For 3-G Systems Tara Larzelere EE 497A Semester Project

WHAT IS A SMART ANTENNA?  An array of antenna elements connected to a digital signal processor  Enhances the capacity of a wireless link through a combination of diversity gain, array gain, and interference suppression.  Therefore more users can be accommodated in a single cell with a higher data rate per user.  Two Main ways to form antenna arrays 1.diversity gain 2.beamforming

Smart Antenna Analogy  Ears represent beamforming antennas  Many “ears” collect signals and add them to magnify sound producing a clear signal then together to create a magnified signal.  Brain represents signal processor  Tunes out other conversations so that your brain can only hear the me the speaker

Why do we need smart antennas? 1) Multi-path Fading -unpredictable set of reflections of a signal which are out of phase with each other 2) Delay spread- result of multi-path fading, difference in propagation among received paths causing inter-symbol interference 3) Co-channel interference – a result of frequency reuse. The desired signal contain not only the desired forward channel from the current cell, but also signals originating in more distant cells

Beamforming vs diversity  For diversity, we rely essentially on the statistical independence of the signals at the different antenna elements.  Implemented in cases where fading is common  Beamforming the antenna elements are close together presenting coherence between the antenna signals  The closeness of the antenna elements allows us to form an antenna pattern with a single main beam that enhances the desired signal and suppresses the interference.  Mathematically speaking, the difference between diversity and beamforming is not dramatic

Three Basic Ways to Provide diversity gain 1.Spatial 2.Polarization 3.Angle Diversity  In radio communications, the ratio of the signal field strength obtained by two or more different elements combining to the signal strength obtained by a single signal path radiocommunicationssignalfield strengthradiocommunicationssignalfield strength  For Diversity gain with M antenna elements an antenna gain of M times can be achieved.

SPACIAL DIVERSITY ARRAY  equally separated antennas for low fading correlation  Simplest implementation: switches to whichever antenna is currently receiving the strongest signal.  More complex systems: signal combining based on weighting according to the signal-to-noise ratio of each of the received signals or according to equal weighting where signals are co-phased and summed.  Not as commonly used because a single antenna requires space and cable runs, and increases installation and maintenance costs significantly.

Polarization Diversity  For polarization diversity horizontal and vertical polarization is used  Can only double diversity gain  Polarization diversity is known to be effective in urban areas.

Angle Diversity  which implements different beam patterns on the different antennas  This combination results in a higher overall gain pattern  Allows the same 120 sectored base station support more users by changing the degree of separation

Beamforming Networks  Most conventional smart antenna systems use a concept known as beamforming, where the signal energy is focused in a particular direction toward the receiver increasing SNR  First, we estimate the directions of arrival of all multi-path components.  Then determine whether the signal from a certain direction comes from a desired user or from an interferer (with the help of user ID)  Algorithms compute the weights for SNR optimization and use this pattern for reception of the data.  The associated antenna pattern can be used to exhibiting nulls toward interfering signals  If chosen only one of the desired multi-path components used  A main lobe towards individual users and attempts to treject interference or noise from outised the main lobe.

Switched beam systems  A fixed beamforming network is implemented  A switch is used to select the best beam to receive a particular signal  Simple to implement, offering many of the advantages of more elaborate smart antenna systems at the fraction of the cost and complexity  An RF switch and control logic is used to select a particular beam with the greatest strength

Adaptive Array  greater performance improvement is possible than are attainable using switched beam systems.  Complex array signal processing is implemented which is the brain of the system utilizing an adaptive array algorithm  Feedback through the system is used to input an adaptive algorithm that adjusts or adapts a weight vector to maximize the quality of the signal received,

Adaptive vs Switched Beam Switched Beam Technology Adaptive Antenna Arrays Give high gain, narrower bandwidthThe antenna array can also combine multi-path signals using space diversity techniques Is a relatively low technology approach so has lesser cost and complexity Antenna beams adaptively track signal direction; a null can be placed in the direction of an interferer Requires only moderate interaction with the base station receiver May have greater capacity increase when compared to switched beams Is unable to take advantage of path diversity by combining coherent multi-paths More intensive signal processing needed via DSPs Intra-cell hand-offs between beams have to be handled Is more expensive to install than a switched beam antenna

Using CDMA with Smart Antenna Technology  In CDMA systems all cells use the same carrier frequency. Users are distinguished by their different codes.  The number of users within one cell is limited mainly by the interference that each user generates for all other users.  By pointing the main beam of the adaptive antenna pattern to the desired user, smart antennas improve the SNIR for one user without increasing interference for the other users.  Note that even an increase of the capacity by only a factor 2 is highly desirable, since it means that twice as many customers can access the network

Notable Capacity Increase when using adaptive array technology

QUESTIONS???? These systems of antennas include a LARGE NUMBER of techniques that attempt to enhance the received signal, increase range coverage, suppress all interference, and increase capacity. These systems of antennas include a LARGE NUMBER of techniques that attempt to enhance the received signal, increase range coverage, suppress all interference, and increase capacity.