33,321 research outputs found
A Wideband Radial Basis Function Decision Feedback Equaliser Assisted Burst-by-Burst Adaptive Modem
No full textThe performance of radial basis function-based decision feedback equalized (RBF DFE) burst-by-burst adaptive quadrature amplitude modulation (AQAM) is presented for transmissions over dispersive wide-band mobile channels. This scheme is shown to give a significant improvement in terms of the mean bit error rate (BER) and bits per symbol (BPS) performance compared to that of the individual fixed modulation modes. The structural equivalence of the RBF DFE to the optimal Bayesian equalizer enables it to potentially outperform the conventional Kalman-filtered AQAM DFE scheme. Index Terms—Adaptive modulation, decision feedback equalization, radial basis function, wide-band modem
Wideband Channel Estimation and Prediction in Single-Carrier Wireless Systems
No full textAbstract—In this contribution wideband channel estimation and prediction designed for single-carrier wideband wireless communications systems are investigated. Specifically, the single-carrier wideband pilot signal received by the receiver is first converted to the frequency-domain. Then, the envelope of the channel transfer function (CTF) is estimated in the frequency-domain, in order to reduce the effects of background noise on the channel prediction step to be invoked. Finally, channel prediction is carried out based on the estimated CTF in the frequency-domain, where a Kalman filter assisted long-range channel prediction algorithm is employed. Our simulation results show that for a reasonable signal-to-noise ratio (SNR) value the proposed frequency-domain based wideband channel estimator is capable of efficiently mitigating the effects of the background noise, hence enhancing the performance of wideband channel prediction
Radial Basis Function Assisted Turbo Equalization
No full textThis paper presents a turbo equalization (TEQ) scheme, which employs a radial basis function (RBF)-based equalizer instead of the conventional trellis-based equalizer of Douillard et al. Structural, computational complexity, and performance comparisons of the RBF-based and trellis-based TEQs are provided. The decision feedback-assisted RBF TEQ is capable of attaining a similar performance to the logarithmic maximum scheme in the context of both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulation, while achieving a factor 2.5 and 3 lower computational complexity, respectively. However, there is a 2.5-dB performance loss in the context of 16 quadrature amplitude modulation (QAM), which suffers more dramatically from the phenomenon of erroneous decision-feedback effects. A novel element of our design, in order to further reduce the computational complexity of the RBF TEQ, is that symbol equalizations are invoked at current iterations only if the decoded symbol has a high error probability. This techniques provides 37% and 54% computational complexity reduction compared to the full-complexity RBF TEQ for the BPSK RBF TEQ and 16QAM RBF TEQ, respectively, with little performance degradation, when communicating over dispersive Rayleigh fading channels. Index Terms—Decision-feedback equalizer (DFE), Jacobian logarithm, neural network, radial basis function (RBF), turbo coding, turbo equalization (TEQ)
Recurrent Neural Network Based Narrowband Channel Prediction
No full textIn this contribution, the application of fully connected recurrent neural networks (FCRNNs) is investigated in the context of narrowband channel prediction. Three different algorithms, namely the real time recurrent learning (RTRL), the global extended Kalman filter (GEKF) and the decoupled extended Kalman filter (DEKF) are used for training the recurrent neural network (RNN) based channel predictor. Our simulation results show that the GEKF and DEKF training schemes have the potential of converging faster than the RTRL training scheme as well as attaining a better MSE performance
Burst-by-Burst Adaptive Turbo-Coded Radial Basis Function-Assisted Decision Feedback Equalization
No full textThe performance of the proposed radial basis function (RBF) assisted turbo-coded adaptive modulation scheme is characterized in a wideband channel scenario. We commence by introducing the novel concept of the Jacobian RBF equalizer, which is a reduced-complexity version of the conventional RBF equalizer. Specifically, the Jacobian logarithmic RBF equalizer generates its output in the logarithmic domain and hence it can be used to provide soft outputs for the turbo-channel decoder. We propose using the average magnitude of the log-likelihood ratio (LLR) of the bits in the received transmission burst before channel decoding as the channel quality measure for controlling the mode-switching regime of our adaptive scheme
Coded Modulation Assisted Radial Basis Function Aided Turbo Equalisation for Dispersive Rayleigh Fading Channels
No full textIn this contribution a range of Coded Modulation (CM) assisted Radial Basis Function (RBF) based Turbo Equalisation (TEQ) schemes are investigated when communicating over dispersive Rayleigh fading channels. Specifically, 16QAM based Trellis Coded Modulation (TCM), Turbo TCM (TTCM), Bit-Interleaved Coded Modulation (BICM) and iteratively decoded BICM (BICM-ID) are evaluated in the context of an RBF based TEQ scheme and a reduced-complexity RBF based In-phase/Quadrature-phase (I/Q) TEQ scheme. The Least Mean Square (LMS) algorithm was employed for channel estimation, where the initial estimation step-size used was 0.05, which was reduced to 0.01 for the second and the subsequent TEQ iterations. The achievable coding gain of the various CM schemes was significantly increased, when employing the proposed RBF-TEQ or RBF-I/Q-TEQ rather than the conventional non-iterative Decision Feedback Equaliser - (DFE). Explicitly, the reduced-complexity RBF-I/Q-TEQ-CM achieved a similar performance to the full-complexity RBF-TEQ-CM, while attaining a significant complexity reduction. The best overall performer was the RBF-I/Q-TEQ-TTCM scheme, requiring only 1.88~dB higher SNR at BER=10-5, than the identical throughput 3~BPS uncoded 8PSK scheme communicating over an AWGN channel. The coding gain of the scheme was 16.78-dB
Student Expectations in the New Millennium
No full textHigher education has experienced vast changes as a result of global political and economic developments. Cultural and social changes in the last decade have also added to the continuing evolution of higher education. These changes inevitably lead to changing expectations of students entering higher education. An adequate understanding of student expectations is crucial in ensuring a good fit between higher educational institutions and their students. This study attempts to carry out a baseline descriptive-quantitative research on student expectations in the higher education of Hong Kong. Four scales have been developed to measure students’ attitude toward: 1. job-oriented curriculum design, 2. user-friendly course delivery method, 3. opportunities for lifelong learning, and 4. student consumerism. Students’ priority of what makes a good university, their reasons for going to university, and their self-perception of ability to cope with university life are also explored. The Student Expectations Questionnaire (developed by the author) was used to gather data from 857 first-year undergrads from nine institutions of higher education in Hong Kong. Analyses include, among others, gender, age, major of study as well as institution comparisons
The urban interior
No full textDuring the pandemic, the house was the place of isolation, the headquarters of lock-down - but as the overall situation is improving we need to solve this paradigma. The introverse environment of the interior of a house gets reflected into the outer public space, with the Interior as a metaphor for the Urban landscape, in which the precedent private spaces are mirrored back into the outside world. Rooms of the house - such as the kitchen, the living room, and the office - keep their character but are transformed into outdoor spaces and services to bridge the gaps and lacks that we suffered during the pandemic: a new gathering opportunity for citizens in the form of a safe environment, which can be shaped according to personal and groups' needs and that relies on a participatory design. A prototype, suitable to different contexts, which can be assembled and which is not only designed FOR people but also BY people.
This historical moment shaped our minds, our necessities, and our spaces: now it's our turn!
The flow is ready, are you
Origin of the Placer Gold of the Barkerville Area, Cariboo District, British Columbia, Canada:
No full textW. L. Uglow and W. A. Johnston.In: Economic Geology. -- Vol. 18. no 6 (1923)
Reduced Complexity In-Phase/Quadrature-Phase M-QAM Turbo Equalization Using Iterative Channel Estimation
No full textA reduced complexity trellis-based turbo equalizer known as the in-phase (I)/quadrature-phase (Q) turbo equalizer (TEQ-IQ) invoking iterative channel impulse response (CIR) estimation is proposed. The underlying principle of TEQ-IQ is based on equalizing the I and Q component of the transmitted signal independently. This requires the equalization of a reduced set of separate I and Q signal components in comparison to all of the possible I/Q phasor combinations considered by the conventional trellis-based equalizer. It was observed that the TEQ-IQ operating in conjunction with iterative CIR estimation was capable of achieving the same performance as the full-complexity conventional turbo equalizer (TEQ-CT) benefiting from perfect CIR information for both 4- and 16-quadrature amplitude modulation (QAM) transmissions, while attaining a complexity reduction factor of 1.1 and 12.2, respectively. For 64-QAM, the TEQ-CT receiver was too complex to be investigated by simulation. However, by assuming that only two turbo equalization iterations were required, which is the lowest possible number of iterations, the complexity of the TEQ-IQ was estimated to be a factor of 51.5 lower than that of the TEQ-CT. Furthermore, at BER = 10-3 the performance of the TEQ-IQ 64-QAM receiver using iterative CIR estimation was only 1.5 dB away from the associated decoding performance curve of the nondispersive Gaussian channel. <br/
- …
