Motivation

Currently, we live on the verge of the fourth industrial revolution (or Industry 4.0), characterized by large-scale automation of manufacturing and industrial processes using modern technology. The massive use of machine-to-machine (M2M) communications and the Internet of things (IoT) shall play a key role as an enabling platform.

Approximating forecasts [1] for mobile data consumption in the coming decade and adopting the famous Moore's law, growth rates for mobile data consumption will continue to double every 18 months in the foreseeable future. This explosive bandwidth demand combined with very low latency requirements is driven by emerging applications such as virtual reality, connected drones, connected self-driving cars, and already mentioned massive deployments of IoT and M2M communications.

The 5^th generation of mobile network (5G) technology is set to become a part of critical infrastructure for Industry 4.0 addressing requirements for high bandwidth (1Gbps per user terminal) required for virtual and augmented reality applications, low latency down to sub-5 ms required for M2M industrial control applications, connection reliability, and robustness.

Harmonization of spectrum in mmWaves (above 6 GHz and in THz frequencies) has been considered as an important resource enabling performance requirements for 5G and coming generations of wireless communications.

Wireless communications in mmWaves

Point-to-multipoint communication

A typical point-to-multipoint application is a connection from the base station (in 5G denominated as gNB) and multiple User Equipment (UE).

The 3GPP Release 16 is harmonizing the use of spectrum in 26 GHz (3GPP and n258) and 28GHz (3GPP band n257) bands for 5G applications. Due to relatively high path loss and characteristics of signal propagation at mmWaves, service providers will need to deploy much denser networks than 4G LTE with a high number of 5G gNB base stations operating at close proximity to their users (up to several hundred meters).

To overcome signal propagation challenges in mmWaves, next-generation wireless networks will need to implement a set of mechanisms allowing UE and gNB to establish highly directional transmission links and managing changing propagation conditions in the channel. Dynamic beamforming and beam steering is an important underlying feature supporting this concept.

By establishing highly directional links between 5G gNB and User Equipment in order to; i) achieve reliable communication by managing the communication channel (beam) ii) reduce interference between the gNB service areas iii) provide spatial multiplexing effect by efficient reuse of spectrum resources iv) reduce power consumption to service customers.

Fronthaul with mmWave point to point links

Fronthaul networks shall connect each 5G gNB with the Distribution Unit (part of 5G RAN architecture) with multiple Gigabits per second. In parallel with direct fiber-optic connections to fronthaul 5G gNB, mmWave point-to-point radio shall be widely used.

According to Grand View Research [2], the global mmWave market is set to grow with CAGR 37,01% between 2020 and 2027, with E-band being the leading mmWave technology with a global market share of 73% (2019).

Beamforming and beam steering becomes extremely important to cope with interferences enabling efficient frequency reuse by using pencil sharp beams, and auto-alignment (beam steering) to compensate for misalignment between the two terminals.

When radio link equipment operating at mmWaves (E-band) are installed on proper telco infrastructure, link misalignment might not be seen as an important operational problem. It changes when many of 5G gNBs in 26/28GHz and above shall be deployed at street level and using available street furniture, like light poles, fittings attached to building structures, etc., thus infrastructure not necessarily optimized for telco applications.

Under these conditions, the link stability may suffer due to the sway of mounting structures and auto-alignment becomes an important feature minimizing operational expenditures and ensuring the quality of service for customers.

Smart electronically steerable antenna

An important part of wireless network hardware is the antenna. Beamforming and beam steering are important features of a modern ESA, especially at mmWave frequencies, even UE can accommodate the antenna array with a large number of elements.

There are three main methods achieving it:

• digital method, relying on semiconductor technology and requiring multiple RF chains (one per antenna element/sub-array) including digital to analog converters. The method provides the best control over beam characteristics, suitable for multi-stream transmission and can serve multiple users simultaneously. The main drawback to this method is the complexity and very high power consumption, which increases linearly to a number of antenna elements,
• analog method, where one RF chain serves multiple tunable phase shifters feeding each antenna element. The method is cost-effective and consumes less power. However, there are challenges implementing multiple stream capability with this method.
• hybrid method, developed with the aim to combine the advantages of both method.

Spatialite Antenna systems find very interesting applications of metamaterials to create and produce smart ESA with beamforming and beam steering capabilities. Approaches of using liquid crystals for smart ESA in mmWaves are known and have been discussed for a decade [4].

References:

[1] Faisal Tariq, Muhammad R. A. Khandaker Muhammad Imran Mehdi Bennis, and M´erouane Debbah, "A speculative study on 6G" IEEE magazine 

[4] A. Gaebler, A.Moessinger, F. Goelden, A.Manabe, M. Goebel, R. Follmann, D. Koether, C.Modes, A. Kipka, M. Deckelmann, T. Rabe, B. Schulz, P. Kuchenbecker, A. Lapanik, S.Mueller, W. Haase, and R. Jakoby "Liquid Crystal-Reconfigurable Antenna Concepts for Space Applications at Microwave and Millimeter Waves", International Journal of Antennas and Propagation Volume 2009