# Emerging Topics in Joint Radio-Based Positioning, Sensing, and Communications
## 1 Introduction and Definitions
[20] ( Reconfigurable Intelligent Surfaces (RIS) advances in THz communications), Ref. [21] (a focus on future space communications), Ref. [22] (holographic communication), Ref. [23] (a quantum computing paradigm in the context of wireless communications), etc. In recent years, however, these three communities have started to converge and address the positioning, sensing, and communication aspects in a joint manner, driven both by the standardization efforts in Third-Generation Partnership Project (3 GPP) towards increased spectral, cost, and hardware efficiency, and by the recent advancements in technologies such as ML/AI and RIS, which are enabling factors for Integrated Sensing and Communications (ISAC) and Simultaneous Localization and Mapping (SLAM) developments. In this editorial, we adopt the broader term of **JPSAC** as an umbrella of all possible combinations of joining two or more of the receiver functionalities related to the positioning, tracking, navigation, sensing, radar, and communications. Thus, JPSAC will be the broader umbrella term including ISAC/ Joint Sensing and Communications (JSAC) and SLAM/ Joint Positioning and Sensing (JPAS), as well as the Joint Communications and Positioning (JCAP) concepts. For a straightforward illustration of how the three different areas of communications, sensing, and positioning have been addressed in a joint manner so far, we refer to the Venn diagram in Figure 1. It is to be noted that ISAC terminology has been used quite loosely in the literature so far, to describe research on both joint communications and sensing and the joint positioning, communication, and sensing. The term ISAC, also known in the literature as JSAC, or, more seldomly, as Integrated Communications and Sensing (ICAS), Joint Communications and Sensing (JCAS), Radar Communications Coexistence (RCC), or Dual-Functional Radar Communications (DFRC), first appeared in the literature around four years ago; a few of the first detailed references to it can be found in [24] (in 2021, discussing ISAC requirements for future 6G systems), Ref. [25] (in 2021, addressing ISAC in the context of Orthogonal Time Frequency Space (OTFS) systems), Ref. [26] (also in 2021, addressing signal-processing solutions for ISAC, which they called Joint Communications and Radar sensing (JCR) in their paper), Ref. [27] (a 2022 study offering a comprehensive survey on JCAS), and [28] (addressing the RIS-assisted JCAS concept in 2022). The authors in [24] defined four categories of ISAC, namely high-accuracy localization and tracking, SLAM, augmented human senses, such as hidden object detection, and gesture and activity recognition, making their interpretation of the ISAC concept equivalent to the definitions of joint positioning, sensing, and communications rather than to the definition of joint sensing and communication, which is more popular in research papers. In general, the main goals of the ISAC involve optimizing the performance of systems that combine sensing and communication functionalities (and sometimes, also positioning functionalities); typically, the optimization of sensing and communication functions is carried out in a joint manner. The ISAC problem is often formulated as an optimization problem [29], when a communication, sensing, or joint sensing-communication metric \(F_{JPSAC}(\cdot)\) is maximized (or minimized) under certain constraints (e.g., in terms of the maximum allowed transmission power, the minimum desired quality of services, etc. ); the optimization is carried out after various design parameters are used, such as the signal modulation order; the number of antenna elements at the transmitter, receiver, or both; the beamforming strategy, the number of subcarriers depending on Orthogonal Frequency Division Multiplexing (OFDM) or OTFS modulations, etc.