11-07-2012, 02:12 PM
CELLULAR AND MOBILE COMMUNICATIONS
[attachment=27444]
Antenna:
Antenna pattern, antenna gain, antenna tilting, and antenna height 6 all affect the cellular system design.
The antenna pattern can be omnidirectional, directional, or any shape in both the vertical and the horizon
planes. Antenna gain compensates for the transmitted power. Different antenna patterns and antenna gains
at the cell site and at the mobile units would affect the system performance and so must be considered in
the system design. The antenna patterns seen in cellular systems are different from the patterns seen in
free space. If a mobile unit travels around a cell site in areas with many buildings, the omnidirectional
antenna will not duplicate the omnipattern. In addition, if the front-to-back ratio of a directional antenna is
found to be 20 dB in free space, it will be only 10 dB at the cell site.
Switching Equipment:
The capacity of switching equipment in cellular systems is not based on the number of switch ports but on
the capacity of the processor associated with the switches. In a big cellular system, this processor should
be large. Also, because cellular systems are unlike other systems, it is important to consider when the
switching equipment would reach the maximum capacity. The service life of the switching equipment is
not determined by the life cycle of the equipment but by how long it takes to reach its full capacity. If the
switching equipment is designed in modules, or as distributed switches, more modules can be added to
increase the capacity of the equipment. For decentralized systems, digital switches may be more suitable.
The future trend seems to be the utilization of system handoff.
Data Links:
The data links are shown in Fig 1. Although they are not directly affected by the cellular system, they are
important in the system. Each data link can carry multiple channel data (10 kbps data transmitted per
channel) from the cell site to the MTSO. This fast-speed data transmission cannot be passed through a
regular telephone line. Therefore, data bank devices are needed. They can be multiplexed, many-data
channels passing through a wideband T-carrier wire line or going through a microwave radio link where
the frequency is much higher than 850MHz.
Explain the direct wave path, line of sight path, out of sight path, and obstructive path?
A direct wave path is a path clear from the terrain contour. The line-of-sight path is a path clear from
buildings. In the mobile radio environment, we do not always have a line-of-sight condition. When a lineof-
sight condition occurs, the average received signal at the mobile unit at a 1-mi intercept is higher,
although the 40 dB/dec path-loss slope remains the same. In this case the short-term fading is observed to
be a rician fading. It results from a strong line-of-sight path and a ground-reflected wave combined, plus
many weak building-reflected waves.
[attachment=27444]
Antenna:
Antenna pattern, antenna gain, antenna tilting, and antenna height 6 all affect the cellular system design.
The antenna pattern can be omnidirectional, directional, or any shape in both the vertical and the horizon
planes. Antenna gain compensates for the transmitted power. Different antenna patterns and antenna gains
at the cell site and at the mobile units would affect the system performance and so must be considered in
the system design. The antenna patterns seen in cellular systems are different from the patterns seen in
free space. If a mobile unit travels around a cell site in areas with many buildings, the omnidirectional
antenna will not duplicate the omnipattern. In addition, if the front-to-back ratio of a directional antenna is
found to be 20 dB in free space, it will be only 10 dB at the cell site.
Switching Equipment:
The capacity of switching equipment in cellular systems is not based on the number of switch ports but on
the capacity of the processor associated with the switches. In a big cellular system, this processor should
be large. Also, because cellular systems are unlike other systems, it is important to consider when the
switching equipment would reach the maximum capacity. The service life of the switching equipment is
not determined by the life cycle of the equipment but by how long it takes to reach its full capacity. If the
switching equipment is designed in modules, or as distributed switches, more modules can be added to
increase the capacity of the equipment. For decentralized systems, digital switches may be more suitable.
The future trend seems to be the utilization of system handoff.
Data Links:
The data links are shown in Fig 1. Although they are not directly affected by the cellular system, they are
important in the system. Each data link can carry multiple channel data (10 kbps data transmitted per
channel) from the cell site to the MTSO. This fast-speed data transmission cannot be passed through a
regular telephone line. Therefore, data bank devices are needed. They can be multiplexed, many-data
channels passing through a wideband T-carrier wire line or going through a microwave radio link where
the frequency is much higher than 850MHz.
Explain the direct wave path, line of sight path, out of sight path, and obstructive path?
A direct wave path is a path clear from the terrain contour. The line-of-sight path is a path clear from
buildings. In the mobile radio environment, we do not always have a line-of-sight condition. When a lineof-
sight condition occurs, the average received signal at the mobile unit at a 1-mi intercept is higher,
although the 40 dB/dec path-loss slope remains the same. In this case the short-term fading is observed to
be a rician fading. It results from a strong line-of-sight path and a ground-reflected wave combined, plus
many weak building-reflected waves.