A Review- Proposed Bidirectional Relaying for Improved Channel Estimation Error and Co-Channel Interference

Wireless Communication has gained a lot of interest as future generation requires higher data rates and more suitable transmission with adequate quality of service. Wireless communication suffers from various problems like Co-Channel Interference (CCI) and Channel Estimation Error (CEE). Cooperative communication is an efficient technique to deal with these types of problems by offering significant multiplexing and diversity gains without increasing power and bandwidth. Our proposed two way relaying helps to improve the overall system performance in wireless networks. Cooperative communications also deals with the various problems like fading and shadowing. It is further investigated that proposed two way relaying is spectrally efficient technique which provides a way to surmount half duplexing loss in one way relay channel

Performance of Relaying Protocols

In wireless systems, cooperative diversity and relaying can exploit the benefit of spatial diversity and combat heavy pathloss without requiring multiple antennas at the receivers and transmitters. For practical networks, the use of relays is motivated by the need for simple, inexpensive terminals with limited power and a single antenna. The motivation for this thesis is to study and propose practical relaying protocols that can reduce the power consumption and ameliorate the performance with minimum additional complexity. Based on a dual-hop communication model, we exploit two upper bounds for the end-to-end SNR. These bounds further inspire us to propose new relaying protocols for wireless communication systems. We examine the case of a single user and relay under Rayleigh and Nakagami-m fading conditions. Based on the general upper bound, a new protocol is introduced: Clipped gain. This protocol makes it possible to save the transmit power by stopping the transmission when the quality of the first hop leads to an outage. We consider also user selection and user scheduling for dual-hop communication with multiple users and relays over a Rayleigh fading channel. We introduce new scheduling protocols based on one-bit feedback information. To the best of our knowledge, most of the available literature uses full channel state information to perform user selection and user scheduling. Interestingly, our protocols based on one bit feedback greatly improve the system performance while adding less additional complexity. To carry out rigorous comparison, close-form expressions are derived and analytical results used to assess the outage probability performance

Esquemas de retransmissão baseados no protocolo decodifica-e-encaminha em redes cognitivas do tipo underlay

Orientador: José Cândido Silveira Santos FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O conceito de compartilhamento de espectro do tipo underlay tem sido proposto como uma técnica promissora para contornar o problema da escassez e da subutilização do espectro, permitindo que usuários não licenciados, chamados de usuários secundários, possam acessar simultaneamente uma banda licenciada, alocada aos usuários primários, desde que o nível de interferência sobre os mesmos seja mantido abaixo de um dado limiar aceitável. Entretanto, isso implica que a potência de transmissão na rede secundária deve ser restringida, comprometendo assim a confiabilidade e a cobertura da comunicação. A fim de contornar esse problema, técnicas de retransmissão cooperativa, as quais proveem um novo tipo de diversidade espacial, podem ser exploradas como um meio eficaz para melhorar o desempenho da rede secundária. De fato, a utilização conjunta de ambas as técnicas ¿ compartilhamento de espectro do tipo underlay e retransmissão cooperativa ¿ em redes cooperativas e cognitivas tem recebido especial atenção, já que a eficiência espectral do sistema e o desempenho da rede secundária podem ser melhorados significativamente. Esta tese apresenta quatro contribuições principais na referida área. Em particular, estuda-se o efeito conjunto de duas restrições de potência importantes sobre o desempenho de outage de redes cooperativas e cognitivas, especificamente, o nível máximo de potência interferente tolerada pelo receptor primário e o valor máximo de potência transmitida nos usuários secundários. Foca-se em esquemas de retransmissão baseados no protocolo decodifica-e-encaminha, abordando cenários em que o enlace direto entre fonte e destino está disponível para transmitir informação útil. Como uma primeira contribuição, analisa-se o desempenho de dois esquemas baseados no protocolo de retransmissão half-duplex incremental, os quais exploram a diversidade espacial dos enlaces diretos em redes cooperativas e cognitivas multiusuário. A segunda contribuição investiga o impacto de estimativas desatualizadas do canal sobre o mecanismo de seleção de destino para um desses esquemas anteriores, focando-se apenas no aspecto cooperativo da rede, ou seja, desconsiderando-se o uso de compartilhamento espectral. A terceira contribuição estuda o desempenho de redes cooperativas e cognitivas baseadas no modo full-duplex. Para esse cenário, avalia-se o impacto tanto da autointerferência residual, que é inerente ao modo full-duplex, bem como das restrições de potência que caracterizam o compartilhamento de espectro do tipo underlay. Como contribuição final, motivada pelo compromisso entre a perda de eficiência espectral e o problema da autointerferência residual, próprios dos modos half-duplex e full-duplex, respectivamente, propõe-se e analisa-se um esquema de transmissão adaptativo para redes cooperativas e cognitivas, através do qual, antes de cada processo de comunicação, um dos seguintes modos de transmissão é selecionado: retransmissão half-duplex, retransmissão full-duplex ou transmissão direta. Para todos os cenários considerados, expressões analíticas exatas para a probabilidade de outage são obtidas. Adicionalmente, uma análise assintótica é realizada a fim de caracterizar a ordem de diversidade e o comportamento de outage da rede secundária no regime assintótico de alta relação sinal-ruído. Simulações de Monte Carlo validam os resultados analíticos apresentadosAbstract: Underlay spectrum sharing has been proposed as a promising technique to alleviate the problem of spectrum scarcity and underutilization, by enabling secondary (unlicensed) users to concurrently access a licensed band, provided that the resulting interference on the primary (licensed) users remains below a given acceptable level. However, such a technique implies that the transmit power at the secondary network must be constrained, thereby compromising the communication reliability and coverage. To counteract this, cooperative relaying techniques, which provide a new form of spatial diversity, can be exploited as an effective means to boost the performance of the secondary network. Indeed, the joint use of both techniques¿underlay spectrum sharing and cooperative relaying¿in cognitive relaying networks has drawn special attention, since the overall spectral efficiency and the secondary-network performance can be significantly improved. This dissertation comprises four main contributions in this field. In particular, we examine the combined effect of two crucial power constraints on the outage performance of cognitive relaying networks, namely, the maximum tolerable interference power at the primary receiver and the maximum transmit power at the secondary users. We focus on relaying schemes operating under the decode-and-forward protocol, for scenarios in which the direct link between source and destination is available to convey useful information. As a first contribution, we analyze the performance of two incremental half-duplex relaying schemes, which exploit the spatial diversity of the direct links in a multiuser scenario. Our second contribution investigates the impact of outdated channel estimates on the destination-scheduling mechanism of one of those incremental schemes, from the perspective of a cooperative network only, that is, in the absence of spectrum sharing. The third contribution addresses cognitive full-duplex relaying networks. More specifically, we assess the system performance as a function of both the residual self-interference, which is inherent to the full-duplex relaying mode, and the underlay spectrum-sharing power constraints. As a final contribution, driven by the tradeoff between the spectral-efficiency loss and the residual self-interference problem, intrinsic to the half- and full-duplex relaying modes, respectively, we propose and analyze an adaptive transmission scheme whereby, before each communication process, one out of the following transmission modes is selected: half-duplex relaying, full-duplex relaying, or direct transmission. For all the considered scenarios, exact analytical expressions for the outage probability are derived. In addition, an asymptotic analysis is performed to obtain further insights on the diversity order and outage behavior of the secondary network at the high signal-to-noise ratio regime. Monte Carlo simulations corroborate the accuracy of the presented mathematical analysisDoutoradoTelecomunicações e TelemáticaDoutor em Engenharia ElétricaCAPE

Cooperative Diversity in CDMA over Nakagami−m Fading Channels

Spatial diversity can be employed by sending copies of the transmitted signal using multiple antennas at the transmitter/receiver, as implemented in multiple-input multipleoutput (MIMO) systems. Spatial receive diversity has already been used in many applications with centralized systems where base station receivers are equipped with multiple antennas. However, due to the power constraints and the small size of the mobile terminal, it may not be feasible to deploy multiple transmit antennas. User cooperation diversity, a new form of space diversity, has been developed to address these limitations. Recently, user cooperative diversity has gained more attention as a less complex alternative to centralized MIMO wireless systems. It revealed the ability to improve wireless communications through reliable reception. One common network of the user cooperation diversity is the direct sequence code division multiple access (DS-CDMA) in which the Rayleigh fading channels are adopted and the orthogonality between users is assumed. The Rayleigh fading channels are unrealistic since they cannot represent the statistical characteristics of the complex indoor environments. On the other hand, Nakagami-m fading model is well known as a generalized distribution, where many fading environments can be modeled. It can be used to model fading conditions ranging from severe, light to no fading, by changing its fading parameter m. The bit-error-rate (BER) and outage probability of uplink cooperative DS-CDMA over Nakagami-m has not been addressed in the literature. Thus, in this thesis, the performance of both decode-and-forward (DF) and amplify-and-forward (AF) cooperative asynchronous DS-CDMA system over Nakagami-m fading channels is investigated. The Rake receiver is used to exploit the advantages of multipath propagation. Besides, multiuser detection (MUD) is used to mitigate the effect of multiple-access interference (MAI). We show that our proposed multi-user system achieves the full system diversity gain. The first part of the thesis introduces a new closed-form expression for the outage probability and the error probability of the DF cooperative DS-CDMA over asynchronous transmission over independent non-identical Nakagami-m fading channels. The underlying system employs MUD such as minimum mean square error (MMSE) and decorrelator detector (DD) to achieve the full diversity. The aforementioned closed-form expression is obtained through the moment generating function (MGF) for the total signal-to-noise ratio (SNR) at the base station where the cumulative density function (CDF) is obtained. Furthermore, we investigate the asymptotic behavior of the system at high SNR to calculate the achievable diversity gain. The results demonstrate that the system diversity gain is fulfilled when MUD is used to mitigate the effect of MAI. In the second part of the thesis, we study the performance of cooperative CDMA system using AF relaying over independent non-identical distribution (i.n.i) Nakagami-m fading channels. Using the MGF of the total SNR at the base station, we derive the outage probability of the system. This enables us to derive the asymptotic outage probability for any arbitrary value of the fading parameter m. The last part of the thesis investigates the optimum power allocation and optimum relay location in AF cooperative CDMA systems over i.n.i Nakagami-m fading channels. Moreover, we introduce the joint optimization of both power allocation and relay location under the transmit power constraint to minimize the outage probability of the system. The joint optimization of both power allocation and relay location is used to minimize the outage performance of the system, thereby achieving full diversity gain

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

TAS-Based Incremental Hybrid Decode–Amplify–Forward Relaying for Physical Layer Security Enhancement

In this paper, a transmit antenna selection (TAS)- based incremental hybrid decode-amplify-forward (IHDAF) scheme is proposed to enhance physical layer security in cooperative relay networks. Specifically, TAS is adopted at the source in order to reduce the feedback overhead. In the proposed TAS-based IHDAF scheme, the network transmits signals to the destination adaptive select direction transmission mode, AF mode or DF mode depending on the capacity of the source-relay link and source-relay link. In order to fully examine the benefits of the proposed TAS-based IHDAF scheme, we first derive its secrecy outage probability (SOP) in a closed-form expression. We then conduct asymptotic analysis on the SOP, which reveals the secrecy performance floor of the proposed TAS-based IHDAF scheme when no channel state information is available at the source. Theoretical analysis and simulation results demonstrate that the proposed TAS-based IHDAF scheme outperforms the selective decode-and-forward (SDF), the incremental decodeand-forward (IDF), and the noncooperative direction transmission (DT) schemes in terms of the SOP and effective secrecy throughout, especially when the relay is close to the destination. Furthermore, the proposed TAS-based IHDAF scheme offer a good trade-off between complexity and performance compare with using all antennas at the source.ARC Discovery Projects Grant DP150103905