Joint space-frequency block codes and signal alignment for heterogeneous networks

In this paper, we propose a new diversity-oriented space-frequency block codes (SFBC) and signal alignment (SA) enabled physical network coding (PNC) method for the uplink of heterogeneous networks. The proposed joint Dual-SFBC with SA-PNC design substantially reduces interference and enables connecting a larger number of users when compared with methods adopting interference alignment (IA) or PNC. The main motivation behind the dual SFBC and SA-PNC design is that it allows the efficient coexistence of macro and small cells without any inter-system channel information requirements. Numerical results also verify that the proposed method outperforms the existing SA-PNC static method without any additional information exchange requirement between the two systems while achieving the main benefits of IA and SA-PNC coordinated methods recently proposed.publishe

다중입출력 간섭 채널에서 알라무티 부호 기반 간섭 정렬 후 제거 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 2. 노종선.본 논문은 알라무티 부호와 협동 통신, 그리고 간섭 정렬에 관한 다음 세 가지 연구 결과를 포함하고 있다. 첫째, 다중입출력 간섭 채널에서 알라무티 부호를 활용하는 기법을 제시한다. 다원 접속 채널에서의 알라무티 부호 기반 간섭 제거 기법이 K-사용자 간섭 채널에서도 활용 가능한 것을 보인다. 수신 단에서 알라무티 구조를 이용하여 간섭 신호를 제거함으로써 심볼 단위 복호가 가능하고 다이버시티 차수 2를 얻을 수 있다. 또한 간섭 정렬 기법과 달리 송신 단에서 채널 상태 정보를 필요로 하지 않는다는 이점이 있다. 그러나 알라무티 부호 기반 간섭 제거 기법이 간섭 정렬 기법과 같은 자유도를 달성하기 위해서는 수신 단에서 많은 수의 안테나를 이용해야만 한다. 수신 안테나의 수를 줄이기 위한 노력의 일환으로, 3-사용자 간섭 채널에서의 알라무티 부호 기반 간섭 정렬 후 제거 기법을 제시한다. 제안된 기법은 송신 단에서 부분적 채널 상태 정보를 필요로 하는 대신에 적은 수신 안테나를 이용하여 간섭 제거 기법과 같은 자유도 및 다이버시티 차수를 얻는다. 본 논문에서는 제안된 두 가지 기법에 대해 쌍 오류 확률을 분석하여 기존의 간섭 정렬 기법보다 우수한 다이버시티 차수를 얻을 수 있다는 것을 증명한다. 본 논문의 두 번째 결과로, 알라무티 부호를 기반으로 한 양방향 중계 기법 두 가지를 제시한다. 첫 번째 기법은 K-사용자 간섭 채널에서의 알라무티 부호 기반 간섭 제거 기법을 양방향 중계 채널에 활용한 것이고, 이를 통해 심볼 단위 복호가 가능할 뿐만 아니라 다이버시티 이득을 얻는다. 더욱 많은 다이버시티 이득을 달성하기 위해 두 번째 양방향 중계 기법에서는 빔형성 행렬을 이용하여 중계기에 신호를 정렬시킨다. 컴퓨터 모의실험을 실시하여 두 기법에 대한 비교를 통해, 제안된 두 번째 기법의 다이버시티 이득이 첫 번째 기법보다 우수하다는 결론을 도출한다. 마지막으로, 여러 개의 중계기를 갖는 연판정 후 전달 협동 통신망에서 중계기 선택 방식을 제안하고, 이의 성능을 분석한다. 제안된 중계기 선택 기법은 가장 큰 end-to-end 신호 대 잡음비를 갖는 중계기를 선택하여 전송에 참여시킨다. 중계기 선택 기법의 쌍 오류 확률과 비트 오류 확률을 분석하고, 이를 모든 중계기가 전송에 참여하는 기존 방식의 성능과 비교한다. Fox H-함수의 극한값으로부터 중계기 선택 방식과 기존 방식의 다이버시티 차수를 구한다. 두 시스템에 대한 비교를 통해, 중계기 선택 방식은 비티 오류 확률이나 전송률 측면에서 기존의 방식보다 우수한 성능을 가짐을 확인한다.This dissertation contains the following three contributions to the interesting research topics on Alamouti code, interference alignment (IA), and cooperative communications. First, the methods on how to apply Alamouti code to MIMO interference channels are proposed. The IC method based on Alamouti codes for the multi-access scenario can be used for the K-user interference channel, which enables the receivers to perform symbol-by-symbol decoding by cancelling interfering signals by utilizing Alamouti structure and achieve diversity order of two. Moreover it does not require channel state information at the transmitters (CSIT) unlike the IA scheme. However, it requires more receive antennas than the IA scheme to achieve the same degrees of freedom (DoF). In order to reduce the number of receive antennas, especially for the three-user MIMO interference channel, an IAC scheme based on Alamouti codes is proposed, which keeps the same DoF as that of the IC scheme, but it requires partial CSIT. It is analytically shown that the IC and IAC schemes enable symbol-by-symbol decoding and achieve diversity order of two, while the conventional IA scheme achieves diversity order of one. In the second part of this dissertation, we propose two schemes for a TWRC based on Alamouti codes. Our IC method based on Alamouti codes for the K-user interference channel can be used for the TWRC, which enables the nodes to perform symbol-by-symbol decoding and achieve diversity order of two. In order to achieve more diversity gain, we propose a new two-way relaying scheme based on Alamouti codes which utilizes beamforming matrices to align signals at the relay node. From the simulation results, it is shown that the proposed scheme achieves diversity order of four. Finally, we analyze the best relay selection scheme for the SDF cooperative networks with multiple relays. The term best relay selectionimplies that the relay having the largest end-to-end signal-to-noise ratio is selected to transmit in the second phase transmission. The upper and lower bounds on the average pairwise error probability (PEP) are analyzed and compared with the conventional multiple-relay transmission scheme, where all the relays participate in the second phase transmission. Using the upper and lower bounds on the PEP and the asymptotes of the Fox's H-function, the diversity orders of the best relay selection and conventional relay schemes for the SDF cooperative networks are derived. It is shown that both schemes have the same full diversity order.Abstract i Contents v List of Tables viii List of Figures ix 1. Introduction 1 1.1. Background .......................................... 1 1.2. Overview of the Dissertation ........................ 5 1.3. Terms and Notations ................................. 7 2. Preliminaries 10 2.1. MIMO Communications ................................ 11 2.2. Space-Time Coding and Selection Diversity .......... 12 2.3. Cooperative Communications ......................... 16 2.3.1. Amplify-and-Forward Protocol ..................... 18 2.3.2. Decode-and-Forward Protocol ...................... 20 2.4. Interference Alignment ............................. 21 3. Interference Alignment-and-Cancellation Scheme Based on Alamouti Codes for the Three-User Interference Channel 25 3.1. Introduction ....................................... 25 3.2. Interference Cancellation Scheme Based on Alamouti Codes 28 3.2.1. Proof of Theorem 3.1 for K = 2 ................... 29 3.2.2. Proof of Theorem 3.1 for K ≥ 3 .................. 34 3.3. Interference Alignment-and-Cancellation Scheme for the Three-User MIMO Interference Channel .................... 36 3.3.1. Transmission and Reception Schemes ............... 37 3.3.2. Diversity Analysis ............................... 40 3.3.2.1. Proof of Theorem 3.2 for Receiver 1 when M = 1 . 41 3.3.2.2. Proof of Theorem 3.2 for Receivers 2 and 3 when M = 1 ............................................ 47 3.3.2.3. Proof of Theorem 3.2 for M ≥ 2 ................ 50 3.3.3. Extension to K-User MIMO Interference Channel .... 52 3.4. Simulation Results ................................. 53 3.5. Conclusions ........................................ 55 4. Two-Way Relaying Schemes with Alamouti Codes 57 4.1. Introduction ....................................... 57 4.2. Two-Way Relaying Scheme I Based on Alamouti Codes .. 58 4.3. Two-Way Relaying Scheme II Based on Alamouti Codes . 60 4.4. Simulation Results ................................. 62 4.5. Conclusion ......................................... 62 5. Analysis of Soft-Decision-and-Forward Cooperative Networks with Multiple Relays 64 5.1. Introduction ....................................... 64 5.2. Soft-Decision-and-Forward Protocol ................. 67 5.3. SDF Protocol with the Conventional Multiple-Relay Transmission ............................................ 72 5.3.1. System Model ..................................... 72 5.3.2. PEP and Diversity Order for the Conventional Scheme .................................................. 75 5.4. SDF Protocol with the Best Relay Selection ......... 77 5.4.1. System Model ..................................... 78 5.4.2. PEP and Diversity Order for the Best Relay Scheme 79 5.5. Simulation Results ................................. 81 5.6. Conclusion ......................................... 84 6. Conclusion 85 Bibliography 88 초록 98Docto

Distributed Quasi-Orthogonal Space-Time coding in wireless cooperative relay networks

Cooperative diversity provides a new paradigm in robust wireless re- lay networks that leverages Space-Time (ST) processing techniques to combat the effects of fading. Distributing the encoding over multiple relays that potentially observe uncorrelated channels to a destination terminal has demonstrated promising results in extending range, data- rates and transmit power utilization. Specifically, Space Time Block Codes (STBCs) based on orthogonal designs have proven extremely popular at exploiting spatial diversity through simple distributed pro- cessing without channel knowledge at the relaying terminals. This thesis aims at extending further the extensive design and analysis in relay networks based on orthogonal designs in the context of Quasi- Orthogonal Space Time Block Codes (QOSTBCs). The characterization of Quasi-Orthogonal MIMO channels for cooper- ative networks is performed under Ergodic and Non-Ergodic channel conditions. Specific to cooperative diversity, the sub-channels are as- sumed to observe different shadowing conditions as opposed to the traditional co-located communication system. Under Ergodic chan- nel assumptions novel closed-form solutions for cooperative channel capacity under the constraint of distributed-QOSTBC processing are presented. This analysis is extended to yield closed-form approx- imate expressions and their utility is verified through simulations. The effective use of partial feedback to orthogonalize the QOSTBC is examined and significant gains under specific channel conditions are demonstrated. Distributed systems cooperating over the network introduce chal- lenges in synchronization. Without extensive network management it is difficult to synchronize all the nodes participating in the relaying between source and destination terminals. Based on QOSTBC tech- niques simple encoding strategies are introduced that provide compa- rable throughput to schemes under synchronous conditions with neg- ligible overhead in processing throughout the protocol. Both mutli- carrier and single-carrier schemes are developed to enable the flexi- bility to limit Peak-to-Average-Power-Ratio (PAPR) and reduce the Radio Frequency (RF) requirements of the relaying terminals. The insights gained in asynchronous design in flat-fading cooperative channels are then extended to broadband networks over frequency- selective channels where the novel application of QOSTBCs are used in distributed-Space-Time-Frequency (STF) coding. Specifically, cod- ing schemes are presented that extract both spatial and mutli-path diversity offered by the cooperative Multiple-Input Multiple-Output (MIMO) channel. To provide maximum flexibility the proposed schemes are adapted to facilitate both Decode-and-Forward (DF) and Amplify- and-Forward (AF) relaying. In-depth Pairwise-Error-Probability (PEP) analysis provides distinct design specifications which tailor the distributed- STF code to maximize the diversity and coding gain offered under the DF and AF protocols. Numerical simulation are used extensively to confirm the validity of the proposed cooperative schemes. The analytical and numerical re- sults demonstrate the effective use of QOSTBC over orthogonal tech- niques in a wide range of channel conditions

협동통신 네트워크에서 다이버시티 및 자유도에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 8. 노종선.This dissertation contains the following three contributions to the interesting research topics on diversity techniques and interference alignment (IA) for cooperative communication networks. *Relay on-off threshold (ROT) for non-orthogonal decode and forward (NDF) protocol with distributed orthogonal space-time block codes (DOSTBCs) - Calculate the optimal ROT for NDF protocol with DOSTBCs in high signal to noise power ratio (SNR) region. - Propose suboptimal ROT for NDF protocol with DOSTBCs in low SNR region. - Analyze the diversity order of the proposed scheme. *New IA schemes aided by relays for quasi-static MX2 X channel - Propose IA scheme aided by one full-duplex relay. - Propose IA scheme aided by two half-duplex relay. - Prove that the proposed IA schemes achieve the maximum degrees of freedom (DoF) for quasi-static MX2 X channel. * Selection diversity on the IA for multi-input and multi-output (MIMO) interference channel - Propose the selection criterion of beamforming matrices of IA for MIMO interference channel. - Analyze the diversity order of the proposed scheme. First, we construct the DOSTBCs using source and relay in the cooperative communication networks. In order to decode the DOSTBCs, the destination uses the linear combining (LC) decoding scheme. In this system models, the symbol error rate (SER) is formulated and the ROT is calculated to minimize the SER. It is proved that the full diversity order of NDF protocol can be achieved by using the relay on-off scheme with the optimal threshold. In the second part of this dissertation, two new IA schemes aided by relays for quasi-static MX2 X channel are proposed. The first proposed scheme uses one full-duplex relay and it can achieves the maximum DoF. However, at the full-duplex relay, the transmit signal can be strong self-interference, called echo and thus it is difficult to implement practically. To resolve this problem, at the second proposed IA scheme, two half-duplex relays are used and it is proved that the second proposed IA scheme can also achieve the maximum DoF of MX2 X channel. Finally, the selection scheme for IA is proposed for MIMO interference channel. Most of IA schemes are focused on DoF but there is only a few research results for diversity order which is a crucial measure of reliability. Therefore, we propose a selection criterion to minimize SER and analyze the diversity order of the proposed scheme in the MIMO interference channel.Abstract i Contents iv List of Tables vii List of Figures viii 1. Introduction 1.1. Background 1.2. Overview of Dissertation 1.3. Terms and Notations 2. Diversity Techniques and Interference Alignment 2.1. MIMO Communications 2.2. Space-Time Coding and Selection Diversity 2.3. Cooperative Communications 2.4. Interference Alignment 3. Relay On-Off Threshold for NDF Protocol with Distributed Orthogonal Space-Time Block Codes 3.1. Introduction 3.2. System Models and Linear Combining Decoding 3.2.1. System Models of NDF Protocol 3.2.2. Linear Combining Decoding 3.3. Relay On-Off Threshold and Diversity Analysis 3.3.1. Relay On-Off Threshold 3.3.2. Relay On-Off Threshold for LC Decoding 3.3.3. Decision of Suboptimal Relay On-Off Threshold in Low SNR Region 3.3.4. Diversity Analysis 3.4. Numerical Analysis 3.5. Conclusion 4. New Interference Alignment Scheme Aided by Relays for Quasi-Static X Channels 4.1. Introduction 4.2. Preliminaries: X Channel and Interference Alignment 4.3. The Proposed Schemes and System Models 4.3.1. Two Proposed Schemes 4.3.2. System Models for the Proposed Schemes 4.4. Achievability of the Proposed IA Schemes 4.4.1. IA Scheme with a Full-Duplex Relay 4.4.2. IA Scheme with Two Half-Duplex Relays 4.5. Achievability of the Proposed IA Schemes for the 2×M X Channel 4.6. Numerical Analysis 4.7. Conclusion 5. Selection Diversity on the Interference Alignment for MIMO Interference Channels 5.1. Introduction 5.2. Characteristic Function of Multivariate Rayleigh Random Variables 5.3. Combining IA and Selection Schemes for 3-User MIMO Interference Channel 5.3.1. System Model and IA for 3-User MIMO Interference Channel 5.3.2. Orthogonalization of Beamforming Matrices 5.3.3. Selection of Beamforming Matrices 5.4. Diversity Analysis 5.5. Simulation Results 5.6. Conclusions 6. Conclusions Bibliography 초록Docto

Spectrally Effiecient Alamouti Code Structure in Asynchronous Cooperative Systems

Cataloged from PDF version of article.A relay communication system with two amplify and forward (AF) relays under flat fading channel conditions is considered where the signals received from the relays are not necessarily time aligned. We propose a new time-reversal (TR)-based scheme providing an Alamouti code structure which needs a smaller overhead in transmitting every pair of data blocks in comparison with the existing schemes and, as a result, increases the transmission rate significantly (as much as 20%) in exchange for a small performance loss. The scheme is particularly useful when the delay between the two relay signals is large, e.g., in typical underwater acoustic (UWA) channels

Distributed space time block coding in asynchronous cooperative relay networks

The design and analysis of various distributed space time block coding schemes for asynchronous cooperative relay networks is considered in this thesis. Rayleigh frequency flat fading channels are assumed to model the links in the networks, and interference suppression techniques together with an orthogonal frequency division multiplexing type transmission approach are employed to mitigate the synchronization errors at the destination node induced by the different delays through the relay nodes. Closed-loop space time block coding is first considered in the context of decode-and-forward (regenerative) networks. In particular, quasi orthogonal and extended orthogonal coding techniques are employed for transmission from four relay nodes and parallel interference cancellation detection is exploited to mitigate synchronization errors. Availability of a direct link between the source and destination nodes is studied, and a new Alamouti space time block coding technique with parallel interference cancellation detection which does not require such a direct link connection and employs two relay nodes is proposed. Outer coding is then added to gain further improvement in end-to-end performance and amplify-and-forward (non regenerative) type networks together with distributed space time coding are considered to reduce relay node complexity. Novel detection schemes are then proposed for decode-and-forward networks with closed-loop extended orthogonal coding which reduce the computational complexity of the parallel interference cancellation. Both sub-optimum and near-optimum detectors are presented for relay nodes with single or dual antennas. End-to-end bit error rate simulations confirm the potential of the approaches and their ability to mitigate synchronization errors. A relay selection approach is also formulated which maximizes spatial diversity gain and attains robustness to timing errors. Finally, a new closed-loop distributed extended orthogonal space time block coding solution for amplify-and-forward type networks which minimizes the number of feedback bits by using a cyclic rotation phase is presented. This approach utilizes an orthogonal frequency division multiplexing type transmission structure with a cyclic prefix to mitigate synchronization errors. End-to-end bit error performance evaluations verify the efficacy of the scheme and its success in overcoming synchronization errors