What is RIS? The probable 6G technology.
The digital world gets busier day by day and so are the demands of fast network connectivity. In India, we are enjoying the fast connectivity and data speed of around 50 megabits per second with 4G Technology. But the 5G with 50 gigabits per second has been already deployed in many countries like South Korea, China, and the United States. Here the network backbone lies completely in MIMO technology where numerous antennas are required to ensure link reliability and connectivity in wireless systems. So what next?
As the demand for data rates increases scientists are struggling to find out new possibilities for increasing data rates. The major problem that scientists face is the limited spectrum available for wireless communications. The wide implementation of millimeter wave communication with frequencies greater than 60GHz poses a great risk for human health and the environment. Can we do something rather than just increase the frequency of wireless communications?
Here is one of the solutions to meet the data rate demands of future 6G that is 1 Terabit per second. Recent studies say that Reflecting intelligent surfaces (RIS) sometimes known as smart reflecting surfaces is a good solution to future 6G networks. RIS uses structures that can be programmed and used to control the propagation of EM waves by altering the electric and magnetic features of the surface. To accomplish this the intelligent surfaces incorporate sensing technology into them. According to the current channel condition and properties of the channel, the intelligent surfaces can be configured in their operating environment. As the intelligent surfaces do not pose any loss this is suitable for long-distance wireless communications. What are the possible RIS scenarios?
The RIS scenarios include implementing reflecting surfaces mounted on a wall to redirect the signals coming from a transmitter unit, e.g., base station, to the external environment. The possible implementation approach to RIS is namely, antenna array systems and meta surfaces. In short, meta surfaces are electrically light and dense 2D arrays of structural elements containing desired properties given by their constitutive elements. What is the operating principle behind RIS?
Similar to reflecting antennas RIS can be used to spontaneously change their radiation patterns. Therefore instead of numerous reflecting antennas, we can employ one reflecting structure containing numerous controlling grids. The eliminates the need for conventional MIMO systems (used in 4G and 5G) where we employ multiple transmit and multiple receive antennas. Now, Is there any difference in the RIS system principle from conventional multiple antenna systems?
In the RIS assisted models, the elements are generally configured to operate independently of each other. This means that is there is no mutual coupling between the elements of the RIS. All the results from theoretical concepts remain the same for RIS antenna array-based reflectors. The future RIS combined technology will be deep learning-based RIS-assisted systems, RIS-assisted simultaneous wireless information and wireless power transfer, RIS-enabled UAV communications, RIS-enabled edge computing, RIS-enabled non-orthogonal multiple access and RIS-enabled terahertz communication.
Other major applications of RIS
1.Under water Communications
Over optical signal transmission methods, in water, we prefer acoustic signal transmission over long distances. Acoustic signal transmission in the underwater medium suffers most from scattering at uneven surfaces, water streams and fish. This leads to a high path loss and extreme frequency selectivity of the communication channel due to the multipath, such that only very narrow signal bandwidths are tolerated. Correspondingly, the effective data rate is very low. Hence, these weaknesses can be mitigated using RIS.
Not only underwater, but RIS can be also implemented in the underground environment. Our goal is to establish wireless connectivity between distributed sensor nodes to monitor seismic activity, structural health of buildings as well as soil quality for the smart agriculture and clever irrigation. Similar to the application mentioned in the underwater medium, the phase shifters of RIS can be optimized to reduce the frequency selectivity and increase the effective signal bandwidth. Correspondingly, a practical design problem would aim at minimizing the delay spread and signal quality after the equalization filter.
3. Disaster Environments
To improve the performance of the wireless networks supporting the rescue operations in disaster environments, RIS can be deployed as part of the original infrastructure, where the future rescue operations would potentially take place. An example of this infrastructure is the mentioned concept of Smart Cities, where most of the buildings are covered by the reflective surfaces to facilitate the massive wireless connectivity. This approach is very beneficial also for the potential danger of a disaster, since parts of the surfaces may still be operational and thus help improving the signal quality
- AMMAR RAFIQUE, August 15, 2021, “Reconfigurable Intelligent Surface(RIS) benchmarking results and simulation code.”, IEEE Dataport, doi: https://dx.doi.org/10.21227/eg0q-y563.
- Kisseleff, Steven et al. “Reconfigurable Intelligent Surfaces in Challenging Environments.” ArXiv abs/2011.12110 (2020)