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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Microwave Waveguide Flange

Introduction to Microwave Waveguide Flanges

A waveguide flange is a connector for joining sections of waveguide, and is essentially the same as a pipe flange—a waveguide, in the context of this article, being a hollow metal conduit for microwave energy. The connecting face of the flange is either square, circular or (particularly for large or reduced-height rectangular waveguides), rectangular. The connection between a pair of flanges is usually made with four or more bolts, though alternative mechanisms, such as a threaded collar, may be used where there is a need for rapid assembly and disassembly. Dowel pins are sometimes used in addition to bolts, to ensure accurate alignment, particularly for very small waveguides where higher accuracy is required for higher frequencies.

Key features of a waveguide join are; whether or not it is air-tight, allowing the waveguide to be pressurized, and whether it is a contact or a choke connection. This leads to three sorts of flange for each size of rectangular waveguide.

For rectangular waveguides there exist a number of competing standard flanges which are not entirely mutually compatible. Standard flange designs also exist for double-ridge, reduced-height, square and circular waveguides.

Microwave Waveguide Flange IEC EIA
EIA and IEC Microwave Waveguide Flange versions

Unpressurised and Pressurised Waveguide Flanges

The atmosphere within waveguide assemblies is often pressurized, either to prevent the ingress of moisture, or to raise the breakdown voltage in the guide and hence increase the power that it can carry. Pressurization requires that all joints in the waveguide be airtight. This is usually achieved by means of a rubber O-ring seated in a groove in the face of at least one of flanges forming each join. Gasket, gasket/cover or pressurizable flanges (such as that on the right of figure 2), are identifiable by the single circular groove which accommodates the O-ring. It is only necessary for one of the flanges in each pressurizable connection to be of this type; the other may have a plain flat face (like that in figure 1). This ungrooved type is known as a cover, plain or unpressurizable flange.

It is also possible to form air-tight seal between a pair of otherwise unpressurizable flanges using a flat gasket made out of a special electrically conductive elastomer. Two plain cover flanges may be mated without such a gasket, but the connection is then not pressurizable.

Electrical continuity

Electric current flows on the inside surface of the waveguides, and must cross the join between them if microwave power is to pass through the connection without reflection or loss.

Microwave Flange Standards

IEC

International Electrotechnical Commission (IEC) standard IEC 60154 describes flanges for square and circular waveguides, as well as for what it refers to as flat, medium-flat, and ordinary rectangular guides.  IEC flanges are identified by an alphanumeric code consisting of; the letter U, P or C for Unpressurizable (plain cover), Pressurizable (with a gasket groove) and Choke (with both choke gasket grooves); a second letter, indicating the shape and other details of the flange and finally the IEC identifier for the waveguide. For standard rectangular waveguide the second letter is A to E, where A and C are round flanges, B is square and D and E are rectangular. So for example UBR220 is a square plain cover flange for R220 waveguide (that is, for WG20, WR42), PDR84 is a rectangular gasket flange for R84 waveguide (WG15, WR112) and CAR70 is a round choke flange for R70 waveguide (WG14, WR137).

MIL-Spec

MIL-DTL-3922 is a United States Military Standard giving detailed descriptions of choke, gasket/cover and cover flanges for rectangular waveguide. MIL_DTL-39000/3 describes flanges for double-ridge waveguide, and formerly also for single-ridge guide.  MIL-Spec flanges have designations of the form UG-xxxx/U where the x’s represent a variable-length catalogue number, not in itself containing any information about the flange.

EIA

The Electronic Industries Alliance (EIA) is the body that defined the WR designations for standard rectangular waveguides. EIA flanges are designated CMR (for Connector, Miniature, Rectangular waveguide) or CPR (Connector, Pressurizable, Rectangular waveguide) followed by the EIA number (WR number) for the relevant waveguide. So for example, CPR112 is a gasket flange for waveguide WR112 (WG15).

RCSC

The Radio Components Standardization Committee (RCSC) is the body that originated the WG designations for standard rectangular waveguides. It also defined standard choke and cover flanges with identifiers of the form 5985-99-xxx-xxxx where the x’s represent a catalogue number, not in itself containing any information about the flange.

What is a Waveguide?

A waveguide is an electromagnetic feed line that is used for high frequency signals. Waveguides conduct microwave energy at lower loss than coaxial cables and are used in microwave communications, radars and other high frequency applications.

The waveguide must have a certain minimum cross section, relative to the wavelength of the signal to function properly. If wavelength of the signal is too long (Frequency is too low) when compared to the cross section of the waveguide, the electromagnetic fields cannot propagate. The lowest frequency range at which a waveguide will operate is where the cross section is large enough to fit one complete wavelength of the signal.

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Microwave Waveguide Sizes & Dimensions

Microwave Waveguide Sizes

Microwave Waveguide
Microwave Waveguide

Due to high frequencies used, Waveguides rather than RF coaxial cables are used to connect Microwave Radios, Antennas and Couplers.  Matched and correct size and dimension of Waveguide is essential for all items in the Microwave link.

What is a Waveguide?

A waveguide is an electromagnetic feed line that is used for high frequency signals. Waveguides conduct microwave energy at lower loss than coaxial cables and are used in microwave communications, radars and other high frequency applications.

The waveguide must have a certain minimum cross section, relative to the wavelength of the signal to function properly. If wavelength of the signal is too long (Frequency is too low) when compared to the cross section of the waveguide, the electromagnetic fields cannot propagate. The lowest frequency range at which a waveguide will operate is where the cross section is large enough to fit one complete wavelength of the signal.

Rectangular, Circular and Double Rigid

Geometrically speaking there are three types of waveguides – Rectangular Waveguides, Double Rigid Waveguides and Circular Waveguides. The tables below will give you details on the various waveguide sizes and their properties.

Rectangular Waveguide Sizes

Waveguide name Recommended frequency Cutoff frequency
lowest order mode
Cutoff frequency
next mode
Inner dimensions of waveguide opening
EIA RCSC * IEC A inch[mm] B inch[mm]
WR2300 WG0.0 R3 0.32 to 0.45 GHz 0.257 GHz 0.513 GHz 23 [584.2] 11.5 [292.1]
WR2100 WG0 R4 0.35 to 0.50 GHz 0.281 GHz 0.562 GHz 21 [533.4] 10.5 [266.7]
WR1800 WG1 R5 0.45 to 0.63 GHz 0.328 GHz 0.656 GHz 18 [457.2] 9 [228.6]
WR1500 WG2 R6 0.50 to 0.75 GHz 0.393 GHz 0.787 GHz 15 [381] 7.5 [190.5]
WR1150 WG3 R8 0.63 to 0.97 GHz 0.513 GHz 1.026 GHz 11.5 [292.1] 5.75 [146.05]
WR975 WG4 R9 0.75 to 1.15 GHz 0.605 GHz 1.211 GHz 9.75 [247.65] 4.875 [123.825]
WR770 WG5 R12 0.97 to 1.45 GHz 0.766 GHz 1.533 GHz 7.7 [195.58] 3.85 [97.79]
WR650 WG6 R14 1.15 to 1.72 GHz 0.908 GHz 1.816 GHz 6.5 [165.1] 3.25 [82.55]
WR510 WG7 R18 1.45 to 2.20 GHz 1.157 GHz 2.314 GHz 5.1 [129.54] 2.55 [64.77]
WR430 WG8 R22 1.72 to 2.60 GHz 1.372 GHz 2.745 GHz 4.3 [109.22] 2.15 [54.61]
WG9 2.20 to 3.30 GHz 1.686 GHz 3.372 GHz 3.5 [88.9] 1.75 [44.45]
WR340 WG9A R26 2.20 to 3.30 GHz 1.736 GHz 3.471 GHz 3.4 [86.36] 1.7 [43.18]
WR4284 WG10 R32 2.60 to 3.95 GHz 2.078 GHz 4.156 GHz 2.84 [72.136] 1.34 [34.036]
WG11 3.30 to 4.90 GHz 2.488 GHz 4.976 GHz 2.372 [60.2488] 1.122 [28.4988]
WR229 WG11A R40 3.30 to 4.90 GHz 2.577 GHz 5.154 GHz 2.29 [58.166] 1.145 [29.083]
WR187 WG12 R48 3.95 to 5.85 GHz 3.153 GHz 6.305 GHz 1.872 [47.5488] 0.872 [22.1488]
WR159 WG13 R58 4.90 to 7.05 GHz 3.712 GHz 7.423 GHz 1.59 [40.386] 0.795 [20.193]
WR137 WG14 R70 5.85 to 8.20 GHz 4.301 GHz 8.603 GHz 1.372 [34.8488] 0.622 [15.7988
WR112 WG15 R84 7.05 to 10 GHz 5.26 GHz 10.52 GHz 1.122 [28.4988] 0.497 [12.6238]
WR102 7.00 to 11 GHz 5.786 GHz 11.571 GHz 1.02 [25.908] 0.51 [12.954]
WR90 WG16 R100 8.20 to 12.40 GHz 6.557 GHz 13.114 GHz 0.9 [22.86] 0.4 [10.16]
WR75 WG17 R120 10.00 to 15 GHz 7.869 GHz 15.737 GHz 0.75 [19.05] 0.375 [9.525]
WR62 WG18 R140 12.40 to 18 GHz 9.488 GHz 18.976 GHz 0.622 [15.7988] 0.311 [7.8994]
WR51 WG19 R180 15.00 to 22 GHz 11.572 GHz 23.143 GHz 0.51 [12.954] 0.255 [6.477]
WR42 WG20 R220 18.00 to 26.50 GHz 14.051 GHz 28.102 GHz 0.42 [10.668] 0.17 [4.318]
WR34 WG21 R260 22.00 to 33 GHz 17.357 GHz 34.715 GHz 0.34 [8.636] 0.17 [4.318]
WR28 WG22 R320 26.50 to 40 GHz 21.077 GHz 42.154 GHz 0.28 [7.112] 0.14 [3.556]
WR22 WG23 R400 33.00 to 50 GHz 26.346 GHz 52.692 GHz 0.224 [5.6896] 0.112 [2.8448]
WR19 WG24 R500 40.00 to 60 GHz 31.391 GHz 62.782 GHz 0.188 [4.7752] 0.094 [2.3876]
WR15 WG25 R620 50.00 to 75 GHz 39.875 GHz 79.75 GHz 0.148 [3.7592] 0.074 [1.8796]
WR12 WG26 R740 60 to 90 GHz 48.373 GHz 96.746 GHz 0.122 [3.0988] 0.061 [1.5494]
WR10 WG27 R900 75 to 110 GHz 59.015 GHz 118.03 GHz 0.1 [2.54] 0.05 [1.27]
WR8 WG28 R1200 90 to 140 GHz 73.768 GHz 147.536 GHz 0.08 [2.032] 0.04 [1.016]
WR6 WG29 R1400 110 to 170 GHz 90.791 GHz 181.583 GHz 0.065 [1.651] 0.0325 [0.8255]
WR7 WG29 R1400 110 to 170 GHz 90.791 GHz 181.583 GHz 0.065 [1.651] 0.0325 [0.8255]
WR5 WG30 R1800 140 to 220 GHz 115.714 GHz 231.429 GHz 0.051 [1.2954] 0.0255 [0.6477]
WR4 WG31 R2200 172 to 260 GHz 137.243 GHz 274.485 GHz 0.043 [1.0922] 0.0215 [0.5461]
WR3 WG32 R2600 220 to 330 GHz 173.571 GHz 347.143 GHz 0.034 [0.8636] 0.017 [0.4318]

Note:

  • The “WR” designation stands for Rectangular Waveguides
  • The Number that follows “WR” is the width of the waveguide opening in mils, divided by 10. For Example WR-650 means a waveguide whose cross section width is 6500 mils.
  • The waveguide width determines the lower cutoff frequency and is equal (ideally) to ½ wavelength of the lower cutoff frequency.

Double-ridge waveguides are rectangular wagevuides with two ridges protruding parallel to the short wall. This increases the E-Field in the waveguide improving performance.

Double Ridge Waveguide Sizes

Designation
(a)=aluminum, (b)=brass, (c)=copper, (s)=silver
fL – fU*
(GHz)
fCO**
(GHz)
Inside
Width
(in)
Inside
Height
(in)
WR U.S. Mil.
__ /U
British
Mil.
IEC
WR975 RG204 (a) 0.75-1.12 0.605 9.750 4.875
WR770 RG205 (a) 0.96-1.45 0.766 7.700 3.850
WR650 RG69 (b)
RG103 (a)
WG6 1.12-1.70 0.908 6.500 3.250
WR510 1.45-2.20 1.157 5.100 2.550
WR430 RG104 (b)
RG105 (a)
WG8 1.70-2.60 1.372 4.300 2.150
WR340  RG112 (b)
RG113 (a)
WG9A 2.20-3.30 1.736 3.400 1.700
WR284 RG48 (b)
RG75 (a)
WG10 2.60-3.95 2.078 2.840 1.340
WR229  RG340 (c)
RG341 (a)
WG11A R40 3.30-4.90 2.577 2.290 1.145
WR187 RG49 (b)
RG95 (a)
WG12 R48 3.95-5.85- 3.152 1.872 0.872
WR159  RG343 (c)
RG344 (a)
WG13 R58 4.90-7.05 3.712 1.590 0.795
WR137 RG50 (b)
RG106 (a)
WG14 R70 5.850-8.200 4.301 1.372 0.622
WR112 RG51 (b)
RG68 (a)
WG15 R84 7.050-10.000 5.260 1.122 0.497
WR90 RG52 (b)
RG67 (a)
WG16 R100 8.20-12.40 6.56 0.900 0.400
WR75  RG346 (c)
RG347 (a)
WG17 10.0-15.0 7.87 0.750 0.375
WR62 RG91 (b)
RG349 (a)
WG18 12.40-18.00 9.49 0.622 0.311
WR51  RG352 (c)
RG351 (a)
WG19 15.00-22.00 11.6 0.510 0.255
WR42 RG53 (b)
RG121 (a)
WG20 18.00-26.5 14.1 0.420 0.170
WR34 RG354 (c) 20.0-33.0 17.4 0.340 0.170
WR28 RG96 (s)
RG271 (c)
WG22 26.50-40.00 21.1 0.280 0.140
WR22 RG97 (s) WG23 33.00-50.00 26.4 0.224 0.112
WR19 WG24 40.00-60.00 31.4 0.188 0.0940
WR15 RG98 (s) WG25 50.00-75.00 39.9 0.148 0.0740
WR12 RG99 (s) WG26 60.00-90.00 48.4 0.122 0.0610
WR10 WG27 75.00-110.0 59.0 0.100 0.0500
WR8 RG138 (s) WG28 90.00-140.0 73.8 0.0800 0.0400
WR7 RG136 (s) 110.0-170.0 90.8 0.0650 0.0325
WR4 RG137 170.0-260.0 137 0.0430 0.0215
WR3 RG139 (s) 220.0-325.0 174 0.0340 0.0170

 

Circular Waveguide Sizes

FrequencyBand Frequency Range Circular WaveguideDiameter, Inches (mm) Cover Flange (Brass)MIL-F- 3922 UG Flange Type
X LOW 8.2-9.97 1.094 (27.79) 53-001 UG-39/U Square
MID 8.5-11.6 0.938 (23.83)
HIGH 9.97-12.4 0.797 (20.24)
Ku LOW 12.4-15.9 0.688 (17.48) 53-005 UG-1666/U Square
MID 13.4-18.0 0.594 (15.08)
HIGH 15.9-18.0 0.500 (12.70)
K LOW 17.5-20.5 0.455 (11.56) 54-001 UG-595/U Square
MID 20-24.5 0.396 (10.06)
HIGH 24-26.5 0.328 (8.33)
Ka LOW 26.5-33 0.315 (8.00) 54-003 UG-595/U Square
MID 33-38.5 0.250 (6.35)
HIGH 38.5-40 0.219 (5.56)
Q LOW 33-38.5 0.250 (6.35) 67B-006 UG-383/U Round
MID 38.5-43 0.219 (5.56)
HIGH 43-50 0.188 (4.78)
U LOW 40-43 0.210 (5.33) 67B-007 UG-383/U-M Round
MID 43-50 0.188 (4.78)
HIGH 50-60 0.165 (4.19)
V LOW 50-58 0.165 (4.19) 67B-008 UG-385/U Round
MID 58-68 0.141 (3.58)
HIGH 68-75 0.125 (3.18)
E LOW 60-66 0.136 (3.45) 67B-009 UG-387/U Round
MID 66-82 0.125 (3.18)
HIGH 82-90 0.094 (2.39)
W LOW 75-88 0.112 (2.84) 67B-010 UG-387/U-M Round
HIGH 88-110 0.094 (2.39)
F LOW 90-115 0.089 (2.26) -UG-387/U-M Round
HIGH 115-140 0.075 (1.91)
D LOW 110-140 0.073 (1.85) -UG-387/U-M Round
HIGH 140-160 0.059 (1.50)
G LOW 140-180 0.058 (1.47) -UG-387/U-M Round
HIGH 180-220 0.045 (1.14)
170-260 0.049 (1.25) -UG-387/U-M Round
220-325 0.039 (0.99) -UG-387/U-M Round

 

WR2100 | WG0 | R4 Waveguide

WR2100 | WG0 | R4 – Rectangular Waveguide Size

WR2100 Waveguide Size

  • EIA Standard:WR2100
  • RSCS Standard (British Military):WG0
  • IEC Standard:R4

WR2100 Specifications

  • Recommended Frequency Band:0.35 to 0.50 GHz
  • Cutoff Frequency of Lowest Order Mode:0.281 GHz
  • Cutoff Frequency of Upper Mode:0.562 GHz
  • Dimension:21 Inches [533.4 mm] x 10.5 Inches [266.7 mm]

 

Microwave Waveguide WR2100
Microwave Waveguide

What is a Waveguide?

A waveguide is an electromagnetic feed line that is used for high frequency signals. Waveguides conduct microwave energy at lower loss than coaxial cables and are used in microwave communications, radars and other high frequency applications.

The waveguide must have a certain minimum cross section, relative to the wavelength of the signal to function properly. If wavelength of the signal is too long (Frequency is too low) when compared to the cross section of the waveguide, the electromagnetic fields cannot propagate. The lowest frequency range at which a waveguide will operate is where the cross section is large enough to fit one complete wavelength of the signal.

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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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Class 4 Microwave Antennas

What is a Class 4 Microwave Antenna?

Class 4 Antennas explained:

CableFree Class 4 Microwave Antenna 1Class 4 antennas provide the current best RF performance allowing mobile operators and Wireless Internet Service Providers (WISP) to increase the link capacity of a network by deploying new microwave links where high levels of interference are present. Class 4 antennas will allow customers to offer the highest performance in even the most congested environments. The higher side lobe suppression supports networks in ultra-dense areas and enables earlier reuse of frequencies. The lower interference increases the carrier-to-interference-ratio and allows smaller antennas with better link throughput, reducing tower leasing fees. The lower interference also enables higher modulation schemes, increasing the data capacity per antenna.

Benefits of a Class 4 Antenna

Increase the link capacity of the network
– Improved radiation patterns for ETSI Class 4 providing better performance
– Less interference and higher carrier-to-interference ratio
– Allows radios to operate at higher modulation levels
• Minimize the total cost of ownership
– Improved network efficiency
– Facilitates better re-use of a frequency channel
– Small antennas with better link throughput reduces tower leasing fees

Intended Use for Class 4 Antennas

CableFree Class 4 Microwave Antenna 1Class 4 antennas are intended for “extremely high interference potential” situations, according to ETSI. For a more detailed treatment of antenna classifications and radiation patterns, see the ETSI document “Fixed Radio Systems; Point to Point Antennas.”

Wider channels, larger capacity

For situations where the operator needs to increase capacity from a wireless backhaul site, the easiest way remains widening the channel size. But at sites that experience extremely high interference, the operator may not be able to coordinate radio frequency pairs in wide channels with Class 3 antennas. However, moving up to Class 4 antennas would allow the operator to optimize the signal-to-noise ratio and let higher modulations come into play, so wide channels could be coordinated with correspondingly higher data rates

Smaller is Better

In cases of high interference, larger antennas can be used to reduce it. For a subset, smaller Class 4 antennas can be used instead of their oversize Class 3 counterparts. Thus, operators who deploy Class 4 antennas gain the added benefit of dropping down a parabolic dish antenna size as compared to a Class 3 antenna in the same application. In general, smaller dishes advantage the operator due to their lighter weight and lower opex tower charges, albeit with an initially bigger upfront capex. Because Class 4 antennas represent an elevated level of precision tooling and more detailed manufacturing versus lower class antennas, capex of these passive, higher-performance infrastructure pieces always weighs in the balance.

 

According to Andy Sutton,  Principal Network Architect at EE:

Using Comsearch’s iQ.linkXG microwave planning software, CommScope analyzed the technical and commercial benefits of using Class 4 Sentinel antennas in the network. The results were most impressive. For the two frequency bands of the microwave backhaul network studied, which is comprised of over 6,200 links in total, the core findings were:

  • Potential savings of $5 million in total cost of ownership (TCO) over five years by enabling a greater link density and therefore reducing the need for third party Ethernet Leased Lines
  • Greater utilization of owned block allocated spectrum reduced the need for link by link licensing (from the national regulator) and therefore could save $44,000 in license fees over five years
  • $4.5 million could be saved per year based on optimizing capacity by freeing congested channels while still ensuring new links met the strict quality of service criteria
  • 96 percent and 31 percent of links which couldn’t be planned due to frequency congestion in 40 and 10 GHz could be assigned a channel, respectively
    • A strong opportunity to trade some of the above by reducing antenna size and thus reducing TCO on tower lease costs

(content from EE above reproduced with acknowledgement from Commscope. Other content including photos from RFS).

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Mean Square Error (MSE) for Microwave Links

What is Mean Square Error ?

Mean Square Error (MSE) is similar to Signal-to-Noise Ratio (SNR) except that it accounts for distortion and interference in addition to noise power.

Mean Square Error MSE Microwave Link
CableFree Microwave ODU

Distortion may come from several sources such as bad Ethernet cables (poor shield, damaged, or low quality), path degradations such as multipath, or Fresnel zone encroachment.

Interference can come from other transmitters on the tower, as well as from sources inside an indoor shelter. High power transmitters inside a shelter can cause interference when near the PoE device or when located very close to the cabling.

There are maximum acceptable MSE values for each modulation which are useful in determining the quality of the link. The MSE value reported is only relevant to one tx-rx path, so the MSE of each tx-rx path must be evaluated to verify the link is operating as expected. The lower the number the better, so a -35dB is better than a -30dB.

Other possible causes for unacceptable MSE

These include

  • XPIC parameters are incorrect
  • Insufficient isolation between polarisations on an XPIC link
  • Insufficient performance to support high QAM modulation
  • Inbalance between paths on an XPIC dual polarity link

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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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