Broadcast Communication Protocol Research Articles

Classical communication through quantum causal structures

Quantum mechanics allows operations to be in indefinite causal order. Recently there have been active discussions on enhanced communication strategies through exotic causal structures. In light of this, through the process matrix formalism, we formulate different classical capacities for a bi-partite quantum process. We find that a one-way communication protocol through an arbitrary process cannot outperform a causally separable process, i.e., we can send at most one bit per qubit. Next, we study bi-directional communication through a causally separable process. Our result shows, a bi-directional protocol cannot exceed the limit of one way communication protocol. Finally, we generalise this result to multi-party broadcast communication protocol through a definite ordered process.

Communication and Consensus Co-Design for Distributed, Low-Latency, and Reliable Wireless Systems

Designing distributed, fast, and reliable wireless consensus protocols is instrumental in enabling mission-critical decentralized systems, such as robotic networks in the Industrial Internet of Things (IIoT), drone swarms in rescue missions, and so forth. However, chasing both low-latency and reliability of consensus protocols is a challenging task. The problem is aggravated under wireless connectivity that may be slower and less reliable, compared to wired connections. To tackle this issue, we investigate fundamental relationships between consensus latency and reliability through the lens of wireless connectivity, and co-design communication and consensus protocols for low-latency and reliable decentralized 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 a closed-form end-to-end (E2E) latency expression of the R2C that guarantees target reliability, and compare it with a baseline consensus protocol, referred to as referendum consensus (RC). The result shows that the R2C is faster compared to the RC and more reliable compared when co-designed with the broadcast protocol compared to that with the gossip protocol.

Distributed Constrained Stochastic Subgradient Algorithms Based on Random Projection and Asynchronous Broadcast over Networks

We consider a distributed constrained optimization problem over a time-varying network, where each agent only knows its own cost functions and its constraint set. However, the local constraint set may not be known in advance or consists of huge number of components in some applications. To deal with such cases, we propose a distributed stochastic subgradient algorithm over time-varying networks, where the estimate of each agent projects onto its constraint set by using random projection technique and the implement of information exchange between agents by employing asynchronous broadcast communication protocol. We show that our proposed algorithm is convergent with probability 1 by choosing suitable learning rate. For constant learning rate, we obtain an error bound, which is defined as the expected distance between the estimates of agent and the optimal solution. We also establish an asymptotic upper bound between the global objective function value at the average of the estimates and the optimal value.

Cryptanalysis of quantum broadcast communication and authentication protocol with a one-time pad**Project supported by the National Natural Science Foundation of China (Grant Nos. 61272057 and 61170270).

Chang et al. [Chin. Phys. B 23 010305 (2014)] have proposed a quantum broadcast communication and authentication protocol. However, we find that an intercept-resend attack can be preformed successfully by a potential eavesdropper, who will be able to destroy the authentication function. Afterwards, he or she can acquire the secret transmitted message or even modify it while escaping detection, by implementing an efficient man-in-the-middle attack. Furthermore, we show a simple scheme to defend this attack, that is, applying non-reusable identity strings.

Cryptanalysis and improvement of quantum broadcast communication and authentication protocol with a quantum one-time pad**Project supported by the National Natural Science Foundation of China (Grant Nos. 61502101 and 61170321), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20140651), the Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20110092110024), and the Project Funded by PAPD

The security of quantum broadcast communication (QBC) and authentication protocol based on Greenberger–Horne–Zeilinger (GHZ) state and quantum one-time pad is analyzed. It is shown that there are some security issues in this protocol. Firstly, an external eavesdropper can take the intercept–measure–resend attack strategy to eavesdrop on 0.369 bit of every bit of the identity string of each receiver without being detected. Meanwhile, 0.524 bit of every bit of the secret message can be eavesdropped on without being detected. Secondly, an inner receiver can take the intercept–measure–resend attack strategy to eavesdrop on half of the identity string of the other’s definitely without being checked. In addition, an alternative attack called the CNOT-operation attack is discussed. As for the multi-party QBC protocol, the attack efficiency increases with the increase of the number of users. Finally, the QBC protocol is improved to a secure one.

A Robust Block-Jacobi Algorithm for Quadratic Programming under Lossy Communications

We address the problem distributed quadratic programming under lossy communications where the global cost function is the sum of coupled local cost functions, typical in localization problems and partition-based state estimation. We propose a novel solution based on a generalized gradient descent strategy, namely a Block-Jacobi descent algorithm, which is amenable for a distributed implementation and which is provably robust to communication failure if the step size is sufficiently small. Interestingly, robustness to packet loss, implies also robustness of the algorithm to broadcast communication protocols, asynchronous computation and bounded random communication delays. The theoretical analysis relies on the separation of time scales and singular perturbation theory. Our algorithm is numerically studied in the context of partition-based state estimation in smart grids based on the IEEE 123 nodes distribution feeder benchmark. The proposed algorithm is observed to exhibit a similar convergence rate when compared with the well known ADMM algorithm with no packet losses, while it has considerably better performance when including moderate packet losses.

Quantum broadcast communication and authentication protocol with a quantum one-time pad

A quantum broadcast communication and authentication protocol with a quantum one-time pad based on the Greenberger—Horne—Zeilinger state is proposed. A binary string is used to express the identity of the receiver, which is encoded as a single sequence of photons. The encoded photon sequence acts as a detection sequence and implements authentication. An XOR operation serves as a one-time pad and is used to ensure the security of the protocol. The binary string is reused even in a noisy channel and proves to be unconditionally secure. In contrast with the protocols proposed by Wang et al. [Chin. Phys. 16 1868 (2007)] and Yang et al. [Chin. Phys. B 19 070304 (2010)], the protocol in this study implements the identity authentication with a reusable binary string; no hash function or local unitary operation is used. The protocol in this study is also easier to implement and highly efficient without losing security.

Distributed Asynchronous Constrained Stochastic Optimization

In this paper, we study two problems which often occur in various applications arising in wireless sensor networks. These are the problem of reaching an agreement on the value of local variables in a network of computational agents and the problem of cooperative solution to a convex optimization problem, where the objective function is the aggregate sum of local convex objective functions. We incorporate the presence of a random communication graph between the agents in our model as a more realistic abstraction of the gossip and broadcast communication protocols of a wireless network. An added ingredient is the presence of local constraint sets to which the local variables of each agent is constrained. Our model allows for the objective functions to be nondifferentiable and accommodates the presence of noisy communication links and subgradient errors. For the consensus problem we provide a diminishing step size algorithm which guarantees asymptotic convergence. The distributed optimization algorithm uses two diminishing step size sequences to account for communication noise and subgradient errors. We establish conditions on these step sizes under which we can achieve the dual task of reaching consensus and convergence to the optimal set with probability one. In both cases we consider the constant step size behavior of the algorithm and establish asymptotic error bounds.

Undecidable problems in unreliable computations

Lossy counter machines are defined as Minsky counter machines where the values in the counters can spontaneously decrease at any time. While termination is decidable for lossy counter machines, structural termination (termination for every input) is undecidable. This undecidability result has far-reaching consequences. Lossy counter machines can be used as a general tool to prove the undecidability of many problems, for example: (1) The verification of systems that model communication through unreliable channels (e.g., model checking lossy fifo-channel systems and lossy vector addition systems). (2) Several problems for reset Petri nets, like structural termination, boundedness and structural boundedness. (3) Parameterized problems like fairness of broadcast communication protocols.