• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.16-29
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• 2022

This paper presents a Doppler shift estimation method and signal processing schemes for Direct Sequence Spread Spectrum (DSSS) transmission to overcome the Doppler shift due to the moving of the underwater communication unit. The proposed method estimates a Doppler shift via 2 step procedures using the preamble with the two 64-length Frank sequences which has a good self-correlation characteristic and is insensitive to the Doppler shift. Furthermore, a packet of DSSS underwater mobile communication and a RAKE receiver are designed using the proposed Doppler shift estimation method. Due to the modulation scheme of the designed DSSS underwater mobile communication using Differential-Quadrature Phase Shift Keying (DQPSK) for the data symbol transmission, the RAKE receiver dose not need a phase tracking and easily makes coherent signals among the combining RAKE branches. The designed RAKE receiving scheme including the proposed Doppler shift estimation method successfully decides information data using the DSSS signal transmitted from the pseudo-moving transmitter with velocity upto about 17.5 m/s.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.39-43
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• 2000

본 논문에서는 IMT-2000 시스템에 대한 제안된 표준안을 기초로 송수신 시스템을 구성하여 광대역 무선채널 환경 및 다양한 시스템 운용환경에서 시스템의 성능을 분석한다. 수신 성능의 개선을 위하여 CCI(Co-Channel Interference) Canceller와 Rake 수신기를 혼합하여 기존의 Rake 수신기에서 제거할 수 없었던 자기 간섭(Auto Interference)을 제거하는 새로운 Rake수신기를 제안하였다. 또한 다중 경로 페이딩 모델로는 ITU-R M.1225에서 제시된 모델을 적용하였다. 성능 분석 결과, 상대적으로 작은 지연 확산을 가지는 채널 A가 중간 지연 확산을 가지는 채널 B보다 수신성능이 양호함을 알 수 있었으며, 채널 A와 B에 관계없이 제안된 레이크 수신기를 채용하였을 경우 자기 간섭의 제거 효과로 인해 수신성능이 기존의 레이크 수신기를 채용하였을 경우에 비해 향상됨은 알 수 있었다. 또한 간섭제거기와 제안된 레이크 수신기를 직렬로 연결한 수신기를 채용하였을 경우 다중접속간섭을 효과적으로 제거할 수 있었으며, 수신성능의 차이는 채널 환경이 양호할수록, $E_{b/}$N/ sub o/값이 커질수록 차이가 커짐을 알 수 있었다.다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4B
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• pp.635-639
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• 2000

The average bit error rate (BER) performance of 2D-RAKE receiver, operating in a correlated Nakagami fading channel, is analyzed. The analysis assumes correlated fading between the array elements with identical fading parameters but with unbalanced average signal-to-noise ratio (SNR). And independent but non-identically distributed frequency-selective fading channel with different fading parameters is assumed. The analyses show that fading correlation, delay profile, average SNR distribution, and fading parameters of combined branches affect the overall performance of 2D-RAKE receiver.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.5
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• pp.975-981
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• 2012

In this paper, we considered the received signal of the wideband CDMA systems using turbo code in the multipath channel environments, and analyze the performance of the system. This study is to analyze the performance for the variable system bandwidth according to the number of branches of rake receiver by passing the received signal through a rake receiver with a turbo code in Rayleigh fading channel environments. For the design of receiver in wideband CDMA systems, we presented the efficient parameters for the number of iterative decoding and the number of branches of rake receiver.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10C
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• pp.995-1006
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• 2003

It is well know that in the wireless communication systems the transmitted signals can suffer from multipath fading due to the wave propagation characteristics and the obstacles over the paths, resulting in serious reduction in the power of the received signals. However, it is possible to take advantage of the inherent diversity imposed in the multipath reception if the underlying channel can be properly estimated. One of the diversity reception methods in this case is Rake processing. In this paper we study the Rake receivers for the direct-sequence spread-spectrum communication systems utilizing PN (pseudo noise) sequences to achieve spread spectrum. A conventional Rake receiver can use the finite-duration impulse (FIR) filter followed by the PN sequence demodulator, where the FIR filter coefficients are the reverse-ordered complex conjugate values of the fading channel impulse response estimates. Here, we propose a new Rake processing method by replacing the aforementioned PN code sequence with a new set of optimum demodulator coefficients. More specifically, the concept of the new optimum Rake processing is first introduced and then the optimum demodulator coefficients are theoretically derived. The performance obtained using the new optimum Rake processing is also calculated. The analytical results are verified by computer simulation. As a result, it is shown that the new optimum Rake processing method improves the MSE performance more than 10 dB over the conventional one using the fixed PN sequence demodulator. It is also shown that the new optimum Rake processing method improves the MSE performance about 10 dB over the Adaptive Correlator that performs the combining of the multipath components and PN demodulation concurrently. And finally, the MSE performance of the optimum Rake demodulator is very close to the MSE performance of OPSK demodulator under the AWGN channel.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.12
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• pp.12-19
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• 2014

In this paper, an advanced UWB (ultra wideband) Rake receiving technique based on the statistical distribution model is studied in the M-ary TH-PPM system with multiple access interference (MAI). In order to improve the performance of the Rake receiver, the stochastic model, which can flexibly express the behavior of MAI-plus-noise, is required and the Laplace distribution and the generalized normal Laplace (GNL) model applied by the curtosis matching method are considered. The performance of Rake receiver based on each probability distribution is evaluated in the IEEE multipath fading channel and compared to that of the conventional Rake receiver. The suggested approach shows a superior BER performance than that of conventional Rake receiver.

• Journal of Satellite, Information and Communications
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• v.12 no.2
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• pp.104-111
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• 2017

Pre-Rake CDMA system using multiple transmit antenna provides a good system performance without equipping a complicated RAKE combiner at the mobile receiver. However, the performance of the Pre-Rake systems are significantly affected by channel estimation error so that the effect of the channel estimation error should be considered and analyzed for evaluating the system performance. In this paper, MISO(Multi-Input Multi-output) Pre-Rake CDMA system with channel estimation error is analyzed by numerical analysis and the results are compared with that of the computer simulation. From the numerical results, it is found that the performance of the Pre-Rake system is more affected by the phase error than the amplitude error.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2C
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• pp.109-116
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• 2006

Many application scenarios of ultra-wideband(UWB) radio assume non-line-of-sigit(non-LoS) signal propagations. Through-material propagation of UWB signal introduces a distortion of the waveform as well as attenuation, which will introduce a decrease of the correlation coefficient between the correlator template and the received signal. A hypothesis test approach to selection of the template waveform for UWB rake receivers is posed. Linde-Buzo-Gray(LBG) algorithm is used to select the candidate waveforms which are used to setup the hypothesis test. The performance of the algorithm is tested using a set of indoor non-LoS propagation measurement data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.593-601
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• 2000

In a multi-bandwidth CDMA system, the performance of multiple order selection combining rake receivers are analyzed according to the spreading bandwidth of the system and the delay spread of the Rayleigh fading channel. The results for various channel environments indicate a tradeoff between total received signal energy and multipath fading immunity. Increasing the occupied bandwidth of the system(wide-bandwidth spreading) gives better performance for small delay spread environments, while gathering more energy(narrow-bandwidth spreading)gives better performance for large delay spread environments. It is shown that the performance difference between low and high order selection combining grows larger as the spreading bandwidth increases. It is also noted that performance degrades by increasing the bandwidth above a certain point and the optimum spreading bandwidth for each channel environment decreases as the delay spread of the channel increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9C
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• pp.899-906
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• 2005

In this paper, the optimum maximum-likelihood rake receiver for impulsive, fading channel is derived, and a sub-optimun rake receiver with reduced complexity is obtained for practical purposes. Numerical results show that, when the noise is impulsive, the rake receivers designed for impulsive noise offer performance improvement over those optimized for Gaussian environment. It is also observed that, as the number of fingers increases, the performance of the rake receivers designed for impulsive environment improves while the rake receiver optimized for Gaussian environment experiences performance degradation in impulsive environment.