Exploring communications technology
Exploring communications technology

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Exploring communications technology

4.9 Summary

Orthogonal frequency division multiplexing (OFDM), which divides a communication channel into narrow subchannels (each with its own subcarrier) provides a spectrally efficient and flexible way to use the channel. OFDM has become an almost ubiquitous part of modulation, both in wired and wireless communication.

The use of QAM modulation for the subcarriers of OFDM is also ubiquitous. Using various orders of QAM (depending on noise conditions) further adds to the flexibility of OFDM.

In DSL broadband, a version of OFDM called Digital Multitone (DMT) is used both because of its spectral efficiency and its adaptability to unpredictable and variable noise conditions.

In 4G, Orthogonal Frequency Division Multiple Access (OFDMA) is used as a flexible way to share access to a radio channel among multiple, transient users. This is done by grouping subchannels into units of resource which are allocated to users dynamically as fluctuating demand requires.

In WiFi, OFDM is exploited as a way of making very efficient use of the available channels. The subchannels are not used for access (as in 4G), but selective nulling of subchannels is used to ensure that transmission power is properly restricted. Multiple access in WiFi is based a ‘listen before transmitting’ protocol known as Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA).

TM355_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus