• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.247-260
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• 2007

This paper solves the problem of finding a suitable sub-channel and power joint allocation method for multiple users in 802.16e OFDMA/TDD cellular systems. The joint allocation is thatfirstly the sub-channel is allocated to the users and then suitable power is allocated. We propose a FASA (Fairness insured Aggressive Sub-channel Allocation) algorithm which is a dynamic channel allocation algorithm considering all users' channel state information conditionally to maximize fairness and throughput. The improved CHC algorithm, which is dynamic power allocation algorithm, is also proposed in this paper The Improved CHC algorithm collects the extra of the downlink transmit power and then re-allocates it to other users. Simulation results show that the proposed improved CHC algorithm additionally increases the fairness and sector throughput.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.125-132
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• 2017

Vehicular safety service reduces traffic accidents and traffic congestion by informing drivers in advance of threats that may occur while driving using vehicle-to-vehicle (V2V) communications in a wireless environment. For vehicle safety services, every vehicle must broadcasts a Basic Safety Message(BSM) periodically. In congested traffic areas, however, network congestion can easily happen, reduce the message delivery ratio, increase end-to-end delay and destabilize vehicular safety service system. In this paper, to solve the network congestion problem in vehicle safety communications, we approximate the relationship between channel busy ratio and the number of vehicles and use it to estimate the total network congestion. We propose a new context-aware transmit power control algorithm which controls the transmission power based on total network congestion. The performance of the proposed algorithm is evaluated using Qualnet, a network simulator. As a result, the estimation of total network congestion is accurately approximated except in specific scenarios, and the packet error rate in vehicle safety communication is reduced through transmit power control.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.5
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• pp.435-444
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• 2015

This paper specifies on a virtual array design of a 77 GHz vehicle radar for detecting a moving target at a time division transmit and a near range. The virtual array designed reduces a hardware complexity, weight and price. However, a synthesized beam of the virtual array has a high side lobe by a phase distortion of receive signals when the moving target is detected at the time division transmit. For this, a subarray receive signal with a same phase is used and the side lobe of the synthesized beam is suppressed above at least 10 dB. Also the virtual array has a beam distortion by a spherical wave when the vehicle radar operates at near range. So a boresight receive signal of each target range is compensated at each receive signal. Therefore the synthesized beam with compensation recovers a normal main lobe and improves the side lobe about 10~15 dB.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1527-1537
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• 2006

The server system of digital contents has to how the context information about client devices to provide the appropriate contents for each device effectively. CC/PP standard specification is an agreement for describing and transmission of the information related with a client device. In this case, the information on device hardware and software, networks and user's preference is included here. In the mean time, WAP forum defined W-HTTP protocol to transmit the CC/PP profile information of a client device to a server system. However, the client devices which use existing HTTP protocol to transmit their information cannot provide the CC/PP profile information to a server. In this paper, we propose an effective method to create and provide the CC/PP profile in the clients which use not only HTTP protocol but also W-HTTP protocol to transmit device information.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2521-2526
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• 2013

In this paper, a novel spatial modulation (SM) with transmit antenna selection (TAS) based on maximizing channel capacity is proposed. Comparing to the conventional TAS technique, the proposed TAS considers the channel capacity of the MIMO channel with antenna selection. The optimal antenna set selection is applied to SM by taking account of the all possible sets, and then, a sub-optimal antenna set selection is also proposed for reducing the computational complexity of the optimal method. Computer simulations show that the proposed TAS significantly outperforms the existing SM scheme based on the magnitude of the channel vectors in terms of bit error rate (BER) in various environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.10
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• pp.2191-2204
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• 1997

An efficient packet transmit scheduling algorithm should be able to allocate the resource to each connection fairly based on the bandwidth and quality of service requirements negotiated during the call admission procedure and it should be able to isolate the effects of users that are behaving badly. In this paper, we propose an effective round-robin packet transmit scheduling mechanism, which we call the delay tolerant packet reserving scheme (DTPRS) based on delay QoS requirments. The proposed scheme can not only provide fairness and but also reduce delay, delay variation, and packet loss rate by reserving output link time slots of delay tolerant packets and assigning the reserved slotsto delay urgent packets. Our scheme is applicable to high speed networks including ATM network because it only requires O(1) work to process a packet, and is simple enough to implement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4C
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• pp.462-467
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• 2007

This paper proposes Minimum Distance Searching Algorithm (MDSA) which reduces the computational complexity (CC) of the ML, the kind of Spatial Multiplexing (SM) MIMO system. The MDSA searchs candidate symbols with a starting symbol, which is called reference bits. We used the linear receiver of MIMO techniques to find a starting symbol. The MDSA searchs the shortest path to a transmitted symbol using reference bits and Minimum Distance(MD) concept. The CC of MDSA is reduced to the 0.21% to the ML as the transmit antennas is 4 in 16QAM. The simulation result shows the BER of MDSA is nearly same to the BER of ML as the transmit antennas is 2 and the receive antennas is 3 in 16QAM and slightly degraded to the BER of ML as the transmit antennas is 4 and the receive antennas is 6 in QPSK.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.2
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• pp.203-211
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• 2015

The implanted telemetry system provides the monitoring of species while they move within their cages. Species monitored include mice, rats, rabbits, dogs, pigs, primates, sheep, horses, cattle, and others. A miniature transmitter implanted in each animal measures one or more parameters. Parameters measured include arterial pressure, intra-pleural pressure, left ventricular pressure, intra-ocular pressure, bladder pressure, ECG, EMG, EEG, EOG, temperature, activity, and other parameters and transmits the data via radio frequency signals to a nearby receiver. Every conventional dedicated transmitter contains one or more sensors, cpu and battery. Due to the expected life of battery, the measuring time is limited. To overcome these problems, electromagnetic inductive coupling based wireless power transmission technology using multiple transmit coils were proposed. Each coil having different active area are driven by the coil driver. In this research, parallel resonance based coil driver was proposed. In addition, the device to detect where the receiver is positioned was proposed. From the experiments we show how to determine the driving condition of coil driver.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.291-296
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• 2012

In this Paper, we propose a multi-hop transmission in cognitive underlay network. In Secondary network, We assume that a secondary source S attempts to transmit D its signal to a secondary destination via N+1 hops with help of N relays $R_1$, $R_2$, ${\ldots}$, $R_N$. At hop k between relay $R_k$ and relay $R_{k+1}$. we assume that there is a primary user $PU_k$. In this paper, we assume that these channels are Rayleigh fading channels. In underlay network, the secondary transmitter has to adapt its power so that the interference caused at the primary user is less than a maximum interference threshold. considering the hop transmission between the transmitter and the repeater, we find transmit power and signal-to-noise ratio(SNR). Between the transmitter from the receiver depending on the number of relay in the underlay network, we compared to find the transmit power and signal-to-noise ratio(SNR). Finally we find optimal number of relay and optimal threshold value.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.9
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• pp.27-34
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• 2011

Cognitive Radio, which is proposed to improve the efficiency of wireless communication systems is the system to share primary user's frequency bands with a secondary user. In this situation, a secondary user uses NC-OFDM (Non-contiguous Orthogonal Frequency Division Multiplexing) to transmit data effectively without interfering with the primary user's spectrum. However, NC-OFDM, in common with contiguous OFDM, degrades the performance of the system by generating high PAPR (Peak-to-Average Power Ratio). In this paper, firstly, we analyse PAPR corresponding to the distribution of subcarriers in NC-OFDM. Then the PAPR reductions that employ the PTS (Partial Transmit Sequence) and SLM (Selective Mapping) are evaluated. Finally, the computational complexities of the PTS and SLM adopting pruned-FFT are compared with conventional PTS and SLM. Further, it is shown that the NC-OFDM with pruned-FFT is more efficient than the contiguous OFDM in terms of computational complexity and PAPR reduction performance.