• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.997-1005
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• 2008

In this paper, we propose an efficient space-time block coding (STBC) scheme in a cooperative satellite-terrestrial system. The proposed STBC scheme has code rate 1 for a 3 transmit antenna scheme. Because the channel matrix of the proposed scheme is orthogonal, we can use a simple linear decoding algorithm and also can expect improved performance over the conventional scheme. The simulation results demonstrate that the proposed scheme has improved performance for bit error rates (BER) than several conventional STBC schemes. In addition, we investigate performance simulation results by power imbalance between the terrestrial repeaters and satellite.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.130-139
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• 2010

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. This paper addresses a number of multiple input multiple output (MIMO) precoding and scheduling techniques across the PHY and MAC layers that can operate under a reduced link budget and collectively improve the transmit power efficiency of a base station, while maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity in both the time, frequency as well as the space domain, are examined. Several fairness-aware resource allocation algorithms are applied to the considered MIMO schemes and a detailed analysis of the tradeoffs between power efficiency and quality of service is presented. This paper explicitly examines the performance of a system serving real-time, VoIP traffic under different traffic loading conditions and transmit power levels. It is demonstrated that by use of efficient scheduling and resource allocation techniques significant savings in terms of consumed energy can be achieved, without compromising QoS.

• Journal of Broadcast Engineering
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• v.28 no.1
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• pp.145-148
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• 2023

Open-loop Octonion space-time block code for 4 transmit antenna system is considered and random phases are applied to 4 transmit antennas for physical layer security. When an illegal hacker estimates the random phases of 1 through 4 transmit antennas with maximum likelihood (ML), this letter analyzes the bit error rate (BER) performances versus signal-to-noise ratio (SNR). And the Octonion code in the literature[1] does not have full orthogonality so, this letter employs the perfect orthogonal Octonion code. When the hacker knows that the random phases are 2-PSK constellations and he should estimate all the 4 random phases, the hacking is impossible until 100dB. When the hacker possibly know that some of the random phases, bit error rate goes down to 10^-3 so, the transmit message could be hacked.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5C
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• pp.391-397
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• 2005

Since space time block code (STBC) technique of a transmission diversity technique was introduced, multiple input multiple output techniques using transmission diversity at the basestation for improving transmission data rate, have been studied extensively. Multiplexed STBC OFDM technique uses multiple groups of two transmit antennas and suppresses the interference signals of other STBC OFDM groups at the receivers. In this paper, I propose a new method of iterative decoding and maximal ratio receive combining technique for multiplexed STBC OFDM systems, and simulated and showed the results in comparison with the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.623-630
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• 2004

The adaptive modulation along with SFBC transmit diversity is a very effective method to increase the capacity of an OFDM system. However, severe performance degradation is resulted when inter-symbol interference is applied due to frequency-selective fading in mobile communications. In this paper, we have proposed and analyzed an OFDM system with SFBC transmit diversity and adaptive modulation scheme based on pre-equalization methods, in order to increase the data transmission rate in the downlink without much increase in system complexity. By introducing subchannel grouping and the pre-equalization method among adjacent subchannels, we could enhance the efficiency of the adaptive modulation a lot. By computer simulation, it has been proven that the proposed schemes show a better BER and throughput performance than the conventional schemes under severely time-varying multipath fading channel.

• Journal of Internet Computing and Services
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• v.8 no.4
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• pp.61-70
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• 2007

In this paper, we propose and observe the Adaptive Modulation system with optimal Turbo Coded V-BLAST(Vertical-Bell-lab Layered Space-Time) technique that is applied the extrinsic information from MAP Decoder in decoding Algorithm of V-BLAST: ordering and slicing. And comparing the proposed system with the Adaptive Modulation system using conventional Turbo Coded V-BLAST technique that is simply combined V-BLAST with Turbo Coding scheme, we observe how much throughput performance and SNR has been improved. In addition, we show that the proposed system using STD(Selection Transmit Diversity) scheme results in on improved result, By using simulation and comparing to conventional Turbo Coded V-BLAST technique with the Adaptive Modulation systems, the optimal Turbo Coded V-BLAST technique with the Adaptive Modulation systems has SNR gain over all SNR range and better throughput gain that is about 350Kbps in 11dB SNR range. Also, comparing with the conventional Turbo Coded V-BLAST technique using 2 transmit and 2 receive antennas, the proposed system with STD scheme show that the improvement of maximum throughput is about 1.77Mbps in the same SNR range and the SNR gain is about 5.88dB to satisfy 4Mbps throughput performance.

• Journal of the Korea Society of Computer and Information
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• v.17 no.7
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• pp.77-86
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• 2012

Using OFDM(Orthogonal Frequency Division Multiplexing) provides the same diversity order as MRRC(Maximal Ratio Receiver Combining). It is assumed that fading channel is constant across two consecutive symbols. Unfortunately, when the channel condition is changed for the two consecutive symbols, the OFDM using STBC(Space Time Block Code) does not offer good performance due to the large doppler shift. In this paper, we have proposed a performance enhancement scheme for OFDM using STBC over time-selective fading channel. Simulation results for various doppler shift rates are presented to robust system performance of OFDM due to using our proposed scheme over time-selective fading channel.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.58
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• pp.61-70
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• 2006

In this paper, we compare the performance of representative MIMO techniques such as space-time block code, closed-loop transmit diversity, and V-BLAST, etc., in IEEE 802.22 environments. We first develope deco-ding algorithms of the representative MIMO techniques and design a MIMO-OFDM system employing QPSK, 16 QAM, 64 QAM to cover several transmission rates. Since the frequency band used for IEEE 802.22 systems belongs mostly to V/UHF band and the angular spread of the received signal at the base station is very small, there Is a significant correlation between the signals from transmit antennas. Thus, in this paper, we compare the performance of MIMO-OFDM systems employing only two Tx antennas in correlated fading environments.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.40-44
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• 2010

A layered coding scheme is one of the adaptive receiving techniques for unidirectional services such as multimedia broadcasting and multicasting services (MBMS), where we cannot utilize feedback information. The layered coding scheme can be used with hierarchical modulations by combining suitable code rates and modulation orders of each. In addition, it has been reported that hybrid and/or integrated satellite systems can effectively achieve transmit diversity gains by appropriate utilization of space time coding combined with turbo codes. This paper proposes a layered turbo coding schemes for hybrid and/or integrated satellite systems. We first introduce the system architecture and operational principle of the proposed scheme, and discuss the applicability.

• The KIPS Transactions:PartC
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• v.13C no.7 s.110
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• pp.865-872
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• 2006

Cooperative communications (CC) have received a great deal of attention recently as an efficient way to obtain the spatial diversity without physical arrays. Thus, space-time block codes (STBC) which are well-known for use in co-located multi-antenna systems can be still utilized for single-antenna users in a distributed fashion. In this paper, we propose a cooperative signaling structure using the $\frac{3}{4}$-rate STBC and derive closed-form BER expression which takes the effect of network geometry and transmit power constraint into account. A variety of simulated and numerical results demonstrated the cooperation considerably outperforms the direct transmission when partners are located in appropriate positions.