• 한국통신학회논문지
• /
• 제34권1C호
• /
• pp.1-8
• /
• 2009

Cooperative diversity is a novel technique to improve diversity gains, capacity gains, and energy saving. This technique involves multiple terminals sharing resources in order to build a virtual antenna array in a distributed fashion. In this paper, we propose a multi-user cooperative diversity protocol called Relay-assisted Multiple Access Channel(R-MAC) that allows multiple source terminals to transmit their signals simultaneously and the relay terminal forwards the aggregated signal received from the source terminals to the destination terminal. The proposed protocol converts the distributed antenna channels into an effective MIMO channel by exploiting a relay, increasing both diversity gain and system throughput. We investigate the performance of the proposed protocol in terms of outage probability and diversity-multiplexing tradeoff where we assume block fading channel environment. Our simulation results show that the proposed protocol outperforms direct transmission in the high spectral efficiency regime where the conventional cooperative diversity protocols cannot outperform direct transmission.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제9권5호
• /
• pp.1682-1701
• /
• 2015

In this paper, we propose an intergraded unified imperfect CSI model and investigate the joined effects of feedback delay and channel estimation errors (CEE) for two-hop relaying systems with transmit beamforming and relay selection. We derived closed-form expressions for important performance measures including the exact analysis and lower bounds of outage probability as well as error performance. The ergodic capacity is also included with closed-form results. Furthermore, diversity and coding gains based on the asymptotic analysis at high SNRs are also presented, which are simple and concise and provide new analytical insights into the corresponding power allocation scheme. The analysis indicates that delay effect results in the coding gain loss and the diversity order loss, while CEE will merely cause the coding gain loss. Numerical results verify the theoretical analysis and illustrate the system is more sensitive to transmit beamforming delay compared with relay selection delay and also verify the superiority of optimum power allocation. We further investigate the outage loss due to the CEE and feedback delays, which indicates that the effect of the CEE is more influential at low-to-medium SNR, and then it will hand over the dominate role to the feedback delay.

• ETRI Journal
• /
• 제43권3호
• /
• pp.400-413
• /
• 2021

This paper theoretically and empirically explores the reliability gain that can be obtained by installing multiple antennas in on-vehicle broadcasting receivers. Analytical derivations reveal that maximal-ratio-combining-based diversity allows a multi-antenna receiver (MR) to achieve significantly better coverage probability than a single-antenna receiver (SR). In particular, the notable MR gains for low-power reception and high-throughput services are highlighted. We also discuss various aspects of mobile MRs, including geometric coverage, volume of the users served, and impact of receiver velocity. To examine the feasibility of MRs in the real world, extensive field experiments were conducted, particularly with on-air ATSC 3.0 broadcast transmissions. Relying on the celebrated erroneous second ratio criterion, MRs with two and four antennas were verified to achieve notable reliability gains over SRs in practice. Furthermore, our results also prove that layered-division multiplexing can cope better with receiver mobility than traditional time-division multiplexing when multiple services are intended in the same radio frequency channel.

• Journal of information and communication convergence engineering
• /
• 제9권5호
• /
• pp.515-522
• /
• 2011

In this paper, we investigate cooperative diversity in a spectrum sharing environment where secondary users utilize primary users' spectrum only if the interference power received at the primary users is maintained below a predetermined level. The outage probability of a selective decode-and-forward (DF) based cooperative diversity scheme in the secondary network is derived to analyze the effects of spectrum sharing on cooperative diversity. Our analytical and simulation results show that the outage probability is saturated at a certain level of transmit power of secondary users due to interference regulation, and, hence, cooperative diversity gains are lost. Through asymptotic analysis, we also identify the critical value of transmit SNR beyond which the outage probability is saturated.

• 한국통신학회논문지
• /
• 제33권10A호
• /
• pp.964-971
• /
• 2008

본 논문에서는 채널이 시간 및 주파수에서 비선택적일 때를 가정하여 복수의 송신 안테나를 사용하는 SC-FDE(Single Carrier with Frequency Domain Equalization) 시스템에서 순환지연 다이버시티 기술과 위상 회전 기술의 성능을 비교한다. OFDM(Orthogonal Frequency Division Multiplexing) 시스템에서는 위상 회전을 이용하여 시간축에서 변화하는 채널을 만드는 것과 순환지연 다이버시티를 사용하여 주파수 선택적 채널을 만드는 것은 유사한 성능을 보인다. 그러나 SC-FDE 시스템에서는 시간축에서 변화하는 채널을 만드는 것이 주파수축에서 변화하는 채널을 만드는 것보다 더 우수한 성능을 보일 수 있다.

• 한국통신학회논문지
• /
• 제33권9A호
• /
• pp.867-873
• /
• 2008

Cyclic delay diversity (CDD) is considered as a simple approach to exploit the frequency diversity in OFDM system. In this paper, we apply CDD to the conventional STBC/SFBC/STFBC-OFDM transmit diversity schemes for Rayleigh fading channels. We compare the performances of STBC/SFBC/STFBC with and without CDD schemes. Simulation results show that the combination of block coding with CDD works well when using the ITU-R M. 1225 channel for both Pedestrian A (Ped A) channel with the mobility of 3 km/h, and Vehicular A (Veh A) channel with the mobility of 120km/h. For a BER of $10^{-3}$, compared to the conventional block coding schemes, a gain of 2dB, 4dB, and 5dB is obtained under the Ped A channel environment by STBC-OFDM, SFBC-OFDM and STFBC-OFDM with CDD, respectively Under the Veh A channel. gains by the combined schemes are 6dB, 2dB, and 4dB, respectivcly.

• 한국통신학회논문지
• /
• 제29권11A
• /
• pp.1237-1243
• /
• 2004

This paper presents and analyses the closed-form expression of the average bit error rate (BER) for an asynchronous direct-sequence code division multiple access (DS-CDMA) system with coherent binary phase shift keying (BPSK) modulation scheme using a maximal ratio combining (MRC) diversity over a Rician fading channel. In addition to the average BER, outage probability, and user capacity of system are estimated as performance measures. The results are general enough so that it includes Rayleigh fading and nonfading channel with zero and infinite Rician factor, respectively, as special cases. The effects of various channel models, processing gains, and diversity orders on the system performances are also considered for the typical multipath delay profiles characterized by Rician fading channel.

• 전기학회논문지P
• /
• 제62권4호
• /
• pp.216-222
• /
• 2013

Handover is a technical methodology to support mobility of wireless communication users, which mainly affects the capacity of wireless communication systems and the quality of service (QoS) of link level signal. However, in OFDMA-based cellular systems, there are few published technical reports investigating handovers with respect to diversity gains and resource consumption depending on what handover technique is adopted. In this paper, we propose handover schemes exploiting transmit diversity and macro-diversity in order to increase capacity of OFDMA-based wireless communication systems, and analyze their performance. In cellular environments, depending on what handover scheme is selected, average signal-to-interference-and-noise ratio is calculated first for a handover user in order to evaluate the link level QoS. Through this technical evaluation for handover schemes, we conclude what handover scheme is suitable for OFDMA-based cellular systems.

• 한국ITS학회 논문지
• /
• 제11권6호
• /
• pp.81-88
• /
• 2012

다중 입출력(MIMO : Multiple-Input Multiple-Output) 시스템은 공간 다이버시티 이득과 공간 다중화 이득을 얻을 수 있게 한다. 본 논문에서는 MIMO 시스템에서 데이터 정보와 안테나 선택 기법을 이용한 공간 부호화 기법을 제안한다. 이 기법은 부호화 이득과 동시에 공간 다이버시티 이득을 얻을 수 있게 한다. BPSK(Binary Phase-Shift Keying) 변조 방식을 사용한 MIMO 시스템에서 BER 성능을 분석하고, 데이터의 편재율에 따라 달라지는 공간 다이버시티 이득을 실험을 통하여 비교하였다.

• 한국통신학회논문지
• /
• 제36권9A호
• /
• pp.776-783
• /
• 2011

본 논문에서는 적응형 복호 후 전송 (decode-and-forward) 중계 프로토콜이 송신을 위해 불완전한 채널정보를 사용할 때, 목적지 노드에서만 다중 안테나를 사용하는 경우, 릴레이 노드에서만 다중안테나를 사용하는 경우, 그리고 소스 노드에서만 다중 안테나를 사용하는 경우에 대한 diversity-multiplexing tradeoff (DMT) 상계 함수들을 유도하여 그 결과를 제시한다. 또한 소스 노드와 목적지 노드, 소스 노드와 릴레이 노드, 릴레이 노드와 목적지 노드 사이의 불완전한 채널정보들이 점근적 조건하에 있을 경우, 적응형 복호 후 전송 중계 프로토콜이 얻을 수 있는 다이버시티 이득을 조사한다.