Sub 6 Unlicensed & Licensed

What does Sub 6GHz Licensed and Unlicensed mean?

Several vendors and operators use this term: Find out what “Sub 6” means in practice.

Sub 6GHz Unlicensed & Licensed Links
Sub 6GHz Unlicensed & Licensed Links

What is Sub 6 ?

“Sub 6” means frequencies below 6GHz.   Though frequencies from 1GHz up to 6GHz are still classified as microwave frequencies, they are often referred to “radio links”, “microwave links”, “microwave radio links” with these terms used interchangeably.

Why Consider Sub 6GHz?

Typically links below 6GHz are used for longer point-to-point links, or point-to-multipoint links for last-mile access to customers.  Frequencies below 6GHz do not suffer significant rain fade.  In addition, these lower frequencies can be used for Non-Line-of-Sight Links, in cases where there is no direct Line of Sight between the locations that require connection.  The radio propagation characteristics of lower-frequency bands make them ideal for urban areas where radio signals may reflect from buildings and other man-made objects, and can – within limitations – penetrate walls, brickwork and concrete structures.

What does Unlicensed and Licensed mean?

The term Unlicensed in radio technology includes commonly used bands which can be used in many countries without need for a frequency license, such as 2.4GHz and 5.x GHz bands including 5.2GHz, 5.4GHz and 5.8GHz.  Please note that in a few countries these frequencies still require licenses, or are not usable by private users.
Unlicensed frequencies have the benefit of not requiring a license to operate (typically, licenses have an annual fee, and are issued by a national regulator or state owned telecom operator).  However, unlicensed links can be interfered with by other users, which can cause reduced throughput or complete link outage.  Such interference is generally heavier in high density population areas and cities, where 100’s or 1000’s of radios may be competing for the same spectrum in a given region.

Conversely, licensed operation means that the equipment user has to obtain a frequency license before using the band.  This can be available on a per-link basis, in which case the regulator allocates specific frequencies for a particular link, holding a central database of all links, or in the case of mobile operator networks, a country-wide license within which the operator self-coordinates the allocation of frequencies and coverage.
The lack of predictability in unlicensed bands is the main reason that operators prefer licensed bands for operation, despite the additional costs of licenses required to operate.

Single Carrier and OFDM Modulation

In the “Sub-6” bands 1-6GHz, a range of Single Carrier, OFDM and OFDM-A technology solutions are available.  OFDM and OFDM-A use multiple subcarriers, and can use the properties of this modulation to overcome multipath fading and reflections from hard surfaces present in dense city areas.  Conversely, Single Carrier radios use dense modulation with high symbol rates on a single radio carrier.  This can give high spectral efficiency and data rates, but limited ability to cope with reflected signals, and hence worse performance in non-LOS situations.

Line of Sight, Non-Line-of-Sight, Near-Line-of-Sight and Radio Propagation

OFDM modulation is generally used in Sub-6 radios and is more suitable to rapidly fading and reflected signals, hence for mobility and non-line-of-sight (non-LOS, NLOS, Near-LOS, nLOS) applications.  Generally, the lower the frequency band, the better non-LOS characteristics it has, improving range and in-building coverage and penetration through windows, walls, brickwork and stone.

4G & 5G Mobile and Fixed Networks

4G 5G Wireless Network Sub-6GHz
4G & 5G Wireless Networks operate in Sub-6GHz bands

Both 4G and 5G technologies defined by the 3GPP use OFDM and OFDM-A technology in the sub-6GHz bands to deliver high speed fixed and mobile data services.  These classify as “sub 6” but are rarely referred to as such.  MIMO (Multiple Input, Multiple Output) technology is added on top of OFDM to increase throughput still higher.  More recently, 5G includes “millimeter wave” bands above 20GHz to add still higher speed services and overcome congestion in lower frequency bands.  It is envisaged that users could roam seamlessly between regions with “Sub 6” and “millimeter wave” coverage with suitable handsets or terminal devices.

Managing the Finite Spectrum Available in 1-6GHz

An obvious downside of Sub-6GHz is the limited spectrum available.  There is just 5GHz of spectrum available between 1-6GHz which has to be allocated between multiple applications for Telecom Operators, Government and Private networks, utilising signals that can travel 10-50km or more and therefore potentially interfering with each other if inadequately managed.  Though most applications are terrestrial, the bands include space for ground-satellite services which again have to avoid interference.  Increasingly, frequency regulation is a global issue with international roaming, and huge spectrum demands and pressure on spectrum from Mobile Network Operators who face ever increasing demands for mobile data users worldwide.  To meet this demand, spectrum is continually re-farmed and re-allocated between older 2G and 3G services to 4G and 5G services which are capable of delivering higher capacity services.  Legacy frequency allocations to Government and Military applications are often released for lease to such operators also.

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Split Mount Radio Microwave Links

Split Mount Radio (IDU+ODU)

A Split Mount Microwave Radio consisted of Indoor plus Outdoor components – specifically Indoor Unit (IDU) and Outdoor Unit (ODU)

Split Mount Microwave Radios offer up to 500 Mbps and 1Gbps Full Duplex payload  and higher up to 6Gbps or more, in 4-42GHz licensed frequency bands.

Indoor Unit (IDU)

CableFree HCR Indoor Unit (IDU) Split Mount Radio
CableFree HCR Indoor Unit (IDU)

A Typical Split Mount Radio consists of a 19″ Rack Mount Indoor Unit which is mounted in a rack, cabinet, comms room, or even roof-mount shelter as possible locations.

Outdoor Unit (ODU)

CableFree Microwave Link ODU using 30cm antenna Split Mount Radio
CableFree Microwave Link Outdoor Unit (ODU) with using 30cm antenna mounted on a pole

The Outdoor Unit (ODU) is typically mounted directly to the Microwave Antenna on a rooftop or tower location, which enables clear Line of Sight (LOS) between both ends of the Microwave link.

For most bands above 6GHz the ODU has a waveguide interface which enables efficient, low-loss connection directly to the antenna.  For lower bands below 6GHz, commonly a coaxial cable is used between the ODU and the antenna.

In certain cases, the ODU can be remote mounted from the antenna, and a waveguide used to connect between them

Comparison with Full Outdoor Radios

A split mount radio is considered a “traditional” design and older radios always feature this.  The Indoor Unit has all the network interfaces and processing in the easy-access indoor location at the foot the tower or building.  Full Outdoor Radios by contrast have all the active items including the modem and user network interfaces inside the rooftop radio element.  This saves on space, materials, installation time and cost.  A downside is that in the event of any failure, a tower climb is almost always needed to rectify any fault, which may be impossible in rough weather, or require permits or have access limitations to reach

Distances and Range Capability of Split Mount Radios

Using suitable antennas and sites, ultra-long-distance links exceeding 100km can be achieved.   Distances depend on:

  • Frequency band
  • Regional Rainfall
  • Required throughput (Mbps)
  • Desired Availability (%)
  • Antenna size (gain)

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Point to Point Microwave Link

Wireless Point-to-Point Microwave Bridge Links

Microwave Point to Point can be tailored to suit the needs and requirements of all applications

CableFree FOR3 Point to Point Microwave P2P PTP Installed in the Middle East
CableFree FOR3 Microwave P2P link Installed in the Middle East

Point to Point links are transparent, acting as an extension of the Ethernet backbone or segment. Licensed Microwave is fully compatible with the Ethernet standard, and supports all Ethernet functionality and applications.

Point to Point Microwave has been the connectivity choice for Telecom carriers, corporate organisations and Government authorities for many of years. Point to Point Radio offers high speeds, high availability over large connection distances, it can be relied upon to carry voice and data traffic in a number of bandwidth-intensive applications, such as:

  • Connecting locations that are unavailable or in poor Broadband areas
  • Private data Networks (WANs, LANs, etc.)
  • Utility Networks (Railways, Pipelines, etc.)
  • Last Mile access for Corporate, SMEs and Local Government
  • Connecting buildings and facilities over large distances

Microwave P2P – Ideal replacement for Fibre Optics and Leased Lines

CableFree Microwave Link using 30cm antenna benefits from ACM giving longer reach and higher availability
CableFree Microwave Link using 30cm antenna benefits from ACM giving longer reach and higher availability

Point to point wireless is the ideal alternative for business communication between two buildings or sites where wired connection is either impossible, costly or impractical. Point to point Ethernet bridge link facilitates a wireless data connection between two or more networks or buildings across distances up to 100 Kilometres and at speeds up to 1Gbps.

Point to point wireless links are an excellent alternative to fibre optics and leased lines, providing businesses with fibre-like speeds for high-speed data, voice and video transfer between business locations.

Asking an expert team to assist with your point to point wireless requirement will ensure you get a well-designed Microwave Link solution and expertise to help you and your business to benefit from high-capacity, low-latency, long distance wireless data transfer. Quality design, installation and support teams are always on-hand to ensure that your project is delivered on time and to the highest standards.

Long Distance Point to Point WiFi

WiFi is sometimes used for outdoor links – with directional antennas – despite the WiFi radio protocol not being optimised for long distance links.  Instead, customised airside protocols on dedicated outdoor radios are far better for security, throughput and link stability.

Point to Point Ethernet bridge

CableFree Microwave Point to Point Radio Links P2P PTP
CableFree Microwave Point to Point Radio Links

A point to point Ethernet bridge link can benefit your business through the elimination of leasing lines or subscription based systems with no loss in performance. Providing highly reliable connections, point to point wireless offers a far lower total cost of ownership and has the versatility of deployment within rural, metropolitan and residential environments.

Whether you are looking to achieve high-speed business networking or to provide wireless backhaul for CCTV connectivity, point to point bridges are the best option.

Where line-of-sight (LOS) exists between two points, point to point bridge pairs can be set-up and installed with the minimum of disruption to your business and can usually be completed within a single day. The ease of install and the resilience to harsh weather conditions make point to point bridge links a viable fibre alternative.

Operating in both licensed and unlicensed spectrums, our point to point solutions ensure that your business has the network uptime and performance for mission-critical data transfer – our links offer 99.999% uptime.

Broadcasting, construction or military environments often require temporary wireless connections. The simplicity of point to point WiFi makes it the perfect solution where temporary wireless connection is required between two points.

Licensed or Unlicensed Point to Point Microwave Links

When selecting the correct point to point wireless link for your business, there are a number of important decisions to be made to ensure that the final outcome meets the initial expectations. Point to point microwave links can be either licenced or unlicensed, both of which have a specific set of capabilities, advantages and disadvantages, the main one being their relative susceptibility to interference-free operation.

For businesses seeking a wireless backhaul which will serve as a direct replacement for leased lines, licensed microwave links – which operate within the ‘licensed’ 4-42GHz bands, – will provide superior bandwidth availability, speed and the interference protection necessary.

Although offering no guaranteed interference protection, unlicensed microwave links which operate in the ‘unlicensed’ frequency bands, either typically in 2.4 and 5GHz bands, in some regions 17GHz and 24GHz, and 58GHz/60GHz (V-band), can provide a more cost effective option as they eliminate any additional costs and can be rapidly deployed.

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ITU-R P.530 RECOMMENDATION

ITU-R P.530 RECOMMENDATION

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:

(1)
(2)

(3)
  • 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.

(4)

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:

(5)

where, for R0.01 ≤ 100 mm/h:

(6)

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
(7)

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:

(8)

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.

(9)

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:

(10)

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:

(11)
(12)

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:

(13)

where is the path length (km).

Step 2:  Calculate the multipath activity parameter η as:

(14)

Step 3:  Calculate the selective outage probability from:

(15)

where:

  • 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:

(16)

where:

  • 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)
(17)

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:

(18)
  • 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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Comparing Microwave Links using 512-QAM, 1024-QAM, 2048-QAM, 4096-QAM

Microwave links using 512QAM, 1024QAM, 2048QAM & 4096QAM (Quadrature Amplitude Modulation)

What is QAM?

Quadrature amplitude modulation (QAM) including 16QAM, 32QAM, 64QAM, 128QAM, 256QAM, 512QAM, 1024QAM, 2048QAM and 4096QAM is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme.

Why are higher QAM levels used?

Modern wireless networks often demand and require higher capacities.  For a fixed channel size, increasing QAM modulation level increases the link capacity.  Note that incremental capacity gain at low-QAM levels is significant; but at high QAM, the capacity gain is much smaller.  For example, increasing
From 1024QAM to 2048QAM gives a 10.83% capacity gain.
From 2048QAM to 4096QAM gives a 9.77% capacity gain.

QAM Increase Capacity Table
QAM Increase Capacity Table

What are the penalties in higher QAM?

The receiver sensitivity is greatly reduced.  For every QAM increment (e.g. 512 to 1024QAM) there is a -3dB degradation in receiver sensitivity.  This reduces the range.  Due to increased linearity requirements at the transmitter, there is a reduction in transmit power also when QAM level is increased.  This may be around 1dB per QAM increment.

Comparing 512-QAM, 1024-QAM, 2048-QAM & 4096-QAM

This article compares 512-QAM vs 1024-QAM vs 2048-QAM vs 4096-QAM and mentions difference between 512-QAM, 1024-QAM, 2048-QAM and 4096-QAM modulation techniques. It mentions advantages and disadvantages of QAM over other modulation types. Links to 16-QAM, 64-QAM and 256-QAM is also mentioned.

Understanding QAM Modulation

Starting with the QAM modulation process at the transmitter to receiver in the wireless baseband (i.e. Physical Layer) chain. We will use the example of 64-QAM to illustrate the process. Each symbol in the QAM constellation represents a unique amplitude and phase. Hence they can be distinguished from the other points at the receiver.

64QAM Quadrature Amplitude Modulation
64QAM Quadrature Amplitude Modulation

Fig:1, 64-QAM Mapping and Demapping

• As shown in the figure-1, 64-QAM or any other modulation is applied on the input binary bits.
• The QAM modulation converts input bits into complex symbols which represent bits by variation in amplitude/phase of the time domain waveform. Using 64QAM converts 6 bits into one symbol at transmitter.
• The bits to symbols conversion take place at the transmitter while reverse (i.e. symbols to bits) take place at the receiver. At receiver, one symbol gives 6 bits as output of demapper.
• Figure depicts position of QAM mapper and QAM demapper in the baseband transmitter and receiver respectively. The demapping is done after front end synchronization i.e. after channel and other impairments are corrected from the received impaired baseband symbols.
• Data Mapping or modulation process is done before the RF upconversion (U/C) in the transmitter and PA. Due to this, higher order modulation necessitates use of highly linear PA (Power Amplifier) at the transmit end.

QAM Mapping Process

64QAM Mapping Modulation
64QAM Mapping Modulation

Fig:2, 64-QAM Mapping Process

In 64-QAM, the number 64 refers to 2^6.
Here 6 represents number of bits/symbol which is 6 in 64-QAM.
Similarly it can be applied to other modulation types such as 512-QAM, 1024-QAM, 2048-QAM and 4096-QAM as described below.

Following table mentions 64-QAM encoding rule. Check the encoding rule in the respective wireless standard. KMOD value for 64-QAM is 1/SQRT(42).

Input bits (b5, b4, b3) I-Out Input bits (b2, b1, b0) Q-Out
011 7 011 7
010 5 010 5
000 3 000 3
001 1 001 1
101 -1 101 -1
100 -3 100 -3
110 -5 110 -5
111 -7 111 -7

QAM mapper Input parameters :    Binary Bits
QAM mapper Output parameters : Complex data (I, Q)

The 64-QAM mapper takes binary input and generates complex data symbols as output. It uses above mentioned encoding table to do the conversion process. Before the coversion process, data is grouped into 6 bits pair. Here, (b5, b4, b3) determines the I value and (b2, b1, b0) determines the Q value.

Example: Binary Input: (b5,b4,b3,b2,b1,b0) = (011011)
Complex Output: (1/SQRT(42))* (7+j*7)

512-QAM modulation

512QAM Modulation
512QAM Modulation

Fig:3, 512-QAM Constellation Diagram

The above figure shows 512-QAM constellation diagram. Note that 16 points do not exist in each of the four quadrants to make total 512 points with 128 points in each quadrant in this modulation type. It is possible to have 9 bits per symbol in 512-QAM also. 512QAM increases capacity by 50% compare to 64-QAM modulation type.

1024-QAM modulation

1024QAM Modulation Constellation
1024QAM Modulation Constellation

The figure shows a 1024-QAM constellation diagram.
Number of bits per seymbol: 10
Symbol rate: 1/10 of bit rate
Increase in capacity compare to 64-QAM: About 66.66%

2048-QAM modulation

2048QAM Modulation Constellation
2048QAM Modulation Constellation

Following are the characteristics of 2048-QAM modulation.
Number of bits per seymbol: 11
Symbol rate: 1/11 of bit rate
Increase in capacity from 64-QAM to 1024QAM: 83.33% gain
Increase in capacity from 1024QAM to 2048QAM: 10.83% gain
Total constellation points in one quadrant: 512

4096-QAM modulation

4096QAM Modulation Constellation
4096QAM Modulation Constellation

Following are the characteristics of 4096-QAM modulation.
Number of bits per symbol: 12
Symbol rate: 1/12 of bit rate
Increase in capacity from 64-QAM to 409QAM: 100% gain
Increase in capacity from 2048QAM to 4096QAM 9.77% gain
Total constellation points in one quadrant: 1024

Advantages of QAM over other modulation types

Following are the advantages of QAM modulation:
• Helps achieve high data rate as more number of bits are carried by one carrier. Due to this it has become popular in modern wireless communication system such as LTE, LTE-Advanced etc. It is also used in latest WLAN technologies such as 802.11n 802.11 ac, 802.11 ad and others.

Disadvantages of QAM over other modulation types

Following are the disadvantages of QAM modulation:
• Though data rate has been increased by mapping more than 1 bits on single carrier, it requires high SNR in order to decode the bits at the receiver.
• Needs high linearity PA (Power Amplifier) in the Transmitter.
• In addition to high SNR, higher modulation techniques need very robust front end algorithms (time, frequency and channel) to decode the symbols without errors.

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ITU Regions

What are ITU Regions?

The International Telecommunication Union (ITU), in its International Radio Regulations, divides the world into three ITU regions for the purposes of managing the global radio spectrum. Each region has its own set of frequency allocations, the main reason for defining the regions.

CableFree-ITU-International_Telecommunication_Union_regions
ITU Regions Global

Boundaries

Lines:

Another chart showing the regions:

CableFree-Microwave-ITU-emergency-regions
ITU Regions

Usage

The definition of the European Broadcasting Area uses some of the definitions of Region 1.

About the ITU

The International Telecommunication Union (ITU; French: Union Internationale des Télécommunications (UIT)), originally the International Telegraph Union (French: Union Télégraphique Internationale), is a specialized agency of the United Nations (UN) that is responsible for issues that concern information and communication technologies.

The ITU coordinates the shared global use of the radio spectrum, promotes international cooperation in assigning satellite orbits, works to improve telecommunication infrastructure in the developing world, and assists in the development and coordination of worldwide technical standards. The International Telecommunication Union is active in areas including broadband Internet, latest-generation wireless technologies, aeronautical and maritime navigation, radio astronomy, satellite-based meteorology, convergence in fixed-mobile phone, Internet access, data, voice, TV broadcasting, and next-generation networks. The agency also organizes worldwide and regional exhibitions and forums, such as ITU Telecom World, bringing together representatives of government and the telecommunications and ICT industry to exchange ideas, knowledge and technology.

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

RECOMMENDATION 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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OFCOM Channel Plans for 7.5GHz and 13GHz

OFCOM Channel Plans for 7.5GHz and 13GHz

Here is a chart showing channel plans for the UK

OFCOM - 7.5GHz & 13GHz
OFCOM – 7.5GHz & 13GHz

Uses & Applications

7.5GHz and 13GHz bands are used for Point to Point (P2P) Microwave Radio Links

Sources of Data and Graphics

All contents (C) OFCOM and taken from:

OfW48 UK Frequency Allocations for Fixed (Point-to-Point) Wireless Services and Scanning Telemetry This document shows the current bands managed by Ofcom that are available for fixed terrestrial (point to point) links and scanning telemetry in the UK.

Technical regulations

The Radio Equipment and Telecommunications Terminal Equipment Directive
99/5/EC (R&TTED) has been implemented in ‘The Radio Equipment and Telecommunications Terminal Equipment Regulations 2000, Statutory
Instrument (SI) 730. In accordance with Articles 4.1 and 7.2 of the R&TTED
the:
• IR2000: The UK Interface Requirement 2000 contains the requirements for the licensing and use of fixed (point-to-point) wireless services in the UK.
• IR2037: The UK Interface Requirement 2037 applies for scanning telemetry services.
• IR2078: The UK Interface Requirement 2078 applies for the 60 GHz band

Notes specific to the frequency charts

The first column describes each available frequency band, represented by a diagram (not to scale). The frequency band limits are listed below the diagram; frequencies below 10 GHz are represented in MHz, while those above 10 GHz are in GHz. The width of each guard band is shown above the diagram, and is always specified in MHz.
The channel arrangements in some bands are staggered, so that the width and position of the guard band vary for different channel spacings. In these cases, a table underneath gives details of the guard bands for different spacings (with all frequencies in MHz).
The first column also includes the title of the relevant international recommendations for each band, produced by the European Conference of Postal and Telecommunications (CEPT) or the International Telecommunication Union (ITU). CEPT recommendations are available at http://www.cept.org/ecc/ and ITU Recommendations at http://www.itu.int.
The final column contains the channel spacing for duplex operation in each frequency band except for bands above 60 GHz. Details of standard systems assigned in the UK are shown in the relevant technical frequency assignment criteria.

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OFCOM Channel Plans 450MHz and 1.4GHz

OFCOM Channel Plans for 450MHz and 1.4GHz

Here is a chart showing channel plans for the UK

OFCOM 450MHz & 1.4GHz
OFCOM 450MHz & 1.4GHz

Uses & Applications

450MHz and 1.4GHz bands are used for Point to Point (P2P) Microwave Radio Links

Sources of Data and Graphics

All contents (C) OFCOM and taken from:

OfW48 UK Frequency Allocations for Fixed (Point-to-Point) Wireless Services and Scanning Telemetry This document shows the current bands managed by Ofcom that are available for fixed terrestrial (point to point) links and scanning telemetry in the UK.

Technical regulations

The Radio Equipment and Telecommunications Terminal Equipment Directive
99/5/EC (R&TTED) has been implemented in ‘The Radio Equipment and Telecommunications Terminal Equipment Regulations 2000, Statutory
Instrument (SI) 730. In accordance with Articles 4.1 and 7.2 of the R&TTED
the:
• IR2000: The UK Interface Requirement 2000 contains the requirements for the licensing and use of fixed (point-to-point) wireless services in the UK.
• IR2037: The UK Interface Requirement 2037 applies for scanning telemetry services.
• IR2078: The UK Interface Requirement 2078 applies for the 60 GHz band

Notes specific to the frequency charts

The first column describes each available frequency band, represented by a diagram (not to scale). The frequency band limits are listed below the diagram; frequencies below 10 GHz are represented in MHz, while those above 10 GHz are in GHz. The width of each guard band is shown above the diagram, and is always specified in MHz.
The channel arrangements in some bands are staggered, so that the width and position of the guard band vary for different channel spacings. In these cases, a table underneath gives details of the guard bands for different spacings (with all frequencies in MHz).
The first column also includes the title of the relevant international recommendations for each band, produced by the European Conference of Postal and Telecommunications (CEPT) or the International Telecommunication Union (ITU). CEPT recommendations are available at http://www.cept.org/ecc/ and ITU Recommendations at http://www.itu.int.
The final column contains the channel spacing for duplex operation in each frequency band except for bands above 60 GHz. Details of standard systems assigned in the UK are shown in the relevant technical frequency assignment criteria.

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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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