• Journal of Advanced Marine Engineering and Technology
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• v.34 no.6
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• pp.852-857
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• 2010

In this paper, we proposed and demonstrated an indoor visible-light communication system using an array of light-emitting diodes (LEDs). The main idea is based on that the LEDs can be used not only for lighting but also for free-space optical communications. Because LEDs offer advantageous properties such as high brightness, reliability, lower power consumption and long lifetime, the indoor visible-light communication systems are going to provide high quality of service by the high radiation power of the LED lighting. Prototype of simplex channel for audio and the full-duplex channel for text message were developed. Results indicates the viability of creating inexpensive free-space optical communication transceivers that might be embedded in commercial light products to supports indoor wireless networking.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.4
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• pp.11-20
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• 1994

The error rate equation of DS-CDMA/DQPSK skgnal adopting ARQ scheme has been derived in indoor radio channel which is characterized by AWGN, multi-user interference (MUI) and Rician fading, Using the derived equation the error performance has been evaluated and shown in figures as a function of direct to diffuse signal power ratio(KS1rT), the number of active users (K), PN code sequence length (N), the number of parity bit of linear code (b), forward channel BER, and ES1bT/NS1OT. From the results it is known that in severe fading environments (KS1rT=6) the performance of DS-CDMA/DQPSK system is not reliable so it is needed to adopt techniques for improvement. When an ARQ scheme is adopted, as a method for improving error performance, the performance improves compared with that of non-ARQ scheme and the degree of improvement is proportional to the number of parity bits of linear code. As increasing the number of parity bits, system performance is improved vut system throughput efficiency must be considered. In severe fading channel Hybrid ARQ scheme is more effective than ARQ scheme. As a result, ARQ scheme is appropriate for the high-reliability data communication systems over the radio channel in which the real time processing is not required.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.9 s.339
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• pp.19-28
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• 2005

We establish a statistical model for the ultra-wide bandwidth (UMB) indoor channel based on over 2000 frequency response measurements campaign in a Practical apartment. The approach is based on the investigation of the statistical properties of the multipath profiles measured in different place with different rooms. Based on the experimental results, a characterization of the propagation channel from theoretic view point is described. Also we describe a method for measurement of the channel impulse response and channel transfer function. Using the measured data, the authors compares channel impulse responses obtained from time-domain and channel transfer functions obtained from frequency-domain with statistical path loss model. The bandwidth of the signal used in this experiment is from 10MHz to 8.01 GHz. The time-domain results such as maximum excess delay, men excess delay and ms delay spread are presented. As well as, omni-directional biconical antenna were used for transmitter and receiver In addition, measurements presented here support m channel model including the antenna characteristics.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.76-82
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• 2013

We evaluate the performance of the time-reversal (TR) prefilter and the weighted TR prefilter in an indoor wireless communication system with channel estimation errors. The TR prefilter uses a time-reversed channel as a prefilter to maximize received peak power. The equivalent channel of the TR prefilter is an 공분산 of the channel and the received peak power is maximized. When there are channel estimation errors, the equivalent channel is not an 공분산 of the channel and the received peak power cannot be maximized. The weighted TR prefilter minimizes the inter-symbol interference and maintains the received peak power. Thus, even when there are some channel estimation errors, the weighted TR prefilter can guarantee the received peak power.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.76-76
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• 2004

• ETRI Journal
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• v.28 no.2
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• pp.247-249
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• 2006

In the development of a new wireless communications system, a versatile and accurate radio channel for indoor communications is needed. In particular, the investigation of radio transmission into buildings is very important. In this letter, we present an improved three-dimensional electromagnetic wave propagation prediction model for indoor wireless communications that takes into consideration building penetration loss. A ray tracing technique based on an image method is also employed in this study. Three-dimensional models can predict any complex indoor environment composed of arbitrarily shaped walls. A speed-up algorithm, which is a modified deterministic ray tube method, is also introduced for efficient prediction and computation.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.45-49
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• 2022

In this paper, we propose a method for estimating the error of the Ultra-Wideband (UWB) distance measurement using the channel impulse response (CIR) of the UWB signal based on machine learning. Due to the recent demand for indoor location-based services, wireless signal-based localization technologies are being studied, such as UWB, Wi-Fi, and Bluetooth. The constructive obstacles constituting the indoor environment make the distance measurement of UWB inaccurate, which lowers the indoor localization accuracy. Therefore, we apply machine learning to learn the characteristics of UWB signals and estimate the error of UWB distance measurements. In addition, the performance of the proposed algorithm is analyzed through experiments in an indoor environment composed of various walls.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.211-218
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• 2000

This paper describes the improvement of broadband radio channel characteristics using a MMSE adaptive equalization technique as a fundamental study of high transmission rates in indoor radio channel. First, the performance of 16-QAM system that employs a MMSE linear adaptive equalizer in Rayleigh fading channel is analyzed. Next, in order to improve broadband radio channel characteristics, we apply an adaptive equalization technique employing the MMSE algorithm to the radio channel measured by using circularly polarized antenna under indoor NLOS(non-line-of sight) environment. Consequently, for 16-QAM with adaptive equalizer, we can achieve the improvement of about 13 dB at $10^{-3}$ error rate as compared with general 16-QAM. Moreover, it was found that the adaptive equalization technique could improve broadband radio channel characteristics over the all measured areas. Also, it was found that the employing both adaptive equalization and polarization diversity technique together could improve broadband radio channel characteristics and reduce fading more effectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4C
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• pp.207-214
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• 2005

In the indoor wireless communication, it is considered the indoor wireless system architecture of single input multiple output (SIMO) that used with multiple antenna in order to cope with the indoor fading characteristic due to severe angler spread. We propose the mean steering vector technique as a method to enhance the system Performance, implement the test bed system composed of a PC and the algorithms of the wireless system, and analysis the performance of those algorithms. In addition, the overall operation scenario, overall architecture, and the execution time of the algorithms, of the test bed for the indoor wireless system are presented.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.1951-1972
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• 2018

Wi-Fi Access Point (AP) optimization approaches are used in indoor positioning systems for signal coverage enhancement, as well as positioning precision improvement. Although the huge power consumption of the AP optimization forms a serious problem due to the signal coverage requirement for large-scale indoor environment, the conventional approaches treat the problem of power consumption independent from the design of indoor positioning systems. This paper proposes a new Fast Water-filling algorithm Group Power Constraint (FWA-GPC) based Wi-Fi AP optimization approach for indoor positioning in which the power consumed by the AP optimization is significantly considered. This paper has three contributions. First, it is not restricted to conventional concept of one AP for one candidate AP location, but considered spare APs once the active APs break off. Second, it utilizes the concept of water-filling model from adaptive channel power allocation to calculate the number of APs for each candidate AP location by maximizing the location fingerprint discrimination. Third, it uses a fast version, namely Fast Water-filling algorithm, to search for the optimal solution efficiently. The experimental results conducted in two typical indoor Wi-Fi environments prove that the proposed FWA-GPC performs better than the conventional AP optimization approaches.