Optimal Rate Adaptation Research Articles

Analysis of analytical capacity for Fisher–Snedecor F fading channels with different transmission schemes

This Letter presents capacity analysis of Fisher-Snedecor F fading channels under different transmission strategies. To this end, novel analytical expressions are proposed for optimal rate adaptation with constant transmit power, channel inversion with a fixed rate and truncated channel inversion with fixed rate schemes in this Letter. Then, analytical results are illustrated for different fading and shadowing parameter values.

Average SEP and channel capacity analysis over Generic/IG composite fading channels: A unified approach

This paper develops an analytical framework to analyse important performance metrics of the wireless communication system over generic fading channels characterized by α−μ/Inverse Gaussian (IG), η−μ/IG, and κ−μ/IG distributions. The important performance metrics, namely, the outage probability (OP), the amount of fading (AOF), the average symbol error probability (SEP) of coherent and non-coherent schemes, the channel capacity under optimal rate adaptation (ORA), channel inversion with fixed rate (CIFR), and truncated CIFR (TCIFR) policy are analysed. Further, low and high signal-to-noise-ratio (SNR) approximations for channel capacity are presented. Furthermore, for asymptotic analysis the approximate composite probability density function (PDF) at the origin was developed and utilized to derive the closed-form expressions for the average SEP of both coherent and non-coherent modulation schemes with maximal ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) diversity schemes. The proposed asymptotic solutions are simple and can be easily used to describe the system behaviour at high SNR. The correctness of the derived results has been verified by comparing them with Monte Carlo simulations.

A Comprehensive Analysis of the Achievable Channel Capacity in $\mathcal{F}$ Composite Fading Channels

The $\mathcal {F}$ composite fading model was recently proposed as an accurate and tractable statistical model for the characterization of the composite fading conditions encountered in realistic wireless communication scenarios. In the present contribution, we capitalize on the distinct properties of this composite model to derive an analytical framework and then to evaluate the achievable channel capacity over $\mathcal {F}$ composite fading channels under different channel state information (CSI) assumptions. To this end, we first consider that the CSI is known only at the receiver, for which we derive novel analytic expressions for the channel capacity under optimum rate adaptation as well as for the corresponding effective capacity. Then, by considering that the CSI is known both at the transmitter and at the receiver, we derive novel analytic expressions for the channel capacity under optimum power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate. The derived analytic expressions for the considered scenarios are provided in closed-form and benefit from being tractable both analytically and numerically. This enables the derivation of simple bounds as well as approximate and asymptotic expressions, which are shown to be useful as they provide meaningful insights on the effect of fading conditions and/or latency on the overall system performance.

Capacity of dual branch MRC system for correlated imbalanced average SNRs over Nakagami-m fading channels using OPRA scheme

The closed-form expressions of the capacity for dual branch Maximal Ratio Combining (MRC) diversity system with correlated and imbalanced average Signal-to-Noise Ratio (SNRs) over Nakagami-m fading channels are presented. Our approach is based on probability density function to find the mathematical expressions for Optimal Power and Rate Adaptation (OPRA) scheme. Numerically evaluated results are shown and compared with the available capacity results of OPRA scheme in the literature. The effect of different practical constraint i.e. - fade correlation and level of imbalanced in average SNRs on the channel capacity of the systems, is analysed.

Schedule Adaptation for Ensuring Reliability in RT-WiFi-Based Networked Embedded Systems

With the ever-growing interests in applying wireless technologies for networked embedded systems to serve as the communication fabric, many real-time wireless technologies have been recently developed to support time-critical sensing and control applications. We proposed in previous work the RT-WiFi protocol that provides real-time high-speed predictable data delivery and enables designs to meet time-critical industrial needs. However, without explicit reliability enforcement mechanisms, our previous RT-WiFi design is either subject to uncontrolled packet loss due to noise and other interferences or may suffer from inefficient communication channel usage. In this article, we explicitly consider interference from both Wi-Fi and non-Wi-Fi based interference sources and propose two sets of effective solutions for reliable data transmissions in RT-WiFi-based networked embedded systems. To improve reliability against general non-Wi-Fi based interference, based on rate adaptation and retransmission techniques, we present an optimal real-time rate adaption algorithm together with a communication link scheduler that has low network management overhead. A novel technique called overbooking is introduced to further improve the schedulability of the communication link scheduler while maintaining the required communication reliability. For Wi-Fi-based interference, we present mechanisms that utilize virtual carrier sensing to provide reliable data transmission while co-existing with regular Wi-Fi networks. We have implemented the proposed algorithms in the RT-WiFi network management framework and demonstrated the system performance with a series of experiments.

S2VC: An SDN-based framework for maximizing QoE in SVC-based HTTP adaptive streaming

HTTP adaptive streaming (HAS) is quickly becoming the dominant video delivery technique for adaptive streaming over the Internet. Still considered as its primary challenges are determining the optimal rate adaptation and improving both the quality of experience (QoE) and QoE-fairness. Most of the proposed approaches have relied on local information to find a result. However, employing techniques that provide a comprehensive and central view of the network resources can lead to more gains in performance. By leveraging software defined networking (SDN), this paper proposes an SDN-based framework, named S2VC, to maximize QoE metrics and QoE-fairness in SVC-based HTTP adaptive streaming. The proposed framework determines both the optimal adaptation and data paths for delivering the requested video files from HTTP-media servers to DASH clients. In fact, by utilizing an SDN controller and its complete view of the network, we introduce an SVC flow optimizer (SFO) application module to determine the optimal solution in a centralized and time slot fashion. In the current approach, we first formulate the problem as a mixed integer linear programming (MILP) optimization model. The MILP is designed in such a way that it applies defined policies, e.g. setting priorities for clients in obtaining video quality. Secondly, we show that this problem is NP-complete and propose an LP-relaxation model to enable S2VC framework for performing rate adaptation on a large-scale network. Finally, we conduct experiments by emulating the proposed framework in Mininet, with the usage of Floodlight as the SDN controller. In terms of improving QoE-fairness and QoE metrics, the effectiveness of the proposed framework is validated by a comparison with different approaches.

Performance analysis of OFDM based 3-hop AF relaying network over mixed Rician/Rayleigh fading channels

In this paper, performance of an orthogonal frequency division multiplexing (OFDM) based 3-hop variable-gain amplify and forward (AF) relaying network is analyzed over independent and non-identically distributed (i.n.i.d.) mixed Rician/Rayleigh fading environment. Analytical expression of outage probability is derived and diversity order of the considered system is found. Further, average symbol error rate (ASER) expressions of general order hexagonal quadrature amplitude modulation (HQAM), general order rectangular QAM (RQAM) and 32-XQAM are derived. A comparative analysis of ASER for different QAM schemes with different constellations is also presented. Ergodic capacity with optimum rate adaptation is also derived for the considered system model. Further, the impact of Rician K-factor on the performance of the considered system is highlighted. Finally, the derived analytical results are verified through Monte-Carlo simulations for different signal-to-noise ratio (SNR) levels.

Fairness‐adjustable opportunistic relay selection in the power‐constrained cooperative networks with adaptive transmission

The existing literatures have not considered either the fair power consumption in multi-user cooperative networks or the fairness-adjustable relay selection scheme. The authors propose a fairness-adjustable opportunistic relay selection in the multi-user dual-hop decode-and-forward cooperative networks with the optimal simultaneous power and rate adaptation under realistic power constraints, where the selection result is determined by the instantaneous signal-to-noise ratios over the relay links, the power load (PL) of the relays and the weight factor. The weight factor, also behaving as the metric of fairness, is introduced to adjust the bias between the average channel capacity for the relaying user and the fair PL distribution and is obtained by the proposed capacity-fairness bias criterion for the required fairness target. The average channel capacity has been derived approximately for the proposed scheme and the numerical results underscore the significant benefits of jointly exploiting the channel capacity and fairness.

Average spectral efficiency analysis of FSO links over turbulence channel with adaptive transmissions and aperture averaging

In our paper, the impact of adaptive transmission schemes: (i) optimal rate adaptation (ORA) and (ii) channel inversion with fixed rate (CIFR) on the average spectral efficiency (ASE) are explored for free-space optical (FSO) communications with On–Off Keying (OOK), Polarization shift keying (POLSK), and Coherent optical wireless communication (Coherent OWC) systems under different turbulence regimes. Further to enhance the ASE we have incorporated aperture averaging effects along with the above adaptive schemes. The results indicate that ORA adaptation scheme has the advantage of improving the ASE performance compared with CIFR under moderate and strong turbulence regime. The coherent OWC system with ORA excels the other modulation schemes and could achieve ASE performance of 49.8 bits/s/Hz at the average transmitted optical power of 6 dBm under strong turbulence. By adding aperture averaging effect we could achieve an ASE of 50.5 bits/s/Hz under the same conditions. This makes ORA with Coherent OWC modulation as a favorable candidate for improving the ASE of the FSO communication system.

A New Closed-Form Expressions of Channel Capacity with MRC, EGC and SC Over Lognormal Fading Channel

In this work, we derive the closed-form expressions of channel capacity with maximal ratio combining, equal gain combining and selection combining schemes under different transmission policies such as optimal power and rate adaptation, optimal rate adaptation, channel inversion with fixed rate (CIFR) and truncated CIFR. Various approximations to the intractable integrals have been proposed using methods such as Holtzman and Gauss–Hermite approximations and simpler expressions are suggested. Moreover, as an application, the channel capacity of lognormally distributed fading channel in the interference-limited environment is discussed. The obtained closed-form expressions have been validated with the exact numerical results.

Energy‐efficient relaying technique for two‐hop diamond networks

Energy-efficiency (EE) is a critical metric in many types of wireless networks and is getting increasingly important for new technologies. In this paper, the authors propose an energy-efficient decode-and-forward relaying strategy for two-hop diamond networks where the source–destination communication is established by the help of two relays which have an inter-relay link. The inter-relay link gives the opportunity of correcting the data packet between relays if only one of them decodes the packet that is received from the source correctly. Hence, both relays are able to send the data packet to the destination with distributed Alamouti coding which provides multipath diversity. In addition, they introduce optimum data rate adaptation for each link separately to maximise EE for the considered network. By exploiting diversity and optimum rate adaptation, it is possible to transmit at higher rates with reasonable outage probability which has critical effects on EE and throughput. They show via computer simulations that the proposed technique is substantially more energy-efficient and has a better throughput than the successive relaying technique given in the literature; moreover, more robust to the changes in system conditions, i.e. relay location and transmission power level.

Effective client-driven three-level rate adaptation (TLRA) approach for adaptive HTTP streaming

Multimedia streaming allows consumers to view multimedia content anywhere. However, quality of service is a major concern amid heightened levels of network traffic caused by increasing user demand. Accordingly, media streaming technology is adopting a new paradigm: adaptive HTTP streaming (AHS). AHS is widely used for real-time streaming content delivery in the Internet environment. In streaming, selection of appropriate bitrate is crucial for adapting media rate to network variations and client processing capabilities while ensuring optimal service for the consumer. We evaluate a proposed client-driven three-level optimized rate adaptation algorithm for adaptive HTTP media streaming. In the first stage, the algorithm chooses a suitable starting bitrate close to the available channel capacity. Next, the algorithm monitors the client parameters in real time, precisely detecting network variations and choosing a likely available bit representation for the next download segment. The algorithm controls and minimizes the effects of buffer stalls and overflow resulting from the brief network variations occurring between consecutive segments. The proposed algorithm is implemented in Dynamic Adaptive Streaming over HTTP (DASH) player and its performance compared to that of commercially available Gstreamer-based HTTP Live Streaming (HLS) and DASH players which use conventional segment fetch time–based adaptation and throughput-based adaptation algorithms respectively. This evaluation uses a real-time cloud server client and test bed streaming setup. The resulting analysis shows that the client-driven three-level rate adaptation (TLRA) approach allows adaptive streaming clients to maximize use of end-to-end network capacity, delivering an ideal user experience by precisely predicting network variations and rapidly adapting to available bandwidth, minimizing rebuffering events and bitrate level changes.

Capacity analysis of α − η − μ channels over different adaptive transmission protocols

In this study, the authors consider the α − η − μ fading channels and derive a new form for the cumulative distribution function of the signal-to-noise ratio (SNR) in terms of the bivariate Fox H-function. They also derive closed-form expressions for the moments and the amount of fading of the SNR. The capacity of α − η − μ fading channels is analysed assuming different adaptive transmission protocols. To this end, they provide analytical closed-form expressions for the average channel capacity with optimal rate adaptation (C ORA), optimal power and rate adaptation (C OPRA), channel inversion with fixed rate (CIFR) (C CIFR), and truncated CIFR (C TIFR). The derived expressions are valid for arbitrary values of the α, η, and μ fading parameters. The derived expressions can also be reduced to study the capacity of other fading distributions such as η − μ, α − μ, Weibull, and Nakagami. Numerical results are provided and compared with simulations to validate of the derived expressions.

Adaptive Transmission in Spectrum Sharing Systems With Alamouti OSTBC Under Spatially Correlated Channels

This paper presents a performance analysis for adaptive transmission techniques in a spectrum sharing system in which a primary user (PU) and a secondary user (SU) employ an Alamouti orthogonal space-time block coding (OSTBC) system under correlated antennas over Rayleigh fading channels. The considered adaptive transmission techniques include practical rate-adaptive modulation techniques and classical adaptive transmission techniques, namely, optimal power and rate adaptation (opra), constant transmit power with optimal rate adaptation (ora), and channel inversion with fixed rate (cifr). Closed-form expressions are derived for the following performance metrics: the average spectral efficiency, the outage probability, the average channel capacity, and the average bit error rate (BER) of the system. Using numerical evaluation results, the impacts of antenna correlation on the performance of each adaptive technique in different cases and under various parameters are evaluated. These results provide comprehensive and useful insights about the performance of the considered system under various adaptive transmission techniques.

A new closed-form of ASEP and channel capacity with MRC and selection combining over Inverse Gaussian shadowing

This paper analyse and investigate the performance of communication system with maximal ratio combining (MRC) and selection combining (SC) over Inverse Gaussian (IG) fading distribution. All formats of coherent and non-coherent modulation schemes are considered and novel analytical expressions of average symbol error probability (ASEP) with diversity are derived. Gamma and IG fading distributions are popularly used as a mathematically less complex solution to lognormal in the open literature. Hence, we provide a comparative analysis between IG and gamma fading with the aim to provide a quantitative measure of the difference between the two distributions in the context of ASEP. Moreover, the novel closed-form expressions of channel capacity under transmission schemes such as optimal rate adaptation (ORA) and channel inversion fixed rate (CIFR) are derived and analysed with MRC and SC diversity over IG fading. The analytical results have been validated with the Monte Carlo simulations and the exact numerical results.

A tight approximate analytical framework for performance analysis of equal gain combining receiver over independent Weibull fading channels

In this paper, a method for approximating the probability distribution of sum of independent and identical Weibull random variables is adopted to analyze the performance of equal gain combiner (EGC) receiver over non-identical Weibull fading channel (WFC). Our main result is to derive a generalized expression of the probability density function (PDF) of the signal-to-noise ratio (SNR) at the EGC output in the case of non-identical WFC. Based on this PDF, accurate approximation of significant performance criteria, such as outage probability (OP), the amount of fading (AoF), and average symbol/bit error probability (ASEP/ABEP), are derived. In addition, we derived the analytical expressions for channel capacities under various adaptation policies such as optimal rate adaptation (ORA), optimal simultaneous power and rate adaptation (OPRA), channel inversion with fixed rate (CIFR), and truncated channel inversion with fixed rate (TCIFR). The proposed mathematical analysis is complemented by several numerical results and validated using Monte Carlo simulation method.

Optimal adaptive estimation of linear functionals under sparsity

We consider the problem of estimation of a linear functional in the Gaussian sequence model where the unknown vector θ ∈ R^d belongs to a class of s-sparse vectors with unknown s. We suggest an adaptive estimator achieving a non-asymptotic rate of convergence that differs from the minimax rate at most by a logarithmic factor. We also show that this optimal adaptive rate cannot be improved when s is unknown. Furthermore, we address the issue of simultaneous adaptation to s and to the variance σ^2 of the noise. We suggest an estimator that achieves the optimal adaptive rate when both s and σ^2 are unknown.

Capacity of dual-branch MRC system over correlated Nakagami-m fading channels with non-identical fading parameters and imbalanced average SNRs

We present the closed-form expressions for the capacity with correlated, non-identical fading parameters and imbalanced average SNRs (Signal-to-Noise Ratios) of dual-branch MRC (Maximal Ratio Combining) diversity system over Nakagami-m fading channels. This capacity is evaluated for ORA (Optimum Rate Adaptation with constant transmit power) and CIFR (Channel Inversion with Fixed Rate) schemes. Numerical results have been presented and compared with the available capacity results of ORA and CIFR schemes in the literature. The effect of different practical constraints, e.g. non-identical fading parameters, fade correlation and level of imbalanced in average SNRs on the channel capacity of the systems, is analysed.

Efficient Analysis of the Ergodic Capacity of Cooperative Non-Regenerative Relay Networks Over Generalized Fading Channels

In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight approximate moment applicable to myriad of fading environments including mixed and composite fading channels. Three distinct adaptive source transmission policies were considered in our analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading environments (especially for the analysis of the mixed fading case)and provides significant advantage to model wireless system for mixed and composite fading channel. In addition to simplifying computation complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.

A very tight approximate results of MRC receivers over independent Weibull fading channels

In this paper, we study the performance of L-branch maximal-ratio combining (MRC) receivers operating over independent Weibull-fading channels. Our main result is a very tight approximation of the probability density function (PDF) of the signal-to-noise ratio (SNR) at the output of the combiner. Based on this result, accurate approximation of significant performance criteria, such as outage probability and average symbol error rate (ASER) are derived. We also evaluate the average bit error rate (ABER) for several coherent and non-coherent modulation schemes, using a closed-form expression for the moment-generating function (MGF) of the output SNR for MRC receivers. In addition, we derive some analytical expressions for channel capacity under various adaptation policies such as optimal rate adaptation (ORA), Optimal simultaneous power and rate adaptation (OPRA), Channel inversion with fixed rate (CIFR), and Truncated channel inversion with fixed rate (TCIFR). The proposed mathematical analysis is complemented by numerous numerical results, which point out the effects of fading severity on the overall system performance. Computer simulations are also performed to verify the validity and the accuracy of the proposed theoretical approach.