Blockchain, as a constantly evolving Peer-to-Peer (P2P) distributed ledger technology with characteristics, such as decentralization, security, interoperation, and trust establishment, can potentially lower the costs of the underpinning infrastructure and maintenance compared with conventional centralized systems. Consequently, the distributed structure of blockchain is naturally suitable for the Internet of Things (IoT), which can be used to build secure and trusted IoT. Despite the advances made in applying blockchain to IoT in the past few years, some research challenges remain to be addressed, including the poor scalability, heterogeneous IoT devices, and the impact of integration on network performance.

Blockchain technology is becoming the cornerstone for the development and deployment of other technologies like Federated Learning (FL) and the Internet of Things (IoT), as it plays a critical role in data sharing and incentives. Blockchains supports decentralization, data-privacy protection, security, and reliability. Assuring secure data sharing in mobile computing and FL is challenging because of untrustworthy participants and unknown data quality. Blockchain provides trust in decentralized environments without requiring trusted third parties. By using smart contracts, blockchain has been able to supporting rich decentralized applications. However, the scalability of blockchain is a challenge that prevents its wide adoption by high-performance applications. To address the blockchain scalability issue, various blockchain sharding technologies and off-chain solutions have been proposed. To improve the network throughput, blockchain sharding divides the entire network into several smaller parallel groups and exploits fast consensus algorithms in blockchain shards. Off-chain solutions, such as payment channel networks (PCNs), transfer the slow on-chain transactions to the off-chain environment, in which transactions can be accelerated. Without consensus and on-chain expensive operations, off-chain scalable solutions significantly reduce transaction costs and increase transaction throughput. This special issue aims to provide a forum for the presentation of state-of-the-art research approaches that advance the construction of intelligent blockchain systems. A total of 27 articles were accepted after a two-round rigorous review process. Based on their topics, we have grouped the accepted articles into four categories: blockchain-based federated learning systems, blockchain and the IoT, blockchain scalability, and high-performance blockchains. In what follows, we introduce these articles and their contributions.

This article presents a novel way to reduce blockchain nodes’ memory requirements using error correcting codes. In particular, LDPC codes are taken as examples to explicitly demonstrate the scheme. The proposed coding scheme encodes data across multiple blocks, respectively, block headers, in the blockchain. This leads to a significant reduction in required memory at each node. We then apply the proposed coding technique to blockchains organized in two different ways. Our first scheme has the same protocol for mining, broadcasting, and verification of blocks, as Bitcoin-type blockchains. Our scheme is different in thatfull nodesdo not have to store all blocks. Instead they will need to store only one block of a group of$t$blocks. In the second scheme, we consider a new block verification protocol and an account-based model under the assumption that transmission between any two nodes can be established, as well as the broadcast transmission. Our block verification protocol uses the Byzantine fault tolerance algorithm and requires sending a newly mined block to only a small number of verification nodes, instead of broadcasting it to the entire network, which leads to a reduction of the network load.

The prevalence of smartphones presents a unique opportunity to develop a system that can have a significant impact on reducing the annual 400,000 fatalities from pedestrian traffic accidents. This system gives 360 degrees, extended range, NLOS view where both the driver and the pedestrian are warned of a possible collision. This, the first of its kind, system was developed from a two year collaborative research effort between Honda and Qualcomm to leverage DSRC so vehicles can communicate with smartphones to preempt a possible collision between a pedestrian (with a smartphone) and an approaching vehicle. This paper describes the pedestrian and vehicle-based algorithms and gives an overview of how this system warns both the driver and the pedestrian so they can take evasive action and prevent a collision. We present the results from our field tests where we demonstrate several pedestrian safety scenarios and present the over- the-air performance data collected in the field tests. Finally, we discuss remaining challenges and present possible approaches to reducing false positives, minimizing spectrum and channel congestion and improving security and localization.

The calculus of deterministic constraints on service and traffic streams offers a rich language to specify service guarantees. In particular, the service curve earliest deadline first (SCED) algorithm has an associated feasibility test given by linear constraints. Users sending streams of data through the server may have differing needs for delay and throughput.We suggest a way based on utility function maximization, subject to the linear constraints of the SCED algorithm, for allocation of service. In addition, a generalization of the SCED algorithm is given which does not require that the deadline sequences within streams be monotone nondecreasing.

This paper explores optimization of paging and registration policies in cellular networks. Motion is modeled as a discrete-time Markov process, and minimization of the discounted, infinite-horizon average cost is addressed. The structure of jointly optimal paging and registration policies is investigated through the use of dynamic programming for partially observed Markov processes. It is shown that there exist policies with a certain simple form that are jointly optimal. An iterative algorithm for policies with the simple form is proposed and investigated. The algorithm alternates between paging policy optimization, and registration policy optimization. It finds a pair of individually optimal policies. Majorization theory and Riesz's rearrangement inequality are used to show that jointly optimal paging and registration policies are given for symmetric or Gaussian random walk models by the nearest-location-first paging policy and distance threshold registration policies.

In this paper, we investigate the delay–throughput tradeoffs in mobilead-hocnetworks. We consider four node mobility models: 1) two-dimensional independent and identically distributed (i.i.d.) mobility, 2) two-dimensional hybrid random walk, 3) one-dimensional i.i.d. mobility, and 4) one-dimensional hybrid random walk. Two mobility time scales are included in this paper. i) Fast mobility, where node mobility is at the same time scale as data transmissions. ii) Slow mobility, where node mobility is assumed to occur at a much slower time scale than data transmissions. Given a delay constraint$D$, we first characterize the maximum throughput per source–destination (S-D) pair for each of the four mobility models with fast or slow mobiles. We then develop joint coding–scheduling algorithms to achieve the optimal delay–throughput tradeoffs.

In recent years, network coding has been investigated as a method to obtain improvements in wireless networks. A typical assumption of previous work is that relay nodes performing network coding can decode the messages from sources perfectly. On a simple relay network, we design a scheme to obtain network coding gain even when the relay node cannot perfectly decode its received messages. In our scheme, the operation at the relay node resembles message passing in belief propagation, sending the logarithm likelihood ratio (LLR) of the network coded message to the destination. Simulation results demonstrate the gain obtained over different channel conditions. The goal of this paper is not to give a theoretical result, but to point to possible interaction of network coding with user cooperation in noisy scenario. The extrinsic information transfer (EXIT) chart is shown to be a useful engineering tool to analyze the performance of joint channel coding and network coding in the network.

rdquoThe VCG-Kelly mechanism is proposed, which is obtained by composing the communication efficient, one- dimensional signaling idea of Kelly with the VCG mechanism, providing efficient allocation for strategic buyers at Nash equilibrium points. It is shown that the revenue to the seller can be maximized or minimized using a particular one-dimensional family of surrogate valuation functions.

This paper explores optimization of paging and registration policies in cellular networks. Motion is modeled as a discrete-time Markov process, and minimization of the discounted, infinite-horizon average cost is addressed. The structure of jointly optimal paging and registration policies is investigated through the use of dynamic programming for partially observed processes. It is shown that there exist policies with a certain simple structure that are jointly optimal, though the dynamic programming approach does not directly provide an efficient method to find the policies. An iterative algorithm for policies with the simple form is proposed and investigated. The algorithm alternates between paging policy optimization and registration policy optimization. It finds a pair of individually optimal policies, but an example is given showing that the policies need not be jointly optimal.