# Future Is Unlicensed: Private 5G Unlicensed Network for Connecting Industries of Future
## 1 Introduction  
The term \"wireless networking\" means widespread connectivity, but we have yet to see that in today's industrial and business-critical domains such as manufacturing, supply chain, transportation systems, and energy [1, 2]. The existing mobile networks designed and deployed for enterprise applications provide opportunities to optimize and redefine business within the limitations of wired (Ethernet/optical) and WiFi networks. For industrial applications, the ability to design mobile networks to meet the coverage, performance, and security requirements of critical applications (such as mobile robots, automated guided vehicles, and head-mounted displays with advanced mobile applications for workers) is fundamental to the new wave of cyber-physical systems known as Industry 4.0 [3, 4]. In its support, a private LTE network that is utilizing dedicated radio equipment to serve the premises of local and independent networks (such as the industrial network) with specific Internet of Things (IoT) applications and services is undergoing investigation under 5G technology [5, 6]. A private network is the Long-Term Evolution (LTE)-based wireless communication technology for local/independentnetworks, which resolves user concerns of reliability and service quality, as well as security and compliance through a single, scalable wireless networking deployment leveraging LTE's technology. However, a private LTE network operating in a licensed spectrum requires a license from the national regulator or an agreement with a license holder, typically a mobile operator [7]. Thus, the use of a scarce licensed spectrum model is limiting the flexibility of private LTE to operate anywhere and everywhere, without a costly spectrum or specialists with expertise in network deployments [8]. Driven by the limited availability of the licensed spectrum, MulteFire [9] and NR-U technology were introduced by 4G in Release 14 [10] and 5G in Release 16 [6], respectively, to generate an opportunity to alleviate the spectrum crunch in future wireless networks by operating in the unlicensed band. MulteFire makes the deployment of standalone LTE [11] radio technology possible in the 5 GHz unlicensed band, whereas 3 GPP proposes 5G New Radio in the Unlicensed band (NR-U), an idea of extending MulteFire in 5G with both standalone and non-standalone modes (anchor with licensed spectrum) [12] of operation in the shared/unlicensed bands. We believe both technologies are potential candidates for next-generation communication for a smart industry that merges the quality of performance of LTE with the deployment ease of WiFi [13]. That is, end-users (enterprises) will install MulteFire/NR-U access points in place of WiFi gateways to provide LTE coverage for the Industry 4.0 scenario. In Table 1, we list the use cases of NR-U in the industrial domain. In this paper, we argue that the unlicensed spectrum plays a crucial role in realizing the industrial communication goals of 5G and beyond by offering ultra-high-speed, high capacity, low latency, and improvement in the reliability of wireless communications, which is essential to address massive-scale and highly-diverse future enterprise networks [15]. However, the unlicensed spectrum places the challenge of \"coexisting networks\" in a shared band [16], which mostly lack the means of coordination and observation. The operation in the unlicensed spectrum is subject to various limitations and restrictions [6], which are regional and band-specific, highly reducing the efficiency of LTE technology. The typical limits are in terms of transmit power, channel bandwidth, power spectral density, and the transmit duration that can be used by each device. In addition, sharing protocols may also be specified in some bands to protect other systems in the band or to allow efficient sharing [17].