# On the Performance of Partial LIS for 6G Systems
## 1 Introduction  
With a view to better optimizing existing resources but being associated with an even higher level of human skills, the fourth industrial revolution (also regarded as Industry 4.0) corresponds with the use of robots that replace humans and is associated with four essential terms: robotics, artificial intelligence (AI), the internet of things (IoT) and big data. The combination of these four elements is transforming the way that companies produce and provide products and services, the way society is organized, and the way human beings live [1]. It thus corresponds with the replacement of humans by machines, or their interaction [2]. Like previous industrial revolutions, it corresponds with a better optimization of existing resources. An example of this is automation, and with it the autonomous vehicle, while the massification of car sharing will be facilitated by the abolition of drivers. The fifth generation of mobile communications (5G), given the contribution of IoT, is an important pillar of the fourth industrial revolution. With this generation, machines communicate with each other, instead of people. This is disruptive, as previous generations of communications have been limited to interconnecting humans rather than machines [3]. This fifth generation of mobile communications corresponds with the initial contribution of IoT to the fourth industrial revolution, while the sixth generation of mobile communications (6G) will correspond with an improvement in this contribution in a more significant and broad way, supporting new services such as the following:  
* Holographic services;
* Extended and augmented reality;* Location and remote-control applications and mapping;
* Future eHealth services--healthcare;
* Next-generation autonomous vehicles;
* More efficient IoT connectivity of low-power devices for smart cities and smart homes;
* Interaction with high-speed unmanned aircraft vehicles. Meanwhile, 6G is expected to include the following requirements:
* Speeds as high as 1 terabit per second;
* Higher network capacity, supporting a much higher number of mobile devices per square kilometre;
* Lower latency, as required for delay-sensitive applications, such as autonomous driving, online gaming or controlling remote devices. With the aim of interconnecting billions of IoT devices with extremely high throughputs and low latencies, 6G requirements are expected to be achieved using mechanisms such as block transmission techniques, advanced error correction codes and large intelligence surfaces (LIS). The LIS system can be viewed as a beyond-massive multiple input multiple output (MIMO) service, with an even higher number of antenna elements and supporting higher capacities and data rates. Wireless communications are commonly established beyond the Fraunhofer distance, that is, in the far-field [4]. Individual antenna elements of the LIS act in the far-field, but the LIS system, as a whole, works in the near field [4; 5; 6]. Therefore, this can be viewed as a near-field beamformer, differing from a traditional beamformer because the beam can also be directed over a distance, in addition to being directed along bearing and elevation planes. This additional property allows for a reduction of interference between users that are aligned in terms of bearing and elevation but located at different distances. Note that the adjacent antenna elements of the LIS are typically spaced apart \(\lambda/2\), while the channel correlation between the antenna elements allows for the creation of the above-described beam. It is worth noting that previous works have addressed the deployment of improved capabilities (better spectral efficiency, increased data rates, lower latencies, better performances) using energy-efficient techniques, such as non-orthogonal multiple access (NOMA), that take into account the received powers. The work published in [7] investigates NOMA-assisted secure offloading for vehicular edge computing networks in the presence of multiple malicious eavesdropper vehicles.