On Orthogonal Frequency Division Multiple Access Research Articles

Femtocell power control methods based on users’ context information in two-tier heterogeneous networks

In this paper, we consider a two-tier macrocell/ femtocell overlaid heterogeneous network based on orthogonal frequency division multiple access (OFDMA) technology. Although the co-channel spectrum allocation provides larger bandwidth for both macrocell and femtocells, the resulting cross-tier interference may prevent macrocell users in the vicinity of femtocells to achieve their minimum required signal-to-interference plus noise ratio (SINR) in downlink. Therefore, we propose femtocell power control strategies for mitigating the interference experienced by macrocell users while preventing the femtocell throughput degradation. In particular, the proposed power control schemes make use of femto and macro users’ context information in terms of positioning for setting the appropriate prioritization weights among the current victim macro users and the femto users in outage. System-level simulations show that our schemes enhance the throughput of macrocell users while maintaining a high performance for femtocell users compared to a conventional power allocation. Moreover, we show that the proposed prioritization weights allow to achieve the required level of macrocell/femtocell throughput trade-off.

Primary users ON/OFF activities over MF-TDMA based Cognitive Radio networks

Spectrum underutilizations are attributed to the primary users (PUs) ON/OFF behavior, thus giving rise to spectrum holes. However, cognitive radio technology (CRT) has being a research paradigm to the identification and exploitation of TV white space (TVWS) across frequency and time. Moreover, several research focus on Orthogonal Frequency Division Multiple Access (OFDMA) as a perfect match for CRT and little or none on Multiple Frequency Time Division Multiple Access (MF-TDMA). This paper focuses on investigating the primary/incumbent users ON/OFF markov activities over MF-TDMA platform in various channel environments (rural, urban and open space) and show the amount of available resources ( OFF mini-slots) in these areas which are very useful for cognitive users (CUs). Simulation was carried out in various scenarios (environments) to see the availability of resources (IDLE/OFF mini-slots) which are of utmost importance to the secondary users. The transition from ON to OFF was adopted from a measured data from theCommunication Research Centre, Harbin Institute of Technology. The experiment shows the state probability matrix and the state transition matrix which depicts a typical ON/OFF behaviour of primary users in the three environments. The simulation of this behavior shows that there are more available resources found in the open space with , closely followed byremote/rural environment with and lastly, by urban areas with . Thus reason being that, urban areas are jam packed with users of all kind. Keywords: cognitive radio network (CRNs), wireless channel, MF-TDMA, Primary users, ON/OFF

QoS-aware composite scheduling using fuzzy proactive and reactive controllers

We consider in this paper downlink scheduling for different traffic classes at the MAC layer of wireless systems based on orthogonal frequency division multiple access (OFDMA), such as the recent 3rd Generation Partnership Project (3GPP) long-term evolution (LTE)/LTE-A wireless standard. Our goal is to provide via the scheduling decisions quality of service (QoS), but also to guarantee fairness among the different users and traffic classes (including delay-sensitive and best-effort traffic). QoS-aware scheduling strategies, such as modified largest weighted delay first (M-LWDF), exponential (EXP), exponential proportional fair (EXP-PF), and the log-based scheduling rules, prioritize delay-sensitive traffic by considering rules based on the head-of-line (HoL) packet delay and the tolerated packet loss rate, whereas they serve best-effort traffic by considering the classical proportional fair (PF) rule. These scheduling rules do not prevent resource starvation for best-effort traffic. On the other side, if both traffic types are scheduled according to the PF rule, then delay-sensitive flows suffer from delay bound violations. In order to fairly distribute the resources among different service classes according to their QoS requirements and channel conditions, we employ the concept of fuzzy logic in our scheduling framework. By employing the fuzzy logic concept, we serve all the traffic classes with one priority rule. Simulation results show better intra-class and inter-class fairness than state-of-the-art scheduling rules. The proposed scheduling framework enables to appropriately balance delay requirements of traffic, system throughput, and fairness.

Uplink-Downlink LTE Multi Cell Capacity: A Performance Analysis in the Presence of ICI, Imperfect Channel Information and Reuse-1 Plan

Long Term Evolution (LTE) technology is based on Orthogonal Frequency Division Multiple Access (OFDMA) technique in the downlink to support multiple users in the same cell at the same time. Such system is known to be susceptible to Inter Cell Interference (ICI) in the downlink. The uplink technology of choice, however, has been SC-FDMA due to low power consumption requirement by the mobile terminal. In order to deliver higher data rates anywhere in the cell in the downlink, especially at the cell edge; many algorithms have been proposed for interference mitigation and avoidance which impose additional complexity on the system and yields minimum capacity enhancements. MIMO techniques have proven to be more efficient than such algorithms. In this paper, a performance analysis of LTE cell capacity is conducted in the presence of several MIMO deployments, where multiple antennas at both the transmitter and the receiver are considered. A comprehensive simulation study of different multiple antenna configurations in the presence of uplink and downlink ICI and cell edge throughput is presented. We also provide insights into the MIMO deployment of choice based on users SINR.

Performance Enhancement of LTE through Interference Reduction Techniques

Long Term Evolution (LTE) is the standard for wireless communication of high speed data and mobile terminal. Among the current emerging technologies like LTE based on orthogonal frequency division multiple access (OFDMA) technique, it found to be more attractive for high speed wireless communication. However co-channel interference (CCI) from the neighbouring cells is one of the limiting factors that degrade the LTE system. Fractional frequency reuse (FFR) technique is proposed to overcome the same as it is suitable for idealized cellular layout since power is not considered in this scheme. In this paper FFR is generalized and sub band allocation among user is made in optimal manner which increases the performance of the system.

Maximum Likelihood Frequency Estimation and Preamble Identification in OFDMA-based WiMAX Systems

In multi-cellular WiMAX systems based on orthogonal frequency-division multiple-access (OFDMA), the training preamble is chosen from a set of known sequences so as to univocally identify the transmitting base station. Therefore, in addition to timing and frequency synchronization, preamble index identification is another fundamental task that a mobile terminal must successfully complete before establishing a communication link with the base station. In this work we investigate the joint maximum likelihood (ML) estimation of the carrier frequency offset (CFO) and preamble index in a multicarrier system compliant with the WiMAX specifications, and derive a novel expression of the relevant Cramer-Rao bound (CRB). Since the exact ML solution is prohibitively complex in its general formulation, suboptimal algorithms are developed which can provide a reasonable trade-off between estimation accuracy and processing load. Specifically, we show that the fractional CFO can be recovered by combining the ML estimator with an existing algorithm that attains the CRB in all practical scenarios. The integral CFO and preamble index are subsequently retrieved by a suitable approximation of their joint ML estimator. Compared to existing alternatives, the resulting scheme exhibits improved accuracy and reduced sensitivity to residual timing errors. The price for these advantages is a certain increase of the system complexity.

4G LTE and LTE-Advanced using Simulation

In this paper, the performance of Long term evolution (LTE) based on orthogonal frequency-division multiple access (OFDMA) is investigated which uses multiple input, multiple output technique (MIMO). This paper gives an peak to power average ratio (PAPR) analysis of MIMO performance along with OFDMA modulation using Matlab of the next generation telecommunication network LTE 3 rd Generation partnership project (3GPP). The downlink is based on orthogonal frequency-division multiple access at the physical layer, while the uplink is based on single carrier frequency-division multiple access. The PAPR reduction to achieve a low clipping rate which is actually done in SC-FDMA, as clipping is low the efficiency is also low which provide great benefit in power consumption. Thus LTE can transmit a packet efficiently with low latency and as well as without transmission error. This paper gives the comparison of LTE release 8 and LTE release 10.It provides communication with a terminal, moving up to 500 km/h.

A Nucleolus-Based Approach for Resource Allocation in OFDMA Wireless Mesh Networks

Wireless mesh networks (WMNs) are emerging as a key solution to provide broadband and mobile wireless connectivity in a flexible and cost-effective way. In suburban areas, a common deployment model relies on orthogonal frequency division multiple access (OFDMA) communications between mesh routers (MRs), with one MR installed at each user premises. In this paper, we investigate a possible user cooperation path to implement strategic resource allocation in OFDMA WMNs, under the assumption that users want to control their interconnections. In this case, a novel strategic situation appears: How much an MR can demand, how much it can obtain, and how this shall depend on the interference with its neighbors. Strategic interference management and resource allocation mechanisms are needed to avoid performance degradation during congestion cases between MRs. In this paper, we model the problem as a bankruptcy game taking into account the interference between MRs. We identify possible solutions from cooperative game theory, namely the Shapley value and the nucleolus, and show through extensive simulations of realistic scenarios that they outperform two state-of-the-art OFDMA allocation schemes, namely, centralized-dynamic frequency planning, and frequency-ALOHA. In particular, the nucleolus solution offers best performance overall in terms of throughput and fairness, at a lower time complexity.

Efficient resource allocation for emerging OFDMA wireless networks

In the context of IEEE 802.16e networks, physical transmission relies on Orthogonal Frequency Division Multiple Access (OFDMA). This mechanism defines resource allocation as a bi-dimensional mapping of spectral resources. Although in the IEEE 802.16e standard the Medium Access Control (MAC) and physical (PHY) layers are well defined, the problem of resource allocation still remains an open issue, encouraging competition between companies to develop new commercial products. As this component is crucial to guaranteeing maximum performance and Quality of Service (QoS) fulfillment, it is critical to define efficient algorithms to solve the problem. Usually, the allocation problem is divided into two sub-problems: the scheduler problem, which decides the amount of resources that must be granted to each connection or user, and the mapping problem, which defines how the granted resources are allocated in the bi-dimensional matrix of spectral resources. Several factors have to be taken into account by the mapping algorithms, such as efficiency, QoS, power consumption and algorithmic complexity. In this work we define an adaptive algorithm to solve the OFDMA mapping problem in IEEE 802.16e networks. The performance of our proposal is extensively evaluated against other state-of-the-art proposals, by means of a simulation tool.

Resource Allocation for OFDMA Cognitive Radios Under Channel Uncertainty

A resource allocation problem for a cognitive radio base station (CR-BS) communicating with multiple CR mobile stations (MSs) is considered in the downlink, which relies on orthogonal frequency-division multiple access (OFDMA). To protect the incumbent primary user (PU) system operating over the same frequency band, the interference inflicted to the PU receiver must be regulated. Since the channel gain estimates from the CR-BS to the PU receiver are typically uncertain in practice, a robust interference power constraint is advocated. Although the latter translates to a second-order cone constraint, the overall optimization problem for joint transmit-power and subcarrier allocation is non-convex, and coupled over all subcarriers in general. To circumvent the resulting computational hurdle, a tight polyhedral approximation of the second-order cone is employed. Practical finite-alphabet constellations are adopted and total weighted achievable rate is maximized. It is shown that a near-optimal solution can be obtained based on the Lagrangian dual.

Multiuser Resource Allocation Optimization Using Bandwidth-Power Product in Cognitive Radio Networks

In this paper, the problem of resource allocation optimization is studied for a single-cell multiuser cognitive radio network in the presence of primary user networks. The spectral access of the cognitive radio network is based on Orthogonal Frequency Division Multiple Access (OFDMA). A joint bandwidth and power allocation is performed so that users' rate requirements are satisfied, and the integrity of primary user communication is preserved. In this work, two unique challenges are addressed. The first is the incorporation of primary user activity in the design of resource allocation technique, and the second is the limited hardware capabilities of cognitive terminals compared to those available at the cognitive base station. To address these problems, a novel resource allocation framework is proposed based on the bandwidth-power product minimization, which is an effective metric in evaluating the spectral resource consumption in a cognitive radio environment. The framework takes into consideration the challenges aforementioned. The results show significant enhancement in spectral efficiency by using our framework compared to classical power adaptive optimization using iterative waterfilling scheme.

A Bidirectional Successive Detection Technique for Asynchronous OFDMA-Based Wireless Mesh Networks

In this correspondence, a minimum-mean-square-error bidirectional successive detection (MMSE-BSD) technique is proposed to mitigate the effects of interferences caused by time difference of arrivals (TDoAs) in wireless mesh networks (WMNs) based on orthogonal frequency-division multiple access (OFDMA). The proposed BSD technique can successfully reduce the error propagation phenomenon in successive detection with low computational complexity by exploiting the subframe structure used in WMNs. It is shown by simulation that the proposed MMSE-BSD technique is robust to multipath channels and can be effectively used in asynchronous OFDMA-based WMNs.

Impact of Downlink Distributed and Adjacent Subcarrier Permutation Modes on the Performance of Mobile WiMAX System in ITU-R Ped. B Channel with Obtaining Optimum Cyclic Prefix

Mobile WiMAX is one of the candidate technologies for 4G wireless systems, promising high data rates and affluent multimedia services. The mobile WiMAX standard (IEEE802.16e-2005)is based on Orthogonal Frequency Division Multiple Access (OFDMA), which allows a very efficient use of bandwidth in a wide frequency range, this is due to the fact that OFDMA uses multi-channel OFDM approach and provides subcarrier access in the time and the frequency domains. In this paper the impact of downlink distributed (FUSC, PUSC) and adjacent (AMC) subcarrier permutation modes used in mobile WiMAX system are investigated using simulation under various modulation and coding schemes (link speeds)with the support of optimum value of the Cyclic Prefix (CP) for the OFDMA symbol duration. The results are expressed in terms of the maximum achievable throughput and operating distance from base station in pedestrian multipath fading channel (ITU-R Ped. B at 3Km/h speed) under a UDP-based application (video streaming), which is the proper application for multimedia services. The results show the optimum cyclic prefix valve for the FUSC, PUSC and AMC subcarrier permutation modes to achieve the best system performance, also the results show differences in PER performance atvarious modulation and coding schemes for the three subcarrier permutation modes (FUSC, PUSC and AMC). These differences in performance are exploited in the present work to show the best threshold SNR to switch from link speed to another link speed in terms of throughput and operating distance. Key words: IEEE802.16e-2005, OFDMA, FUSC, PUSC, AMC, ITU-R Ped. B channel, PER.

SGSA: A SDMA–OFDMA greedy scheduling algorithm for WiMAX networks

Future wireless networks need to address the predicted growth in mobile traffic volume, expected to have an explosive growth in the next 5years mainly driven by video and web applications. Transmission schemes based on Orthogonal Frequency Division Multiple Access (OFDMA) combined with Space Division Multiple Access (SDMA) techniques are key promising technologies to increase current spectral efficiencies. A Joint SDMA–OFDMA system has to allocate resources in time, frequency and space dimensions to different mobile stations, resulting in a highly complex resource allocation problem. In contrast to related work approaches, in this paper we take a comprehensive view at the complete SDMA–OFDMA scheduling challenge and propose a SDMA–OFDMA Greedy Scheduling Algorithm (sGSA) for WiMAX systems. The proposed solution considers feasibility constraints in order to allocate resources for multiple mobile stations on a per packet basis by using (i) a low complexity SINR prediction algorithm, (ii) a cluster-based SDMA grouping algorithm and (iii) a computationally efficient frame layout scheme which allocates multiple SDMA groups per frame according to their packet QoS utility. A performance evaluation of the proposed sGSA solution as compared to state of the art solutions is provided, based on a comprehensive WiMAX simulation tool.

Generalizing and optimizing fractional frequency reuse in broadband cellular radio access networks

For broadband cellular access based on orthogonal frequency division multiple access (OFDMA), fractional frequency reuse (FFR) is one of the key concepts for mitigating inter-cell interference and optimizing cell-edge performance. In standard FFR, the number of OFDMA sub-bands and the reuse factor are fixed. Whereas this works well for an idealized cell pattern, it is neither directly applicable nor adequate for real-life networks with irregular cell layouts. In this article, we consider a generalized FFR (GFFR) scheme to allow for flexibility in the total number of sub-bands as well as the number of sub-bands in each cell-edge zone, to enable network-adaptive FFR. In addition, the GFFR scheme takes power assignment in consideration. We formalize the complexity of the optimization problem, and develop an optimization algorithm based on local search to maximize the cell-edge throughput. Numerical results using networks with realistic radio propagation conditions demonstrate the applicability of the GFFR scheme in performance engineering of OFDMA networks.

Energy-efficient dynamic resource allocation with opportunistic network coding in OFDMA relay networks

Network coding is significantly able to save system resources for wireless networks, and has been widely studied for the 802.11 wireless local area network and traditional cellular networks. The relay technology was introduced in 802.16j, 802.16m, and Long Term Evolution-Advanced (LTE-A) standards. Recently, the application of network coding to multi-hop wireless relay networks has been taken into consideration. Although the introduction of relay stations (RSs) may bring more energy consumption, it provides opportunities for network coding to save spectrum resources. Nevertheless, the benefits of network coding are diminished by high multiuser diversity based on orthogonal frequency division multiple access (OFDMA). For ensuring the superiority, network coding is performed opportunistically according to the channel state. Hence dynamic resource allocation (DRA) subject to rate constraints is combined with the idea of opportunistic network coding to minimize the total transmission power in a frame. A fixed set of discrete modulation levels in an OFDMA relay system is also considered. By taking the characteristic of a half-duplex decode-and-forward (DF) mode relay, a solution is proposed for the optimal problem of each subframe after separating power-aware relay selection. Simulation results show that DRA with opportunistic network coding can improve system energy efficiency. Further, it is more efficient for saving energy than DRA with static network coding compared solely to DRA.

Virtual access network embedding in wireless mesh networks

Network virtualization of a wireless mesh network (WMN) is an economical way for different subscribers to customize their exclusive access networks through a common network infrastructure. The most critical task of network virtualization is virtual network embedding, which can be divided into two sub-problems: node mapping and link mapping. Although there exist approaches to virtual network embedding in wired networks, the characteristics of WMNs make virtual network embedding become a unique and challenging problem. In this paper, virtual access network embedding is studied for WMNs. To support flexible resource allocation in virtual access network embedding, each access node is designed based on orthogonal frequency division multiple access (OFDMA) dual-radio architecture. Through subcarrier allocation on each link, virtual access networks are gracefully separated from each other. To coordinate channel assignment across different links under the constraint of a limited number of orthogonal channels, a novel channel allocation algorithm is proposed to exploit partially-overlapped channels to improve resource utilization. Since the virtual access network embedding problem is NP-hard, a heuristic algorithm is developed based on an enhanced genetic algorithm to obtain an approximate but effective solution. Simulation results illustrate that the virtual access network embedding framework developed in this paper works effectively in WMNs.

OFDM for Next-Generation Optical Access Networks

In this tutorial overview, the principles, advantages, challenges, and practical requirements of optical orthogonal frequency division multiplexing (OFDM)-based optical access are presented, with an emphasis on orthogonal frequency division multiple access (OFDMA) for application in next-generation passive optical networks (PON). General OFDM principles, including orthogonality, cyclic prefix use, frequency-domain equalization, and multiuser OFDMA are summarized, followed by an overview of various optical OFDM(A) transceiver architectures for next-generation PON. Functional requirements are outlined for high-speed digital signal processors (DSP) and data converters in OFDMA-PON. A techno-economic outlook for such a “software-defined,” DSP-based optical access platform is also provided.

A Gain-Computation Enhancements Resource Allocation for Heterogeneous Service Flows in IEEE 802.16 m Mobile Networks

This paper deals with radio resource allocation in fourth generation (4G) wireless mobile networks based on Orthogonal Frequency Division Multiple Access (OFDMA) as an access method. In IEEE 802.16 m standard, a contiguous method for subchannel construction is adopted in order to reduce OFDMA system complexity. In this context, we propose a new subchannel gain computation method depending on frequency responses dispersion. This method has a crucial role in the resource management and optimization. In a single service access, we propose a dynamic resource allocation algorithm at the physical layer aiming to maximize the cell data rate while ensuring fairness among users. In heterogeneous data traffics, we study scheduling in order to provide delay guaranties to real-time services, maximize throughput of non-real-time services while ensuring fairness to users. We compare performances to recent existing algorithms in OFDMA systems showing that proposed schemes provide lower complexity, higher total system capacity, and fairness among users.

지연 허용적인 수중 센서 네트워크에서 노드 그룹핑을 이용한 매체 접속 제어 프로토콜

본 논문에서는 수중환경에서의 거리에 따른 전파 손실 특성을 이용한 직교 주파수 분할 다중 접속 방식(Orthogonal Frequency Division Multiple Access, OFDMA) 기반의 새로운 에너지 효율적인 매체 접속 제어(Medium Access Control, MAC) 프로토콜을 제안한다. 제안하는 방식은 센서 노드들을 싱크 노드를 중심으로 싱크 노드와의 거리에 따라 그룹을 나눈 후, 그룹에 서로 다른 주파수 대역을 각각 할당하여 사용하도록 한다. 이러한 방식으로 네트워크 전체의 전송 전력 소모를 줄이고 각 센서 노드에게 최소 허용 신호 대 잡음비 (Accepted Minimum SNR, AMS)를 보장한다. 추가적으로 싱크 노드는 동적 인 부채널 할당 (dynamic sub-channel allocation)으로 데이터 전송률을 향상한다. 모의실험을 통해 제안하는 매체 접속 제어 프로토콜의 수중 센서 네트워크에서의 성능을 확인할 수 있었다. In this paper, we propose a novel energy efficient MAC protocol which is based on orthogonal frequency division multiple access (OFDMA) and exploits the physical characteristic that propagation loss of acoustic wave depends on the distance. In the proposed scheme, sensor nodes are grouped according to the distance to sink node. Then, each group uses a different frequency band. The proposed scheme not only enables all sensor nodes to maintain the signal-to-noise ratio above a certain required level (Accepted Minimum SNR, AMS), but also reduces overall transmission power consumption. In addition, the dynamic sub-channel allocation is employed in order to improve data transmission rate. Simulations show that proposed MAC protocol has better performance in a delay-tolerant underwater acoustic sensor networks.