• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1059-1066
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• 2009

In this paper, we propose the precoder with superimposed pilots for orthogonal frequency-division multiple access (OFDMA) systems in order to enhance the transmission efficiency of the system and reduce peak-to-average power ratio (PAPR) which is the problem in OFDMA uplink. In wireless communication systems, the way to improve transmission efficiency is 1) to reduce bit error rate (BER) or 2) to increase data rate. In the proposed scheme, we design the precoder and superimposed pilots in the transmitter and use them in the receiver for increasing data rate, caused by the saved transmission bandwidth thanks to the superimposed pilots. In addition, we improve BER performance with the help of the frequency diversity gain caused by precoding. Also using superimposed pilots, we enhance the PAPR performance by increasing the average output power of the signal.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.611-613
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• 2017

This paper proposes a new method to reduce the overhead by pilots for single carrier frequency domain equalization (SC-FDE) transmission. In the conventional SC-FDE transmission structure, the overhead by transmitting pilot are heavy because the pilot are transmitted at every SC-FDE block. The proposed SC-FDE structure has fewer pilots and many SC-FCE blocks are transmitted between pilots. The channel estimation and equalization is performed at the pilot period and the channels between pilots are estimated through linear interpolation. This reduces the pilot overhead by reducing the pilot transmission compared with the conventional structure, and enables reliable channel estimation and equalization.

• Journal of IKEEE
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• v.16 no.3
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• pp.258-264
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• 2012

Although linear channel estimation for the frequency selective fading channel has been widely deployed, its accuracy depends on the number of pilots to probe the channel. Thus, it is unavoidable to employ large number of pilots to enhance the channel estimation performance, which essentially leads to the degradation of the transmission efficiency. It even does not utilize the sparseness of the multipath channel. In this paper a sparse channel estimation scheme based on the matching pursuit algorithm and a pilot assignment method, which minimizes the coherence, are proposed. The simulation results reveal that the proposed algorithm shows superior channel estimation performance with fewer pilots to the LS based ones.

• Journal of IKEEE
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• v.15 no.3
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• pp.235-240
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• 2011

The scattered pilots employed in DVB-T take advantage of the merits of both the block type and comb type pilot arrangement to increase the transmission efficiency. To estimate the channel transfer functions for data subcarriers, it is required to conduct time-frequency domain 2D estimation using the pilots. Though 2D Wiener estimator is optimal in sense of MSE (mean square error), it is too complex to implement in hardware. In this paper a new channel estimation method for the scattered pilot based OFDM system by measuring the power of AWGN and removing the noise in the LS (least square) estimate of the channel is proposed. And the simulation results reveal the proposed method outperforms the 2D linear interpolation in the fading channel.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.10
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• pp.21-29
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• 1999

This paper is concerning about the demapping method using the pilots inserted in transmitter in COFDM(Coded Orthogonal Frequency Division Multiplexing) demodulator which is the standard transmission method of terrestrial digital TV system in Europe(DVB-T). We have presented a simple and efficient method of CSI(Channel State Information) generation and demapping method using CSI. The CSI was derived from the pilot carriers inserted with comb-type among the received active carriers, which is defined as a SNR. From the simulation results for the 3 different constellations of the receiver, we could confirm that the system performance comparing with conventional soft decision method has been improved under DVB-T standard Rayleigh and Ricean fading channel.

• ETRI Journal
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• v.45 no.6
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• pp.952-962
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• 2023

In this study, a space-time transmission scheme is proposed to tackle the limitations of channel estimation with orthogonal pilot information in colocated multiple-input multiple-output systems with several transmitting and receiving antennas. Channel information is obtained using orthogonal pilots. Channel estimation introduces pilot heads required to estimate a channel. This leads to bandwidth insufficiency. As a result, trade-offs exist between the number of pilots required to estimate a channel versus spectral efficiency. The detection of data symbols is performed using the maximum likelihood decoding method as it provides a consistent approach to parameter estimation problems. The moment-generating function of the instantaneous signal-to-noise ratio is used to drive an approximate expression of the symbol error rate for the proposed scheme. Furthermore, the order of diversity is less by one than the number of receiver antennas used in the proposed scheme. The effect of the length of a pilot sequence on the proposed scheme's performance is also investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.9
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• pp.773-778
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• 2014

Aircraft communication system which provides internal communications between pilots in an aircraft and external communications between pilots and operators in ground tower with them. It is very important equipment in terms of mission and safety. It wouldn't meet performance requirements with only functions of transmission and receiving of signals. It should provide highly clear voice quality without any noise. This paper analyzes the cause of noise during internal communications and summarizes the design changes applying single point ground concept to solve the problem. It also describes the results of fight test to verify the design changes.

• The Journal of the Acoustical Society of Korea
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• v.29 no.6
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• pp.365-373
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• 2010

For effective underwater digital communications, a frame structure is used, which includes pilots in time and frequency domains for channel estimation at a receiver. To estimate channel precisely, the each pilot should be located less than coherence time and coherence bandwidth. This paper measured underwater communication environments to provide coherence time and coherence bandwidth. Based on the measurement, the paper exhibits the calculated coherence time and coherent bandwidth is adequate by computer simulations.

• International Journal of Contents
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• v.14 no.2
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• pp.1-6
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• 2018

In a wireless mobile communication system, a pilot signal has been considered to be a necessary signal for estimating a changing channel between a base station and a terminal. All mobile communication systems developed so far have a specification for transmitting pilot signals. However, although the pilot signal transmission is easy to estimate the channel,(Ed: unclear wording: it is easy to use the pilot signal transmission to estimate the channel?) it should be minimized because it uses radio resources for data transmission. In this paper, we propose a pilotless channel estimation scheme (PCE) by introducing the clustering method of unsupervised learning used in our deep learning into channel estimation.(Ed: highlight- unclear) The PCE estimates the channel using only the data symbols without using the pilot signal at all. Also, to apply PCE to a real system, we evaluated the performance of PCE based on the resource block (RB), which is a resource allocation unit used in LTE. According to the results of this study, the PCE always provides a better mean square error (MSE) performance than the least square estimator using pilots, although it does not use the pilot signal at all. The MSE performance of the PCE is affected by the number of data symbols used and the frequency selectivity of the channel. In this paper, we provide simulation results considering various effects(Ed: unclear, clarify).

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.12
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• pp.6243-6259
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• 2019

As a foundation of next-generation air transportation systems, automatic dependent surveillance-broadcast (ADS-B) helps pilots and air traffic controllers create a safer and more efficient national airspace system. Owing to the open communication environment, it is easy to insert fake aircraft into the system via spoofing or the insertion of false messages. Efforts have thus been made in academic research and practice in the aviation industry to ensure the security of transmission of messages of the ADS-B system. An identity-based batch verification (IBV) scheme was recently proposed to enhance the security and efficiency of the ADS-B system, but current IBV schemes are often too resource intensive because of the application of complex hash-to-point operations or bilinear pairing operations. In this paper, we propose a lightweight IBV signature scheme for the ADS-B system that is robust against adaptive chosen message attacks in the random oracle model, and ensures the security of batch message verification and against the replaying attack. The proposed IBV scheme needs only a small and constant number of point multiplication and point addition computations instead of hash-to-point or pairing operations. Detailed performance analyses were conducted to show that the proposed IBV scheme has clear advantages over prevalent schemes in terms of computational cost and transmission overhead.