OFDMA Cellular Networks Research Articles

Analysis and emulation of proposed testbed for OFDMA 4G and 5G cellular networks

AbstractIn order to investigate and analyze the behavior of 4G and 5G OFDMA cellular networks in real time, it is essential to have a real‐time testbed to emulate these cellular networks. We developed the experimental testbed in this work and proposed a real‐time approach to emulating these networks. We take real‐time measurements in indoor and outdoor environments. From the results, we say the proposed testbed can be used to identify the activity of spectrum occupancy of 4G and 5G cellular systems within a specified time, and one can also test their algorithm, protocols, and solutions using our developed testbed.

Adaptive Uplink Scheduling and UAV Association in UAV-Assisted OFDMA Cellular Networks: A Game-Theoretical Approach

Adaptive Uplink Scheduling and UAV Association in UAV-Assisted OFDMA Cellular Networks: A Game-Theoretical Approach

Green communication for OFDMA cellular networks with multiple antennas

The green communication which requires the maximum reduction of energy consumption has become a strong need for the new wireless system designs because of the massive increasing number of mobile subscriptions. Thus, in this paper, energy efficiency (EE) maximization problem is considered for multiple-input single-output orthogonal frequency division multiple access (MISO-OFDMA) cellular networks. The EE maximization problem is defined for a downlink communication model by considering the total transmit power and circuit power constraints. Quality of service (QoS) constraints which guarantee the minimum data rate requirement of the users are also accounted. The considered problem belongs to the category of mixed-integer non-linear programming problem (MINLP), and thus is NP-hard. To cope up with this complexity, a two-step resource allocation algorithm, which contains an heuristic subchannel allocation algorithm and the iterative power allocation algorithm with fast convergence based on the Dinkelbach method, is proposed. Numerical results are provided to demonstrate the effectiveness of the proposed algorithm and the convergence and energy efficiency performance of the proposed scheme is validated.

Device-to-device communications under transceiver impairments in OFDMA cellular networks

Device to Device communication (D2D) would be a part of 5G to cater variety of services along with cellular offloading. In order to leverage the benefits of D2D communication it needs be adapted for robust conditions. In physical layer we use OFDM for cellular and D2D communication. OFDM based systems are inherently associated with transceiver impairments. Using OFDM for D2D communication thereby involves the impact of these transceiver impairments on D2Ds and their feasibility zone of operation. As the D2D transmitter power is small, the transceiver impairments effect becomes predominant and hence it becomes important to study D2D performance under transceiver impairments. As there is limited literature on the effect of transceiver impairments onto the performance of D2D enabled cellular networks, it becomes essential to analyse this aspect. We analysed the impact of these impairments on the cellular and the D2D modes and the zone where D2Ds can be operated under these impairments. Our conclusion is that due to transceiver impairments there is fall in throughput of both cellular and D2D mode. D2D communication which is beneficial at the cellular edges loses its operational advantage. Besides we also conclude that under the effect of transceiver impairments the switch-over distance to D2D mode moves towards eNB. We also analyse that D2D communication could be harnessed even under the case of transceiver impairments if we do threshold adjustment in the physical layer. We get an advantage of approximately 5 Mbps in throughput at distance 150 metres from eNB after threshold adjustment.

Load Management, Power and Admission Control in Downlink Cellular OFDMA Networks

We present a resource management framework for load-coupled downlink cellular OFDMA networks considering the load factor of an individual base station (BS) per resource block (RB), i.e., the number of adjacent sub-carriers (SCs), as the variable of interest in the resource management problem. The load factor of a BS per RB, which corresponds to the fraction of active SCs in the BS per RB, is an indicator of the level of resource consumption, and it affects the interference caused to that RB reused in other BSs, and thereby, results in a load-coupled OFDMA system. We first propose two distributed schemes to minimize: (i) the total load factor of the BSs (which would in turn increase the number of supportable users in the system), and (ii) the total downlink transmit power level of the BSs. Then, we derive the necessary and sufficient conditions for checking the feasibility of given target-rate requirements (also referred to as demand vector) for users. Accordingly, an iterative and distributed scheme is proposed to check the feasibility of a given demand vector. Next, for a priority-based load-coupled network, we propose a priority-based gradual removal algorithm to support the maximal number of low-priority users while satisfying the demands of the high-priority users. To evaluate the performance of our proposed schemes for resource management and admission control in load-coupled OFDMA networks, the theoretical investigations are complemented with Monte Carlo simulations.

Energy and Spectral Efficiency Analysis for a Device-to-Device-Enabled Millimeter-Wave OFDMA Cellular Network

The spectral efficiency (SE) and energy efficiency (EE) performance of a millimeter-wave (mmWave) cellular network is studied where a user device can associate with a base station (BS) or another user for device-to-device (D2D) communication based on an interference-aware D2D distance threshold. Using the tools of stochastic geometry, the mean interference, coverage probability, area SE, and network EE are derived under the proposed association scheme. Performance of the proposed scheme is compared with that of the minimum path loss (Min PL)-based and maximum biased-received-power (Max BRP)-based association schemes. The proposed scheme is shown to give the best coverage probability performance in noise-limited networks, while the three schemes converge in performance in interference-limited networks in the high coverage threshold regime (>20 dB). Further, the proposed scheme achieves up to 60% increase in the area SE and EE, compared to the Min PL-based scheme that gives the next best performance. Lastly, the paper proposed a goal attainment algorithm that achieves up to a seven-fold decrease in the mean deviation from a preset SE objective and 50% savings in EE, compared to the achievable performance under a constant transmit power and bandwidth allocation scheme.

Fairness Analysis of Inter-cell Relay in Downlink OFDMA Cellular Networks

In the OFDMA cellular network, in order to improve the throughput of the cell system and the overall resource utilization of the system as well as the quality of service and fairness of the system users. In this paper, we propose a load balancing schema based on the inter-cell relay for the downlink OFDMA cellular networks, and then we research the fairness of intra cell and whole cell system. Based on the frequency reuse pattern, we propose a new type of spectrum division and time slot division model. And then, we calculate the remaining subcarriers by deriving the interference formula according to the SIR. Then, we propose a distance-based fairness scheduling algorithm, which is used for the redistribution of the remaining sub-carriers in the BS and RS region. Besides, we consider the optimization of the relay radius when the fairness of the system is as higher as possible. Finally, the feasibility of the proposed scheme is verified by simulation.

Higher Order Sectorization in FFR-Aided OFDMA Cellular Networks: Spectral- and Energy-Efficiency

Higher Order Sectorization in FFR-Aided OFDMA Cellular Networks: Spectral- and Energy-Efficiency

A Base Station DTX Scheme for OFDMA Cellular Networks Powered by the Smart Grid

Discontinuous transmission (DTX) is an efficient technology to improve the energy efficiency of the wireless cellular networks. DTX enables the deactivation of some components of the base station in sufficient short time, which can decrease the energy consumption without affecting the normal operation of the mobile networks. In addition, we consider distributed smart grid which can power the cellular networks using renewable and conventional energy. The distributed smart grid has many different energy retailers with variant energy resource, such as solar energy, wind energy, and conventional energy. Comparing with conventional energy, the renewable energy is more environmental friendly, but more expensive. As a result, it is necessary to obtain a good tradeoff between the operation cost and greenhouse gas (GHG) emission. In this paper, we jointly optimize the DTX, resource allocation, and smart grid energy procurement to maximize the profit of the network operators and minimize the GHG emission. We formulate the joint optimization problem as a mixed integer programming problem. By exploiting the structure of the coupled constraint of the problem, we propose a suboptimal distributed algorithm based on the Lagrangian dual method, and the algorithm can be performed at cellular network and smart grid alternately, which can significantly decrease the signaling and computational overhead. Simulation results illustrate that the proposed DTX scheme can significantly enhance the energy saving, and further improve the energy efficiency of the cellular networks.

Distributed Power Allocation for D2D Communications Underlaying/Overlaying OFDMA Cellular Networks

The implementation of device-to-device (D2D) underlaying or overlaying preexisting cellular networks has received much attention due to the potential of enhancing the total cell throughput, reducing the power consumption, and increasing the instantaneous data rate. In this paper, we propose a distributed power allocation scheme for D2D OFDMA communications and, in particular, we consider the two operating modes amenable to a distributed implementation: dedicated and reuse modes. The proposed schemes address the problem of maximizing the users’ sum rate subject to power constraints, which is known to be nonconvex and, as such, extremely difficult to be solved exactly. We propose here a fresh approach to this well-known problem, capitalizing on the fact that the power allocation problem can be modeled as a potential game. Exploiting the potential games property of converging under better response dynamics, we propose two fully distributed iterative algorithms, one for each operation mode considered, where each user updates sequentially and autonomously its power allocation. Numerical results, computed for several different user scenarios, show that the proposed methods, which converge to one of the local maxima of the objective function, exhibit performance close to the maximum achievable optimum and outperform other schemes presented in the literature.

Distributed Resource Allocation for Multi-cell Cooperative OFDMA Networks with Decode-and-Forward Relaying

In this paper, the downlink resource allocation is investigated for multi-cell cellular OFDMA networks with relaying, and a low-complexity distributed scheme is proposed. The target is to maximize the system weighted sum rate as well as provide fair services for each class of users. The problem is formulated as a mixed integer programming with the individual power constraints of the base station and relay station. The iterative multilevel water-filling is exploited in the power allocation in each cell, and different cells interact and cooperative with one another implicitly, which reduces the signal overhead and the computational complexity. Furthermore, subcarrier pairing and grouping are also discussed to enhance the system throughput or reduce the signaling overhead. Simulation results show that the algorithm converges fast, and outperforms some traditional schemes in terms of system throughput, and achieves fair and ubiquitous data coverage for heterogeneous users.

Distributed WRBG Matching Approach for Multiflow Two-Way D2D Networks

Device-to-device (D2D) communication has great potential to improve spectrum efficiency and offload traffic for cellular networks. In this paper, we focus on a multiflow two-way D2D network with decode-and-forward (DF) relays, coexisting with OFDMA cellular network. The spectrum sharing and relay selection are considered to minimize the outage probability of the device in D2D networks. The induced problem is a complicated probabilistic integral programming. A novel weighted random bipartite graph (WRBG)-based minimum weight maximum matching (MWMM) approach will be proposed in this paper. To offload not only the traffic but also the signaling and computation overhead, the improved min-sum algorithm will be applied to find the MWMM in the distributed manner with only polynomial complexity. The proposed approach enjoys an advantage that the close-form approximation formulas for optimal outage probability and diversity-multiplexing tradeoff can be derived by analyzing the properties of MWMM on WRBG. Both the theoretical derivations and simulation results will illustrate that the proposed approach for multiflow two-way D2D networks achieves the same performance as single-flow two-way D2D systems. Therefore, the distributed WRBG matching approach yields not only a practical distributed algorithm, but also a simple and elegant theoretical framework for multiflow two-way D2D networks.

Resource Allocation for D2D Links in the FFR and SFR Aided Cellular Downlink

Device-to-device (D2D) communication underlying cellular networks, allows direct transmission between two devices in each other’s proximity that reuse the cellular resource blocks in an effort to increase the network capacity and spectrum efficiency. However, this imposes severe interference that degrades the system’s performance. This problem may be circumvented by incorporating fractional frequency reuse (FFR) or soft frequency reuse (SFR) in OFDMA cellular networks. By carefully considering the downlink resource reuse of the D2D links, we propose beneficial frequency allocation schemes, when the macrocell has employed FFR or SFR as its frequency reuse technique. The performance of these schemes is quantified using both the analytical and simulation results for characterizing both the coverage probability and the capacity of D2D links under the proposed schemes that are benchmarked against the radical unity frequency reuse scheme. The impact of the D2D links on the coverage probability of macrocellular users (CUs) is also quantified, revealing that the CUs performance is only modestly affected under the proposed frequency allocation schemes. Finally, we provide insights concerning the power control design in order to strike a beneficial tradeoff between the energy consumption and the performance of D2D links.

Opportunistic scheduling and incentive mechanism for OFDMA networks with D2D relaying

The device-to-device (D2D) relaying is considered one of promising technologies to improve the spectral efficiency and extend the coverage of the cellular system with low additional costs. In the system with D2D relaying, some of user equipments (UEs) can act as relay stations (RSs) that forward other UEs’ data from/to the base station (BS). Compared with the RS, the D2D relaying has several advantages such as low deployment costs and high flexibility. We study an opportunistic subchannel scheduling problem in the OFDMA cellular network with D2D relaying in this paper. We formulate a stochastic optimization problem to maximize the sum-rate of the system with D2D relaying while satisfying the minimum average data rate requirement for each UE, and then develop an opportunistic scheduling algorithm by solving it. Due to a high computational complexity of the optimal scheduling algorithm, we also propose a heuristic algorithm with a lower computational complexity. In addition, since UEs that participate in D2D relaying sacrifice their resources to relay other UEs’ data, we also study incentive mechanisms to compensate their sacrifices. Through simulation results, we show the performance of our algorithms and the effects of our incentive mechanisms.

Theoretical expression of link performance in OFDM cellular networks with MIMO compared to simulation and measurements

The objective of this paper is to establish a theoretical expression of the link performance in the downlink of a multiple input multiple output (MIMO) cellular network and compare it to the real Long-Term Evolution (LTE ) performance. In order to account for the interference, we prove that the worst additive noise process in the MIMO context is the white Gaussian one. Based on this theoretical result, we build an analytic expression of the link performance in LTE cellular networks with MIMO. We study also the minimum mean square error (MMSE) scheme currently implemented in the field, as well as its improvement MMSE-SIC (successive interference cancellation) known to achieve the MIMO capacity. Comparison to simulation results as well as to measurements in the field shows that the theoretical expression predicts well practical link performance of LTE cellular networks. This theoretical expression of link performance is the basis of a global analytic approach to the evaluation of the quality of service perceived by the users in the long run of their arrivals and departures.

Resource allocation in full-duplex communications for future wireless networks

The recent significant progress in realizing full-duplex~(FD) systems has opened up a promising avenue for improving quality of service (QoS) and quality of experience (QoE) in future wireless networks. There is an urgent need to address the diverse set of challenges regarding different aspects of FD network design, theory, and development. In addition to the self-interference cancelation signal processing algorithms, network protocols such as resource management are also essential in the practical design and implementation of FD wireless networks. This article aims to present the latest development and future directions of resource allocation in different full duplex systems by exploring the network resources in different domains, including power, space, frequency, and device dimensions. Four representative application scenarios are considered: FD MIMO networks, FD cooperative networks, FD OFDMA cellular networks, and FD heterogeneous networks. Resource management problems and novel algorithms in these systems are presented, and key open research directions are discussed.

In-Band Device-to-Device Communication in OFDMA Cellular Networks: A Survey and Challenges

Direct communication between two or more devices without the intervention of a base station, known as device-to-device (D2D) communication, is a promising way to improve performance of cellular networks in terms of spectral and energy efficiency. The D2D communication paradigm has been largely exploited in non-cellular technologies such as Bluetooth or Wi-Fi but it has not yet been fully incorporated into existing cellular networks. In this regard, a new proposal focusing on the integration of D2D communication into LTE-A has been recently approved by the 3GPP standardization community as discussed in this paper. In cellular networks, D2D communication introduces several critical issues, such as interference management and decisions on whether devices should communicate directly or not. In this survey, we provide a thorough overview of the state of the art focusing on D2D communication, especially within 3GPP LTE/LTE-A. First, we provide in-depth classification of papers looking at D2D from several perspectives. Then, papers addressing all major problems and areas related to D2D are presented and approaches proposed in the papers are compared according to selected criteria. On the basis of the surveyed papers, we highlight areas not satisfactorily addressed so far and outline major challenges for future work regarding efficient integration of D2D in cellular networks.

Energy-Efficient Resource Allocation for OFDMA Cellular Networks With User Cooperation and QoS Provisioning

In this paper, an energy-efficient resource allocation scheme is designed for orthogonal frequency-division multiple-access cellular wireless networks with multiuser cooperation. Joint relay selection, subcarrier allocation and pairing, and power-allocation algorithms are developed with the objective of maximizing the energy efficiency of the system considering the quality-of-service requirements of the users. The optimization problem is a mixed-integer nonlinear program (MINLP), which is generally very difficult to solve in its original form. The energy efficiency metric is a fractional and nonlinear function, which complicates the problem further. We provide a novel optimization framework to solve such nonlinear and nonconvex optimization problems. The MINLP optimization problem is reformulated to a convex problem by relaxing the integer variables and by introducing the "Dinkelbach" method to tackle the nonlinear fractional objective function. We prove that our proposed solution of the relaxed problem is optimal and has integer values. Based on the dual-decomposition method, we propose a solution to the joint optimization problem, which is optimal and computationally efficient with polynomial-time complexity. Numerical results demonstrate the effectiveness of our proposed scheme.

Opportunistic resource scheduling for D2D communication in OFDMA networks

In this paper, we study a resource scheduling problem for D2D communication in OFDMA cellular networks. In addition to opportunistically scheduling power and subchannels to users as in the conventional OFDMA network, we also consider two distinguishing features for D2D communication to fully utilize the advantages of D2D communication: transmission mode selection and channel reuse. First, we allow each D2D user to opportunistically select its transmission mode between direct one-hop transmission and indirect two-hop transmission through the BS. Second, we allow channel reuse within a cell such that users can share the same subchannel within a cell. We formulate an optimization problem that aims at maximizing the average weighted sum-rate of users, while satisfying the QoS requirement of each user. Our problem is a non-convex and coupled optimization problem, which is inherently difficult to solve, especially due to channel reuse within a cell. Despite of it, we develop an optimal opportunistic resource scheduling algorithm that solves the problem. In addition, we also propose two simple heuristic algorithms to reduce the computational complexity of the optimal algorithm. Through simulations, we show our opportunistic scheduling algorithms achieve a high performance with appropriately utilizing the advantages of D2D communication.

Nonconcave Utility Maximization in Locally Coupled Systems, With Applications to Wireless and Wireline Networks

Motivated by challenging resource allocation issues arising in large-scale wireless and wireline communication networks, we study distributed network utility maximization problems with a mixture of concave (e.g., best-effort throughputs) and nonconcave (e.g., voice/video streaming rates) utilities. In the first part of the paper, we develop our methodological framework in the context of a locally coupled networked system, where nodes represent agents that control a discrete local state. Each node has a possibly nonconcave local objective function, which depends on the local state of the node and the local states of its neighbors. The goal is to maximize the sum of the local objective functions of all nodes. We devise an iterative randomized algorithm, whose convergence and optimality properties follow from the classical framework of Markov Random Fields and Gibbs Measures via a judiciously selected neighborhood structure. The proposed algorithm is distributed, asynchronous, requires limited computational effort per node/iteration, and yields provable convergence in the limit. In order to demonstrate the scope of the proposed methodological framework, in the second part of the paper we show how the method can be applied to two different problems for which no distributed algorithm with provable convergence and optimality properties is available. Specifically, we describe how the proposed methodology provides a distributed mechanism for solving nonconcave utility maximization problems: 1) arising in OFDMA cellular networks, through power allocation and user assignment; 2) arising in multihop wireline networks, through explicit rate allocation. Several numerical experiments are presented to illustrate the convergence speed and performance of the proposed method.