• Journal of Korea Society of Industrial Information Systems
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• v.6 no.1
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• pp.15-23
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• 2001

In this paper, we propose a system to cancel the multi-user interference of synchronous BPSK DS/CDMA systems. In this CDMA scheme, the spectrum of the user's signal is directly spread by means of the Simplex code or the phase offsetted PN code. But in arbitrary bit interval, we use the one spreading code of the Simplex code and the phase offsetted PN code. The receiver cancel the multi-user interference and demodulate information bits by using reference correlator. This paper presents a interference cancellation model and analyzes this system mathematically. The suggested system show that the interference resulting from other users are remarkably reduced. In AWGN and Nakagami fading environment we analyze interference generated from other users and compare the resulting performance with that of the conventional receiver in same user side.

• Journal of the Korean Institute of Navigation
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• v.6 no.2
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• pp.13-33
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• 1982

The NAVSTAR/GPS is a satellite-based navigation system that will provide extremely accurate three-dimensional position and velocity information to users anywhere on or near the earth. This system has been studied primarly for military use and thus the results of studies are seldom obtainable for civilian use up to date. Expecting this system to be opened to civilian use in the future, this paper aims to the collection of basic data of the PN phase modulated communication system adopted in the GPS system by computer simulation. The results of studies are as follows; 1) The PN phase modulation of the speed of 106b/s can be simulated by Fourier summation, the spectrum region which can be restricted is in the region of 0.5-1.5 MHz and spectrum number required is over than 270. 2) By computer simulation, it is verified that optimum r.f filter bandwidth is about 0.3 MHz for the case of $10^6$b/s PN codes phase modulated in 1.575GHz carrier. 3) In case that PN rate to data rate is between 10 and 100, the allowable minimum SNR to demodulate data signal correctly by optimum LPF is about 0.3. It is also verified that the larger the frequency ratio of PN code to the data code, the lower the allowable minimum SNR required.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.8
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• pp.24-31
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• 2010

A receiver architecture with low complexity for chirp spread spectrum (CSS) of IEEE 802.15.4a is proposed. To demodulate the received signal at the highest signal to noise power ratio, matched filter is generally adopted for the receiver of wireless communication systems. It is, however, not resonable to adjust the matched filter to the receiver of CSS whose objectives are low complexity, low cost and low power consumption since complexity of the matched filter is high. In this paper, we propose a new receiver architecture using differential multiplication and accumulator not matched filter for demodulation. Also, bi-orthogonal decoder implemented by only adder/subtractor is proposed. The hardware resources for implementation are reduced in the proposed receiver architecture, although bit error rate performance is low compared with the receiver architecture based on the matched filter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5B
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• pp.566-572
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• 2011

The satellite communication is an important method for maritime communications. Binary offset carrier (BOC) signal is a promising candidate of next generation global navigation satellite systems (GNSS). Synchronization of BOC signal is one of the most important processes to demodulate BOC signal in GNSS. However, in maritime environment, the synchronization of BOC signal is suffered from the problem of side-peak of BOC autocorrelation function and multipath fading caused by the sea surface reflection. In this paper, we proposed a novel synchronization scheme which can eliminate side-peak perfectly and is robust in multipath channel. Simulation results show that the proposed scheme has better performance than conventional schemes in multipath channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.10
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• pp.2187-2193
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• 2010

A specific radar system can be implemented more easily using the frequency modulated continuous wave comparing with the pulse Doppler radar. It also has the advantage of LPI (low probability of interception) because of the low power and wide bandwidth characteristics. These radars are usually used to cover the short range area and to obtain the high resolution measurements of the target range and velocity information. The transmitted waveform is used in the mixer to demodulate the received echo signal and the resulting beat signal can be obtained. This beat signal is analyzed using the FFT method for the purpose of clutter removal, detection of a target, extraction of velocity and range information, etc. However, for the case of short signal acquisition time, this FFT method can cause the serious leakage effect which disables the detection of weaker echo signals masked by strong side lobes of the clutter. Therefore, in this paper, the weighting window method is analyzed to suppress the strong side lobes while maintaining the proper main lobe width. Also, the results of FFT beat spectrum analysis are shown under various environments.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.1
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• pp.43-48
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• 2009

We constructed a simple wavelength readout system for a tunable fiber laser which was used for a fiber Bragg grating sensor array system. A quadrature sampling method was used to demodulate wavelength variations of the tunable laser which consisted of a SOA(semi-conductor optical amplifier) and a fiber-optic Fabry-Perot filter. Internal triggers, which have a 90 degree phase period, have been generated by using a double-pass Mach-Zehnder interferometer. From Lissajous plots with quadrature sampled data, a mean phase error of ${\sim}2.51$ mrad was obtained. From the wavelength readout experiments, an accurate and fast linear wavelength demodulation has been confirmed.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.103-113
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• 2010

In this paper, a tradeoff between the total energy consumption-per-bit and the end-to-end rate under spatial reuse in wireless multi-hop network is developed and analyzed. The end-to-end rate of the network is the number of information bits transmitted (end-to-end) per channel use by any node in the network that is forwarding the data. In order to increase the bandwidth efficiency, spatial reuse is considered whereby simultaneous relay transmissions are allowed provided there is a minimum separation between such transmitters. The total energy consumption-per-bit includes the energy transmitted and the energy consumed by the receiver to process (demodulate and decoder) the received signal. The total energy consumption-per-bit is normalized by the distance between a source-destination pair in order to be consistent with a direct (single-hop) communication network. Lower bounds on this energy-bandwidth tradeoff are analyzed using convex optimization methods. For a given location of relays, it is shown that the total energy consumption-per-bit is minimized by optimally selecting the end-to-end rate. It is also demonstrated that spatial reuse can improve the bandwidth efficiency for a given total energy consumption-per-bit. However, at the rate that minimizes the total energy consumption-per-bit, spatial reuse does not provide lower energy consumption-per-bit compared to the case without spatial reuse. This is because spatial reuse requires more receiver energy consumption at a given end-to-end rate. Such degraded energy efficiency can be compensated by varying the minimum separation of hops between simultaneous transmitters. In the case of equi-spaced relays, analytical results for the energy-bandwidth tradeoff are provided and it is shown that the minimum energy consumption-per-bit decreases linearly with the end-to-end distance.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.6
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• pp.28-36
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• 2008

This paper describes a low-power CMOS analog front-end block for UHF band RFID tag chips. It satisfies ISO/IEC 18000-6C and includes a memory block for test. For reducing power consumption, it operates with an internally generated power supply of 1V. An ASK demodulator using a current-mode schmitt trigger is proposed and designed. The proposed demodulator can more exactly demodulate than conventional demodulator with low current consumption. It is designed using a $0.18{\mu}m$ CMOS technology. Measurement results show that it can operate properly with an input as low as $0.25V_{peak}$ and consumes $2.63{\mu}A$. The chip size is $0.12mm^2$.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.156-161
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• 2007

In a TDD system, the length of slots can be unequal, and the number of downlink (DL) and uplink (UL) slots per frame can be different as well. The advantage of using TDD is the capability to accommodate asymmetric high-bit-rate services for the DL and It, which will be one of the prominent features in 4G systems. This paper analyzes the performance of TDD system on mobile channel environments like indoor pedestrian and vehicular channel, and proposes optimum modulation/demodulation method in TDD system. A rectangular QAM (RQAM) used in various communication systems has good BER performance but the much more signal amplitudes also have become one of the barriers to implement receiver. While PSK receiver is implemented easily because it has a constant amplitude, but it's BER performance is worse than RQAM. APSK proposed in this paper integrates merits of RQAM and PSK, and minimizes demerits of then And a simple method is also proposed to demodulate the soft symbol. The results indicate that the proposed APSK has a little worse performance than RQAM but the dynamic range of APSK is about 4 dB, 8 dB better than RQAM at 16-ary, 64-ary modulation/demodulation respectively.

• Journal of Advanced Navigation Technology
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• v.16 no.5
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• pp.810-816
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• 2012

In this paper, BER(Bit Error Ratio) performances of the TransferJet system, which is the standard of a close proximity inductive wireless communication system, are presented and analyzed. Comparing to other wireless communication systems, the TransferJet system has some advantages such as short communication range(i.e., high security in the wireless communication environments), fewer effects of multipath distortion, and higher transmission rate. In order to demodulate the received signal, either SC(Soft-decision Combining) or HC(Hard-decision Combining) can apply to the despreader and demodulator of the receiver. When the spreading factor is more than 4, the SC scheme approximately has a minimum signal-to-noise ratio gain of 2 dB over the HC scheme. Moreover, from simulation results, we can conclude that the quantization bits of 3 bits are an optimum value for the SC scheme in the TransferJet system since the 3-bit quantization achieves nearly the performance as that attained by double-precision floating-point.