Resource Allocation For Multi Cell Orthogonal Frequency Multiplexing Access Based Cooperative Relay Network

The combination of relay transmission with orthogonal frequency division multiplexing (OFDM) technique is deemed as the candidate for the fourth generation (4G) wireless networks. This thesis addresses the resource allocation problem in OFDM based relay networks. Different scenarios of relay networks are considered, e.g., the multi-user relay networks, the multi-relay networks, and the cognitive radio (CR) relay networks. The resource management strategies are developed to analyse: how to optimally distribute available resources among different users, how resource optimization enhances the performance under cooperative communication, how to maximize the lifetime of multi-hop wireless sensor networks (WSNs), and how to improve CR transmission without degrading the performance of the primary network? For each relay transmission scenario, two or more resources are optimized to enhance the system performance under various constraints. The resources include: the power allocation at the source terminal, the power allocation at the relay nodes, the sub-carrier allocation among different users, and the sub-carrier matching over different hops. Multi-user transmission adopts orthogonal frequency division multiple access (OFDMA) technique and is subject to separate power constraint at each terminal. Initially, the resource management issue in multi-user uplink relay transmission is discussed. Then, the similar resource allocation problem is solved when OFDMA multi-user system operates under the bidirectional relay transmission. The multi-relay dual hop transmission is optimized under different transmission schemes, specifically, the non-orthogonal transmission where all the terminals transmit simultaneously in the second time slot and the time division multiple access (TDMA) based transmission where each relay transmits in the pre-defined time slot. The resource allocation in CR relay networks is considered which ensures that the interference caused by the secondary network is not harmful to the primary system. Convex optimization techniques are exploited to solve the problems for each relay transmission and the near optimal solutions are developed. Further, several suboptimal algorithms are also designed to reduce the computational complexity.

In wireless systems, resource allocation is still an important challenge to satisfy user requirements and to ensure good system performances with always greedy data applications. Multicarrier techniques especially the Orthogonal Frequency Division Multiplexing (OFDM) techniques are generally used to carry data into orthogonal subcarriers. Furthermore, relaying strategies are used to enhance cell edge performances. Many types of relays can be investigated as fix relays being part of the network infrastructure or mobile relays without additional deployment cost.In this thesis, we mainly consider the resource allocation for an uplink Orthogonal Frequency Division Multiple Access (OFDMA) system for a cellular system model ensuring Quality of Service (QoS) requirements and fairness between users. The most used resource allocation algorithms are presented and a novel Weighted Proportional Fair (WPF) algorithm is proposed to approach upper bounds of both throughput and fairness. The WPF algorithm considers user weights to allocate more subcarriers in the cell center than in the cell edge keeping sufficient fairness between users. We establish a theoretical analysis to compare the behavior of the proposed WPF algorithm to the classical Proportional Fair (PF) algorithm. Then, we extend this WPF algorithm to a multi-cell system model where the Inter-Cell Interference (ICI) limits the system performance. Moreover, we study ICI mitigation strategies and propose a novel method to reduce the ICI based on Base Station (BS) cooperation and interference indicators. We propose the Enhanced Interference Indicator (EII) with integer values to be exchanged by the BSs indicating interference levels for the subcarriers. Function of these communicated EII values, each BS allocates dynamically subcarriers in order to reduce the ICI. Our contributions in the multi-cell system model are the WPF and the EII.Moreover, we investigate in this dissertation the cooperative communication using mobile relays and propose multiple contributions. For this, simple mobile users with advantageous positions can relay cell edge users to carry data to the BS in addition to their own data. A Decode and Forward (DF) relay multiplex then its own data and relayed data before transmitting to the BS. The resource allocation is formulated as an optimization problem aiming to minimize the system transmit power and respecting a required target data rate per user constraint. In a first time, we propose an initialization method for the paring step to associate source-relay pairs and propose an iterative heuristic to optimize both power and Resource Blocks (RB) allocations. In a second time, we consider the relay selection as an optimization variable in addition of power and RB allocations. For resolution, Lagrangian decomposition and Dual method are used and the global problem is divided into subproblems iterativelly resolved to approach the optimal solution. Finally, we extend this cooperative system model to a Multiple Input Multiple Output (MIMO) system model to study the influence of multiple antennas on the system transmit power. The features to optimize are relay selection, power and RBs allocation. Moreover, to allocate power in the different antennas for each user, both Equal Power Allocation (EPA) and beamforming are studied. Theoretical expressions are established and simulations results are presented to compare EPA, beamforming and non-cooperative system.

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.

Driven by the significant consumer demand for reliable and high data rate communications, the future-generation cellular systems are expected to employ cutting-edge techniques to improve the service provisioning at substantially reduced costs. Cooperative relaying is one of the primary techniques due to its ability to improve the spectrum utilization by taking advantage of the broadcast nature of wireless signals. This dissertation studies the physical layer cooperative relaying technique and resource allocation schemes in the cooperative cellular networks to improve the spectrum and energy efficiency from the perspectives of downlink transmission, uplink transmission and device-to-device transmission, respectively. For the downlink transmission, we consider an LTE-Advanced cooperative cellular network with the deployment of Type II in-band decode-and-forward relay stations (RSs) to enhance the cell-edge throughput and to extend the coverage area. This type of relays can better exploit the broadcast nature of wireless signals while improving the utilization of existing allocated spectral resources. For such a network, we propose joint orthogonal frequency division multiplexing (OFDM) subcarrier and power allocation schemes to optimize the downlink multi-user transmission efficiency. Firstly, an optimal power dividing method between eNB and RS is proposed to maximize the achievable rate on each subcarrier. Based on this result, we show that the optimal joint resource allocation scheme for maximizing the overall throughput is to allocate each subcarrier to the user with the best channel quality and to distribute power in a water-filling manner. Since the users' Quality of Service (QoS) provision is one of the major design objectives in cellular networks, we further formulate a lexicographical optimization problem to maximize the minimum rate of all users while improving the overall throughput. A sufficient condition for optimality is derived. Due to the complexity of searching for the optimal solution, we then propose an efficient, low-complexity suboptimal joint resource allocation algorithm, which outperforms the existing suboptimal algorithms that simplify the joint design into separate allocation. Both theoretical and numerical analyses demonstrate that our proposed scheme can drastically improve the fairness as well as the overall throughput. As the physical layer uplink transmission technology for LTE-Advanced cellular network is based on single carrier frequency division multiple access (SC-FDMA) with frequency domain equalization (FDE), this dissertation further studies the uplink achievable rate and power allocation to improve the uplink spectrum efficiency in the cellular network. Different from the downlink OFDM system, signals on all subcarriers in the SC-FDMA system are transmitted sequentially rather than in parallel, thus the user's achievable rate is not simply the summation of the rates on all allocated subcarriers. Moreover, each user equipment (UE) has its own transmission power constraint instead of a total power constraint at the base station in the downlink case. Therefore, the uplink resource allocation problem in the LTE-Advanced system is more challenging. To this end, we first derive the achievable rates of the SC-FDMA system with two commonly-used FDE techniques, zero-forcing (ZF) equalization and minimum mean square error (MMSE) equalization, based on the joint superposition coding for cooperative relaying. We then propose optimal power allocation schemes among subcarriers at both UE and RS to maximize the overall throughput of the system. Theoretical analysis and numerical results are provided to demonstrate a significant gain in the system throughput by our proposed power allocation schemes. Besides the physical layer technology, the trend of improving energy efficiency in future cellular networks also motivates the network operators to continuously bring improvements in the entire network infrastructure. Such techniques include efficient base station (BS) redesign, opportunistic transmission such as device-to-device and cognitive radio communications. In the third part of this dissertation, we explore the potentials of employing cooperative relaying in a green device-to-device communication underlaying cellular network to improve the energy efficiency and spectrum utilization of the system. As the green base station is powered by sustainable energy, the design objective is to enhance both sustainability and efficiency of the device-to-device communication. Specifically, we first propose optimal power adaptation schemes to maximize the network spectrum efficiency under two practical power constraints. We then take the dynamics of the charging and discharging processes of the energy buffer at the BS into consideration to ensure the network sustainability. To this end, the energy buffer is modeled as a G/D/1 queue where the input energy has a general distribution. Power allocation schemes are proposed based on the statistics of the energy buffer to further enhance the network efficiency and sustainability. Theoretical analysis and numerical results are presented to demonstrate that our proposed power allocation schemes can improve the network throughput while maintaining the network sustainability at a certain level. Our analyses developed in this dissertation indicate that the cooperative transmission based on cooperative relaying can significantly improve the spectrum efficiency and energy efficiency of the cellular network for downlink transmission, uplink transmission and device-to-device communication. Our proposed cooperative relaying technique and resource allocation schemes can provide efficient solutions to practical design and optimization of future-generation cellular networks.

Abstract: The main objectives of next-generation wireless networks are to accommodate the increasing user demand and to achieve ubiquitous high data rate coverage. Wireless multi hop relaying is therefore among the envisioned solutions. Relays cost less than base stations, and they can extend coverage and improve detection in a cooperative manner. Orthogonal frequency division multiple access (OFDMA) as the prospective air interface. The synergy of multi hop relaying and OFDMA techniques present a set of opportunities but, render an unsuitable environment for static resource planning. Therefore, intelligent radio resource management (RRM) schemes are required to combat the interference and to operate the relays in a dynamic and opportunistic manner so that bandwidth is efficiently utilized. Consequently, a reliable and ubiquitous service is achieved regardless of users' locations and channel conditions. In this project we did simulation using Matlab Tool and a graph of the number of user vs capacity of a channel is plotted, which shows that as the number of users increase, the throughput of the system becomes stable.

A self-contained guide to the state-of-the-art in cooperative communications and networking techniques for next generation cellular wireless systems, this comprehensive book provides a succinct understanding of the theory, fundamentals and techniques involved in achieving efficient cooperative wireless communications in cellular wireless networks. It consolidates the essential information, addressing both theoretical and practical aspects of cooperative communications and networking in the context of cellular design. This one-stop resource covers the basics of cooperative communications techniques for cellular systems, advanced transceiver design, relay-based cellular networks, and game-theoretic and micro-economic models for protocol design in cooperative cellular wireless networks. Details of ongoing standardization activities are also included. With contributions from experts in the field divided into five distinct sections, this easy-to-follow book delivers the background needed to develop and implement cooperative mechanisms for cellular wireless networks.

Supported by the expert-level advice of pioneering researchers, Orthogonal Frequency Division Multiple Access Fundamentals and Applications provides a comprehensive and accessible introduction to the foundations and applications of one of the most promising access technologies for current and future wireless networks. It includes authoritative cove

The first book on Cloud Radio Access Networks (C-RANs), covering fundamental theory, current techniques, and potential applications.

Non-orthogonal multiple access (NOMA) has been considered as an essential enabling technology for fifth generation (5G) and beyond 5G (B5G) cellular networks to meet the increasing demands on low latency, high reliability, massive connectivity, improved fairness, and high throughput. Cooperative relay networks, on the other hand, have been shown to significantly improve the throughput, coverage, and achievable rates of wireless networks, in which, the relay nodes assist the communication between the source node and the destination node when the direct channel is poor. There has been extensive research on the subject of NOMA and cooperative relay networks. However, most of the existing research relies on two main assumptions: flat fading channels and perfect channel state information (CSI) at the transmitting nodes. Instead of those idealistic assumptions, we study NOMA in cooperative relay networks under practical assumptions: frequency selective multipath fading channels and statistical CSI at the transmitting nodes. This dissertation begins with an overview of the basic concept of NOMA. Then, it focuses on downlink NOMA transmissions in a cooperative relay network. Specifically, a base station communicates with two paired mobile users simultaneously via superposition coded orthogonal frequency division multiplexing (OFDM) transmissions with the help of a half-duplex relay under either the decode-and-forward (DF) or amplify-and-forward (AF) scheme, where the power splitting between two mobile users depends on the statistical CSI. We derive the ergodic rates under Rayleigh fading channels and present an ad-hoc approach to determine the power splitting parameters when the target data rates are given. After that, this dissertation presents uplink NOMA transmissions in a cooperative relay network. Specifically, two users, a near user and a far user, communicate with a base station at the same time with existence of a half-duplex relay employing the DF scheme to assist the far user. At the transmitting nodes, the power allocation factors are decided based on the statistical CSI while, at the receiving nodes, the effect of imperfect successive interference cancellation (SIC) implementation is taken into account. Under Rayleigh fading channels, we derive the exact ergodic rate for the near user and the upper bound of the ergodic rate for the far user, then present an ad-hoc approach to determine the power allocation factors when the target data rates are given, and we study the outage probability of the two users at the base station. The last part of this dissertation extends the study into an energy harvesting cooperative wireless sensor network. We consider a two-hop network consisting of a source, two parallel half-duplex relay nodes, and two destinations. While the destinations have adequate power supply, the source and relay nodes rely on harvested energy for data transmission. Different from all existing works, the two relay nodes can also transfer their harvested energy to each other via energy conferencing channels. For such a system, an optimization problem is formulated with the objective of maximizing the total data rate and conserving the source and relay transmission energy.