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The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot. [ABSTRACT FROM AUTHOR]

Peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) may be reduced by reserving several tones to generate a peak-canceling signal (PCS). However, this method suffers from high computational complexity. To address this problem, this paper proposes an algorithm based on peak-windowing residual noise, which is generated by windowing the signal samples that exceed the predetermined threshold. Filtering the residual noise to satisfy tone reservation (TR) constraints and scaling with a scaling factor determined to minimize the out-of-range power generates the PCS. Simulation results show that the proposed algorithm can achieve 6.9-dB PAPR reduction with much lower complexity than other schemes. [ABSTRACT FROM AUTHOR]

The effect of distortion on the error vector magnitude (EVM) performance of orthogonal frequency-division multiplexing (OFDM) signals with different numbers of subcarriers and the connection to the peak-to-average power ratio (PAPR) of such signals is investigated. A low-cost and low-complexity directly modulated radio-over-fiber link is used in experiments as an example of a link limited by distortion. Statistical distributions of the EVM over a large number of transmitted OFDM frames are gained from experimental measurements and analyses of idealized processes. The measurement results show that as the number of subcarriers is reduced, the distribution means are more affected by extreme values. This effect results in mean EVMs for signals with different numbers of subcarriers that are not dependent in the expected way on the statistical PAPR of the transmitted OFDM signals. Instead, it is shown that in regions of moderate distortion, the median of the EVM is more closely related to the statistical PAPR and to the required back-off for signals with different numbers of subcarriers. [ABSTRACT FROM AUTHOR]

Use of Wireless communications for Metropolitan Area Network (MAN) in consumer electronics has increased significantly in the recent past. This paper, presents the performance analysis of four different channel coding and interleaving schemes for MIMO-OFDM communications systems. A comparison is done based on the BER, hardware implementation resources requirement, and power dissipation. It also presents a memory-efficient and low-latency interleaver implementation technique for the MIMO-OFDM communication system. It is shown that among the four coding and interleaving schemes studied, the crossantenna coding and per-antenna interleaving performs the best under all SNR conditions and for all modulation schemes. It is also the best scheme as far as the hardware resource implication and power dissipation are concerned, which are particularly important in the context of consumer electronics. Next, using the proposed interleaver, a MIMO-OFDM based transmitter employing a double data stream 2?2 MIMO spatial multiplexing system is built. [ABSTRACT FROM PUBLISHER]

The European Digital Video Broadcasting-Return Channel Terrestrial (DVB-RCT) standard represents a wireless In-Band return channel solution based on Orthogonal Frequency Division Multiple Access to provide interactive services in Digital Video Broadcasting-Terrestrial (DVB-T) systems. In this paper, the performance of DVB-RCT standard is evaluated and compared with another possible wireless broadband technology to convey feedback traffic. Firstly, the performance of a DVB-T/RCT single cell system has been evaluated using an interactive traffic source model assuming uniform geographical user distribution with adaptive modulation and coding. The obtained results have confirmed the suitability of using DVB-RCT as a technological solution for the return channel in both rural and urban areas. Additionally, the performance of DVB-T/RCT system has been compared to IEEE 802.16-2004 using a published performance evaluation research of the latter as a benchmark. Assuming that the 802.16 published results are correct, such comparison shows a clear advantage of the DVB-T/RCT system. [ABSTRACT FROM AUTHOR]

Orthogonal frequency-division multiple access (OFDMA) has been integrated into emerging broadband wireless systems such as the IEEE 802.16 WirelessMAN. One critical problem in OFDMA is to assign multiple frequency bands (called subcarriers) to different users. Taking advantage of the frequency and multiuser diversities in OFDMA systems, dynamic subcarrier assignment mechanisms have been shown to achieve much higher downlink capacity than static assignment. A rich literature exists, which proposes medium-access-control- and physical-layer (MAC/PHY) schemes, aiming at exploiting the diversity gain with low implementation complexity. In this paper, we propose a cross-layer approach that explores the joint advantage of network coding and dynamic subcarrier assignment. With network coding, it becomes possible to assign the same subcarriers to different downlinks without causing interference. Consequently, our coding-aware assignment scheme improves the bandwidth efficiency and increases the downlink throughput by a substantial margin. In designing the scheme, we identify a tradeoff between diversity gain and the network coding advantage, which is critical to network performance in terms of throughput and fairness. To explore the tradeoff, we formulate the coding-aware assignment scheme as a mixed integer program and design a polynomial-time approximation algorithm that can be used in practical systems. We prove the asymptotic performance bound of the algorithm and demonstrate that it closely approximates the optimum under realistic experimental settings. [ABSTRACT FROM PUBLISHER]

IEEE 802.16 orthogonal frequency-division multiple access (OFDMA) downlink subframes have a special 2-D channel-time structure. Allocation resources from such a 2-D structure incur extra control overheads that hurt network performance. Existing solutions try to improve network performance by designing either the scheduler in the medium access control layer or the burst allocator in the physical layer, but the efficiency of overhead reduction is limited. In this paper, we point out the necessity of “codesigning” both the scheduler and the burst allocator to efficiently reduce overheads and improve network performance. Under the partial-usage-of-subcarriers model, we propose a cross-layer framework that covers overhead reduction, real-time and non-real-time traffic scheduling, and burst allocation. The framework includes a two-tier priority-based scheduler and a bucket-based burst allocator, which is more complete and efficient than prior studies. Both the scheduler and the burst allocator are tightly coupled together to solve the problem of arranging resources to data traffic. Given available space and bucket design from the burst allocator, the scheduler can well utilize the frame resource, reduce real-time traffic delays, and maintain fairness. On the other hand, with priority knowledge and resource assignment from the scheduler, the burst allocator can efficiently arrange downlink bursts to satisfy traffic requirements with low complexity. Through analysis, the cross-layer framework is validated to give an upper bound to overheads and achieve high network performance. Extensive simulation results verify that the cross-layer framework significantly increases network throughput, maintains long-term fairness, alleviates real-time traffic delays, and enhances frame utilization. [ABSTRACT FROM PUBLISHER]

In this paper, we consider the detection of orthogonal frequency-division multiplexing (OFDM) signals under frequency-selective fading channels for cognitive radio. First, we propose a new decision statistic for the signal detection based on the special feature-cyclic prefix embedded in OFDM signals. The probability distribution function (pdf) of the statistic is derived under the hypothesis of signal presence or absence. Then, the generalized likelihood ratio test (LRT) and the pdf's under the two hypotheses are derived to obtain the theoretical false-alarm rate (FAR) and the probability of detection (PD). After that, a suboptimal test is proposed to resolve the interference/noise uncertainty problems met for many detection algorithms such as the energy detection in practice. The theoretical FAR and PD are derived, and the theoretical threshold for any given FAR according to Neyman-Pearson criterion is accordingly given. Finally, extensive simulations are performed to confirm the derived theoretical results and demonstrate the promising detection. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a single-stage 90-nm CMOS power amplifier (PA) for 2.3-2.7-GHz WiMAX (802.16e) band applications. An integrated balun is used to match the output to 50-Ω load. The PA gain and saturated power (PSAT) are +18 and +32 dBm, respectively, working from a 3.3-V supply, with a peak power-added efficiency of 48%. A digital-predistortion technique is used to enhance the PA linearity. The measured error vector magnitude for a 64 quadrature amplitude modulation orthogonal frequency-division multiplexing signal is improved from -24 to -30 dB at +25-dBm output power. Compliance with the 802.16e standard 10-MHz WiMAX mask and Federal Communications Commission regulations is demonstrated at +25 dBm of output power with power efficiency of 25% and with a measured second harmonic level of -31 dBm/MHz. Using a crest factor reduction technique, mask compliance is achieved at +27 dBm with tradeoff on EVM = -dB, sufficient for quadrature phase-shift keying. [ABSTRACT FROM AUTHOR]

Generally, optimization techniques for resource allocation of orthogonal frequency-division multiple-access (OFDMA) systems are infeasible for real-time applications. In this paper, with consideration of grouping for subscriber stations (SSs), a resource-allocation scheme by an optimization technique of a genetic algorithm is proposed for the uplinks of IEEE 802.16 OFDMA systems. The genetic algorithm with SS grouping resource-allocation (GGRA) scheme first designs a rate assignment strategy that is applied with a predefined residual lifetime to dynamically allocate resource to each service. It then aggregates high-correlation SSs into the same group, where the SSs will be allocated to different slots to avoid mutual user interference. Finally, the GGRA scheme finds an optimal assignment matrix for the system by the genetic algorithm based on the SS groups to greatly lessen the computation complexity. The GGRA scheme can also maximize the system throughput and fulfill the quality-of-service (QoS) requirements. Simulation results show that the proposed GGRA scheme performs better than the efficient and fair scheduling (EFS) algorithm and the maximum largest weighted delay first (MLWDF) algorithm in system throughputs, voice/video packet drop rates, unsatisfied ratios of hypertext transfer protocol (HTTP) users/packets, and file transfer protocol (FTP) throughputs. The computation complexity of the GGRA scheme is also tractable and, thus, feasible for real-time applications. [ABSTRACT FROM AUTHOR]

Feedback reduction in multiuser orthogonal frequency-division multiplexing (OFDM) systems has become an important issue due to the excessive amount of feedback required to use opportunistic scheduling, particularly when the number of users and carriers is large. In this paper, we propose a novel feedback-reduction scheme for efficient downlink scheduling. In the proposed scheme, each user determines the amount of feedback based on the so-called feedback efficiency in a distributed manner. The key idea is to give more of an opportunity for feedback to users who are more often scheduled. Simulation results demonstrate that the proposed scheme can substantially decrease the feedback load while achieving almost the same scheduling performance as in the case of full feedback. In addition, the proposed scheme offers unique advantages over existing ones. First, it is not tailored to a specific scheduling policy; thus, it has adaptability to the change of the underlying scheduling policy. Second, the total feedback load can be maintained below a target level, regardless of the number of users in the system. [ABSTRACT FROM AUTHOR]

In linear-minimum-mean-square-error (LMMSE) channel estimation for multicarrier systems, one needs to know the channel correlation function. This poses a problem for systems with a small number of pilots operating in time-varying channels. We propose to approximate the channel power-delay profile (PDP) with a shape that can completely be described in two parameters, namely, the mean delay and the root-mean-square (RMS) delay spread. Furthermore, we develop a simple technique to estimate these delay parameters. The approximate PDP is then used to generate the LMMSE filter coefficients for data-subcarrier channel estimation. Mathematical expressions are derived that can be used to predict the accuracy of the various estimates, and they are verified by simulation. The proposed technique is applicable to both point-to-point communication and multiaccess communication where different users may experience different channel conditions. As a practical application, we also specialize the proposed technique to Mobile WiMAX signals and investigate the resulting performance. [ABSTRACT FROM AUTHOR]

This correspondence presents an algorithm for compensation of I/Q imbalance for a direct-conversion packet-switched orthogonal frequency-division-multiplexing (OFDM) communications system, which accounts for transmitter I/Q imbalance, receiver I/Q imbalance, phase/frequency error, and dispersive multipath fading. The proposed estimation algorithm is then presented, which operates within the framework of existing multiuser OFDM radio standards (802.11a). It is shown that this algorithm accurately estimates and corrects transceiver I/Q imbalance on a packet-by-packet basis, all within the receiver's digital baseband. [ABSTRACT FROM AUTHOR]

This paper proposes a joint channel-estimation method for the desired and interfering channels for cell edge users in reuse-1 orthogonal frequency-division multiplexing (OFDM) cellular systems. The following assumptions are made in proposing the algorithm: 1) The desired and interferer's channel multipath delays do not overlap; 2) the same pilot sequence is sent from the desired and interfering base stations (BSs); and 3) reuse-3 preamble symbols, as in the preamble structure in IEEE 802.16d/e (Wimax) systems, are used to obtain initial channel estimates without interference. If we make these assumptions, then it is possible to estimate the desired and interfering channels, even with reuse-1 pilots. The proposed pilot-based channel estimation technique exploits the delay subspace structure to reduce the impact of cochannel interference (CCI) on channel estimation. Delay subspace refers to the set of basis vectors spanning the frequency response of the desired and interfering multipath channels. This enables us to jointly estimate and track the desired and interfering channels with a lower mean-squared error (MSE), when compared with the conventional modified least-squares (mLS) technique, which ignores the structure of interference. The significance of accurate channel estimates in symbol detection schemes is demon- strated for systems employing two or more receiver antennas. The proposed channel estimator significantly improves the performance of symbol-detection schemes based on either interference nulling combiner (INC) or minimum MSE diversity combiner (MMSE-DC), when compared with detection schemes using mLS-based channel estimates. Analytical expressions are derived for the MSE of the estimated multipath delays. Simulation results are also provided to show the improved performance for the proposed channel-estimation method compared with the mLS-based channel estimation method, when used in conjunction with INC and MMSE-DC detectors. [ABSTRACT FROM AUTHOR]

A novel practical low-complexity multicell orthogonal frequency-division multiple access (OFDMA) downlink channel-assignment method that uses a graphic framework is proposed in this paper. Our solution consists of two phases: 1) a coarse-scale intercell interference (ICI) management scheme and 2) a fine-scale channel-aware resource-allocation scheme. In the first phase, state-of-the-art ICI management techniques such as ICI coordination (ICIC) and base-station cooperation (BSC) are incorporated in our framework. In particular, the ICI information is acquired through inference from the diversity set of mobile stations and is presented by an interference graph. Then, ICIC or BSC is mapped to the MAX k-CUT problem in graph theory and is solved in the first phase. In the second phase, channel assignment is accomplished by taking instantaneous channel conditions into account. Heuristic algorithms are proposed to efficiently solve both phases of the problem. Extensive simulation is conducted for various practical scenarios to demonstrate the superior performance of the proposed solution compared with the conventional OFDMA allocation scheme. The proposed scheme can be used in next-generation cellular systems such as the 3GPP Long-Term Evolution and IEEE 802.16m. [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of a new estimator for Fine Frequency Offset in OFDM packed-based applications. The estimator, which operates in the frequency domain, is based on the Inter-Carrier Interference (ICI) in the received preamble. A new theoretical expression for the estimator as a function of the input frequency offset is proposed. The estimator performance is evaluated for WIMAX receivers, showing an estimation error variance similar to that obtained with other well-known methods based on the processing in the time domain. [ABSTRACT FROM AUTHOR]

A framework for analyzing the performance of coded OSTBC-OFDM systems over arbitrary correlated generalized Ricean fading channels is established. The moment generating function of the signal-to-noise ratio at the input to the channel decoder is derived assuming correlated transmitter and receiver antennas and correlated paths in frequency selective channels. The probability of outage, the pairwise error probability, and the bit error rate are then evaluated. Bit-interleaved and iteratively decoded turbo product codes, Gray encoded M-ary quadrature amplitude modulation, and other parameters of the IEEE 802.16 Standard are used to illustrate numerical results. [ABSTRACT FROM AUTHOR]

This paper presents a new method for measuring the I/Q impairments affecting the worldwide interoperability for microwave access (WiMAX) transmitters through the analysis of the signal acquired through a general-purpose I/Q receiver. Based on a model of the effects of the I/Q impairments on the output signal that is suitable for orthogonal frequency-division multiplexing (OFDM) systems like WiMAX, the method is designed to correctly take into account the peculiarities of systems compliant with the IEEE 802.16-2004 standard, such as the potentially noxious effects of the impairments on signal normalization and threshold decisions. The results of the experiments carried out on the standard-compliant signals are given. [ABSTRACT FROM AUTHOR]

The number of multiple-input-multiple-output (MIMO) orthogonal frequency-division multiple-access (OFDMA) systems is expected to sharply increase in the near future. Engineers who need to test these systems face two difficulties: 1) the lack of descriptive instructions to conduct reliable measurements and 2) the increased hardware cost due to the need for multiple transmitters and receivers. This paper first introduces all the measurable parameters of MIMO-OFDMA systems and provides a clear guide in performing the measurements specific to various parts of the system. Then, it proposes the implementation of the reception of MIMO-OFDMA signals using a single receiver rather than multiple receivers. For this purpose, impairments related to each of the radio frequency front-end components are investigated. The challenges of MIMO-OFDMA measurements are addressed in comparison with single-input single-output measurements. A complete procedure is provided to receive and perform impairment estimation for Worldwide Interoperability for Microwave Access (WiMAX) MIMO signals using a single receiver according to the IEEE 802.16 Standards. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the interference coordination (IFCO) in cellular orthogonal frequency division multiple access (OFDMA) networks. It accounts on the uses of the OFDMA and the possible mitigation of IFCO through code division multiple access. It provides an overview of the IEEE 802.16e standard or the WiMAX networks which uses OFDM transmission technique and the classification of the IFCO schemes. The area-dependent and area-independent metrics were discussed to evaluate the performance of the interference coordination algorithms. It delineates the use of IFCO in the global system knowledge of ad hoc networks and cellular OFDMA networks. It discusses the possibilities of applying IFCO in the local system knowledge.

Mobile WiMAX was successfully adopted by ITU as one of the IMT-2000 technologies in November 2007. Since then mobile WiMAX (a.k.a. IP-OFDMA) has officially become a major global cellular wireless standard along with 3GPP UMTS/HSPA and 3GPP2 CDMA/EVDO. Mobile WiMAX is an OFDM-based technology available for deployment today, and new WIMAX devices come to market at much reduced cost than that of current 3G solutions. Currently over 260 service providers are deploying fixed, portable and mobile WiMAX networks in 110 countries. This article provides an overview of the mobile WiMAX system and its performance under various configurations, channel conditions, and types of data traffic. Furthermore, the article provides an overview of mobile WiMAX evolution. [ABSTRACT FROM AUTHOR]

Mobile WiMAX is a fast growing broadband access technology that enables low-cost mobile Internet applications, and realizes the convergence of mobile and fixed broadband access in a single air interface and network architecture. Mobile WiMAX combines OFDMA and advanced MIMO schemes along with flexible bandwidth and fast link adaptation, creating a highly efficient air interface that exceeds the capacity of existing and evolving 3G radio access networks. WiMAX networks, built on all-IP network architecture for plug and play network deployments, can support a mix of different usage and service models. While some consider mobile WiMAX as a candidate for the fourth generation of mobile networks, others view it as the first generation of mobile Internet technologies emerging from a wider ecosystem targeting to extend the success of WiFi over wide area networks supporting mobility. This article provides a high-level overview of mobile WiMAX technology and its evolution roadmap from both radio and network perspectives. [ABSTRACT FROM AUTHOR]

The radio-over-fiber(ROF) network has been proved to the best candidate for the wireless-access technology, and the orthogonal frequency division multiplexing (OFDM) tehnique has been accepted as the core transmitting technology, so the OFDM-ROF sytem is the hot topic in the international academia. An OFDM-ROF system simulation model basing on IEEE 802. 16a physical layer protocol had been built up. Special attention had been paid on the high peak-to-average power ratio (PAPR) of the OFDM signal which greatly constrained the performance of the OFDM-ROF system. A clipping and filtering technology had been investigated and simulated. Compared with the Naquist sampled, the two over sampled signal had a better performance in reducing PAPR. The bit error rate (BER) error flow research had been done with transmitting the chipped signal in nonlinear distorted ROF link And the QAM had been testified for the preferred technique in OFDM-ROF link. [ABSTRACT FROM AUTHOR]

Although the voice over Internet protocol (VoIP) service is expected to be widely supported in wireless mobile networks, the feasibility and capacity of the protocol have not previously been studied in relation to the emerging IEEE 802.16e orthogonal frequency-division multiple access (OFDMA) system. Informing subscriber stations about new downlink or uplink resource assignments creates a signaling overhead that influences the system throughput. In particular, the performance of VoIP services is seriously affected by the signaling overhead because the symmetry between the downlink and uplink causes immense downlink overheads. However, previous research on the IEEE 802.16e OFDMA system has not taken the signaling overhead into consideration. In the analytical model presented here, the signaling overhead is considered in the evaluation of the uplink and downlink performance of VoIP services in the IEEE 802.16e OFDMA system. [ABSTRACT FROM AUTHOR]

Multimedia stream service provided by broadband wireless networks has emerged as an important technology and has attracted much attention recently. An all-IP network architecture with reliable high-throughput air interface makes orthogonal frequency division multiplexing access (OFDMA)-based mobile worldwide interoperability for microwave access (mobile WiMAX) a viable technology for wireless multimedia services, such as voice over IP (VoIP), mobile TV, and so on. One of the main features in a WiMAX MAC layer is that it can provide differentiated services among different traffic categories with individual QoS requirements. In this article, we first give an overview of the key aspects of WiMAX and describe multimedia broadcast multicast service (MBMS) architecture of the 3GPP. Then, we propose a multicast and broadcast service (MBS) architecture for WiMAX that is based on MBMS. Moreover, we enhance the MBS architecture for mobile WiMAX to overcome the shortcoming of limited video broadcast performance over the baseline MBS model. We also give examples to demonstrate that the proposed architecture can support better mobility and offer higher power efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a new amplifier architecture based on the outphasing technique intended for the efficiency enhancement of linear amplification with nonlinear components (LINC) transmitters. The proposed mode-multiplexing linear amplification with nonlinear components (MM-LINC) scheme operates according to the LINC concept for input signal magnitude drive levels below a certain threshold and as a balanced amplifier beyond this threshold. The setting of this threshold level influences the performance of the amplifier in terms of average power-added efficiency and linearity. A 2-W up-link transmitter prototype for worldwide interoperability for microwave access (WiMAX) applications was designed using this new architecture and optimized for a WiMAX signal with an 11.3-dB peak-to-average power ratio. The experimental results revealed a significant increase in power-added efficiency, from 6% for a LINC transmitter to 21% for the MM-LINC amplifier, while maintaining an error vector magnitude value under 8%, which is compliant with the standard requirement. [ABSTRACT FROM AUTHOR]

The recent Orthogonal Frequency Division Multiple Access (OFDMA) transmission technique is gaining popularity as a preferred technology in the Broadband Wireless Access (BWA) emerging standards. In standards 802.16-2004 and 802.16e, the basic allocation units are comprised of sub-channels and OFDMA time symbols; each sub-channel is a group of sub-carriers, so that all the sub-channels are considered equally adequate to all users. We study the naturally arising new approach of two-dimensional mapping of incoming requests into the matrix that represents the system resources, where each allocation is of an arbitrary multi-rectangular shape (to the best of our knowledge, this approach has not been discussed elsewhere). We define a cost model and constraints related to practical OFDMA systems, which depend on the spatial shape of the two-dimensional allocation; the main objective function is the spatial efficiency. We show that the arising problem, even in its simplest form, is NP-hard [1}. We present run-time efficient heuristic solutions for various mapping problems, taking into account the above Q0S and OFDMA related constraints. In particular, a novel solution for two-dimensional mapping under priority constraints is suggested. Extensive simulations with parameters of real systems were used to investigate the performance of the proposed solutions in terms of throughput, delay and system load. The results show that high throughput can be achieved with relatively simple mapping algorithms. We believe that the proposed two-dimensional mapping approach is prospective, due to its fitness to modern standards. [ABSTRACT FROM AUTHOR]

We propose a novel pilot-aided algorithm for estimation of rapidly varying wireless channels in OFDM systems. Our approach is specifically designed for channels varying on the scale of a single OFDM symbol duration, which occur, for example, in mobile WiMAX, WAVE, and DVB-T. From the pilot information, we recover information about the channel taps in the framework of the Basis Expansion Model (BEM). We derive explicit formulas for the BEM coefficients in terms of the receive signal. Algebraically, the algorithm is FFT-based, and can be easily implemented in hardware. For a system with L channels taps, our method uses \cal O(L log L) operations and \cal O(L) memory per OFDM symbol. This complexity is the best possible up to the order of magnitude. Previously published methods require \cal O(L^2) operations and \cal O(L^2) memory. Numerical simulations illustrate performance gains achieved by our estimator at sufficiently high Doppler frequencies. Our approach does not assume any prior statistical information. [ABSTRACT FROM AUTHOR]

The growing demands for advanced mobile multimedia let the wireless mobile Internet access be developed rapidly. The Mobile WiMAX (IEEE 802.16e) is capable of providing high data rate and flexible Quality of Service (QoS) mechanisms. However, one of killer applications, mobile streaming video service from mobile station (MS) to fixed internet network can't still avoid a traditional QoS degradation problem caused by unreliable mobile channel environment. The previous researches show that streaming video service based on downward cross-layer design over OFDMA channel has improved robust features to channel errors, but requires modifications of the existing schedulers, packet ordering, and channel allocation strategies in base station (BS). Now, our goal is that we develop a high error resilient and robust method to channel errors on the OFDMA mobile video device without the modification of conventional functions in WiMAX BS. In this paper, we introduce OFDMA channel aware error resilient video coding method using an upward cross-layer design. Through the extensive simulation results, we prove that the proposed channel-aware intra-refresh coding can recover video damages more efficiently than traditional intra-refresh one over OFDMA channel environment. This error resilience feature can be adapted to all types of streaming video server devices. [ABSTRACT FROM PUBLISHER]

The Probability Density Function (PDF) or Cumulative Distribution Function (CDF) of the effective Signal to Noise Ratio (SNR) is an important statistical characterization in the performance analysis of an Orthogonal Frequency Division Multiple Access (OFDMA) system using Exponential Effective SNR Mapping (EESM). However, the exact closed form of PDF is extremely difficult to obtain. A general approximation method known as Moment Matching Approximating (MMA) is used to approximate the distribution of effective SNR by a simple expression. In this paper, the approximation by Gaussian, Generalized Extreme Value (GEV) and Pearson distribution are studied. Results show that Gaussian approximation is very useful when the number of sub-carriers is sufficiently large. Both GEV and Pearson approximation are accurate enough in approximating the distribution of effective SNR in a general case. [ABSTRACT FROM AUTHOR]

In this paper a novel technique for reducing the peak to average power ratio (PAPR) in OFDM systems by using the combination of the dummy sequence insertion (DSI) and partial transmit sequence (PTS) is proposed. In DSI increasing the number of dummy sequence decrease the transmission efficiency (TE) and in PTS the complexity increases when the number of subblock increases. Unlike the conventional PTS which needs several inverse fast fourier transform (IFFT) operations, the proposed DSI-PTS technique requires half IFFT operations only, while the PAPR performance is even better. So, it can remarkably reduce the computational complexity. Simulation results are examined with IEEE 802.16-2004 standard. By applying the DSI-PTS method about 0.5 dB reduction in PAPR at complementary cumulative distribution function (CCDF) of 0.01% is achieved compared to the conventional PTS while the complexity is reduced1. [ABSTRACT FROM AUTHOR]