Opportunistic Large Array Research Articles

Opportunistic Large Array Propagation Models: A Comprehensive Survey.

Enabled by the fifth-generation (5G) and beyond 5G communications, large-scale deployments of Internet-of-Things (IoT) networks are expected in various application fields to handle massive machine-type communication (mMTC) services. Device-to-device (D2D) communications can be an effective solution in massive IoT networks to overcome the inherent hardware limitations of small devices. In such D2D scenarios, given that a receiver can benefit from the signal-to-noise-ratio (SNR) advantage through diversity and array gains, cooperative transmission (CT) can be employed, so that multiple IoT nodes can create a virtual antenna array. In particular, Opportunistic Large Array (OLA), which is one type of CT technique, is known to provide fast, energy-efficient, and reliable broadcasting and unicasting without prior coordination, which can be exploited in future mMTC applications. However, OLA-based protocol design and operation are subject to network models to characterize the propagation behavior and evaluate the performance. Further, it has been shown through some experimental studies that the most widely-used model in prior studies on OLA is not accurate for networks with networks with low node density. Therefore, stochastic models using quasi-stationary Markov chain are introduced, which are more complex but more exact to estimate the key performance metrics of the OLA transmissions in practice. Considering the fact that such propagation models should be selected carefully depending on system parameters such as network topology and channel environments, we provide a comprehensive survey on the analytical models and framework of the OLA propagation in the literature, which is not available in the existing survey papers on OLA protocols. In addition, we introduce energy-efficient OLA techniques, which are of paramount importance in energy-limited IoT networks. Furthermore, we discuss future research directions to combine OLA with emerging technologies.

Impact of Intra-Flow Interference on the Performance of 2-D Multi-Hop Cooperative Network

A mathematical model is proposed to study the effects of intra-flow interference caused due to multi-packet propagation in a 2-D cooperative opportunistic large array network. Specifically, the outage probability of node is derived in the presence of interfering signals using the ratio distribution of generalized integer gamma random variables. The outage probability expression is used along with a Markov chain-based transmission model to quantify the state distribution probabilities, coverage of the network, and network throughput. The results show that the network performance is highly dependent on intra-flow interference especially at high signal-to-noise ratio. Moreover, the coverage of network can be improved by increasing SNR, array gain, and packet insertion rate.

Opportunistic large array concentric routing algorithms with relay nodes for wireless sensor networks

This paper proposes two architectures, including an Opportunistic Large Array Concentric Routing Algorithm with Geographic Relay Nodes (OLACRA-GRN) architecture, and an Opportunistic Large Array Concentric Routing Algorithm with Relay Nodes (OLACRA-RN) architecture. First, the OLACRA-GRN architecture with the geographic information of relay nodes reduces node energy consumption and finds the optimum number of relay nodes to forward the data; an analysis of the characteristics of the energy model is also presented. Besides, the OLACRA-RN architecture without the geographic information of relay nodes is proposed, which can find the number layer of concentric circles in the sensing field. The optimal number layer of concentric circles is calculated according to the distance between the sink and field boundary. Simulation results show that our proposed OLACRA-GRN and OLACRA-RN architectures can effectively reduce node energy consumption more than Opportunistic Large Array Concentric Routing Algorithm (OLACRA) architecture.

An Opportunistic Large Array Concentric Geographic Routing Algorithm with a Relay Node in Wireless Sensor Networks

Wireless sensor networks (WSNs) are a group of wireless sensor nodes, those sensor nodes with sensing and monitoring of environmental information. Energy consumption is an important topic; the node's power is limited. Therefore, we proposed an Opportunistic Large Array Concentric Geographic Routing Algorithm (OLACGRA) to reduce the node’s energy consumption and analysis the characteristic of energy model. The sink position of our proposed OLACGRA is at the center of concentric topology architecture. The source node wants to transmit data that it needs to calculate the distance between source node and sink node. If this distance bigger than threshold value, we use the multi-hop manner. Otherwise, source node transmits data to sink node directly. Simulation results show that our proposed algorithm can effectively reduce the node’s energy consumption.

On cooperative transmission range extension in multi-hop wireless ad-hoc and sensor networks: A review

Range extension is a promising feature offered by cooperative transmission (CT), also known as virtual multiple-input–single-output (VMISO). Many authors have considered how the diversity and array gains from CT may benefit a wireless multi-hop network, when the gains are used for increasing link reliability and reducing transmit power. However, relatively less attention has been given to the benefits of CT range extension and few testbed implementations of CT have been demonstrated. In this paper, we focus on how CT range extension can impact the lower three layers, especially medium access control (MAC) and routing for ad hoc and sensor multi-hop networks (AHSMNs). We assume cooperators decode and forward the packets. Various analytical models, performance analyses, and experimental results using software-defined radios in an indoor office environment are discussed. For wireless sensor networks (WSNs), we review CT range extension at the network layer, to eliminate the energy hole that forms around sink nodes in non-CT networks, and we review cooperator selection and duty cycle scheduling algorithms at Layer 2, to maximize the lifetime of a multi-hop WSN. For ad hoc networks, we emphasize a family of lightweight broadcasting and unicasting protocols based on a simple form of CT called the opportunistic large array (OLA). Experimental results, including OLA-based unicast routing and diversity order effects in two-hop CT networks, are discussed.

A New Approach for Coverage Analysis of Multihop Cooperative Networks Subject to Lognormal-Rice Fading

A strip-shaped sensor network is considered, where randomly placed nodes communicate cooperatively by forming an opportunistic large array (OLA). The transmission from a group of cooperating nodes to another group of nodes is modeled with a quasi-stationary Markov chain, where the transmission channel is assumed to experience lognormal shadowing and Rice fading. The distribution of received power at a node is calculated as a three-step process, which includes finding the distribution of random distance between nodes in addition to other channel impairments, that is, fading and shadowing. It is shown that, in the presence of all three channel impairments, the received power at a node follows a lognormal distribution. This approximation uses a series of steps that involves techniques such as moment matching and moment generating function (MGF). Using the underlying Markov chain properties, the one-hop success probability of the network is derived. The system performance and coverage range of the network are quantified as a function of various network parameters and node topologies. The theoretical results are validated by performing computer simulations.

Stochastic Modeling of Cooperative Multi-Hop Strip Networks With Fixed Hop Boundaries

In this paper, a strip-shaped cooperative multi-hop wireless network is modeled stochastically with quasi-stationary Markov chain. The network is considered to be a fixed boundary decode-and-forward Opportunistic Large Array (OLA), where each level is of the same size and contains the same number of nodes placed randomly. The state of the system is represented by the number of nodes that decode the message in the current level. The distribution of the received power at a node is derived to formulate the transition probability matrix. For the distribution of power, a closed-form expression of the distribution of distance between a pair of nodes in disjoint levels is derived. It is seen that the distribution of distance can be well-approximated by the Weibull distribution. The Weibull approximation is then carried forward to find the distribution of the received power at a node assuming all nodes transmit with the same power and the channel has Rayleigh fading and path loss with an arbitrary exponent. The coverage and outage characteristics for various network sizes and path loss exponents are quantified. The signal-to-noise ratio (SNR) margin required for a given network coverage is determined by using the Perron-Frobenius theorem of non-negative matrices. Numerical simulations are performed to validate the theoretical results.

Multi-Packet Opportunistic Large Array Transmission on Strip-Shaped Cooperative Routes or Networks

The Opportunistic Large Array (OLA) is one type of cooperative transmission, which provides fast and reliable broadcasts and unicasts in multi-hop networks. While the existing literature on OLAs assumes one-shot transmission with a single packet, we analyze multi-packet OLA transmission within a single flow along strip-shaped networks or OLA-based cooperative routes. When multiple packets are transmitted from the same source using the same channel before the previous packet has cleared the network, which is called spatial pipelining, intra-flow interference is produced by OLAs transmitting co-channel packets. Using the continuum assumption (approximated by high density networks), the authors optimize the throughput. This paper theoretically shows spatial pipelining over strip networks is always feasible for path loss exponent α≥2, which is not true for disk-shaped networks. Moreover, the impacts of system parameters are analyzed, and the upper bound of the optimal packet spacing (the lower bound of the optimal throughput) is derived. Also, spatial pipelining in finite networks is studied with numerical results, which confirm the theoretical analysis.

Green Cooperative Web of Trust for Securityin Cognitive Radio Networks

Spectrum is a scarce and very essential resource for the ever growing mobile communication applications. Radio networks (CRN) is the best evolved solution towards spectrum scarcity. Cooperative spectrum sensing is a well-known and proven mechanism in the CRNs. As compared to other traditional wireless networks, CRNs are more delicate and open to the wireless environments due to their heterogeneous nature. Therefore, the CRNs have more security threats than the conventional wireless networks. The spectrum sensing and sharing mechanisms are inherently vulnerable to the malicious behaviors in the wireless networks due to its openness. This paper proposes an energy efficient lightweight cryptographic Cooperative web of trust (CWoT) for the spectrum sensing in CRNs which is proved to be appropriate for the resource constrained wireless sensor networks (WSNs). Development of trust based authentication and authorization mechanism for the opportunistic large array (OLA) structured CRNs is the main objective of this paper. Received signal strength (RSS) values obtained can be utilized to avoid Primary user emulation attacks (PUEA) in CRNs.

Analysis of an opportunistic large array line network with Bernoulli node deployment

A linear multi-hop cooperative network is considered where the relay nodes are deployed in a random fashion according to a Bernoulli random process. The transmission from one hop to another is modelled as a discrete-time Markov process while taking into account the random locations of the participating nodes along with the Rayleigh fading channel model. Quasi-stationary theory of Markov chains has been applied to study the various properties of the network under consideration, including successful probability of hops as well as network coverage. It is shown that there is a loss of one-hop success probability when the random deployment is done compared to a regular deployment. However, an additional signal-to-noise ratio margin has also been quantified for obtaining a desired quality of service and one-hop success probability.

Multi-Packet Interference in Opportunistic Large Array Broadcasts over Disk Networks

The Opportunistic Large Array (OLA) is a simple form of cooperative transmission, in which a group of single-antenna nodes decode the same packet, then a short time later relay the packet simultaneously in orthogonal or space-time coded channels. The authors have previously shown that OLA transmissions can be adequately synchronized so they appear to a receiver as having come from a conventional array with co-located antennas doing transmit diversity. OLAs have been considered as a basis for rapid single-packet broadcasting in multi-hop networks, however, there are few studies that consider OLA broadcasting of multiple co-channel packets. Using the continuum assumption (approximated by high density networks), we focus on broadcast throughput optimization, as determined by the packet insertion rate at the source. We consider spatial pipelining, which means broadcasting a packet before the previous co-channel packet has cleared the network. We show theoretically that for infinitely large networks the feasibility of spatial pipelining depends on the path loss exponent. For finite networks, we study the propagation behavior of spatially pipelined packets using numerical analysis.

Opportunistic large array concentric routing algorithm (OLACRA) for upstream routing in wireless sensor networks

An opportunistic large array (OLA) is a form of cooperative diversity in which a large group of relays or forwarding nodes operate without any mutual coordination, but naturally fire together in response to energy received from a single source or another OLA. When used for broadcast, OLAs form concentric rings around the source, and have been shown to use less transmit energy than conventional multi-hop protocols during broadcasting. The OLA concentric routing algorithm (OLACRA) and its variants, the main contributions of this paper, leverage the concentric ring structure of the OLAs during the initialization phase to limit the node participation on the upstream connection. For the simulation scenarios considered in this paper, OLACRA is shown to save over 80% of the transmit energy relative to other OLA-based schemes. This paper analyzes the performance of OLACRA over ‘deterministic channels’ or non-faded orthogonal channels and on ‘diversity’ or Rayleigh flat-fading channels with limited orthogonality. Enhancements to OLACRA to further improve its energy efficiency by limited broadcasting in the initial upstream level and limiting the downlink ‘step-sizes’ are also considered. A simple contention avoidance scheme for WSNs with multiple flows is also proposed. In addition to this, the robustness of OLACRA over mobile channels is also studied. The protocols are tested using Monte Carlo evaluation.

Analysis of a Simple Recruiting Method for Cooperative Routes and Strip Networks

The opportunistic large array (OLA) is the basis for a simple cooperative transmission protocol that is suitable for broadcasting in wireless sensor networks and in which every node transmits once per broadcast. OLA with transmission threshold (OLA-T) is an energy-efficient extension of the OLA protocol that limits node participation during broadcasting. Performance of OLA-T has been studied for disc-shaped networks. In this paper, we propose a method to systematically set the transmission threshold and design the OLAs for two-dimensional strip-shaped networks. Theoretical bounds and conditions for achieving sustained OLA propagation and reducing the total energy consumption in the network using OLA-T have been derived in this paper. These results would also apply to arbitrarily shaped networks that have node participation limited to strip-shaped collections.

Alternating opportunistic large arrays in broadcasting for network lifetime extension

We propose a protocol for broadcasting in wireless multihop networks that is based on a form of cooperative transmission called the opportunistic large array (OLA). An SNR ("transmission") threshold is used to define two mutually exclusive sets of OLAs, such that the union of the sets includes all the nodes in the network. The broadcast protocol then alternates between the sets for each broadcast and is called Alternating OLA with Transmission Threshold (A-OLA-T). Under A-OLAT, all participating nodes transmit with the same low power, therefore the energies of the nodes in the network drain efficiently and uniformly, extending the network life relative to broadcasts that use simple OLA or non-alternating OLAs with a transmission threshold. In this paper, we optimize the A-OLA-T protocol under the continuum assumption (very high node density).

Opportunistic large arrays: cooperative transmission in wireless multihop ad hoc networks to reach far distances

The technique we propose in this paper allows efficient flooding of a wireless network with information from a source, which we refer to as the leader. At the same time, it permits us to transmit reliably to far destinations that the individual nodes are not able to reach without consuming rapidly their own battery resources, even when using multihop links (the reach-back problem). The synchronization constraints are extremely loose and can be fulfilled in a distributed manner. The key idea is to have the nodes simply echo the leader's transmission operating as active scatterers while using adaptive receivers that acquire the equivalent network signatures corresponding to the echoed symbols. The active nodes in the network operate either as regenerative or nonregenerative relays. The intuition is that each of the waveforms will be enhanced by the accumulation of power due to the aggregate transmission of all the nodes while, if kept properly under control, the random errors or the receiver noise that propagate together with the useful signals will cause limited deterioration in the performance. The avalanche of signals triggered by the network leaders form the so-called opportunistic large array (OLA). The main advantages of the OLA are its great flexibility and scalability.