242 research outputs found

    Intersymbol and Intercarrier Interference in OFDM Transmissions through Highly Dispersive Channels

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    This work quantifies, for the first time, intersymbol and intercarrier interferences induced by very dispersive channels in OFDM systems. The resulting achievable data rate for \wam{suboptimal} OFDM transmissions is derived based on the computation of signal-to-interference-plus-noise ratio for arbitrary length finite duration channel impulse responses. Simulation results point to significant differences between data rates obtained via conventional formulations, for which interferences are supposed to be limited to two or three blocks, versus the data rates considering the actual channel dispersion

    SGD Frequency-Domain Space-Frequency Semiblind Multiuser Receiver with an Adaptive Optimal Mixing Parameter

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    A novel stochastic gradient descent frequency-domain (FD) space-frequency (SF) semiblind multiuser receiver with an adaptive optimal mixing parameter is proposed to improve performance of FD semiblind multiuser receivers with a fixed mixing parameters and reduces computational complexity of suboptimal FD semiblind multiuser receivers in SFBC downlink MIMO MC-CDMA systems where various numbers of users exist. The receiver exploits an adaptive mixing parameter to mix information ratio between the training-based mode and the blind-based mode. Analytical results prove that the optimal mixing parameter value relies on power and number of active loaded users existing in the system. Computer simulation results show that when the mixing parameter is adapted closely to the optimal mixing parameter value, the performance of the receiver outperforms existing FD SF adaptive step-size (AS) LMS semiblind based with a fixed mixing parameter and conventional FD SF AS-LMS training-based multiuser receivers in the MSE, SER and signal to interference plus noise ratio in both static and dynamic environments

    Sparse Equalizers for OFDM Signals with Insufficient Cyclic Prefix

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    The cyclic prefix (CP) is appended in orthogonal frequency division multiplexing (OFDM) signals to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) induced by the communication channel, which limits its spectral efficiency. Therefore, inserting an insufficient CP and equalizing the resulting ICI and ISI is a method that has been circulating the literature for a while, aiming at increasing the efficiency of OFDM systems. In this paper, we propose a reduced-complexity sparse linear equalizer and a decision-feedback equalizer for OFDM signals with insufficient CP. A performance-complexity trade-off is highlighted, where we show that it is possible to equalize the received signal with a reduced complexity equalizer while having a limited performance loss. Our proposed equalizer designs are not only less complex to realize, but are shown to provide a higher data rate. The proposed equalizers are further evaluated in terms of the worst-case coherence, a metric determining the effectiveness of our used approach. Numerical results show that we can significantly and reliably reduce the order of the design complexity while performing very close to the conventional complex optimal equalizers. 2013 IEEE.This work was supported by GSRA from the Qatar National Research Fund (a member of Qatar Foundation) under Grant 2-1-0601-14011. The statements made herein are solely the responsibility of the authors.Scopu

    Iterative (turbo processing) receiver design of OFDM systems in the presence of carrier frequency offset.

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    In this paper, based on the principle of turbo processing, we propose two iterative receiver schemes for carrier fre- quency offset (CFO) compensation in orthogonal frequency division multiplexing (OFDM) systems. Our CFO compensation designs, one in time domain and the other in frequency domain, are based on joint estimation of time-varying channel and CFO. In our schemes, the random CFO problem, a challenge for conventional pilot-aid methods, can be effectively solved using iter- ative (turbo processing) schemes. Furthermore, our comparative study shows that time domain compensation (TDC) is simpler to implement but frequency domain cancellation consisting of an iterative equalizer (FDC-IE) has better bit error rate (BER) performance

    Maximum SINR Synchronization Strategies in Multiuser Filter Bank Schemes

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    We consider synchronization in a multiuser filter bank uplink system with single-user detection. Perfect user synchronization is not the optimal choice as the intuition would suggest. To maximize performance the synchronization parameters have to be chosen to maximize the signal-to-interference-plus-noise ratio (SINR) at each equalizer subchannel output. However, the resulting filter bank receiver structure becomes complex. Therefore, we consider two simplified synchronization metrics that are based on the maximization of the average SINR of a given user or the aggregate SINR of all users. Furthermore, a relaxation of the aggregate SINR metric allows implementing an efficient multiuser analysis filter bank. This receiver deploys two fractionally spaced analysis stages. Each analysis stage is efficiently implemented via a polyphase filter bank, followed by an extended discrete Fourier transform that allows the user frequency offsets to be partly compensated. Then, sub-channel maximum SINR equalization is used. We discuss the application of the proposed solution to Orthogonal Frequency Division Multiple Access (OFDMA) and multiuser Filtered Multitone (FMT) systems

    Advanced DSP Algorithms For Modern Wireless Communication Transceivers

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    A higher network throughput, a minimized delay and reliable communications are some of many goals that wireless communication standards, such as the fifthgeneration (5G) standard and beyond, intend to guarantee for its customers. Hence, many key innovations are currently being proposed and investigated by researchers in the academic and industry circles to fulfill these goals. This dissertation investigates some of the proposed techniques that aim at increasing the spectral efficiency, enhancing the energy efficiency, and enabling low latency wireless communications systems. The contributions lay in the evaluation of the performance of several proposed receiver architectures as well as proposing novel digital signal processing (DSP) algorithms to enhance the performance of radio transceivers. Particularly, the effects of several radio frequency (RF) impairments on the functionality of a new class of wireless transceivers, the full-duplex transceivers, are thoroughly investigated. These transceivers are then designed to operate in a relaying scenario, where relay selection and beamforming are applied in a relaying network to increase its spectral efficiency. The dissertation then investigates the use of greedy algorithms in recovering orthogonal frequency division multiplexing (OFDM) signals by using sparse equalizers, which carry out the equalization in a more efficient manner when the low-complexity single tap OFDM equalizer can no longer recover the received signal due to severe interferences. The proposed sparse equalizers are shown to perform close to conventional optimal and dense equalizers when the OFDM signals are impaired by interferences caused by the insertion of an insufficient cyclic prefix and RF impairments

    Downlink scheduling and resource allocation for 5G MIMO-multicarrier: OFDM vs FBMC/OQAM

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    OAPA The definition of the next generation of wireless communications, so-called 5G networks, is currently underway. Among many technical decisions, one that is particularly fundamental is the choice of the physical layer modulation format and waveform, an issue for which several alternatives have been proposed. Two of the most promising candidates are: (i) orthogonal frequency division multiple (OFDM), a conservative proposal that builds upon the huge legacy of 4G networks, and (ii) filterbank multicarrier/offset quadrature amplitude modulation (FBMC/OQAM), a progressive approach that in frequency selective channels sacrifices subcarrier orthogonality in lieu of an increased spectral efficiency. The comparative merits of OFDM and FBMC/OQAM have been well investigated over the last few years but mostly, from a purely physical layer point of view and largely neglecting how the physical layer performance translates into user-relevant metrics at the upper-layers. This paper aims at presenting a comprehensive comparison of both modulation formats in terms of practical network indicators such as goodput, delay, fairness and service coverage, and under operational conditions that can be envisaged to be realistic in 5G deployments. To this end, a unifying cross-layer framework is proposed that encompasses the downlink scheduling and resource allocation procedures and that builds upon a model of the queueing process at the data-link control layer and a physical layer abstraction that can be chosen to model either OFDM or FBMC/OQAM. Extensive numerical results conclusively demonstrate that most of the apriori advantages of FBMC/OQAM over OFDM do indeed translate into improved network indicators, that is, the increase in spectral efficiency achieved by FBMC/OQAM makes up for the distortion caused by the loss of orthogonality.Peer ReviewedPostprint (published version

    Spatial Frequency Scheduling for Uplink SC-FDMA based Linearly Precoded LTE Multiuser MIMO Systems

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    This paper investigates the performance of the uplink single carrier (SC) frequency division multiple access (FDMA) based linearly precoded multiuser multiple input multiple output (MIMO) systems with frequency domain packet scheduling. A mathematical expression of the received signal to interference plus noise ratio (SINR) for the studied systems is derived and a utility function based spatial frequency packet scheduling algorithms is investigated. The schedulers are shown to be able to exploit the available multiuser diversity in time, frequency and spatial domains
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