First-hop-quality-aware dynamic resource allocation for amplify-and-forward opportunistic relaying assisted SC-FDMA

In this paper we exploit the benefits of the diversity gains arising from a cluster of opportunistic relays (OR) and from the independently fading subcarriers of multiple users. Our goal is to improve the energy-efficiency of the OR assisted single-carrier frequency-division multiple-access (SC-FDMA) uplink using amplify-and-forward (AF), where the direct transmission (DT) link is unavailable. By assuming that the pilot aided channel quality information (CQI) of all the users may be exchanged amongst the cooperating relays, we propose two joint dynamic resource allocation (DRA) schemes based on the so-called ’first-hop quality awareness’. Our results demonstrate that compared to the DT benchmark, the proposed joint DRA schemes are capable of achieving a power reduction of 10dB for a single-antenna base station (BS) receiver, albeit for a multi-antenna BS the power-reduction remains more modest

Frequency-Domain Turbo Equalisation in Coded SC-FDMA Systems: EXIT Chart Analysis and Performance

In this paper, we investigate the achievable performance of channel coded single-carrier frequency division multiple-access (SC-FDMA) systems employing various detection schemes, when communicating over frequency-selective fading channels. Specifically, three types of minimum mean-square error (MMSE) based frequency-domain (FD) turbo equalisers are considered. The first one is the turbo FD linear equaliser (LE). The second one is a parallel interference cancellation (PIC)-assisted turbo FD decision-feedback equaliser (DFE). The final one is the proposed hybrid interference cancellation (HIC)-aided turboFD-DFE, which combines successive interference cancellation (SIC) with iterative PIC and decoding. The benefit of interference cancellation (IC) is analysed with the EXtrinsic Information Transfer (EXIT) charts. The performance of the coded SC-FDMA systems employing the above-mentioned detection schemes is investigated with the aid of simulations. Our studies show that the IC techniques achieve an attractive performance at a moderate complexity

The Power of the Situation: Variability and Stability in Chinese University Students’ Willingness to Communicate in English Classrooms

Willingness to communicate (WTC) used to be studied as a relatively stable, trait-like predisposition; however, recent attention has been shifted to more dynamic, state-like components of WTC, i.e. possible fluctuations in state WTC over time. This research investigates variability and stability in both trait and state WTC. It particularly focuses on within-person variability in state WTC, which may lead to stable between-person differences, and situational antecedents that can either promote or hinder state WTC in L2 classrooms. Published research on state WTC was systematically reviewed, and frequently reported situational antecedents of state WTC were organised into a framework composed of three inter-linked layers: situation cues, situation characteristics, and underlying dimensions. Two high-density repeated measurement studies conducted in English classrooms in a Chinese university, investigating whether, how and why state WTC varied during a semester (Study 1) and during a lesson (Study 2), respectively. The two studies found that (a) state WTC varied both within a lesson and across different lessons during a semester; (b) within-person variability in state WTC was systematically related to the situational antecedents proposed in the framework (e.g. support, task-importance, task-interest, etc.); and (c) systematic within-person variability in state WTC predicted English learning performance, particularly in terms of communicative competence. This research provides novel insights into how within-person variability in state-like variables can be studied, and the proposed framework can be used as guidance for future research on state WTC and its situational antecedents. This research also suggests practical strategies for educators and language L2 teachers who would like to facilitate student state WTC by systematically shaping classroom learning situations

Achievable Rate of Rician Large-Scale MIMO Channels with Transceiver Hardware Impairments

Transceiver hardware impairments (e.g., phase noise, in-phase/quadrature-phase (I/Q) imbalance, amplifier non-linearities, and quantization errors) have obvious degradation effects on the performance of wireless communications. While prior works have improved our knowledge on the influence of hardware impairments of single-user multiple-input multiple-output (MIMO) systems over Rayleigh fading channels, an analysis encompassing the Rician fading channel is not yet available. In this paper, we pursue a detailed analysis of regular and large-scale (LS) MIMO systems over Rician fading channels by deriving new, closed-form expressions for the achievable rate to provide several important insights for practical system design. More specifically, for regular MIMO systems with hardware impairments, there is always a finite achievable rate ceiling, which is irrespective of the transmit power and fading conditions. For LS-MIMO systems, it is interesting to find that the achievable rate loss depends on the Rician $K$-factor, which reveals that the favorable propagation in LS-MIMO systems can remove the influence of hardware impairments. However, we show that the non-ideal LS-MIMO system can still achieve high spectral efficiency due to its huge degrees of freedom.Comment: 7 pages, 1 table, 3 figures, accepted to appear in IEEE Transactions on Vehicular Technolog