04-02-2012, 04:59 PM
smart antenna
[attachment=17162]
INTRODUCTION
Antennas Radio antennas couple electromagnetic energy from one medium (space) to another (e.g., wire, coaxial cable, or waveguide). Physical designs can vary greatly.
Omnidirectional Antennas Since the early days of wireless communications, there has been the simple dipole antenna, which radiates and receives equally well in all directions. To find its users, this single-element design broadcasts omnidirectionally in a pattern resembling ripples radiating outward in a pool of water. While adequate for simple RF environments where no specific knowledge of the users' whereabouts is available, this unfocused approach scatters signals, reaching desired users with only a small percentage of the overall energy sent out into the environment.
Diversity Systems
In the next step toward smart antennas, the diversity system incorporates two antenna elements at the base station, the slight physical separation (space diversity) of which has been used historically to improve reception by counteracting the negative effects of multipath .
Diversity offers an improvement in the effective strength of the received signal by using one of the following two methods:
• switched diversity—Assuming that at least one antenna will be in a favorable location at a given moment, this system continually switches between antennas (connects each of the receiving channels to the best serving antenna) so as always to use the element with the largest output. While reducing the negative effects of signal fading, they do not increase gain since only one antenna is used at a time.
• Diversity combining—This approach corrects the phase error in two multipath signals and effectively combines the power of both signals to produce gain. Other diversity systems, such as maximal ratio combining systems, combine the outputs of all the antennas to maximize the ratio of combined received signal energy to noise.
Switched Beam Systems
Switched beam antenna systems 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. Instead of shaping the directional antenna pattern with the metallic properties and physical design of a single element (like a sectorized antenna), switched beam systems combine the outputs of multiple antennas in such a way as to form finely sectorized (directional) beams with more spatial selectivity than can be achieved with conventional, single-element approaches.
ADVANTAGES OF SMART ANTENNA SYSTEMS
1. The effect of multiple path fading in wireless communications environments can be significantly reduced.
2. Hand sets of a smart antenna systems have longer battery life because the power required to transmit to the base station is lower than that of conventional systems.
3. Smart antenna system can significantly improve signal-to-interference ratio of a wireless communications systems, and thus significantly increase the capacity of the system.
DISADVANTAGES
1. smart antenna systems are increased base station complexity, increased need for computational power.
2. cost is high.
APPLICATIONS
1. smart antenna systems are used in MIMO systems due to there tremendous spectral efficiency
3. smart antenna systems are used in CDMA techniques
CONCLUSION
This paper gives the brief idea about the smart antenna systems and their types which we are using to avoid the multipath and co-channel interference.These antennas having advance features like higher efficiency, higher reliability than the normal antennas.By using these antennas there is a reduction in the equipment size so these are expected to use in the future wireless systems.
[attachment=17162]
INTRODUCTION
Antennas Radio antennas couple electromagnetic energy from one medium (space) to another (e.g., wire, coaxial cable, or waveguide). Physical designs can vary greatly.
Omnidirectional Antennas Since the early days of wireless communications, there has been the simple dipole antenna, which radiates and receives equally well in all directions. To find its users, this single-element design broadcasts omnidirectionally in a pattern resembling ripples radiating outward in a pool of water. While adequate for simple RF environments where no specific knowledge of the users' whereabouts is available, this unfocused approach scatters signals, reaching desired users with only a small percentage of the overall energy sent out into the environment.
Diversity Systems
In the next step toward smart antennas, the diversity system incorporates two antenna elements at the base station, the slight physical separation (space diversity) of which has been used historically to improve reception by counteracting the negative effects of multipath .
Diversity offers an improvement in the effective strength of the received signal by using one of the following two methods:
• switched diversity—Assuming that at least one antenna will be in a favorable location at a given moment, this system continually switches between antennas (connects each of the receiving channels to the best serving antenna) so as always to use the element with the largest output. While reducing the negative effects of signal fading, they do not increase gain since only one antenna is used at a time.
• Diversity combining—This approach corrects the phase error in two multipath signals and effectively combines the power of both signals to produce gain. Other diversity systems, such as maximal ratio combining systems, combine the outputs of all the antennas to maximize the ratio of combined received signal energy to noise.
Switched Beam Systems
Switched beam antenna systems 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. Instead of shaping the directional antenna pattern with the metallic properties and physical design of a single element (like a sectorized antenna), switched beam systems combine the outputs of multiple antennas in such a way as to form finely sectorized (directional) beams with more spatial selectivity than can be achieved with conventional, single-element approaches.
ADVANTAGES OF SMART ANTENNA SYSTEMS
1. The effect of multiple path fading in wireless communications environments can be significantly reduced.
2. Hand sets of a smart antenna systems have longer battery life because the power required to transmit to the base station is lower than that of conventional systems.
3. Smart antenna system can significantly improve signal-to-interference ratio of a wireless communications systems, and thus significantly increase the capacity of the system.
DISADVANTAGES
1. smart antenna systems are increased base station complexity, increased need for computational power.
2. cost is high.
APPLICATIONS
1. smart antenna systems are used in MIMO systems due to there tremendous spectral efficiency
3. smart antenna systems are used in CDMA techniques
CONCLUSION
This paper gives the brief idea about the smart antenna systems and their types which we are using to avoid the multipath and co-channel interference.These antennas having advance features like higher efficiency, higher reliability than the normal antennas.By using these antennas there is a reduction in the equipment size so these are expected to use in the future wireless systems.
