Comparison of QAM Modulation Types

Comparing QAM Modulation

Comparison between 8, 16, 32, 64, 128, and 256 QAM types of Quadrature Amplitude Modulation

Gigabit Wireless Networks commonly use QAM modulation to achieve high data rate transmission.  So what is QAM?

Introducing Quadrature Amplitude Modulation

QAM, Quadrature amplitude modulation is widely used in many digital data radio communications and data communications applications. A variety of forms of QAM are available and some of the more common forms include 16 , 32 , 64 , 128 and 256 QAM. Here the figures refer to the number of points on the constellation, i.e. the number of distinct states that can exist.

The various flavours of QAM may be used when data-rates beyond those offered by 8-PSK are required by a radio communications system. This is because QAM achieves a greater distance between adjacent points in the I-Q plane by distributing the points more evenly. And in this way the points on the constellation are more distinct and data errors are reduced. While it is possible to transmit more bits per symbol, if the energy of the constellation is to remain the same, the points on the constellation must be closer together and the transmission becomes more susceptible to noise. This results in a higher bit error rate than for the lower order QAM variants. In this way there is a balance between obtaining the higher data rates and maintaining an acceptable bit error rate for any radio communications system.

Applications

QAM is in many radio communications and data delivery applications. However some specific variants of QAM are used in some specific applications and standards.

For domestic broadcast applications for example, 64 and 256 QAM are often used in digital cable television and cable modem applications. In the UK, 16 and 64 QAM are currently used for digital terrestrial television using DVB – Digital Video Broadcasting. In the US, 64 and 256 QAM are the mandated modulation schemes for digital cable as standardised by the SCTE in the standard ANSI/SCTE 07 2000.

In addition to this, variants of QAM are also used for many wireless and cellular technology applications.

Constellation diagrams

The constellation diagrams show the different positions for the states within different forms of QAM, quadrature amplitude modulation. As the order of the modulation increases, so does the number of points on the QAM constellation diagram.

The diagrams below show constellation diagrams for a variety of formats of modulation:

modulation-constellation-bpsk
modulation-constellation-16qam
modulation-constellation-32qam
modulation-constellation-64qam

Bits per symbol

The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to carry more bits of information per symbol. By selecting a higher order format, the data rate of a link can be increased.

The table below gives a summary of the bit rates of different forms of QAM and PSK.

MODULATION BITS PER SYMBOL SYMBOL RATE
BPSK 1 1 x bit rate
QPSK 2 1/2 bit rate
8PSK 3 1/3 bit rate
16QAM 4 1/4 bit rate
32QAM 5 1/5 bit rate
64QAM 6 1/6 bit rate

QAM noise margin

While higher order modulation rates are able to offer much faster data rates and higher levels of spectral efficiency for the radio communications system, this comes at a price. The higher order modulation schemes are considerably less resilient to noise and interference.

As a result of this, many radio communications systems now use dynamic adaptive modulation techniques. They sense the channel conditions and adapt the modulation scheme to obtain the highest data rate for the given conditions. As signal to noise ratios decrease errors will increase along with re-sends of the data, thereby slowing throughput. By reverting to a lower order modulation scheme the link can be made more reliable with fewer data errors and re-sends.

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The Real Cost of Fiber Cuts: How to solve using Gigabit Wireless

Fiber Cuts – The Real Cost – How to solve using Gigabit Wireless

Fibre Optic Cable - Fibre Cuts cost time and moneyOften you can’t avoid fiber cuts: they happen on public land or under public streets, outside your control.  The vast majority of corporate LAN connections, cable, Internet and LTE backhaul, is done over fiber optic cable.   In one report CNN stated that about 99 percent of all international communications occur over undersea cabling. Alan Mauldin, research director at U.S.-based research firm Telegeography, noted that while some major cabling projects can come with high price tags, fiber optics is considered more robust and more cost-effective than common wireless alternatives like satellite.

Gigabit Wireless solves Fibre Cut outagesBut while fiber optic cabling is traditionally seen as the safer option, that may be a misconception.  When installed correctly, fiber optics is the “perfect” media, transmitting Gigabits of data without interruption.  However, any disruption to the fragile fiber causes data outages which take days or weeks to locate and repair. According to data from the Federal Communications Commission. about a quarter of all network outages that happened between 1993 and 2001 were from cables being cut. Regardless of how the fiber cut occurred, such outages can be particularly damaging.

How easy is it to repair a fiber cut?

Fiber is not a “self healing” media: skilled teams with specialist fiber-splicing and terminating equipment are required to repair a broken fiber connection.  Most data communication engineers do not have this equipment or training on using them. fiber repair is a specialist business and getting trained people and splicing equipment to site costs time and money.  Factoring the anticipated cost of a fiber repair into a budget for “downtime” and “unproductivity” for corporates – and missing SLA’s for uptime for Service Providers – is a serious issue, including business continuity planning.  For rural areas, access to sites can be limited, with some locations limited by poor weather, and for islands sometimes only with infrequent access by sea or air.

Common causes of fiber cut outages

As these instances show, there are many different ways in which fiber optic cabling can be disrupted:

By vandalism – This type of fiber cut outage has been worryingly common of late. According to CNN, there have been 11 separate incidents involving the cutting of fiber optic cable in the Bay Area since July 2015. The FBI noted that there have been more than 12 in the region since January, and that it’s been hard to stop in part because there is so much critical cabling in the area and because cables are typically clearly marked, The Wall Street Journal reported. Authorities noted that these incidents show no sign of slowing down either, as they don’t have a clear suspect(s) or motive at this time. The Journal also noted that some instances of fiber optic-related downtime are not due to vandalism, but rather someone trying to steal metal.
fiber cut duct causes outageBy accident – This is perhaps one of the most common causes of fiber cuts, but nevertheless they are just as damaging. In one example a 75-year-old woman in the country of Georgia was digging in a field when she accidentally severed a fiber optic cable, in an article in The Guardian. As a result of the mishap, close to 90 percent of Armenia and parts of Azerbaijan and Georgia were completely without Internet for five plus hours.

Fire and Ice cause cable outage network downtimeBy force of nature – Tornadoes, hurricanes, earthquakes and other major natural disasters all have the potential to cut or entirely destroy fiber optic cabling. Other seemingly more benign forces of nature can also cripple connectivity, as Level 3 reported that 28 percent of all damages it sustained to its infrastructure in 2010 were caused by squirrels.

Calculating the impact of a fiber outage

trench digging causes fiber optic cut network outageIn some of these fiber cut outage incidents, the fallout can be relatively minor. A cut that occurs in the middle of the night on a redundant line can be easy enough to deal with, with service providers sometimes able to reroute traffic in the interim. Unfortunately however, such incidents often lead to much bigger problems for end users. For example, a cut fiber optic cable in northern Arizona in April caused many thousands of people and businesses to go about 15 hours with telephone and Internet service. This meant many shops had to either close or resort to manual tracking, and that personal Internet usage grinded to a halt, The Associated Press reported. More importantly, 911 emergency communications were disrupted in the incident.

It’s not just a hassle for end users, as cut fiber can severely impact public health when emergency services like police departments, fire stations and EMTs can’t take and receive calls. Plus, such incidents are very costly for service providers, forced to repair expensive infrastructure. They can also lead to canceled service, as customers become irate at service providers for failing to provide reliable connectivity at all times.

What’s a solution to fiber cut outages?

One easy way to avoid the problems related to cut fiber is to not have fiber at all and instead pursue a wireless dark fiber alternative. For example, after a cable snafu caused residents of Washington state’s San Juan Islands to go without telephone, Internet and cell service for 10 days in 2013, CenturyLink installed a wireless mobile backhaul option there, according to The AP.

By opting for a solution like a Gigabit Wireless Microwave, MMW, Free Space Optics or MIMO OFDM Radio, service providers gain a wireless alternative to cabling that is just as robust and fast as fiber. With the Gigabit Wireless link in place, cut fiber optic cabling is less disruptive to end users and ISPs.

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Planning a Gigabit Wireless Network

Planning a Gigabit Wireless Network

Planning involves a Gigabit Wireless network requires some consideration to ensure a reliable, high performance network and choice of appropriate technologies.
Some topics include:

Gigabit Wireless Technology
Gigabit Wireless Technology

Site Survey

  • Does Line of Sight (LOS) exist?
  • Desktop Survey / feasibility check
  • Physical Survey
  • RF / Spectral Survey
  • Distances required to cover

Choice of Technology:

Our expert team has over 18 years experience in planning and deploying Gigabit Wireless Networks in over 65 countries, including indoor and outdoor wireless networks.  Our team will be delighted to assist with all aspects of design, planning and deployment.

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Gigabit Wireless Technologies

Gigabit Wireless Technologies

Which technologies can we consider for a modern Gigabit Wireless Network?

Building a Gigabit Wireless Network
Building a Gigabit Wireless Network

Building a modern Gigabit Wireless Network will require choosing the appropriate technology for the precise network requirements.  With wireless, there is no “magic technology” or “one size fits all” approach – a successful network deployment will consider which technologies are best suited

Choosing the correct technology for a Gigabit Wireless Network is essential to ensure you have the very best throughput, capacity and network uptime.

Ask our team of experts who will be delighted to assist in designing an choosing exactly the right products and solutions to meet your needs

Contact us with any questions and requirements:

 

Welcome to Gigabit-Wireless.com!

Welcome to Gigabit-Wireless.com

Welcome – to the informational site for Gigabit Wireless Networking.  We consider the available technologies for Gigabit Wireless Metropolitan Area Networks including:

Welcome to Gigabit-Wireless.com
Welcome to Gigabit-Wireless.com

Feel welcome to read our site and find out more about building modern, reliable and scalable Gigabit Wireless Networks for Wireless Metropolitan Area Networks (Wi-Man), 4G/LTE backhaul networks, Small Cell Backhaul, Corporate Networks and Campus and CCTV wireless networks.

We include technology introduction papers as well as usage cases to guide users in the very latest in Gigabit Wireless technology and deployment.  Modern wireless products can reach 10Gbps or higher capacity.

Applications for Wireless

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Gigabit Wireless Technology

Gigabit Wireless networks are used in a wide range of applications which include

  • Safe Cities
  • Smart Cities
  • 4G/LTE Backhaul Networks
  • Broadband Wireless
  • Last Mile Networks
  • Campus Sites
  • Corporate Networks
  • Education networks
  • Metro WiFi
  • Security and CCTV

If you are considering a wireless network with 10Gbps or higher capacity, please ask our team of experts who will be delighted to assist:

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