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A First Course on Wireless Communication

Welcome to the exciting field of wireless communication. If you are looking for a first introduction into this area, this page may help you with suggestions. We propose that you follow this procedure:

Step 1: Read this page entirely without clicking on any hypertext link.
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The importance of wireless communication

Wireless communication started with the invention of the wireless telegraph. This innovation allowed communication with ships on the oceans. Wireless telegraphy was also used for communication across the Atlantic and the Pacific, particularly after the events of World War I showed the vulnerability of undersea telegraph cables.

Wireless voice communication became technically feasible around 1915. Around 1920, broadcasters began to transmit their programs "over the air". World War II gave a strong impetus to radio communication technology, but for a long time speech communication by radio was only available to the military and to closed user groups, such as law enforcement officers. Advances in (micro) electronics accelerated further development of mobile communication systems. Analog automatic public telephony appeared in the seventies. A switch-over to digital systems is currently underway. The systems of today can also provide other services than just telephony, for instance short message services, data communications and facsimile.

Nowadays wireless radio communication plays an increasing role in providing flexible and convenient access to the fixed communication infrastructure (the "information highway"). Most technical limitations are now well understood, and many issues can well be handled by state of the art technology. Modern systems provide transmit rates and Quality of Service that make wireless multi-media services possible.

Who were the pioneers of wireless telegraphy?
How has the role of wireless changed over the years?
What are the main issues in wireless communication?
How will wireless systems evolve?

The principles of cellular telephony

In 1974, the FCC allocated 40 MHz of radio spectrum to public radio telephony. In the late seventies, it became clear that the existing radio telephone system would not be able to accommodate the increasing demand from subscribers. Research into more efficient use of the radio spectrum led to the development of cellular frequency reuse. The service area of an operator is divided into many small areas, each covered by a base station. A fundamental question is under which conditions cells may share the same frequency.

Why do people call (AMPS) wireless phones "cellular phones"?
What are the basic principles of cellular frequency reuse?
How big is a cell?
What happens if a cellular phone moves out of the coverage area of its base station?
Is sprectum scarcity still an issue?
What is the difference between cellular and cordless phones?

Cellular Telephone Systems

The U.S. analog AMPS system attracted many subscribers. One of the main success factors was that the entire U.S. uses a single common standard for analog cellular telephony. This is in contrast to the situation in Europe, where many non-compatible analog systems and standards were in use.

The European countries developed an innovative new digital system, called GSM, which is on its way to becoming a global success. In the U.S., two standards compete, with significantly different transmission standards.

Is there a spectrum-conservation reason to switch to digital systems?
What are the important factors that contributed to the success of GSM?
GSM is a TDMA system. What does that mean?
Which two systems compete for the US digital cellular standard? What is the main technical difference between these two systems?

Other Wireless Systems and Services

Several Research & Development initiatives aim at standardizing a universal personal communications system, capable of providing a multitude services, working reliably in any propagation environment. Meanwhile, we have seen the introduction of several different new network concepts in the last decade. Mostly, these systems provide only a limited set of functionality. Examples are systems for cordless telephony, paging, digital broadcasting and wireless local area networking.

Data over cellular
- Why are telephone networks less suitable for data transmission?
- Which special data transmission services can be provided through GSM?
- What is the name of the standard allowing data transmission in the U.S. AMPS network?
Cordless
- Why is the DECT system particularly suitable for office data communication?
Wireless LANs
- Which frequency bands are of interest for license-free operation of wireless LANs?
Broadcast Systems
- Why do only few broadcasters use digital systems?
- Can analog FM broadcast radio provide digital data services?
- What other services can Digital Audio Broadcasting provide besides disseminating radio programmes?
- What are the three transmission media envisaged for Digital Television?

Wireless Propagation

One of the main challenges in wireless communication is to achieve reliable transmission over the "hostile" mobile radio channel. The mobile propagation channel is notoriously poor. The main problems are rapid time variations of the channel and frequency selectivity.

Which three mechanisms affect wireless propagation?
How rapidly do radio signals get weaker if one moves the receiver away from from the transmitter?
If I loose my radio signal while waiting for a traffic light, why do I receive the signal clearly if I move only half a meter.
If a mobile antenna receives a signal over different paths, what is the effect of the angle of arrival of such a path?
What is the effect of a delay spread on a digital signal?
To what extent does the indoor channel differ from macro-cellular propagation?

Transmission Methods

Good and cost effective solutions to combat the effects of multipath fading depend on the environment and system requirements.

A good modulation method is spectrum efficient, robust against noise, interference, fading and multipath delay spread, and allows a simple and power-efficient implementation of the portable terminal.

What factors determine the signal outage probability?
How can diversity improve the BER?
What modulation method is used in GSM?
What kind of systems use spread-spectrum transmission?
How does a Direct Sequence transmitter work?
How can slow frequency hopping improve the performance or capacity of a cellular telephone network?

Multiple Access

As the radio spectrum has limited bandwidth, radio communication resources must be shared efficiently amoung many users. The basic unit of spectrum resources is "Hz . sec . square kilometer", i.e., it involves bandwidth, time and area factors. To a cellular operator, employing a more spectrum-efficient system means that he can accommodate more subscribers in the same bandwidth.

For data and multi-media traffic, resource management is more complicated than for telephony. Because of the bursty nature of the traffic, the system must rapidly adapt to the changing needs of the users.

What are the basic principles of assinging spectrum resources to a fixed group of users?
What is the main difference between ALOHA and CSMA?
What can happen if the ALOHA protocol is unstable?
What is the hidden terminal problem and how can it be resolved?