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This paper proposes an analytical framework and a system of distortion-aware receiver structures for single-carrier uplink hybrid beamforming-based multiple-input-multiple-output (MIMO) channels. Proposed single-user processing units cooperate at the base station (BS) in an iterative manner for multi-user symbol detection under hardware impairments. Firstly, in the proposed system, an iterative nonlinear interference cancellation (nIC) based on feedforward neural network (NN) modeling is developed to eliminate the nonlinear distortion effects of power amplifiers (PAs). Furthermore, depending on the fading pattern of the instantaneous channel, it is analytically shown that a large gain may be applied to the distortion signal during the equalization stage, which yields distortion amplification causing a significant decrease in the signal-to-distortion-plus-noise ratio (SDNR). A reduced complexity distortion aware detector, based on a bank of fractionally delayed iterative block decision feedback equalization (IB-DFE) receivers, is introduced to adjust the combiner weights for fractionally delayed IB-DFE outputs so that distortion power is minimized before detection. Consequently, multi-user detection capability is enhanced considerably. Secondly, an asymptotic SDNR analysis is performed. The theoretical analysis, verified via numerical evaluations, clearly shows that distortion amplification limits the achievable SDNR at the BS, and the proposed reduced complexity multi-user receiver architecture improves the BER performance by effectively mitigating this effect. • Fractionally delayed FDE bank for hybrid MIMO systems. • Low complexity nonlinear distortion aware receiver for MU hybrid MIMO systems. • Performance evaluation for hybrid MIMO systems impaired by nonlinear PAs. [ABSTRACT FROM AUTHOR]

Underwater acoustic digital communications suffer from inter-symbol interference deriving from signal distortions caused by the channel propagation. Facing such kind of impairment becomes particularly challenging when dealing with shallow water scenarios characterized by short channel coherence time and large delay spread caused by time-varying multipath effects. Channel equalization operated on the received signal represents a crucial issue in order to mitigate the effect of inter-symbol interference and improve the link reliability. In this direction, this contribution presents a preliminary performance analysis of acoustic digital links adopting pulse position modulation in severe multipath scenarios. First, we show how the spectral redundancy offered by pulse position modulated signals can be fruitfully exploited when using fractional sampling at the receiver side, which is an interesting approach rarely addressed by the current literature. In this context, a novel blind equalization scheme is devised. Specifically, the equalizer is blindly designed according to a suitably modified Bussgang scheme in which the zero-memory nonlinearity is replaced by a M-memory nonlinearity, M being the pulse position modulation order. Numerical results not only confirm the feasibility of the technique described here, but also assess the quality of its performance. An extension to a very interesting complex case is also provided.

This paper presents a novel space-time recursive least-squares adaptive algorithm, which performs filter coefficients updates in space and postponed filtering in time. The algorithm is used for intersymbol interference suppression in optical camera communications, which is a subgroup of visible light communication systems. Optical camera communications uses image sensor receivers, as those available in smartphones, tablets, and laptops, to detect changes in light intensity in order to allow data transmission. The achievable data transmission rate of optical camera communication systems is nowadays constrained by the frame-per-second rate achieved by those devices, so that the spatial dimension, e.g., multiple-input multiple-output techniques, are typically exploited. Spatial intersymbol interference could arise and image blurring can be an issue especially when the link distance grows and/or when the receiver is in mobility. We present here a semiblind spatial fractionally spaced equalizer that uses a novel space-time recursive least-square adaptive algorithm to counteracts the blur introduced by the optical channel. Numerical results show how the bit error rate can be drastically reduced in both motion and out-of-focus blur scenarios. [ABSTRACT FROM PUBLISHER]

This paper considers the problem of lossy compression for the computation of a function of two correlated sources, both of which are observed at the encoder. Due to presence of observation costs, the encoder is allowed to observe only subsets of the samples from both sources, with a fraction of such sample pairs possibly overlapping. The rate-distortion function is characterized for memoryless sources, and then specialized to Gaussian and binary sources for selected functions and with quadratic and Hamming distortion metrics, respectively. The optimal measurement overlap fraction is shown to depend on the function to be computed by the decoder, on the source statistics, including the correlation, and on the link rate. Special cases are discussed in which the optimal overlap fraction is the maximum or minimum possible value given the sampling budget, illustrating non-trivial performance trade-offs in the design of the sampling strategy. Finally, the analysis is extended to the multi-hop set-up with jointly Gaussian sources, where each encoder can observe only one of the sources. [ABSTRACT FROM AUTHOR]

To achieve diversity with a single antenna, fractional sampling has been proposed. The imaging component of a desired signal must be transmitted by increasing the baseband filter bandwidth. This paper proposes and evaluates a system in which the imaging component is transmitted on the adjacent channel to the desired signal. The adjacent channel interference is cancelled by the precoding generated based on the basis of the channel state information of all the terminals. In this paper, the performance with perfect feedback and limited feedback is evaluated. Numerical results obtained through computer simulation show that the proposed scheme with a 6 bit random codebook for QPSK modulation improves the performance compared with that with the conventional scheme in the low $$E_b/N_0$$ region. [ABSTRACT FROM AUTHOR]

In impulse-radio or DS/SS UWB communications, a prerake scheme has been proposed to achieve path diversity while reducing computational complexity in a mobile terminal. On the other hand, in an OFDM system, fractional sampling (FS) has been proposed to achieve path diversity with a single antenna. However, in the FS-OFDM system, it is necessary to oversample a received signal that leads to larger power consumption in the terminal side. In this paper, a precoded transmit path diversity scheme in an OFDM system has been proposed. The proposed scheme can achieve path diversity without oversampling the received signal. [ABSTRACT FROM AUTHOR]

This paper considers the problem of blind adaptive equalization of infinite impulse response (IIR) channels without requiring the channel diversity condition. That is, the subchannels in the fractionally sampled model can have common factors. We analyze the case of two parallel channels, and develop an equalizer based on IIR prediction of the received signal. The predictor parameters are estimated by using the recursive extended least squares (RELS) algorithm. It is proved that with probability one the adaptive equalizer is globally stable, the parameter estimates are consistent, and the prediction error converges toward a scalar multiple of the input symbol sequence. [ABSTRACT FROM AUTHOR]

Many useful relations between the Gabor transform (GT) and the fractional Fourier transform (FRFT) have been derived. First, we find that, like the Wigner distribution function (WDF), the FRFT is also equivalent to the rotation operation of the GT. Then, we show that performing the scaled inverse Fourier transform (WI) along an oblique line of the GT of f(t) can yield its FRFT. Since the GT is closely related to the FRFT, we can use it for analyzing the characteristics of the FRFT. Compared with the WDF, the GT does not have the cross-term problem. This advantage is important for the applications of filter design, sampling, and multiplexing in the FRFT domain. Moreover, we find that if the GT is combined with the WDF, the resultant operation [called the Gabor-Wigner transform (GWT)] also has rotation relation with the FRFT. We also derive the general form of the linear distribution that has rotation relation with the FRFT. [ABSTRACT FROM AUTHOR]

Underwater acoustic digital communications suffer from inter-symbol interference deriving from signal distortions caused by the channel propagation. Facing such kind of impairment becomes particularly challenging when dealing with shallow water scenarios characterized by short channel coherence time and large delay spread caused by time-varying multipath effects. Channel equalization operated on the received signal represents a crucial issue in order to mitigate the effect of inter-symbol interference and improve the link reliability. In this direction, this contribution presents a preliminary performance analysis of acoustic digital links adopting pulse position modulation in severe multipath scenarios. First, we show how the spectral redundancy offered by pulse position modulated signals can be fruitfully exploited when using fractional sampling at the receiver side, which is an interesting approach rarely addressed by the current literature. In this context, a novel blind equalization scheme is devised. Specifically, the equalizer is blindly designed according to a suitably modified Bussgang scheme in which the zero-memory nonlinearity is replaced by a M-memory nonlinearity, M being the pulse position modulation order. Numerical results not only confirm the feasibility of the technique described here, but also assess the quality of its performance. An extension to a very interesting complex case is also provided. [ABSTRACT FROM AUTHOR]