Quasi-static Fading Channels Research Articles

RS-Coded Cooperation Scheme Based on 2 × 2 Labeling Diversity

This paper investigates the novel labeling diversity (LD) technique with two transmit antennas and receive antennas applied in the Reed-Solomon coded cooperative (RSCC) system to propose a novel RSCC-LD scheme over the Rayleigh quasi-static fading and frequency-flat fast-fading channels. Two separate RS codes over the same Galois field are deployed at the source and relay terminals, respectively with the relay RS code providing more extra redundancy. To optimize the use of the information contained in two RS codes, a novel joint decoding approach is developed at the destination terminal. The results of numerical simulation demonstrate that the proposed RSCC-LD has an obviously better performance than the non-cooperative RS coding scheme and RSCC scheme without LD. Furthermore, the performance of the RSCC-LD reveals the superiority of some other existing schemes.

Resource Allocation for OFDM-Based Status Update Systems: A Timeliness Perspective

Increasingly more time-sensitive applications emerge in Internet of things (IoT), requiring fresh status updates. Efficient resource allocation is critical for improving the timeliness of information. This paper investigates how to allocate bandwidth and configure the transmission in an orthogonal frequency division multiplexing (OFDM)-based IoT systems for timely status updating. Specifically, a general resource allocation problem is formulated using age of information (AoI) as the timeliness metric. We first consider a static channel case where we propose a fixed time slot length policy, a fixed blocklength policy, an iterative optimization algorithm, and an approximate optimal policy to address the optimal resource allocation and transmission configuration. Then, we extend the study to quasi-static fading channel cases. In particular, sticking to the transmission rate and spectral efficiency, the four policies designated for static channel case are tailored for the quasi-static fading channel case. We show that the iterative algorithms can improve the timeliness of the system significantly. Besides, the approximate optimal policy achieves an AoI performance competitive with the iterative algorithm, while reduces the computation complexity in both channel cases.

Secrecy Performance Evaluation of Scalable Cell-Free Massive MIMO Systems: A Stochastic Geometry Approach

This paper presents the first performance analysis of physical layer downlink secure transmissions in a scalable cell-free massive MIMO (SCF-mMIMO) system. A stochastic geometry approach is used to model the locations of the access points (APs), user equipments (UEs) and eavesdroppers (Eves) as independent homogeneous Poisson point processes (HPPPs). In addition to applying maximum ratio transmission (MRT) to send the confidential messages, null-space artificial noise is also injected for secrecy enhancement. We analytically characterize the secrecy performance in terms of both the outage-based secrecy transmission rate (STR) and the ergodic secrecy rate (ESR), appropriate for slow quasi-static fading channels and fast block-fading channels, respectively. By utilizing moment matching and Gil-Pelaez inversion theorem, we are able to obtain mathematically tractable approximations for the performance metrics. These approximations are shown to have high accuracy as compared to simulation results. Our numerical results reveal useful design insights that cannot be inferred from existing studies. These insights answer important questions such as whether it is best to deploy as many APs each with fewer antennas and to what extent the artificial noise insertion is beneficial.

Goodput Maximization With Quantized Feedback in the Finite Blocklength Regime for Quasi-Static Channels

In this paper, we study a quantized feedback scheme to maximize the goodput of a finite blocklength communication scenario over a quasi-static fading channel. It is assumed that the receiver has perfect channel state information (CSI) and sends back the CSI to the transmitter over a resolution-limited error-free feedback channel. With this partial CSI, the transmitter is supposed to select the optimum transmission rate, such that it maximizes the overall goodput of the communication system. This problem has been studied for the asymptotic blocklength regime, however, no solution has so far been presented for finite blocklength. Here, we study this problem in two cases: with and without constraint on reliability. We first formulate the optimization problems and analytically solve them. Iterative algorithms that successfully exploit the system parameters for both cases are presented. It is shown that although the achievable maximum goodput decreases with shorter blocklengths and higher reliability requirements, significant improvement can be achieved even with coarsely quantized feedback schemes.

Adaptive Coding and Channel Shaping Through Reconfigurable Intelligent Surfaces: An Information-Theoretic Analysis

A communication link aided by a reconfigurable intelligent surface (RIS) is studied in which the transmitter can control the state of the RIS via a finite-rate control link. Channel state information (CSI) is acquired at the receiver based on pilot-assisted channel estimation, and it may or may not be shared with the transmitter. Considering quasi-static fading channels with imperfect CSI, capacity-achieving signalling is shown to implement joint encoding of the transmitted signal and of the response of the RIS. This demonstrates the information-theoretic optimality of RIS-based modulation, or "single-RF MIMO" systems. In addition, a novel signalling strategy based on separate layered encoding that enables practical successive cancellation-type decoding at the receiver is proposed. Numerical experiments show that the conventional scheme that fixes the reflection pattern of the RIS, irrespective of the transmitted information, as to maximize the achievable rate is strictly suboptimal, and is outperformed by the proposed adaptive coding strategies at all practical signal-to-noise ratio (SNR) levels.

Adaptive Coding and Channel Shaping Through Reconfigurable Intelligent Surfaces: An Information-Theoretic Analysis

A communication link aided by a reconfigurable intelligent surface (RIS) is studied in which the transmitter can control the state of the RIS via a finite-rate control link. Channel state information (CSI) is acquired at the receiver based on pilot-assisted channel estimation, and it may or may not be shared with the transmitter. Considering quasi-static fading channels with imperfect CSI, capacity-achieving signalling is shown to implement joint encoding of the transmitted signal and of the response of the RIS. This demonstrates the information-theoretic optimality of RIS-based modulation, or “single-RF MIMO” systems. In addition, a novel signalling strategy based on separate layered encoding that enables practical successive cancellation-type decoding at the receiver is proposed. Numerical experiments show that the conventional scheme that fixes the reflection pattern of the RIS, irrespective of the transmitted information, as to maximize the achievable rate is strictly suboptimal, and is outperformed by the proposed adaptive coding strategies at all practical signal-to-noise ratio (SNR) levels.

Covert Wireless Communications Under Quasi-Static Fading With Channel Uncertainty

Covert communications enable a transmitter to send information reliably in the presence of an adversary, who looks to detect whether the transmission took place or not. We consider covert communications over quasi-static block fading channels, where users suffer from channel uncertainty. We investigate the adversary Willie’s optimal detection performance in two extreme cases, i.e., the case of perfect channel state information (CSI) and the case of channel distribution information (CDI) only. It is shown that in the large detection error regime, Willie’s detection performances of these two cases are essentially indistinguishable, which implies that the quality of CSI does not help Willie in improving his detection performance. This result enables us to study the covert transmission design without the need to factor in the exact amount of channel uncertainty at Willie. We then obtain the optimal and suboptimal closed-form solution to the covert transmission design. Our result reveals fundamental difference in the design between the case of quasi-static fading channel and the previously studied case of non-fading AWGN channel.

Performance of Full Rate Non-Orthogonal STBC in Spatially Correlated MIMO Systems

Spatial correlation is a crucial impairment for practical Multiple Input Multiple Output (MIMO) wireless communication systems. It is important to consider spatial correlation between antennas in actual communication scenario at both sides, i.e. transmit and receive side. Furthermore, we have considered nonorthogonal full rate STBC in MIMO systems equipped with four transmit antennas and four receive antennas in a quasi-static Rayleigh fading channel. In this paper, Bit Error Rate (BER) performance of full rate non-orthogonal Space Time Block code (STBC) is obtained using simulations in MIMO wireless communication systems. Spatial correlation is assumed between antennas at both the transmitter and the receiver sides. For this analysis, we have considered various transmit antenna spacing values of d t = 0.1π, 0.2π, and 0.4π keeping fixed d r = 0.1π and various receive antenna spacing values of d r = 0.1π, 0.2π, and 0.4π keeping fixed d t = 0.1π. The obtained results show that the transmitting diversity is more serious than the receiving diversity in the spatially correlated antenna environment for the specified signal-to-noise ratio. This study will be useful for actual wireless communication implementation where spatial correlation antennas are present in the practical environment of the MIMO wireless communication system.

On the Secrecy Performance and Power Allocation in Relaying Networks With Untrusted Relay in the Partial Secrecy Regime

Recently, three useful secrecy metrics based on the partial secrecy regime were proposed to analyze secure transmissions on wireless systems over quasi-static fading channels, namely: generalized secrecy outage probability, average fractional equivocation, and average information leakage. These metrics were devised from the concept of fractional equivocation, which is related to the decoding error probability at the eavesdropper, so as to provide a comprehensive insight on the practical implementation of wireless systems with different levels of secrecy requirements. Considering the partial secrecy regime, in this paper we examine the secrecy performance of an amplify-and-forward relaying network with an untrusted relay node, where a destination-based jamming is employed to enable secure transmissions. In this regard, a closed-form approximation is derived for the generalized secrecy outage probability, and integral-form expressions are obtained for the average fractional equivocation and the average information leakage rate. Additionally, equal and optimal power allocation schemes are investigated and compared for the three metrics. From this analysis, we show that different power allocation approaches lead to different system design criteria. The obtained expressions are validated via Monte Carlo simulations.

Block-Level Utility Maximization for NOMA-Based Layered Broadcasting

Layered transmission is studied in this paper to accommodate various device capabilities and channel conditions. The problem of efficiently broadcasting a common set of layer-encoded data from a single base station to multiple users over quasi-static fading channels is examined. Considering the maximum tolerable delay, a block-level utility is defined in terms of average probability of successful reception of each layer. Based on non-orthogonal multiple access scheme, we propose a complete algorithm to jointly optimize power allocation and transmission rates. By utilizing the idea of opportunistic scheduling, we first derive the success probability of one single layer in homogeneous scenarios, then extend the results to heterogeneous scenarios where users are subject to different channel statistics. The multi-layer optimization is realized by iteratively repeating the single-layer operations. Starting from the base layer, we first choose an optimal subset of users as the corresponding target group, then apply the single-layer allocation process until no power resources are left. Computer simulation and discussion confirm that our method maximizes the block-level utility at the same time balances the tradeoff between multiuser diversity gain and multicast gain.

On Numerical Evaluation of Packet-Error Rate for Binary Phase-Modulated Signals Reception over Generalized-K Fading Channels

We present a numerical evaluation of packet error rate (PER) for digital binary phase modulations over wireless communication channels. The analysis is valid for a quasistatic fading communication channel, where multipath fading and shadowing appear simultaneously. The approach is based on numerical evaluation of signal-to-noise ratio threshold that is further used in PER computation. We analyze the threshold and PER dependence on signal power, multipath fading and shadowing severity, as well as packet length.

Statistical QoS provisioning for MTC networks under finite blocklength

This paper analyzes the effective capacity of delay-constrained machine-type communication (MTC) networks operating in the finite blocklength regime. First, we derive a closed-form mathematical approximation for the effective capacity in quasi-static Rayleigh fading channels. We characterize the optimum error probability to maximize the concave effective capacity function with reliability constraint and study the effect of signal-to-interference-plus-noise ratio (SINR) variations for different delay constraints. The trade-off between reliability and effective capacity maximization reveals that we can achieve higher reliability with limited sacrifice in effective capacity specially when the number of machines is small. Our analysis reveals that SINR variations have less impact on effective capacity for strict delay-constrained networks. We present an exemplary scenario for massive MTC access to analyze the interference effect proposing three methods to restore the effective capacity for a certain node which are power control, graceful degradation of delay constraint, and joint compensation. Joint compensation combines both power control and graceful degradation of delay constraint, where we perform the maximization of an objective function whose parameters are determined according to the delay and SINR priorities. Our results show that networks with stringent delay constraints favor power controlled compensation, and compensation is generally performed at higher costs for shorter packets.

An Expurgated Union Bound of Punctured Space-Time Turbo Codes

This paper presents a new technique to obtain an expurgated union bound on the frame error rate of punctured space-time turbo codes (STTuC) in quasi-static Rayleigh fading channels. The STTuC scheme is composed of two component space-time trellis encoders connected in parallel via an interleaver. An adjacent matrix of an augmented state diagram is defined which allows the enumeration of each punctured component encoder. The distance spectrum of the STTuC is then obtained using the concept of uniform interleaver. A method to identify the dominant error events is proposed and an expurgated union bound on the frame error rate of STTuC schemes is computed using these dominant error events. Comparisons with simulated results reveal that the expurgated union bound is tight for codes with different construction criteria for a wide range of signal to noise ratio.

Design of Distributed Protograph LDPC Codes for Multi-Relay Coded-Cooperative Networks

This paper studies protograph low-density parity-check coded cooperation (CC) schemes for two-hop multi-relay systems with $L$ relays over Nakagami- $m$ quasi-static fading (QSF) channels. We propose two CC schemes, namely schemes I and II, with different maximum code rates to satisfy different transmission requirements. We further design a family of distributed rate-compatible root-protograph (RCRP) codes to achieve full diversity in CC-based multi-relay QSF channels. In particular, our RCRP codes with $L+1$ sub-codewords can realize full diversity in scheme I, and our RCRP codes with two sub-codewords can achieve full diversity in scheme II with a maximum-ratio combiner. In addition, we estimate the asymptotic word error rate and bit error rate of our RCRP codes using a generalized protograph extrinsic information transfer algorithm, which is able to characterize the error performance of finite-length codewords accurately. Analysis and simulation show that our RCRP codes can achieve outage-limit-approaching performance in both multi-relay CC architectures. This makes the RCRP coding framework extremely attractive for multi-relay cooperative communication applications with slow-varying fading.

Trellis Code Design of Block Interleaved CIOD-STBCs for Time Varying Channels

A trellis-code design scheme is proposed for a coordinate interleaved orthogonal design space-time block code (CIOD-STBC) system employing a time interleaver. The pairwise error probability (PEP) for the block interleaved CIOD-STBC is analytically derived, and the PEPs are evaluated to search the best systematic feedback encoder to provide the maximum diversity and coding gain for several numbers of states. We expand the signal set such that the expanded set has the same transmit symbol set to keep both the bandwidth and the peak-to-average power ratio the same as the uncoded system. It is noteworthy that the proposed system provides approximately 9-dB SNR gain over the uncoded system at bit error rate ${10^{-5}}$ in the quasi-static Rayleigh fading channel with 32 state trellis coded CIOD. Simulation results are also provided to verify the theoretical analysis.

Artificial Noise Injection for Securing Single-Antenna Systems

We propose a novel artificial noise (AN) injection scheme for wireless systems over quasi-static fading channels, in which a single-antenna transmitter sends confidential messages to a half-duplex receiver in the presence of an eavesdropper. Different from classical AN injection schemes, which rely on a multi-antenna transmitter or external helpers, our proposed scheme is applicable to the scenario where the legitimate transceivers are very simple. We analyze the performance of the proposed scheme and optimize the design of the transmission. Our results highlight that perfect secrecy is always achievable by properly designing the AN injection scheme.

Effects of CEE and Feedback Error on Performance for AF-ORS with PSA-CE Schemes Over Quasi-Static Rayleigh Fading Channels

In this paper, we propose the analytical approach for amplify-and-forward (AF) opportunistic relaying schemes (ORS). When operation of AF-ORS consists of relay selection and data transmission phases based on pilot symbol assisted-channel estimation (PSA-CE) methods over quasi-static Rayleigh fading channels, we show that the relay selection phase can be implemented by pilots symbols transmission for source-relay and relay-destination. Moreover, the feedback method for the selected relay index is proposed to have a simple fashion. Then, we investigate the effects of both a channel estimation error and an estimated noise variance, which are obtained by PSA-CE methods, on the received signal-to-noise ratio (SNR). The average SNR loss is also derived in terms with the number of pilots in PSA-CE methods. Moreover, the average symbol error rate, the outage probability, and the normalized channel capacity of the ORS are derived in approximated closed-form expressions for an arbitrary link SNR when the channel state information in the source-relay-destination link is estimated based on transmitted pilots symbols. As the number of pilot symbols, the derived analytical approach is verified, and by comparing it with simulation results, the accuracy is demonstrated. In addition, it is verified that the effect of the feedback error can be neglected for PAS-CE methods over quasi-static fading channels.

Performance of LTE-A Full Rate and Full Diversity STBC under Real Scattered Environment

Objectives/Background: In Long Term Evaluation- Advance (LTE-A), there are different specialized elements accessible like odd time slots transmission, use of adaptive modulation etc. Notwithstanding, the BER performance analysis is required in genuine scattered environment like spatially correlated antennas at transmitter side and blemished channel state information accessible at the receiver (CSIR) for adaptive modulation. Method/Statistical Analysis:We are exhibiting Bit Error Rate (BER) performance of LTE-A full rate full diversity STBC under quasi-static fading channels with real practical assumption of spatially correlated antennas at transmitter side and blemished channel state information accessible at the receiver (CSIR). The spatial correlation between two antennas is supposed to be , where is spatial correlation among two transmit antennas and imperfe

Non-Data-Aided Measurement of Noise Variance for OFDM System in Frequency-Selective Channels

In this paper, we propose a non-data-aided (NDA) method to estimate the noise variance for orthogonal frequency division multiplexing (OFDM) system in frequency-selective channels. The proposed method is developed based on the signal correlation introduced by the use of the cyclic prefix (CP) and uses the difference between two discrete Fourier transform (DFT) outputs in the CP interval to estimate the noise variance. Analytical result shows that the obtained noise variance is an unbiased estimate in a quasi-static fading channel. Simulation results show that, even in the case in which the maximum delay spread is equal to the CP length and the channel is not quasi-static, the proposed method still works well.

On Secrecy Metrics for Physical Layer Security Over Quasi-Static Fading Channels

Theoretical studies on physical layer security often adopt the secrecy outage probability as the performance metric for wireless communications over quasi-static fading channels. The secrecy outage probability has two limitations from a practical point of view: a) it does not give any insight into the eavesdropper's decodability of confidential messages; b) it cannot characterize the amount of information leakage to the eavesdropper when an outage occurs. Motivated by the limitations of the secrecy outage probability, we propose three new secrecy metrics for secure transmissions over quasi-static fading channels. The first metric establishes a link between the concept of secrecy outage and the decodability of messages at the eavesdropper. The second metric provides an error-probability-based secrecy metric which is typically used for the practical implementation of secure wireless systems. The third metric characterizes how much or how fast the confidential information is leaked to the eavesdropper. We show that the proposed secrecy metrics collectively give a more comprehensive understanding of physical layer security over fading channels and enable one to appropriately design secure communication systems with different views on how secrecy is measured.