Microwave Links power ISP backbones in the Middle East

Implementing Microwave for High Speed Internet ISP Backbones in the Middle East

CableFree FOR3 Microwave links are being installed by ISPs in Iraq for Internet Backbone Connectivity. These links offer 880Mbps full duplex capacity with easy upgrade capability to 2+0 for 1.76Gbps full duplex, and are typically installed on towers or buildings for clear Line of Sight between network node locations.

CableFree FOR3 Microwave Installation in Middle East
CableFree FOR3 Microwave Installation in Middle East – pictures from Noor AKD

High Capacity Microwave

CableFree FOR3 can expand to 3.5Gbps and above for ultra high capacity links.  Microwave links are fast to install and can be deployed within hours, and distances up to 100km or more on suitable towers.
Microwave is low cost alternative to fibre optic and leased line connectivity and are highly reliable with uptimes of 99.999% or higher possible.
Pictures from Iraq from CableFree regional partner Noor AKD.

CableFree Products are used extensively in the Middle East region with installations in countries including Iraq, UAE, Saudi Arabia, Kuwait, Egypt, Lebanon, Turkey and several others

CableFree Microwave Link on a Tower in Iraq
CableFree Microwave Link on a Tower in Iraq near Baghdad

Microwave Product Data

Please visit our website for Product Data here:
http://www.cablefree.net/for3

Other CableFree products offer up to 10Gbps capacity using MMW technology.

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.

For Further Information

For More Information on High Capacity Microwave Solutions, Please Contact Us

 

ACM: Adaptive Coding and Modulation

Automatic Coding and Modulation (ACM)

Microwave Adaptive Coding and Modulation (ACM)
Microwave Adaptive Coding and Modulation (ACM)

Adaptive Coding and Modulation or Link adaptation 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.). In a digital Microwave Link ACM 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 ACM

ACM with 1024 QAM Modulation
ACM with 1024 QAM Modulation

The goal of Adaptive Modulation and Coding  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 1024QAM 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)

Importance to Operators of ACM

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

Adaptive Coding and Modulation increases the capacity of microwave links without sacrificing distance or availability, and without requiring larger antennas.  The penalty – reduced capacity during heavy fade/rainfall – is usually considered an acceptable trade-off compared to the benefits, especially for IP networks where a variable capacity is generally considered acceptable, compared to legacy PDH (NxE1/T1) and SDH connections which are fixed capacity applications.  Conversely, ACM allows operators to minimise costs by using smaller antennas, meet higher availability targets (e.g. 99.999% availability) and customer SLA (service level agreement) and also fit within aesthetic and planning constraints in dense urban areas and regions of natural beauty where large antennas may be prohibited by planners or building owners.

For Further Information on ACM and Microwave Links

For more information on Microwave Links with ACM please Contact Us

FDD and TDD Explained

The difference between FDD and TDD in Microwave Transmission

Microwave ODU with Antenna using FDD (Frequency Division Duplex)
Microwave ODU with Antenna using FDD (Frequency Division Duplex)

Microwave links typically use Frequency-division duplexing (FDD) which is a method for establishing a full-duplex communications link that uses two different radio frequencies for transmitter and receiver operation. The transmit direction and receive direction frequencies are separated by a defined frequency offset.

Advantages of FDD

In the microwave realm, the primary advantages of this approach are:

  • The full data capacity is always available in each direction because the send and receive functions are separated;
  • It offers very low latency since transmit and receive functions operate simultaneously and continuously;
  • It can be used in licensed and license-exempt bands;
  • Most licensed bands worldwide are based on FDD; and
  • Due to regulatory restrictions, FDD radios used in licensed bands are coordinated and protected from interference, though not immune to it.
Microwave FDD (Frequency Division Duplexing)
Microwave FDD (Frequency Division Duplexing)

Disadvantages to FDD

The primary disadvantages of the FDD approach to microwave communication are:

  • Complex to install. Any given path requires the availability of a pair of frequencies; if either frequency in the pair is unavailable, then it may not be possible to deploy the system in that band;
  • Radios require pre-configured channel pairs, making sparing complex;
  • Any traffic allocation other than a 50:50 split between transmit and receive yields inefficient use of one of the two paired frequencies, lowering spectral efficiency; and
  • Collocation of multiple radios is difficult.

TDD compared with FDD

Time-division duplexing (TDD) is a method for emulating full-duplex communication over a half-duplex communication link. The transmitter and receiver both use the same frequency but transmit and receive traffic is switched in time. The primary advantages of this approach as it applies to microwave communication are:

  • It is more spectrum friendly, allowing the use of only a single frequency for operation and dramatically increasing spectrum utilization, especially in license-exempt or narrow-bandwidth frequency bands ;
  • It allows for the variable allocation of throughput between the transmit and receive directions, making it well suited to applications with asymmetric traffic requirements, such as video surveillance, broadcast and Internet browsing;
  • Radios can be tuned for operation anywhere in a band and can be used at either end of the link. As a consequence, only a single spare is required to serve both ends of a link.

Disadvantages of TDD

The primary disadvantages of traditional TDD approaches to microwave communications are:

  • The switch from transmit to receive incurs a delay that causes traditional TDD systems to have greater inherent latency than FDD systems;
  • Traditional TDD approaches yield poor TDM performance due to latency;
  • For symmetric traffic (50:50), TDD is less spectrally efficient than FDD, due to the switching time between transmit and receive; and
  • Multiple co-located radios may interfere with one another unless they are synchronized.

 

Microwave ODU

Microwave ODU (Outdoor Unit)

The term ODU is used in Split-Mount Microwave systems where an Indoor Unit (IDU) is typically mounted in an indoor location (or weatherproof shelter) connected via a coaxial cable to the ODU which is mounted on a rooftop or tower top location.

CableFree Microwave ODU
CableFree Microwave ODU

Often the ODU is direct mounted to a microwave antenna using “Slip fit” waveguide connection.  In some cases, a Flexible Waveguide jumper is used to connect from the ODU to the antenna.

ODU functions

The ODU converts data from the IDU into an RF signal for transmission. It also converts the RF signal from the far end to suitable data to transmit to the IDU. ODUs are weatherproofed units that are mounted on top of a tower either directly connected to a microwave antenna or connected to it through a wave guide.

Generally, Microwave ODUs designed for full duplex operation, with separate signals for transmit and receive.  On the airside interface this corresponds to a “pair” of frequencies, one for transmit, the other for receive.  This is known as “FDD” (Frequency Division Duplexing)

ODU Power and data signals

The ODU receives its power and the data signals from the IDU through a single coaxial cable. ODU parameters are configured and monitored through the IDU.  The DC power, transmit signal, receive signal and some command/control telemetry signals are all combined onto the single coaxial cable.  This use of a single cable is designed to reduce cost and time of installation.

ODu Frequency bands and sub-bands

Each ODU is designed to operate over a predefined frequency sub-band. For example 21.2 – 23.6GHz for a 23GHz system, 17.7 – 19.7GHz for a 18GHz system and 24.5 – 26.5GHz for a 26GHz system as for ODUs.    The sub-band is set in hardware (filters, diplexer) at time of manufacture and cannot be changed in the field.

1+0, 1+1, 2+0 Deployments

Microwave ODUs can be deployed in various configurations.

Microwave ODU in 1+0 Configuration with Antenna
Microwave ODU in 1+0 Configuration with Antenna

The most common is 1+0 which has a single ODU, generally connected directly to the microwave antenna.  1+0 means “unprotected” in that there is no resilience or backup equipment or path.

 

 

 

Two Microwave ODUs in 1+1 HSB or 2+0 configuration with Coupler and Antenna
Two Microwave ODUs in 1+1 HSB or 2+0 configuration with Coupler and Antenna

For resilient networks there are several different configurations.  1+1 in “Hot Standby” is common and typically has a pair of ODUs (one active, one standby) connected via a Microwave Coupler to the antenna.  There is typically a 3dB or 6dB loss in the coupler which splits the power either equally or unequally between the main and standby path.

Other resilient configurations are 1+1 SD (Space Diversity, using separate antennas, one ODU on each) and 1+1 FD (Frequency Diversity)

The other non-resilient configuration is 2+0 which has two ODUs connected to a single antenna via a coupler.  The hardware configuration is identical to 1+1 FD, but the ODUs carry separate signals to increase the overall capacity.

Grounding & Surge Protection

Suitable ground wire should be connected to the ODU ground lug to an appropriate ground point on the antenna mounting or tower for lightning protection.  This grounding is essential to avoid damage due to electrical storms.

In-line Surge Suppressors are used to protect the ODU and IDU from surges that could travel down the cable in the case of extreme surges caused by lightning

The specification of a typical Microwave ODU is shown below.

Typical ODU Features and Specifications:

  • 4-42GHz frequency bands available
  • Fully synthesized design
  • 3.5-56MHz RF channel bandwidths
  • Supports QPSK and 16 to 1024 QAM.  Some ODUs may support 2048QAM
  • Standard and high power options
  • High MTBF, greater than 92.000 hours
  • Software controlled ODU functions
  • Designed to meet FCC, ETSI and CE safety and emission standards
  • Supports popular ITU-R standards and frequency recommendations
  • Software configurable microcontroller for ODU monitor and control settings
  • Low noise figure, low phase noise and high linearity
  • Compact and lightweight design
  • Very high frequency stability +/-2.5 ppm
  • Wide operating temperature range: -40°C to +65°C

For Further information

For More Information about Microwave ODUs, we will be delighted to answer your questions. Please Contact Us

Microwave Backhaul for 5G Mobile Networks

5G Mobile networks, Microwave Backhaul and future trends in Mobile Networks

CableFree 5G Mobile Wireless Network
CableFree 5G Mobile Wireless Network

With 5G mobile communication becoming available around 2020, the industry has already started to develop a fairly clear view of the main challenges, opportunities and key technology components it involves. 5G will extend the performance and capabilities of wireless access networks in many dimensions, for example enhancing mobile broadband services to provide data rates beyond 10 Gbps with latencies of 1 ms.

Microwave is a key element of current backhaul networks and will continue to evolve as part of the future 5G ecosystem. An option in 5G is to use the same radio access technology for both the access and the backhaul links, with dynamic sharing of the spectrum resources. This can provide a complement to microwave backhaul especially in very dense deployments with a larger number of small radio nodes.

Today, microwave transmission dominates mobile backhaul, where it connects some 60 percent of all macro base stations. Even as the total number of connections grows, microwave’s share of the market will remain fairly constant. By 2019, it will still account for around 50 percent of all base stations (macro and outdoor small cells (see Figure 3). It will play a key role in last mile access and a complementary role the aggregation part of the network. At the same time, fibre transmission will continue to increase its share of the mobile backhaul market, and by 2019 will connect around 40 percent of all sites. Fibre will be widely used in the aggregation/metro parts of the networks and increasingly for last-mile access. There will also be geographical differences, with densely populated urban areas having higher fibre penetration than less populated suburban and rural areas, where microwave will prevail for both short-haul and long-haul links.

Spectral efficiency

CableFree 5G Mobile Backhaul Wireless Tower
CableFree 5G Mobile Backhaul Wireless Tower

Spectrum efficiency (that is, getting more bits per Hz) can be achieved through techniques like higher-order modulation and adaptive modulation, the superior system gain of a well-designed solution, and Multiple Input, Multiple Output (MIMO).

Modulation

The maximum number of symbols per second transmitted on a microwave carrier is limited by the channel bandwidth. Quadrature Amplitude Modulation (QAM) increases the potential capacity by coding bits on to each symbol. Moving from two bits per symbol (4 QAM) to 10 bits per symbol (1024 QAM) delivers a more than five-fold capacity increase.

Higher-order modulation levels have been made possible through advances in component technologies that have reduced equipment-generated noise and signal distortion. In the future there will be support for up to 4096 QAM (12 bits per symbol), but we are approaching the theoretical and practical limits. Higher-order modulation means increased sensitivity to noise and signal distortion. The receiver sensitivity is reduced by 3 dB for every increased step in modulation, while the related capacity gain gets smaller (in percentage terms). As an example, the capacity gain is 11 percent when moving from 512 QAM (9 bits per symbol) to 1024 QAM (10 bits per symbol).

Adaptive modulation

5G Backhaul Microwave Link
CableFree Microwave Link installed on a telecom tower

Increasing modulation makes the radio more sensitive to propagation anomalies such as rain and multi-path fading. To maintain microwave hop length, the increased sensitivity can be compensated for by higher output power and larger antennas. Adaptive modulation is a very cost-effective solution to maximize throughput in all propagation conditions. In practice, adaptive modulation is a prerequisite for deployment with extreme high-order modulation.

Adaptive modulation enables an existing microwave hop to be upgraded from, for example, 114 Mbps to as much as 500 Mbps. The higher capacity comes with lower availability. For example, availability is reduced from 99.999 percent (5 minutes’ yearly outage) at 114 Mbps to 99.99 percent of the time (50 minutes’ yearly outage) at 238 Mbps. System gain Superior system gain is a key parameter for microwave. A 6 dB higher system gain can be used, for example, to increase two modulation steps with the same availability, which provides up to 30 percent more capacity. Alternatively it could be used to increase the hop length or decrease the antenna size, or a combination of all. Contributors to superior system gain include efficient error correction coding, low receiver noise levels, digital predistortion for higher output power operation, and power-efficient amplifiers, among others.

MIMO Multiple Input, Multiple Output (MIMO)

MIMO is a mature technology that is widely used to increase spectral efficiency in 3GPP and Wi-Fi radio access, where it offers a cost-effective way to boost capacity and throughput where available spectrum is limited. Historically, the spectrum situation for microwave applications has been more relaxed; new frequency bands have been made available and the technology has been continuously developed to meet the capacity requirements. However in many countries the remaining spectrum resources for microwave applications are starting to become depleted and additional technologies are needed to meet future requirements. For 5G Mobile Backhaul, MIMO at microwave frequencies is an emerging technology that offers an effective way to further increase spectrum efficiency and so the available transport capacity.

Unlike ‘conventional’ MIMO systems, which are based on reflections in the environment, for 5G Mobile Backhaul, channels are ‘engineered’ in point-to-point microwave MIMO systems for optimum performance. This is achieved by installing the antennas with a spatial separation that is hop distance-and frequency-dependent. In principle, throughput and capacity increase linearly with the number of antennas (at the expense of additional hardware cost, of course). An NxM MIMO system is constructed using N transmitters and M receivers. Theoretically there is no limit for the N and M values, but since the antennas must be spatially separated there is a practical limitation depending on tower height and surroundings. For this reason 2×2 antennas is the most feasible type of MIMO system. These antennas could either be single polarized (two carrier system) or dual polarized (four carrier system). MIMO will be a useful tool for scaling microwave capacity further, but is still at an early phase where, for example, its regulatory status still needs to be clarified in most countries, and its propagation and planning models still need to be established. The antenna separation can also be challenging especially for lower frequencies and longer hop lengths.

More Spectrum

Another section of the microwave capacity toolbox for 5G Mobile Backhaul involves getting access to more spectrum. Here the millimeter-wave bands – the unlicensed 60 GHz bands and the licensed 70/80 GHz band – are growing in popularity as a way of getting access to new spectrum in many markets (see Microwave Frequency Options section for more information). These bands also offer much wider frequency channels, which facilitate deployment of cost-efficient, multi-gigabit systems which enable 5G Mobile Backhaul.

Throughput efficiency

Throughput efficiency (that is, more payload data per bit), involves features like multi-layer header compression and radio link aggregation/bonding, which focus on the behaviour of packet streams.

Multi-layer header compression

Multi-layer header compression removes unnecessary information from the headers of the data frames and releases capacity for traffic purposes, as shown in Figure 7. On compression, each unique header is replaced with a unique identity on the transmitting side, a process which is reversed on the receiving side. Header compression provides relatively higher utilization gain for packets of smaller frame size, since their headers comprise a relatively larger part of the total frame size. This means the resulting extra capacity varies with the number of headers and frame size, but is typically a 5–10 percent gain with Ethernet, IPv4 and WCDMA, with an average frame size of 400–600 bytes, and a 15–20 percent gain with Ethernet, MPLS, IPv6 and LTE with the same average frame size.

These figures assume that the implemented compression can support the total number of unique headers that are transmitted. In addition, the header compression should be robust and very simple to use, for example offering self-learning, minimal configuration and comprehensive performance indicators.

Radio Link Aggregation (RLA, Bonding)

Radio link bonding in microwave is akin to carrier aggregation in LTE and is an important tool to support continued traffic growth, as a higher share of microwave hops are deployed with multiple carriers, as illustrated in Figure 8. Both techniques aggregate multiple radio carriers into one virtual one, so both enhancing the peak capacity as well as increasing the effective throughput through statistical multiplexing gain. Nearly 100 percent efficiency is achieved, since each data packet can use the total aggregated peak capacity with only a minor reduction for protocol overhead, independent of traffic patterns. Radio link bonding is tailored to provide superior performance for the particular microwave transport solution concerned. For example, it may support independent behaviour of each radio carrier using adaptive modulation, as well as graceful degradation in the event of failure of one or more carrier (N+0 protection).

Just like carrier aggregation, radio link bonding will continue to be developed to support higher capacities and more flexible carrier combinations, for example through support for aggregation of more carriers, carriers with different bandwidths and carriers in different frequency bands.

Network optimization

The next section of the capacity toolbox is network optimization. This involves densifying networks without the need for extra frequency channels through interference mitigation features like super high performance (SHP) antennas and automatic transmit power control (ATPC). SHP antennas effectively suppress interference through very low sidelobe radiation patterns, fulfilling ETSI class 4. ATPC enables the transmit power to be automatically reduced during favorable propagation conditions (that is, most of the time), effectively reducing the interference in the network. Using these features reduces the number of frequency channels needed in the network and could deliver up to 70 percent more total network capacity per channel. Interference due to misalignment or dense deployment is limiting backhaul build-out in many networks. Careful network planning, advanced antennas, signal processing and the use of ATPC features at a network level will reduce the impact from interference.

Looking to the future, 5G and Beyond

CableFree 5G Mobile Wireless Technology
CableFree 5G Mobile Wireless Technology

Over the coming years, microwave capacity tools for 5G Mobile Networks will be evolved and enhanced, and used in combination enabling capacities of 10 Gbps and beyond. Total cost of ownership will be optimized for common high-capacity configurations, such as multi-carrier solutions.

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

For more information on this topic, please contact us

Microwave Mobile Backhaul

Packet Microwave Radios for Mobile Backhaul

To deliver a compelling quality of experience for subscribers, you must respond quickly to growing traffic demands. Modern Packet Microwave Mobile Backhaul products help you maximize the network’s performance by enabling rapid deployment of scalable backhaul to cell sites.  Modern solutions include a portfolio of microwave products to address the backhaul needs of 2G, 3G, and LTE macro cells and 3G, LTE, and Wi-Fi® small cells. Radio spectrum is maximized using innovative techniques to maximize payload capacity to support the evolution to LTE and heterogeneous networks. Unique, common radio support for indoor and outdoor deployments enhances savings potential.

Packet Microwave Mobile Backhaul is a key component in a modern end-to-end mobile backhaul solution, which provides the flexibility, scale and operational simplicity to lower the total cost of ownership and simultaneously enhance the mobile service experience.

BENEFITS

CableFree Microwave for Mobile Backhaul
CableFree Microwave for Mobile Backhaul

Economic benefits

Rapidly support the optimal cell site location

  • Complete backhaul portfolio for macro cells and small cells
  • Support for all sites including both end and intermediate cell sites
  • Space and power efficiency
  • Full outdoor option to meet different microwave site space requirements

Achieve maximum spectral performance

  • Maximum bandwidth per band
  • Intelligent compression
  • Advanced quality of service levels supporting subscriber quality of experience

Scale the network cost effectively

  • Reliably bond radio channels to create larger microwave links
  • Any topology, any number of microwave link directions
  • Network awareness for both Carrier Ethernet and/or IP/MPLS networks

Be operationally efficient

  • Common radio for all cell sites
  • Evolutionary path from hybrid microwave to packet microwave at the touch of a button
  • Management beyond basic IP partner integration

Deployment, management, end-user benefits

Grow and retain subscribers by maximizing the mobile experience

  • Infrastructure support for increased subscriber bandwidth demands
  • Ability to react quickly to subscriber demand with optimally-located cell sites
  • Increased capacity that supports high bandwidth data applications

COMPONENTS

4G/LTE Mobile Backhaul
4G/LTE Mobile Backhaul

Packet Microwave Mobile Backhaul integrates a modern microwave portfolio with small cell optimized products to provide a complete backhaul offering for small cells and/or macro cells.

Read on in our following pages to find out more about technologies used in mobile backhaul applications

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

Enterprise

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.

For Further Information on Microwave

To find out more about Microwave Link Technology and how CableFree can assist with your wireless network, please Contact Us

QAM Modulation for Microwave Links

1. What is QAM?

Modulation is a data transmission technique that transmits a message signal inside another higher frequency carrier by altering the carrier to look more like the message. Quadrature Amplitude Modulation (QAM) is a form of modulation that uses two carriers—offset in phase by 90 degrees—and varying symbol rates (i.e., transmitted bits per symbol) to increase throughput. The table in this blog post (Figure 1) describes the various common modulation levels, associated bits/symbol and incremental capacity improvement above the next lower modulation step.

CableFree QAM Modulation Table
CableFree QAM Modulation Table

2. Must all operators who use microwave backhaul use higher-order QAMs?

Higher-order QAMs are not necessarily a must-have for all network operators. However, higher-order modulations do provide one method of obtaining higher data throughput and are a useful tool for meeting LTE backhaul capacity requirements.

3. What is the main advantage of using higher-order QAMs with microwave radios?

The main advantage is increased capacity, or higher throughput. However, capacity improvement diminishes with every higher modulation step (i.e., moving from 1024QAM to 2048QAM the improvement is only about 10 percent!), so the real capability of higher-order modulations alone to address the objective of increasing capacity is very limited. Other techniques will be needed.

4. What are the tradeoffs of higher-order QAMs on RF performance?

First, with each step increase in QAM the RF performance of the microwave radio is degraded as per the Carrier-to-Interference (C/I) ratio. For example, going from 1024QAM to 2048QAM will produce an increase of 5 dB in C/I (Figure 2). This results in the microwave link having much higher sensitivity to interference, making it more difficult to coordinate links and reducing link density. Along with this increase in phase noise there will be an increase in design complexity cost.

CableFree QAM Modulation Tradeoffs
CableFree QAM Modulation Tradeoffs

Also, by increasing from 1024QAM to 2048QAM, system gain will decrease from above 80 dB to just above 75 dB (Figure 2). With much lower system gain microwave links will have to be shorter and larger antennas will have to be employed—increasing total cost of ownership and introducing additional link design and path planning problems.

All of the above are the results of linear functions: they degrade in a one-to-one relationship with the move to higher-order QAMs. Meanwhile, the capacity increases derived from higher-order QAMs are the function of a flattening curve: Each step increase in QAM results in a reduced percentage increase in capacity compared to prior increases in QAM. The added capacity benefits are diminished when considering the added costs of higher C/I and lower system gain.

5. Do you need to use Adaptive Coding and Modulation (ACM) while using higher-order QAMs?

ACM should be implemented while employing high-order QAMs to offset lower system gain. However, while ACM does help mitigate the effects of more difficult propagation when using higher-order modulations, it cannot help offset increased C/I.

6. What gives CableFree a “heads-up” here when other big name companies seem to be supporting the technology?

CableFree realizes higher-order modulations are not a panacea—a cure-all. While every minor technology improvement in throughput can help, a focus on technologies that grow capacity in hundreds of percentage points vs. tens of percentage points is most critical now. CableFree believes that these hundreds-of-percentage-points-of-improvement-in-capacity solutions will be the most important moving forward. It is in these technologies that CableFree has a “heads-up.” Such techniques include deploying more spectrum—particularly in the form of multichannel RF bonding (N+0) solutions—to achieve a minimum of 200 percent capacity increase. This technique is subject to frequency availability, but with flexible N+0 implementations (such as being able to use frequency channels in different bands and different channel sizes) many congestion issues can be avoided.

Second, intelligently dimensioning the backhaul network based on proven rules, best practices and L2/L3 quality of service (QoS) capabilities is another technique to provide potentially very large gains in backhaul capacity. Higher-order modulations can be one tool to achieve required capacity increases in the backhaul network. However, their inherent drawbacks should be well understood, while the most attention should be paid to other techniques that deliver more meaningful and quantifiable benefits.

7. Will operators need to “retrofit” microwave radios to be capable of higher-order QAM operation in their existing microwave infrastructure? Or will completely new hardware be required?

This depends on the age and model of the existing radios. Older microwave systems will likely need to be “retrofitted” to support 512QAM and higher modulations. Recently installed microwave systems should be able to support these technologies without new hardware.

8. How will QAM evolve in the future? Is the introduction of higher-order QAMs an indefinite process, with no end in sight?

The introduction of higher-order QAMs is not an endless process. As per Figure 1 above in this blog post, the law of diminishing returns applies: Throughput percentage improvement declines as modulation rates increase. The cost and complexity of implementing higher-order QAMs probably is not worth the capacity increase benefits derived—not past 1024QAM, in any event.