• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9A
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• pp.871-877
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• 2007

In this paper, we propose a new transmit diversity scheme using window functions in orthogonal frequency division multiplexing (OFDM) system. Transmit diversity of the scheme is varied with window functions and the condition of the window function to maximize transmit diversity is derived. The proposed scheme can be considered as a generalization of the diversity schemes such as cyclic delay diversity (CDD), orthogonal transmit diversity (OTD), and frequency switched transmit diversity (FSTD).

• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.99-103
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• 2010

Motivated by recent works on spectrum-sharing systems, this paper investigates the effects of transmit diversity on the peak interference power limited cognitive radio(CR) networks. In particular, we derive the ergodic and outage capacities of a spectrum-sharing system with multiple transmit-antennas. To derive the capacities, peak interference power constraint is imposed to protect the primary receiver. In a CR transmitter and receiver pair with multiple antennas at the transmitter side, the allowable transmit power is distributed over the transmit-antennas to achieve transmit diversity at the receiver. We investigate the effect of this power distribution when a peak interference power constraint is imposed to protect the primary receiver. We show that the transmit diversity does not improve the ergodic capacity compared to the single-antenna system. On the other hand, the transmit diversity significantly improves the outage capacity. For example, two transmit-antennas improve the outage capacity 10 times compared to the single-antenna with a 0 dB interference constraint.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.4
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• pp.200-205
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• 2011

In multipath fading channel, diversity is essential to mitigate the impairments. In this paper, we have proposed the angle diversity scheme called ATTD(Angle Time Transmit Diversity) instead of Alamouti's STTD(Space Time Transmit Diversity) and have analyzed the performance of the proposed scheme when signal powers caused by the transmission to different angles are different. Based on it, we have measured the wireless vector-channel in the urban area, which has lots of high-story buildings, using the data collected from the 8 by 4 smart array antenna system that we made. According to the measured data, the received signals from different angles have different signal powers. Our performance analysis results show that the proposed scheme has better performance than the space diversity scheme when the received path signal power is at least -7dB compare to the strongest path signal power.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.239-242
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• 2003

Transmit diversity using STBC(Space Time Block Code) provides the same diversity gain as MRRC(Maximal Ratio Receiver Combining), when the fading channel is constant across two consecutive symbols. But, when the channel condition is changed for the two consecutive symbols, the transmit diversity using STBC does not offer good performance due to the large doppler shift. In this paper, we have proposed a interference cancellation scheme for performance enhancement in transmit diversity using STBC over time selective fading channel. Simulation results for various doppler shift rates are presented for the transmit diversity using the proposed scheme.

• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.451-463
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• 2016

The misalignment errors and fluctuations in irradiance due to atmospheric turbulence can severely degrade the performance of free-space optical (FSO) systems. In this paper, we investigate the asymptotic bit error rate (BER) performance and diversity orders of FSO links using parallel transmit-diversity schemes. The BER expressions of FSO links with the switch-and-examine transmit (SET), switch-and-examine transmit with post-selection (SETps), dual-branch transmit laser selection (Dual-TLS), and group transmit laser selection (Group-TLS) schemes are derived, based on an approximate channel model. Then numerical simulations for these four schemes in the region of high average signal-to-noise ratio (SNR) are presented under different channel conditions. The results show that the four transmit-diversity schemes can reduce system complexity and overcome the limitation of peak power, without much BER deterioration.

• Journal of electromagnetic engineering and science
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• v.6 no.4
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• pp.222-228
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• 2006

In this paper, the performance of a multiuser diversity system combined with a multi-element transmit antenna system is analyzed under the assumption of independent Rayleigh fading. A measure of system .level performance is an average channel capacity as a function of the number of users and antennas. Average channel capacity is obtained from the instantaneous signal-to-noise ratio(SNR) distribution combined by both transmit diversity(TD) at each link and multiuser diversity at system level. Numerical results show that closed-loop antenna techniques provide an additional gain with multiuser diversity system due to array gain, even though space diversity gain reduces multiuser diversity gain. On the other hand, the space-time block coding(STBC) that provides full order space diversity gain only has a destructive influence on multiuser diversity.

• Journal of Communications and Networks
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• v.10 no.4
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• pp.444-450
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• 2008

This paper studies the performance of multiuser data networks with transmit diversity under correlated fading channels. Previous work shows that correlated fading reduces the link performance of multiple antenna systems, but how correlated fading affects the throughput of multiuser data networks is still unknown since the throughput depends not only on the link performance but also on the multiuser diversity. We derive the throughput of the multiuser data networks with various transmit diversity schemes under correlated fading channels. The impact of correlated fading on the throughput is investigated. Analytical and simulation results show that, although correlated fading is harmful for link performance, it increases the throughput of the multiuser data networks if the transmit scheme is appropriately selected.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.727-732
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• 2008

The transmit diversity as well as beamforming can increase the performance of wireless communication systems. It is well known that the requirement for the spacing between the neighboring antennas in transmit diversity and beamforming is contradictive to each other. Therefore it is necessary to find the optimum configuration of multiple antennas for getting the maximum performance under the condition that the total number of antennas at transmitter site and the total power of transmitter are fixed. In this paper, the procedure for finding the optimum configuration of multiple antennas was derived through searching the maximum capacity and BER in the combined system with the transmit diversity (Tx diversity) and beamforming.

• Journal of the Korea Society of Computer and Information
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• v.11 no.2 s.40
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• pp.201-211
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• 2006

The standardization of third Generation Partnership Project(3GPP) has been performed in of order to support interactive multimedia services under mobile environments. In this 3GPP, transmit diversity solutions are applied to increase the available diversity effectively using 2 or more antennas. In this paper, we analyzer the performances on STTD(Space Time Transmit Diversity) technique and its modified techniques such as STTD-OTD, CL-STTD, and 4TX-STTD out of open loop transmit diversities that the standardization of 3GPP has released. We also propose the open loop transmitter and receiver diversities to add the receiver diversity. We analyze and discuss the performance of the proposed techniques and using the Matlab simulation under the flat fading channel environment.

• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.65-68
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• 2001

The selection transmit diversity is an effective way to avoid the deep fading in a wireless channel. However, it may not completely eliminate the SNR fluctuation of a received signal at the receiver. This letter presents an application of an adaptive modulation effectively exploiting the SNR variation over time for a higher spectral efficiency to the conventional selection transmit diversity. Numerical results show that the proposed scheme can achieve a SNR gain of about 7 dB over the conventional selection diversity in a flat Rayleigh fading environment, when a BER of 10$^{-3}$ and a spectral efficiency of 2 bps/Hz are required..