• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7C
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• pp.725-734
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• 2006

As a sequel to Part 1, the performance characteristics of the cell averaging (CA), greatest of (GO), and smallest of (SO) constant false alarm rate (CFAR) processors in nonhomogeneous environment are obtained and compared when receiving antenna diversity is employed in the pseudonoise (PN) code acquisition of direct-sequence code division multiple access (DS/CDMA) systems. Unlike in homogeneous environment, the GO CFAR processor is observed to exhibit the best performance in nonhomogeneous environment, with the CA CFAR processor performing the second best.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.1A
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• pp.99-106
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• 2004

In this Paper, the matched filter for searching initial synchronization in DSSS (direct sequence spread spectrum) receiver is studied. The matched filter with a single data flow path is described which can be presented by HDL (Hardware Description Language). In order to improve the processing time of operations for the filter, equations are arranged to represent two data flow paths and the associated hardware model is proposed. The model has an architecture based on parallelism and pipeline for fast processing, in which two data flow paths with a series of memory, multiplier and accumulator are placed in parallel. The performance of the model is analyzed and compared with the matched filter with a single data flow path.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.3
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• pp.53-59
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• 2000

A received signal in mobile communication environments exhibits variation in both amplitude and phase due to the multipath fading. Therefore we analyzed the performance of DS/CDMA(Direct Sequence/code Division Multiple Access) DPSK(Differential Phase Shift Keying) system for the variations of PLL(Phase Locked Loop) gain with Tikhonov probability density function, assuming that the phase difference between transmitter and receiver signals is phase error. As a result, it is discovered that the performance of system could be improved by the control of PLL gain in compared with the DPSK system which does not consider the phase error. If the PLL gain is 1dB, the difference of two systems is 4.8dB and 0.4dB at 7dB. and if 30dB, it coincides. From above, it

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1700-1706
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• 2016

To improve the number of simultaneous transmissions of machine-to-machine traffic in a spread spectrum ALOHA channel, we propose a new spreading technique called doubly truncated cyclic code shift keying (DTCCSK). By truncating the codeset of cyclic code shift keying, DTCCSK freely adjusts the spreading factor and the symbol length. As a result, DTCCSK exhibits both a high spectral efficiency of M-ary signaling and low implementation complexity of a direct sequence.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.45-53
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• 2011

This paper is technical review about Direct Sequence Spread Spectrum(DSSS) to apply in launch vehicle system. First, we introduce communication protocol(carrier frequency, code length, process gain, data rate, chip rate etc) about several application system using DSSS. And then, we survey and summarize the effect of doppler shift to the DSSS. The doppler shift is important error factor for PN code tracking in the fast moving system like launch vehicle. So, spread spectrum code acquisition technique for a direct sequence system in the presence of doppler effect must be investigated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2141-2152
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• 1998

In this paper, we design and implement an indoor wireless modem using small signal of ISM band regulation, which can tranceive reliable data streams. We use direct sequence spead spectrum (DS-SS) signaling with synchronous BPSK and QPSK modulation, convolutional coding with viterbi decoding. The radio frequency module uses frequency devision duplexing in 900 MHz band, and the digital module is implemented with FPGAs for the purpose fo ASIC design. The perfomrance of our own acquistion and tracking circuit consisting digital matched filter and decision logic is proved by experiments, and the possibility of file transfer at indoor environment with the entrie system that the modem is connected the PC through RS-232C port is verified.

• Journal of Digital Contents Society
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• v.5 no.3
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• pp.219-224
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• 2004

In This paper, we have analyzed the power spectrum of DS-TH Ulhawideband (Direct Sequence-Time Hopping UWB) system which used pseudo-noise (PN) code. The DS-TH UWB system proposed in this paper multiplies the information signal with PN code to construct pulse train with random pattern and then the chips in pulse train are bundled into several groups to map to the particular value. The (+)/(-) pulse is tented in the time slot of frame by comparing a particular value with timing information that was stored in the lookup table. Thus, the energy spark (Comb Line) which is generated certainly in convantional system can be suppressed efficiently by PN code. And we knew that the proposed DS-TH UWB System even could have very smoothing power spectrum ctaracteristic without applying high speed Time-Hopping code.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.276-282
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• 2013

Self-encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading code from a random information source, rather than using the traditional pseudo-random noise (PN) codes. In this paper, we present our study of the SESS system performance under pulsed-noise jamming and show that iterative detection can significantly improve the bit error rate (BER) performance. The jamming performance of the SESS with correlation detection is verified to be similar to that of the conventional direct sequence spread spectrum (DSSS) system. On the other hand, the time diversity detection of the SESS can completely mitigate the effect of jamming by exploiting the inherent temporal diversity of the SESS system. Furthermore, iterative detection with multiple iterations can not only eliminate the jamming completely but also achieve a gain of approximately 1 dB at $10^{-3}$ BER as compared with the binary phase shift keying (BPSK) system under additive white gaussian noise (AWGN) by effectively combining the correlation and time diversity detections.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7C
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• pp.666-674
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• 2005

A hybrid multicarrier CDMA/FDM system with a truncated adaptive transmission scheme is analyzed in forward link based on the feedback information from the mobile station. In the single cell environment, the prop(mea scheme outperforms the adaptive FH/DS system as well as the MC DS/CDMA system when orthogonal signature sequences are used. In the multiple cell environment also, the proposed scheme has better performance characteristics than the adaptive FH/DS system when orthogonal and random codes are used as spreading sequences.

• Information and Communications Magazine
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• v.13 no.11
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• pp.181-191
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• 1996

In this paper we discuss narrow-band interference rejection schemes for spectrum overlay communications where direct sequence spread spectrum (DS/SS) communication system and narrow-band communication systems share the same frequency band. In this case, it is essential to reject the narrow-band signals to guarantee the performance of DS/SS system, while it is not necessarily required to reject the DS/SS signal to recover the narrow-band signal. We discuss several schemes such as time domain processing, frequency domain processing and exploiting the device characteristics to reduce the effect of narrow-band signal on DS/SS communication systems. Furthermore, we suggest a structure of tunable notch filter using gyrator that can easily be customized to ASIC.