Indoor positioning system is a critical part in location-based services. Highly precise positioning systems can support different mobile applications in future wireless systems. Positioning systems using existing wireless networks have low deployment costs, but the position error can be up to several meters. While there are positioning systems proposed in the literature that have low position error, they require extra hardware and are therefore costly to deploy. In this paper, we propose an indoor positioning system based on visible light communications (VLC). In contrast to existing works on VLC for positioning, our system estimates the location of the receiver in three dimensions even without: the knowledge of the height of the receiver from ground; and requiring the alignment of the receiver's normal with the LED's normal. Our system has low installation cost as it uses existing lighting sources as transmitters. Light sensor and accelerometer, which can be found in most smartphones, are used at the receiver's side. They are used to measure the received light intensity and the orientation of the smartphone. A low-complexity algorithm is then used to find out the receiver's position. Our system does not require the knowledge of the LED transmitters' physical parameters. Experimental results show that our system achieves average position errors of less than 0.25 m.

This paper proposes two novel and practical designs of angle diversity receivers to achieve multiple-input-multiple-output (MIMO) capacity for indoor visible light communications (VLC). Both designs are easy to construct and suitable for small mobile devices. By using light emitting diodes for both illumination and data transmission, our receiver designs consist of multiple photodetectors (PDs), which are oriented with different inclination angles to achieve high-rank MIMO channels and can be closely packed without the requirement of spatial separation. Due to the orientations of the PDs, the proposed receiver designs are named pyramid receiver (PR) and hemispheric receiver (HR). In a PR, the normal vectors of PDs are chosen the same as the normal vectors of the triangle faces of a pyramid with equilateral N-gon base. On the other hand, the idea behind HR is to evenly distribute the PDs on a hemisphere. Through analytical investigation, simulations and experiments, the channel capacity and bit-error-rate (BER) performance under various settings are presented to show that our receiver designs are practical and promising for enabling VLC-MIMO. In comparison to induced link-blocked receiver, our designs do not require any hardware adjustment at the receiver from location to location so that they can support user mobility. Besides, their channel capacities and BER performance are quite close to that of link-blocked receiver. Meanwhile, they substantially outperform spatially-separated receiver. This study reveals that using angle diversity to build VLC-MIMO system is very promising.

This paper provides a comprehensive review of the literature concerning the utilization of Natural Language Processing (NLP) techniques, with a particular focus on transformer-based large language models (LLMs) trained using Big Code, within the domain of AI-assisted programming tasks. LLMs, augmented with software naturalness, have played a crucial role in facilitating AI-assisted programming applications, including code generation, code completion, code translation, code refinement, code summarization, defect detection, and clone detection. Notable examples of such applications include the GitHub Copilot powered by OpenAI’s Codex and DeepMind AlphaCode. This paper presents an overview of the major LLMs and their applications in downstream tasks related to AI-assisted programming. Furthermore, it explores the challenges and opportunities associated with incorporating NLP techniques with software naturalness in these applications, with a discussion on extending AI-assisted programming capabilities to Apple’s Xcode for mobile software development. This paper also presents the challenges of and opportunities for incorporating NLP techniques with software naturalness, empowering developers with advanced coding assistance and streamlining the software development process.

Private information retrieval scheme for coded data storage is considered in this paper. We focus on the case where the size of each data record is large and hence only the download cost (but not the upload cost for transmitting retrieval queries) is of interest. We prove that the tradeoff between storage cost and retrieval/download cost depends on the number of data records in the system. We propose a class of linear storage codes and retrieval schemes, and derive conditions under which our schemes are error-free and private. Tradeoffs between the storage cost and retrieval costs are also obtained.

This is the first part of a two-part paper on the information theoretic study of biometric security systems. In this paper, the design of single-use biometric security systems is analyzed from an information theoretic perspective. A fundamental trade-off between privacy, measured by the normalized equivocation rate of the biometric measurements, and security, measured by the rate of the key generated from the biometric measurements, is identified. The privacy-security region, which characterizes the above-noted trade-off, is derived for this case. The scenario in which an attacker of the system has side information is then considered. Inner and outer bounds on the privacy-security region are derived in this case. Finally, biometric security systems with perfect privacy are studied, which is shown to be possible if and only if common randomness can be generated from two biometric measurements.

Fano's inequality relates the error probability of guessing a finitely-valued random variable X given another random variable Y and the conditional entropy of X given Y. It is not necessarily tight when the marginal distribution of X is fixed. This paper gives a tight upper bound on the conditional entropy of X given Y in terms of the error probability and the marginal distribution of X. A new lower bound on the conditional entropy for countably infinite alphabets is also found. The relationship between the reliability criteria of vanishing error probability and vanishing conditional entropy is also discussed. A strengthened form of the Schur-concavity of entropy which holds for finite or countably infinite random variables is given.