OFDMA Research Papers - Academia.edu (original) (raw)

An efficient variable length FFT processor is required for the downlink module of Orthogonal Frequency Division Multiple Access (OFDMA) system. This system is used in the mobility mode of the IEEE 802.16 Wireless MAN standard, commonly referred as WiMAX .In OFDMA system the carrier space is constant across different channel bandwidths.FFT is required to keep the carrier spacing constant across different channel bandwidths. In this paper the variable input FFT processor is designed to meet the requirements of OFDMA system. This design considers different FFT lengths. For this we use the 2D Fourier Transform algorithm, VHDL language to present the design in detail, ModelSim for the simulation and verify on the Spartan 3E FPGA.

- by
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- FPGA, Vhdl, OFDMA

Multicasting is emerging as an enabling technology for multimedia transmissions over wireless networks to support several groups of users with flexible quality of service (QoS) requirements. Although multicast has huge potential to push the limits of next generation communication systems; it is however one of the most challenging issues currently being addressed. In this survey, we explain multicast group formation and various forms of group rate determination approaches. We also provide a systematic review of recent channel-aware multicast scheduling and resource allocation (MSRA) techniques proposed for downlink multicast services in OFDMA based systems. We study these enabling algorithms, evaluate their core characteristics, limitations and classify them using multidimensional matrix. We cohesively review the algorithms in terms of their throughput maximization, fairness considerations, performance complexities, multi-antenna support, optimality and simplifying assumptions. We discuss existing standards employing multicasting and further highlight some potential research opportunities in multicast systems.

- by Aresh Dadlani
- •
- Optimization (Mathematics), Resource Allocation, Survey Research, OFDMA

It is fascinating to know that the multiplexing can be employed and defined
from different points of views and different disciplines. For example, Dr. E. Julius
Dasch, former manager of the NASA National Space Grant Program, defines multiplexing on his dictionary book [1] as:
…the simultaneous transmission of different data from a spacecraft using a single
channel. The data stream is separated into frames that carry codes for different
information, such as temperatures, pressures, and the state of on-board computers.
In a media and communication dictionary book [2], multiplexing is mentioned as:
Digital television transmission allows for multiplexing, whereby multiple channels
are bundled together and sent simultaneously in a single stream of data.
In a computer science dictionary book [3], multiplexing is described as:
…the process of combining multiple messages simultaneously on the same physical or
logical transmission medium. There are two main types: time division multiplexing
(TDM) and frequency division multiplexing (FDM).
The list continues for the Internet, optic engineering, graphics, phytography,
laser and photonics geology, earth sciences, and many more.

Due to the spectacular growth of the wireless services and demands in recent years, Orthogonal Frequency Division Multiplexing (OFDM) is a latest and suiTable modulation scheme for commercial high-speed broadband wireless communication systems. OFDM is one of the main techniques proposed to be employed in 4th Generation Wireless Systems. One of the OFDM key parameters is a cyclic Prefix (CP). Cyclic prefix is a guard time length padded with every OFDM symbol to completely alleviate Inter-symbol Interference (ISI) and to preserve orthogonality among OFDM subcarriers as long as the guard time length is sufficiently greater than channel delay spread. This paper analyzes OFDM system and the effect of cyclic prefix and length of cyclic prefix on OFDM system. Besides, compare the performance of the system with and without cyclic prefix. The simulations were carried out over AWGN and Rayleigh fading channels, and the results have been compared with the theoretical ones.

- by Ghassan Qasmarrogy
- •
- IEEE 802.16 (WiMAX), OFDMA

Wireless Networking has become an important area of research in industry and academics in recent years. The main objectives of this paper are to gain knowledge about the WiMAX technology, its security and application. WiMAX (Worldwide Interoperability for Microwave Access) technology is based upon the IEEE 802.16 standard (IEEE Wireless MAN Air Interface) which enables wireless broadband services anytime, anywhere. The WiMAX specification provides symmetrical bandwidth over large area and range with stronger encryption and typically less interference. WiMAX based system can be used to transmission of signal over maximum 50 km. WiMAX outdistances WiFi by miles. WiMAX can deliver high data rate to multiple users. The WiMAX Forum describes WiMAX as " a standards-based technology enabling the delivery of last-mile wireless broadband access as an alternative to cable and DSL ". The main goal/purpose of this technology is to deliver wireless communications with quality of service in a secured environment. This standard was developed to deliver line-of-sight (LoS) and non-line-of-sight (NLoS) wireless services between subscriber and base station and to address " last mile " problem.

- by Leonardo Iheme
- •
- Wireless Communications, Channel Coding, Information Theory and coding, OFDMA
- by yaser barayan
- •
- Wireless Communications, Scheduling, Long Term Evolution (LTE), LTE
- by Global Technocrats and Intellectual Association and +1
- •
- Wireless Communications, LTE, OFDMA, MIMO

3GPP LTE has utilized the OFDMA for the downlink which oversees assortment versatility, inborn impenetrability to Inter picture Interference (ISI) and several more unmistakable. At any rate, 3GPP LTE structures delight in the unwell impacts of a really standard trouble called height to normal power share. The general paper attempted to discuss the section and secluding fundamentally basically based approaches for unmarried individual OFDMA structures. We have attempted our generations for L=1-4 oversampling cost and 256 FFT system and 128 sporadic substances bits to diminish the PAPR with the guide of dismissing at the correlative blend scattering work. It's far found inside the reproduction that top to regular power share diminishes to the tune of 8db from the unique unmodified machine.

- by Ijariit Journal
- •
- Wireless Communications, OFDM, OFDMA, Clipping

The Intercell Interference (ICI) problem is one of the main challenges in Long Term Evolution (LTE) downlink system. In order to deal with the ICI problem, this paper proposes a joint resource block and transmit power allocation scheme in LTE downlink networks. The proposed scheme is implemented in three phases: (1) the priority of users is calculated based on interference level, Quality of Service (QoS) and Head of Line (HoL) delay;(2) users in each cell are scheduled on the specified subbands based on their priority; and (3) eNodeBs dynamically control the transmit power using a fuzzy logic system and exchanging messages to each other. Simulation results demonstrate that the proposed priority scheme outperforms the existing Reuse Factor one (RF1) and Soft Frequency Reuse (SFR) schemes in terms of cell throughput, cell edge user throughput, delay and interference level.

- by Mansi Chalwadi
- •
- Computer Science, Information Security, Wireless Communications, Security
- by Editor IJRET
- •
- Wireless Communications, Long Term Evolution (LTE), OFDMA
- by Abolfazl Ghassemi
- •
- MIMO-OFDM systems, OFDMA, OFDM in FPGA

In this work I provide the intent of long term evolution advanced technology is set forth high level of speed in data application its requirements and contend with different technique. Different Technique like relaying carrier aggregation .for multiple input and same for multiple output and heterogeneous network provide higher throughputs , low latency and let LTE become a best standard for wireless broadband .Due to almost exponetional increases in demand for high rate of data it is expected that network will consist the occupied by more data resource it is required for better performance of LTE system suitability exhibition schedule is adopting to 4G system to achieve Orthogonal Frequency Division Multiple Access (OFDMA) potentiality in time domain system (TDS) and Frequency Domain scheduling systems (FDS) this paper scoring at totalize the implementation of suitability fair algorithm by create future assessment of Channel Quality Indicator to exhibit high data rate in all proposed algorithm on the downlink is measured in terms of throughput and block error rate using a math lab based system level simulator.

- by Ijariit Journal
- •
- Wireless Communications, LTE, OFDMA, Lte-A
- by Karim Banawan
- •
- MIMO Systems, LTE, OFDMA, SC-FDMA
- by IOSR Journals
- •
- Wireless Communications, OFDMA, Cr, CP

— Traditional wireless and mobile network focuses on higher throughout, coverage and larger capacity. In future, energy efficiency is of vital importance for wireless networks due to a large number of connected and battery constrained mobile devices. In Long Term Evolution Advanced (LTE-Advanced), Carrier Aggregation (CA) is proposed to increase the transmission bandwidth and hence data rate. This paper studies the effect of CA on the total power transmitted by the LTE-Advanced eNodeB based on the Orthogonal Frequency Division Multiple Access (OFDMA) downlink while taking the users Quality of Service (QoS) constraints into consideration. The numerical analysis and results show that by using CA a reduction in total power consumption can be achieved. Keywords— Energy-efficient mobile network; LTE-A; OFDMA downlink; Carrier Aggregation ; QoS.

- by Basel Barakat
- •
- Energy efficiency, OFDMA, LTE-Advanced and beyond, Quality of Service (QoS)

In this paper, we propose an analytical model for dimensioning of Orthogonal Frequency Division Multiple Access (OFDMA) systems in 5G networks by considering Internet of Thing (IoT) application using stochastic geometry. In these systems, some communication is lost when the number of required subcarriers is greater than the number of the available subcarriers. We compute the upper bound of the lost communication probability for downlink. In such a system, the position of the receiving users is modeled by the Poisson point process (PPP). The number of subcarriers dedicated to each user depends on its Signal to Noise Ratio (SNR), position and the shadowing, hence for calculating the number of subcarriers, it is needed to use stochastic geometry. Since the focus of our work is on IoT application in 5G networks, a multi-group user system with each group of users having its own application and throughput requirement is considered. For having dimensioning in terms of subcarriers, we present concentration inequality for functions defined on PPP to calculate the upper bound of loss probability. The performance of the upper bound in different range of user intensity is investigated.

- by IJICTR Journal
- •
- OFDMA, Dimensioning, Stochastic Geometry
- by Mario Marques da Silva
- •
- Computer Science, Wireless Communications, MIMO-OFDM systems, MIMO Systems

In this paper, we propose a baseband, correlation based blind estimation method for the identification of LTE and WiMAX signals in the uplink communication scheme. LTE and WiMax standards are centerd around orthogonality using the FFT and IFFT techniques. The time parameter estimation based algorithms sequentially estimate the symbol duration and the cyclic prefix whereby useful timeslots can be calculated through these estimates. The proposed technique works over LTE and WiMax standard with a limited sample of data without any prior information like SNR level and symbol rate. The Matlab simulations display fast and accurate performance for both AWGN channel and Rayleigh fading channel. The proposed algorithm can also be used for identifying various radio access systems and hence a single terminal can be used for the reception of multiple air interfaces.

Wireless broadband networks are designed to provide high quality services to multiple mobile users using OFDMA schema for frame structure. This schema defines rectangular resource allocation schema of time slots and frequency carriers. This structure is used for arranging incoming user requests. Our goal was to increase bandwidth utilization while arranging the incoming user requests into an effective way. For this reason Bin-Packing algorithms were considered and evaluated. Therefore, we have analyzed using software engineering methodologies; designed while presenting the algorithm’s workflows; implemented with Java programming language; and tested through NetBeans IDE; a working version of a program while incorporating five algorithms of Bin-Packing family.

- by Adelina Basholli
- •
- Wireless Communications, OFDMA, Bin Packing Problem

Long Term Evolution (LTE-Advanced) is a preliminary mobile communication standard formally submitted as a candidate for 4G systems to the ITU-T. LTE-A is being standardized by the 3rd Generation Partnership Project (3GPP) as a major enhancement of the 3GPP Long Term Evolution (LTE-Release 8) standard, which proved to be sufficient to satisfy market‟s demand. The 3GPP group has been working on different aspects to improve LTE performance, where the purpose of the framework provided by LTE-Advanced, includes higher order MIMO, carrier aggregation (carriers with multiple components), peak data rate, and mobility. This paper presents a study on LTE evolution toward LTE-Advanced in terms of LTE enabling technologies (Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO)), and also focuses on LTEAdvanced technologies MIMO enhancements for LTE-Advanced, Coordinated Multi Point transmission (CoMP).

- by SDIWC Organization
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- Computer Science, Information Technology, MIMO Systems, LTE

This paper presents a Generalized Power Allocation (GPA) scheme for different users in Non-Orthogonal Multiple Access (NOMA) based wireless communication system. The power allocation to the users becomes complex with the increased number of users. There are some conventional schemes for power allocation in NOMA but they have to optimize some parameters arbitrarily. In this paper, a simple but effective power allocation scheme has been formulated and tested by simulations. The proposed GPA scheme does not need any parameter adjustment. Theoretical power distribution to different users of NOMA has been calculated using the proposed GPA technique. The calculated powers of individual users with the proposed scheme are different and more distributed than the arbitrary power allocation scheme which satisfies the basic condition of NOMA. The total of calculated powers with GPA scheme shows only 01% variation with the arbitrary power allocation scheme which shows the consistency of GPA scheme with other schemes. The performance of NOMA based wireless communication system with GPA scheme has been simulated under various conditions using Matlab. The simulated BER performance for NOMA based wireless communication system using different modulation techniques show similar results with other conventional schemes which validates the formulation of GPA scheme.

Channel-dependent scheduling of transmission of data packets in a wireless system is based on measurement and feedback of the channel quality. To alleviate the performance degradation due to simultaneous multiple imperfect channel quality information (CQI), a simple and efficient packet scheduling (PS) algorithm is developed in downlink LTE system for real time traffic. A frequency domain channel predictor based on Kalman filter is first developed to restore the true CQI from erroneous channel quality feedback. Then, a time domain grouping technique employing the joint of Proportional Fair (PF) and Modified Largest Weighted Delay First (M-LWDF) algorithms is used. It was proved this proposal achieves better performance in terms of system throughput and packet loss ratio by simulation results.

- by Mohammed Mossaad
- •
- MIMO Systems, LTE, OFDMA, SC-FDMA

Growth in technology has led to unprecedented demand for high speed architectures for complex signal processing applications. In 4G wireless communication systems, bandwidth is a precious commodity, and service providers are continuously met with the challenge of accommodating more users with in a limited allocated bandwidth. To increase data rate of wireless medium with higher performance, OFDM (orthogonal frequency division multiplexing) is used. Recently DWT (Discrete wavelet transforms) is adopted in place of FFT (Fast Fourier transform) for frequency translation. Modulation schemes such as 16-QAM, 32-QAM, 64-QAM and 128-QAM (Quadrature amplitude modulation) have been used in the developed OFDM system for both DWT and FFT based model. In this paper we propose a DWT-IDWT based OFDM transmitter and receiver that achieve better performance in terms SNR and BER for AWGN channel. It proves all the wavelet families better over the IFFT-FFT implementation. The OFDM model is developed using Simulink, various test cases have been considered to verify its performance. The DWT-OFDM using Lifting Scheme architecture is implemented on FPGA optimizing hardware, speed & cost. The wavelet filter used for this is Daubechies (9, 7) with N=2. The RTL code is written in Verilog-HDL and simulated in Modelsim. The design is then synthesized in Xilinx and implemented on Virtex5 FPGA board and the results were validated using ChipScope.

Performance optimization of the communication networks with quality of service (QoS) considerations for all active users is of great practical importance in highly delay-sensitive applications like multipoint videoconferences and interactive video games. Using minimum data rate as the primary criterion for the QoS and the BER as a second one, in this paper, we provide the optimum discrete bit loading for an OFDMA downlink in which the QoS of all users are satisfied. We formulate the problem and solve the dual problem efficiently and without any suboptimality. Albeit the problem is non-convex, it has been shown that the duality gap tends zero in practical scenarios. We propose a novel approach to solve the dual problem by decomposing dual function and finding discrete rate allocation solution for practical applications. Also, we present a novel fast converging iterative algorithm to find the solution with much less complexity compared to that of well-known ellipsoid optimization algorithm. We analyze the complexity of these solutions, and using simulation results, show the superiority of our novel approach.

- by Mahmood Mohassel Feghhi
- •
- OFDMA, Power allocation, Quality of Service (QoS)

This paper deals with the transmission of group-oriented services, considered as the main value-added for the future 4G broadband wireless systems. In this scenario, the design of proper resource allocation strategies is a key issue in order to offer high quality services to involved users and to efficiently exploit the available radio resources. In this paper we extend the works existing in literature by evaluating the impact of frequency selectivity on the performance in terms of spectral efficiency achieved when group-oriented services are provided in Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems. We conducted exhaustive simulation campaigns in order to define the scenarios that could benefit of the exploitation of frequency selectivity in multicast resource allocation. We investigated single- and multi-group scenarios with different application profiles, such as real time video flows, and we considered several deployment cases addressing different channel bandwidth and user configurations.

Multiplexing of the Orthogonal Frequency Division (OFDM) is now the preferred wireless contact modulation technique. OFDM is able to have ample robustness to radio channel impairments with high data levels. Several testing facilities across the globe have expert teams employed to refine OFDM for numerous uses. Throughout the time domain, the transmit signals in an OFDM network may have large peak value s because several subcarrier components are inserted in an IFFT process. OFDM systems, therefore, are considered to have a strong PAPR (Peak-to-Average Capacity Ratio) relative to single-carrier systems. In reality, the high PAPR is one of the most negative aspects of the OFDM system as it increases the Analog-to-Digital Converter and Digital-to-Analog Converter Signal-to-Quantization Noise Ratio while deteriorating the transmitter's power amplifier performance g. The PAPR issue becomes more relevant in uplink as power amplifier output becomes crucial because of the small battery y capacity in a mobile terminal. This research paper explores many methods used in an OFDM method to reduce PAPR. Multiplexing is a specific type of multi-carrier modulation that is especially suited for transmission over a dispersive wave.

- by IJRASET Publication
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- Posttraumatic Stress Disorder (PTSD), OFDMA, DFT calculation, ISI journal

In this paper, a channel estimator using neural network is presented for Long Term Evolution (LTE) uplink. This paper considers multiuser SC-FDMA uplink transmissions with doubly selective channels. This channel estimation method uses knowledge of pilot channel properties to estimate the unknown channel response at non-pilot sub-carriers. First, the neural network estimator learns to adapt to the channel variations then it estimates the channel frequency response. Simulation results show that the proposed method has better performance, in terms of complexity and quality, compared to the conventional methods least square (LS), MMSE and decision feedback and it is more robust at high speed mobility.

T
w
o major challenges for evolving
LTE
(Long Term Evolution)
networks
are to
achieve enhanced
system capacity
and cell coverage
compared with WCDMA (Wideband Code Division Multiple Access)
system
.
Effectiv
e utilization of radio
resources as well as dense spectrum reuse are
at the core
to attain
these targets.
However, dense frequency
reuse may increase inter
-
cell interference, which in turn
severely limits the capacity of
users
in the system
. Inter
-
cell interference can
re
strict
overall system
performance in terms of throughput and spe
ctral efficiency, especially for the users located at the cell
edge area.
Hence,
careful management of inter
-
cell
interference
s becomes crucial
to improve LTE
system performance.
In this paper,
interference
mitigation
schemes
for LTE downlink networks are
investigated.

- by shanmukha swamy
- •
- Henri Bergson, Bertrand Russell, OFDM, OFDMA

The main techniques applied to provide quality of service guarantees in metropolitan area networks are OFDMA and MCS. OFDMA organizes the information within a bidimensional frame considering the time and frequency domains while MCS defines the level of robustness of a transmission. The loca-lization of the data within the frame are defined in map messages transmitted in each frame. Thus, the main contribution this paper is to present a deep analysis of the overhead generated by these map messages. This analysis presents the behavior of the network in several scenarios that consider variations in the amount of data transmitted and in the quantity of mobile stations. Furthermore, we consider the variability of the wireless channel. Resumo. As principais técnicas utilizadas para prover garantias de qualidade de serviço em redes sem fio metropolitanas são OFDMA e MCS. A técnica OFDMA organiza as informações nos domínios tempo e frequência, formando um quadro bidimensional, enquanto a técnica MCS define o nível de robustez da transmissão. Nesse contexto, para os dados serem dispostos no quadro, deve-se utilizar informações de mapas que indicam a localização destes dados. Assim, a principal contribuição deste artigó e apresentar uma profunda análise relativa ao overhead causado pelos mapas no quadro OFDMA. Essa análise apresenta o comportamento da rede em diversos cenários, variando a quantidade de da-dos transmitidos e a quantidade de estações móveis, bem como considerando a diversidade do meio sem fio.

- by Lisandro Z Granville and +1
- •
- OFDMA, Overhead Lines

This paper presents a comparative performance analysis of wireless orthogonal frequency division multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE) method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are employed. The OFDM system simulation has been carried out with Matlab and the performance is analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and 64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on the BER performance is also investigated.

A new work has been proposed in this paper in order to overcome one of the main drawbacks that found in the Orthogonal Frequency Division Multiplex (OFDM) systems, namely Peak to Average Power Ratio (PAPR). Furthermore, this work will be compared with a previously published work that uses the neural network (NN) as a solution to remedy this deficiency. The proposed work could be considered as a special averaging technique (SAT), which consists of wavelet transformation in its first stage, a globally statistical adaptive detecting algorithm as a second stage; and in the third stage it replaces the affected peaks by making use of moving average filter process. In the NN work, the learning process makes use of a previously published work that is based on three linear coding techniques. In order to check the proposed work validity, a MATLAB simulation has been run and has two main variables to compare with; namely BER and CCDF curves. This is true under the same bandwidth occupancy and channel characteristics. Two types of tested data have been used; randomly generated data and a practical data that have been extracted from a funded project entitled by ECEM. From the achieved simulation results, the work that is based on SAT shows promising results in reducing the PAPR effect reached up to 80% over the work in the literature and our previously published work. This means that this work gives an extra reduction up to 15% of our previously published work. However, this achievement will be under the cost of complexity. This penalty could be optimized by imposing the NN to the SAT work in order to enhance the wireless systems performance.

Multi Carrier Code Division Multiple Access (MC-CDMA) isa well known techniquefor highs peed wireless data transmission .Two advanced technologywas included in the MC-CDMA structure, such as orthogonal frequency division multiplex(OFDM) and the code division multiple access (CDMA),so that it benefits from the robustness of OFDM against multipath environment and from the capability of multiusermultiplexingservices that is achieved via (CDMA) system. MC-CDMA is a multicarrier spread spectrum system which is classified as the candidate scheme for future mobile radio systems.In this paperMC-CDMA system, with Rayleigh fading channel and 16QAM array modulation, was simulatedto investigate the effects of different parameters on the system performance, such as processing gain; number of paths; number of users;interleaving;and coding ratio.MC-CDMA performances can be considerably improved by proper selection of these parameters. As expected, results shows that MC-CDMA has a better performance overCDMA system.

Wireless broadband networks are designed to provide high quality services to multiple mobile users simultaneously. The IEEE 802.16e Mobile WiMAX standard uses Orthogonally Frequency Division Multiple Access (OFDMA) schema for frame structure. OFDMA defines rectangular resource allocation of time slots and frequency carriers, separating in this way the channel into multiple subcarriers. This structure is used for arranging the incoming user requests. Aimed to increase the bandwidth utilization, while arranging the incoming user requests into an effective way, we have considered and evaluated Bin-Packing algorithms. Subsequently in the following sections are presented analysis and design of various Bin packing algorithms developed in our simulator. Moreover, a combined algorithm is proposed, named Guillotine First Fit Algorithm and a new version of the Shelf First Fit Algorithm. Simulation’s results concerning performance of implemented algorithms in different input values are gathered, analyzed and compared. The results are encouraging and provide indications regarding usage of the proposed algorithms in practice.

- by Thomas Lagkas
- •
- Radio Resource Management, IEEE 802.16 (WiMAX), OFDMA, Bin Packing Problem
- by eshaan verma
- •
- Wireless Communications, OFDM, OFDMA, Clipping

Long Term Evolution (LTE) is the emerging 4G wireless technology developed to provide high quality services in mobile environments. It is foreseen that multimedia services and mobile TV will assume an important role for the LTE proliferation in mobile market. However, several issues are still open and meaningful improvements have to be introduced for managing physical resources when group-oriented services should be supplied. To this end, we propose a Frequency Domain Packet Scheduling (FDPS) algorithm for efficient radio resource management of Multimedia Broadcast/Multicast Services (MBMS) in LTE networks. The proposed scheduler exploits an optimization process to organize multicast subscribers in subgroups according to channel quality feedbacks provided by users. Optimization is driven by the aim of minimizing the ”user dissatisfaction” with a consequent improvement in the network capacity. The effectiveness of the proposed scheduling algorithm is evaluated through simulation; obtained results demonstrate significant improvement in the multicast traffic performance.

Next generation cellular networks require high capacity, enhanced efficiency of energy and guaranteed quality of service (QoS). To reach these goals, device-to device (D2D) communication is a candidate technologie for future 5th Generation especially applications that require the reuse, the hop and the proximity gain. The present paper studies the energy efficient power control for the uplink of an OFDMA (orthogonal frequency-division multiple access) system composed of both regular cellular users and device-to-device (D2D) pairs. First, we analyze and model mathematically the prerequisites for D2D communications and classical cellular links in terms of minimum rate and maximum power requirement. Second, we use fractional programming in order to convert the initial problem into a concave one and we apply non-cooperative game theory in order to characterize the equilibrium. Then, we got the solution of the problem from the results of a water-filling power allocation. Moreover, we employ a distributed design for power allocation by means of three methods: a) Theory of fractional programming b) Closed form expression (the novelty is the use of Wright Omega function). c) Inverse water filling. Finally, simulations in both static and dynamic channel setting are realized to demontrate the enhanced gain in term of EE, SE (spectral efficiency) and time of execution of the iterative algorithm (Dinkelbach) than the closed form algorithms.

This paper demonstrates the use of some novel cognitive techniques we propose to improve the throughput of a mobile WIMAX network and minimize the packet losses. We propose a novel method called Orthogonal Frequency Division Most Congested Access First (OFDMCAF), to modify the spectrum sharing technique of (Time Division Multiple Access) TDMA and (Orthogonal Frequency Division Multiple Access) OFDMA and to manage the spectrum access. The heavy multimedia traffic is managed by OFDMCAF with novel spectrum sharing and buffer management methods we propose. By use of novel cognitive methods, real time voice and video packet transmissions have been provided with full success and the packet loss rate of data packets has been minimized. The simulation results are confirmed by comparing them with results of other publications and comparing with results of packet loss calculations we made. The results are usable in designing unicast mobile multimedia network with improved system throughput.

The emerging demand for diverse data applications in next generation wireless networks entails both high data rate wireless connections and intelligent multiuser scheduling designs. Orthogonal frequency division multiple access is capable of delivering high speed connections in a multipath environment by dividing an entire channel into many orthogonal narrow band subcarriers and thus eliminating inter symbol interferences, which limits the available data rates. In this paper, we have investigated about resource allocation problem for the downlink of Orthogonal Frequency Division Multiple Access (OFDMA) wireless multicast systems. It is assumed that the Base Station (BS) consists of multiple antennas in a Distributed Antenna System (DAS) or Collected Antenna System (CAS), whereas each user is equipped with a single antenna., The allocation unit is a set of contiguous subcarriers (chunk) in conventional OFDMA systems. The aim of this investigation is to propose an efficient algorithm to maximize the total throughput with respect to total available power and average Bit Error Rate (BER) over a chunk.

- by IJAERS Journal
- •
- Resource Allocation, OFDMA
- by IJERA Journal
- •
- FPGA, Vhdl, OFDMA, DCT

Filter bank multicarrier (FBMC) is considered a competitive waveform candidate for 5G that can replace orthogonal frequency division multiplexing (OFDM). However, channel estimation (CE) is a big challenge in FBMC because it suffers from intrinsic interference which is due to the orthogonality of the subcarrier functions in the real field only. In this paper, we investigate a proposed modified interference approximation scheme (M-IAM) by approximating the intrinsic interference from the neighbouring pilots to accommodate the complex channel frequency and thus improving CE performance besides simplifying its processing. The M-IAM scheme has a larger pseudo pilot magnitude than other conventional preamble schemes, namely the interference approximation method (IAM) with its versions (IAM-C) and (E-IAM-C); in addition to the novel preamble design (NPS). In addition, the proposed (M-IAM) scheme is characterized by the lower transmitted power needed. The CE performance of the M-IAM is investigated through 512 and 2048 subcarriers via different types of outdoor and indoor multipath fading channels that are time-invariant such as IEEE 802.22, IEEE 802.11, Rician, and additive white Gaussian noise (AWGN), as well as time-varying channels such as Rayleigh and Vehicular A (Veh-A). Simulation results demonstrate that the proposed M-IAM scheme achieves a lower bit error rate (BER), lower normalized mean square error (NMSE) and lower peak-to-average power ratio (PAPR) over the conventional preamble schemes under the aforementioned channel models. The proposed scheme has the advantage of saving the transmitted power, a requirement that could match 5G low power requirements. KEYWORDS Filter bank multicarrier (FBMC), intrinsic interference, preamble based channel estimation methods

In this paper, we propose to evaluate the performance of channel estimation techniques for Long Term Evolution (LTE) Downlink systems based on Zero Padding technique (ZP) instead of Cyclic Prefixing (CP). LTE Downlink system is a multiuser system based on a MIMO-OFDMA technology. Usually, in OFDM systems, a guard interval is inserted in order to mitigate both inter-carrier interference (ICI) and inter-symbol interference (ISI). LTE Downlink systems are based on CP-OFDM technique which consists of a copy a last OFDM symbols inserted at the beginning of each transmitted OFDM symbol. Although this technique shows good performances, the CP-LTE system suffers from a power efficiency loss. With the number of present OFDM symbols in LTE Downlink radio frame, the bandwidth loss becomes more important. Instead of CP, we propose to evaluate the performance of ZP-LTE systems in order to avoid the power efficiency .In this paper, we interest to evaluate the performance of channel estimation techniques for the two LTE Downlink systems. Simulations results show that although ZP-LTE systems outperform CP-LTE Downlink systems in terms of power efficiency, the CP-LTE systems show better performance than ZP-LTE systems and especially for high SNR values. MATLAB Monte–Carlo simulations are used to evaluate the performance of LS, LMMSE and Lr-LMMSE estimators in terms of Mean Square Error (MSE) and Bit Error Rate (BER) for 2x2 LTE Downlink systems.

OFDM (Orthogonal Frequency Division Multiplexing) has been raised a new modulation technique. Due to its advantages in multipath fading channel e.g. robust against ISI, ICI and some other advantages like best QoS for multiple users, efficient usage of bandwidth it is suggested to be the modulation technique for next generation 4G networks e.g. LTE. But along with all its advantages there are some disadvantages also e.g. High PAPR (Peak to Average Power Ratio) at the transmitter end and BER (Bit Error Rate) at the receiving end. Since OFDM is only used in the downlink of 4G networks. To reduce the problems of OFDM some techniques e.g. SLM, PTS, Clipping, Coding, & Pre-coding etc are suggested but none of them is reduce the PAPR and BER to an acceptable value. This Paper will discuss some techniques of PAPR & BER reduction, and their advantages and disadvantages in detail.

Direct-conversion architectures can offer highly integrated low-cost hardware solutions to communication transceivers. However, it has been demonstrated that radio frequency (RF) impairments, such as amplifier nonlinearities, phase noise and in-phase/quadrature-phase imbalances (IQI), can lead to a severe degradation in the performance and fairness. To this end, we study the power allocation (PA) problem in an orthogonal frequency-division multiple access (ODFMA) system, when the served user equipments (UEs) suffer from different levels of IQI. Additionally, we present a novel low-complexity solution with directly calculated PA policies, given the Lagrange multiplier, which mitigates the impact of IQI and achieves fairness in terms of capacity for the served UEs, by maximizing the minimum achievable capacity of the UEs. The effectiveness of the offered solution is validated through simulation results, which reveal that it can drastically increase the minimum achievable UEs' capacity.

- by Abolfazl Ghassemi
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- MIMO-OFDM systems, OFDMA, OFDM in FPGA