Advanced Communication Systems -Wireless Communication Technology Dr. Junwei Lu The School of Microelectronic Engineering Faculty of Engineering and Information Technology
Outline Introduction to Wireless Communication Smart Antenna for Wireless Systems Cellular Radio Personal Communication System Satellite-Based Wireless Systems The Future of Wireless
Introduction to Wireless Communication Brief History of Wireless Telecommunication Elements of a Wireless Communication System Signals and Noise The Frequency Domain The Radio-Frequency Spectrum Convergence and Wireless Communication
Brief History of Wireless Telecommunication The Beginning Wireless telecommunication began only a little later than the wired variety. Morse`s telegraph (1837) and Bell`s telephone (1876) were soon followed by Hertz`s first experiments with radio (1887). Hertz`s system was a laboratory curiosity, but Marconi communicated across the English Channel in 1899 and across the Atlantic Ocean in 1901. These successes led to the widespread use of radio for ship-to-ship and ship-to-shore communication using Morse code.
Postwar Expansion Soon after the end of World War II, two systems were developed that that presaged modern wireless communication. AT&T introduced its Improved Mobile Telephone Service (IMTS) in 1946, featuring automatic connection of mobile subscribers to the public switched telephone network (PSTN). The Cellular Revolution The world`s first cellular radio service was installed in Japan in 1979, followed in 1983 by North American services. The first cellular systems used analog FM transmission, but digital modulation schemes, witch provide greater privacy and can use bandwidth more efficiently, are used in all the new systems.
Elements of a Wireless Communication System The most basic possible wireless system consists of a transmitter, a receiver, and a channel, usually a radio link, as shown in Figure 1.1. Fig. 1.1 elements of a communication system
Simplex and Duplex Communication Figure 1.1 represents a simplex communication system. The communications one way only, from transmitter to receiver. Most of the systems we discuss here involve two-way communication. This is called full-duplex communication. Fig. 1.2 Full-duplex communication system
Some two-way communication systems do not require simultaneous communication in both directions. An example of this half-duplex type of communication is a conversation over citizens` band (CB) radio. Fig. 1.3 Half-duplex communication system
Wireless Networks The full- and half-duplex communication systems shown so far involve communication between only two users. When there are more than two simultaneous users, or when the two users are too far from each other for direct communication, some kind of network is required.
Network can take many forms. Probably the most common basic structure in wireless communication is the classic star network, shown in Figure 1.4. Fig. 1.4 Star network
Signals and Noise Communication systems described here differ in many ways, but they have two things in common, signal and noise. Modulated Signals Noise Signal-to-Noise Ratio Noise Figure and Noise Temperature
The Frequency Domain Fourier Series Effect of Filtering on Signals Noise in the Frequency Domain
The Radio-Frequency Spectrum Bandwidth Requirements As soon as the signal is modulated to transmit information, however, the bandwidth increases. Frequency Reuse Spectrum space in wireless systems is nearly always in short supply. Even with the communication bandwidth restricted as much as possible, there is often more traffic than can be accommodated. The spectrum used for a given purpose in one area can be reused for a different purpose in an other area that is physically far enough away that signals do not travel from one area to the other with sufficient strength to cause unacceptable interference levels.
Convergence and Wireless Communication There has been much talk recently about convergence, the merger of all kinds of previously separate electronic systems, for example, Telephony (both wireline and wireless), Broadcast and cable television, And data communication (most notably the Internet)
Smart Antenna for Wireless Systems Impairments Smart antenna techniques Smart and adaptive antenna arrays Applications of smart antennas Smart antennas at mobile terminals