Multipath Diversity Research Articles

A QoE Evaluation Method for RT-HDMV Based on Multipath Relay Service

Multipath diversity leads to a possible higher performance for real-time high definition video, especially for medical video transmission, which would improve the stability of multiple transmission paths in the symmetrical state, and avoid the potential losses of imaging information in the communication process. Most of the previous works are always based on the single-path end-to-end transmission, although the service had been demonstrated that it is unable to meet the rigorous demand for the RT-HDMV. In the paper, a multipath relay service based on the QoE (quality of experience) evaluation method is proposed for the RT-HDMV (real-time high definition medical video). The method eliminates several of the limitations in the existing methods for some conventional single-path transmission. It can fully utilize the finite network resources and transmission bandwidth to meet the users’ demands of the RT-HDMV to get a better score of the QoE. We use a four-stage framework to evaluate the QoE, which consists of constructing the multipath relay transmission for the RT-HDMV, calculating the weights of diversified QoS parameters in the multipath, designing the load distribution strategy by the mapping between the QoS (quality of service) and QoE, and redefining the rule of the QoE evaluation. Many experiments show that the proposed design scheme achieves weighting of the transmission sub-paths and computes the QoE score. Compared with the state-of-art methods in the single path transmission scene, our framework mainly gains the excellent performance for the RT-HDMV.

Backscatter-Aided Cooperative Relay Communications in Wireless-Powered Hybrid Radio Networks

Wireless backscatter communications has been introduced as a promising technique for data transmissions without a conventional energy supply from a battery or power outlet. It shares some similarity with RF energy harvesting powered wireless transmissions. Many benefits can be achieved when both techniques are integrated. In this article, we introduce the concept of a hybrid radio that is an integrated design of wireless-powered active RF communications and backscatter communications. We then discuss a few use cases of hybrid radio networks to suggest potential applications and to improve network performance. Furthermore, we consider a specific case in which hybrid radios act as passive relays to assist active RF communications. The passive relays backscatter the RF signals from the source to the receiver which, by experiments, shows to improve the transmission rate due to the enhanced multi-path diversity gain. We also introduce an optimization to quantify the performance improvement achievable by the radios' cooperation in the hybrid radio network.

A Multi-Dimension Spatial Method for Topology Awareness and Multipath Generating

Multipath diversity significantly impacts multipath transmission quality. Enough multipath diversity would minimize the negative influence brought by an individual path, thus improving tolerance capability of network congestion and failure. However, multipath diversity is hard to guarantee on overlay networks because of inaccurate awareness of underlay network and multipath generating methods considering little about underlay diversity. In this paper, we design a multi-dimension spatial method for topology awareness and multipath generating. Analyzing that the complicated underlay networks with multiple autonomous systems reduce the accuracy of network positioning for topology awareness, we decompose the underlay networks into multiple dimensions, namely intra and inter autonomous system dimensions. We generate independent views for each autonomous system and merge views by embedding exchange points. Then, we design some spatial mechanisms to evaluate link diversity and to constrain multipath generating. Based on the multi-dimensional view, multipath generating is conducted in inter and intra autonomous system phases. Experiments demonstrate that the proposed method improves topology awareness accuracy and guarantees multipath diversity better and the transmission quality is improved.

Blockchain-Based Distributive Auction for Relay-Assisted Secure Communications

Physical layer security (PLS) is considered as a promising technique to prevent information eavesdropping in wireless systems. In this context, cooperative relaying has emerged as a robust solution for achieving PLS due to multipath diversity and relatively lower transmission power. However, relays or the relay operators in the practical environment are unwilling for service provisioning unless they are incentivized for their cost of services. Thus, it is required to jointly consider network economics and relay cooperation to improve system efficiency. In this paper, we consider the problem of joint network economics and PLS using cooperative relaying and jamming. Based on the double auction theory, we model the interaction between transmitters seeking for a particular level of secure transmission of information and relay operators for suitable relay and jammer assignment, in a multiple source-destination networks. In addition, theoretical analyses are presented to justify that the proposed auction mechanism satisfies the desirable economic properties of individual rationality, budget balance, and truthfulness. As the participants in the traditional centralized auction framework may take selfish actions or collude with each other, we propose a decentralized and trustless auction framework based on blockchain technology. In particular, we exploit the smart contract feature of blockchain to construct a completely autonomous framework, where all the participants are financially enforced by smart contract terms. The security properties of the proposed framework are also discussed.

Channel Estimation and Equalization for SS-OOFDM System With High Mobility

When orthogonal frequency-division multiplexing (OFDM) is used in high-speed mobile scenarios, the traditional implementation of the OFDM receiver causes significant performance degradation. This letter proposes a subband superposed oversampled OFDM (SS-OOFDM) scheme for accommodating the diverse scenarios, including the scenarios with high mobility. To track the fast-varying mobile channel, a time-domain channel estimation method is developed to first obtain the channel impulse response (CIR) values at pilots by means of the basis expansion model. Subsequently, by utilizing Slepian sequences-based interpolation, the CIR values at data symbols are reconstructed. Furthermore, we design a subband decision feedback and feedforward equalizer for exploiting the Doppler and multipath diversity gains. Simulation results show that the SS-OOFDM, especially in high-speed mobile channels, outperforms the traditional OFDM receiver in terms of the bit-error-rate performance.

Orthogonal Chirp Division Multiplexing for Underwater Acoustic Communication.

The objective of this study is to investigate a novel Underwater Acoustic Communication (UWAC) system based on a modulated chirp signal termed as Orthogonal Chirp Division Multiplexing (OCDM). Originating from the Fresnel transform, OCDM uses chirp signals to exploit the multipath diversity of the channel, achieving a good robustness against frequency fading, especially in the underloaded scenario where only a subset of the available waveforms is modulated. The implementation of the OCDM system for the UWAC scenario is described, and the performance results over an experimental water tank and realistic replayed underwater channel are compared against the traditional Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme.

Reliable and Low-Latency Fronthaul for Tactile Internet Applications

With the emergence of Cloud-RAN as one of the dominant architectural solutions for the next-generation mobile networks, the reliability and latency on the fronthaul (FH) segment become critical performance metrics for applications such as the Tactile Internet. Ensuring FH performance is further complicated by the switch from point-to-point dedicated FH links to packet-based multi-hop FH networks. This change is largely justified by the fact that packet-based fronthauling allows the deployment of FH networks on the existing Ethernet infrastructure. This paper proposes to improve the reliability and latency of packet-based fronthauling by means of multi-path diversity and erasure coding of the MAC frames transported by the FH network. Under a probabilistic model that assumes a single service, the average latency required to obtain reliable FH transport and the reliability-latency tradeoff is first investigated. The analytical results are then validated and complemented by a numerical study that accounts for the coexistence of the enhanced mobile broadband and ultra-reliable low-latency services in fifth-generation networks by comparing orthogonal and non-orthogonal sharing of FH resources.

Dynamic Attack-Resilient Routing in Software Defined Networks

The scale of connected devices in the modern communication network and its heterogeneous nature have made securing the network more challenging. However, with the advent of software defined networking (SDN), the algorithmic complexity is handled at a centralized control plane and the network elements perform only data forwarding based on control plane decisions. This enables researchers to design innovative security protocols at the control plane to dynamically defend against attacks. In this paper, we propose a dynamic attack-resilient routing (ARR) approach and develop an optimization formulation for fragmented multipath routing taking reliability and load into consideration for SDN-enabled networks. Though erasure encoding has been well studied for resilient data storage, it is rarely mentioned in the context of network routing owing to its complexity, redundancy, and difficulty of satisfying practical routing constraints. In this paper, we dynamically determine the optimal route for erasure-encoded fragments of the data, in terms of attack resilience, under the constraint on allowable encoding redundancy. Since the ARR algorithm is computationally prohibitive for larger networks, we develop a heuristic solution for the same using a multipath-tree. The proposed algorithm dynamically routes the data fragments along a set of reliable and lightly loaded paths to achieve multipath diversity and thereby improve data availability at the destination even in the presence of attacks. We demonstrate the effectiveness of our proposed approach in terms of weighted path reliability, resilience, and blocking performance through simulations.

Energy-Aware Concurrent Multipath Transfer for Real-Time Video Streaming Over Heterogeneous Wireless Networks

The advancements in networking technologies and hand-held devices enable mobile users to concurrently receive real-time multimedia streaming (e.g., high-definition video) with different radio interfaces (e.g., Wi-Fi and LTE networks). Stream control transmission protocol (SCTP) is an important transport-layer solution to implement concurrent multipath transfer (CMT) over heterogeneous wireless networks with multihomed terminals. However, it is challenging to distribute multimedia content to resource-limited mobile devices because of the contradiction between energy consumption and streaming quality. To deliver the energy-efficient and quality-aware multimedia streaming over multiple wireless networks, this paper presents an Energy and goodPut Optimized CMT (EPOC) solution. First, we develop an analytical framework to model the relationship between energy consumption and goodput performance for real-time multimedia transmission to multihomed mobile devices. Second, we propose a joint forward error correction coding and rate allocation scheme to minimize energy consumption while satisfying goodput constraint. EPOC effectively leverages the energy-goodput tradeoff and multipath diversity to optimize mobile multimedia transmission in heterogeneous networking environment. We conduct the performance evaluation through extensive semi-physical emulations in Exata involving H.264 video streaming. Compared with the reference CMT schemes using SCTP, EPOC achieves appreciable improvements in energy conservation, goodput, and video peak signal-to-noise ratio.

Distributed Space Time Block Transmission and QRD Based Diversity Detector in Asynchronous Cooperative Communications Systems

Based on the zero prefix (ZP) structure, we propose an efficient block transmission algorithm using distributed space-time codes in the asynchronous cooperative communication systems. To accomplish the new frame, ZP is inserted in front of the data block to combat the relative delay between the asynchronous relays, while zero suffix (ZS) is appended at the end of the block to remove the interblock interference caused by the time dispersing channel; so, we employ this ZP–ZS precoding form to make the coded frames synchronous. It should be noted that single carrier transmission and orthogonal frequency division multiplexing (OFDM) are both compatible with the frame. For single carrier transmission, conventional space-time equalizers can be investigated at the destination node to cancel the multipath interference. To further improve the performance, an improved QR decomposition-based recursive interference cancellation (QRD-RIC) detector is employed, where joint QRD is adopted on the combination of channel matrices from different relays, and then spatial-and-multipath diversity combinations are introduced and improved into the proposed system, where the spatial and multipath diversities are acquired. For OFDM, the fractionally spaced frequency-domain MMSE diversity receiver is employed, since the guard interval in our framing scheme implies oversampling in the frequency domain. Numerical simulations show that the proposed algorithms are effective for the asynchronous transmissions under frequency selective fading channels.

FUSO: Fast Multi-Path Loss Recovery for Data Center Networks

To achieve low TCP flow completion time (FCT) in data center networks (DCNs), it is critical and challenging to rapidly recover loss without adding extra congestion. Therefore, in this paper, we propose a novel loss recovery approach fast multi-path loss recovery (FUSO) that exploits multi-path diversity in DCN for transport loss recovery. In FUSO, when a multi-path transport sender suspects loss on one sub-flow, recovery packets are immediately sent over another sub-flow that is not or less lossy and has spare congestion window slots. FUSO is fast in that it does not need to wait for timeout on the lossy sub-flow, and it is cautious in that it does not violate the congestion control algorithm. Testbed experiments and simulations show that FUSO decreases the latency-sensitive flows’ $99^{th}$ percentile FCT by up to ~82.3% in a 1-Gb/s testbed, and up to ~87.9% in a 10 Gb/s large-scale simulated network.

Secure Blockchains for Dynamic Spectrum Access: A Decentralized Database in Moving Cognitive Radio Networks Enhances Security and User Access

In this article, we propose a blockchain verification protocol as a method for enabling and securing spectrum sharing in moving cognitive radio (CR) networks. The spectrum-sharing mechanism is used as a medium-access protocol for accessing wireless bandwidth among competing CRs. We introduce a virtual currency, called Specoins, for payment to access the spectrum. An auction mechanism based on a first-come-first-served queue is used, with the price for the spectrum advertised by each primary user in a decentralized fashion. The blockchain protocol facilitates the transactions between primary and secondary users and is used to validate and save each user's virtual wallet. Also important for mobile networks, the blockchain serves as a distributed database that is visible by all participating parties, and any node can volunteer to update the blockchain. The volunteer nodes are called miners, and they are awarded with Specoins. We propose diverse methods to exchange the Specoins to make leasing possible even by CRs that are not miners. We show the improvement of the proposed algorithm compared with the conventional Aloha medium-access protocol in terms of spectrum usage. This difference is investigated using small-scale fading variation in the wireless channel to compare the performance of our secure method with the conventional medium access used in vehicular communications. The secure blockchain verification protocol is not only secure but also outperforms the conventional system in moderate cases of small-scale fading. In the case of severe small-scale fading, the blockchain protocol will outperform the conventional system if multipath diversity is not used.

A Novel Diversity Receiver Design for Cooperative Transmission System

In this paper, we consider the performance of an amplify-and-forward relaying-based multiple-input multiple-output space–time-block-coded cooperative communication system. We propose an efficient two-stage receiver design for a relay-assisted transmission scenario over frequency-selective channels. It is also demonstrated that the receiver is able to achieve the full diversity order of the system by incorporating linear processing techniques. With this method, the potential spatial diversity and multipath diversity can be obtained by using the diversity-combining technique, which frequency-selective fading channels can be equivalently transformed. Simulation results show that the proposed scheme significantly outperforms the minimum mean square error and ZF receivers, while maintaining nearly linear complexity.

Partial intersection sphere decoding with weighted voting for sparse rotated V-OFDM systems

Vector orthogonal frequency division multiplexing (V-OFDM) is a general system that builds a bridge between OFDM and single-carrier frequency domain equalization in terms of intersymbol interference level and receiver complexity. In this paper, we focus on a rotated V-OFDM system over a broadband sparse channel owing to its large time delay spread and fewer nonzero taps. In order to collect the multipath diversity, a simple rotation matrix is designed, independent of the number of subchannels at the transmitter. For the rotated V-OFDM receiver, a partial intersection sphere decoding with weighted voting method is proposed by exploiting the sparse nature of the multipath channel. The proposed receiver chooses the transmitted vector from the set with the maximum likelihood estimation generated using the partial intersection sphere decoding method. For an extreme case, such as when a candidate set is empty, which usually occurs at a low signal-to-noise ratio (SNR), an efficient weighted voting system is used to estimate the transmitted vectors symbol-by-symbol. Simulation results indicate that the proposed receiver improves the symbol error rate performance with reduced complexity, especially for low SNR scenarios.

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.

Modeling and Performance Analysis of Wireless Networks With Ambient Backscatter Devices

Ambient backscatter is an intriguing wireless communication paradigm that allows small devices to compute and communicate by using only the power they harvest from far-field radio-frequency (RF) signals in the air. Ambient backscattering devices reflect RF signals emitted by existing or legacy communications systems, such as digital TV broadcasting, cellular, or Wi-Fi ones, which are designed for transporting information and are not intended for RF energy transfer. This paper deals with mathematical modeling and performance analysis of wireless broadband networks operating over fading channels with ambient backscatter devices. After introducing a detailed signal model of the relevant communication links, we study the influence of physical parameters on the capacity of both legacy and backscatter channels, by considering different receiver architectures. We analytically show that, under reasonable operative conditions, a legacy system-employing an orthogonal frequency-division multiplexing (OFDM) modulation scheme-can turn the RF interference arising from the backscatter process into a form of multipath diversity that can be exploited to increase its performance. Moreover, our analysis proves that a backscatter system-transmitting one symbol per OFDM symbol of the legacy system-can achieve satisfactory data rates over relatively short distances, especially when the intended recipient of the backscatter signal is co-located with the legacy transmitter, i.e., they are on the same device.

Finite-SNR Diversity-Multiplexing Tradeoff for Network Coded Cooperative OFDMA Systems

Network-coded cooperation (NCC) is an effective method to improve the throughput efficiency in cooperative wireless networks. The combined use of orthogonal frequency division multiplexing (OFDM) with NCC has been further studied in the literature to exploit the multipath diversity gains. In this paper, we consider orthogonal frequency division multiple access (OFDMA), an extension of OFDM to a multiuser system where subsets of carriers are assigned to different users. We first derive a closed-form expression for the outage probability of NCC-OFDMA over Rician fading channels and then present the asymptotical and finite-SNR DMT expressions. Our results provide insight into the performance mechanisms under practical SNR regime of NCC-OFDMA systems and demonstrate that NCC-OFDMA is able to fully exploit both frequency and spatial diversity. We also show that the derived finite-SNR DMT converges to an asymptotical one as expected. Furthermore, special cases for our derived analytical expressions are presented, to show that the derived expression is a generalized case of the related the state of the art results. Simulation results are further presented to verify our theoretical analyses.

Achieving upper mutual information bound precoding for V‐OFDM with MMSE receiver

Traditional vector orthogonal frequency division multiplexing (V-OFDM) can obtain both multi-path diversity and outage gain by transforming an inter-symbol interference (ISI) channel into multiple ‘ISI-free’ channel vectors. To achieve full multi-path diversity and acquire better outage performance, a low-complexity precoding scheme combined with simple minimum mean square error (MMSE) equalisation for V-OFDM system is proposed in this study. First, the upper mutual information bound of the V-OFDM system is derived with channel state information at transmitter. Based on the upper bound, an optimal precoding scheme for V-OFDM is presented. Meanwhile, the closed-form and asymptotic expressions on outage probability of the proposed scheme are derived. Simulations show that this low-complexity scheme can achieve full multi-path diversity and result in lower outage probability than the traditional V-OFDM scheme. Besides, the proposed scheme in ISI fading channel is capable of approaching the upper bound with <0.1 bits/s/Hz performance gap and improving average channel capacity with 2 bits/s/Hz over the traditional V-OFDM scheme.

Dual-Mode Time-Domain Index Modulation for Nyquist-Criterion and Faster-Than-Nyquist Single-Carrier Transmissions

In this paper, we propose a novel dual-mode time-domain single-carrier (SC) index modulation (DM-SCIM) scheme, where the combination of two constellation modes carries information bits further to modulated symbols, hence increasing the transmission rate. Accordingly, the proposed DM-SCIM scheme is capable of attaining a higher transmission rate than the conventional SC and SCIM schemes, without imposing any additional performance penalty. Furthermore, in order to maintain the detection complexity low enough to be tractable at the handset receiver, a successive detection algorithm, comprising minimum mean-square error (MMSE)-based frequency-domain equalization and log-likelihood ratio detection, is developed for both the conventional SCIM and the proposed DM-SCIM schemes. We also derive the error-rate bound of the proposed DM-SCIM scheme under the assumption of a channel-uncoded scenario. Moreover, in order to further increase bandwidth efficiency, the proposed DM-SCIM scheme is extended to the scenario supporting faster-than-Nyquist signaling, where the symbol interval in the time domain is set to be smaller than that defined by the Nyquist criterion. Our simulation results demonstrate the explicit performance advantage of the proposed schemes over the existing SC schemes. It is also revealed that our DM-SCIM scheme is capable of achieving a significantly lower peak-to-average power ratio than orthogonal frequency division multiplexing (OFDM) and OFDM with index modulation, while benefiting from a high reliability, which is achievable by multipath diversity.

Performance Evaluations and Measurements of the REALFLOW Routing Protocol in Wireless Industrial Networks

Industrial wireless sensor and actuator networks (IWSANs) offer significant advantages to industrial automation. However, high-reliability demands and hard communication deadlines pose challenges to its practical applications. To achieve this goal, flooding is considered as a promising approach due to multipath diversity and simplicity. In this paper, an enhanced version of REALFLOW, a flooding-based routing protocol for IWSANs is presented. Compared to the original REALFLOW, network management and network stability are improved. REALFLOW is compared with four other flooding protocols via simulations. The simulation results show that REALFLOW has better performance in terms of reliability and consecutive transmission errors when considering deadlines. Compared with normal flooding, REALFLOW achieves comparable reliability performance with decreased redundancy. Measurements from a prototype implementation conducted in an industrial manufacturing workshop reveal that high-reliability and low-application failure rates can be achieved, giving more confidence in providing reliable wireless sensing and actuating for industrial automation.