Wireless Network Design: Optimization Models and Solution ...

Chapter 3
Channel Models for Wireless Communication
Systems
K. V. S. Hari
3.1 Introduction
Wireless communication has evolved significantly, over the past several decades,
to meet the ever-growing demand for high data rates over the wireless medium.
Systems have been designed for indoor applications and outdoor applications where
mobility is a very important aspect of system specification. One of the key elements
in the design of such systems is understanding the characteristics of the wireless
channel [7, 10, 13, 16, 22, 23, 25, 28, 31, 30, 34].
3.2 Wireless Channel
The wireless signal propagates in space, based on the laws of physics. An electromagnetic
Radio Frequency (RF) signal which travels in a medium suffers an
attenuation (path loss) based on the nature of the medium. In addition, the signal
encounters objects and gets reflected, refracted, diffracted, and scattered. The
cumulative effect results in the signal getting absorbed, signal traversing multiple
paths, signal’s frequency being shifted due to relative motion between the source
and objects (Doppler effect), thus getting modified significantly. It is clear that the
RF signal is a space-time-frequency signal and can be represented as s(x,y,z,t, f )
where x,y,z are the space variables and t, f are time and frequency variables, respectively.
If we represent the transmitted signal as sT (xT ,yT ,zT ,t, fT ) and the received
signal as sR(xR,yR,zR,t, fR), one can relate both space-time-frequency signals
as sR(xR,yR,zR,t, fxxR) = H(sT (xT ,yT ,zT ,t, fT )). H(.) is a function which can be
called the Wireless Channel. The wireless channel is also dependent on factors like
K. V. S. Hari
Department of ECE, Indian Institute of Science, Bangalore 560012, India, e-mail:
hari@ece.iisc.ernet.in
J. Kennington et al. (eds.), Wireless Network Design: Optimization Models and Solution
Procedures, International Series in Operations Research and Management Science 158,
DOI 10.1007/978-1-4419-6111-2_3, © Springer Science+Business Media, LLC 2011
47