• Journal of information and communication convergence engineering
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• v.16 no.1
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• pp.17-22
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• 2018

In massive multiple-input multiple-output (MIMO) systems, linear channel estimation algorithms are widely applied owing to their simple structures. However, they may cause pilot contamination, which affects the subsequent data detection performance. Therefore, herein, for an uplink multicell massive multiuser MIMO system, we consider using an alternating projection (AP) for channel estimation to eliminate the effect of pilot contamination and improve the performance of data detection in terms of the bit error rates as well. Even though the AP is nonlinear, it iteratively searches the best solution in only one dimension, and the computational complexity is thus modest. We have analyzed the mean square error with respect to the signal-to-interference ratios for both the cooperative and non-cooperative multicell scenarios. From the simulation results, we observed that the channel estimation results via the AP benefit the following signal detection more than that via the least squares for both the cooperative and non-cooperative multicell scenarios.

• Journal of Sensor Science and Technology
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• v.25 no.3
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• pp.189-195
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• 2016

In this paper, we newly introduce a visible light communication (VLC) repeater using the LED array in an LED lamp. The LED array is used for a light source in the repeater, which radiates light both for illumination and data transmission. A VLC repeater is made by adding some electronic circuits to the LED array including a photodetector, a demodulator, and a modulator. The repeater is installed on the ceiling of a room like a conventional LED lamp, receives the VLC signal from an arbitrary transmitter, recovers data, and radiates the signal to wide area in the room. We used a carrier frequency of 100 kHz for the uplink from a transmitter to the repeater, and 500 kHz for the downlink from the repeater to a receiver. The repeater is useful for increasing the transmission path to wide area over the obstacles that may exist between VLC transmitters and receivers.

• 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.

• Journal of Korea Multimedia Society
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• v.12 no.12
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• pp.1769-1777
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• 2009

With the advent of the ubiquitous technology age, the progress of network technology has enabled a robust sensor communication, not just in cities, but also in poor surroundings such as deserts, polar regions, or underwater environments. In this paper, we propose a Multiple Acknowledgement (MA) technique to replace the conventional Automatic Repeat request (ARQ) technique. The MA mechanism is to send an Ack to many receivers simultaneously. The CH (master, coordinator) of the unit cluster broadcasts a Beacon frame where Ack information of the previously transmitted data is included. This technique can reduce the number of transmissions and overhead significantly. The proposed technique is a scheme improving the efficiency of an underwater sensor network where the uplink data transmission is the mainstream. The Performance of the ARQ, Block Ack, Pervasive Block Ack and the proposed method were compared with one another and analyzed. The proposed method showed significant performance improvement as compared with the ARQ, BA, and PBA in its channel efficiency.

• International Journal of Advanced Culture Technology
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• v.11 no.1
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• pp.389-394
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• 2023

Based on intelligent visual information and 5G, this paper studies the intelligent visual communication of landscape bamboo buildings, and provides a new method of intelligent perception and interactive computing for the real world, which can represent, model, Perception and cognition; through the integration of virtual and real, the situational understanding of the human-machine-material fusion environment and the interaction with nature. The 5G network can well meet the combination of high-bandwidth uplink transmission and low-latency downlink control. At the same time, 5G-based AR intelligent inspection, remote operation and maintenance guidance, and machine vision inspection. Taking the bamboo building as an example, through field inspections to analyze tourism Bamboo buildings before and after development, and the intelligentization of bamboo buildings based on 5G and visual modeling.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.916-922
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• 2001

A medium access control protocol is proposed for integrated voice and data services in the packet CDMA network with a small coverage. Uplink channels are composed of time slots and multiple spreading codes for each slot. This protocol gives higher access priority to the delay-sensitive voice traffic than to the data traffic. During a talkspurt, voice terminals reserve a spreading code to transmit multiple voice packets. On the other hand, whenever generating a data packet, data terminals transmit a packet based on the status Information of spreading codes in the current slot, which is received from base station. In this protocol, voice packet does not come into collision with data packet. Therefore, this protocol can increase the maximum number of voice terminals.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.6
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• pp.1-9
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• 2008

This paper presents transmission parameters of DH(Dog-Horse) systems based on IEEE802.16e(WiBro) systems. DH requires higher uplink multimedia data rate, which is different from commercial WiBro systems. This paper designes some transmission parameters satisfying the DH system requirements and demonstrates link performance evaluation based on the parameters. For the transmission parameters, the number dwon/up link OFDM symbols are determined by 6/30, respectively. For reliable transmission of control signals, downlink modulation and coding rate are selected by QPSK, 1/2 coding rate and that of uplink is chosen by 16QAM 1/2 and 3/4 coding rate. Based on these parameters, computer simulations demonstrate the system performance of DH system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.145-152
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• 2009

IEEE 802.16e standard, a kind of WMAN standard, was established to support data services with cheaper cost to mobile users than traditional mobile communications system and wireless LAN system can do. In this paper, we propose an uplink QoS packet-scheduler for VoIP service which can be installed in IEEE 802.16 system and evaluate its performance with NS-2 network simulator. The proposed QoS packet-scheduler consists of three procedures: determining scheduler interval, determining the amount of resource assignment, and deciding which mobile station the base station should serve first among multiple mobile stations. According to numerical results, the proposed QoS packet-scheduler can provide more increased system capacity by 220% than UGS service scheme does and by 25 % than ertPS service scheme does.

• The Journal of the Korea Contents Association
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• v.5 no.1
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• pp.89-99
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• 2005

HPI system provides 1-3 Mbps data transmission speed to terminals moving up to 60 km/sec. Since HPI supports rtPS, nrtPS, and BE services requiring different QoS, it needs an efficient scheduling method based on those different QoSs. This paper suggests an uplink scheduling method which gives priority to services in the order of rtPS, nrtPS and BE services but which reserves some bandwidth for the low priority services before it allocates the bandwidth to higher priority services. Simulation results show that it can improve the uplink performance by reserving mean transmission rate to each nrtPS terminal and by reserving bandwidth, which amounts to about 1.5 times the mean transmission rate of the whole BE terminals, to the whole BE terminals.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.3
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• pp.537-542
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• 2017

In this paper, we propose a new scheduling scheme to reduce the complexity and overhead in TDD uplink cellular networks. In a TDD network, users can estimate the interference causing to neighboring BSs by measuring the signals transmitted from them. In the existing max SGIR scheduling scheme, each user calculates SGIR and feeds back to BS. Then, the BS selects a user having the largest SGIR value to transmit data. This scheme has a problem that as the number of BSs increases, the number of interference channels to be measured by the users increases, and thus the hardware and algorithm complexity of the user increases. We propose a max SmGIR (Signal-to-max generating interference ratio) scheduling scheme that can reduce the user complexity by predicting the SGIR value based on only the largest interference information. According to computer simulations, the proposed scheme has similar performance to the existing max SGIR scheme despite this low complexity.