Orthogonal Frequency Division Multiplexing Access Systems Research Articles

Performance analysis of wireless transmission of compressed images using DCT‐OFDMA system with different compression schemes

AbstractTransmitting images over an Orthogonal Frequency Division Multiplexing Access (OFDMA) system poses a significant challenge. The process entails sending a substantial amount of data, which consumes a significant amount of bandwidth. Consequently, compressing the transmitted image becomes essential to reduce the required bandwidth. The aim of this paper is to examine and analyse the wireless transmission of a compressed image via Discrete Cosine Transform (DCT‐OFDMA). A comparison is made with Discrete Fourier Transform (DFT‐OFDMA), across various subcarrier mapping schemes (localized and inter‐leaved), and different modulation schemes (16 Quadrature Amplitude Modulation (16QAM) and Quadrature Phase Shift Keying (QPSK)) using vehicular A, Stanford University Interim (SUI3), and uniform channel models. To evaluate the performance of the system, the minimum Signal‐to‐Noise Ratio (SNR) necessary to recover the transmitted compressed image is calculated. This work considers nine standard compression techniques. The results are carried out using the MATLAB simulator. According to the simulation results, the minimum SNR required to recover the transmitted compressed image was found to be 19 dB. This result was achieved when using Discrete Cosine Transform‐Loaclized‐Orthogonal Frequency Division Multiplexing Access (DCT‐LOFDMA) with QPSK modulation and set partitioning in hierarchical trees (SPIHT) compression method over the SUI3 channel model. Moreover, it was observed that the DCT‐LOFDMA and DFT‐IOFDMA systems attained equal SNR while utilizing the SPIHT_3D compression technique and QPSK modulation on the SUI3 channel model. Overall, the results suggest that the performance of DCT‐based localized OFDMA is somewhat superior to DFT‐based localized OFDMA, particularly when utilizing the SUI3 channel model and the QPSK modulation scheme. Therefore, it is feasible to transmit and receive a compressed image effectively over an OFDMA system with DCT.

Adaptive Downlink OFDMA System With Low-Overhead and Limited Feedback in Time-Varying Underwater Acoustic Channel

Because of the time-varying characteristic and the large propagation delay in underwater acoustic (UWA) channel, adaptive resource allocation in UWA orthogonal frequency-division multiplexing access (OFDMA) system cannot be performed with the assumption of perfect channel state information (CSI) at the transmitter. Therefore, this paper focuses on the outdated CSI and proposes an adaptive downlink OFDMA system with low-overhead and limited feedback in time-varying UWA channel. First, a data fitting method is proposed for channel reconstruction, which shows better performance and lower overhead than the traditional group quantization method in simulations. Second, we define the per-subcarrier channel temporal correlation (PSCTC) and long-term statistical mean value as two indicators of outdated CSI, for optimizing CSI feedback in UWA channel with large propagation delay. Finally, a CSI selection method based on channel correlation attenuation (CCA) factor is proposed, where CSI used for feedback is selected between outdated-instantaneous CSI and outdated-average CSI according to the CCA factor in the current observation period. Sea trail results show that the CSI reconstruction based on data fitting method has lower bit error ratio and less overhead than traditional group quantization method. The PSCTC coefficient is related to the feedback delay, and the long-term statistics is stationary, which means that the outdated-average CSI is suitable for channel feedback. The CSI selection method based on CCA factor has better performance than that only uses outdated-instantaneous CSI or outdated-average CSI under different time-varying channel conditions in experimental results.

Energy efficiency and spectral efficiency tradeoff in downlink OFDMA systems with imperfect CSI

In this paper, we investigate the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in downlink orthogonal frequency division multiplexing access (OFDMA) systems, whilst considering the channel estimation cost and the corresponding effect of imperfect channel state information (CSI) on SE and EE. The problem is formulated as a multi-objective optimization to determine the optimal pilot transmission power, data transmission power and subcarrier assignment, and then transformed into a single-objective optimization problem, which is a non-convex mixed-integer nonlinear programming (NCMINP) and NP-hard. To address it, we propose an efficient algorithm by adopting alternating optimization and convex optimization methods in lower power region as well as approximate conversion and branch-and-bound methods in high power region. Simulation results analyze and validate the performance of EE-SE tradeoff.

Investigation of Enhanced Particle Swarm Optimization Algorithm for the OFDMA Interference Management in Heterogeneous Network

In orthogonal frequency division multiplexing Access (OFDMA) systems resource allocation to the subcarrier is essential owing to the insufficient resources available at the base station. In OFDMA, subcarrier and power allocation are not separate; thereby this two allocation are not self-governing. This paper proposes the subcarrier allocation approach through investigating previous methods, and also the Enhanced Particle Swarm Optimization (PSO) algorithm is analyzed. The both of the algorithms cross functionality is analyzed and compared the performance of the subcarrier allocation of OFDMA systems in Heterogeneous Network (HetNet). The simulation results show that the PSO approach efficiently allocates the OFDMA subcarriers.

Modified Cooperative Subchannel Allocation Algorithms and PSO Based Power Allocation for an Alamouti Decode and Forward Relaying Protocol in Multiuser OFDMA Systems

The present work is a discussion on the performance analysis of Modified Cooperative Subchannel Allocation (CSA) Algorithms which is used in Alamouti Decoded and Forward (Alamouti DF) Relaying Protocol for wireless multi-user Orthogonal Frequency Division Multiplexing Access (OFDMA) systems. In addition, the performance of approximate Symbol Error Rate (SER) for the Alamouti DF Relaying Protocol with the Cooperative Maximum Ratio Combining Technique (C-MRC) is analyzed and compared with SER upper bound. The approximate SER is asymptotically tight bound at higher Signal-to-Noise Ratio (SNR). From the asymptotic tight bound approximate SER, Particle Swarm Optimization (PSO) based Power Allocation (PA) is determined for the Alamouti DF Relaying Protocol. The simulation results suggested that the Modified Throughput based Subchannel Allocation Algorithm achieved an improved throughput of 6% to 33% compared to that of existing cooperative diversity protocol. Further, the Modified Fairness based Subchannel Allocation Algorithm rendered fairness of 7.2% to 17% among the multiuser against the existing cooperative diversity protocol.

Resource Allocation for H-FDD OFDMA Systems

Half-frequency-division duplexing (H-FDD) has recently attracted attention since it can serve as a cost-effective solution for machine-to-machine (M2M) communication networks. This letter proposes a method to jointly optimize resource allocation, mobile station grouping, and frame partitioning for H-FDD orthogonal frequency-division multiplexing access systems. We develop a near-optimal and low-complexity algorithm that is also applicable to frequency-division duplexing and time-division duplexing as special cases. Simulation results demonstrate that our algorithm with reduced computation can provide performance close to that of the optimal but time-consuming exhaustive search.

Protocol Design and Capacity Analysis in Hybrid Network of Visible Light Communication and OFDMA Systems

Visible light communication (VLC) uses a vast unregulated and free light spectrum. It is considered to be a solution for overcoming the crowded radio spectrum for wireless communication systems. However, duplex communication, user mobility, and handover mechanisms are becoming challenging tasks in a VLC system. This paper proposes a hybrid network model of VLC and orthogonal frequency-division multiplexing access (OFDMA) in which the VLC channel is only used for downlink transmission, whereas OFDMA channels are served for uplinks in any situation or for downlinks only without VLC hotspots coverage. A novel protocol is proposed combined with access, horizontal, and vertical handover mechanisms for mobile terminal (MT) to resolve user mobility among different hotspots and OFDMA system. A new VLC network scheme and its frame format are presented to deal with the multiuser access problems in every hotspot. In addition, a new metric ρ is defined to evaluate the capacity of this hybrid network as the spatial density of interarrival time of MT requests in s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> under the assumption of the homogenous Poisson point process (HPPP) distribution of MTs. Analytical and simulation results show improvements in capacity performance of the hybrid, when compared to OFDMA system.

Physical Layer Security in OFDM-PON Based on Dimension-Transformed Chaotic Permutation

A physical layer security enhanced orthogonal frequency division multiplexing (OFDM) passive optical network based on dimension-transformed chaotic permutation is proposed and experimentally demonstrated. In this scheme, a large key space is obtained by multidomain jointed Rossler permutation, and the corresponding complexity scale caused by multidomain encryption can be reduced through dimension-transformed permutation. An experiment with 10.61-Gb/s encrypted optical OFDM access system is performed to demonstrate the proposed method.

다중빔 형성기법을 가진 MIMO-OFDMA시스템 성능

이 논문에서는 주파수 효율을 높이기 위하여 부분적으로 동일 부반송파를 할당한 MIMO(Multi-Input Multi-Out)-OFDMA(Orthogonal Frequency Division Multiplexing Access) 시스템에서 동일 부반송파 간섭과 다중 경로 신호를 제거하기 위한 다중 적응 빔 형성기법을 제안한다. 제안된 기법에 의해 간섭제거 이외에 다중 안테나로 부터 도착된 각 DOA마다 빔 패턴이 형성되어 다이바시티 이득을 얻을 수 있고 지연 시간에 따른 성능열화를 방지 할 수 있다. MIMO-OFDMA 시스템에 제안된 다중 적용 빔 형성기를 적용할 경우 성능 및 제시된 개선 효과를 모의 실험을 통하여 확인한다. In this paper, we propose the adaptive multibeamforming algorithm to remove the same subcarrier interference and multipath signals in the MIMO(Multi-Input Multi-Out)-OFDMA (Orthogonal Frequency Division Multiplexing Access)system allocated the same subcarrier partially in order to improve spectrum efficiency. In addition to removing the interference, we can get diversity gain and combat the detriment of the performance according to time delay by the proposed approach. BER performance improvement and combating the delay spread detrimental effects of the proposed approach is investigated through computer simulation by applying it to MIMO-OFDMA.

Joint subcarrier and power allocation in uplink OFDMA systems based on stochastic game

In uplink orthogonal frequency division multiplexing access (OFDMA) systems, efficient resource allocation can greatly improve system performance. Therefore, in this paper, we present a game-theoretical approach to achieve a joint subcarrier and power allocation in a distributed way. Particularly, the subcarrier allocation problem is modeled as a multi-player discrete, stochastic and finite strategy game, where each of the subcarriers is viewed as a player to choose the most satisfying user. The subcarriers of each user are allocated with equal power. For the proposed game model, on the one hand, we exploit the support and programming methods to obtain the Nash equilibriums, and analyze their theoretical properties. On the other hand, we propose a lowcomplexity algorithm based on the linear reward-inaction (LR-I) algorithm to search for the Nash equilibriums. And the relationship between the convergence results of this algorithm and the Nash equilibriums is discussed. Extensive simulation results demonstrate the effectiveness of the resource allocation game model and algorithm.

Multi-cell uplink power allocation game for user minimum performance guarantee in OFDMA systems

The multi-cell uplink power allocation problem for orthogonal frequency division multiplexing access (OFDMA) cellular networks is investigated with the uplink transmission power allocation on each co-frequency subchannel being defined as a multi-cell non-cooperative power allocation game (MNPG). The principle of the design of the utility function is given and a novel utility function is proposed for MNPG. By using this utility function, the minimum signal to interference plus noise ratio (SINR) requirement of a user can be guaranteed. It can be shown that MNPG will converge to the Nash equilibrium and that this Nash equilibrium is unique. In considering the simulation results, the effect of the algorithm parameters on the system performance is discussed, and the convergence of the MNPG is verified. The performance of MNPG is compared with that of traditional power allocation schemes, the simulation results showing that the proposed algorithm increases the cell-edge user throughput greatly with only a small decrease in cell total throughput; this gives a good tradeoff between the throughput of cell-edge users and the system spectrum efficiency.

Robust OFDMA Uplink Synchronization by Exploiting the Variance of Carrier Frequency Offsets

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, the uplink frequency offset estimation for orthogonal frequency-division multiplexing access (OFDMA) is discussed. We consider a general subcarrier allocation scheme where each user subcarrier group need not be contiguous. For an OFDMA uplink, we model the frequency offset for each user as an independent and identically distributed (i.i.d.) random variable with mean zero and variance <formula formulatype="inline"><tex>$\sigma_{ \epsilon}^{2}$</tex></formula>. An analysis of multiple access interference (MAI) is performed, and the Cramer–Rao lower bound (CRLB) for the estimation of variance of each user is derived. The signal-to-interference-plus-noise ratio (SINR) is derived as a function of the variance of the frequency offset. The variance of the frequency offset estimation error is lower bounded as a function of the signal-to-noise ratio (SNR). Successive interference cancellation (SIC) and iterative frequency offset estimation are considered. An estimate of the variance of the frequency offset is derived as a function of SINR and SNR. An estimate of the range of frequency offsets is derived using the assumption of uniformly distributed frequency offsets. Based on this estimate of the range of frequency offsets, the accuracy of any existing algorithm can be improved. Thus, new versions of the SIC-based frequency offset estimation and differential estimation algorithms are derived. Extensive simulation results are provided for a 16-user, 256-subcarrier OFDMA system over a multipath fading channel. </para>

Performance Analysis of the Extended Low Complexity User Scheduling Algorithm over Up-Link Multi-User MIMO OFDMA Systems

The low complexity tree-structure based user scheduling algorithm is extended into up-link MLD-based multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing access (OFDMA) wireless systems. The system sum capacity is maximized by careful user selection on a defined tree structure. The calculation load is reduced by selecting the M most possible best branches and sampling in frequency dimension. The performances of the proposed scheduling algorithm are analyzed within three kinds of OFDMA systems and compared with conventional throughput-based algorithm. Both the theoretical analysis and simulation results show that the proposed algorithm obtains better performance with much low complexity.

Performance analysis of dynamic OFDMA systems with inband signaling

Within the last decade, the orthogonal frequency- division multiplexing (OFDM) transmission scheme has become part of several standards for wireless systems. Today, OFDM is even a candidate for fourth-generation wireless systems. It is well known that dynamic OFDMA systems potentially increase the spectral efficiency. They exploit diversity effects in time, space, and frequency by assigning system resources periodically to terminals. Informing the terminals about new assignments creates a signaling overhead. Up to now, this overhead has not been taken into account in studies on dynamic orthogonal frequency-division multiplexing access (OFDMA) systems. Yet this is crucial for a realistic notion of the performance achieved by dynamic approaches. In this paper, we close this gap. We introduce two forms of representing the signaling information and discuss how these affect system performance. The study of the signaling impact on the performance is conducted for an exemplary dynamic approach. We find that the throughput behavior of dynamic OFDMA systems is significantly influenced by the signaling overhead. In many situations, neglecting the overhead leads to wrong performance conclusions. Also, the performance difference between dynamic and static schemes is now much more sensible to the specific parameter set of the transmission scenario (e.g., frame length, subcarrier number, etc.). This leads to the proposal of access points which should adapt certain system parameters in order to provide optimal performance.