Showing papers on "Orthogonal frequency-division multiplexing published in 2007"

Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA): A Tutorial Review

Abstract: Orthogonal frequency division multiple access (OFDMA) has recently attracted vast research attention from both academia and industry and has become part of new emerging standards for broadband wireless access. Even though the OFDMA concept is simple in its basic principle, the design of a practical OFDMA system is far from being a trivial task. Synchronization represents one of the most challenging issues and plays a major role in the physical layer design. The goal of this paper is to provide a comprehensive survey of the latest results in the field of synchronization for OFDMA systems, with tutorial objectives foremost. After quantifying the effects of synchronization errors on the system performance, we review some common methods to achieve timing and frequency alignment in a downlink transmission. We then consider the uplink case, where synchronization is made particularly difficult by the fact that each user's signal is characterized by different timing and frequency errors, and the base station has thus to estimate a relatively large number of unknown parameters. A second difficulty is related to how the estimated parameters must be employed to correct the uplink timing and frequency errors. The paper concludes with a comparison of the reviewed synchronization schemes in an OFDMA scenario inspired by the IEEE 802.16 standard for wireless metropolitan area networks.

Channel estimation for wireless ofdm systems

Abstract: Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system. The techniques exploit the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel for multi-carrier communication systems, such systems using OFDM modulation. A transmitter transmits data through a communication channel according to the modulation format. A receiver includes a demodulator to demodulate the data and an estimator to estimate the channel based on the demodulated data. The channel estimator applies a power-law operation to the demodulated data to identify the channel. The techniques can be used in both blind and semi-blind modes of channel estimation.

Linear Transceiver Design in Nonregenerative Relays With Channel State Information

Abstract: This paper deals with the design of nonregenerative relaying transceivers in cooperative systems where channel state information (CSI) is available at the relay station. The conventional nonregenerative approach is the amplify and forward (AF first hop channel and second hop channel (between relay and destination) information, or a third situation where the relay may have complete cooperative channel information including all the links: first and second hop channels and also the direct channel between source and destination. Despite the latter being a more unrealistic situation, since it requires the destination to inform the relay station about the direct channel, it is useful as an upper benchmark. In this paper, we consider the last two cases relating to CSI. We compare the performance so obtained with the performance for the conventional A&F approach, and also with the performance of regenerative relays and direct noncooperative transmission for two particular cases: narrowband multiple-input multiple-output transceivers and wideband single input single output orthogonal frequency division multiplex transmissions

Pilot-Assisted Time-Varying Channel Estimation for OFDM Systems

Abstract: In this paper, we deal with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems. The channels are assumed to be time-varying (TV) and approximated by a basis expansion model (BEM). Due to the time-variation, the resulting channel matrix in the frequency domain is no longer diagonal, but approximately banded. Based on this observation, we propose novel channel estimators to combat both the noise and the out-of-band interference. In addition, the effect of a receiver window on channel estimation is also studied. Our claims are supported by simulation results, which are obtained considering Jakes' channels with fairly high Doppler spreads

Multiuser MIMO-OFDM for Next-Generation Wireless Systems

Abstract: This overview portrays the evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station's or radio port's coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment in multiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems.

Performance of Optical OFDM in Ultralong-Haul WDM Lightwave Systems

Abstract: We show, using simulations, that a combination of orthogonal frequency division multiplexing (OFDM) and optical single sideband modulation can be used to compensate for chromatic dispersion in ultralong-haul wavelength-division multiplexed (WDM) systems. OFDM provides a high spectral efficiency, does not require a reverse feedback path for compensation, and has a better sensitivity than nonreturn to zero. This paper provides design rules for 800-4000-km optical-OFDM systems. The effects of WDM channel number and spacing, fiber dispersion, and input power per channel on the received Q are studied using extensive numerical simulations. These effects are summarized as a set of design rules

Effects of Phase Noise on OFDM Systems With and Without PLL: Characterization and Compensation

Abstract: In this paper, we propose an algorithm for suppressing intercarrier interference due to phase noise in coded orthogonal frequency division multiplexing (OFDM) systems. The algorithm approximates the phase-noise waveform by using a Fourier series approximation for the current phase-noise realization. Thereby, it cancels the effects of the phase noise beyond the standard common phase error correction used in contemporary OFDM standards. The algorithm requires that the correlation properties of the intercarrier interference are known. We calculate these properties in terms of the phase-noise spectral correlation matrix for both Wiener and Ornstein-Uhlenbeck phase-noise models, respectively. This modeling corresponds to a free-running oscillator, as well as a phase-locked loop realization of the local oscillator in orthogonal frequency division multiplexing transceivers. For both transceiver configurations, we investigate the performance of the proposed algorithm. It is demonstrated that the new algorithm achieves as much as one order of magnitude better performance in terms of packet/bit error rate when compared to a receiver with only the common phase error suppression.

Blind Channel Estimation for MIMO-OFDM Systems

Abstract: By combining multiple-input multiple-output (MIMO) communication with the orthogonal frequency division multiplexing (OFDM) modulation scheme, MIMO-OFDM systems can achieve high data rates over broadband wireless channels. In this paper, to provide a bandwidth-efficient solution for MIMO-OFDM channel estimation, we establish conditions for channel identifiability and present a blind channel estimation technique based on a subspace approach. The proposed method unifies and generalizes the existing subspace-based methods for blind channel estimation in single-input single-output OFDM systems to blind channel estimation for two different MIMO-OFDM systems distinguished according to the number of transmit and receive antennas. In particular, the proposed method obtains accurate channel estimation and fast convergence with insensitivity to overestimates of the true channel order. If virtual carriers (VCs) are available, the proposed method can work with no or insufficient cyclic prefix (CP), thereby potentially increasing channel utilization. Furthermore, it is shown under specific system conditions that the proposed method can be applied to MIMO-OFDM systems without CPs, regardless of the presence of VCs, and obtains an accurate channel estimate with a small number of OFDM symbols. Thus, this method improves the transmission bandwidth efficiency. Simulation results illustrate the mean-square error performance of the proposed method via numerical experiments

OFDM Baseband Receiver Design for Wireless Communications

Abstract: Orthogonal frequency-division multiplexing (OFDM) access schemes are becoming more prevalent among cellular and wireless broadband systems, accelerating the need for smaller, more energy efficient receiver solutions. Up to now the majority of OFDM texts have dealt with signal processing aspects. To address the current gap in OFDM integrated circuit (IC) instruction, Chiueh and Tsai have produced this timely text on baseband design. OFDM Baseband Receiver Design for Wireless Communications covers the gamut of OFDM technology, from theories and algorithms to architectures and circuits. Chiueh and Tsai give a concise yet comprehensive look at digital communications fundamentals before explaining modulation and signal processing algorithms in OFDM receivers. Moreover, the authors give detailed treatment of hardware issues -- from design methodology to physical IC implementation. Closes the gap between OFDM theory and implementation Enables the reader to transfer communication receiver concepts into hardware design wireless receivers with acceptable implementation loss achieve low-power designs Contains numerous figures to illustrate techniques Features concrete design examples of MC-CDMA systems and cognitive radio applications Presents theoretical discussions that focus on concepts rather than mathematical derivation Provides a much-needed single source of material from numerous papers Based on course materials for a class in digital communication IC design, this book is ideal for advanced undergraduate or post-graduate students from either VLSI design or signal processing backgrounds. New and experienced engineers in industry working on algorithms or hardware for wireless communications devices will also find this book to be a key reference.

Reducing the Peak-to-Average Power Ratio of OFDM Signals Through Precoding

Abstract: Orthogonal-frequency-division-multiplexing (OFDM) techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However, they are very sensitive to nonlinear effects due to the high peak-to-average power ratio (PAPR) owned by their transmitted signals. This paper proposes an efficient technique for reducing the PAPR of OFDM signals. The proposed technique is data-independent and, thus, does not require new processing and optimization for each transmitted OFDM block. The reduction in PAPR of the OFDM signal is obtained through a proper selection of a precoding scheme that distributes the power of each modulated symbol over the OFDM block. The obtained results show that this precoding scheme is an attractive solution to the PAPR problem of OFDM signals. It is shown, through computer simulations, that the PAPR of precoded OFDM signals approaches that of single-carrier signals. The good improvement in PAPR given by the present technique permits the reduction of the complexity and cost of the transmitter significantly. The precoding schemes also take advantage of the frequency variations of the communication channel and can provide considerable performance gain in fading-multipath channels

Technical Review on Chinese Digital Terrestrial Television Broadcasting Standard and Measurements on Some Working Modes

Abstract: Technical details of the recently announced Chinese Digital Terrestrial Television Broadcasting Standard which defines the physical layer transmission protocol including the frame structure, channel coding and modulation schemes are discussed in this paper. The major differences between Chinese DTV standard in multi-carrier working mode and DVB-T standard, all occupying the same 8 MHz baseband bandwidth, are addressed. The measurement results of several working modes showing satisfactory receiving performance of high and standard definition TV signals under both indoor and outdoor environments for the fixed and mobile reception are also presented

OFDM Visible Light Wireless Communication Based on White LEDs

Abstract: White LEDs are set to penetrate many areas of everyday life. An interesting property of these devices (in addition to their lightening capabilities) is that they can be utilised for data transmission. In the past, primarily OOK (on-off keying) has been used for digital data modulation of such devices. OOK imposes limitations on the achievable data rates. Therefore, in this paper OFDM is considered in combination with higher order modulation schemes. A hardware demonstrator with an entire link chain (transmitter and receiver) is developed and measured BER (bit error ratio) results are reported. The system uses pilot sub-carriers to correct frequency synchronisation errors, training sequences for channel estimation and time synchronisation routines. Forward error correction (FEC) coding is used. It is shown that for COFDM (coded OFDM) with QPSK (quadrature phase shift keying) modulation and a single LED, a BER of 2 times 10-5 is achieved for a distance of 90 cm between transmitter and receiver.

Phase Estimation for Coherent Optical OFDM

Abstract: Phase estimation is one of the enabling functionalities in coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) receivers. In this letter, we compare pilot-aided and data-aided phase estimation methods for a CO-OFDM transmission experiment at 8 Gb/s over 1000-km standard single-mode fiber without optical dispersion compensation. We also show that as few as five subcarriers are sufficient for pilot-aided phase estimation

Non-cooperative resource competition game by virtual referee in multi-cell OFDMA networks

Abstract: In this paper, a distributive non-cooperative game is proposed to perform sub-channel assignment, adaptive modulation, and power control for multi-cell multi-user orthogonal frequency division multiplexing access (OFDMA) networks. Each individual user's goal is to minimize his/her own transmitted power in a distributed manner under the constraints that the desirable rate is achieved and the transmitted power is bounded. The pure non-cooperative game may result in non-convergence or some undesirable Nash Equilibriums with low system and individual performances. To enhance the performances, a virtual referee is introduced to the networks and is in charge of monitoring and improving the outcome of non-cooperative competition for resources among the distributed users. If the game outcome is not desirable, either the required transmission rates should be reduced or some users should be prevented from using some radio resources such as sub-channels, so that the rest of users can share the limited resources more efficiently. Moreover, it can be shown that the introduction of the virtual referee does not increase the complexity of the networks. From the simulation results in a two-cell case, the proposed scheme reduces the transmitted power by 80% and 25% compared with the fixed channel assignment algorithm and the iterative water-filling algorithm in the literature, respectively. The achievable rate can be improved by 10%. In a multi-cell case, the proposed scheme can have up to 40% power reduction compared with the iterative water-filling algorithm when the co-channel interferences are severe.

Bandwidth asymmetric communication system based on ofdm and tdma

Abstract: The present invention relates to a communication system comprising a plurality of terminals each having an uplink transmission unit (1) for transmitting radio frequency OFDM signals at a radio frequency and an access point having an uplink receiving unit (4) for concurrently receiving said radio frequency OFDM signals from at least two terminals, said OFDM signals being Orthogonal Frequency Division Multiplex (OFDM) modulated, wherein the bandwidth of said uplink transmission units and of the transmitted radio frequency OFDM signals is smaller than the bandwidth of said uplink receiving unit, that the bandwidth of at least two uplink transmission units and of their transmitted radio frequency OFDM signals is different and that the uplink transmission unit is adapted to assign different connections for concurrently transmitting radio frequency OFDM signals to different sub-carriers in the same time slots or to the same or different sub-carriers in different time slots.

Channel equalization in filter bank based multicarrier modulation for wireless communications

Abstract: Channel equalization in filter bank based multicarrier (FBMC) modulation is addressed. We utilize an efficient oversampled filter bank concept with 2x-oversampled subcarrier signals that can be equalized independently of each other. Due to Nyquist pulse shaping, consecutive symbol waveforms overlap in time, which calls for special means for equalization. Two alternative linear low-complexity subcarrier equalizer structures are developed together with straightforward channel estimation-based methods to calculate the equalizer coefficients using pointwise equalization within each subband (in a frequency-sampled manner). A novel structure, consisting of a linear-phase FIR amplitude equalizer and an allpass filter as phase equalizer, is found to provide enhanced robustness to timing estimation errors. This allows the receiver to be operated without time synchronization before the filter bank. The coded error-rate performance of FBMC with the studied equalization scheme is compared to a cyclic prefix OFDM reference in wireless mobile channel conditions, taking into account issues like spectral regrowth with practical nonlinear transmitters and sensitivity to frequency offsets. It is further emphasized that FBMC provides flexible means for high-quality frequency selective filtering in the receiver to suppress strong interfering spectral components within or close to the used frequency band.

A Novel Multi-Cell OFDMA System Structure using Fractional Frequency Reuse

Abstract: In this paper, we propose a novel frequency reuse scheme for multi-cell orthogonal frequency division multiplexing access (OFDMA) systems for co-channel interference reduction. Each cell is partitioned into three sectors. All the available subcarriers are divided into two groups. One is reused in the central region of the sectors, and another is divided into three parts used orthogonally for the edge of the three sectors (no overlap). Which subcarrier group a user can use is dependent on the location or the received signal to interference plus noise ratio (SINR) of the user. Thus, intra-cell orthogonality is guaranteed, and inter-cell interference can be greatly reduced. All the subcarriers may use the same transmit power in this scheme. Simulation results show that this scheme can bring higher system throughput and lower CCI, and it also can increase the data rate at the cell edge.

Multicast Broadcast Services Support in OFDMA-Based WiMAX Systems [Advances in Mobile Multimedia]

Abstract: Multimedia stream service provided by broadband wireless networks has emerged as an important technology and has attracted much attention. 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.

Opportunistic Beamforming and Scheduling for OFDMA Systems

Abstract: Orthogonal frequency-division multiple access (OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses three problems in multiuser diversity for OFDMA systems. First, we propose a way to significantly reduce the amount of channel state information (CSI) feedback without sacrificing performance too much, by selective and adaptive feedback. Second, we propose a way to increase the cell throughput and fairness by applying an opportunistic beamforming scheme to orthogonal frequency-division multiplexing. This beamforming scheme increases the frequency fading rate, which increases the multiuser diversity effect. Thirdly, we deal with the issue of fairness and quality-of-service (QoS) in opportunistic systems by proposing a modified proportional fair (PF) scheduler for OFDMA. Key features in the scheduler are that it incorporates QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate the performance of the proposed schemes. The opportunistic beamforming scheme performed well in comparison with several other schemes. The modified PF scheduler was able to give users different QoS, based on their requirements, while still exploiting multiuser diversity

Efficient DFT-based channel estimation for OFDM systems on multipath channels

Abstract: An improved discrete Fourier transform (DFT)-based channel estimation for orthogonal frequency division multiplexing systems is proposed. Conventional DFT-based channel estimations improve the performance by suppressing time domain noise. However, they potentially require information on channel impulse responses and may also result in mean-square error (MSE) floor due to incorrect channel information such as channel delay spread. In contrast, our purposed channel estimation can improve the performance by deciding significant channel taps adaptively without requiring any channel statistical information. Significant channel taps are detected on the basis of a predetermined threshold. The optimal threshold to reduce the MSE of the estimation is also derived, and it is confirmed by computer simulation. Simulation results demonstrate that the proposed algorithm can improve the MSE performance ~6.5 dB compared with the conventional DFT-based estimation, and the MSE floor is not observed in any channels.

The OFDM-IDMA approach to wireless communication systems

Abstract: This article outlines the basic principles of OFDM-IDMA. Comparisons with other alternative technologies such as OFDM-CDMA and OFDMA are provided. Some attractive features of OFMD-IDMA are explained, including low-cost iterative multi-user detection, flexible rate adaptation, frequency diversity, and significant advantages regarding spectral and power efficiency.

Space-Time/Frequency Coding for MIMO-OFDM in Next Generation Broadband Wireless Systems

Abstract: With the advent of next generation (4G) broadband wireless communications, the combination of multiple-input multiple-output (MIMO) wireless technology with orthogonal frequency division multiplexing (OFDM) has been recognized as one of the most promising techniques to support high data rate and high performance. In particular, coding over the space, time, and frequency domains provided by MIMO-OFDM will enable a much more reliable and robust transmission over the harsh wireless environment. In this article we provide an overview of space-time (ST) coding, space-frequency (SF) coding, and space-time-frequency (STF) coding for MIMO-OFDM systems. Performance results show that STF coding can achieve the maximum diversity gain in an end- to-end MIMO-OFDM system over broadband wireless channels. Furthermore, for orthogonal frequency division multiple access (OFDMA), we propose a multiuser SF coding scheme that can achieve the maximum diversity for each user while minimizing the interference introduced from all the other users.

Equalization Techniques for Distributed Space-Time Block Codes With Amplify-and-Forward Relaying

Abstract: In this paper, we investigate equalization methods for cooperative diversity schemes over frequency-selective fading channels. Specifically, we consider three equalization schemes proposed originally for conventional space-time block codes (STBC) and extend them to distributed STBC in a cooperative transmission scenario with amplify-and-forward relaying. The distributed STBC equalization schemes are named after their original counterparts as distributed time-reversal (D-TR) STBC, distributed single-carrier (D-SC) STBC, and distributed orthogonal frequency division multiplexed (D-OFDM) STBC. The underlying orthogonality of distributed STBC results in decoupled data streams at the receiver side allowing low-complexity implementations. Without loss of generality, we consider a single-relay scenario where the source-to-relay SrarrR, relay-to-destination RrarrD, and source-to-destination SrarrD links experience possibly different channel delay spreads. Under the assumption of perfect power control for the relay terminal and high signal-to-noise ratio (SNR) for the underlying links, our performance analysis demonstrates that D-TR-STBC, D-SC-STBC, and coded D-OFDM-STBC schemes are able to achieve a maximum diversity order of min(L1,L3)+L2+2 where L1, L2, and L3 are the channel memory lengths for SrarrR, SrarrD, and RrarrD links, respectively. This illustrates that the minimum of the multipath diversity orders experienced in SrarrR and RrarrD links becomes the performance bottleneck for the relaying path. For the case of a nonfading relaying path where line-of-sight propagation is possible in either one of these underlying links, we demonstrate that diversity orders of L1+L2+2 and L3+L2+2 are achievable assuming nonfading SrarrR and RrarrD links, respectively. An extensive Monte Carlo simulation study is presented to corroborate the analytical results and to provide detailed performance comparisons among the three candidate equalization schemes

Power Allocation in OFDM-Based Cognitive Radio Systems

Abstract: In this paper, we investigate the optimal power allocation strategy that aims at maximizing the capacity in OFDM- based cognitive radio systems. We show that the traditional water-filling algorithm applied in general OFDM systems needs to be modified due to the per subchannel power constraints in such systems. An iterative partitioned water-filling algorithm is proposed and proved to be optimal based on the convex optimization theory.

Design of an OFDM Cooperative Space-Time Diversity System

Abstract: In this paper, we propose a wireless system that realizes theoretical benefits of space-time cooperation. Specifically, we design a space-time cooperative system based on orthogonal frequency division multiplexing (OFDM), which we refer to as a cooperative (CO)-OFDM system. Our design includes a two-phase space-time cooperation protocol, as well as a transmitter and receiver architecture that facilitates cooperation. Furthermore, we devise a frame structure, on which we build practical timing and frequency synchronization algorithms and a channel estimation algorithm. In particular, the proposed frequency synchronization algorithm utilizes the underlying structure of the cooperation protocol, and the proposed channel estimation algorithm is based on a pairwise orthogonal construction of two sequences. We validate the performance of the proposed synchronization and channel estimation algorithms through simulations. We then present simulation results that demonstrate the overall performance advantage of the CO-OFDM system over an OFDM system without cooperation, not only under idealistic assumptions but also under realistic situations where the proposed algorithms are employed.

A Simple Alamouti Space–Time Transmission Scheme for Asynchronous Cooperative Systems

Abstract: In this letter, we propose a simple orthogonal frequency-division multiplexing (OFDM) scheme for an asynchronous cooperative system, where OFDM is implemented at the source node, and time-reversion and complex conjugation are implemented at the relay nodes. The cyclic prefix (CP) at the source node is used for combating the timing errors from the relay nodes. In this scheme, the received signals at the destination node have the Alamouti code structure on each subcarrier, and thus, it has the fast symbol-wise ML decoding. It should be emphasized that the relay nodes only need to implement the time-reversion, some sign changes from plus to minus, and/or the complex conjugation to the received signals, and no IDFT or DFT operation is needed. It is shown that this simple scheme achieves second-order diversity gain without the synchronization requirement at the relay nodes.

Compensation of Phase Noise in OFDM Wireless Systems

Abstract: Phase noise causes significant degradation in the performance of orthogonal frequency division multiplexing (OFDM)-based wireless communication systems. The presence of phase noise can reduce the effective signal-to-noise ratio (SNR) at the receiver, and consequently, limit the bit error rate (BER) and data rate. In this paper, the effect of phase noise on OFDM wireless systems is studied, and a compensation scheme is proposed to mitigate the common phase error and intercarrier interference (ICI) caused by phase noise. In the proposed scheme, the communication between the transmitter and receiver blocks consists of two stages. In the first stage, block-type pilot symbols are transmitted and the channel coefficients are jointly estimated with the phase noise in the time domain. In the second stage, comb-type OFDM symbols are transmitted such that the receiver can jointly estimate the data symbols and the phase noise. It is shown both by theory and computer simulations that the proposed scheme can effectively mitigate the ICI caused by phase noise and improve the BER of OFDM systems. Another benefit of the proposed scheme is that the sensitivity of OFDM receivers to phase noise can be significantly lowered, which helps simplify the oscillator and circuitry design in terms of implementation cost and power consumption.

A Modified SLM Scheme With Low Complexity for PAPR Reduction of OFDM Systems

Abstract: In this paper, we propose a new peak-to-average power ratio (PAPR) reduction scheme of orthogonal frequency division multiplexing (OFDM) system, called a modified selected mapping (SLM) scheme, which considerably reduces the computational complexity with keeping the similar PAPR reduction performance compared with the conventional SLM scheme. The proposed scheme is analytically and numerically evaluated for the OFDM system specified in the IEEE 802.16 standard. For the OFDM system with 2048 subcarriers, the proposed scheme with 4 binary phase sequences can reduce the complex multiplications by 63.5% with the similar PAPR reduction compared with the SLM scheme with 16 binary phase sequences.

Iterative Methods for Cancellation of Intercarrier Interference in OFDM Systems

Abstract: We consider orthogonal frequency-division multiplexing systems with intercarrier interference (ICI) due to insufficient cyclic prefix and/or temporal variations Intersymbol interference (ISI) and ICI lead to an error floor in conventional receivers We suggest two techniques for the equalization of ICI The first, called "operator-perturbation technique" is an iterative technique for the inversion of a linear system of equations Alternatively, we show that serial or parallel interference cancellation can be used to drastically reduce the error floor Simulations show that, depending on the SNR and the origin of the ICI, one of the schemes performs best In all cases, our schemes lead to a drastic reduction of the bit error rate

Joint compensation of transmitter and receiver impairments in OFDM systems

Abstract: The implementation of OFDM-based systems suffers from impairments such as in-phase and quadrature-phase (IQ) imbalances in the front-end analog processing. Such imbalances are caused by the analog processing of the radio frequency (RF) signal and can be present at both the transmitter and receiver. The resulting IQ distortion limits the achievable operating SNR at the receiver and the achievable data rates. In this paper, the effect of both the transmitter and receiver IQ imbalances in an OFDM system is studied and algorithms are developed to compensate for such distortions in the digital domain. The algorithms include post-FFT least-squares and adaptive equalization, as well as a pre-distortion scheme at the transmitter and a pre-FFT correction at the receiver