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Quadrature Amplitude Modulation (QAM) for Network Operators

May 26, 2016

Quadrature Amplitude Modulation (QAM) for Network Operators

QAM controls digital information when it is transmitted between two points by enabling analog signals to transmit digital data efficiently. It also enables more bits to be transmitted in the same period, effectively increasing the bandwidth.

QAM is a modulation scheme that changes the amplitude (power level) of two signals when data is transmitted. The first signal is in phase with the data that comes in, while the second is out of phase by 90 degrees. How QAM is referred to, is based on the number of bits of information encoded in a time period. Eight bits for example defines the number of combinations that can be made with the two signals. If 256 combinations are possible with the eight bits, it is referred to as 256 QAM. Using a single period to transmit 10 bits would be known as 1024 QAM.

QAM systems are used by multi-system operators (MSO) in the cable television industry to deliver data, voice and video services. QAM is used to format format services in headends and hubs. These facilities process and distribute signals over a cable system and delivers them to user's homes where embedded multimedia terminal adapters (eMTA), cable modems and set top boxes convert the QAM signals back into useful video, data and voice.

Due to the ever increasing demand by consumers for high-definition television, high-speed data, network personal video recording, video-on-demand, digital phone service and Internet Protocol cable television, network operators have an ever increasing need for an increasing number of QAM channels. Looking at overall costs, QAMs are important to MSOs as they represent a substantial part of the capital used to deploy digital video services. Previously, individual services, such as video-on-demand, broadcast cable television and high-speed internet each had their own QAM modulator and RF splitters and combiners were used to multiplex the service line. This resulted in many QAM racks, modulators and multifaceted networks to combine everything.

Wideband edge QAM devices are now used to simplify the profusion of QAM modulators. QAM modulators were developed as a result of individual services being managed to needing to manage multiple services. Another factor in the development was small groups of QAM carriers working to support the full 50 MHz–1 GHz spectrum on each port. Wideband edge QAM devices are scalable, dense solutions that are vital to support additional next-generation, advanced services over HFC (hybrid fiber coaxial) networks. It allows both cable operators and MSOs to seamlessly integrate new service offerings into their business.

Current wideband edge QAM modulators have an unbelievable density of up to 2,560 QAM channels per chassis. They are able to manage all the digital services offered by MSOs across the full downstream spectrum from each RF port.

The deployment of wideband edge QAMs adds value for network operators and moves them to a platform controlled by software from which they can seamlessly reconfigure or add services. At the same time, both their operational and capital expenditures are reduced.


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  • I’ve seen the term modulation used in several blogs, but this quadrature amplitude modulation tutorial is the first time it’s made sense. You explain the advantages of qam quite well (can’t recall ever seeing so many “Q’s” in a sentence). I know it’s not listed here, but where could I find a good example of a quadrature amplitude modulation block diagram? I’m in a ham radio club and I think it would be fun to throw it at my colleagues. I know this is somewhat different, but they’ll be intrigued by the principles behind it.

    Bryce White on
  • Absolutely no idea there was a thing called quadrature amplitude modulation until I read this blog. It’s another compelling story of the public’s need for fast data speeds, clear TV signals, etc. We the public want it now and we want it fast. If you say you can provide a movie on demand, it’d better not buffer. If you say you have the strongest cell phone network, there better not be any dropped calls. I’m glad cell phone boosters are just one way for people to get strong signals on their phones. There are a number of things for phones and other devices.

    Steve Mueller on
  • I read this and you guys do a thorough job explaining difficult concepts involving technology. I was reading another article about DAS design elsewhere on your site and it gave me a good grasp of the concept. All I can say though is these network operators have their hands full and their brains must be buzzing keeping up with all this new technology. These guys (and gals) must be geniuses to stay ahead on all the technology. I wouldn’t know where to begin.

    Tully McBride on

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