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Today, mobile
handheld devices are capable of communicating over several frequency bands and
radio technologies. Competing for your mobile delivery needs are systems that
include global system for mobile communications (GSM), universal mobile
telecommunications system (UMTS or 3G) and LTE.
Wireless channel
modeling is especially difficult due to the inherent propagation complexities. Wireless
channel modeling involves reflections, scattering, diffraction and transmission
through a large number of irregular objects. Multiple antenna systems deliver a
matrix of transfer functions with a corresponding Transmission and Receipt antenna
element. Multipath components often times arrive in clusters which provide
insight into the physics of the propagation and allow for more compact
modeling.
When measuring
channel characteristics, measurements can be taken on impulse responses and the
transfer functions between transmission and receipt antennas. With the data
collected from those measurements, secondary parameters can be established.
Careful planning of what is to be measured, where and how often it is measured
allow for the necessary conclusions to be made.
Tools such as a Vector
network analyzer (VNA) can be used to measure the reflection and transmission co-efficient
of a two-port system over wide bandwidths. The main benefit of the VNA is
flexible frequency control along with all the related hardware synchronizations.
The VNA is often used with virtual array measurements. The VNA uses a stepped
frequency sweep to measure the channel in the frequency domain, and hence,
wider bandwidth results in slower measurement of the channel. Another
measurement tool is called a Channel Sounder. Channel Sounders are a measurement
system consisting of a transmitter, receiver, and a fast data acquisition unit.
The main difference between channel sounders and the VNA is that the
transmitter and the receiver rely individually on accurate, synchronized
reference local oscillators (LO), and therefore, the transmitter and
receiver(s) can be far apart.
The interest
towards various propagation environments such as rural, macro- and microcellular,
indoor, and outdoor to indoor dictates that the equipment has to adapt for each.
Also, highly time-variant channels, such as the car-to-car channels increase
the demand for fast sampling rates of the channel.
Traditional
stationary techniques of antenna and propagation channel measurement do not
take into account the increased data points, distance between devices and
current wireless device mobility. With the increased bandwidth required of
newer and more densely feature packed phones, the challenges for accurately
locating and measuring the signal has increased.
Sources:
http://lib.tkk.fi/Diss/2010/isbn9789526030531/isbn9789526030531.pdf
http://wides.usc.edu/research/propagation-channel-measurement-and-modeling/
http://users.ece.utexas.edu/~wireless/radiochannel.php
http://wireless.per.nl/
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