HOW SMART ANTENNAS EVOLVED? In the first cellular radio systems deployed, each base station was equipped with an omnidirectional antenna with a typical amplitude pattern. Because only a small percentage of the total energy reached the desired user, the remaining energy was radiated in undesired directions.
As the number of users increased, also interference increases, thereby reducing capacity. An immediate solution to this problem was to subdivide a cell into smaller cells, this technique is referred to as cell splitting
CELL SPLITTING It subdivides a congested cell into smaller cells called microcells, each with its own base station. The disadvantages of cell splitting are costs incurred from the installation of new base stations. The increase in the number of handoffs
SECTORIZED SYSTEMS The number of frequencies assigned to a cell eventually became insufficient. A cellular design technique that provide more frequencies per coverage area is knawn as Cell Sectoring. In this technique single omnidirectional antenna is replaced at the base station with several directional antennas. Typically, a cell is sectorized into thre sectors of 120◦ each.
SECTORIZED ANTENNAS Cell sectoring did not provide the adequate solution needed for the capacity problem. Therefore, a system required that could dynamically sectorize a cell.
SMART ANTENNAS“Smart Antennas are arrays of antenna elements that change their antenna pattern dynamically to adjust to the noise, interference in the channel that effects on the signal of interest.” Smart antennas are not smart, it is the digital signal processing, along with the antennas, which makes the system smart. Smart-antenna systems are basically an extension of cell sectoring in which the sector coverage is composed of multiple beams.
SMART ANTENNAS ANALOGY WITH HUMAN The functionality of many engineering systems is readily understood when it is related to our human body system.
TYPES OF SMART ANTENNASSmart Antenna systems are of two types: Switched Beam Antenna System Adaptive Array Antenna System
SWITCHED BEAM ANTENNA SYSTEMS It is an extension of cell sectoring as each sector is subdivided into smaller sectors. As the mobile unit moves throughout the cell, the switched- beam system detects the signal strength and continually switches the beams as necessary. The overall goal of the switched-beam system is to increase the gain according to the location of the user.
If there is an interferer near the center of the active beam, it may be enhanced more than the desired user.
ADAPTIVE ARRAY ANTENNA SYSTEMS They can direct the main beam toward the SOI(Signal Of Interest) while suppressing the antenna pattern in the direction of the interferers or SNOIs. Adaptive array systems can customize an appropriate radiation pattern for each individual user. Adaptive array systems can locate and track signals (users and interferers) Dynamically adjust the antenna pattern to enhance reception while minimizing or fully rejecting interference using signal- processing algorithms.
Comparison of Switched Beam Antenna & Adaptive ArraysCRITERIA SWITCHED BEAM ADAPTIVE ARRAYSINTEGERATION • Easy to implement • Transceiver complexity • Low cost • High costRANGE/COVERAGE • More coverage •More coverage compared compared to to switched beam system conventional systems • Less coverage compared to adaptive arrayINTERFERENCE •Difficulty in • Focusing is narrower.REJECTION distinguishing between desired signal and • Capable of nulling interferer . interfering signals • Does not react to the movement of nterferers.
SDMA SDMA (Space Division Multiple Access) is the most- sophisticated utilization of smart-antenna technology. This means that more than one user can be allocated to the same physicalcommunication channel in the same cell simultaneously, with only an angle separation.
Smart Antenna’s Benefits The primary reason for the growing interest in smart- antenna systems is the capacity increase. Smart-antenna systems provides increase of range. because smart antennas are more directional than omnidirectional and sectorized antennas. Another added advantage of smart-antenna systems is security.
Smart antennas make it more difficult to tap a connection because the intruder must be positioned in the same direction as the user. They can be used to locate humans in emergencies.
Smart Antenna’s Drawbacks Their transceivers are much more complex than traditional base station transceivers. To have pattern-adaptive capabilities and reasonable gain, an array of antenna elements is necessary. Smart-antenna base stations must be equipped with very powerful digital signal processors. This tends to increase the system costs in the short term.
Smart Antennas on Mobile Handsets RESEARCH A single base station often serves hundreds to thousands of mobile stations. It is more economical to add equipment to BTS rather than at each MS. Adaptive beamforming is a practical and effective technique for reducing the effect of multipath fading, it is rarely used at a MS due to cost, size and available power of the MS. With 3G systems increasing growth of mobile phone users has created a need for even higher capacity in cellular network .
Two Types OF Mobile Handset Adaptive Antennas The Intelligent Quadrifilar Helix Antenna was invented in the University of Surrey by A. A. Agius, S. M. Leach, P. Suvannapattana and S. R. Saunders.Specifications of the antenna are listed in the following : The QHA consists of four twisted wires in a form of a helix It permits reception inside the buildings where signals are too weak to be picked up by standard antennas Designed to improve performance and minimize radiation into the human head.
The signal is produced through use of a torch beam which means that instead of radiation going in all directions, it will use a narrow beam traveling towards the nearest base station. It makes batteries last longer
The solid state antennaSpecifications of the antenna are listed in the following: Surface mounted to motherboard Approximately one tenth size of conventional copper antenna The antenna is steerable Life of the battery is increased as the handset only points in the direction of the base station so more efficient transmission is achieved
Minimizes RF health issue by directing the RF emissions away from the head or body.