경에서 무선 전송을 위한 동기식 디지털 이중화 방식)

  • Park, Chang-Hwan;Ko, Yo-Han;Park, Kyung-Won;Jeon, Won-Gi;Paik, Jong-Ho;Lee, Seok-Pil;Cho, Yong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.12C
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    • pp.971-982
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    • 2008
  • In this paper, we propose a new digital duplexing scheme, called SDD(Synchronous Digital Duplexing), which can increase data efficiency and flexibility of resource by transmitting uplink signal and downlink signal simultaneously. In order to transmit uplink data and downlink data simultaneously, the proposed SDD obtains mutual informations between AP(access point) and each SSs(subscriber station), SS and other SSs by mutual ranging procedure. These informations are used for selection of transmission time, decision of CS insertion, setting of CS length, and FFT duration resetting, etc. It is shown that the proposed SDD is appropriate for duplexing scheme in indoor environments over the conventional TDD(Time Division Duplexing) and FDD(Frequency Division Duplexing).

An ICI Canceling 5G System Receiver for 500km/h Linear Motor Car

  • Suguru Kuniyoshi;Rie Saotome;Shiho Oshiro;Tomohisa Wada
    • International Journal of Computer Science & Network Security
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    • v.23 no.6
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    • pp.27-34
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    • 2023
  • This paper proposed an Inter-Carrier-Interference (ICI) Canceling Orthogonal Frequency Division Multiplexing (OFDM) receiver for 5G mobile system to support 500 km/h linear motor high speed terrestrial transportation service. A receiver in such high-speed train sees the transmission channel which is composed of multiple Doppler-shifted propagation paths. Then, a loss of sub-carrier orthogonality due to Doppler-spread channels causes ICI. The ICI Canceler is realized by the following three steps. First, using the Demodulation Reference Symbol (DMRS) pilot signals, it analyzes three parameters such as attenuation, relative delay, and Doppler-shift of each multi-path component. Secondly, based on the sets of three parameters, Channel Transfer Function (CTF) of sender sub-carrier number 𝒏 to receiver sub-carrier number 𝒍 is generated. In case of 𝒏≠𝒍, the CTF corresponds to ICI factor. Thirdly, since ICI factor is obtained, by applying ICI reverse operation by Multi-Tap Equalizer, ICI canceling can be realized. ICI canceling performance has been simulated assuming severe channel condition such as 500 km/h, 2 path reverse Doppler Shift for QPSK, 16QAM, 64QAM and 256QAM modulations. In particular, for modulation schemes below 16QAM, we confirmed that the difference between BER in a 2 path reverse Doppler shift environment and stationary environment at a moving speed of 500 km/h was very small when the number of taps in the multi-tap equalizer was set to 31 taps or more. We also confirmed that the BER performance in high-speed mobile communications for multi-level modulation schemes above 64QAM is dramatically improved by the use of a multi-tap equalizer.

Design and Performance Evaluation of Selective DFT Spreading Method for PAPR Reduction in Uplink OFDMA System (OFDMA 상향 링크 시스템에서 PAPR 저감을 위한 선택적 DFT Spreading 기법의 설계와 성능 평가)

  • Kim, Sang-Woo;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.18 no.3 s.118
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    • pp.248-256
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    • 2007
  • In this paper, we propose a selective DFT spreading method to solve a high PAPR problem in uplink OFDMA system. A selective characteristic is added to the DFT spreading, so the DFT spreading method is mixed with SLM method. However, to minimize increment of computational complexity, differently with common SLM method, our proposed method uses only one DFT spreading block. After DFT, several copy branches are generated by multiplying with each different matrix. This matrix is obtained by linear transforming the each phase rotation in front of DFT block. And it has very lower computational complexity than one DFT process. For simulation, we suppose that the 512 point IFFT is used, the number of effective sub-carrier is 300, the number of allowed sub-carrier to each user's is 1/4 and 1/3 and QPSK modulation is used. From the simulation result, when the number of copy branch is 4, our proposed method has more than about 5.2 dB PAPR reduction effect. It is about 1.8 dB better than common DFT spreading method and 0.95 dB better than common SLM which uses 32 copy branches. And also, when the number of copy branch is 2, it is better than SLM using 32 copy branches. From the comparison, the proposed method has 91.79 % lower complexity than SLM using 32 copy branches in similar PAPR reduction performance. So, we can find a very good performance of our proposed method. Also, we can expect the similar performance when all number of sub-carrier is allocated to one user like the OFDM.

Design and Implementation of 5G mmWave LTE-TDD HD Video Streaming System for USRP RIO SDR (USRP RIO SDR을 이용한 5G 밀리미터파 LTE-TDD HD 비디오 스트리밍 시스템 설계 및 구현)

  • Gwag, Gyoung-Hun;Shin, Bong-Deug;Park, Dong-Wook;Eo, Yun-Seong;Oh, Hyuk-Jun
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.27 no.5
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    • pp.445-453
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    • 2016
  • This paper presents the implementation and design of the 1T-1R wireless HD video streaming systems over 28 GHz mmWave frequency using 3GPP LTE-TDD standard on NI USRP RIO SDR platform. The baseband of the system uses USRP RIO that are stored in Xilinx Kintex-7 chip to implement LTE-TDD transceiver modem, the signal that are transceived from USRP RIO up or down converts to 28 GHz by using self-designed 28 GHz RF transceiver modules and it is finally communicated HD video data through self-designed $4{\times}8$ sub array antennas. It is that communication method between USRP RIO and Host PC use PCI express ${\times}4$ to minimize delay of data to transmit and receive. The implemented system show high error vector magnitude performance above 25.85 dBc and to transceive HD video in experiment environment anywhere.