Maximum-rate Transmission with Improved Diversity Gain for Interference Networks

Interference alignment (IA) was shown effective for interference management to improve transmission rate in terms of the degree of freedom (DoF) gain. On the other hand, orthogonal space-time block codes (STBCs) were widely used in point-to-point multi-antenna channels to enhance transmission reliability in terms of the diversity gain. In this paper, we connect these two ideas, i.e., IA and space-time block coding, to improve the designs of alignment precoders for multi-user networks. Specifically, we consider the use of Alamouti codes for IA because of its rate-one transmission and achievability of full diversity in point-to-point systems. The Alamouti codes protect the desired link by introducing orthogonality between the two symbols in one Alamouti codeword, and create alignment at the interfering receiver. We show that the proposed alignment methods can maintain the maximum DoF gain and improve the ergodic mutual information in the long-term regime, while increasing the diversity gain to 2 in the short-term regime. The presented examples of interference networks have two antennas at each node and include the two-user X channel, the interferring multi-access channel (IMAC), and the interferring broadcast channel (IBC).Comment: submitted to IEEE Transactions on Information Theor

Uplink Multiuser MIMO Detection Scheme with Reduced Computational Complexity

The wireless communication systems with multiple antennas have recently received significant attention due to their higher capacity and better immunity to fading channels as compared to single antenna systems. A fast antenna selection scheme has been introduced for the uplink multiuser multiple-input multiple-output (MIMO) detection to achieve diversity gains, but the computational complexity of the fast antenna selection scheme in multiuser systems is very high due to repetitive pseudo-inversion computations. In this paper, a new uplink multiuser detection scheme is proposed adopting a switch-and-examine combining (SEC) scheme and the Cholesky decomposition to solve the computational complexity problem. K users are considered that each users is equipped with two transmit antennas for Alamouti space-time block code (STBC) over wireless Rayleigh fading channels. Simulation results show that the computational complexity of the proposed scheme is much lower than the systems with exhaustive and fast antenna selection, while the proposed scheme does not experience the degradations of bit error rate (BER) performances

A quaternion-based approach to interference alignment with Alamouti coding

Based on the representation of Alamouti space-time codewords as quaternions, this paper proposes a scheme that combines interference alignment (IA) with Alamouti signals. The proposed formulation allows for a separation of the space-time block coding (to gain spatial diversity) and the IA precoding (to reduce or ideally suppress interference). Although this separation is not necessarily optimal, the splitting of alignment precoding and Alamouti encoding is particularly convenient because it enables the independent optimization of the IA solution using quaternionic versions of standard alternating optimization techniques such as the maximum signal-to-interference-plus-noise algorithm. Some numerical simulations are included to compare the performance of the proposed quaternion IA+Alamouti algorithm with standard IA algorithms in the complex domain as well as with interference cancellation schemes at the receiver side.This work has been supported by the Ministerio de Economía, Industria y Competitividad (MINECO) of Spain, under grants TEC2013-47141-C4-R (RACHEL), TEC2016-75067-C4-4-R (CARMEN), and FPI grant BES-2014-06978

Physical-Layer Transmission Cooperative Strategies for Heterogeneous Networks

The deployment of small cells within the boundaries of a macro-cell is considered to be an effective solution to cope with the current trend of higher data rates and improved system capacity. In the current heterogeneous configuration with the mass deployment of small cells, it is preferred that these two cell types coexist over the same spectrum, because acquiring additional spectrum licenses for small cells is difficult and expensive. However, the coexistence leads to cross-tier/inter-system interference. In this context, this contribution investigates interference alignment (IA) methods in order to mitigate the interference of macro-cell base station towards the small cell user terminals. More specifically, we design a diversity-oriented interference alignment scheme with space-frequency block codes (SFBC). The main motivation for joint interference alignment with SFBC is to allow the coexistence of two systems under minor inter-system information exchange. The small cells just need to know what space-frequency block code is used by the macro-cell system and no inter-system channels need to be exchanged, contrarily to other schemes recently proposed. Numerical results show that the proposed method achieves a performance close to the case where full-cooperation between the tiers is allowed

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