Designing fast and reliable distributed consensus protocols is a key to enabling mission-critical and real-time controls of industrial Internet of Things (IIoT) nodes communicating over wireless links. However, chasing both low-latency and reliability of a consensus protocol at once is a challenging task. The problem is even aggravated under wireless connectivity that is slower and less reliable, compared to wired connections presumed in traditional consensus protocols. To tackle this issue, we investigate fundamental relationships between consensus latency and reliability under wireless connectivity, and thereby co-design communication and consensus protocols for low-latency and reliable IIoT systems. Specifically, we propose a novel communication-efficient distributed consensus protocol, termed Random Representative Consensus (R2C), and show its effectiveness under gossip and broadcast communication protocols. To this end, we derive closed-form end-to-end (E2E) latency expression of R2C that guarantees a target reliability, and compare this with a baseline consensus protocol, referred to as Referendum Consensus (RC).
Nonetheless, most of the aforementioned algorithms postulate that nodes are communicating over fast and reliable wired links. To support large-scale systems, wireless connectivity is mandatory in consensus operations, and its impact on consensus reliability and latency should be carefully examined. On this account, wireless distributed consensus protocols have recently been studied in several works @cite_31 @cite_29 @cite_15 @cite_23 @cite_0 @cite_18 @cite_25 @cite_20 . For instance, a Hashgraph-motivated wireless distributed consensus protocol has been introduced in @cite_31 , in the context of distributed wireless spectrum access applications. For power grid applications, an Ethereum-based smart contract structure and its operation protocol has been studied in @cite_9 .
@cite_18 @cite_15 @cite_29 @cite_9 @cite_0 @cite_23 @cite_31 @cite_25 @cite_20
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Reaching consensus in a network is an important problem in control, estimation, and resource allocation. While many algorithms focus on computing the exact average of the initial values in the network, in some cases it is more important for nodes to reach a consensus quickly. In a distributed system establishing two-way communication may also be difficult or unreliable. In this paper, the effect of the wireless medium on simple consensus protocol is explored. In a wireless environment, a node's transmission is a broadcast to all nodes which can hear it, and due to signal propagation effects, the neighborhood size may change with time. A class of non-sum preserving algorithms involving unidirectional broadcasting is extended to a time-varying connection model. This algorithm converges almost surely and its expected consensus value is the true average. A simple bound is given on the convergence time. We develop and analyze low-complexity cooperative diversity protocols that combat fading induced by multipath propagation in wireless networks. The underlying techniques exploit space diversity available through cooperating terminals' relaying signals for one another. We outline several strategies employed by the cooperating radios, including fixed relaying schemes such as amplify-and-forward and decode-and-forward, selection relaying schemes that adapt based upon channel measurements between the cooperating terminals, and incremental relaying schemes that adapt based upon limited feedback from the destination terminal. We develop performance characterizations in terms of outage events and associated outage probabilities, which measure robustness of the transmissions to fading, focusing on the high signal-to-noise ratio (SNR) regime. Except for fixed decode-and-forward, all of our cooperative diversity protocols are efficient in the sense that they achieve full diversity (i.e., second-order diversity in the case of two terminals), and, moreover, are close to optimum (within 1.5 dB) in certain regimes. Thus, using distributed antennas, we can provide the powerful benefits of space diversity without need for physical arrays, though at a loss of spectral efficiency due to half-duplex operation and possibly at the cost of additional receive hardware. Applicable to any wireless setting, including cellular or ad hoc networks-wherever space constraints preclude the use of physical arrays-the performance characterizations reveal that large power or energy savings result from the use of these protocols. A fundamental problem in large scale wireless networks is the energy efficient broadcast of source messages to the whole network. The energy consumption increases as the network size grows, and the optimization of broadcast efficiency becomes more important. In this paper, we study the optimal power allocation problem for cooperative broadcast in dense large-scale networks. In the considered cooperation protocol, a single source initiates the transmission and the rest of the nodes retransmit the source message if they have decoded it reliably. Each node is allocated an-orthogonal channel and the nodes improve their receive signal-to-noise ratio (SNR), hence the energy efficiency, by maximal-ratio combining the receptions of the same packet from different transmitters. We assume that the decoding of the source message is correct as long as the receive SNR exceeds a predetermined threshold. Under the optimal cooperative broadcasting, the transmission order (i.e., the schedule) and the transmission powers of the source and the relays are designed so that every node receives the source message reliably and the total power consumption is minimized. In general, finding the best scheduling in cooperative broadcast is known to be an NP-complete problem. In this paper, we show that the optimal scheduling problem can be solved for dense networks, which we approximate as a continuum of nodes. Under the continuum model, we derive the optimal scheduling and the optimal power density. Furthermore, we propose low-complexity, distributed and power efficient broadcasting schemes and compare their power consumptions with those-of-a traditional noncooperative multihop transmission. Recently, several research contributions have justified that wireless communication is not only a security burden. Its unpredictable and erratic nature can also be turned against an adversary and used to augment conventional security protocols, especially key agreement. In this paper, we are inspired by promising studies on such key agreement schemes, yet aim for releasing some of their limiting assumptions. We demonstrate the feasibility of our scheme within performance-limited wireless sensor networks. The central idea is to use the reciprocity of the wireless channel response between two transceivers as a correlated random variable. Doing so over several frequencies results in a random vector from which a shared secret is extracted. By employing error correction techniques, we are able to control the trade-off between the amount of secrecy and the robustness of our key agreement protocol. To evaluate its applicability, the protocol is implemented on MicaZ sensor nodes and analyzed in indoor environments. Further, these experiments provide insights into realistic channel behavior, available information entropy, and show a high rate of successful key agreements, up to 95 .