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This is an introduction to smart RF [Radio Frequency] antennas or smart antennas. Many of the antenna design parameters for pico, micro, and macrocell smart antenna system are affected by channel parameters such as Doppler, Delay, and Angular Spread. According to the leading sources such as the IEEE and others, the choice of algorithm, the signal processing power required and the physical design array geometry are influenced by channel parameters. That is, it is unlikely there will be a single antenna solution that is applicable to all types of cell environment which mean in practical terms environmentally-designed solutions will dominate the landscape.

Doppler RF spread describes the RF dispersion spread of the channel as determined by the velocity of the mobile device. Sometimes referred to as Correlation Time, it explains how fast the RF signal decorrelates (dissipates or is reduced) with time (correlation describes the relationship between two different variables).

Delay RF spread describes the time dispersion of the channel and explains how fast the channel decorrelates with frequency (correlation bandwidth). That is, the higher the frequency the greater dispersion/absorption. Angular RF spread explains the angular dispersion of the RF signal channel and its speed the channel decorrelates with distance.

Gain can be spherical in all directions or directional in some directions or unidirectional in one direction. In TDMA [Time Division Multiple Access] systems, SDMA [Spatial Division Multiple Access] uses adaptive nulling (RF signal suppression) to allow two or more wireless devices in the same cell to share the same frequency and time slot. One beam is formed for each mobile with nulls in the direction of the other mobiles. SDMA can be implemented in isolation in single cells (e.g. traffic hot spots). SDMA may not be appropriate in CDMA [Code Division Multiple Access] systems because it suggests reuse of spreading codes. SFIR [Spatial Filtering for Interference Reduction] is a method or scheme where nulls (no RF) are formed in the direction of interference sources in transmission uplink and reception downlink. This improves the CI [Carrier to Interference] ratio and allows the frequency reuse pattern to be narrowed resulting in increased capacity. Beamsteering and SFIR can both be used in TDMA and CDMA.

Smart antenna systems communicate directionally by forming specific antenna beam patterns. However, AAA [Adaptive Antenna Array] Systems or antenna arrays use DSP [Digital Signal Processing] algorithms (programmed rules ) to continuously monitor signals, multipath, and interfering signals as well as calculate their directions of arrival. That is, use of the same frequency simultaneously is a practical advantage. AAA uses a mix of spatial, time and RF processing to provide a higher level of measurement and analysis of the scattering aspects of the RF environment. With microsecond adjustments and adjusting to an RF environment (including weather) or the spatial origin of signals), AAA technology can dynamically alter the signal patterns to almost infinitely to optimize performance.

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