• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1665-1676
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• 2001

The effect of spreading gain control on the throughput of a CDMA slotted ALOHA system is considered. Mobile users transmit packets over a shared channel, and the packets transmitted in the same time slot over the shared channel act as simultaneous access interference (SAI). When using spread-spectrum signal, a CDMA slotted ALOHA channel achieves high probability of capture due to the property of high title resolution, and the bit rate of user information is determined by spreading gain. When the SAI level gets larger, the high value of spreading gain enhances the packet throughput by increasing the probability of a successful packet transmission, while it degrades the of the effective throughput by reducing the user information bits carried within a packer. To solve the problem, we investigated the effect of the capture probability and the SAI level on these system throughputs, and evaluated the throughput performance of the system for each spreading gain control scheme. The results showed that the maximum effective throughput could be achieved with an unified method despite the variation of the SAI level by deriving an optimal value of the spreading gain according to 171e system states.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.73-76
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• 2002

In this paper, we consider an algorithm for effectively providing data services for mobile users with different levels of priorities in a DS-CDMA system. The priority level of a user is specified by a factor that is a weighting on the instantaneous data throughput of the user. We define tile weighted instantaneous aggregate data throughput and use it to characterize the performance of the prioritized data service. Our prioritized data service is implemented so that the weighted instantaneous aggregate data throughput is maximized via efficient power and spreading gain allocation. We present efficient algorithms for computing tile optimal power and spreading gain allocation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.775-781
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• 1999

A multi-media variable processing gain DS/CDMA system are considered. Two types of information sources with different rates and transmitting powers are assumed to be stransmitted simultaneously in the same channel. Average signal-to-noise ratios at the correlation receiver outputs for each type of information sources are analytically derived as funtions of partial cross-correlations between spreading code sequences. As the difference of information rates between information sources increase, the difference between signal-to-noise ratio regarding random spreading code and that regarding pseudo random spreading code increases (maximum 1.3dB). The result can provide a analytical tools for use in multi-media DS/CDMA system design.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.374-385
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• 2003

The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multiband UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.182-188
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• 2018

In order to increase the robustness of the uplink for UAS(Unmanned Aerial System), we propose a jamming signal rejection algorithm. In the UAS datalink system, DSSS (direct sequence spread spectrum) is used to reduce the radio noise or jamming signal. In general, jamming signals below the spreading gain are recoverable but the signals beyond the spreading gain can not be recovered. In this paper, these jamming signals beyond spreading gain are detected using the threshold detector in the spectrum area then, generate the estimated signals from the sine wave generator. Finally, we obtain the desired signal to remove jamming signals from the received signals. The proposed scheme can eliminate jamming signals while minimizing the hardware complexity and the original signal loss.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.12A
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• pp.1833-1843
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• 1999

in this paper, we analyze the effects of PN sequence phase on the multiple access interference (MAI) of multi-media multi-rate DS/CDMA system with variable spreading gain (VGS) scheme, and furthermore derive the bit error rate (BER) equation for MAI users with different powers and spreading gains. In the sequel, we verify the influences of deterministic sequences on the bit error rate performance. As the results of the bit error rate of a desired user against interfering users with different spreading gains and different transmit powers, it is shown that the domain factor to determine the MAI component could be different according to the data transmission rate of a desired user. We also show that any kind of PN sequence phase does not yield considerable advantage, unless $E_b/N_o$ is considerably greater than 10dB, since below that value AWGN dominates. However, when the higher $E_b/N_o$, the performance of both MSQCC/CO and CO/MSQCC criterion give the better results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9C
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• pp.721-728
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• 2010

CAMC (constant amplitude multi-code) has a better performance of error correction in iterative decoding than SPCPC (single parity check product code). CAMC benefits from a processing gain since it belongs to a spread spectrum signal. We show that the processing gain enhances the performance of CAMC. Additional correction of bit errors is achieved in the de-spreading of iteratively decoded signal. If the number of errors which survived the iterative decoding is less than or equal to ($\sqrt{N}/2-1$), all of the bit errors are removed after the de-spreading. We also propose a stopping criterion in the iterative decoding, which is based on the histogram of EI (extrinsic information). The initial values of EI are randomly distributed, and then they converge to ($-E_{max}$) or ($+E_{max}$) over the iterations. The strength of the convergence reflects how successfully error correction process is performed. Experimental results show that the proposed method achieves a gain of 0.2 dB in Eb/No.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10B
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• pp.1714-1721
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• 2000

In the mobile communication using DS-CDMA systems the problem of multiple user interference which reduce the performance is generated by multiple user access. In this paper to solve this problem we proposed the direct decision blind adaptive receiver with knowledge of only the desired user's spreading sequence. Simulation result present that the total user's power has equal gain The gain of signal to interference ratio for the proposed blind DD-LMS receiver has about 6[dB] than conventional receiver at additive white Gaussian noise and large gain at multipath channels. And when interference user's power has more large gain than desired user's power the gain of SIR for the proposed receiver has large value. And simulation result of bit error rate present that DD-LMS receiver has higher performance than LCCMA receiver. Thus the proposed blind DD-LMS receiver has robustness against interference of high power user and multipath channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2229-2236
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• 2014

In this paper, we proposed and implemented the automated cable-spreading program which can be done effectively cabling plan for electrical equipment in power plant. Cause the process of existing cable-spreading design was written in by hand, there are grossly inefficient gain by a personal and time investment with cable omission and unfixed overfill value. Proposed automation program for cable-spreading, which is coded cable and raceway, can calculate the overfill value and raceway change. Some experiments are conducted so as to verify the proposed model, and as a result, implemented cable-spreading program is well performed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.10-17
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• 2000

In this paper, we evaluate the correlation properties and the optimization of PN sequence phase for multi-media DS/CDMA system with variable spreading gain (VSG) scheme. In multi-media multi-rate DS/CDMA systems, the optimization of PN sequence phase is not a tractable problem, since the sequences should be optimized against both sequences of the same length and other sequences with different length. Hence, we verify the correlation properties of PN sequence phase in multi-rate system environment and furthermore, we propose the new phase criterion, MIN-AIP (minimum-average interference parameter), to minimize the bit error rate (BER). As the results of performance evaluations, it is shown that the performance of MIN-AIP criteria gives the best results.