1. Description

The ITU-R Recommendation P.530, “Propagation data and prediction methods required for the design of terrestrial line-of-sight systems” provides a number of propagation models useful for the evaluation of propagation effects in microwave radiocommunications systems.

This Recommendation provides prediction methods for the propagation effects that should be taken into account in the design of digital fixed line-of-sight links, both in clear-air and rainfall conditions. It also provides link design guidance in clear step-by-step procedures including the use of mitigation techniques to minimize propagation impairments. The final outage predicted is the base for other ITU-R Recommendations addressing error performance and availability.

Different propagation mechanisms, with a variety of effects on the radio links, are addressed in the Recommendation. The ranges of application of the prediction methods are not always coincident.

A brief description of the implemented prediction methods is given in the following sections.

2. Fading due to multipath and related mechanisms

Fading is the most important mechanism that affects the performance of digital radio links. Multipath in the troposphere can cause deep fades, especially in longer paths or at higher frequencies. The prediction method for all percentages of time is graphically illustrated in figure 1.

For small percentages of time, fading follows a Rayleigh distribution, with an asymptotic variation of 10 dB per probability decade. This can be predicted by the following expression:


  • K : geoclimatic factor
  • dN: point refractivity gradient in the lowest 65 m of the atmosphere not exceeded for 1% of an average year
  • sa : area terrain roughness, defined as the standard deviation of terrain heights (m) within a 110 km x 110 km area with a 30 s resolution
  • d : Link path distance (km)
  • f : Link frequency (GHz)
  • hL : altitude of the lower antenna above sea level (m)
  • |εp| : absolute value of the path inclination (mrad)
  • p0 : multipath occurrence factor
  • pw : percentage of time fade depth A is exceeded in average worst month

Figure 1: Percentage of time, pw, fade depth, A, exceeded in average worst month, with p0 ranging from 0.01 to 1 000

If is made equal to the receiver margin, the probability of link outage due to multipath propagation is equal to pw /100. For a link with hops, the probability of outage PT takes into account the possibility of a small correlation between fades in consecutive hops.


In (4), , for most practical cases. Pi is the outage probability predicted for the i-th hop, and di its distance. C = 1 if A exceeds 40 km or the sum of the distances exceeds 120 km.

3. Attenuation due to hydrometeors

Rain can cause very deep fades, particularly at higher frequencies. The Rec. P. 530 includes the following simple technique that may be used for estimating the long-term statistics of rain attenuation:

Step 1:  Obtain the rain rate R0.01 exceeded for 0.01% of the time (with an integration time of 1 min).

Step 2:  Compute the specific attenuation, γR (dB/km) for the frequency, polarization and rain rate of interest using Recommendation ITU-R P.838.

Step 3:  Compute the effective path length, deff, of the link by multiplying the actual path length by a distance factor r. An estimate of this factor is given by:


where, for R0.01 ≤ 100 mm/h:


For R0.01 > 100 mm/h, use the value 100 mm/h in place of R0.01.

Step 4:  An estimate of the path attenuation exceeded for 0.01% of the time is given by:

A0.01 = γR deff = γR d

Step 5:  For radio links located in latitudes equal to or greater than 30° (North or South), the attenuation exceeded for other percentages of time in the range 0.001% to 1% may be deduced from the following power law:


Step 6:  For radio links located at latitudes below 30° (North or South), the attenuation exceeded for other percentages of time in the range 0.001% to 1% may be deduced from the following power law.


The formulas (8) and (9) are valid within the range 0.001% – 1%.

For high latitudes or high link altitudes, higher values of attenuation may be exceeded for time percentage due to the effect of melting ice particles or wet snow in the melting layer. The incidence of this effect is determined by the height of the link in relation to the rain height, which varies with geographic location. A detailed procedure is included in the Recommendation [1].

The probability of outage due to rain is calculated as p / 100, where is the percentage of time rain attenuation exceeds the link margin.

4. Reduction of cross-polar discrimination (XPD)

The XPD can deteriorate sufficiently to cause co‑channel interference and, to a lesser extent, adjacent channel interference. The reduction in XPD that occurs during both clear-air and precipitation conditions must be taken into account.

The combined effect of multipath propagation and the cross-polarization patterns of the antennas governs the reductions in XPD occurring for small percentages of time in clear-air conditions. To compute the effect of these reductions in link performance a detailed step-by-step procedure is presented in the Recommendation [1].

The XPD can also be degraded by the presence of intense rain. For paths on which more detailed predictions or measurements are not available, a rough estimate of the unconditional distribution of XPD can be obtained from a cumulative distribution of the co-polar attenuation (CPA) for rain (see section 3) using the equi-probability relation:


The coefficients and V(f) are in general dependent on a number of variables and empirical parameters, including frequency, f. For line-of-sight paths with small elevation angles and horizontal or vertical polarization, these coefficients may be approximated by:


An average value of U0 of about 15 dB, with a lower bound of 9 dB for all measurements, has been obtained for attenuations greater than 15 dB.

A step-by-step procedure is given to calculate the outage due to XPD reduction in the presence of rain.

5. Distortion due to propagation effects

The primary cause of distortion on line-of-sight links in the UHF and SHF bands is the frequency dependence of amplitude and group delay during clear-air multipath conditions.

The propagation channel is most often modeled by assuming that the signal follows several paths, or rays, from the transmitter to the receiver. Performance prediction methods make use of such a multi-ray model by integrating the various variables such as delay (time difference between the first arrived ray and the others) and amplitude distributions along with a proper model of equipment elements such as modulators, equalizer, forward‑error correction (FEC) schemes, etc.. The method recommended in [1] for predicting error performance is a signature method.

The outage probability is here defined as the probability that BER is larger than a given threshold.

Step 1:  Calculate the mean time delay from:


where is the path length (km).

Step 2:  Calculate the multipath activity parameter η as:


Step 3:  Calculate the selective outage probability from:



  • Wx : signature width (GHz)
  • Bx : signature depth (dB)
  • τr,x : the reference delay (ns) used to obtain the signature, with denoting either minimum phase (M) or non-minimum phase (NM) fades.

If only the normalized system parameter Kn is available, the selective outage probability in equation (15) can be calculated by:



  • T : system baud period (ns)
  • Kn,x : the normalized system parameter, with denoting either minimum phase (M) or non-minimum phase (NM) fades.

6. Diversity techniques

There are a number of techniques available for alleviating the effects of flat and selective fading, most of which alleviate both at the same time. The same techniques often alleviate the reductions in cross-polarization discrimination also.

Diversity techniques include space, angle and frequency diversity. Space diversity helps to combat flat fading (such as caused by beam spreading loss, or by atmospheric multipath with short relative delay) as well as frequency selective fading, whereas frequency diversity only helps to combat frequency selective fading (such as caused by surface multipath and/or atmospheric multipath).

Whenever space diversity is used, angle diversity should also be employed by tilting the antennas at different upward angles. Angle diversity can be used in situations in which adequate space diversity is not possible or to reduce tower heights.

The degree of improvement afforded by all of these techniques depends on the extent to which the signals in the diversity branches of the system are uncorrelated.

The diversity improvement factor, I, for fade depth, A, is defined by:

I = p(A) / pd(A)

where pd(A) is the percentage of time in the combined diversity signal branch with fade depth larger than and p(A) is the percentage for the unprotected path. The diversity improvement factor for digital systems is defined by the ratio of the exceedance times for a given BER with and without diversity.

The improvement due to the following diversity techniques can be calculated:

  • Space diversity.
  • Frequency diversity.
  • Angle diversity.
  • Space and frequency diversity (two receivers)
  • Space and frequency diversity (four receivers)

The detailed calculations can be found in [1].

7. Prediction of total outage

The total outage probability due to clear-air effects is calculated as:

  • Pns : Outage probability due to non-selective clear-air fading (Section 2).
  • Ps : Outage probability due to selective fading (Section 5)
    PXP : Outage probability due XPD degradation in clear-air (Section 4).
  • Pd : Outage probability for a protected system (Section 6).

The total outage probability due to rain is calculated from taking the larger of Prain and PXPR.

  • Prain : Outage probability due to rain fading (Section 3).
  • PXPR : Outage probability due XPD degradation associated to rain (Section 4).

The outage due to clear-air effects is apportioned mostly to performance and the outage due to precipitation, predominantly to availability.

8. References

[1] ITU-R Recommendation P.530-13, “Propagation data and prediction methods required for the design of terrestrial line-of-sight systems”, ITU, Geneva, Switzerland, 2009.


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Rec. ITU-R PN.837-1

Rec. ITU-R PN.837-1


This document contains information on the statistics of precipitation intensity is needed for the prediction of attenuation and scattering caused by precipitation;

This data with Rain Zones is used for planning of Microwave Links and Radio Links worldwide, especially for Rain Fade and Link Availability Calculations

When the rain climate zone is required in computer applications for any given set of geographic coordinates, the program RAINZONE be used. (The software for RAINZONE may be obtained from the ITU Radiocommunication Bureau.)

Rec. ITU-R PN.837-1 1

Table 1 is used to obtain the expected median cumulative distribution of rain rate for the rain climate

Rain climatic zones

Rainfall intensity exceeded (mm/h) (Reference to Figs. 1 to 3)

ITU-837-1 Table 1



The above charts show the rain zones around the world in for each country and region.  This data is available in more up-to-date formats and used in many radio planning tools.

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Microwave Rain Fade Planning ITU-R P.837-6


ITU-R P.837-6 P.0837-01  – Characteristics of precipitation for propagation modelling Radiowave propagation for Terrestrial Microwave Links and Radio Links for Point to Point (P2P, PTP) and Point to Multipoint (P2MP, PTMP) deployments.

Calculations can be made for Link Availability (%) for all frequency bands, to take into account link budgets, transmit power, receive sensitivity, antenna gain, target availability and other factors.  Typical Link Availability Targets are 99.99%, 99.999% and higher.

ITU-R P.837-6 P.0837-01

ITU-R P.837-6 P.0837-01
ITU-R P.837-6 P.0837-01

Recommendation ITU-R P.837 contains maps of meteorological parameters that have been obtained using the European Centre for Medium-Range Weather Forecast (ECMWF) ERA-40 re-analysis database, which are recommended for the prediction of rainfall rate statistics with a 1-min integration time, when local measurements are missing.
Rainfall rate statistics with a 1-min integration time are required for the prediction of rain attenuation in terrestrial and satellite links. Data of long-term measurements of rainfall rate may be available from local sources, but only with higher integration times. This Recommendation provides a method for the conversion of rainfall rate statistics with a higher integration time to rainfall rate statistics with a 1-min integration time.

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1024QAM Microwave Links

1024QAM Microwave Links for High Capacity Wireless Transmission

High Capacity Microwave Links from leading vendors use 1024QAM modulation to achieve high capacity, spectral density and efficiency without sacrificing reliability.  This technology sets a new benchmark for microwave transmission capacity for operators including 4G / LTE Backhaul links for mobile operators as well as last-mile links, backbone and other applications.

High Capacity Links require High Order QAM modulation

CableFree Microwave 1024QAM increase from 4QAMLeading long-haul microwave equipment vendors are now using dependable long-distance transmissions using 1024 QAM. Relative to the industry-standard 256 QAM, this represents a 25% increase in capacity (and up to double the capacity of legacy SDH links), with all other factors the same. Compared to older 4QAM modulation the increase to 1024QAM is five-fold. Operators of long-haul microwave links will certainly enjoy the boost to their capacity with 1024 QAM, especially when these upgrades are relatively painless and generally require only a minor and quick swap of equipment.

Adaptive Coding and Modulation (ACM)

ACM with 1024QAM ModulationLeading microwave equipment vendors are able to keep their long-haul transmission links operational even in transient fade and noisy conditions. The enabling technology is ACM: Adaptive Coding and Modulation. Microwave links with ACM technology automatically sense the quality of the transmission link and can automatically decrease the modulation technique in case of degraded signal quality due to interference or other microwave propagation problems such as weather. So, if a microwave transmission is operating at maximum capacity using 1024QAM and suddenly encounters interference or high rainfall, a system such as the CableFree microwave system automatically steps down the modulation to lower levels until the transmission network, although at lower capacity now, maintains the ultra high level of link reliability and availability. As the temporary weather effects disappear, the microwave system automatically re-applies more efficient higher-order modulation techniques to regain full capacity.

Overcoming Tradeoffs due to High Order QAM Modulation

CableFree 1024QAM modulation tradeoffsWith increasing modulation the receiver sensitivity is greatly reduced, and generally transmit power has to be reduced due to linearity constraints in the transmitter.  For fixed modulation speeds the result is either increase of antenna size or reduced distances, which may prevent an operator upgrading to higher capacity.  The use of ACM allows use of 1024QAM whilst avoiding sacrifice of distance or antenna sizes, by graceful step-down of modulation to lower rates during rare periods of high rainfall.

Use along with other bandwidth-enhancing technologies such as XPIC

1024QAM modulation is fully compatible with other methods to increase capacity such as XPIC (Cross Polar Interference Cancellation).  An advanced microwave modem featuring 1024QAM and XPIC can greatly increase capacity.  XPIC alone offers double the capacity compared to a single polarised non-XPIC solution.

1024QAM Microwave Summary

These latest advancements in advanced microwave modulation offer network operators an easy and inexpensive upgrade path to higher capacities to meet demand. Advanced modulation technology of 1024QAM is fully shipping and available today and offers a very cost-effective way to boost capacity in long-haul microwave applications.

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Rain Fade on Microwave Links

Rain Fade on Microwave Links

Microwave Link Rain FadeRain 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.

Two models are generally used for Rain modelling: Crane and ITU.  The ITU model is generally preferred by microwave planners.  A global map of Rain distribution according to the ITU model is shown below:

Global ITU Rain Fade Map for Microwave Link Availability Planning
Global ITU Rain Fade Map for Microwave Link Availability Planning

Used in conjunction with appropriate planning tools, this data can be used to predict the expected Operational Availability (in %) of a microwave link.  Useful Operational Availability figures typically vary from 99.9% (“three nines”) to 99.999%  (“five nines”), and are a function of the overall link budget including frequency band, antenna sizes, modulation, receiver sensitivity and other factors.

Another useful Rain Fade map is shown here, showing the 0.01% annual rainfall exceedance rate:

CableFree ITU-R Rain Fade Map - Global for 0.01% annual rainfall exceedance rate
CableFree ITU-R Rain Fade Map – Global for 0.01% annual rainfall exceedance rate

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Microwave Link Technology

Introduction to Microwave

Example of a CableFree Microwave Link Installation
Example of a CableFree Microwave Link Installation

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.

Microwave Link over English Channel, 1931
Microwave Link over English Channel, 1931

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

CableFree Microwave Communication Tower
Microwave Communication Tower

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

CableFree FOR2 Microwave Link 400Mbps
CableFree FOR2 Microwave Link 400Mbps

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
  • Environmental constraints, including rain fade
  • Cost of licenses for required frequency bands

Microwave Frequency Bands

Microwave Frequency Bands
Microwave Frequency Bands

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

Microwave Link Rain FadeRain 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

Example of a 1+0 Unprotected Microwave Link
Example of a 1+0 Unprotected Microwave Link

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)

Microwave Adaptive Coding and Modulation (ACM)
Microwave Adaptive 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

CableFree Microwave Cellular Network
Microwave Backhaul in Cellular Networks


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.

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