• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.6
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• pp.30-36
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• 1999

Jamming is an important factor in the military satellite communication system. In this paper, link capacity and jamming margin of the DS-CDMA(Direct Sequence-Code Division Multiple Access) military satellite communication system are analyzed and calculated under a multitone jamming. The analysis was performed with two types of transponders loaded on a geosynchronous satellite. Calculation methods for link capacity and jamming margin were obtained. The results of the analysis show that capacity of a transponder which does modulation/demodulation, decoding/encoding in addition to despreading/respeading is twice as much as that of a tranponder which does despreading /respreading only.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.115-122
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• 2021

In this paper, we propose a dynamic slot allocation scheme to improve the slot utilization rate in tactical multi-hop networks in which the channel condition varies due to node movements. The proposed scheme takes advantage of the fact that nodes that are more than three hops apart can use the same slot simultaneously. The frame is divided into two parts: the control period and the data period. To know the available slot information within two-hop distance, the node exchanges a slot allocation information with one-hop neighbors during the control period. The node can get the information on idle slots that are not used within two-hop distance but assigned already to other nodes that are more than three-hop away. The identified idle slot can be used by the node, which increases the slot utilization rate. The performance analysis results of the proposed scheme show that it increases the slot utilization rate sufficiently despite the overhead of the control period in the multi-hop networks of the future soldier system.

• Journal of IKEEE
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• v.2 no.2 s.3
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• pp.294-298
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• 1998

We propose an efficient method for updating the inverse of the signature waveform cross-correlations (SWC) matrix when the number of users in the synchronous direct-sequence code-division multiple-access (DS/CDMA) system changes. It is shown that the computational complexity of the proposed method is $O(n^2)$ in which n represents the number of active users in the system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11B
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• pp.1640-1650
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• 2010

To prepare for the network centric warfare, Korea Joint Tactical Data Link System(KJTDLS) has been developed by the South Korean military recently and its development is divided into two phases: basic and complete ones. Due to the limited bandwidth and low transmission efficiency of the developing KJTDLS (basic), lots of problems could be occurred when the TDMA protocol in Link-16 is applied. In this paper, a new dynamic TDMA frame structure for KJTDLS(basic) is proposed and the performance of the proposed is evaluated through the implementation of simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.6-12
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• 2008

In uplink cable modem link operated in time-division multiple access mode, it is crucial to employ a suitable preamble pattern enabling frame detection, coarse timing/carrier recovery. Preamble pattern based on the constant envelope zero autocorrelation sequence is proposed for the uplink cable modem compliant to the data over cable service interface specification. Frame detection, coarse/fine timing and carrier recovery algorithms suitable for the proposed preamble pattern are also proposed. We check up the performances using numerical results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.2035-2042
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• 1997

We consider the design of soft decision functions for each stage of multistage detection for coherent demodulation in an asynchronous code-division multiple-access(CDMA) system. In particular, the sigmoid function, which is shown to be optimal under the mean square error(MSE) criterion, andmultilevel quantizers that best approximate the sigmoid function are derived. At each stage of multistage detection, the parameters of these decision functions are adjusted depending on estimated input statistics. Computer simulation results demonstrate that multistage detectors employing these soft decision functions perform considerably better than those with hard decision.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1159-1166
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• 2004

This paper follows up the previous work on the linearly constrained, modified minimum mean-squared error(MMSE) detection for direct-sequence code-division multiple-access DS-CDMA) systems in fading channels. We find a condition to avoid the breakdown of joint modified MMSE detection and pilot symbol-aided channel estimation (PSACE). The linearly constrained, modified MMSE solution is theoretically shown to be robust against time variations in Rayleigh fading channels. This fact is consistent with the simulation results. We also show that under some conditions the linearly constrained, modified MMSE detection maximizes the output signal-to-interference-plus-noise ratio.(SINR)

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10A
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• pp.823-829
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• 2011

Recently, wireless body area network (WBAN) has received much attention as an application for the ubiquitous healthcare system. In WBAN, each sensor nodes and a personal base station such as PDA have an energy constraint and computation overhead should be minimized due to node's limited computing power and memory constraint. The reliable data transmission also must be guaranteed because it handles vital signals. In this paper, we propose a systematic network coding scheme for WBAN to reduce the network coding overhead as well as total energy consumption for completion the transmission. We model the proposed scheme using Markov chain. To minimize the total energy consumption for completing the data transmission, we made the problem as a minimization problem and find an optimal solution. Our simulation result shows that large amount of energy reduction is achieved by proposed systematic network coding. Also, the proposed scheme reduces the computational overhead of network coding imposed on each node by simplify the decoding process.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.107-114
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• 2008

In wireless access systems, there has been much interest in enhancing the performance of orthogonal frequency division multiplexing OFDM) in a frequency selective fading channel. If the channel is static and is perfectly known to both the transmitter and the receiver, the water-filling technique with adaptive modulation is known to be optimal. However, for OFDM systems, this requires intensive traffic overheads for reporting channel side information on all subcarriers to the transmitter In this paper, we propose an adaptive modulation and coding scheme for bit-interleaved coded OFDM (BIC-OFDM) for downlink packet transmissions with reduced feedback information. To minimize the feedback information, we employ a rate adaptation method based on the OFDM symbol rather than on each subcarrier. To illustrate the performance gap between the optimal water-filling and the proposed scheme, we will compare cutoff rates for both schemes. It is shown that the loss is less than 2dB while the proposed scheme significantly reduces the feedback payloads. Also, the OFDM system in multiuser environment with subcarrier grouping is considered. It is shown that by exploiting multiuser diversity the throughput of the proposed scheme approaches the channel outage capacity as the number of users and the number of subcarrier groups increase.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.6
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• pp.749-756
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• 2015

In this paper, we propose a unique systolic structure and communication algorithm that maintains a solid link between nodes using synchronous digital communication and enables low power communication. This system was designed by using CC2500 RF transceiver, CC2590 RF front end and C8051F330 low power microcontroller. The measurement of power consumption in the network link shows below $400{\mu}W$ in data transfer rate 320bps. The system constitutes the base unit of low power wireless network that was composed of each seven link nodes having eight sensor nodes. Results of the experiments show that link nodes using a 4Ah battery could operate over 3 years without replacement.