A smart antenna system combines multiple antenna elements with a signal-processing capability to optimize its radiation and/or reception pattern automatically in response to the signal environment.In truth, antennas are not smart—antenna systems are smart. Generally co-located with a base station, a smart antenna system combines an antenna array with a digital signal-processing capability to transmit and receive in an adaptive, spatially sensitive manner. Switched beam and adaptive array systems enable a base station to customize the beams they generate for each remote user effectively by means of internal feedback control. Listening to the cell.(uplink processing).Speaking to the users(downlink processing
Smart antenna systems are customarily categorized, as either switched beam or adaptive array systems. · Switched beam—a finite number of fixed, predefined patterns or combining strategies (sectors) Adaptive array—an infinite number of patterns (scenario-based) that are adjusted in real time There are basically two types of smart antennas: Switched beam systems and adaptive array systems.
It form multiple fixed beams with heightened sensitivity in particular directions. These antenna systems detect signal strength, choose from one of several predetermined, fixed beams, and switch from one beam to another as the mobile moves throughout the sector. switched beam systems combine the outputs of multiple antennas in such a way as to form finely sectorized (directional) beams with more selectivity .The switched beam system comprises only basic switching between separate directional antennas or predefined beams of an array while enabling high directivity and gain In this approach, an antenna arraygenerates overlapping beams that cover the surrounding areaThese antenna systems detect signal strength, choose from one of several predetermined, fixed beams, and switch from one beam to another as the mobile moves throughout the sector.
Switched beam systems can be further divided into two groups: single beam and multi beam directional antennas. In single beam directional antenna systems, only one beam is active at a given time. No simultaneous transmissions are allowed, because in this system there is only one transceiver as shown in Fig.2 (a). On the other hand, multiple beam directional antenna system is an example of Spatial Division Multiple Access (SDMA) system. Here, each directional antenna can be used and transmissions are allowed at the same time and frequency. The number of beams is equal to the number of transceivers as shown in Fig.2 (b).
Adaptive antenna technology represents the most advanced smart antenna approach by using a variety of new signal-processing algorithms. It provides optimal gain while simultaneously identifying, tracking, and minimizing interfering signals. The second technique is adaptive beam forming where a Direction of Arrival (DoA) algorithm is used to determine the direction of the signal received from the user. By this way continuous tracking of users can be achieved. Also, the detection of the interferers can be added to these systems, so that interference is cancelled by adjusting the radiation pattern nulls to increase the Signal to Interference Ratio (SIR). Clearly, adaptive beam forming is more complex than switched beam systems
Block diagram of adaptive array system
There are two kinds of adaptive beam forming: In single user beam forming, the antenna beam is adjusted to track a user and cancel interferers. In this case, a single transceiver is sufficient where only one user is active at a given time as shown in Fig.3 (a). In multi user beam forming, there are different beam patterns, and each beam tracks one user. Therefore, simultaneous transmissions are allowed and SDMA is achieved. As shown in Fig.3 (b), there is more than one transceiver-beam pair in multi user beam forming.
Space division multiple accessMore than one user can be allocated to the same physical communications channel simultaneously in the same cell separated by angle only.This is the next step in an evolutionary path toward increasing the capacity of cellular systems.
The purpose of a smart antenna system is to augment the signal quality of the radio-based system through more focused transmission of radio signals while enhancing capacity through increased frequency reuse
Smart antenna technology can significantly improve wireless system performance and economics for a range of potential users. It enables operators of PCS, cellular, and wireless local loop (WLL) networks to realize significant increases in signal quality, capacity, and coverage
Smart antennas can help systems meet these requirements in the following manner:First, both phased and adaptive arrays provide increased power by providing higher gain for the desired signal. In terms of interference suppression, phased arrays reduce the probability of interference with the narrower beam, and adaptive arrays adjust the beam pattern to suppress interferenceEnhance coverage through Range extensionImprove building penetration and Hole fillingReduce delay spread (time dispersion) because fewer scatters are illuminatedReduce co-channel interference (CCI) and multiple access interference (MAI)Link quality can be improved through multipath managementImprove system capacityHelps to isolate the uplink signals from different users, reduce the power control burden
What is Smart Antenna?
A smart antenna consists of an antenna array, that
changes the array pattern in response to Signal
environment to improve the performance of a
Switched Beam Antennas
Single beam directional antenna
Only one beam is active
Only transceiver exists
Multiple beam directional antenna:
Example of SDMA system
Many directional antennas are used
No. of beams = No. of transceivers
Adaptive Array Antennas
Direction of algorithm(DOA)
Minimizing interfering signals
Adaptive Array Coverage
Adaptive Array Antennas
Single user tracking:
•Beam is adjusted to track a user
•Single transceiver is enough since one user is active
Multi user tracking:
Different beam patterns
Multi transceiver beam pair
The goals of a smart antenna system
The features of a smart antenna system are
- signal gain.
- inference rejection.
SMART ANTENNA VS OTHER ANTENNAS
They can null out interference from other nodes.
Contains an array of antennas elements and decide
on which elements to receive signals (or transmit on)
from and how much power to use on each element.
Advantages of smart antenna
Building penetration and Hole filling
Multiple access interference
cellular and wireless networks
electronic warfare (EWF) as a
counter measure to electronic