Large Scale Fading값만을 피드백하는 분산 안테나 시스템을 위한 최적 전력 할당

임동호(Dongho Lim),최권휴(Kwonhue Choi) 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.6A

본 논문에서는 time-varying Rayleigh fading channel에서 분산 안테나 시스템의 최적 전력 분배 기법을 제안한다. 기존 관련 연구에서는 각 기지국으로부터 수신되는 전력의 차이를 기지국간 전력 분배에 고려하지 않았으나, 최근 들어 빠르게 변하는 small scale fading까지 Channel State Information (CSI)로하여 전력 분배를 하는 경우에 대한 연구가 진행되었다. 하지만, 실제 무선통신 환경에서 송수신단간의 거리 차이 때문에 피드백이 반영된 신호가 수신될 때의 페이딩 채널은 피드백을 하는 시점과는 차이가 있고, 이로 인한 성능저하가 나타난다. 본 논문에서는 이러한 성능저하를 극복하고 CSI 피드백의 부담을 경감시키기 위하여 small scale fading을 제외하고, 느리게 변하는 경로손실과, 섀도잉에 의한 large scale fading값만을 피드백하는 분산 안테나 시스템을 제안하고 Bit Error Rate (BER)을 최소화하기 위한 최적 전력 분배 공식을 유도했다. 빠른 페이딩 환경에서, 제안된 최적 전력분배 기법이 small scale fading까지 고려한 전력 분배 기법보다 월등히 좋은 성능을 보이며, 피드백 지연이 없는 환경에서도 1dB 이내의 성능을 보이는 것을 확인했다. 또한, 본 논문에서 Rayleigh fading channel을 가정하여 유도한 전력 분배 기법이 Line-of-Sight(LOS) 성분의 크기가 작은 Ricean fading channel에서도 최소의 BER과 거의 비슷한 값을 달성함을 보였다. We propose the Optimum Power Allocation (OPA) scheme for Distributed Antenna Systems(DAS) in the time-varying Rayleigh fading channel. Recently, the OPA schemes which uses the Channel State Information (CSI) including a small scale (fast) fading have been proposed. However, the channel is changing vary fast over time due to small scale fading, therefore Bit Error Rate (BER) increases. Because of this reason, we derive the OPA for minimizing BER in DAS, which only uses a large scale fading to CSI and excepts a small scale fading. The simulation results show that the proposed OPA achieves better BER performance than conventional OPA considering a small scale fading in time-varying Rayleigh fading channel, and also has similar performance in Rayleigh flat-fading environment. The BER performance of proposed OPA which derived in Rayleigh fading channel is similar to minimum BER of Ricean fading channel which has small Line-of-Sight (LOS).

Analysis of Improved Cyclostationary Spectrum Sensing with SLC Diversity over Composite Multipath Fading-Lognormal Shadowing Channels

( Ying Zhu ),( Jia Liu ),( Zhiyong Feng ),( Ping Zhang ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.3

Spectrum sensing is a key technical challenge for cognitive radio (CR). It is well known that multi-cycle cyclostationarity (MC) detector is a powerful method for spectrum sensing. However, conventional MC detector is difficult to implement due to its high computational complexity. This paper pays attention to the fact that the computation complexity can be reduced by simplifying the test statistic of conventional MC detector. Based on this simplification process, an improved MC detector is proposed. Compared with the conventional one, the proposed detector has the low-computational complexity and sufficient-accuracy on sensing performance. Subsequently, the sensing performances are further investigated for the cases of Rayleigh, Nakagami-m, Rician, composite Rayleigh fading-lognormal shadowing and composite Nakagami fading-lognormal shadowing channels, respectively. Furthermore, the square-law combining (SLC) is introduced to improve the detection capability over fading-shadowing channels. The corresponding closed-form expressions of average detection probability are derived for each case by the moment generation function (MGF) approach. Finally, illustrative and analytical results show that the efficiency and reliability of proposed detector and the improvement on sensing performance by SLC over composite fading-shadowing channels.

Schur Complement Based Analysis of MIMO Zero-Forcing for Rician Fading

Siriteanu, Constantin,Takemura, Akimichi,Kuriki, Satoshi,Richards, Donald St. P.,Hyundong Shin IEEE 2015 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.14 No.4

<P>For multiple-input/multiple-output (MIMO) spatial multiplexing with zero-forcing detection (ZF), signal-to-noise ratio (SNR) analysis for Rician fading involves the cumbersome noncentral-Wishart distribution (NCWD) of the transmit sample-correlation (Gramian) matrix. An approximation with a virtual CWD previously yielded for the ZF SNR an approximate (virtual) Gamma distribution. However, analytical conditions qualifying the accuracy of the SNR-distribution approximation were unknown. Therefore, we have been attempting to exactly characterize ZF SNR for Rician fading. Our previous attempts succeeded only for the sole Rician-fading stream under Rician-Rayleigh fading, by writing the ZF SNR as scalar Schur complement (SC) in the Gramian. Herein, we pursue a more general matrix-SC-based analysis to characterize SNRs when several streams may undergo Rician fading. On one hand, for full-Rician fading, the SC distribution is found to be exactly a CWD if and only if a channel-mean-correlation condition holds. Interestingly, this CWD then coincides with the virtual CWD ensuing from the approximation. Thus, under the condition, the actual and virtual SNR-distributions coincide. On the other hand, for Rician-Rayleigh fading, the matrix-SC distribution is characterized in terms of the determinant of a matrix with elementary-function entries, which also yields a new characterization of the ZF SNR. Average error probability results validate our analysis vs. simulation.</P>

Performance of the Long Code MMSE Detector With Pilot Channel in the Presence of Rayleigh Fading

Lee, Yun-Soo,Chinn, Yong-Oak The Korea Institute of Information and Commucation 2007 Journal of information and communication convergen Vol.5 No.4

In this paper we propose a new structure of the long code MMSE receiver with pilot channel, which maintians excellent symbol detection capability even in the presence of Rayleigh fading. We explain analytically how the stability of the receiver weight vector, which is critical to the system performance, can be achieved by compensating the error signal as well as received signal vector distorted by fading channel. Computer simulation shows while maintaining better performance than the conventional matched filter receiver, the proposed long code MMSE receiver can extend its period up to $16{\times}T_b$ in a fading environment.

Maximum Likelihood SNR Estimation for QAM Signals Over Slow Flat Fading Rayleigh Channel

( Nida Ishtiaq ),( Shahzad A. Sheikh ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.11

Estimation of signal-to-noise ratio (SNR) is an important problem in wireless communication systems. It has been studied for various constellation types and channels using different estimation techniques. Maximum likelihood estimation is a technique which provides efficient and in most cases unbiased estimators. In this paper, we have applied maximum likelihood estimation for systems employing square or cross QAM signals which are undergoing slow flat Rayleigh fading. The problem has been considered under various scenarios like data-aided (DA), non-data-aided (NDA) and partially data-aided (PDA) and the performance of each type of estimator has been evaluated and compared. It has been observed that the performance of DA estimator is best due to usage of pilot symbols, with the drawback of greater bandwidth consumption. However, this can be catered for by using partially data-aided estimators whose performance is better than NDA systems with some extra bandwidth requirement.

Outage probability and channel capacity for the <i>N</i>th best relay selection AF relaying over INID Rayleigh fading channels

Ko, K.,Woo, C. John Wiley Sons, Ltd 2012 International Journal of Communication Systems Vol.25 No.11

<P><B>SUMMARY</B></P><P>Cooperative diversity systems have recently been proposed as a way to form virtual antenna schemes without utilizing collocated multiple antennas. In this paper, we consider the <I>N</I>th best opportunistic amplify‐and‐forward (AF) cooperative diversity systems. The AF type can be regarded as one on the basis of modified channel state information. Wireless channels between any pair of nodes (i.e., direct and dual hop links) are assumed quasi‐static independent and nonidentically distributed (INID) Rayleigh fading. The best opportunistic AF (OAF) scheme requires two phases of transmission. During the first phase, the source node transmits a signal to all relays and the destination. In the second phase, the best relay is only selected on the basis of highest signal‐to‐noise ratio (SNR) scheme to forward the source signal to the destination. Therefore, the indirect link (i.e., source‐selected relay destination) can give the highest received SNR. However, the best relay selection cannot be available so that we might choose the second, third, or generally the <I>N</I>th best relay. In this paper, we derive the approximated outage probability and channel capacity for the <I>N</I>th best OAF relay systems over INID Rayleigh fading channels. At first, the indirect link's received SNR is approximated as harmonic mean upper bound. With this information, we obtain the given relay's <I>N</I>th best selection probability as the closed form. Finally, both outage probability and channel capacity are derived as the closed forms. Simulation results are finally presented to validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd.</P>

On Practical Issue of Non-Orthogonal Multiple Access for 5G Mobile Communication

Kyuhyuk Chung 한국인터넷방송통신학회 2020 International Journal of Internet, Broadcasting an Vol.12 No.1

The fifth generation (5G) mobile communication has an impact on the human life over the whole world, nowadays, through the artificial intelligence (AI) and the internet of things (IoT). The low latency of the 5G new radio (NR) access is implemented by the state-of-the art technologies, such as non-orthogonal multiple access (NOMA). This paper investigates a practical issue that in NOMA, for the practical channel models, such as fading channel environments, the successive interference cancellation (SIC) should be performed on the stronger channel users with low power allocation. Only if the SIC is performed on the user with the stronger channel gain, NOMA performs better than orthogonal multiple access (OMA). Otherwise, NOMA performs worse than OMA. Such the superiority requirement can be easily implemented for the channel being static or slow varying, compared to the block interval time. However, most mobile channels experience fading. And symbol by symbol channel estimations and in turn each symbol time, selections of the SIC-performing user look infeasible in the practical environments. Then practically the block of symbols uses the single channel estimation, which is obtained by the training sequence at the head of the block. In this case, not all the symbol times the SIC is performed on the stronger channel user. Sometimes, we do perform the SIC on the weaker channel user; such cases, NOMA performs worse than OMA. Thus, we can say that by what percent NOMA is better than OMA. This paper calculates analytically the percentage by which NOMA performs better than OMA in the practical mobile communication systems. We show analytically that the percentage for NOMA being better than OMA is only the function of the ratio of the stronger channel gain variance to weaker. In result, not always, but almost time, NOMA could perform better than OMA.

An Analysis of Combining Methods in Cooperative Spectrum Sensing over Rayleigh Fading Channel

Tran Thanh Truc,Hyung-Yun Kong 한국전자파학회JEES 2010 Journal of Electromagnetic Engineering and Science Vol.10 No.3

This paper evaluates the performance of two methods of spectrum sensing: the linear combining method and the selection combining method which is based on maximum SNR of sensing channel. We proposed a rule for global detection for the purpose of combating hidden terminal problems in spectrum sensing. Our analysis considers a situation when sensing channels experience the non-identically, independently distributed(n.i.d) Rayleigh fading. The average probabilities of global detection in these methods are derived and compared. In the scope of this paper, the reporting channels are assumed to be the AWGN channel with invariant and identical gain during the system’s operation.

레일리 페이딩하에서 slotted_CDMA_ALOHA 프로토콜의 성능해석

양성룡 거제전문대학 1997 論文集 Vol.5 No.-

CDMA technique has been largely focused for wireless network. ALOHA protocol also has been proven to be effective for packet radio network regardless of low throughput due to channel collisions. In this paper, we analysis the performance of a S_CDMA_ALOHA system within BER for multiple access interference and Rayleigh fading. As the result, the performance of S_CDMA_ALOHA system show a more important role that short-term fading and multiple access interference.

Performance of $M$-ary Turbo Coded Synchronous FHSS Multiple Access Networks with Noncoherent MFSK under Rayleigh Fading Channels

홍성남,전경훈,임현택,조성혜 한국통신학회 2013 Journal of communications and networks Vol.15 No.6

The performance of M-ary turbo coded synchronous,fast frequency-hopping spread spectrum multiple-access (FHSSMA)networks with M-ary frequency shift keying (MFSK) andnoncoherent detection is analyzed under Rayleigh fading. Resultsindicate thatM-ary turbo codes dramatically enhance the performanceof FHSS-MA networks using MFSK compared to binaryturbo codes.