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

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

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

INTERFERENCE MANAGEMENT IN LTE SYSTEM AND BEYOUND

The key challenges to high throughput in cellular wireless communication system are interference, mobility and bandwidth limitation. Mobility has never been a problem until recently, bandwidth has been constantly improved upon through the evolutions in cellular wireless communication system but interference has been a constant limitation to any improvement that may have resulted from such evolution. The fundamental challenge to a system designer or a researcher is how to achieve high data rate in motion (high speed) in a cellular system that is intrinsically interference-limited. Multi-antenna is the solution to data on the move and the capacity of multi-antenna system has been demonstrated to increase proportionally with increase in the number of antennas at both transmitter and receiver for point-to-point communications and multi-user environment. However, the capacity gain in both uplink and downlink is limited in a multi-user environment like cellular system by interference, the number of antennas at the base station, complexity and space constraint particularly for a mobile terminal. This challenge in the downlink provided the motivation to investigate successive interference cancellation (SIC) as an interference management tool LTE system and beyond. The Simulation revealed that ordered successive interference (OSIC) out performs non-ordered successive interference cancellation (NSIC) and the additional complexity is justified based on the associated gain in BER performance of OSIC. The major drawback of OSIC is that it is not efficient in network environment employing power control or power allocation. Additional interference management techniques will be required to fully manage the interference.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Conditional Decoding for X Channels

The conditional decoder is a low complexity and optimal decoder for multiplexed orthogonal designs in point-to-point channels. We extend this notion to X channels and differentiate between two interference scenarios. First, the interference is perfectly aligned in a different sub-space than the intended information symbols. For this scenario, the conditional decoder is applied as a one stage and two stages decoder to cancel the interference and decode the desired signal. Second, the interference is misaligned. In this case, the conditional decoder attempts to jointly cancel the interference and decode the intended signal while achieving a performance gain over other interference cancellation schemes. We consider the two user scenario where Alamouti codes are used at the transmitters and then extend our investigation to three user channels with arbitrary signal structure. Our numerical results establish the superiority of our decoder to previously proposed zero-forcing and decoupling techniques, in terms of performance. It is further shown that the proposed decoder achieves the same performance as the sphere decoder; while enjoying a much lower implementation complexity

Implementação e avaliação no system generator de um sistema cooperativo para os futuros sistemas 5G

With the arrival of 5G it is expected the proliferation of services in the different fields such as healthcare, utility applications, industrial automation, 4K streaming, that the former networks can not provide. Additionally, the total number of wireless communication devices will escalate in such a manner that the already scarce available frequency bandwidth won’t be enough to pack the intended objectives. Cisco’s Annual Internet Report from 2018 predicts that by 2023 there will be nearly 30 billion devices capable of wireless communication. Due to the exponential expiation of both services and devices, the challenges upon both network data capacity and efficient radio resourse use will be greater than ever, thus the urgency for solutions is grand. Both the capacity for wireless communications and spectral efficiency are related to cell size and its users proximity to the access point. Thus, shortening the distance between the transmitter and the receiver improves both aspects of the network. This concept is what motivates the implementation of heterogeneous networks, HetNets, that are composed of many different small-cells, SCs, overlaid across the same coexisting area of a conventional macro-cell, shortening the distance between the cell users and its access point transceivers, granting a better coverage and higher data rates. However, the HetNets potential does not come without any challenges, as these networks suffer considerably from communication interference between cells. Although some interference management algorithms that allow coexistence between cells have been proposed in recent years, most of them were evaluated by software simulations and not implemented in real-time platforms. Therefore, this master thesis aims to give the first step on the implementation and evaluation of an interference mitigation technique in hardware. Specifically, it is assumed a downlink scenario composed by a macro-cell base station, a macro-cell primary user and a small cell user, with the aim of implementing an algorithm that eliminates the downlink interference that the base station may cause to the secondary users. The study was carried out using the System Generator DSP tool, which is a tool that generates code for hardware from schematics created in it. This tool also offers a wide range of blocks that help the creation, and fundamentally, the simulation and study of the system to be implemented, before being translated into hardware. The results obtained in this work are a faithful representation of the behavior of the implemented system, which can be used for a future application for FPGA.Com a chegada do 5G, espera-se a proliferação de serviços nas mais diversas áreas tal como assistência médica, automação industrial, transmissão em 4k, que não eram possíveis nas redes das gerações anteriores. Além deste fenómeno, o número total de dispositivos capazes de conexões wireless aumentará de tal maneira que a escassa largura de banda disponível não será suficiente para abranger os objetivos pretendidos. O Relatório Anual de 2018 sobre a Internet da Cisco prevê que até 2023 haverá quase 30 bilhões de dispositivos capazes de comunicação sem fio. Devido ao aumento exponencial de serviços e dispositivos, os desafios sobre a capacidade de dados da rede e o udo eficiente dos recursos de rádio serão maiores que nunca. Por estes motivos, a necessidade de soluções para estas lacunas é enorme. Tanto a capacidade da rede e o uso eficiente do espectro de frequências estão relacionados ao tamanho da célula e à proximidade dos usuários com o ponto de acesso da célula. Ao encurtar a distância entre o transmissor e o recetor ocorre um melhoramento destes dois aspetos da rede. Este é o principal conceito na implementação de redes heterogéneas, HetNets, que são compostas por diversas células pequenas que coexistem na área de uma macro célula convencional, diminuído a distância entre os utilizadores da célula e os pontos de acesso, garantindo uma melhor cobertura e taxa de dados mais elevadas. No entanto, o potencial das HatNets não vem sem nenhum custo, pois estas redes sofrem consideravelmente de interferência entre as células. Embora nos últimos anos foram propostos alguns algoritmos que permitem a coexistência das células, a maioria destes foi só testado em simulações de software e não em plataformas em tempo real. Por esse motivo, esta dissertação de mestrado visa dar o primeiro passo na implementação e a avaliação de uma técnica de mitigação de interferência em hardware. Mais especificamente no cenário de downlink entre uma estação base de uma macro célula, um utilizador primário da macro célula e um utilizador secundário de uma célula pequena, com o principal objetivo de cancelar a interferência que a estação base possa fazer ao utilizador secundário. O estudo foi realizado utilizando a ferramenta System Generator DSP, que é uma ferramenta que gera código para hardware a partir de esquemáticos criados na mesma. Esta ferramenta também oferece uma vasta gama de blocos que ajudam a criação, e fundamentalmente, a simulação e o estudo do sistema a implementar antes de ser traduzido para hardware. Os resultados obtidos neste trabalho são uma fiel representação do comportamento do sistema implementado. O quais podem ser utilizados para uma futura aplicação para FPGA.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Técnicas de equalização e pré-codificação para sistemas MC-CDMA

Mestrado em Engenharia Eletrónica e TelecomunicaçõesO número de dispositivos com ligações e aplicações sem fios está a aumentar exponencialmente, causando problemas de interferência e diminuindo a capacidade do sistema. Isto desencadeou uma procura por uma eficiência espectral superior e, consequentemente, tornou-se necessário desenvolver novas arquitecturas celulares que suportem estas novas exigências. Coordenação ou cooperação multicelular é uma arquitectura promissora para sistemas celulares sem fios. Esta ajuda a mitigar a interferência entre células, melhorando a equidade e a capacidade do sistema. É, portanto, uma arquitectura já em estudo ao abrigo da tecnologia LTE-Advanced sob o conceito de coordenação multiponto (CoMP). Nesta dissertação, considerámos um sistema coordenado MC-CDMA com pré-codificação e equalização iterativas. Uma das técnicas mais eficientes de pré-codificação é o alinhamento de interferências (IA). Este é um conceito relativamente novo que permite aumentar a capacidade do sistema em canais de elevada interferência. Sabe-se que, para os sistemas MC-CDMA, os equalizadores lineares convencionais não são os mais eficientes, devido à interferência residual entre portadoras (ICI). No entanto, a equalização iterativa no domínio da frequência (FDE) foi identificada como sendo uma das técnicas mais eficientes para lidar com ICI e explorar a diversidade oferecida pelos sistemas MIMO MC-CDMA. Esta técnica é baseada no conceito Iterative Block Decision Feedback Equalization (IB-DFE). Nesta dissertação, é proposto um sistema MC-CDMA que une a pré-codificação iterativa do alinhamento de interferências no transmissor ao equalizador baseado no IB-DFE, com cancelamento sucessivo de interferências (SIC) no receptor. Este é construído por dois blocos: um filtro linear, que mitiga a interferência inter-utilizador, seguido por um bloco iterativo no domínio da frequência, que separa eficientemente os fluxos de dados espaciais na presença de interferência residual inter-utilizador alinhada. Este esquema permite atingir o número máximo de graus de liberdade e permite simultaneamente um ganho óptimo de diversidade espacial. O desempenho deste esquema está perto do filtro adaptado- Matched Filter Bound (MFB).The number of devices with wireless connections and applications is increasing exponentially, causing interference problems and reducing the system’s capacity gain. This initiated a search for a higher spectral efficiency and therefore it became necessary to develop new cellular architectures that support these new requirements. Multicell cooperation or coordination is a promising architecture for cellular wireless systems to mitigate intercell interference, improving system fairness and increasing capacity, and thus is already under study in LTE-Advanced under the coordinated multipoint (CoMP) concept. In this thesis, efficient iterative precoding and equalization is considered for coordinated MC-CDMA based systems. One of the most efficient precoding techniques is interference alignment (IA), which is a relatively new concept that allows high capacity gains in interfering channels. It is well known that for MC-CDMA systems standard linear equalizers are not the most efficient due to residual inter carrier interference (ICI). However, iterative frequency-domain equalization (FDE) has been identified as one of the most efficient technique to deal with ICI and exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems, namely the one based on Iterative Block Decision Feedback Equalization (IB-DFE) concept. In this thesis, it is proposed a MC-CDMA system that joins iterative IA precoding at the transmitter with IB-DFE successive interference cancellation (SIC) based receiver structure. The receiver is implemented in two steps: a linear filter, which mitigates the inter-user aligned interference, followed by an iterative frequency-domain receiver, which efficiently separates the spatial streams in the presence of residual inter-user aligned interference. This scheme provides the maximum degrees of freedom (DoF) and allows almost the optimum space-diversity gain. The scheme performance is close to the matched filter bound (MFB)

Optimising Cooperative Spectrum Sensing in Cognitive Radio Networks Using Interference Alignment and Space-Time Coding

In this thesis, the process of optimizing Cooperative Spectrum Sensing in Cognitive Radio has been investigated in fast-fading environments where simulation results have shown that its performance is limited by the Probability of Reporting Errors. By proposing a transmit diversity scheme using Differential space-time block codes (D-STBC) where channel state information (CSI) is not required and regarding multiple pairs of Cognitive Radios (CR’s) with single antennas as a virtual MIMO antenna arrays in multiple clusters, Differential space-time coding is applied for the purpose of decision reporting over Rayleigh channels. Both Hard and Soft combination schemes were investigated at the fusion center to reveal performance advantages for Hard combination schemes due to their minimal bandwidth requirements and simplistic implementation. The simulations results show that this optimization process achieves full transmit diversity, albeit with slight performance degradation in terms of power with improvements in performance when compared to conventional Cooperative Spectrum Sensing over non-ideal reporting channels. Further research carried out in this thesis shows performance deficits of Cooperative Spectrum Sensing due to interference on sensing channels of Cognitive Radio. Interference Alignment (IA) being a revolutionary wireless transmission strategy that reduces the impact of interference seems well suited as a strategy that can be used to optimize the performance of Cooperative Spectrum Sensing. The idea of IA is to coordinate multiple transmitters so that their mutual interference aligns at their receivers, facilitating simple interference cancellation techniques. Since its inception, research efforts have primarily been focused on verifying IA’s ability to achieve the maximum degrees of freedom (an approximation of sum capacity), developing algorithms for determining alignment solutions and designing transmission strategies that relax the need for perfect alignment but yield better performance. With the increased deployment of wireless services, CR’s ability to opportunistically sense and access the unused licensed frequency spectrum, without causing harmful interference to the licensed users becomes increasingly diminished, making the concept of introducing IA in CR a very attractive proposition. For a multiuser multiple-input–multiple-output (MIMO) overlay CR network, a space-time opportunistic IA (ST-OIA) technique has been proposed that allows spectrum sharing between a single primary user (PU) and multiple secondary users (SU) while ensuring zero interference to the PUs. With local CSI available at both the transmitters and receivers of SUs, the PU employs a space-time WF (STWF) algorithm to optimize its transmission and in the process, frees up unused eigenmodes that can be exploited by the SU. STWF achieves higher performance than other WF algorithms at low to moderate signal-to-noise ratio (SNR) regimes, which makes it ideal for implementation in CR networks. The SUs align their transmitted signals in such a way their interference impairs only the PU’s unused eigenmodes. For the multiple SUs to further exploit the benefits of Cooperative Spectrum Sensing, it was shown in this thesis that IA would only work when a set of conditions were met. The first condition ensures that the SUs satisfy a zero interference constraint at the PU’s receiver by designing their post-processing matrices such that they are orthogonal to the received signal from the PU link. The second condition ensures a zero interference constraint at both the PU and SUs receivers i.e. the constraint ensures that no interference from the SU transmitters is present at the output of the post-processing matrices of its unintended receivers. The third condition caters for the multiple SUs scenario to ensure interference from multiple SUs are aligned along unused eigenmodes. The SU system is assumed to employ a time division multiple access (TDMA) system such that the Principle of Reciprocity is employed towards optimizing the SUs transmission rates. Since aligning multiple SU transmissions at the PU is always limited by availability of spatial dimensions as well as typical user loads, the third condition proposes a user selection algorithm by the fusion centre (FC), where the SUs are grouped into clusters based on their numbers (i.e. two SUs per cluster) and their proximity to the FC, so that they can be aligned at each PU-Rx. This converts the cognitive IA problem into an unconstrained standard IA problem for a general cognitive system. Given the fact that the optimal power allocation algorithms used to optimize the SUs transmission rates turns out to be an optimal beamformer with multiple eigenbeams, this work initially proposes combining the diversity gain property of STBC, the zero-forcing function of IA and beamforming to optimize the SUs transmission rates. However, this solution requires availability of CSI, and to eliminate the need for this, this work then combines the D-STBC scheme with optimal IA precoders (consisting of beamforming and zero-forcing) to maximize the SUs data rates