Characteristics of Wireless Networks
von Christoph K am Apr.30, 2009, in Grundlagen, In English
In the following I describe how the characteristics of wireless networks affect the audiovisual quality of 3G video telephony and especially IVVR (Interactive Voice & Video Response) applications. The impact of these characteristics need to be considered when designing IVVR applications and services:
Wireless networks are inherently error prone. Bitrates in wireless systems tend to fluctuate more as compared with wired networks. In wired networks, phenomena such as fading, shadowing, or reflection are non-existent so that, for the most part, the same bandwidth and much higher bandwidths are present during transmission. Influences on signal propagation cause the constant changing bandwidths in wireless systems. Generally, the receiving power depends on the distance between sender and receiver. The receiving power p decreases proportionally to the square of the distance between sender and receiver:
p=1/d2
where d is the distance between sender and receiver (Schiller).
Receiving power is influenced further by frequency dependent fading, shadowing, reflection at large obstacles, refraction depending on the density of the medium, scattering at small objects, and diffraction at edges.
The effect of multipath propagation can cause jitter when the radio signal reaches the receiver by two or more paths at different times. Moreover, the mobility of the user adds another set of problems that results in fading of received power over time; the channel characteristics change over time and location. This exacerbates the effect of multipath propagation because signal path change will be increased as the user changes his or her location. Changes in the distance between sender and receiver cause different delay variations of different signal parts.
The phenomenon of
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