• Journal of electromagnetic engineering and science
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• 제6권4호
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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.

• 한국통신학회논문지
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• 제32권7A호
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• pp.694-699
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• 2007

본 논문에서는 레일리 페이딩 채널환경에서 폐루프 송신 안테나 다이버시티 시스템을 위한 최적의 안테나 가중치 방식을 연구한다. 평균전력 및 첨두 전력의 제한이 있는 경우에 폐루프 송신 안테나 다이버시티의 평균 비트 오류율을 최소화하는 최적의 송신 안테나 가중치를 닫힌 형식의 수학식으로 유도한다. 본 논문의 결과로부터 첨두 전력의 제한으로 인한 평균 비트 오류율 성능의 열화는 사용가능 한 평균전력이 커질수록 그리고/또는 송신 안테나 개수가 증가할수록 그 성능 열화의 정도가 더욱 커짐을 알 수 있다.

• Journal of electromagnetic engineering and science
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• 제10권3호
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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.

• Journal of information and communication convergence engineering
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• 제10권3호
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• pp.215-219
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• 2012

This paper applies transmit antenna selection algorithms to spatial-temporal combining-based spatial multiplexing (SM) ultra-wideband (UWB) systems. The employed criterion is based on the largest minimum output signal-to-noise ratio of the multiplexed streams. It is shown via simulations that the bit error rate (BER) performance of the SM UWB systems based on the two-dimensional Rake receiver is significantly improved by antenna diversity through transmit antenna selection on a log-normal multipath fading channel. When the transmit antenna diversity through antenna selection is exploited in the SM UWB systems, the BER performance of the spatial-temporal combining-based zero-forcing (ZF) receiver is also compared with that of the ZF detector followed by the Rake receiver.

• Journal of Communications and Networks
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• 제13권5호
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• pp.456-462
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• 2011

This paper investigates the outage behavior of peak interference power limited cognitive radio (CR) networks with multiple transmit antennas. In CR-multi-input single-output (MISO) channel, the total transmit power is distributed over the transmitantennas. First, we use the orthogonal space-time codes (STC) to achieve the transmit diversity at CR-receiver (rx) and investigate the effect of the power distribution on the interference power received at the primary-receiver (P-rx). Then, we investigate the transmit antenna selection (TAS) scheme in which the CR system selects the best transmit antenna and allocates all the power to the selected best antenna. Two transmit antenna selection strategies are proposed depending on if feedback channel is available or not. We derive the closed form expressions of outage probability and outage capacity of all schemes with arbitrary number of transmit-antennas. We show that the proposed schemes significantly improve the outage capacity over the single antenna systems in Rayleigh fading environment. We also show that TAS based scheme outperforms the STC based scheme when peak interference power constraint is imposed on the P-rx only if a feedback channel from CR-rx to CR-transmitter is available.

• 전자공학회논문지
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• 제51권4호
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• pp.3-9
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• 2014

ECMA-392는 개인 휴대용 장치를 위한 최초의 CR (cognitive radio) 표준으로서, 2개까지의 전송 안테나를 지원하며 이를 위한 전송 다이버시티 기법으로는 개방루프 방식만을 지원한다. 본 논문에서는 ECMA-392 시스템을 위한 간단한 형태의 부반송파 그룹핑(sub-carrier grouping) 기반 폐루프 전송 다이버시티 기법을 설계하고자 한다. ECMA-392 시스템에 적합한 부반송파 그룹핑 방법을 제시할 것이며, 각각의 부 반송파 그룹에 대해 채널 환경에 따른 전송 안테나 선택 방법을 제안한다. 이때 피드백 정보량을 줄이기 위해, 채널 환경에 따른 전송 안테나 결정을 수신단에서 하고 결정된 전송 안테나의 인덱스 값만을 송신단에 보내주는 방식을 사용한다. ECMA-392 표준에서 제시하는 개방루프 전송 다이버시티 기법들과의 성능비교를 통해, ECMA-392 시스템에 폐루프 전송 다이버시티 기법의 도입 여부에 대한 판단 근거를 제시하고자 한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -3
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• pp.1960-1963
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• 2002

Transmit diversity schemes we an effective capacity improvement method for down link of wideband code division multiple access (W-CDMA) systems. In this paper, we propose to use transmit antenna subset selection scheme in conjunction with closed loop transmit adaptive array (TxAA). The proposed scheme selects N$\_$s/ optimum antennas among N$\_$${\gamma}$/(>N$\_$s/) transmit antennas in order to maximize diversity gain from selected antennas, and also reduces the cost of RE chains by employing two different types of RF modules fur the selected and the unselected antenna group, respectively. Computer simulation results show performance improvement by the proposed scheme over the conventional TxAA when considering up link control information feedback.

• 전기학회논문지P
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• 제60권4호
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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.

• ETRI Journal
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• 제34권3호
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• pp.319-329
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• 2012

Closed-loop transmit diversity is considered an important technique for improving the link budget in the third generation and future wireless communication standards. This paper proposes several transmit diversity algorithms suitable for small wireless terminals and presents performance assessment in terms of average signal-to-noise ratio (SNR) and outage improvement, convergence, and complexity of operations. The algorithms presented herein are verified using data from measured indoor channels with variable antenna spacing and the results explained using measured radiation patterns for a two-element array. It is shown that for a two-element array, the best among the proposed techniques provides SNR improvement of about 3 dB in a tightly spaced array (inter-element spacing of 0.1 wavelength at 2 GHz) typical of small wireless devices. Additionally, these techniques are shown to perform significantly better than a single antenna device in an indoor channel considering realistic values of latency and propagation errors.

• Journal of electromagnetic engineering and science
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• 제3권2호
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• pp.99-103
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• 2003

For mobile multimedia systems that equip transmit diversity for a forward channel, it is well known that the Tx diversity technique is appropriate for high rate mobile multimedia communications. In this paper, we propose a STTD (Space Time Transmit Diversity) receiver, which incorporates the design of the Tx diversity receiver without the mutual interference of antenna by using a CCI cancellation technique. The new STTD receiver is simulated and its performance is analyzed in a DS-CDMA/QPSK. Adopting the proposed STTD receiver at $10^{-2}$TEX>∼$10^{-4}$TEX> in bit error rate, SNR of 0.5 ㏈∼2 ㏈ performance improvement in AWGN and Rayleigh fading environments has been achieved.