Page 180 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes Meteor Burst Communications

Meteor burst communications (MBC), also referred to as meteor scatter communications, is a
radio propagation mode that exploits the ionizedtrails of meteors during atmospheric entry to
establish brief communications paths between radio stations up to 2,250 kilometres (1,400 mi)
apart. As the earth moves along its orbital path, billions of particles known as meteors enter the
earth’s atmosphere every day; a small fraction of which have properties useful for point to point
communication. When these meteors begin to burn up, they create a trail of ionized particles in
the E layer of the atmosphere that can persist for up to several seconds. The ionization trails can
be very dense and thus used to reflect radio waves. The frequencies that can be reflected by any
particular ion trail are determined by the intensity of the ionization created by the meteor, often a
function of the initial size of the particle, and are generally between 30 MHz and 50 MHz.

The distance over which communications can be established is determined by the altitude at
which the ionization is created, the location over the surface of the Earth where the meteor
is falling, the angle of entry into the atmosphere, and the relative locations of the stations
attempting to establish communications. Because these ionization trails only exist for fractions of
a second to as long as a few seconds in duration, they create only brief windows of opportunity
for communications.

Self-Assessment

Fill in the blanks:
6. The cellular system uses …………………....... to transmit signals. Radio Waves
7. 7. Cellular networks offer a different solution called …………………....... Frequency Reuse

8. 8. …………………....... sizes range from one kilometer to 50 kilometers in radius. Cell
9. 9. …………………....... that orbit the Earth at an altitude of 22,237 miles revolve around the
Earth at the same speed that the Earth rotates. Satellites

10. 10. With the explosion of wireless users, consortiums of companies have invested huge
sums of money to create …………………....... satellite networks. LEO

11.3 Short Message Service (SMS) Applications

SMS stands for Short Message Service. It is a technology that enables the sending and receiving
of messages between mobile phones. SMS first appeared in Europe in 1992. It was included in
the GSM (Global System for Mobile Communications) standards right at the beginning. Later it
was ported to wireless technologies like CDMA and TDMA. The GSM and SMS standards were
originally developed by ETSI.

Did u know? ETSI is the abbreviation for European Telecommunications Standards Institute.
Now the 3GPP(Third Generation Partnership Project) is responsible for the development
and maintenance of the GSM and SMS standards.
As suggested by the name “Short Message Service”, the data that can be held by an SMS message
is very limited. One SMS message can contain at most 140 bytes (1120 bits) of data, so one SMS
message can contain up to:

z z 160 characters if 7-bit character encoding is used. (7-bit character encoding is suitable for
encoding Latin characters like English alphabets.)

z z 70 characters if 16-bit Unicode UCS2 character encoding is used. (SMS text messages
containing non-Latin characters like Chinese characters should use 16-bit character
encoding.)

174 LOVELY PROFESSIONAL UNIVERSITY