Orthogonal Frequency Division Multiplexing Access Research Articles

Dynamic Source quick Route Rebuilding Algorithm for Random-access OFDMA Adhoc Network

paper focusses on maintaining message continuity in a mobile Adhoc network. The dynamic source quick route rebuilding algorithm (DSQRRA) provides continuity in packet routing to reach the next possible neighboring node in order to avoid resending the packet from the source. DSQRRA calls for mobility management and scalable design. Mobility management is done through information exchanges between moving hosts in the Adhoc wireless network. The DSQRRA uses cooperative protocols to coordinate with the Adhoc on demand Distance Vector routine (AODV) protocol for shortest route rebuilding in Random Access OFDMA network. The algorithm gives next alternative route immediately once there is a break in the link. Simulations have been performed to analyze the performance of AODV with and without DSQRRA. The AODV with DSQRRA reduced memory occupation and route broadcasting. It has minimized packet looping. Simulations also show that DSQRRA provides quick delivery of packet from source to destination. Keywordsratio, OFDMA, RDF, SNR

A CFO Matrix Method for Interleaved Uplink OFDMA Systems

Abstract In this paper, a CFO matrix method is presented for carrier frequency offset (CFO) estimation in interleaved uplink orthogonal frequency division multiplexing access (OFDMA) system. The proposed method utilizes the information of eigenvalues and eigenvectors of the defined CFO matrix to estimate the CFOs of all involved users. Compared with the previous works, the main advantages of the proposed approach are that it can obtain the CFOs of all users simultaneously within only one OFDMA block without pilot symbols, provides better performance such as smaller estimation error and superior noise-resistant capability. Simulation results verify the high accuracy and effectiveness of the proposed method.

ML Detection with Successive Group Interference Cancellation for Interleaved OFDMA Uplink

To mitigate the interference caused by multiple carrier frequency offsets (CFO) of distributed users, a maximum likelihood (ML) detection with group-wise successive interference cancellation (GSIC) is proposed for interleaved Orthogonal Frequency Division Multiplexing Access (OFDMA) uplink. By exploiting the interference characteristics and the finite alphabet property of transmitted symbols, the proposed scheme first extracts the block diagonal of the frequency domain channel matrix and then employs ML detection via sphere decoding in each block. The decisions obtained from the detected blocks are used to mitigate the interference to the residual blocks. Numerical results show that the proposed scheme outperforms both the minimum mean square error (MMSE) detection and parallel interference cancellation (PIC) with affordable computational complexity.

Low Complexity Pilot Assisted Carrier Frequency Offset Estimation for OFDMA Uplink Systems

In this letter, we propose a low complexity pilot aided carrier frequency offset (CFO) estimation algorithm for orthogonal frequency division multiplexing access (OFDMA) uplink systems based on two consecutive received OFDMA symbols. Assuming that the channels and the CFOs are static over the two consecutive symbols, we express the second received OFDMA symbol in terms of the CFOs and the first OFDMA symbol. Based on this signal model, a new estimation algorithm which obtains the CFOs by minimizing the mean square distance between the received OFDMA symbol and its regenerated signal is provided. Also, we implement the proposed algorithm via fast Fourier transform (FFT) operations by utilizing the block matrix inversion lemma and the conjugate gradient method. Simulation results show that the proposed algorithm approaches the average Cramer Rao bound for moderate and high signal to noise ratio (SNR) regions. Moreover, the algorithm can be applied for any carrier assignment schemes with low complexity.

A Low-Complexity Resource Allocation Algorithm for MIMO-OFDMA Multicast Systems with Spectrum-Guarantee Provisioning

We study the important problem of resource allocation for the downlink of Multiple-Input Multiple output (MIMO) Multicast Wireless Systems operating over frequency-selective channels and we propose a low-complexity but efficient resource allocation algorithm for MIMO-enabled OFDMA systems. The proposed solution guarantees a minimum spectrum share for each user while also takes advantage of the multicast transmission mode. The presence of multiple antennas in both transmitter and receiver offers spatial diversity to the system along with the frequency diversity added by the OFDMA access scheme. The computational complexity is reduced from exponential to linear and validation of the proposed solution is achieved through various simulation scenarios in comparison with other multicast and unicast reference schemes used in MIMO-OFDMA systems. Numerical results and complexity analysis demonstrate the feasibility of the proposed algorithm.

SOCP Approach for Reducing PAPR System SCFDMA in Uplink via Tone Reservation

The 3rd generation partnership project (3GPP) long term evolution (LTE) standard uses single carrier frequency division multiple access (SC-FDMA) scheme for the uplink transmissions and orthogonal frequency division multiplexing access (OFDMA) in downlink. In this paper, we point on the Peak-to-Average Power Ratio (PAPR) reduction for the uplink SC-FDMA system. Firstly, the conventional Tone Reservation (TR) is investigated. Then, the approach SOCP (Second Order Cone Programming) is applied for the complex baseband signals of SC-FDMA system with different subcarrier mapping. For the method TR, these subcarriers are located on unused subcarriers of SC-FDMA and we use a raised-cosine pulse. Besides, we prove that the IFDMA can be reduced the PAPR more than the localized FDMA (LFDMA) and distributed FDMA (DFDMA). Finally, this method does not degrade the bit-error-rate (BER) and the data bit rate and no side information (SI) transmission is obligatory.

Graph-based interference coordination scheme in orthogonal frequency-division multiplexing access femtocell networks

Femtocell technology has gained widespread attention recently due to its advantages, such as infrastructure cost reduction, improved service coverage and high data throughput in indoor environments. As femtocell networks are customer-deployed without proper network planning, their interference environment tends to be much more complicated than traditional cellular networks. The authors present the framework of channel allocation in orthogonal frequency-division multiplexing access (OFDMA) femtocell network with the graphical approaches. A novel graph-based interference coordination scheme is proposed to maximise the system throughput while ensuring proportional rate fairness among femtocells. The scheme explicitly uses the received signal-to-interference-plus-noise-ratio to generate the interference graph of OFDMA femtocell networks, so as to guarantee the acceptable inter-cell interference for all the links. First, all the femtocells are partitioned into different groups by applying a greedy graph colouring algorithm to maximise the sum throughput of each group. The femtocells in the same group share the assigned subchannels while those in different groups are allocated to orthogonal subchannels. Then, an optimisation problem is formulated to determine the number of subchannels assigned to each group. Further, an approximation method is proposed to solve the optimisation problem. Simulation results are conducted to demonstrate the effectiveness of the proposed scheme in terms of throughput and fairness index.

Resource Allocation in Hybrid Access OFDMA Femtocell Networks

Femtocell(飞小区)能够有效加强室内覆盖和系统容量。混合接入(hybrid access)方式可以兼顾授权用户和非授权用户的业务体验。针对下行混合接入方式下的正交频分复用接入(OFDMA) Femtocell网络，该文提出带权重的比例公平(WPF)调度算法，为不同类型的用户提供不同的调度权重。该文提出两种算法确定用户的调度权重，一种是自适应权重的比例公平算法，实时调整调度权重；另一种是静态权重的比例公平算法，基于WPF调度的渐近性分析得到静态最优调度权重。仿真结果表明该文提出的两种算法均能在授权用户和非授权用户间合理分配资源，保证不同用户的速率需求。

Raised Cosine-Like Companding Scheme for Peak-to-Average Power Ratio Reduction of SCFDMA Signals

The 3rd generation partnership project long term evolution standard uses orthogonal frequency division multiplexing access in downlink and single carrier frequency division multiple access (SCFDMA) scheme for the uplink transmissions, which utilizes single carrier modulation and frequency domain equalization. In this paper, we proposed a Raised Cosine-like companding scheme to reduce the peak-to-average power ratio (PAPR) of SCFDMA signals. The proposed scheme can transform the original SCFDMA signals into Raised Cosine-like-distributed. Moreover, this scheme can compress the large signals, while maintaining the average power constant. Computer simulation results show that the proposed companding scheme can offer better PAPR reduction by properly choosing the parameters.

Design and Comparison of FFT VLSI Architectures for SoC Telecom Applications with Different Flexibility, Speed and Complexity Trade-Offs

The design of Fast Fourier Transform (FFT) integrated architectures for System-on-Chip (SoC) telecom applications is addressed in this paper. After reviewing the FFT processing requirements of wireless and wired Orthogonal Frequency Division Multiplexing (OFDM) standards, including the emerging Multiple Input Multiple Output (MIMO) and OFDM Access (OFDMA) schemes, three FFT architectures are proposed: a fully parallel, a pipelined cascade and an in-place variable-size architecture, which offer different trade-offs among flexibility, processing speed and complexity. Silicon implementation results and comparisons with the state-of-the-art prove that each macrocell outperforms the known works for a target application. The fully parallel is optimized for throughput requirements up to several GSamples/s enabling Ultra-wideband (UWB) communications by using all channels foreseen in the standard. The pipelined cascade macrocell minimizes complexity for large size FFTs sustaining throughput up to 100 MSamples/s. The in-place variable-size FFT macrocell stands for its flexibility by allowing run-time reconfigurability required in OFDMA schemes while attaining the required throughput to support MIMO communications. The three architectures are also compared with common case-studies and target technology.

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.

Laser phase noise and OFDM symbol duration effects on the performance of direct-detection based optical OFDM access network

In this paper, we present numerical and experimental demonstration about the impacts of the laser phase noise in direct-detection based optical orthogonal frequency division multiplexing system for access-network transmission. We analyzed the system performance in the presence of the laser phase noise for various orthogonal frequency division multiplexing symbol durations. A significant phase-noise-effect difference between the access-network and long-haul transmission was verified in terms of the orthogonal frequency division multiplexing symbol duration.

Artificial Bee Colony and Tabu Search Enhanced TTCM Assisted MMSE Multi-User Detectors for Rank Deficient SDMA-OFDM System

In this paper, we propose two novel and computationally efficient metaheuristic algorithms based on Artificial Bee Colony (ABC) and Tabu Search (TS) principles for Multi User Detection (MUD) in Turbo Trellis Coded Modulation based Space Division Multiple Access Orthogonal Frequency Division Multiplexing system. Unlike gradient descent methods, both ABC and TS methods ensure minimization of the objective function without the solution being trapped into local optima. These techniques are capable of achieving excellent performance in the so called overloaded system, where the number of transmit antennas is higher than the number of receiver antennas, in which the known classic MUDs fail. The performance of the proposed algorithms are compared with each other and also against Genetic Algorithm (GA) and K-Best sperical decoding algorithm based MUD. Simulation results establish better performance, computational efficiency and convergence characteristics for ABC and TS methods. It is seen that the proposed detectors achieve similar performance to that of well known optimum Maximum Likelihood Detector (MLD) at a significantly lower computational complexity and outperforms the traditional MMSE MUD.

A Cross-Layer Resource Allocation Algorithm with Dynamic Buffer Allocation Mechanism

A novel cross-layer wireless resource allocation algorithm called DBMQT is proposed which distributes the resource based on dynamic buffer allocation mechanism for orthogonal frequency division multiplex access (OFDMA) system. The aim of allocation algorithm is to maximize system throughput while satisfying the QoS requirement for multi-user and multi-service. The algorithm consists of two steps. Firstly, with the assumption of a finite queue model for arrival packets, the scheme adjusts users’ buffer according to dynamic buffer allocation mechanism. In the second step, a distinct scheduling priority is defined for each user integrates MAC QoS requirements, queue status and PHY Channel State Information (CSI), assuming that the power is uniformly allocated on each subcarrier. Using these scheduling priorities, a scheduling rule for mixed traffics is proposed. Simulation results indicate that the proposed algorithm can achieve better performance in terms of system throughput, packet loss rate and efficiency of the buffer than tradition algorithm under enhancing QoS guarantees for different services.

Linear suppression of intercarrier interference in time-varying OFDM systems: From the viewpoint of multiuser detection

Intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems, which causes substantial performance degradation in time-varying fading channels, is analyzed. An equivalent spreading code formulation is derived based on the analogy of OFDM and code division multiple access (CDMA) systems. Techniques as linear multiuser detection in CDMA systems are applied to suppress the ICI in OFDM systems. The performance of linear detection, measured using multiuser efficiency and asymptotic multiuser efficiency, is analyzed given the assumption of perfect channel state information (CSI), which serves as an upper bound for the performance of practical systems. For systems without CSI, time domain and frequency domain channel estimation based linear detectors are proposed. The performance gains and robustness of a linear minimum mean square error (LMMSE) filter over a traditional filter (TF) and matched filter (MF) in the high signal-to-noise ratio (SNR) regime are demonstrated with numerical simulation results.

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.

OFDMA-based LAN emulation in long-reach hybrid PON system

A novel long-reach, hybrid wavelength-division multiplexing (WDM) and time-division multiplexing (TDM) passive optical network (PON) architecture which supports local area network (LAN) emulation among customers is proposed. Orthogonal frequency division multiplexing access (OFDMA) technology is used in optical network units (ONUs) to transmit the LAN data. The optical LAN data from an ONU is converted into the electrical signal and combined with TDM downstream access data in the extended box for delivery to other ONUs. This scheme has many advantages on LAN emulation, such as dynamic allocation of LAN bandwidth, no bandwidth cost of TDM business, supporting multiple concurrent LAN services and so on. Simulations are performed to verify the scheme. Tolerance of dispersion and factors that influence the performance of various independent services are all investigated and analyzed.

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.

A novel ECDM-OFDM-PON architecture for Next-Generation optical access network

This paper proposes a novel architecture for next-generation passive optical network (PON) based on electrical code division multiplexing orthogonal frequency division multiplexing (ECDM-OFDM) access. The feasibility of bidirectional transmission with the same wavelength has been experimentally demonstrated under this architecture. An error-free transmission of two PON channels has been successfully demonstrated in the experiment.

Performance Analyses of OFDM–CDMA Receivers in Multipath Fading Channels

Orthogonal frequency-division multiplexing (OFDM) is a promising scheme for multicarrier (MC) transmission. The combination of OFDM and code-division multiple access (CDMA) which is referred to as OFDM-CDMA, has recently attracted much research interest in wireless communications. In this paper, we evaluate the downlink performance for two forms of adaptive OFDM-CDMA receivers in multipath fading channels: 1) MC-CDMA and 2) MC-direct sequence (DS)-CDMA. We propose theoretical minimum mean square errors (MMSEs) for MC-CDMA and MC-DS-CDMA to compare the performances in different situations. Moreover, one drawback of OFDM schemes is the rate reduction due to the cyclic prefix (CP) overhead, which significantly affects the channel utilization in MC-DS-CDMA systems. We propose adaptive receiver structures with both subcarrier- and code-interval equalizations to improve the performance of MC-DS-CDMA systems with shorter or no CP. Simulation results demonstrate the effectiveness of the proposed receivers and the correctness of the theoretical derivations.