10-05-2014, 12:20 PM
DESIGN PARAMETRES AT BASE STATION
DESIGN PARAMETRES.pptx (Size: 389.62 KB / Downloads: 11)
BASE STATION
It is a structure which connect mobile phones within its range to the regular landline phone system.
A cellular base station acts as low power, multi-channel two-way radio
Base stations consist of two main portions
Antenna
the tower or mast which raises the antenna above the ground
The use and construction of a cellular base station is regulated by FCC
The antennas must be kept inaccessible to the public and at a safe range.
DESIGN PARAMETERS OF ANTENNA
Broadside array delivers the maximum possible directivity if all its elements are excited with equal co-phased currents
Beam shaping require non uniform element currents for side lobe suppression and null fill
Power
Base station power depend on type of antenna, the number of analog and digital channels that operate at a given time and at their maximum strength, and antenna gain
Power received by an antenna is :
Beamwidth
Azimuthal Beamwidth
Depend on vertical radiating element and reflecting surface behind it
It is a function of frequency
Typically 65° ±3° or 90° ±5° over the whole band
Base stations support three cells spaced 120° apart in azimuth
Elevation Beamwidth
Elevation beamwidth of a BS array is a function of its electrical length in the vertical plane
Smaller the elevation beamwidth larger the physical dimension of antenna
Control of elevation beamwidth improves C/I ratio in neighboring cells as well as increase field strength of user in intended cell
Passive Intermodulation Product
When multiple-frequency transmissions occur, if any conductor or joint has a nonlinear voltage/current relationship passive intermodulation(PIM) products will be generated
PIM are spurious signals with frequencies related to those that give rise to them.