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Author: Navod D. Suraweera Publisher: ISBN: Category : Radio Languages : en Pages : 177
Book Description
The cancellation of co-channel interference (CCI) is extremely vital in the nextgeneration wireless systems, where universal frequency reuse is commonly used to maximize the capacity. The implementation of CCI cancellation at the receivers instead of the transmitters minimizes the additional overhead associated with CCI cancellation. Optimum combining (OC) enables the cancellation of CCI in multiple-antenna receivers. Cooperative relaying creates a virtual antenna array, which enables the cancellation of CCI using OC in single antenna receivers. The cancellation of CCI in cooperative relay networks using OC is the main focus of this thesis. More specifically, 1) the modeling and the application of optimum combining for cooperative relay networks 2) carrying out the performance analyses in different system and channel models to obtain performance metrics and 3) the evaluation of the robustness and the feasibility of practical implementation of OC in cooperative relaying, are carried out. The performance of OC in decode-and-forward and amplify-and-forward relay protocols, and in opportunistic relay selection is studied. The deterministic interference model, which can be used to model conventionally planned networks, and the random interference model, which can be applied for fourth-generation ad hoc and heterogeneous networks, are considered in the performance analysis. The impact of imperfect estimations of the desired and interferer channels on OC in cooperative relaying is analyzed. Optimum combining improves the performance of cooperative relay networks significantly with a minimum additional overhead, which allows the capacity to be maximized using universal frequency reuse at each transmitter.
Author: Navod D. Suraweera Publisher: ISBN: Category : Radio Languages : en Pages : 177
Book Description
The cancellation of co-channel interference (CCI) is extremely vital in the nextgeneration wireless systems, where universal frequency reuse is commonly used to maximize the capacity. The implementation of CCI cancellation at the receivers instead of the transmitters minimizes the additional overhead associated with CCI cancellation. Optimum combining (OC) enables the cancellation of CCI in multiple-antenna receivers. Cooperative relaying creates a virtual antenna array, which enables the cancellation of CCI using OC in single antenna receivers. The cancellation of CCI in cooperative relay networks using OC is the main focus of this thesis. More specifically, 1) the modeling and the application of optimum combining for cooperative relay networks 2) carrying out the performance analyses in different system and channel models to obtain performance metrics and 3) the evaluation of the robustness and the feasibility of practical implementation of OC in cooperative relaying, are carried out. The performance of OC in decode-and-forward and amplify-and-forward relay protocols, and in opportunistic relay selection is studied. The deterministic interference model, which can be used to model conventionally planned networks, and the random interference model, which can be applied for fourth-generation ad hoc and heterogeneous networks, are considered in the performance analysis. The impact of imperfect estimations of the desired and interferer channels on OC in cooperative relaying is analyzed. Optimum combining improves the performance of cooperative relay networks significantly with a minimum additional overhead, which allows the capacity to be maximized using universal frequency reuse at each transmitter.
Author: Md Shamsul Alam Publisher: ISBN: Category : Languages : en Pages :
Book Description
Next generation wireless communication networks are expected to provide ubiquitous high data rate coverage and support heterogeneous wireless services with diverse quality-of-service (QoS) requirements. This translates into a heavy demand for the spectral resources. In order to meet these requirements, Orthogonal Frequency Division Multiple Access (OFDMA) has been regarded as a promising air-interface for the emerging fourth generation (4G) networks due to its capability to combat the channel impairments and support high data rate. In addition, OFDMA offers flexibility in radio resource allocation and provides multiuser diversity by allowing subcarriers to be shared among multiple users. One of the main challenges for the 4G networks is to achieve high throughput throughout the entire cell. Cooperative relaying is a very promising solution to tackle this problem as it provides throughput gains as well as coverage extension. The combination of OFDMA and cooperative relaying assures high throughput requirements, particularly for users at the cell edge. However, to fully exploit the benefits of relaying, efficient relay selection as well as resource allocation are critical in such kind of network when multiple users and multiple relays are considered. Moreover, the consideration of heterogeneous QoS requirements further complicate the optimal allocation of resources in a relay enhanced OFDMA network. Furthermore, the computational complexity and signalling overhead are also needed to be considered in the design of practical resource allocation schemes. In this dissertation, we conduct a comprehensive research study on the topic of radio resource management for relay-based cooperative OFDMA networks supporting heterogeneous QoS requirements. Specifically, this dissertation investigates how to effectively and efficiently allocate resources to satisfy QoS requirements of 4G users, improve spectrum utilization and reduce computational complexity at the base station. The problems and our research achievements are briefly outlined as follows. Firstly, a QoS aware optimal joint relay selection, power allocation and subcarrier assignment scheme for uplink OFDMA system considering heterogeneous services under a total power constraint is proposed. The relay selection, power allocation and subcarrier assignment problem is formulated as a joint optimization problem with the objective of maximizing the system throughput, which is solved by means of a two level dual decomposition and subgradient method. The computational complexity is finally reduced via the introduction of two suboptimal schemes. The performance of the proposed schemes is demonstrated through computer simulations based on OFDMA network. Numerical results show that our schemes support heterogeneous services while guaranteeing each user's QoS requirements with slight total system throughput degradation. Secondly, we investigate the resource allocation problem subject to the satisfaction of user QoS requirements and individual total power constraints of the users and relays. The throughput of each end-to-end link is modeled considering both the direct and relay links. Due to non-convex nature of the original resource allocation problem, the optimal solution is obtained by solving a relaxed problem via two level dual decomposition. Numerical results reveal that the proposed scheme is effective in provisioning QoS of each user's over the conventional resource allocation counterpart under individual total power constraints of the users and relays . Lastly, decentralized resource allocation schemes are proposed to reduce the computational complexity and CSI feedback overhead at the BS. A user centric distributed (UCD) scheme and a relay centric distributed (RCD) scheme are proposed, where the computation of the centralized scheme is distributed among the users and relays, respectively. We also proposed suboptimal schemes based on simplified relay selection. The suboptimal schemes can be combined with the distributed schemes to further reduce of signalling overhead and computational complexity. Numerical results show that our schemes guarantee user's satisfaction with low computational complexity and signalling overhead, leading to preferred candidates for practical implementation. The research results obtained in this dissertation can improve the resource utilization and QoS assurance of the emerging OFDMA networks.
Author: Qingxiong Deng Publisher: ISBN: Category : Languages : en Pages : 340
Book Description
Abstract: Fading is one of the most fundamental impairments to wireless communications. The standard approach to combating fading is by adding redundancy - or diversity - to help increase coverage and transmission speed. Motivated by the results in multiple-input multiple-output technologies, which are usually used at base stations or access points, cooperation commutation has been proposed to improve the performance of wireless networks which consist of low-cost single antenna devices. While the majority of the research in cooperative communication focuses on flat fading for its simplicity and easy analysis, in practice the underlying channels in broadband wireless communication systems such as cellular systems (UMTS/LTE) are more likely to exhibit frequency selective fading. In this dissertation, we consider a frequency selective fading channel model and explore distributed diversity techniques in broadband wireless relay networks, with consideration to practical issues such as channel estimation and complexity-performance tradeoffs. We first study a system model with one source, one destination and multiple decode-and-forward (DF) relays which share a single channel orthogonal to the source. We derive the diversity-multiplexing tradeoff (DMT) for several relaying strategies: best relay selection, random relay selection, and the case when all decoding relays participate. The best relay selection method selects the relay in the decoding set with the largest sum-squared relay-to-destination channel coefficients. This scheme can achieve the optimal DMT of the system at the expense of higher complexity, compared to the other two relaying strategies which do not always exploit the spatial diversity offered by the relays. Different from flat fading, we find special cases when the three relaying strategies have the same DMT. We further present a transceiver design and prove it can achieve the optimal DMT asymptotically. Monte Carlo simulations are presented to corroborate the theoretical analysis. We provide a detailed performance comparison of the three relaying strategies in channels encountered in practice. The work has been extended to systems with multiple amplify-and-forward relays. We propose two relay selection schemes with maximum likelihood sequential estimator and linear zero- forcing equalization at the destination respectively and both schemes can asymptotically achieve the optimal DMT. We next extend the results in the two-hop network, as previously studied, to multi-hop networks. In particular, we consider the routing problem in clustered multi-hop DF relay networks since clustered multi-hop wireless networks have attracted significant attention for their robustness to fading, hierarchical structure, and ability to exploit the broadcast nature of the wireless channel. We propose an opportunistic routing (or relay selection) algorithm for such networks. In contrast to the majority of existing approaches to routing in clustered networks, our algorithm only requires channel state information in the final hop, which is shown to be essential for reaping the diversity offered by the channel. In addition to exploiting the available diversity, our simple cross-layer algorithm has the flexibility to satisfy an additional routing objective such as maximization of network lifetime. We demonstrate through analysis and simulation that our proposed routing algorithm attains full diversity under certain conditions on the cluster sizes, and its diversity is equal to the diversity of more complicated approaches that require full channel state information. The final part of this dissertation considers channel estimation in relay networks. Channel state information is vital for exploiting diversity in cooperative networks. The existing literature on cooperative channel estimation assumes that block lengths are long and that channel estimation takes place within a fading block. However, if the forwarding delay needs to be reduced, short block lengths are preferred, and adaptive estimation through multiple blocks is required. In particular, we consider estimating the relay-to-destination channel in DF relay systems for which the presence of forwarded information is probabilistic since it is unknown whether the relay participates in the forwarding phase. A detector is used so that the update of the least mean square channel estimate is made only when the detector decides the presence of training data. We use the generalized likelihood ratio test and focus on the detector threshold for deciding whether the training sequence is present. We also propose a heuristic objective function which leads to a proper threshold to improve the convergence speed and reduce the estimation error. Extensive numerical results show the superior performance of using this threshold as opposed to fixed thresholds.
Author: Venkat Reddy Marepally Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 69
Book Description
Wireless network sharing has been the principal idea in the recent developments of wireless communication systems not only for improvement in capacity, data rates and coverage area but when considering an emergency service model, establishing reliable communication is the foremost requirement. With the inception of cooperative relaying technology, a novel wireless relaying method of sharing the terminal node capabilities to forward the signal created a new paradigm to greatly improve the quality of the services and soon became the significant research area in 3G/4G cellular networks. The cooperative terminals (relays) exploit a larger form of space diversity to relay signals to destinations when placed in between source and destination to combat the effects of fading induced by multipath signal propagation. However, the position of the relay in between the source and destination plays a significant role in affecting the overall network performance. Our attempt in this thesis is to show how a cooperative relay can be used to provide improved coverage at the cell edge with certain reliability and also extend the cell radius by effectively positioning the relay. First, we investigate the famous 3-node relay assisted cellular system model and study the receiver diversity combining results by changing the relay positions with a relay forwarding the signal using the amplitude and forward protocol (AAF). The figure of merit of the considered 3-node system model is expressed in terms of Bit error rate (BER) and signal to noise ratio (SNR). The BER vs. SNR plots are computed for various linear receiver diversity combining techniques and are used to evaluate performance of the system. These results are also compared to the conventional cellular network performance with a single point-to-point link between source and destination. Second, we provide the problem formulation of the diversity results observed and solve to find the effective relay position with respect to the source and also compute the effective cell radius of the 3-node system model. To compute effective relay position, we use the Bernardin's coverage area probability relation with cell radius at the cell edge of the source where the relay is assumed to be placed with its probability of successfully forwarding the signal conditionally depending on its cell edge probability. We have obtained results of the two above problem formulations using MATLAB simulations. We have emulated the cooperative relaying technique in a cellular system to achieve 2nd order diversity when compared to the conventional cellular system. The BER vs. SNR plots for each of the combining techniques show the significant difference in the diversity results when the channel quality estimations are used compared to the other methods which don't. Signal to noise ratio combining (SNRC) and Estimated SNRC (ESNRC) perform 4[equal sign with tilde above]5dB better than the other combining methods provided their SNR estimation is accurate. The highest diversity order (2nd) is achieved when the relay is placed close to the source and drops as the relay is moved towards the destination. Cell range extension results show that moving the relay to its optimal position between source and destination in a cell provides capabilities to extend the cell range to nearly 1.5 times the cell radius of the source and still performs within the acceptable coverage area probabilities.
Author: Praveen Kumar Devulapalli Publisher: CRC Press ISBN: 1040051561 Category : Computers Languages : en Pages : 123
Book Description
This book covers wireless cooperative communication and advanced communication techniques for research scholars and post-graduate students. Features: • This book will be the reference book for cooperative communication. • It addresses the problems in small-scale cooperative communication. • It presents cooperative routing algorithms for large-scale cooperative networks with the constraint of throughput and transmission time. • It presents energy- efficient transmission approach by making use of multiple radio terminals. • It presents adaptive routing algorithm for large-scale cooperative network under mobility environment.
Author: Gayan Lasintha Amarasuriya Aruma Baduge Publisher: ISBN: Category : Antennas (Electronics) Languages : en Pages : 180
Book Description
Cooperative relay technologies are currently being researched to address the ever-increasing demand for higher data rates, extended coverage, greater mobility, and enhanced reliability. This thesis thus focuses on (1) developing new physical-layer wireless technologies for cooperative relay networks and (2) ascertaining their viability through performance analysis. Specifically, (i) new system and channel models, (ii) signaling and relay-processing algorithms, (iii) joint relay-antenna selection strategies, (iv) joint transmit-receive beamforming techniques, and (v) comprehensive performance analysis frameworks are developed for one-way, two-way, and multi-way cooperative relay networks. Our first research focuses on developing a comprehensive analytical framework for deriving closed-form performance bounds of multi-hop amplify-and-forward (AF) relay networks. Specifically, mathematically-tractable, asymptotically-exact end-to-end signal-to-noise ratio bounds are first formulated, and thereby, the outage probability and average bit error rate bounds are derived. In our second work, adaptive multiple-relay selection strategies are designed and analyzed for multi-relay AF networks to optimize the tradeoffs among the system performance, complexity, and wireless resource usage. Our third research investigates joint antenna and relay selection strategies, which are optimal in the sense of the achievable diversity gains, for multiple-input multiple-output (MIMO) one-way relay networks and MIMO two-way relay networks. Finally, joint transmit/receive zero forcing transmission strategies are developed for MIMO multi-way relay networks for optimizing the achievable diversity-multiplexing trade-off. The key design criterion of the aforementioned transmission designs is to leverage spatial diversity and/or spatial multiplexing gains available among distributed single-antenna and/or multiple-antenna wireless terminals through distributed transmission and efficient signal processing. Moreover, the fundamental relationships among the data rate, coverage, and reliability metrics are characterized, and thereby, the detrimental impact of practical wireless transmission impairments on the performance of the aforementioned transmission strategies are quantified. The insights obtained through these analyses are then used to refine our physical-layer designs to achieve desirable trade-offs between the system performance, resource usage and implementation complexity.
Author: Navod D. Suraweera
Author: Navod D. Suraweera
Author: Md Shamsul Alam
Author: Salama Said Ikki
Author: Qingxiong Deng
Author: Venkat Reddy Marepally
Author: Akram Salem Bin Sediq
Author: Praveen Kumar Devulapalli
Author: Gayan Lasintha Amarasuriya Aruma Baduge
Author: Oluwatobi Opeyemi Olabiyi
Author: Hao Chen