OFDMA Cellular Networks Research Articles

Efficient and Fair Power and Subchannel Allocation in Multiuser OFDM Networks

We present an efficient and fair scheme for allocating resources in the downlink of multiuser OFDMA cellular networks based on Nash Bargaining Solution (NBS). Although NBS provides a fair and optimum approach in order to maximize the total rate of the network, there is no simple solution for the case of K users. The proposed algorithm satisfies the minimum rate requirement of each user first and allocates the excess subchannels by searching over the K × N subchannels to noise ratio matrix based on the bargaining process happening between the base station and the users. Hence, the complexity reduces from order O(K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sup> ) to O(N × K).

Bandwidth Partitioning and SINR Threshold Analysis of Fractional Frequency Reuse in OFDMA Cellular Networks for Real Time and Best Effort Traffic

To achieve high capacity in cellular networks, frequency reuse factor of unity is used. However, it suffers from heavy co-channel interference at cell edge regions. This leads to poor Signal to Interference plus Noise Ratio (SINR) and hence poor performance. fractional frequency reuse (FFR) is one of the methods being considered to improve cell edge performance. In this work we present the impact of SINR threshold and bandwidth partitioning on the successful deployment of FFR scheme. We have considered both real time (RT) and best effort (BE) traffic. In FFR, the total frequency resource is divided logically into cell center and cell edge user bands. However, while frequency resource is partitioned into two segments, the amount of bandwidth required by cell center and cell edge users is quite different and influences the system performance. We developed the semi analytical approach to evaluate the average bandwidth required by cell center and edge band users. From the analysis and simulation results it is seen that while grade of service (GoS) fair based method of choosing bandwidth partitioning ratio is best for RT traffic, while the only feasible method for BE traffic is dividing the bandwidth based on probability of a user to be in a given band which we termed as `Probability' method.

Discovery Signal Design and its Application to Peer-to-Peer Communications in OFDMA Cellular Networks

This paper proposes a unique discovery signal as an enabler of peer-to-peer (P2P) communication which overlays a cellular network and shares its resources. Applying P2P communication to cellular network has two key issues: 1. Conventional ad hoc P2P connections may be unstable since stringent resource and interference coordination is usually difficult to achieve for ad hoc P2P communications; 2. The large overhead required by P2P communication may offset its gain. We solve these two issues by using a special discovery signal to aid cellular network-supervised resource sharing and interference management between cellular and P2P connections. The discovery signal, which facilitates efficient neighbor discovery in a cellular system, consists of un-modulated tones transmitted on a sequence of OFDM symbols. This discovery signal not only possesses the properties of high power efficiency, high interference tolerance, and freedom from near-far effects, but also has minimal overhead. A practical discovery-signal-based P2P in an OFDMA cellular system is also proposed. Numerical results are presented which show the potential of improving local service and edge device performance in a cellular network.

Self-organising cluster-based cooperative load balancing in OFDMA cellular networks

Mobility load balancing MLB redistributes the traffic load across the networks to improve the spectrum utilisation. This paper proposes a self-organising cluster-based cooperative load balancing scheme to overcome the problems faced by MLB. The proposed scheme is composed of a cell clustering stage and a cooperative traffic shifting stage. In the cell clustering stage, a user-vote model is proposed to address the virtual partner problem. In the cooperative traffic shifting stage, both inter-cluster and intra-cluster cooperations are developed. A relative load response model is designed as the inter-cluster cooperation mechanism to mitigate the aggravating load problem. Within each cluster, a traffic offloading optimisation algorithm is designed to reduce the hot-spot cell's load and also to minimise its partners' average call blocking probability. Simulation results show that the user-vote-assisted clustering algorithm can select two suitable partners to effectively reduce call blocking probability and decrease the number of handover offset adjustments. The relative load response model can address public partner being heavily loaded through cooperation between clusters. The effectiveness of the traffic offloading optimisation algorithm is both mathematically proven and validated by simulation. Results show that the performance of the proposed cluster-based cooperative load balancing scheme outperforms the conventional MLB. Copyright © 2013 John Wiley & Sons, Ltd.

Two Novel High Spectral Efficient Frequency Reuse Schemes in OFDMA Cellular Relay Networks

In this paper, two novel high spectral efficient frequency reuse schemes are proposed to improve the system throughput of the OFDMA cellular relay networks. Both the interference avoiding scheme and Multi-hop Relay Soft Frequency Reuse (MR-SFR) concept are introduced and modified in the proposed schemes. In order to reduce the interference level, the former of the two proposed schemes allows only the two relays which are located farthest from each other in one cell to have the same frequency distribution to avoid the interference from the relays, whereas two adjacent relays will have the same frequency distribution in the latter to avoid the interference from the adjacent BS. Simulation results show that both schemes can improve the spectral efficient greatly and maintain a low outage probability at the same time. Comparing the two proposed schemes shows that the latter scheme has better performance than the former.

Flow-Level Analysis of Energy Efficiency Performance for Device-to-Device Communications in OFDM Cellular Networks

In this paper, the energy efficiency performance of device-to-device (D2D) communications in orthogonal frequency division multiplexing cellular networks is studied. Different from previous work that was based on the static interference model, we assume a dynamic number of competing flows, such as continuous transfers of file transport protocol or web browsing sessions. The complex, dynamic interaction of the amount of backlogged traffic at the D2D and cellular links introduced by the strong impact of interference between them is captured by the coupled-processors server in the formulated model. The energy efficiency and spectral efficiency of the different resource-sharing strategies are analyzed using the semidefinite optimization approach. It is shown that the simulation results match well with the analytical bounds under different traffic loads and topologies.

Joint Opportunistic Spectrum Sharing and Dynamic Full Frequency Reuse in OFDMA Cellular Relay Networks

This paper considers the problem of spectrum sharing in orthogonal frequency division multiple access cellular relay networks. Firstly, a novel dynamic full frequency reuse scheme is proposed to improve the spectral efficiency. Different from the conventional full frequency reuse scheme which only allows the base station (BS) reusing the subcarriers in the specific regions, an improved full frequency reuse scheme is proposed to allow the BS reusing all the subcarriers in the whole BS coverage region to exploit additional multiuser diversity gain. In order to dynamically reuse the frequency resource among the BS and relay stations (RSs) to further improve the spectral efficiency, the adaptive subcarrier scheduling is introduced into the improved full frequency reuse scheme to obtain more multi-user diversity gain, which forms the proposed novel dynamic full frequency reuse scheme. Secondly, in order to further increase the system throughput, the opportunistic spectrum sharing scheme is introduced to allow the RSs selectively reusing the subcarriers among each other, which joint with the proposed dynamic full frequency reuse scheme to intelligently allocates the subcarriers originally reused by the BS and a RS to another suitable RS which can best improve the system performance after considering the additional interference. Thirdly, in order to select The optimal reusing combination scheme of BS and RSs to exploit more potential system performance, a heuristic approach based on genetic algorithm is proposed to search the optimal BS and RSs combination to opportunistically share the frequency resource. Simulation results show that the proposed dynamic full frequency reuse scheme can obtain high spectral efficiency, fine fairness and low outage probability compared to the conventional full frequency reuse scheme. Furthermore, the system performance can be improved when considering the opportunistic spectrum sharing among RSs. Finally, after adopting the genetic algorithm, the system performance can be greatly improved by the frequency reusing among the optimal BS and RSs combination.

Non-Cooperative Multi-Cell Resource Allocation and Modulation Adaptation for Maximizing Energy Efficiency in Uplink OFDMA Cellular Networks

We address the optimization problem of maximizing uplink energy efficiency, defined as sum of users bits-per-joule (bpj), in a multi-cell multi-user OFDMA network. Firstly, we propose a non-cooperative distributed scheme, in which mobile stations (MS) in different cells with given subcarrier assignment (SA) adjust the modulation and transmit power non-cooperatively, to optimize its own bpj. An advanced non-cooperative BS-controlled resource allocation scheme, in which the base station in each cell jointly performs SA, modulation adaptation, and power control for MSs in a non-cooperative manner, is proposed. Numerical results illustrate the tradeoff between energy and spectral efficiency, and show the proposed scheme makes great improvement on bpj with marginal loss of throughput as compared to other conventional scheme.

Single- and multi- user uplink energy-efficient resource allocation algorithms with users’ power and minimum rate constraint in OFDMA cellular networks

In this paper, single- and multi- user Resource Allocation (RA) optimization problems considering transmit power and minimum rate constraint of Mobile Station (MS) for maximizing MS' energy efficiency, measured as bits-per-joule (bpj), are addressed. Assume channel state information of all MSs is known by base station. We propose uplink RA algorithms, performing subcarrier assignment and power allocation, for optimizing bpj of MS in a single-cell OFDMA-based cellular network for both single- and multi- user scenarios. In the single-user case, we propose RA algorithms, which utilize the closed-form solution derived by applying Lambert-W function and an iterative approach based on Karush---Kuhn---Tucker conditions respectively to achieve optimal bpj of MS. In the multi-user case, centralized iterative multi-user RA algorithms for maximizing sum of MS' bpj, performing joint subcarrier assignment and power allocation iteratively, are proposed by utilizing the proposed single-user RA schemes. In particular, tradeoffs between energy efficiency and spectral efficiency are fully investigated, and the influence of MS' power and minimum rate constraints on bpj performance is also studied. The effectiveness of proposed algorithms is presented by numerical experiments. Numerical results demonstrate the proposed algorithms can enhance bpj significantly with limited loss of total throughput compared to the sum-rate maximization algorithm (in Moretti et al., IEEE Trans Veh Technol 60(4):1788---1798, 2011).

Relay Sharing and Soft Frequency Reuse Based Frequency Planning in OFDMA Cellular Networks

This paper proposed a relay sharing and soft frequency reuse based (RSSFR) frequency planning scheme, which reaches high data rates while using the precious frequency resource efficiently, system performance is analysed and evaluated as well. System performance is enhanced in four aspects: 1) Co-channel interference is reduced significantly, which broadens the area of high achievable data rates in each cell. 2) Base stations (BSs) communicate with fixed relay stations through narrow beam antennas, which boosts the resource efficiency without bringing much interference to mobile stations (MSs). 3) The relay sharing strategy can not only bring down network cost, but also provide a better coverage to cell edge users. 4) Soft frequency reuse on shared relay increases the frequency resource efficiency further. Simulation results show that, a better tradeoff between cell throughput and frequency resource efficiency is achieved in RSSFR.

Impact of Channel Partitioning and Relay Placement on Resource Allocation in OFDMA Cellular Networks

Tremendous growth in the demand for wireless applications such as streaming audio/videos, Skype and video games require high data rate irrespective of user’s location in the cellular network. However, the Quality of Service (QoS) of users degrades at the cell boundary. Relay enhanced multi-hop cellular network is one of the cost effective solution to improve the performance of cell edge users. Optimal deployment of Fixed Relay Nodes (FRNs) is essential to satisfy the QoS requirement of edge users. We propose new schemes for channel partitioning and FRN placement in cellular networks. Path-loss, Signal to Interference and Noise Ratio (SINR) experienced by users, and effects of shadowing have been considered. The analysis gives more emphasis on the cell-edge users (worst case scenario). The results show that these schemes achieve higher system performance in terms of spectral efficiency and also increase the user data rate at the cell edge.

Energy-Saving Massive Access Control and Resource Allocation Schemes for M2M Communications in OFDMA Cellular Networks

Machine-to-Machine communication recently becomes a popular issue in 4G Standardization Committee, such as IEEE 802.16p and LTE-A. In an OFDMA cellular network embedded with a M2M system, the energy consumption (EC) minimization problem is formulated with the consideration of transmission and circuit energy consumed. We propose joint massive access control and resource allocation (RA) schemes, which perform machine node grouping, coordinator selection, and coordinator RA, and also determine the proper number of groups under a 2-hop transmission protocol, to minimize total EC in both flat- and frequency-selective fading channel. Numerical results show that proposed schemes can achieve sub-optimal EC.

A Statistical Inter-Cell Interference Model for Uplink Cellular OFDMA Networks Under Log-Normal Shadowing and Rayleigh Fading

The performance of uplink cellular OFDMA networks transmitting multiple QAM symbols per hop is evaluated under log-normal shadowing and Rayleigh fading without resorting to a Gaussian approximation of the inter-cell interference. The derived interference statistic is observed to deviate significantly from the Gaussian distribution which may be exploited to dramatically enhance the network performance. It is also observed that the network performance is highly dependent on the number and the geometry of the QAM symbols transmitted within a hop, especially for large code frame lengths.

Opportunistic Resource Scheduling for OFDMA Networks with Network Coding at Relay Stations

In this paper, we study an opportunistic resource scheduling problem for the relay-based OFDMA cellular network where relay stations (RSs) perform opportunistic network coding with downlink and uplink sessions of a mobile station (MS). To this end, we consider time-division duplexing (TDD) where each time-slot is divided into three phases according to the type of transmitter nodes, i.e., the base station (BS), MSs, and RSs. Moreover, to improve the flexibility for resource allocation, we allow dynamic TDD, in which the time duration of each phase in each time-slot can be adjusted. For opportunistic network coding, we introduce a novel model for network coding aware RSs with which an opportunistic network coding problem can be reduced to an opportunistic subchannel scheduling problem. We formulate an optimization problem that aims at maximizing the average weighted-sum rate for both downlink and uplink sessions of all MSs, while satisfying the quality-of-service (QoS) requirements of each MS. By solving it, we develop a resource scheduling algorithm that optimally and opportunistically schedule subchannel, transmission power, network coding, and time duration of each phase in each time-slot. Through the numerical results, we study how each of network coding strategy and dynamic TDD affects the network performance with various network environments.

On the dimensioning of cellular OFDMA networks

In this paper, we address the issue of cellular OFDMA network dimensioning. Network design consists of evaluating cell coverage and capacity and may involve many parameters related to environment, system configuration, and quality of service (QoS) requirements. In order to quickly study the impact of each of these parameters, analytical formulas are needed. The key function for network dimensioning is the Signal to Interference Ratio (SIR) distribution. We thus analyze in an original way the traditional issue of deriving outage probabilities in OFDMA cellular networks. Our study takes into account the joint effect of path-loss, shadowing, and fast fading effects. Starting from the Mean Instantaneous Capacity (MIC), we derive the effective SIR distribution as a function of the number of sub-carriers per sub-channel. Our formula, based on a fluid model approach, is easily computable and can be obtained for a mobile station (MS) located at any distance from its serving base station (BS). We validate our approach by comparing all results to Monte Carlo simulations performed in a hexagonal network, and we show how our analytical study can be used to analyze outage capacity, coverage holes, and network densification. The proposed framework is a powerful tool to study performances of cellular OFDMA networks (e.g. WiMAX, LTE).

Effect of opportunistic scheduling on the quality of service perceived by the users in OFDMA cellular networks

Our objective is to analyze the impact of fading and opportunistic scheduling on the quality of service perceived by the users in an orthogonal frequency-division multiple access cellular network. To this end, assuming Markovian arrivals and departures of customers that transmit some given data volumes, as well as some temporal channel variability (fading), we study the mean throughput that the network offers to users in the long run of the system. Explicit formulas are obtained in the case of allocation policies, which may or may not take advantage of the fading, called respectively opportunistic and non-opportunistic. The main practical results of the present work are the following: Firstly, we evaluate for the non-opportunistic allocation the degradation due to fading compared to additive white Gaussian noise (AWGN; that is, a decrease of at least 13% of the throughput). Secondly, we evaluate the gain induced by the opportunistic allocation. In particular, when the traffic demand per cell exceeds some value (about 2 Mbits/s in our numerical example), the gain induced by opportunism compensates the degradation induced by fading compared to AWGN.

Optimal power control in OFDMA cellular networks

AbstractThis article addresses the problem of allocating users to radio resources in the downlink of an OFDMA cellular system. We consider a classical multicellular environment with a realistic interference model and a margin adaptive approach, i.e., we aim at minimizing total transmission power while maintaining a certain given rate for each user. We discuss computational complexity issues of the resulting model and present a heuristic approach that finds optima under suitable conditions or reasonably good solutions in the general case. Computational experiments show the effectiveness of the proposed heuristic in a comparison with both a commercial state‐of‐the‐art optimization solver and other approaches from the literature. © 2011 Wiley Periodicals, Inc. NETWORKS, 2011

Analytical Evaluation of Fractional Frequency Reuse for OFDMA Cellular Networks

Fractional frequency reuse (FFR) is an interference management technique well-suited to OFDMA-based cellular networks wherein the cells are partitioned into spatial regions with different frequency reuse factors. To date, FFR techniques have been typically been evaluated through system-level simulations using a hexagonal grid for the base station locations. This paper instead focuses on analytically evaluating the two main types of FFR deployments - Strict FFR and Soft Frequency Reuse (SFR) - using a Poisson point process to model the base station locations. The results are compared with the standard grid model and an actual urban deployment. Under reasonable special cases for modern cellular networks, our results reduce to simple closed-form expressions, which provide insight into system design guidelines and the relative merits of Strict FFR, SFR, universal reuse, and fixed frequency reuse. We observe that FFR provides an increase in the sum-rate as well as the well-known benefit of improved coverage for cell-edge users. Finally, a SINR-proportional resource allocation strategy is proposed based on the analytical expressions, showing that Strict FFR provides greater overall network throughput at low traffic loads, while SFR better balances the requirements of interference reduction and resource efficiency when the traffic load is high.

QoS-Aware Resource Allocation Algorithm for Cooperative Relay-based OFDM Cellular Networks

针对基于中继的OFDM蜂窝网络，该文考虑具有不同QoS要求的混合业务场景，引入合作传输机制，提出了一种基于合作中继的QoS感知资源调度算法，解决了合作中继节点选取，子载波分配以及功率控制等问题。以最大化系统效用为目标，在考虑QoS业务的速率要求与基站功率约束的同时，针对中继结构引入了中继节点的功率约束。为降低计算复杂度，将原非线性组合优化问题分解为子载波分配与功率控制两个子问题。仿真结果表明，该文所提算法在能量节约、系统效用，吞吐量等性能方面都有显著优势。

A Statistical Inter-Cell Interference Model for Downlink Cellular OFDMA Networks Under Log-Normal Shadowing with Ricean Fading

In this letter, an approximation to the performance of downlink cellular orthogonal frequency division multiple access networks under log-normal shadowing and Ricean fading is evaluated. The interference statistic is shown to significantly deviate from the Gaussian distribution as shown in previous results under Rayleigh fading.