• Title/Summary/Keyword: Uplink signal

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Optimum Uplink Power/Rate Control for Minimum Delay in CDMA Networks

  • Choi, Kwon-Hue;Kim, Soo-Young
    • ETRI Journal
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    • v.25 no.6
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    • pp.437-444
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    • 2003
  • We derive a new joint power and rate control rule with which we can minimize the mean transmission delay in CDMA networks for a given mean transmission power. We show that it is optimal to respectively control the power inverse-linearly and the rate linearly to the square root of channel gain while maintaining the signal-to-interference ratio at a constant. We also show that the proposed joint power/rate control rule achieves excellent performance results in terms of the probability of the instantaneous delay being within a target delay against one-dimensional control schemes.

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Efficient Interference Alignment for Uplink MIMO/FDD Systems with Limited Feedback (제한된 궤환 채널 기반 상향링크 MIMO/FDD 시스템에서의 효율적인 간섭 정렬 기법)

  • Cho, Sung-Yoon;Jang, Jin-Young;Kim, Dong-Ku
    • Journal of Advanced Navigation Technology
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    • v.16 no.6
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    • pp.988-996
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    • 2012
  • Assuming perfect channel state information (CSI), the conventional interference alignment (IA) algorithm in the uplink cellular system suppresses inter-cell interference (ICI) by aligning ICI to a randomly selected reference vector. However, IA in practice relies on limited feedback between base stations and users, resulting in residual ICI. In this paper, we propose the optimization of the reference vector that minimizes the upper-bound of residual ICI power. Secondly, the iterative IA that designs the direction of transmit and receive filter is proposed to minimize the residual ICI as well as maximize the desired signals. Moreover, we propose the user scheduling method combined with proposed IA schemes which provides the multiuser diversity gain in multi-cell environments. Finally, the performance gain of the proposed IA algorithms compared with the existing IA are analyzed and demonstrated by simulation results.

Uplink Frequency Offset Compensation Scheme for High-Speed Moving Terminals (고속 이동체를 위한 상향링크 주파수 옵셋 보상 방법)

  • Choi, Sung-woo;Kim, Ilgyu;Ahn, Jae Min
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.9
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    • pp.1699-1709
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    • 2015
  • Moving terminals like high-speed-train undergo high Doppler frequency shift, and this leads to carrier frequency offsets that have to be compensated to avoid degradation of communication performance. In multiple access mechanism like OFDMA, base-stations need complex hardware to compensate the uplink frequency offset. In this paper, we propose a method, which can reduce burden of the base-station and makes frequency offset estimation and compensation simple. This method contains transmitting new synchronization signal, estimating frequency offsets in base-station, transmitting feedback information to terminal, and compensating the offset in uplink transmission. Simulation results show the proposed method operates well in high Doppler frequency shift conditions of 500 km/h which is the requirements of 5G mobile communication.

A Tradeoff of Multiplexing Gain and Pilot Overhead in Multi-User OFDM Virtual MIMO Uplink Systems (상향링크 다중 사용자 기반 가상적 MIMO-OFDM 시스템의 파일럿 오버헤드와 다중화 이득의 트레이드오프)

  • Ran, Rong;Cho, Sung-Yoon;Kim, Yo-Han;Kim, Dong-Ku
    • Journal of Advanced Navigation Technology
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    • v.12 no.5
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    • pp.437-443
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    • 2008
  • In this paper, we derive the optimum number of users which can maximize the information theoretic sum capacity in multiuser OFDM virtual MIMO uplink system. In which, there are multiple antennas at the base station and a number of users with single transmit antenna. Pilot-assisted channel state estimation is assumed for a block fading channel and time-varying fading channel. We analyze the tradeoff between the multiplexing gain and pilot overhead especially in low SNR regime and conclude that the optimum number of users is min ($N_r$,LT/2 ) in frequency nonselective block fading channel and approximately equal to min ($N_r$, ${\lfloor}{\sqrt{LT+1}}-1{\rfloor}$) in time varying fading channel. assuming the same pilot and signal pwoer.

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The Error Performance of PSK Satellite Communication System with a Soft Limiter Type Transponder in Jamming Environments (소프트리미터형 중계기를 장치한 PSK 위성통신 시스템의 Jamming 환경하에서의 오율특성)

  • 강영흥;조성언;조성준
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.16 no.11
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    • pp.1084-1094
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    • 1991
  • Upon introducing satellite communication system to korea, one of the important problems to copy with is the effect from the probable intentional interference i. e. jamming. In this paper, we have considered the M any PSK signal and the soft limiter type, which contains hard limiter, nonhnear satellite transponder in environments of uplink tone or noise jamming plus Gaussian noise and downlink Gaussian noise. Using the derived error rate equation, we have evaluated numerically the error performance of BPSK and QPSK system, and shown in figures in terms of upink and downink earner to jamming rater(CJR) and limiting level. From the results we have known that tone jamming effect on the error performance in BPSK and QPSK signals in nonlinear satelhie shnnel become less with increasing the uplink CNR and with decreasing the liniting level. And in a tone jamming, the limiting level affects hardly on the error performance of both BPSK and QPSK signals. When limiting leveri is zero, BPSK and QPSK signals show the best error rate performance.

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A Tx-Rx Beam Tracking Technique for Cellular Communication Systems with a mmWave Link (밀리미터 웨이브 링크를 갖는 셀룰러 통신 시스템을 위한 송·수신 빔 추적 기법)

  • Kim, Kyu Seok;Lim, Tae Sung;Choi, Joo Hyung;Cho, Yong Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39C no.12
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    • pp.1327-1337
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    • 2014
  • In cellular communication systems employing millimeter wave (mmWave) bands for a link, a large amount of training time and network resources will be required to find a serving BS with the best transmit and receive (Tx-Rx) beam pair if downlink control signals are used. In this paper, a tracking technique for OFDM-based cellular communication systems with a mmWave link, where an analog beamforer is used at the mobile station (MS) and a digital beamformer is used at the BS, is proposed using an uplink signal. A technique to select a serving BS with the best beam pair is described using the uplink preamble sequence based on Zadoff-Chu sequence and a metrics which can be used to identify parameters such as beam ID (BID), MS ID (MID), and direction-of-arrival (DoA). The effectiveness of the proposed technique is verified via simulation with the spatial channel model (SCM) for a moving MS in mmWave cellular systems.

Performance Analysis of Asynchronous OFDMA Uplink Systems with Timing Misalignments over Frequency-selective Fading Channels (주파수 선택적 페이딩 채널에서 시간오차에 의한 비동기 OFDMA 상향 시스템의 성능 분석)

  • Park, Myong-Hee;Ko, Kyun-Byoung;Park, Byung-Joon;Lee, Young-Il;Hong, Dae-Sik
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.2A
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    • pp.34-42
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    • 2005
  • In orthogonal frequency-division multiple access (OFDMA) uplink environments, asynchronously received signals can cause multiple access interference (MAI). This paper focuses on the performance degradation due to the MAI over frequency-selective fading channels. We first introduce the timing misalignment, which is defined as the relative timing difference between asynchronous timing error of uplink user and reference time of the base station, and analytically derive the MAI using the power delay profile of wide-sense stationary uncorrelated scattering (WSSUS) channel model. Then, the effective signal-to-noise ratio (SNR) and the average symbol error probability (SEP) are derived. The proposed analytical results are verified through simulations with respect to the region of the timing misalignment and the number of asynchronous users.

Interference Mitigation Scheme using Edge Side-lobe Suppressors for OFDMA uplink Systems (직교 주파수 분할 다중 접속 방식 상향 링크에서 측부엽 억제 신호를 이용한 간섭 완화 기법)

  • 유화선;정성순;한상철;홍대식;강창언
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.12C
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    • pp.1217-1224
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    • 2003
  • In this paper, we propose an edge side-lobe suppressor (ESS) for the uplink of OFDMA systems, which mitigates the interference introduced by different frequency offsets between a desired user and the other users. We evaluate the proposed ESS scheme by measuring average signal to interference ratio (SIR) and average bit error rate (BER). The simulation results confirm that the proposed ESS scheme improves system performance by approximately 5∼10 dB SIR as compared to conventional OFDMA systems. Because the additional operations for the proposed scheme can be performed by a real-valued look-up table, the implementation of the ESS hardly requires increasing transmitter and receiver complexity.

Frequency translation approach for transmission beamforming in FDD wireless communication systems with basestation arrays (기지국 안테나 배열을 이용한 FDD 방식의 무선통신 시스템에서 송신 빔 형성을 위한 주파수 변환 방식)

  • ;Shawn P.Stapleton
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.34S no.5
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    • pp.1-14
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    • 1997
  • We consider transmission beamforming techniques for frequency-division-duplex (FDD) wireless communication systems using adaptive arrays to improve the signal quality of the array transmission link. We develop a simple effective transmission beamforming technique based on an approximated frequency tranlsation (AFT) to derive the tranmsiion beamforming weights from the uplink channel vector. This technique exploits the invariance of the short-time averaged fast fading statistics to small frequency translations. A simple approximate relationship that relates the transmission channel vector to the reception channel vector is derived. We have developed its practical alternative in which the frequency translation of the channel vector is performed at the principal angle of arrival (AOA) of the u;link synthestic angular spectrum instead of the mean AOA. To analyze the performance of the proposed methods, we consider the power loss incurred by applying the estimated channel vector instead of the true downlink channel vector. The performance is analyzed as a function of the mean AOA, the angular spread, the number of elements, frequncy difference between the uplink and the downlink, and the angle distribution. Their performance is also compared with that of the direct weight reuse method and the AOA based methods.

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Performance Analysis of OFDMA Uplink Systems with Symbol Timing Misalignment (사용자간 상대적인 시간오차에 의한 OFDMA 역방향 시스템의 성능 분석)

  • Park Myonghee;Hong Daesik
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.42 no.2 s.332
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    • pp.17-22
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    • 2005
  • This paper presents our investigation for the effect of symbol timing errors in orthogonal frequency division multiple access (OFDMA) uplink systems. We express the symbol timing errors between users as the symbol timing misalignments with respect to the desired user. Then, we derive an explicit expression of the average effective signal-to-interference-plus-noise ratio. (SINR) as a function of the maximum value of the symbol timing misalignments. Based on the resulting SINR degradation, we evaluate the SINR gain with guard subcarriers in order to mitigate the effect of the symbol timing misalignments.