70-80 GHz E-Band
Millimeter-wave radios have swiftly become the fastest point-to-point radio option on the market due to the huge amount of bandwidth accessible in the 70 and 80 GHz E-Band spectrum.
Today, radio transmission products with full-duplex data rates of up to 10 Gbps over several kilometers, and carrier-class availability levels are available. Due to their lower cost, mmWave radios have the potential to revolutionize business models for mobile backhaul providers and metro/enterprise “Last-Mile” access connectivity.
What is E-Band?
Millimeter Wave on the E-Band spectrum is a high-speed (up to 10Gbps) high-capacity wireless communication technology that is excellent for metropolitan settings. Links can be deployed densely in congested cities using high frequency microwaves without causing interference, and without the need to dig for cables and fiber optics, which can be costly, sluggish, and disruptive.
mmWave links can be set up in hours, and transferred and utilized on multiple sites as network requirements change.
Recently, backhaul products operating in the millimeter frequency spectrum have seen tremendous expansion.
Because theoretical distances are subject to rain attenuation, and different settings can have different characteristic attenuations, it is vital to calculate these distances carefully and precisely. The antenna size, channel size, and availability target all play a role in determining the maximum transmission distance for 70 - 80GHz radios.
Antenna size: The larger your antenna, the greater the transmission distance your links can cover.
Channel size: The smaller the channel size, the greater the maximum transmission distance.
Availability target: This is the level of availability you need to serve customer expectations.
Due to atmospheric absorption for millimeter waves, the frequency bands used by the 70 - 80GHz radios are more susceptible to rain attenuation than lower frequency bands. Cities with more yearly rainfall will, on average, have a shorter range than cities with drier climates.
Under clear weather conditions, the transmission distances exceed several kilometers due to low atmospheric attenuation values.
Even under these circumstances, air attenuation varies with frequency. At lower microwave frequencies, up to around 38 GHz, air attenuation is relatively minimal, with values as low as a few tenths of a decibel per kilometer (dB/km). Absorption by oxygen molecules creates a big rise in attenuation around 60 GHz. Radio transmission distances at 60 GHz are severely hampered by this huge increase in oxygen absorption.
A broader low attenuation zone opens up beyond the 60 GHz oxygen absorption peak, where attenuation drops to roughly 0.5 dB/km. This window of low attenuation is commonly referred to as E-band. The E-band attenuation values are similar to what conventional microwave radios encounter. At higher frequencies above 100GHz, air attenuation normally increases, and there are multiple molecule absorption bands caused by oxygen and water absorption.
E-band frequencies are desirable for high-capacity wireless transmission because of the low atmospheric attenuation window between 70 and 100 GHz.
As with all high-frequency radio propagation, rain attenuation typically determines the practical limits on transmission distances. In the presence of rain, radio systems operating in the E-band frequency range can undergo significant attenuation, as shown in the diagram below.
The International Telecommunications Union (ITU) and other research organizations have collected decades of rainfall data from all over the world. Rainfall characteristics and relationships between rainfall rate, statistical rain duration, rain drop sizes, and other factors are generally well understood, and using this information, it is possible to engineer radio links to withstand even the worst weather events or predict the durations of weather-related outages on long-distance radio links operating at specific frequencies.
The ITU rain zone classification scheme shows the expected statistical rainfall rates in alphabetical order. While areas that experience the least rainfall are classified as “Region A,” the highest rainfall rates are in “Region Q.”
By combining the results of rainfall rate vs. attenuation and using the ITU rainfall charts, it is possible to calculate the availability of a particular radio system operating in a certain part of the world. You can do so using the link budget calculator provided by Siklu.
Alternative High Data Rate Wireless Technologies
As alternatives to E-band wireless technology, there are a limited number of viable technologies capable of supporting high data-rate connectivity.
Fibre-optic cable has the most bandwidth of any viable transmission technology, enabling extremely high data rates to be delivered across long distances. Despite the availability of thousands of kilometers of fibre around the world in long-haul and inter-city networks, “Last-Mile” access is still limited.
Fiber connectivity can be challenging due to the significant and often prohibitively expensive upfront expenditures of digging trenches and laying terrestrial fiber, as well as right-of-way issues.
Long delays are also common, not just as a result of the physical process of trenching fiber, but also as a result of environmental concerns and probable bureaucratic hurdles involved.
Microwave Radio Solutions
Fixed point-to-point microwave radios in the 4 - 42 GHz band can support higher data rates, such as full-duplex 100 Mbps Fast Ethernet or up to 500 Mbps per carrier. When compared to E-Band, the spectrum in more traditional microwave bands is limited, often congested, and typical licensed spectrum channels are quite small.
The frequency channels available for licensing are typically no more than 56 megahertz (MHz), with the majority being 30 MHz or less. Wide 112MHz channels with 880Mbps per carrier may be accessible in some bands, but only in higher frequency bands appropriate for short distances.
As a result, radios running at higher data speeds in these bands must use highly sophisticated system architectures with modulation methods as high as 1024 Quadrature Amplitude Modulation (QAM).
Because of the complexity of these systems, distances are constrained, and capacity is still limited to 880Mbps in the largest channels.
Due to the limited amount of spectrum available in these bands, the wider antenna beamwidth patterns, and the sensitivity of high QAM modulation towards any kind of interference, denser deployment of traditional microwave solutions in urban or metropolitan areas is extremely problematic.
Commercially Available Millimeter-Wave Solutions
Highly reliable wireless solutions are available to meet today's high capacity network interconnectivity requirements, providing fibre-like performance at a fraction of the cost of laying fiber or leasing high capacity fiber connections.
In the E-band spectrum, Siklu's product line offers point-to-point radio solutions with speeds up to 10 Gbps. The systems are offered in a variety of antenna sizes to satisfy the customer's availability requirements over precise deployment distances, all at the most competitive pricing points.