5G technology promises to revolutionize our word. With billions of connected devices and super-fast speeds, 5G will undoubtedly change the way we communicate, work, and perceive the environment we live in. 5G Technology is ready to launch with the first 5G deployments in 2019.
The 5G network development will heavily depend on the availability of frequency spectrum since wireless frequencies are the actual medium for radio communications. Millimeter-wave spectrum is expected to provide the means on which broadband services will be expanded upon, especially when it comes down to the early Enhanced Mobile Broadband (eMBB) 5G services where super high speeds are required to provide UHD video, video on demand and various VR/AR applications. More available spectrum results in more capacity, and more capacity to higher data rate services to the end-user. Thus, millimeter-wave, with sizeable available bandwidths and low current footprint will provide the means for efficient 5G network development.
Existing Radio Frequency Spectrum
Cellular communications use wireless links to provide point-to-multipoint (P2MP) connectivity from each radio base station to the end-users. Point-to-point microwave radio links are used to wirelessly transmit the mobile services by backhauling the signal from the radio base stations towards the core network.
Cellular bands: Cellular bands are in the sub 6GHz region. Usual frequency areas range from 800MHz up to 2600MHz. In the US, 2G GSM technologies operate at 850 and 1900MHz, while for 3G UMTS, Verizon and AT&T are using the 850 & 1900MHz, Sprint 800 and 1900MHz and T-Mobile 1700 & 2100MHz frequency bands. For 4G LTE coverage, Verizon and AT&T extended their operation in the 700MHz and 1700/2100MHz bands, while T-Mobile added the 700MHz frequency band and Sprint the 2500MHz band in their portfolio. Similar frequencies are used in Europe and other parts of the world.
Wireless Backhaul Bands: Conventional microwave bands are in the range of 6-42GHz. Sub 6GHz frequencies may also be used for wireless transmission, especially for near/non-LOS individual cases. In the last several years, many Mobile Operators are moving to the millimeter-wave region, especially in the 80GHz (E-band). The millimeter-wave frequency links market share is expected to increase exponentially, as far as wireless backhauling is concerned, in the years to come in order to support the 5G network architecture.
Frequency Spectrum Characteristics
The microwave radio frequency electromagnetic spectrum ranges in the area of 300MHz to 300GHz with resulting wavelengths from 1m down to 1mm. These frequencies cover a broad range of radio spectrum with different characteristics of radio propagation.
Sub 6GHz frequencies operate below 6GHz and are typically used for cellular communication, i.e., the communication of a radio base station to the end-user devices (cell phones) and wi-fi connectivity at the 2.4 and 5.6GHz unlicensed bands. Due to the lower frequency and the higher wavelengths, these signals can penetrate specific fabrics like walls and can be used for outdoor and indoor connectivity. They also take advantage of diffraction and reflection phenomena which can assist in mobility and the connection between moving objects via reflections. In that sense, these type of signals do not require a Line of Sight (LOS) between the two points of communication and are therefore applicable to near and non-Line of Sight (n/NLOS) connectivity.
Moving to higher frequencies above 6GHz the wavelengths become shorter and signal penetration is more difficult. These frequencies usually need a direct Line of Sight to communicate correctly, and that is why they are typically used for static connections between different radio base stations and for backhauling the signal to the core network points.
5G NR Millimeter-wave Spectrum
According to 3GPP, 5G NR spectrum is separated into two distinct regions. Frequency Range 1 (FR1), which typically describes 5G NR usage in the sub 6GHz area and Frequency Range 2 (FR2) which extends 5G NR usage in the millimeter-wave region.
3GPP 5G NR has specified the 3.5GHz and the 26/28 GHz millimeter-wave spectrum for 5G Fixed Wireless Access (FWA) connectivity to provide high data rate 5G broadband services. 60 GHz frequency band will also be used for 5G FWA taking into account the WiGig radio technology to support Multi-gigabit connectivity.
5G Wireless Backhaul Millimeter-wave spectrum
The lower part of the millimeter-wave spectrum at 26/28 GHz and 32/38 GHz has already been used for wireless backhaul and is part of the traditional microwave frequency bands. Wireless backhaul systems are also using higher millimeter-wave bands such as the 80GHz E-band which can provide more available spectrum and higher bandwidths, resulting in a single carrier point-to-point radio with up to 10Gbps transmission capacity. This 10G capacity may seem enough to serve early 5G deployments, but Mobile Operators together with vendors are targeting to use new technologies to support even higher capacity needs. Standardization is underway to exploit commercially new frequency bands, such as W-Band (90 GHz) and D-Band (130 – 174.8 GHz) which will be able to provide capacities of 50Gbps to 100Gbps data rates in a single radio unit.
Millimeter-Wave Spectrum Characteristics
Low footprint: Spectrum in the 6 – 42 GHz region is used for many years for mobile backhauling and has become exhausted. During the last decades, Mobile Operators have based their network development on these traditional frequency bands, and there is little room left for extra deployment in that region. Millimeter-wave, on the other hand, is a relatively new spectrum area with low current implementations. Mobile Operators are now moving towards this area since there is plenty of room for network expansion for 5G.
Spectrum Availability: Millimeter waves are radio frequencies that cover the range above 24GHz in the electromagnetic frequency spectrum. Millimeter-wave spectrum expands above the traditional frequency bands and has larger available bandwidths for spectrum usage. This spectrum can serve the high capacities needed to support the new 5G high-data-rate services. V-band at 60 GHz has a sufficient range of 9GHz (57-66GHz), while E-band at 80GHz has an available bandwidth of 10GHz (71-16 & 81-86GHz). D-Band is also another new millimeter frequency above 100GHz to support a broader range of high capacity needs with up to 45GHz total spectrum available (130 – 174.8 GHz).
Unlicensed or Light-licensed schemes: Regulatory Authorities have given incentives for millimeter-wave migration by applying flexible unlicensed and light-licensed schemes. The unlicensed scheme is used in the V-band 60GHz band while light-licensing schemes are used for the E-band 80GHz and the new millimeter-wave technologies under development at W-band and D-band.
Small Form-factor: Due to the nature of these high-frequency bands, with short wavelengths and narrow pencil-like beams and with the aid of advanced techniques such as MIMO and antenna beam-forming, millimeter-waves can achieve high throughput with a small form factor compared to traditional microwave bands.
Shorter Distances: Frequencies above the 10GHz range suffer from signal attenuation during severe weather phenomena such as rain, hail, sleet, and snow. This attenuation is due to the oxygen absorption and water vapor that degrade the received signal strength. Signal degradation limits the effective distance of the radio link, and since higher frequencies are typically more susceptible to rain phenomena and flat fading, millimeter-wave links are, therefore, used to cover shorter distances than the traditional microwave radios. These distances range from less than 5Km, even down to a couple of hundreds of meters as in the case of 60GHz due to a peak at the oxygen levels curve.
5G Small Cells & Network Densification
5G networks will have to support ultra-fast data rates and provide massive connectivity between end-points. Specifically, in urban areas, 5G network infrastructure should be able to offer high speeds and broadband connectivity in small geographical areas, such as an office district or marketplaces and plazas.
This is where 5G small cells come to place. Mobile Operators target to cover these high capacity needs with 5G small cells. In a dense urban environment, instead of deploying several lower frequency cells, a higher number of 5G small cells can be implemented to cover the same geographical area. By increasing the number of cells in the same area, the distance between the new micro radio base stations will be smaller.
Millimeter-waves use very high frequencies and are more susceptible to rain phenomena and can, therefore, can cover shorter distances, However, with the expected network density, the increased number of cells per area and the shorter distances between the endpoints, millimeter-waves are the best candidate for future 5G deployments.
Mobile Operators aim to migrate to the millimeter-wave region to support 5G multi-gigabit connectivity and higher capacity needs. One thing is, therefore, certain, whether we are referring to 5G NR or 5G backhaul, Millimeter-wave is definitely the New Black!
