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  • 1. Biernacki, Arkadiusz
    et al.
    Tutschku, Kurt
    Blekinge Institute of Technology, School of Computing.
    Comparative Performance Study of LTE Downlink Schedulers2014In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 7, no 2, p. 585-599Article in journal (Refereed)
    Abstract [en]

    Long time evolution (LTE) represents an emerging and promising technology for providing broadband, mobile Internet access. Because of the limitation of available spectrum resource, high spectrum efficiency technologies such as channel-aware scheduling need to be explored. In this work, we evaluate the performance of three scheduling algorithms proposed for LTE downlink transmission. The evaluation takes place in mixed traffic scenarios and aims at exploring strengths and weaknesses of the proposed algorithms. Simulation results illustrate the importance of real-time traffic awareness by schedulers when a specified level of quality of service is required. The research shows that lack of prioritisation of multimedia traffic will lead to severe degradation of video and VoIP services even with a relatively low network load.

  • 2. Duong, Quang Trung
    et al.
    Nguyen, Ngoc-Tien
    Hoang, Trang
    Nguyen, Viet-Kinh
    Pairwise Error Probability of Distributed Space--Time Coding Employing Alamouti Scheme in Wireless Relays Networks2009In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 51, no 2, p. 231-244Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze the pairwise error probability (PEP) of distributed space-time codes, in which the source and the relay generate Alamouti space--time code in a distributed fashion. We restrict our attention to the space-time code construction for Protocol III in [1]. In particular, we derive two closed-form approximations for PEP when the relay is either close to the destination or source and an upper bound for any position of the relay. Using the alternative definition of $Q$-function, we can express these PEPs in terms of finite integral whose integrand is composed of trigonometric functions. We further show that with only one relay assisted source-destination link, system still achieves diversity order of two, assuming single-antenna terminals. We also perform Monte-Carlo simulations to verify the analysis.

  • 3. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Cross-Layer Design for MRT Systems with Channel Estimation Error and Feedback Delay2011In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 58, no 4, p. 681-694Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze the effect of channel estimation error and delayed feedback on the performance of a cross-layer scheme combining adaptive modulation for maximum ratio transmission (MRT) at the physical layer and truncated automatic repeat request (T-ARQ) at the link layer. The cross-layer attempts to maximize the spectral efficiency under predetermined quality of service requirements, namely, delay and packet-loss constraints. In particular, we derive closed-form expressions for the average packet error rate, average achievable spectral efficiency, and the outage probability, hence, enabling to evaluate the performance of the cross-layer scheme in the presence of imperfect channel estimation at the receiver and delayed feedback path between the receiver and transmitter. The final expressions are given in terms of the minimum and maximum number of transceiver antennas as well as the channel estimation error and feedback delay parameters. We further show that with a small amount of channel estimation error and/or feedback delay the system performance is severely degraded. Specifically, numerical results demonstrate that with channel estimation error and feedback delay the performance of the cross-layer scheme is even worse than that of T-ARQ only. We also observe an irreducible outage probability floor appearing in the high signal-to-noise regime.

  • 4.
    Khan, Muhammad Gufran
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Sällberg, Benny
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Nordberg, Jörgen
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Tufvesson, Fredrik
    Claesson, Ingvar
    Blekinge Institute of Technology, School of Engineering, Department of Electrical Engineering.
    Non-Coherent Fourth-Order Detector for Impulse Radio Ultra Wideband Systems: Empirical Evaluation Using Channel Measurements2013In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 68, no 1, p. 27-46Article in journal (Refereed)
    Abstract [en]

    Low-complex and low-power non-coherent energy detectors (EDs) are interesting for low data rate impulse radio (IR) ultra wideband (UWB) systems, but suffer from a loss in performance compared to coherent receivers. The performance of an ED also strongly depends on the integration interval (window size) of the integrator and the window position. This paper presents a non-coherent fourth-order detector (FD) which can discriminate between Gaussian noise signals and non-Gaussian IR-UWB signals by directly estimating the fourth-order moment of the received signal. The performance of the detectors is evaluated using realistic channels measured in a corridor, an office and a laboratory environment. The results show that bit-error-rate (BER) performance of the proposed FD receiver is slightly better than the ED in low signal-to-noise ratio (SNR) region and its performance improves as the SNR increases. In addition, BER of the FD receiver is less sensitive to overestimation of the integration interval making it relatively robust to variations of the channel delay spread. Finally, a criteria for the selection of integration time of the proposed detector is suggested.

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