The Issues in Wireless Communications

In the seventies, the principal design problem encountered in wireless or mobile radio was how to overcome the distortion of received signals by a time-varying and frequency-selective propagation path. Radio waves near the ground do not travel over a single well-defined radio path as in free space; they are scattered against reflecting obstacles in the vicinity of the mobile antenna. Reflected waves may add destructively, causing the received signal to disappear or become heavily attenuated at certain locations. A moving user, as in vehicular telephony, receives a resulting signal that is rapidly varying in time. This effect is called `fading'. Moreover, waves excessively delayed by remote reflections cause distortion of the shape of transmitted waveforms.

Modern (digital) signal processing (DSP-)techniques can mitigate these effects to a great extent. As a result, nowadays the most quoted critical issues of wireless systems are no longer directly related to multipath fading, but are

the scarcity of radio spectrum and the resulting mutual interference among users
the power consumption of portable terminals and the inadequacy of existing battery and other energy storage technologies, and
the complexity of the software needed to support user mobility, e.g. from cell to cell or from operator to operator.

In the past 10 years, the general emphasis of radio communications designs has shifted away from maximizing the capacity of individual links, limited by gaussian noise and available bandwidth, onto optimizing the capabilities of multi-user networks. The decisive interference now seldom comes from outside (as in military systems), but is produced by authorized users of the very same wireless network. Users thus share an interest in developing and adhering to the best possible protocols and standards for allocating the joint network resources. Accordingly, wireless systems engineering has developed into a conscious search for the best common culture for multiple users in a real environment. The traffic capacity, spectrum efficiency and cost-effectiveness of modern radio networks is no longer won from nature (or an adversary) in a classical pursuit of individual gain.

Start page of video from Short Course by BMRC
Video from Wireless Communications Networks Short Course
"First of all, the receive signal is not a strong line-of-sight signal but are a lot of reflections from obstacles. That's called multipath reception..... But this can be resolved if you design a system in an appropriate way, using digital processing techniques. What has become very important in the last few years are three issues ..... "
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Wireless Communication

Chapter: Business and Regulatory Aspects

The Issues in Wireless Communications

Video from Wireless Communications Networks Short Course

Wireless Communication © 1993, 1995.