Information Theory (cs.IT)

Abstract: The problem of goal-oriented semantic filtering and timely source coding in multiuser communication systems is considered here. We study a distributed monitoring system in which multiple information sources, each observing a physical process, provide status update packets to multiple monitors having heterogeneous goals. Two semantic filtering schemes are first proposed as a means to admit or drop arrival packets based on their goal-dependent importance, which is a function of the intrinsic and extrinsic attributes of information and the probability of occurrence of each realization. Admitted packets at each sensor are then encoded and transmitted over block fading wireless channels so that served monitors can timely fulfill their goals. A truncated error control scheme is derived, which allows transmitters to drop or retransmit undelivered packets based on their significance. Then, we formulate the timely source encoding optimization problem and analytically derive the optimal codeword lengths assigned to the admitted packets which maximize a weighted sum of semantic utility functions for all pairs of communicating sensors and monitors. Our analytical and numerical results provide the optimal design parameters for different arrival rates and highlight the improvement in timely status update delivery using the proposed semantic filtering, source coding, and error control schemes.

Abstract: This paper puts forth a new metric, dubbed channel cycle time, to measure the short-term fairness of communication networks. Channel cycle time characterizes the average duration between two successful transmissions of a user, during which all other users have successfully accessed the channel at least once. Compared with existing short-term fairness measures, channel cycle time provides a comprehensive picture of the transient behavior of communication networks, and is a single real value that is easy to compute. To demonstrate the effectiveness of our new approach, we analytically characterize the channel cycle time of slotted Aloha and CSMA/CA. It is shown that CSMA/CA is a short-term fairer protocol than slotted Aloha. Channel cycle time can serve as a promising design principle for future communication networks, placing greater emphasis on optimizing short-term behaviors like fairness, delay, and jitter.

Abstract: BCH codes are an important class of cyclic codes due to their efficient encoding and decoding algorithms, antiprimitive BCH codes have taken a lot of attention in recent years. In this paper, we mainly study a class of BCH codes of length $n=\frac{q^{m}+1}{\lambda}$, where $\lambda\mid (q+1)$ is an integer. We give several classes of BCH codes with good parameters in this paper, containing many optimal linear codes. We also present the first few largest coset leaders modulo $n$, so two conjectures about BCH codes are partially solved.

Abstract: Thanks to the recent advances in metamaterials, reconfigurable intelligent surface (RIS) has emerged as a promising technology for future 6G wireless communications. Benefiting from its high array gain, low cost, and low power consumption, RISs are expected to greatly enlarge signal coverage, improve system capacity, and increase energy efficiency. In this article, we systematically overview the emerging RIS technology with the focus on its key basics, nine fundamental issues, and one critical problem. Specifically, we first explain the RIS basics, including its working principles, hardware structures, and potential benefits for communications. Based on these basics, nine fundamental issues of RISs, such as ``What's the differences between RISs and massive MIMO?'' and ``Is RIS really intelligent?'', are explicitly addressed to elaborate its technical features, distinguish it from existing technologies, and clarify some misunderstandings in the literature. Then, one critical problem of RISs is revealed that, due to the ``multiplicative fading'' effect, existing passive RISs can hardly achieve visible performance gains in many communication scenarios with strong direct links. To address this critical problem, a potential solution called active RISs is introduced, and its effectiveness is demonstrated by numerical simulations.