Single-input Single-output Channels Research Articles

Feedback Approach for the Relay Channel with Noisy Feedback and Its Security Analysis.

Relay channels capture the essence of several important communication scenarios such as sensor network and satellite communication. In this paper, first, we propose an efficient coding scheme for an additive white Gaussian noise (AWGN) relay channel in the presence of AWGN feedback, which generalizes the conventional scheme for the AWGN relay channel with noiseless feedback by introducing a lattice-based strategy to eliminate the impact of the feedback channel noise on the performance of the original scheme. Next, we further extend the proposed scheme to the multi-input single-output (MISO) fading relay channel (FRC) with noisy feedback. The key to this extension is to use a pre-coding strategy to transform the MISO channel into a single-input single-output (SISO) channel and applying a two-dimensional lattice coding strategy to deal with the feedback fading channel noise. Finally, we analyze the security performance of our proposed scheme in several cases, and the results of this paper are further illustrated by numerical examples.

Blind MMSE Equalization of SISO IIR Channels Using Oversampling and Multichannel Linear Prediction

In this correspondence, a novel linear prediction based blind equalization algorithm for Single Input Single Output (SISO) IIR channels is proposed. The new algorithm is based on second-order statistics and it does not require channel order estimation. By oversampling the channel output, the SISO channel model is converted to a special Single Input Multiple Output (SIMO) model. Two forward linear predictors with consecutive prediction steps are applied to the subchannel outputs of the SIMO model. It is proved that the partial parameters of the SIMO model can be estimated from the difference between the prediction errors when the length of the predictors is sufficiently large. The sufficient filter length for achieving the optimal prediction is also derived. Based on the estimated parameters, both batch and adaptive Minimum-Mean-Square-Error (MMSE) equalizers are developed. The performance of the proposed equalizers is evaluated by computer simulations and compared with existing algorithms.

Multifrequency Wireless Channel Measurements and Characterization in Large Indoor Office Environments

This paper performs extensive channel measurements and characteristics analysis to investigate large-scale fading (LSF) and small-scale fading (SSF) of wireless local area network (WLAN) channels in large indoor office environments. Multi-frequency single-input single-output (SISO) channel measurements are conducted at 3, 5.5, and 6.5 GHz under the same conditions to explore the frequency dependence of LSF, delay spread (DS), and K-factor (KF). Then, SISO channel measurements with different half-power beamwidths (HPBWs) of antennas are performed at 5.5 GHz in access point (AP) to user equipment (UE) and AP to AP scenarios. The effects of antenna HPBW on LSF, DS, and KF are investigated, thereby inspiring the AP deployment in high density (HD) scenarios. Finally, 32×64 multiple-input multiple-output (MIMO) channel measurements at 5.5 GHz are conducted to study the SSF of the time non-stationarity and multi-link correlation. The time non-stationarity, including the parameters drifting and cluster evolution caused by the movement of the UE, is verified by measurement results. Multi-link correlations are illustrated from perspectives of the angular power spectral density (APSD) and correlation matrix collinearity (CMC). The results show that the distance between users and separation angle can affect the multi-link correlation.

Measurement and Estimation Methodology for EMC and OTA Testing in the VIRC

In recent years, promising results have been reported with the vibrating intrinsic reverberation chamber (VIRC) combining performance and cost-efficiency for electromagnetic compatibility (EMC) measurements. This also makes it a potentially attractive solution for over-the-air (OTA) testing, which is yet to be investigated. Therefore, this article proposes the first systematic and thorough methodology to characterize the VIRC for use in EMC and OTA testing of wireless baseband algorithms of narrow-band single-input single-output channels. This methodology has been developed to measure and estimate the channel first- and second-order temporal and spectral characteristics taking into consideration the effect of different carrier frequencies, rotational speeds of VIRC motors, and loading conditions. It is then applied to a channel setup inside a VIRC for a preliminary investigation before the VIRC itself is fully characterized. It is shown that mounting an absorber in a specific location on the hatch significantly improves the rejection rate of the chi-squared goodness-of-fit test for Rician distribution without increasing the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$K$</tex-math></inline-formula> -factor above <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB over the frequency range 755–2740 MHz in the VIRC under investigation. However, the proposed methodology has been devised to be universal to any reverberation chamber, and the obtained results can be used to improve EMC testing due to the better understanding of the unique VIRC environment.

Accurate Analysis of Implicit SISO Channel Estimation Without DC Offset Using ZCZ Training Sequence

In this letter, an accurate analysis of implicit single-input single-output (SISO) channel estimation is provided. The appropriate correlation properties of the training sequence that result in a closed form solution for the variance of the channel estimate were derived. Indeed, it was shown that only a specific zone in the autocorrelation of the training sequence needs to be equal to zero. As a result, it is now possible to find sequences that simultaneously satisfy the balance and autocorrelation property. In fact, only a special type of sequence called zero correlation zone (ZCZ) sequences have this property and therefore can be used to provide an optimal implicit channel estimation performance when the channel length is inside the zero zone. In addition, by using balanced ZCZ sequences, the harmful Direct Current (DC) offset can be directly removed. Consequently, balanced ZCZ sequences greatly simplifies the implementation of the implicit channel estimation method.

On the Capacity of MISO Optical Intensity Channels With Per-Antenna Intensity Constraints

This paper investigates the capacity of general multiple-input single-output (MISO) optical intensity channels (OICs) under per-antenna peak- and average-intensity constraints. We first consider the MISO equal-cost constrained OIC (EC-OIC), where, apart from the peak-intensity constraint, average intensities of inputs are <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">equal to</i> arbitrarily preassigned constants. The second model of our interest is the MISO bounded-cost constrained OIC (BC-OIC), where, as compared with the EC-OIC, average intensities of inputs are <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">no larger than</i> arbitrarily preassigned constants. By leveraging tools from quantile functions, stop-loss transform and convex ordering of nonnegative random variables, we prove two decomposition theorems for bounded and nonnegative random variables, based on which we equivalently transform both the EC-OIC and the BC-OIC into respective single-input single-output channels under a peak-intensity and several stop-loss mean constraints. Capacity lower and upper bounds for both channels are established, based on which the asymptotic capacity at high and low signal-to-noise-ratio are determined.

Cooperative Spectrum Sensing under SISO and MIMO Environment for Cognitive Radio Networks

Background: Increasing demand for wireless devices leads to the efficient use of spectrum resources. Despite the limited availability of spectrum resources, all licensed users do not utilize their spectrum all the time. Objective: Cognitive Radio (CR) is used to detect free channels in the available spectrum resources and access them dynamically without interfering with licensed users. Various spectrum sensing (SS) techniques are available to sense the spectrum of licensed users. Methods: The spectrum sensing technique, energy detector (ED), is analysed under a Rayleigh fading channel. Further, Single Input Single Output (SISO) and Multiple Input Multiple Output (MIMO) channel models are developed in the consumer environment. The ED technique is further analysed with cooperative spectrum sensing (CSS) to overcome detection problems for a single CR user. Results: The ED achieves a probability of detection (PD) of 0.9 and a probability of false alarm (PFA) of 0.1 at the lowest SNR of −20 dB, which is the requirement for a standard IEEE 802.22 Wireless Regional Area Network (WRAN). Conclusion: Various receiver operating characteristics are determined by conducting practical simulations and theoretical calculations for each SISO and MIMO channel model with and without the CSS scenario to achieve the target PD and PFA .

Capacity Results for Range-Limited SISO and MISO Dimmable VLC Channels

This paper investigates the capacity results of dimmable visible light communications (VLCs) channel under practical range-limited constraints. Upper and lower bounds for both single-input single-output (SISO) and multiple-input single-output (MISO) scenarios which are valid in all signal-to-noise (SNR) region are derived. We reveal that the SISO capacity is a symmetrical function of the dimming target, and is strictly increasing at its left half. Tight MISO upper bounds are obtained by solving non-convex problems, and alternating optimization method is employed with constraint transformations.

On the Capacity of Intensity-Modulation Direct-Detection Gaussian Optical Wireless Communication Channels: A Tutorial

Optical wireless communication (OWC) using intensity-modulation and direct-detection (IM/DD) has a channel model which possesses unique features, due to the constraints imposed on the channel input. The aim of this tutorial is to overview results on the capacity of IM/DD channels with input-independent Gaussian noise as a model of OWC channels. It provides the reader with an entry point to the topic, and highlights some major contributions in this area. It begins with a discussion on channel models and how this IM/DD Gaussian channel model comes about, in addition to an explanation of input constraints. Then, it discusses the capacity of the single-input single-output channel, its computation, and capacity bounds and asymptotic capacity results. Then, it extends the discussion to the multiple-input multiple-output setup, and reviews capacity bounds for this channel model. Finally, it discusses multi-user channels modelled as a broadcast channel (downlink) or a multiple-access channel (uplink), with their associated capacity bounds.

Millimeter wave channel characteristics of outdoor microcellular based on improved ray tracing method and BP neural network algorithm

The millimeter-wave single-input single-output (SISO) channel and single input multiple output (SIMO) channel are modeled and simulated in the outdoor microcellular scenarios at 28 GHz and 39 GHz based on improved ray tracing method and back propagation (BP) neural network algorithm. Based on the simulation data of wireless channel, the propagation characteristics of millimeter wave channel, such as path loss, root-mean-square (RMS) delay spread and received power, are analyzed and researched. The correctness and effectiveness of the improved ray tracing method are verified by comparing the measured results of the published literature with the simulated results. The results of path loss model parameters fitted by BP neural network algorithm are compared with those of path loss parameters simulated by improved ray tracing method. It is found that the results of path loss parameters fitted by BP neural network algorithm are in good agreement with those obtained by simulation of improved ray tracing method, which verifies that BP neural network algorithm can well predict large-scale parameters of outdoor microcellular millimeter-wave channel. Meanwhile, a universal path loss model for 28 GHz and 39 GHz millimeter-wave channels in outdoor microcellular line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios is presented. The results show that the RMS delay spread and received power in LoS scenario are smaller than those in NLoS scenario. The cumulative distribution function (CDF) of RMS delay spread, horizontal direction angle of arrival and the number of multipath clusters in LoS and NLoS scenarios are found to fit the Gaussian distribution properly. As the frequency increases, the RMS delay spread tends to increase, and the cluster of multipath arriving at receivers shows sparsity in the microcellular scenarios at millimeter-wave band.

Optimized Precoded Spatio-Temporal Partial-Response Signaling Over Frequency-Selective MIMO Channels

Due to the continuous demand for higher bit rates, the management of the spatio-temporal intersymbol interference in frequency-selective multiple-input multiple-output (MIMO) channels becomes increasingly important. For single-input single-output channels, equalized precoded partial-response signaling is capable of handling a large amount of intersymbol interference, but, to date, no equalization scheme with general partial-response signaling has been presented for the frequency-selective MIMO channel. Not only does this contribution extend partial-response signaling to the MIMO channel by proposing a general spatio-temporal partial-response precoder, but it also develops a minimum mean-squared-error optimization framework in which the equalization coefficients and the spatio-temporal target response are jointly optimized. Three iterative optimization algorithms are discussed, which update (part of) a row of the target impulse response matrix in each iteration. In particular, the third algorithm reformulates this row optimization as a lattice decoding problem. Numerical simulations confirm that the general partial-response signaling clearly outperforms the traditional full-response signaling in terms of the mean squared error and the bit error rate. The third optimization algorithm has a better performance but a higher complexity, compared to the first and the second algorithm.

Identification of channels with single and multiple inputs and outputs under linear constraints

The channel identification problem for multiple-input multiple-output (MIMO) channels under linear constraints can be formulated as solving a linear system which involves finite-dimensional Gabor matrices and a pre-determined unstructured matrix that represents the linear constraints. While matrices of the latter type are fixed a priori by the constraints, Gabor matrices depend on the choice of their generating windows which is often chosen by the user. This is important since even if the matrix associated with the linear constraints is ill-conditioned, the full system may be solvable if the windows are designed appropriately.We prove that linear constraints consisting of a single equation always remove a single degree of freedom in the channel identification problem, in the sense that preknowledge of such constraints allows identification of MIMO channels with support size one greater than the fundamental limit. However, we give an explicit example showing that this statement does not generalize to the case of multiple constraints. In the single-input single-output (SISO) case, we provide some sufficient conditions on the linear side constraints under which the corresponding SISO channels are identifiable.

Adaptation to the LEDs flicker requirement in visible light communication systems through CE-OFDM signals

Constant-envelope OFDM signals based on electrical phase modulation are proposed in visible light communication (VLC) systems to adapt to the LEDs flicker requirements. Experimental results demonstrate that this peak-to-average power ratio (PAPR) reduction technique thoroughly adapts to the flicker requirements in line-of-sight single-input single-output (SISO) VLC channels, at a cost of performance penalties, as indicated by the numerical evaluations provided in this paper. The performance of a 272.87 Mb/s CE-OFDM system, with 64-QAM subcarrier mapping in a bandwidth of 100 MHz, is compared with the performance of a conventional OFDM system, after propagation through SISO and multiple-input single-output (MISO) VLC channel models. Besides the strong dependence on the phase modulation index 2πh, the simulation results show that, in the SISO scenario, the CE-OFDM technique introduces performance penalties. However, with 2πh=1.3, the phase modulation based scheme outperforms traditional OFDM systems in the MISO architecture, due to the transmission of low PAPR signals.

Sampling and Reconstruction of Multiple-Input Multiple-Output Channels

Based on the recent development of sampling and reconstruction results for slowly time-varying single-input single-output channel operators, we derive sampling results in the multiple-input multiple-output setting where all subchannels satisfy an underspread condition, that is, their spreading functions are supported on individual sets of small measure. At the center of our work is the extension of the single-input single-output dual tiling condition to this setting; it characterizes which periodic weighted delta trains can be used to identify a given class of multiple-input multiple-output channel operators satisfying a spreading support constraint. Building on the dual tiling condition, we compute reconstruction formulas for the operator's symbol in closed form and discuss the problem of identifying multiple-input multiple-output operators where only restrictions in size, but not on location and geometry, of the subchannel spreading supports are known.

A NOMA Scheme for a Two-User MISO Downlink Channel With Unknown CSIT

The notion of non-orthogonal multiple access (NOMA) for 5G essentially relies on the availability of the channel state information at the transmitter (CSIT). Such knowledge is used to judiciously allocate power among users to make their signals separable at their respective receivers while employing successive interference cancellation (SIC). Feeding back the CSI from the users to the BS (transmitter) is obviously bandwidth consuming. Reducing such an overhead is of great importance and has been of interest in recent years. Furthermore, existing NOMA techniques become inapplicable when the CSI is unavailable at the BS. In this case, the BS has only the option of allocating power among users blindly, including equal power splitting, which has been shown to yield poor performance in terms of outage probability and error probability. This motivates us to develop a NOMA scheme that does not require CSI knowledge at the BS. We make use of a nonlinear interference alignment technique that we have proposed recently, namely, interference dissolution, to develop the proposed NOMA scheme, which allows the BS to communicate with two users simultaneously while keeping signals perfectly separable at their respective receivers. We develop the proposed scheme for multiple-input single-output and single-input single-output downlink channels. We analyze the proposed technique analytically in terms of the achievable degrees-of-freedom and achievable rate per user. We show that the proposed NOMA scheme outperforms existing NOMA techniques in terms of the outage probability and error probability.

Secrecy Rate Closed-Form Expressions for the SISO VLC Wiretap Channel With Discrete Input Signaling

We study in this letter the secrecy performance of a degraded single-input single-output visible-light communication wiretap channel. It has been shown in the literature that the secrecy capacity-achieving input distribution for this system is discrete with a finite support set. However, neither the secrecy capacity nor its achieving distribution has been derived in closed-form. In this letter, we derive in closed-form the achievable secrecy rate as a function of the discrete input distribution. We propose a class of discrete input distributions in an effort to enhance the achievable secrecy rate and approach the secrecy capacity. We also derive expressions for the achievable secrecy rate for different scenarios including the one in which the locations of the terminals are randomly located. We provide several examples that demonstrate the accuracy of the derived expressions and show the substantial secrecy rate improvements provided by the proposed scheme over existing ones.

Nested Precoding in MU-MIMO Channels: The Superposition Transmission of Space-Time Coding and Spatial-Division Multiplexing

Nonorthogonal multiple access (NOMA) can improve the spectrum efficiency through reusing the power-level space by different users. Although NOMA in single-input single-output channels has been thoroughly explored, it is still underexploited in multiple-input multiple-output (MIMO) channels. Precoding design in multiuser MIMO channels with nonorthogonal transmission is a multidimensional nesting problem, it is hard to compare two matrix channels if only their power levels are considered. In this paper, we first propose a method to compare the covariance matrices of two channel matrices, and then derive a channel condition under which the linear precoding scheme can achieve the sum capacity. Considering arbitrary realizations of multiuser channels, we provide a nested precoding algorithm that can work well in highly correlated multiuser channels. Based on this idea, a specialized superposition transmission scheme between signaling and data information is proposed, where plenty of resources beneath the signaling signal are utilized to transmit data information for dedicated users, and a large amount of extra rates are achieved. In addition, space-time coding is used for signaling information and spatial-division multiplexing is used for multiuser data information. Under the constraint that signaling information should be correctly decoded at any position in the cell, we seek to maximize the sum rate of the underneath multiuser data streams. To this end, the optimal and a low-complexity simplified precoding algorithms are developed. Finally, simulation results verify the throughput improvement and the correct decoding probability of the signaling information.

Decoupled beamforming techniques for distributed MIMO two-way multi-relay networks with imperfect CSI

This paper investigates decoupled beamforming techniques for the distributed multi-input multi-output (MIMO) two-way relay networks (TWRN) with imperfect channel state informations (CSIs). The objective of this paper is to maximize the weighted sum rate (SR) with semi-infinite relay power constraints. Since the objective problem is difficult to be solved directly, considering the high signal-to-residual-interference-plus-noise ratio (SRINR) and employing the Cauchy-Schwarz inequality and S-lemma, the problem can be approximately converted into a source beamforming decoupled one. In addition, with the optimal relay beamforming design and maximum ratio combining (MRC) at the receiver, the MIMO channels are decoupled into parallel single-input single-output (SISO) channels. By this way, the suboptimal relay beamforming matrix can be efficiently obtained with minimal relay power constraint. Specifically, the semi-infinite constraints can be reformulated into a linear matrix inequality (LMI), which can be efficiently solved by using an alternating optimization algorithm. Numerical results demonstrate that our proposed decoupled beamforming scheme outperforms the existing works in terms of the SR and the computational complexity with satisfactory convergence.

A Triply Selective MIMO Channel Simulator Using GPUs

A methodology for implementing a triply selective multiple‐input multiple‐output (MIMO) simulator based on graphics processing units (GPUs) is presented. The resulting simulator is based on the implementation of multiple double‐selective single‐input single‐output (SISO) channel generators, where the multiple inputs and the multiple received signals have been transformed in order to supply the corresponding space correlation of the channel under consideration. A direct consequence of this approach is the flexibility provided, which allows different propagation statistics to each SISO channel to be specified and thus more complex environments to be replicated. It is shown that under some specific constraints, the statistics of the triply selective MIMO simulator are the same as those reported in the state of art. Simulation results show the computational time improvement achieved, up to 650‐fold for an 8 × 8 MIMO channel simulator when compared with sequential implementations. In addition to the computational improvement, the proposed simulator offers flexibility for testing a variety of scenarios in vehicle‐to‐vehicle (V2V) and vehicle‐to‐infrastructure (V2I) systems.

Performance Analysis of Distributed Single Carrier Systems With Distributed Cyclic Delay Diversity

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain.