• Title/Summary/Keyword: fading estimation

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Improved Parameter Estimation with Threshold Adaptation of Cognitive Local Sensors

  • Seol, Dae-Young;Lim, Hyoung-Jin;Song, Moon-Gun;Im, Gi-Hong
    • Journal of Communications and Networks
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    • v.14 no.5
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    • pp.471-480
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    • 2012
  • Reliable detection of primary user activity increases the opportunity to access temporarily unused bands and prevents harmful interference to the primary system. By extracting a global decision from local sensing results, cooperative sensing achieves high reliability against multipath fading. For the effective combining of sensing results, which is generalized by a likelihood ratio test, the fusion center should learn some parameters, such as the probabilities of primary transmission, false alarm, and detection at the local sensors. During the training period in supervised learning, the on/off log of primary transmission serves as the output label of decision statistics from the local sensor. In this paper, we extend unsupervised learning techniques with an expectation maximization algorithm for cooperative spectrum sensing, which does not require an external primary transmission log. Local sensors report binary hard decisions to the fusion center and adjust their operating points to enhance learning performance. Increasing the number of sensors, the joint-expectation step makes a confident classification on the primary transmission as in the supervised learning. Thereby, the proposed scheme provides accurate parameter estimates and a fast convergence rate even in low signal-to-noise ratio regimes, where the primary signal is dominated by the noise at the local sensors.

A Study on Improving Indoor Positioning Accuracy Using Map Matching Algorithm (맵 매칭 알고리즘을 이용한 실내 위치 추정 정확도 개선에 대한 연구)

  • Kwangjae Sung
    • Journal of the Semiconductor & Display Technology
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    • v.22 no.2
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    • pp.50-55
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    • 2023
  • Due to the unavailability of global positioning system (GPS) indoors, various indoor pedestrian positioning methods have been designed to estimate the position of the user using received signal strength (RSS) measurements from radio beacons, such as wireless fidelity (WiFi) access points and Bluetooth low energy (BLE) beacons. In indoor environments, radio-frequency (RF) signals are unpredictable and change over space and time because of multipath associated with reflection and refraction, shadow fading caused by obstacles, and interference among different devices using the same frequencies. Therefore, the outliers in the positional information obtained from the indoor positioning method based on RSS measurements occur often. For this reason, the performance of the positioning method can be degraded by the characteristics of the RF signal. To resolve this issue, a map-matching (MM) algorithm based on maximum probability (MP) estimation is applied to the indoor positioning method in this study. The MM algorithm locates the aberrant position of the user estimated by the positioning method within the limits of the adjacent pedestrian passages. Empirical experiments show that the positioning method can achieve higher positioning accuracy by leveraging the MM algorithm.

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Bit-Rate Control Using Histogram Based Rate-Distortion Characteristics (히스토그램 기반의 비트율-왜곡 특성을 이용한 비트율 제어)

  • 홍성훈;유상조;박수열;김성대
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.24 no.9B
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    • pp.1742-1754
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    • 1999
  • In this paper, we propose a rate control scheme, using histogram based rate-distortion (R-D) estimation, which produces a consistent picture quality between consecutive frames. The histogram based R-D estimation used in our rate control scheme offers a closed-form mathematical model that enable us to predict the bits and the distortion generated from an encoded frame at a given quantization parameter (QP) and vice versa. The most attractive feature of the R-D estimation is low complexity of computing the R-D data because its major operation is just to obtain a histogram or weighted histogram of DCT coefficients from an input picture. Furthermore, it is accurate enough to be applied to the practical video coding. Therefore, the proposed rate control scheme using this R-D estimation model is appropriate for the applications requiring low delay and low complexity, and controls the output bit-rate ad quality accurately. Our rate control scheme ensures that the video buffer do not underflow and overflow by satisfying the buffer constraint and, additionally, prevents quality difference between consecutive frames from exceeding certain level by adopting the distortion constraint. In addition, a consistent considering the maximum tolerance BER of the voice service. Also in Rician fading channel of K=6 and K=10, considering CLP=$10^{-3}$ as a criterion, it is observed that the performance improment of about 3.5 dB and 1.5 dB is obtained, respectively, in terms of $E_b$/$N_o$ by employing the concatenated FEC code with pilot symbols.

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Performance Evaluation of Underwater Acoustic Communication in Frequency Selective Shallow Water (주파수 선택적인 천해해역에서 수중음향통신 성능해석)

  • Park, Kyu-Chil;Park, Jihyun;Lee, Seung Wook;Jung, Jin Woo;Shin, Jungchae;Yoon, Jong Rak
    • The Journal of the Acoustical Society of Korea
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    • v.32 no.2
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    • pp.95-103
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    • 2013
  • An underwater acoustic (UWA) communication in shallow water is strongly affected by the water surface and the seabed acoustical properties. Every reflected signal to receiver experiences a time-variant scattering in sea surface roughness and a grazing-angle-dependent reflection loss in bottom. Consequently, the performance of UWA communication systems is degraded, and high-speed digital communication is disrupted. If there is a dominant signal path such as a direct path, the received signal is modeled statistically as Rice fading but if not, it is modeled as Rayleigh fading. However, it has been known to be very difficult to reproduce the statistical estimation by real experimental evaluation in the sea. To give an insight for this scattering and grazing-angle-dependent bottom reflection loss effect in UWA communication, authors conduct experiments to quantify these effects. The image is transmitted using binary frequency shift keying (BFSK) modulation. The quality of the received image is shown to be affected by water surface scattering and grazing-angle-dependent bottom reflection loss. The analysis is based on the transmitter to receiver range and the receiver depth dependent image quality and bit error rate (BER). The results show that the received image quality is highly dependent on the transmitter-receiver range and receiver depth which characterizes the channel coherence bandwidth.

An Enhanced Frequency Synchronization Algorithm for 3GPP LTE FDD/TDD Dual Mode Downlink Receiver (3GPP LTE FDD/TDD 듀얼 모드 하향 링크 수신기를 위한 개선된 주파수 동기 알고리즘)

  • Shim, Myung-Jun;Jang, Jun-Hee;Choi, Hyung-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.1C
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    • pp.103-112
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    • 2010
  • In this paper, we propose a coarse and fine frequency synchronization method which is suitable for the 3GPP(3rd Generation Partnership Project) LTE(Long Term Evolution) FDD(Frequency Division Duplexing) / TDD(Time Division Duplexing) dual mode system. In general, PSS(Primary Synchronization Signal) correlation based estimation method and CP(Cyclic Prefix) correlation based tracking loop are applied for coarse and fine frequency synchronization in 3GPP LTE OFDMA(Orthogonal Frequency Division Multiple Access) system, respectively. However, the conventional coarse frequency synchronization method has performance degradation caused by fading channel and squaring loss. Also, the conventional fine frequency synchronization method cannot guarantee stable operation in TDD mode because of signal power difference between uplink and downlink subframe. Therefore, in this paper, we propose enhanced coarse and fine frequency synchronization methods which can estimate more accurately in multi-path fading channel and high speed channel environments and has stable operation for TDD frame structure, respectively. By computer simulation, we show that the proposed methods outperform the conventional methods, and verify that the proposed frequency synchronization method can guarantee stable operation in 3GPP LTE FDD/TDD dual mode downlink receiver.

Analysis on the Performance Degradation of MIMO-OFDM Receiver and Hybrid Interference Cancellation with Low Complexity for the Performance Improvement Under High-Mobility Condition (MIMO-OFDM 수신기의 성능 열화 분석 및 고속 이동환경에서의 성능 향상을 위한 저복잡도 HIC 간섭제거 기법)

  • Kang, Seung-Won;Kim, Kyoo-Hyun;Chang, Kyung-Hi
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.2C
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    • pp.95-112
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    • 2007
  • Spatial Multiplexing techniques, which is a kind of Multiple antenna techniques, provide high data transmission rate by transmitting independent data at different transmit antenna with the same spectral resource. OFDM (Orthogonal Frequency Division Multiplexing) is applied to MIMO (Multiple-Input Multiple-Output) system to combat ISI (Inter-Symbol Interference) and frequency selective fading channel, which degrade MIMO system performance. But, orthogonality between subcarriers of OFDM can't be guaranteed under high-mobility condition. As a result, severe performance degradation due to ICI is induced. In this paper, both ICI and CAI (Co-Antenna Interference) which occurs due to correlation between multiple antennas, and performance degradation due to both ICI and CAI are analyzed. In addition to the proposed CIR (Channel Impulse Response) estimation method for avoiding loss in data transmission rate, HIC (Hybrid Interference Cancellation) approach for guaranteeing QoS of MIMO-OFDM receiver is proposed. We observe the results on analytical performance degradation due to both ICI & CAI are coincide with the simulation results and performance improvement due to HIC are also verified by simulation under SCM-E Sub-urban Macro MIMO channel.

Localization using Neural Networks and Push-Pull Estimation based on RSS from AP to Mobile Device (통신기지국과 모바일장치간의 수신신호강도를 기반으로 하는 신경망과 푸쉬-풀 평가를 이용한 위치추정)

  • Cho, Seong-Jin;Lee, Sung-Young
    • The KIPS Transactions:PartD
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    • v.19D no.3
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    • pp.237-246
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    • 2012
  • Although the development of Global Positioning System (GPS) are more and more mature, its accuracy is just acceptable for outdoor positioning, not positioning for the indoor of building and the underpass. For the positioning application area for the indoor of building and the underpass, GPS even cannot achieve that accuracy because of the construction materials while the requirement for accurate positioning in the indoor of building and the underpass, because a space, a person is necessary, may be very small space with several square meters in the indoor of building and the underpass. The Received Signal Strength (RSS) based localization is becoming a good choice especially for the indoor of building and the underpass scenarios where the WiFi signals of IEEE 802.11, Wireless LAN, are available in almost every indoor of building and the underpass. The fundamental requirement of such localization system is to estimate location from Access Point (AP) to mobile device using RSS at a specific location. The Multi-path fading effects in this process make RSS to fluctuate unpredictably, causing uncertainty in localization. To deal with this problem, the combination for the method of Neural Networks and Push-Pull Estimation is applied so that the carried along the devices can learn and make the decision of position using mobile device where it is in the indoor of building and the underpass.

BER Performance for Satellite DMB System E in Tunnel Environment (터널 환경에서 위성 DMB 시스템 E의 BER 성능)

  • Jo Han-shin;Kim Do-youn;Mun Cheol;Yook Jong-gwan
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.5A
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    • pp.397-401
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    • 2005
  • A different alternative method for simulating bit error rate(BER) performance of Satellite Digital Multimedia Broadcasting(DMB) in tunnel environments is presented. The method based on a channel model obtained by ray-tracing is able to support BER estimation over the channel presents arbitrary statistics that are difficult to fit to an analytic expression. The BER performance for System E over the tunnel fading channel that obtained by ray-tracing is predicted by the monte-carlo method. It can be observed that the BER performance for a straight tunnel channel is better than that for a line-of-sight(LOS) area in curved tunnel. Also, the BER performance for LOS areas in a curved tunnel outperforms that for non-line-of-sight(NLOS) areas in a curved tunnel. The BER performances for straight, curved LOS and curved NLOS tunnel channels are better than that for a Rayleigh channel(K=0) and less than that for a Rician channel with K=3. Moreover, for BER=10-3, it can be seen that there is approximately a $1{\sim}1.5\;dB$ difference between those three types of tunnel channels and a Rayleigh channel.

A Study on the performance improvement by loop interference cancellation and adaptive equalizer in OFDMA based Wibro relay station (OFDMA 기반 Wibro 중계국에서 루프 간섭 제거 및 적응 등화기를 이용한 성능 개선에 관한 연구)

  • Lee, Chong-Hyun;Lim, Seung-Gag
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.43 no.11 s.353
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    • pp.141-148
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    • 2006
  • This paper deals with the performance improvement by eliminating loop interference signal and inserting adaptive equalizer for phase compensation in OFDMA based Wibro relay station. The Wibro relay station is used for the extension of communication service area and for throughput improvement of base station. The loop interference is important factor of performance determination of relay station when transmitter and receiver is very closely located. In order to design interference canceller, we generated base-band OFDMA signal and then transmitted the signal along with pilot tones alined with two different combinations for training mode. And then, we generated received fading signal due to the loop interference added noise to the received signal. In the receiver, the transmitted signal is recovered by elimination of the interference signal with channel estimate and compensating phase by adaptive equalizer. The performance improvement was verified by computer simulation which show channel estimation, constellation of signal and BER characteristics according to the variation of SNR ratio.

Estimation of the Medium Transmission Using Graph-based Image Segmentation and Visibility Restoration (그래프 기반 영역 분할 방법을 이용한 매체 전달량 계산과 가시성 복원)

  • Kim, Sang-Kyoon;Park, Jong-Hyun;Park, Soon-Young
    • Journal of the Institute of Electronics and Information Engineers
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    • v.50 no.4
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    • pp.163-170
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    • 2013
  • In general, images of outdoor scenes often contain degradation due to dust, water drop, haze, fog, smoke and so on, as a result they cause the contrast reduction and color fading. Haze removal is not easier problem due to the inherent ambiguity between the haze and the underlying scene. So, we propose a novel method to solve single scene dehazing problem using the region segmentation based on graph algorithm that has used a gradient value as a cost function. We segment the scene into different regions according to depth-related information and then estimate the global atmospheric light. The medium transmission can be directly estimated by the threshold function of graph-based segmentation algorithm. After estimating the medium transmission, we can restore the haze-free scene. We evaluated the degree of the visibility restoration between the proposed method and the existing methods by calculating the gradient of the edge between the restored scene and the original scene. Results on a variety of outdoor haze scene demonstrated the powerful haze removal and enhanced image quality of the proposed method.