Full-duplex mode in amplify-and-forward relay channels: outage probability and ergodic capacity

This paper investigates the outage probability and ergodic capacity performances for full-duplex mode in two-way amplify-andforward relay channels. The two-way relay channels which consist of two source nodes and a single relay node working in full-duplex mode, are assumed as independent and identically distributed as Rayleigh fading. The self-interference or loop interference of the relay is unavoidably investigated for full-duplex mode. And the close-form expressions for the outage probability and ergodic capacity of full-duplex mode are derived, considering both loop interference and the coefficients of two-way relay amplify-andforward channels. To further facilitate the performance of full-duplex mode, the half-duplex modes over different transmission time slots are analyzed. Simulation results point out the effect of loop interference on outage probability and ergodic capacity of twoway amplify-and-forward relay channels with full-duplex mode and show that full-duplex mode can achieve better performance in terms of capacity and even outperform half-duplex modes in the presence of loop interference

On the performance of multiuser MIMO systems relying on full-duplex CSI acquisition

IEEE In this paper, we propose a combined full duplex (FD) and half duplex (HD) based transmission and channel acquisition model for open-loop multiuser multiple-input multipleoutput (MIMO) systems. Assuming residual self interference (SI) at the BS, the idea is to utilize the FD mode during the uplink (UL) training phase in order to achieve simultaneous downlink (DL) data transmission and UL CSI acquisition. More specifically, the BS begins serving a user when its CSI becomes available, while at the same time, it also receives UL pilots from the next scheduled user. We investigate both zero-forcing (ZF) and maximum ratio transmission (MRT) MIMO beamforming techniques for the DL data transmission in the FD mode. The BS switches to the HD mode once it receives the CSI of all users and it employs ZF beamforming for the DL data transmission until the end of the transmission frame. Furthermore, we derive closedform approximations for the lower bounded ergodic achievable rate relying on the proposed model. Our numerical results show that the proposed FD-HD transmission and channel acquisition approach outperforms its conventional HD counterpart and achieves higher data rates

Outage Probability Analysis of Full-Duplex Amplify-and-Forward MIMO Relay Systems

abstract: Multiple-input multiple-output systems have gained focus in the last decade due to the benefits they provide in enhancing the quality of communications. On the other hand, full-duplex communication has attracted remarkable attention due to its ability to improve the spectral efficiency compared to the existing half-duplex systems. Using full-duplex communications on MIMO co-operative networks can provide us solutions that can completely outperform existing systems with simultaneous transmission and reception at high data rates. This thesis considers a full-duplex MIMO relay which amplifies and forwards the received signals, between a source and a destination that do not a have line of sight. Full-duplex mode raises the problem of self-interference. Though all the links in the system undergo frequency flat fading, the end-to-end effective channel is frequency selective. This is due to the imperfect cancellation of the self-interference at the relay and this residual self-interference acts as intersymbol interference at the destination which is treated by equalization. This also leads to complications in form of recursive equations to determine the input-output relationship of the system. This also leads to complications in the form of recursive equations to determine the input-output relationship of the system. To overcome this, a signal flow graph approach using Mason's gain formula is proposed, where the effective channel is analyzed with keen notice to every loop and path the signal traverses. This gives a clear understanding and awareness about the orders of the polynomials involved in the transfer function, from which desired conclusions can be drawn. But the complexity of Mason's gain formula increases with the number of antennas at relay which can be overcome by the proposed linear algebraic method. Input-output relationship derived using simple concepts of linear algebra can be generalized to any number of antennas and the computation complexity is comparatively very low. For a full-duplex amplify-and-forward MIMO relay system, assuming equalization at the destination, new mechanisms have been implemented at the relay that can compensate the effect of residual self-interference namely equal-gain transmission and antenna selection. Though equal-gain transmission does not perform better than the maximal ratio transmission, a trade-off can be made between performance and implementation complexity. Using the proposed antenna selection strategy, one pair of transmit-receive antennas at the relay is selected based on four selection criteria discussed. Outage probability analysis is performed for all the strategies presented and detailed comparison has been established. Considering minimum mean-squared error decision feedback equalizer at the destination, a bound on the outage probability has been obtained for the antenna selection case and is used for comparisons. A cross-over point is observed while comparing the outage probabilities of equal-gain transmission and antenna selection techniques, as the signal-to-noise ratio increases and from that point antenna selection outperforms equal-gain transmission and this is explained by the fact of reduced residual self-interference in antenna selection method.Dissertation/ThesisMasters Thesis Electrical Engineering 201

Outage Probability of Multi-hop Networks with Amplify-and-Forward Full-duplex Relaying

abstract: Full-duplex communication has attracted significant attention as it promises to increase the spectral efficiency compared to half-duplex. Multi-hop full-duplex networks add new dimensions and capabilities to cooperative networks by facilitating simultaneous transmission and reception and improving data rates. When a relay in a multi-hop full-duplex system amplifies and forwards its received signals, due to the presence of self-interference, the input-output relationship is determined by recursive equations. This thesis introduces a signal flow graph approach to solve the problem of finding the input-output relationship of a multi-hop amplify-and-forward full-duplex relaying system using Mason's gain formula. Even when all links have flat fading channels, the residual self-interference component due to imperfect self-interference cancellation at the relays results in an end-to-end effective channel that is an all-pole frequency-selective channel. Also, by assuming the relay channels undergo frequency-selective fading, the outage probability analysis is performed and the performance is compared with the case when the relay channels undergo frequency-flat fading. The outage performance of this system is performed assuming that the destination employs an equalizer or a matched filter. For the case of a two-hop (single relay) full-duplex amplify-and-forward relaying system, the bounds on the outage probability are derived by assuming that the destination employs a matched filter or a minimum mean squared error decision feedback equalizer. For the case of a three-hop (two-relay) system with frequency-flat relay channels, the outage probability analysis is performed by considering the output SNR of different types of equalizers and matched filter at the destination. Also, the closed-form upper bounds on the output SNR are derived when the destination employs a minimum mean squared error decision feedback equalizer which is used in outage probability analysis. It is seen that for sufficiently high target rates, full-duplex relaying with equalizers is always better than half-duplex relaying in terms of achieving lower outage probability, despite the higher RSI. In contrast, since full-duplex relaying with MF is sensitive to RSI, it is outperformed by half-duplex relaying under strong RSI.Dissertation/ThesisMasters Thesis Electrical Engineering 201

양방향 릴레이 시스템을 위한 다중 홉 협력 릴레이 통신 방식 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2012. 8. 김성철.본 논문에서는 멀티 홉 릴레이에 적용할 수 있는 양방향 릴레이 알고리즘의 개발 과정을 다루고 있다. 기지국 만을 이용하는 기존의 통신 시스템의 경우 Line-of-Sight를 확보하기 힘들고 상대적으로 통신 거리가 멀어 시스템의 채널 용량을 확보하는 데에 어려움이 있다. 또한, 기지국을 많이 건설함으로써 통신 용량을 증대시키고 Line-of-Sight를 확보하는 방법에는 비용이 많이 소요된다. 멀티 홉 릴레이 시스템은 상대적으로 낮은 전송 파워와 짧은 거리를 이용하여, Line-of-Sight를 효과적으로 확보할 수 있고, 비용도 적게 소모된다는 장점이 있다. 멀티 홉 릴레이 시스템은 송수신 방법에 따라 반이중 릴레이 시스템 (HDR)과 양방향 릴레이 시스템 (FDR)으로 나눌 수 있다. 반이중 릴레이 시스템은 릴레이가 송신과 수신을 시간 혹은 주파수 대역으로 나누어 송/수신 함으로써 릴레이의 송신과 수신 사이에 간섭이 일어나지 않지만, 상대적으로 통신 자원을 효율적으로 사용하지 못한다는 단점이 있다. 양방향 릴레이 시스템은 같은 시간 및 주파수 대역을 이용하여 송수신을 하여 통신 자원을 효율적으로 사용할 수 있지만, 릴레이의 송수신 안테나 사이에서 자기 간섭이 발생하여 그 성능을 크게 저하시킨다는 단점을 갖는다. 따라서 본 논문은 릴레이의 자기 간섭을 제거하고 그 장점을 극대화 할 수 있는 프리코딩을 제안하여 양방향 릴레이의 성능을 향상시키고자 한다. 본 논문은 크게 Block-Diagonalization을 이용한 FDR 시스템과 Limited Feedback Precoding을 이용한 FDR 시스템으로 나눌 수 있다. 기존에 연구된 양방향 릴레이 시스템 관련 연구의 경우, Dirty Paper Coding을 이용하여 Rate bound를 구하거나, 실질적으로 릴레이 프리코딩을 고려하지 않고 성능을 구한 것이 대부분이다. 실제 시스템을 고려하여 양방향 릴레이를 연구한 논문의 경우 기지국과 단말에 한 개의 송수신 안테나를 적용하고 릴레이에만 두 개의 송수신 안테나를 적용하여 자기 간섭 채널의 영공간을 구해 양방향 릴레이 알고리즘을 구현하였다. 그러나, 이러한 방법의 경우 MIMO를 이용하여 채널 용량을 향상 시킬 수 없으며, 릴레이가 기지국보다도 오히려 많은 수의 송수신 안테나를 사용해야 한다. 또한, 릴레이가 여러 개 존재하는 상황이나 사용자가 여러 명 존재하는 상황을 고려하지 못하여 이러한 상황에 효과적으로 대처할 수 없다는 단점이 있다. 본 논문에서 제안하는 Block-Diagonalization을 이용한 FDR 시스템은 통신 채널 및 자기 간섭 채널을 결합하여 영공간을 구함으로써 기지국과 릴레이 및 사용자가 같은 수의 송수신 안테나를 사용하여 통신을 할 수 있도록 하였으며, MIMO 시스템을 적용할 수 있도록 하여 안테나 수를 늘려서 통신 시스템의 성능을 향상 시킬 수 있도록 하였다. 또한, 여러 개의 릴레이가 있는 시나리오와 여러 명의 사용자가 있는 시나리오를 고려하여 이러한 상황에서도 양방향 릴레이를 사용할 수 있도록 하였다. Limited Feedback Precoding을 이용한 FDR 시스템은 Limited Feedback Precoding을 이용한 양방향 릴레이 알고리즘을 제안한다. Limited Feedback Precoding은 Channel State Information을 필요로 하는 기존 알고리즘과 달리 최고의 성능을 나타내는 precoding의 index만을 feedback 함으로써 feedback 양을 줄이면서 양방향 릴레이 시스템의 성능을 향상 시킬 수 있다. 또한, Iterative Limited Feedback 알고리즘을 제안함으로써 Multi Relay 및 Multi User 시나리오에서도 더 적은 feedback 양으로 양방향 릴레이 알고리즘을 적용할 수 있도록 하였다.The promising concept of multi-hop relay has recently stimulated intensive research to improve the performance of wireless systems. It is well known that a cooperative link that uses a relay station (RS) not only enhances coverage but also increases the capacity of the communication system in a shadow region, wherein the strength of a signal transmitted from a base station (BS) might be less than the receiver sensitivity because of signal obstruction by geographical structures [1]. In a single-relay single-user (SRSU) half-duplex relay (HDR) system, two links (the link between a BS and an RS is called the BS-RS link and that between an RS and a mobile station (MS) is called the RS-MS link) exist with only one link operating at any given instant. Although this type of relay system is beneficial in terms of hardware simplicity, it suffers from the drawback of capacity reduction due to partitioned resources. In contrast, the advantage of a full-duplex relay (FDR) over an HDR system in terms of system capacity is that an RS in an FDR system can simultaneously transmit and receive signals in the same frequency band. Even though this advantage of an FDR system can improve system capacity, an FDR system suffers from the crucial limitation of self-interference that occurs between the signals transmitted from and received by the same RS (RS-RS link) [2]. This dissertation proposes the FDR precodings for the SRSU, multi-relay single-user (MRSU) and single-relay multi-user (SRMU) systems. In the SRSU and MRSU system, it is crucial to design an FDR precoding scheme in order to prevent aforementioned self-interference imposed by the transmitting antennas on the receiving antennas in the same relay station. In the SRMU FDR system, the multi-user interference caused by co-channel MSs must be considered. In this dissertation, I propose a precoder scheme that mitigates the residual self-interference of the relay station using block-diagonalization (BD) [3] and limited feedback precoding [4]-[5]. The proposed precoding scheme not only prevents self-interference but also provides the improved system capacity compared to HDR system. I propose the BD beamforming vectors that are designed in terms of BD criteria. The conventional technique requires 2 transmitting and receiving antennas in SISO SRSU system [6]. Compared to the conventional scheme, the proposed algorithm relaxes this restriction of the number of transmitting antennas by combining channel matrices and saves the transmit power of RSs. The proposed scheme can be adopted in multiple-input multiple-output (MIMO) SRSU, MRSU and SRMU systems. I also propose the FDR systems that are designed in terms of limited feedback criteria. The conventional FDR precodings require the channel state information of all communication channels. In the limited feedback precoding, the receiver selects one of the beamformers with the best signal-to-interference ratio (SINR) for that receiver and feeds back only the index of the optimal precoder. The proposed precoding scheme based on limited feedback precoding prevents self-interference and multi-user interference for the SRSU, MRSU and SRMU systems. I also propose iterative limited feedback precoding for the FDR system. The iterative limited feedback precoding only requires the channel state information of the adjacent relay and users. The proposed scheme not only provides less computational complexity but also achieves system performance closely to the centralized limited feedback precoding. Numerical results are illustrated to show the capacity analysis of the limited feedback and iterative limited feedback precodings for the SRSU, MRSU and SRMU systems.Contents Abstract i Contents v List of Figures viii List of Tables xi Chapter 1 Introduction １ 1.1 Relay Communications １ 1.2 Half-duplex relay and Full-duplex relay ３ 1.3 Block Diagonalization (BD) and Limited Feedback precoding ５ 1.4 Dissertation Outline ６ Chapter 2 BD FDR Precoding for the SRSU System ８ 2.1 Motivation ８ 2.2 System Model １０ 2.3 Channel Capacity of the SRSU HDR System １１ 2.4 Proposed Precoding Scheme for the SRSU FDR System １４ 2.5 Channel Capacity of the SRSU FDR System １８ 2.6 Simulation Results and Discussion １９ 2.7 Conclusion ２２ Chapter 3 BD FDR Precoding for the MRSU System ２３ 3.1 Motivation ２３ 3.2 System Model ２４ 3.3 Channel Capacity of the MRSU HDR System ２８ 3.4 Proposed Precoding Scheme for the MRSU FDR System ３０ 3.5 Channel Capacity of the MRSU FDR System ３４ 3.6 Simulation Results and Discussion ３６ 3.7 Conclusion ４０ Chapter 4 BD FDR Precoding for the SRMU System ４１ 4.1 Motivation ４１ 4.2 System Model ４２ 4.3 Channel Capacity of the SRMU HDR System ４５ 4.4 Proposed FDR Precoding Scheme for the SRMU System ４７ 4.5 Channel Capacity of the SRMU FDR System ５１ 4.6 Simulation Results and Discussion ５２ 4.7 Conclusion ５６ Chapter 5 Limited Feedback FDR Precoding for the SRSU System ５８ 5.1 Motivation ５８ 5.2 System Model ５９ 5.3 Proposed FDR Precoding Scheme for the SRSU System ６１ 5.4 Centralized Limited Feedback Precoding Scheme for the SRSU FDR System ６３ 5.5 Iterative Limited Feedback Precoding Scheme for the SRSU FDR System ６３ 5.6 Simulation Results and Discussion ６４ 5.7 Conclusion ６８ Chapter 6 Limited Feedback FDR Precoding for the MRSU System ６９ 6.1 Motivation ６９ 6.2 System Model ７０ 6.3 Proposed FDR Precoding Scheme for the MRSU System ７２ 6.4 Centralized Limited Feedback Precoding Scheme for the MRSU FDR System ７５ 6.5 Iterative Limited Feedback Precoding Scheme for the MRSU FDR System ７６ 6.6 Simulation Results and Discussion ７６ 6.7 Conclusion ８２ Chapter 7 Limited Feedback FDR Precoding for the SRMU System ８４ 7.1 Motivation ８４ 7.2 System Model ８５ 7.3 Proposed FDR Precoding Scheme for the SRMU System ８７ 7.4 Centralized Limited Feedback Precoding Scheme for the SRMU FDR System ８９ 7.5 Iteratrive Limited Feedback Precoding Scheme for the SRMU FDR System ８９ 7.6 Simulation Results and Discussion ９１ 7.7 Conclusion ９７ Chapter 8 Conclusion ９８ Bibliography １００Docto

Full-duplex wireless communications: challenges, solutions and future research directions

The family of conventional half-duplex (HD) wireless systems relied on transmitting and receiving in different time-slots or frequency sub-bands. Hence the wireless research community aspires to conceive full-duplex (FD) operation for supporting concurrent transmission and reception in a single time/frequency channel, which would improve the attainable spectral efficiency by a factor of two. The main challenge encountered in implementing an FD wireless device is the large power difference between the self-interference (SI) imposed by the device’s own transmissions and the signal of interest received from a remote source. In this survey, we present a comprehensive list of the potential FD techniques and highlight their pros and cons. We classify the SI cancellation techniques into three categories, namely passive suppression, analog cancellation and digital cancellation, with the advantages and disadvantages of each technique compared. Specifically, we analyse the main impairments (e.g. phase noise, power amplifier nonlinearity as well as in-phase and quadrature-phase (I/Q) imbalance, etc.) that degrading the SI cancellation. We then discuss the FD based Media Access Control (MAC)-layer protocol design for the sake of addressing some of the critical issues, such as the problem of hidden terminals, the resultant end-to-end delay and the high packet loss ratio (PLR) due to network congestion. After elaborating on a variety of physical/MAC-layer techniques, we discuss potential solutions conceived for meeting the challenges imposed by the aforementioned techniques. Furthermore, we also discuss a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc. Finally, a variety of new directions and open problems associated with FD technology are pointed out. Our hope is that this treatise will stimulate future research efforts in the emerging field of FD communication

Partial network coding with cooperation : a study over multi-hop communications in wireless networks

The imperfections of the propagation channel due to channel fading and the self-generated noise from the RF front-end of the receiver cause errors in the received signal in electronic communication systems. When network coding is applied, more errors occur because of error propagation due to the inexact decoding process. In this dissertation we present a system called Partial Network Coding with Cooperation (PNC-COOP) for wireless ad hoc networks. It is a system which combines opportunistic network coding with decode-and-forward cooperative diversity, in order to reduce this error propagation by trading off some transmission degrees of freedom. PNC-COOP is a decentralized, energy efficient strategy which provides a substantial benefit over opportunistic network coding when transmission power is a concern. The proposed scheme is compared with both opportunistic network coding and conventional multi-hop transmission analytically and through simulation. Using a 3-hop communication scenario, in a 16-node wireless ad hoc network, it is shown that PNC-COOP improves the BER performance by 5 dB compared to opportunistic network coding. On average, it reduces the energy used by each sender node around 10% and reduces the overall transmitted energy of the network by 3.5%. When retransmission is applied, it is shown analytically that PNC-COOP performs well at relatively low to medium SNR while the throughput is comparable to that of opportunistic network coding. The effectiveness of both opportunistic network coding and PNC-COOP depends not only on the amount of network coding but also on other factors that are analyzed and discussed in this dissertation.Keywords: opportunistic network coding, Telecommunications, cooperative diversity, network coding, user cooperatio