10-06-2017, 07:09 AM
SMART ANTENNA FOR MOBILE COMMUNICATION
[attachment=173]
Definition:
A smart antenna consists of several antenna elements, whose signal are processed adaptively in order to exploit the spatial domain of the mobile radio channel . Usually the signals received at the different antenna elements are multiplied with complex weights W and then summed up the weights are chosen adaptively not the antenna itself, but the whole antenna system including the signal processing is called adaptive .
Types of Smart Antenna Systems:
Terms commonly heard today that embrace various aspects of a smart antenna system technology include intelligent antennas, phased array, SDMA, spatial processing, digital beam
forming, adaptive antenna systems, and others. Smart antenna systems
Adaptive Antennas:
Adaptive antenna technology represents the most advanced smart antenna approach to date. Using a variety of new signal-processing algorithms, the adaptive system takes advantage of its ability to effectively locate and track various types of signals to dynamically minimize interference and maximize intended signal reception. Both systems attempt to increase gain according to the location of the user.
What Makes Them So Smart:
A simple antenna works for a simple RF environment. Their smarts reside in their digital signal-processing facilities. In adaptive antenna systems, this fundamental signal-processing capability is augmented by advanced techniques that are applied to control operation in the presence of complicated combinations of operating conditions.
Features and Benefits:
Signal gain: Inputs from multiple antennas are combined to optimize available power required establish given level of coverage
better range/ coverage: Focusing the energy sent out into the cell increases base station range and coverage lower power requirements also enable a greater battery life and smaller/lighter handset size.
Interference rejection: Antenna pattern can be generated toward co-channel interference sources improving the signal to interference ratio of the received signals.
Increased capacity: Precise control of signals quality and mitigation of interference combined to frequency re use reduce distance, improving capacity.
Spatial diversity: Composite information from the array is used to minimize fading, other undesirable effects of multi path propagation.
Multipath rejection: It can reduce the effective delay spread of the channel allowing higher bit rates to be supported without the use of an equalizer.
Power efficiency: It combines the input s to multiple elements to optimize available processing gain in the downlink(toward user).
Reduced expence : lower amplifier costs, power consumption, and higher reliability will resul.
Phase cancellation:
When waves of two multipath signals are rotated to exactly 1800 out of phses, the signals will cancel each other. While this sounds severe, it is rarely sustained on any given call (and most air interface standards are quite resilient to phase cacellation). In other words, a call can be maintained for a certain period of time while there is no signal, although with very poor quality. The effect is of more concern when the control channel signal is canceled out, resulting in a black hole, a service area in which call set-ups will occasionally fail.