• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.7
• /
• pp.1590-1598
• /
• 1997

The paper first introduces the new concept of potential diversity and signal decomposability, which establish a foundaton to generalize the existing concepts of path and frequency diversities. Then it presents a new DS/CDMA system called chip-spreading OCDM system, which is an embodiment of the petential diversity concept that combines the path diversity of the DS/CDMA system and the frequency diversity of the OFDM/CDMA system. In the chip-spreading OCDM system the chip sequences in each symbol interval are first converted into aralled streams, which then simultaneously modulate different orthogonal Walsh basis functions. In the receiver, the received signal is matched to each extended basis-function which is the union of the transmitter basis-functions and their delayed replicas, and the matched-filtered chip samples are combined together after individual channel compensation. The conventional DS/CDMA system using the maximal ratio combining. In addition, it effectively resolves the high PAR and high sensitivity to frequency offset problems which are critical in multi-carrier systems.

• Proceedings of the IEEK Conference
• /
• 2001.09a
• /
• pp.959-962
• /
• 2001

Turbo codes of long block sizes have been known to show very good performance in an AWGN channel and the turbo code has been strongly recommended as error correction code for IMT-2000 in 3GPP(3rd Generation Partnership Project). Recently, turbo codes of short block sizes suitable for real time communication systems have attracted a lot of attention. Thus, in this paper we consider the turbo code of 1/3 code rate and short frame size of 192 bits in ITU-R channel model. We analyzed the performance of W-CDMA systems of 10MHz bandwidths employing RAKE receiver with not only MRC diversity but also turbo code.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.4C
• /
• pp.370-378
• /
• 2007

The most appropriate low density parity check (LDPC) code for hybrid automatic repeat request (HARQ) system suitable for future multimedia communication systems is presented in this paper. HARQ system with punctured LDPC code is investigated at first. And two transmission schemes with parallel concatenated LDPC code are also presented and their performances are analyzed according to the various values of mean column weight (MCW). As a result, the parallel concatenated LDPC code with the diversity effect of information bit is considered to be more appropriate for HARQ system considering the throughput as well as error performance.

• Proceedings of the IEEK Conference
• /
• 2001.06a
• /
• pp.217-220
• /
• 2001

Turbo codes of long block sizes have been known to show very good performance in an AWGN channel and the turbo code has been strongly recommended as error correction code for IMT-2000 in 3GPP(3$^{rd}$ Ceneration Partnership Project). Recently, turbo codes of short block sizes suitable for real time communication systems have attracted a lot of attention. Thus in this paper we consider the turbo code of 1/3 code rate and short frame size of 192 bits in ITU-R channel model. We analyzed the performance of W-CDMA systems of 10MHz bandwidths employing RAKE receiver with not only MRC diversity but also turbo code..

• Journal of Communications and Networks
• /
• v.9 no.1
• /
• pp.50-55
• /
• 2007

We propose to apply chip interleaving and iterative detection to self-encoded multiple access (SEMA) communications. In SEMA, the spreading code is obtained from user bit information itself without using a pseudo noise code generator. The proposed scheme exploits the inherent diversity in self encoded spread spectrum signals. Chip interleaving not only increases the diversity gain, but also enhances the performance of iterative detection. We employ user-mask and interference cancellation to decouple self-encoded multiuser signals. This paper describes the proposed scheme and analyzes its performance. The analytical and simulation results show that the proposed system can achieve a 3 dB power gain and possess a diversity gain that can yield a significant performance improvement in both Rayleigh and multipath fading channels.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.4 no.4
• /
• pp.509-528
• /
• 2010

The random access systems, with retransmission diversity (RD) employment, over large random spreading code division multiple access (CDMA) channel subject to fading is investigated, under the assumption of infinite number of users and infinite spreading gain with their ratio converging to a constant. The low bound of the signal to interference and noise ratio (SINR) is shown to converge almost surely to a constant. The throughput, spectrum efficiency and energy efficiency in the dominating systems are obtained. The analytical results are confirmed by simulations. We find that in high traffic loads the throughput with fading is higher than that without. When the energy efficiency increases, the spectrum efficiency tends to two contrary values due to SNR increases or decreases. For the ordinary stable systems, the stability region is shown to shrink as the traffic increases and enlarge with RD employment.

• Proceedings of the IEEK Conference
• /
• 2005.11a
• /
• pp.85-88
• /
• 2005

Space-time code is a good solution to get transmit diversity. During the last years a number of space-time block codes have been proposed for use in multiple transmit antenna systems. This code, however, was presented only for the special case of the certain numbers of transmit antennas and the certain modulation schemes. and designed under the assumption that the transmitter has no knowledge about the channel. In this work, on the other hand, we consider the case when the transmitter has partial, but not perfect knowledge about the channel. This system can have full diversity for arbitrary number of the transmit antennas with a little bits of feedback.

• Journal of Broadcast Engineering
• /
• v.9 no.1
• /
• pp.32-42
• /
• 2004

In this paper we apply space-time block code with multiple transmitter/receiver antennas to the Advanced Television Systems Committee (ATSC) terrestrial broadcasting systems. Especially, we apply Aiamouti scheme with two transmitter antennas and multiple receiver antennas to the ATSC broadcasting system. Also. diversity technique with multiple receiver antennas and space-time block code scheme with multiple transmitter/receiver antennas are compared. Our simulation results show that the ATSC broadcasting system with multiple transmitter/receiver antennas has an extremely good performance than the scheme with single transmitter/receiver antenna in the Rayleigh fading channel.

• Proceedings of the IEEK Conference
• /
• 2002.07c
• /
• pp.1932-1935
• /
• 2002

This paper introduces the downlink Eigen-beamformer with Space-Time Block Code (STBC) 〔1,2〕employed on the MISO (Multiple Input Multiple Output) systems. The proposed scheme is acquired both transmit diversity gain from STBC and beamforming gain from Eigen-beamformer. In general, it is well described that the diversity gain be maximized when channel parameters associated to fingers are mutually independent. Major role f utilizing Eigen-beamformer is to enforce channel parameters being uncorrelated. According to this, the proposed STBC combined with Eigen-beamformer on the downlink significantly improves its performance under the spatially correlated channel. Simulation results are accomplished under three distinct channel conditioned with varying the degree of their correlations. The result indicates hat our proposed scheme is good performance in spatially correlated channel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.21 no.7
• /
• pp.1787-1802
• /
• 1996

In this paper, the performance for FH/CPFSK system with limiter-discriminator detection and integrage-and-dump post-detection filtering under thermal noie, partial-band noise jamming and rayleigh fading have been analyzed. The method of hard-decision diversity of which the transmitter repeated L times on different hops for each data symbol in a way to mutigate the effects of the jamming has been applied, and the receiver has been combined the L chips. Also, error-correcting code have been applied for improving performance of system. The thermal noise and partial-band noise jamming, intersymbol interference for all eight of the possible adjacent bit data patterns, and FM noise click for evaluating systems have been considered. Also optimum parameters to improve performance of FH/CPFSK system have been obtained and validities have been proved through computer simulation.