A popular choice for modern IP networks is the Full Outdoor Radio (FOR). Also called “Zero Footprint Radio”, “All Outdoor Radio”, “Outdoor IP Radio”.
In an FOR, the radio includes the modem, user network interface and all RF processing sections in a single unit. This is typically mounted on the customer rooftop or tower site mated to a high gain directional antenna.
Connectivity is typically Power over Ethernet (POE) and optional Fibre Optics (SFP) connection
The Full Outdoor Radio (FOR) architecture is popular with:
Internet Service providers (ISP)
Wireless ISPs (WISPs)
Full Outdoor Microwave Radios offer up to 400(364) Mbps and 800(728) Mbps Full Duplex payload (1.6Gbps aggregate capacity) and higher up to 3Gbps or more, 6-38GHz licensed frequency bands.
Using suitable antennas and sites, ultra-long-distance links exceeding 100km can be achieved. Distances depend on:
Required throughput (Mbps)
Desired Availability (%)
Antenna size (gain)
For more information on Full Outdoor Radios and Microwave Networks please Contact Us
Microwave is a line-of-sight wireless communication technology that uses high frequency beams of radio waves to provide high speed wireless connections that can send and receive voice, video, and data information.
Microwave links are are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it.
Microwave radio transmission is commonly used in point-to-point communication systems on the surface of the Earth, in satellite communications, and in deep space radio communications. Other parts of the microwave radio band are used for radars, radio navigation systems, sensor systems, and radio astronomy.
The higher part of the radio electromagnetic spectrum with frequencies are above 30 GHz and below 100 GHz, are called “millimeter waves” because their wavelengths are conveniently measured in millimeters, and their wavelengths range from 10 mm down to 3.0 mm. Radio waves in this band are usually strongly attenuated by the Earthly atmosphere and particles contained in it, especially during wet weather. Also, in wide band of frequencies around 60 GHz, the radio waves are strongly attenuated by molecular oxygen in the atmosphere. The electronic technologies needed in the millimeter wave band are also much more complex and harder to manufacture than those of the microwave band, hence cost of Millimeter Wave Radios are generally higher.
History of Microwave Communication
James Clerk Maxwell, using his famous “Maxwell’s equations,” predicted the existence of invisible electromagnetic waves, of which microwaves are a part, in 1865. In 1888, Heinrich Hertz became the first to demonstrate the existence of such waves by building an apparatus that produced and detected microwaves in the ultra high frequency region. Hertz recognized that the results of his experiment validated Maxwell’s prediction, but he did not see any practical applications for these invisible waves. Later work by others led to the invention of wireless communications, based on microwaves. Contributors to this work included Nikola Tesla, Guglielmo Marconi, Samuel Morse, Sir William Thomson (later Lord Kelvin), Oliver Heaviside, Lord Rayleigh, and Oliver Lodge.
In 1931 a US-French consortium demonstrated an experimental microwave relay link across the English Channel using 10 foot (3m) dishes, one of the earliest microwave communication systems. Telephony, telegraph and facsimile data was transmitted over the 1.7 GHz beams 40 miles between Dover, UK and Calais, France. However it could not compete with cheap undersea cable rates, and a planned commercial system was never built.
During the 1950s the AT&T Long Lines system of microwave relay links grew to carry the majority of US long distance telephone traffic, as well as intercontinental television network signals. The prototype was called TDX and was tested with a connection between New York City and Murray Hill, the location of Bell Laboratories in 1946. The TDX system was set up between New York and Boston in 1947.
Modern Commercial Microwave Links
A microwave link is a communications system that uses a beam of radio waves in the microwave frequency range to transmit video, audio, or data between two locations, which can be from just a few feet or meters to several miles or kilometers apart. Examples of Commercial Microwave links from CableFree may be see here. Modern Microwave Links can carry up to 400Mbps in a 56MHz channel using 256QAM modulation and IP header compression techniques. Operating Distances for microwave links are determined by antenna size (gain), frequency band, and link capacity. The availability of clear Line of Sight is crucial for Microwave links for which the Earth’s curvature has to be allowed
Microwave links are commonly used by television broadcasters to transmit programmes across a country, for instance, or from an outside broadcast back to a studio. Mobile units can be camera mounted, allowing cameras the freedom to move around without trailing cables. These are often seen on the touchlines of sports fields on Steadicam systems.
Planning of microwave links
CableFree Microwave links have to be planned considering the following parameters:
Required distance (km/miles) and capacity (Mbps)
Desired Availability target (%) for the link
Availability of Clear Line of Sight (LOS) between end nodes
Towers or masts if required to achieve clear LOS
Allowed frequency bands specific to region/country
Microwave signals are often divided into three categories:
ultra high frequency (UHF) (0.3-3 GHz);
super high frequency (SHF) (3-30 GHz); and
extremely high frequency (EHF) (30-300 GHz).
In addition, microwave frequency bands are designated by specific letters. The designations by the Radio Society of Great Britain are given below.
Microwave frequency bands
Designation Frequency range
L band 1 to 2 GHz
S band 2 to 4 GHz
C band 4 to 8 GHz
X band 8 to 12 GHz
Ku band 12 to 18 GHz
K band 18 to 26.5 GHz
Ka band 26.5 to 40 GHz
Q band 30 to 50 GHz
U band 40 to 60 GHz
V band 50 to 75 GHz
E band 60 to 90 GHz
W band 75 to 110 GHz
F band 90 to 140 GHz
D band 110 to 170 GHz
The term “P band” is sometimes used for ultra high frequencies below the L-band. For other definitions, see Letter Designations of Microwave Bands
Lower Microwave frequencies are used for longer links, and regions with higher rain fade. Conversely, Higher frequencies are used for shorter links and regions with lower rain fade.
Rain Fade on Microwave Links
Rain fade refers primarily to the absorption of a microwave radio frequency (RF) signal by atmospheric rain, snow or ice, and losses which are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a storm front. Rain fade can be caused by precipitation at the uplink or downlink location. However, it does not need to be raining at a location for it to be affected by rain fade, as the signal may pass through precipitation many miles away, especially if the satellite dish has a low look angle. From 5 to 20 percent of rain fade or satellite signal attenuation may also be caused by rain, snow or ice on the uplink or downlink antenna reflector, radome or feed horn. Rain fade is not limited to satellite uplinks or downlinks, it also can affect terrestrial point to point microwave links (those on the earth’s surface).
Possible ways to overcome the effects of rain fade are site diversity, uplink power control, variable rate encoding, receiving antennas larger (i.e. higher gain) than the required size for normal weather conditions, and hydrophobic coatings.
Diversity in Microwave Links
In terrestrial microwave links, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity plays an important role in combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience different levels of fading and interference. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured indecibels.
The following classes of diversity schemes are typical in Terrestrial Microwave Links:
Unprotected: Microwave links where there is no diversity or protection are classified as Unprotected and also as 1+0. There is one set of equipment installed, and no diversity or backup
Hot Standby: Two sets of microwave equipment (ODUs, or active radios) are installed generally connected to the same antenna, tuned to the same frequency channel. One is “powered down” or in standby mode, generally with the receiver active but transmitter muted. If the active unit fails, it is powered down and the standby unit is activated. Hot Standby is abbreviated as HSB, and is often used in 1+1 configurations (one active, one standby).
Frequency diversity: The signal is transmitted using several frequency channels or spread over a wide spectrum that is affected by frequency-selective fading. Microwave radio links often use several active radio channels plus one protection channel for automatic use by any faded channel. This is known as N+1 protection
Space diversity: The signal is transmitted over several different propagation paths. In the case of wired transmission, this can be achieved by transmitting via multiple wires. In the case of wireless transmission, it can be achieved by antenna diversity using multiple transmitter antennas (transmit diversity) and/or multiple receiving antennas (reception diversity).
Polarization diversity: Multiple versions of a signal are transmitted and received via antennas with different polarization. A diversity combining technique is applied on the receiver side.
Diverse Path Resilient Failover
In terrestrial point to point microwave systems ranging from 11 GHz to 80 GHz, a parallel backup link can be installed alongside a rain fade prone higher bandwidth connection. In this arrangement, a primary link such as an 80GHz 1 Gbit/s full duplex microwave bridge may be calculated to have a 99.9% availability rate over the period of one year. The calculated 99.9% availability rate means that the link may be down for a cumulative total of ten or more hours per year as the peaks of rain storms pass over the area. A secondary lower bandwidth link such as a 5.8 GHz based 100 Mbit/s bridge may be installed parallel to the primary link, with routers on both ends controlling automatic failover to the 100 Mbit/s bridge when the primary 1 Gbit/s link is down due to rain fade. Using this arrangement, high frequency point to point links (23GHz+) may be installed to service locations many kilometers farther than could be served with a single link requiring 99.99% uptime over the course of one year.
Automatic Coding and Modulation (ACM)
Link adaptation, or Adaptive Coding and Modulation (ACM), is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link (e.g. the pathloss, the interference due to signals coming from other transmitters, the sensitivity of the receiver, the available transmitter power margin, etc.). For example, EDGE uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission. The process of link adaptation is a dynamic one and the signal and protocol parameters change as the radio link conditions change.
The goal of Adaptive Modulation is to improve the operational efficiency of Microwave links by increasing network capacity over the existing infrastructure – while reducing sensitivity to environmental interferences.
Adaptive Modulation means dynamically varying the modulation in an errorless manner in order to maximize the throughput under momentary propagation conditions. In other words, a system can operate at its maximum throughput under clear sky conditions, and decrease it
gradually under rain fade. For example a link can change from 256QAM down to QPSK to keep “link alive” without losing connection. Prior to the development of Automatic Coding and Modulation, microwave designers had to design for “worst case” conditions to avoid link outage The benefits of using ACM include:
Longer link lengths (distance)
Using smaller antennas (saves on mast space, also often required in residential areas)
Higher Availability (link reliability)
Automatic Transmit Power Control (ATPC)
CableFree Microwave links feature ATPC which automatically increases the transmit power during “Fade” conditions such as heavy rainfall. ATPC can be used separately to ACM or together to maximise link uptime, stability and availability. When the “fade” conditions (rainfall) are over, the ATPC system reduces the transmit power again. This reduces the stress on the microwave power amplifiers, which reduces power consumption, heat generation and increases expected lifetime (MTBF)
Uses of microwave links
Backbone links and “Last Mile” Communication for cellular network operators
Backbone links for Internet Service Providers (ISPs) and Wireless ISPs (WISPs)
Corporate Networks for Building to Building and campus sites
Telecommunications, in linking remote and regional telephone exchanges to larger (main) exchanges without the need for copper/optical fibre lines.
Broadcast Television with HD-SDI and SMPTE standards
Because of the scalability and flexibility of Microwave technology, Microwave products can be deployed in many enterprise applications including building-to-building connectivity, disaster recovery, network redundancy and temporary connectivity for applications such as data, voice and data, video services, medical imaging, CAD and engineering services, and fixed-line carrier bypass.
Mobile Carrier Backhaul
Microwave Links are a valuable tool in Mobile Carrier Backhaul: Microwave technology can be deployed to provide traditional PDH 16xE1/T1, STM-1 and STM-4, and Modern IP Gigabit Ethernet backhaul connectivity and Greenfield mobile networks. Microwave is far quicker to install and lower Total Cost of Ownership for Cellular Network Operators compared to deploying or leasing fibre optic networks
Low Latency Networks
CableFree Low Latency versions of Microwave links uses Low Latency Microwave Link Technology, with absolutely minimal delay between packets being transmitted and received at the other end, except the Line of Sight propagation delay. The Speed of Microwave propagation through the air is approximately 40% higher than through fibre optics, giving customers an immediate 40% reduction in latency compared to fibre optics. In addition, fibre optic installations are almost never in a straight line, with realities of building layout, street ducts and requirement to use existing telecom infrastructure, the fibre run can be 100% longer than the direct Line of Sight path between two end points. Hence CableFree Low Latency Microwave products are popular in Low Latency Applications such as High Frequency Trading and other uses.
For Further Information on Microwave
To find out more about Microwave Link Technology and how CableFree can assist with your wireless network, please Contact Us
In radio communications, a Fresnel zone (/freɪˈnɛl/ fray-nel), , is one of a (theoretically infinite) number of concentric ellipsoids which define volumes in the radiation pattern of a (usually) circular aperture. Fresnel zones result from diffraction by the circular aperture. The cross section of the first (innermost) Fresnel zone is circular. Subsequent Fresnel zones are annular (doughnut-shaped) in cross section, and concentric with the first. The Fresnel Zone is named after the physicist Augustin-Jean Fresnel.
Importance of Fresnel zones
If unobstructed, radio waves will travel in a straight line from the transmitter to the receiver. But if there are reflective surfaces along the path, such as bodies of water or smooth terrain, the radio waves reflecting off those surfaces may arrive either out of phase or in phase with the signals that travel directly to the receiver. Waves that reflect off of surfaces within an even Fresnel zone are out of phase with the direct-path wave and reduce the power of the received signal. Waves that reflect off of surfaces within an odd Fresnel zone are in phase with the direct-path wave and can enhance the power of the received signal. Sometimes this results in the counter-intuitive finding that reducing the height of an antenna increases the signal-to-noise ratio.
Fresnel provided a means to calculate where the zones are–where a given obstacle will cause mostly in phase or mostly out of phase reflections between the transmitter and the receiver. Obstacles in the first Fresnel zone will create signals with a path-length phase shift of 0 to 180 degrees, in the second zone they will be 180 to 360 degrees out of phase, and so on. Even numbered zones have the maximum phase cancelling effect and odd numbered zones may actually add to the signal power.
To maximize receiver strength, one needs to minimize the effect of obstruction loss by removing obstacles from the radio frequency line of sight (RF LOS). The strongest signals are on the direct line between transmitter and receiver and always lie in the first Fresnel zone.
Determining Fresnel zone clearance
The concept of Fresnel zone clearance may be used to analyse interference by obstacles near the path of a radio beam. The first zone must be kept largely free from obstructions to avoid interfering with the radio reception. However, some obstruction of the Fresnel zones can often be tolerated. As a rule of thumb the maximum obstruction allowable is 40%, but the recommended obstruction is 20% or less.
For establishing Fresnel zones, first determine the RF Line of Sight (RF LOS), which in simple terms is a straight line between the transmitting and receiving antennas. Now the zone surrounding the RF Line of Sight is said to be the Fresnel zone.
Unlicensed and light licence wireless links is the most cost effective of all links and can be deployed in a matter of days. Currently in most countries there are a few unlicensed ISM-band frequencies that are used for point to point links and a few light licensed frequencies that provide interference free operation.
What is a Light Licensed microwave link?
Regional regulators (typically, in each country) are responsible for Spectrum Management of the Radio Spectrum. This naturally varies in each country due to different history of usage and allocation.
A Light License is where the licensee pays a small licence fee to register his/her radio link with regional regulators such as OFCOM (UK).
The regulator (such as OFCOM in the UK) use the licence to inform other potential users of the spectrum that there is already a radio link or links in the area when they register their own link prior to deployment. This information is also used to resolve disputes should interference arise.
Depending on which country you are in, these can include:
Licence free spectrum are the 5Ghz, 24Ghz, and 60GHz frequencies
Light licence spectrum operate in the 64-66GHz and 70/80GHz
Why consider unlicensed or light license links?
Low density areas not suffering from RF interference
Non-critical data transmission
When are licensed links mostly used?
Organisations looking to create a LAN across multiple buildings on the same site
Organisations looking to reduce the cost of existing leased lines
In low density areas where RF interference is low or free
When to consider opting for a licenced over unlicensed?
High density areas suffering from RF interference
Mission-critical data transmission
Is unlicensed or light licenced microwave right for you?
If you are looking for the simple answer, please contact Wireless Excellence for details. Our very experienced team are happy to discuss your requirements and advise on the best solution whatever your needs.
Modulation is a data transmission technique that transmits a message signal inside another higher frequency carrier by altering the carrier to look more like the message. Quadrature Amplitude Modulation (QAM) is a form of modulation that uses two carriers—offset in phase by 90 degrees—and varying symbol rates (i.e., transmitted bits per symbol) to increase throughput. The table in this blog post (Figure 1) describes the various common modulation levels, associated bits/symbol and incremental capacity improvement above the next lower modulation step.
2. Must all operators who use microwave backhaul use higher-order QAMs?
Higher-order QAMs are not necessarily a must-have for all network operators. However, higher-order modulations do provide one method of obtaining higher data throughput and are a useful tool for meeting LTE backhaul capacity requirements.
3. What is the main advantage of using higher-order QAMs with microwave radios?
The main advantage is increased capacity, or higher throughput. However, capacity improvement diminishes with every higher modulation step (i.e., moving from 1024QAM to 2048QAM the improvement is only about 10 percent!), so the real capability of higher-order modulations alone to address the objective of increasing capacity is very limited. Other techniques will be needed.
4. What are the tradeoffs of higher-order QAMs on RF performance?
First, with each step increase in QAM the RF performance of the microwave radio is degraded as per the Carrier-to-Interference (C/I) ratio. For example, going from 1024QAM to 2048QAM will produce an increase of 5 dB in C/I (Figure 2). This results in the microwave link having much higher sensitivity to interference, making it more difficult to coordinate links and reducing link density. Along with this increase in phase noise there will be an increase in design complexity cost.
Also, by increasing from 1024QAM to 2048QAM, system gain will decrease from above 80 dB to just above 75 dB (Figure 2). With much lower system gain microwave links will have to be shorter and larger antennas will have to be employed—increasing total cost of ownership and introducing additional link design and path planning problems.
All of the above are the results of linear functions: they degrade in a one-to-one relationship with the move to higher-order QAMs. Meanwhile, the capacity increases derived from higher-order QAMs are the function of a flattening curve: Each step increase in QAM results in a reduced percentage increase in capacity compared to prior increases in QAM. The added capacity benefits are diminished when considering the added costs of higher C/I and lower system gain.
5. Do you need to use Adaptive Coding and Modulation (ACM) while using higher-order QAMs?
ACM should be implemented while employing high-order QAMs to offset lower system gain. However, while ACM does help mitigate the effects of more difficult propagation when using higher-order modulations, it cannot help offset increased C/I.
6. What gives CableFree a “heads-up” here when other big name companies seem to be supporting the technology?
CableFree realizes higher-order modulations are not a panacea—a cure-all. While every minor technology improvement in throughput can help, a focus on technologies that grow capacity in hundreds of percentage points vs. tens of percentage points is most critical now. CableFree believes that these hundreds-of-percentage-points-of-improvement-in-capacity solutions will be the most important moving forward. It is in these technologies that CableFree has a “heads-up.” Such techniques include deploying more spectrum—particularly in the form of multichannel RF bonding (N+0) solutions—to achieve a minimum of 200 percent capacity increase. This technique is subject to frequency availability, but with flexible N+0 implementations (such as being able to use frequency channels in different bands and different channel sizes) many congestion issues can be avoided.
Second, intelligently dimensioning the backhaul network based on proven rules, best practices and L2/L3 quality of service (QoS) capabilities is another technique to provide potentially very large gains in backhaul capacity. Higher-order modulations can be one tool to achieve required capacity increases in the backhaul network. However, their inherent drawbacks should be well understood, while the most attention should be paid to other techniques that deliver more meaningful and quantifiable benefits.
7. Will operators need to “retrofit” microwave radios to be capable of higher-order QAM operation in their existing microwave infrastructure? Or will completely new hardware be required?
This depends on the age and model of the existing radios. Older microwave systems will likely need to be “retrofitted” to support 512QAM and higher modulations. Recently installed microwave systems should be able to support these technologies without new hardware.
8. How will QAM evolve in the future? Is the introduction of higher-order QAMs an indefinite process, with no end in sight?
The introduction of higher-order QAMs is not an endless process. As per Figure 1 above in this blog post, the law of diminishing returns applies: Throughput percentage improvement declines as modulation rates increase. The cost and complexity of implementing higher-order QAMs probably is not worth the capacity increase benefits derived—not past 1024QAM, in any event.
Find out information on technology, deployment and applications for modern Digital Microwave Links
Microwave links are widely used for connectivity in modern digital IP networks. With capacities up to 6Gbps and beyond, a modern Microwave Link network can deliver bandwidth in a reliable, cost-effective and flexible manner – without need for disruption and delay caused by digging up streets and avoiding costly leased-line or leased fibre optic alternatives.
On this website you can find more information about radio link deployment and technology. Also we invite you to contact our experts with any questions by sending a message to us on our contact page.
Microwave links are used extensively in 4G & 5G LTE backhaul networks, 2G (GSM) and 3G (UMTS) mobile operators, wireless metropolitan area networks (Wi-MAN) and corporate networks where high performance, flexibility, speed of deployment and low operating costs are required. Key features of links include high spectral efficiency (256QAM, 1024QAM, 2048QAM and 4096QAM), Automatic Transmit Power Control (ATPC) and Adaptive Coding and Modulation (ACM).
Globally, MW radio links are used for around 60% of all mobile backhaul connections due to the compelling technical and commercial arguments in favour of MW radio compared to leased line and trenched fibre alternatives. Speed of deployment and flexibility – the ability to move sites or provision rapidly – are greatly in favour of MW radio over fibre and cabled alternatives.
A link typically features a radio unit and a parabolic antenna, which may vary in size from 30cm up to 4m diameter depending on required distance and capacity. The radio unit is generally either a “Full Outdoor”, “Split Mount” or “Full Indoor” design depending on operator preference, deployment, features and available indoor space for specific sites and installation.
For More information on MW Radio Links please Contact Us