By HUSSEIN TUAMA HAZIM

(525018)ME.CN

Smart Antenna

Generally, an antenna is a device which is used for radiating electromagnetic energy into space or for collecting electromagnetic energy from space.

Isotropic: Hypothetic omnidirectional antenna, a point in space, radiates power in all directions equally.

Half wave-dipole: A commonly used omnidirectional antenna, which radiates and receives signals almost equally in all directions.

Antenna

Traditional directional antennas:◦ Such as Helix, Yagi-Uda, Aperture horn and reflector

Electronically steerable or smart antenna system◦ A smart antenna is an antenna array consists of

a set of antenna elements

directional antennas

Reflector Grid

In communication environments serious problems such as a multi-path fading caused by a reflection by any physical structures Fig(a)

When passing through multi-path, the signals are delayed and out of phase from the signals through direct-path, as in Fig(b) that causes the signal strength to be weakened at a receiver and hence receiving quality is also reduced.

Its “Raleigh Fading”. Its important to configure receiver and transmitter flexibly in response to the signal environment.

Several techniques: Phased array antenna and Diversity antenna using active array configurations can adapt the antenna pattern according to the change of mobile communication environment.

Adaptive/Smart Antenna:

A system capable of automatically changing the directionality of its radiation patterns (beams) in response to its signal environment. Increases capacity and quality of a wireless system. An “Adaptive/Smart Antenna” system uses spatially separated antennas called array antenna and processes received signals with a digital signal processor after analog to digital conversion The name is derived from an “Adaptive Filter” or “Adaptive Filter Signal Processing”.

Antenna that is combined with a digital signal processor is also called by the name of “Smart Antenna” or “Software Antenna” or “Digital Beamforming Antenna (DBF Antenna)” that all mean an intelligent antenna different from a conventional omni-directional antenna  

Smart Antenna Radio Interface

◦ Smart Antenna allows signals to be directed to a device Increase the quality of the signals Only installed at the Base Station, not the handset Increase the usage of the BS

Increased frequency reuse

Omni Directional

Directed(Smart Antenna)

Smart Antenna Frequency reuse

◦ It is possible to make each user in a particular direction the only user as far as the device is concerned Directing communications to the device Currently though replies will be omni-directional

Directed(Smart Antenna)

Smart Antenna Types

Switched BeamAdaptive Array Antenna

• Smart Antenna two main types– Switched Beam– Adaptive Array Antenna

Smart Antenna

Radio Interface ◦ Adaptive Array Antennas

These devices track a communicating device The power can be adjusted to exactly what is required for

successful communications They can minimise interference by controlling the power in

a particular direction The transmission of the signal can be directed to the user and

follow them. This removes any interference from other users Reduces the effect of signal propagation As the signal is directed

Smart Antenna Advantages

◦ Integration Switched beam can be added to current infrastructure Adaptive antenna, require consideration to the network and there use

◦ Range Switched beam can increase range between 20 – 200% over a normal cell

Depending on local conditions Switched beam power can not be adapted as the user moves, as the power and

shape are pre-defined Adaptive Array can cover larger area due to the directing of the signals to a

device◦ Interference Suppression

Switched beam Interference from beams which are away from where they are expected are ignored As the beams are pre-determined at the development stage, interference is still possible

Switched Beam has problems with interference from device which are close to the BS

Adaptive array is more resistant to interference as the signal is narrowed towards the actual device

◦ Capacity Increased with SDMA

Smart Antenna

Smart Antenna Capacity◦ Spatial Division Multiple Access (SDMA)

More efficient use of the allocated frequency By controlling

Amount of interference Multi-path Propagation Multi-path interference

Allowing 2 users in the same cell to use the same transmission slot

Potentially having a single user per allocation slot This is more of a consideration with WCDMA rather than GSM tech It has been defined as a essential development for the use of 4G

communications