ABSTRACT

One of the most rapidly developing areas of communications is Smart Antenna systems. This paper deals with the principle and working of smart antennas and the elegance of their applications in various fields such a 4G telephony system, best suitability of multi carrier modulations such as OFDMA etc..,This paper mainly concentrates on use of smart antennas in mobile communications that enhances the capabilities of the mobile and cellular system such a faster bit rate, multi use interference, space division multiplexing (SDMA),increase in range, Multi path Mitigation, reduction of errors due to multi path fading and with one great advantage that is a very high security. The signal that is been transmitted by a smart antenna cannot tracked or received any other antenna thus ensuring a very high security of the data transmitted. This paper also deals the required algorithms that are need for the beam forming in the antenna patters.The applications of smart antennas such as in WI-FI transmitter, Discrete Multi Tone modulation (DMT), OFDMA and TD-SCDMA is already in real world use is also incorporatd.

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Table of Content

Chapter 1:- Introduction

Chapter 2:- Antenna and Antenna Systems

2.1:-Antenna

2.1.1:- Omnidirectional Antenna

2.1.2:- Directional Antenna

2.2:- Antenna System

2.2.1:-Sectorised System

2.2.2:-Diversity System

2.2.2.1:- Switched Divesity

2.2.2.2:- Diversity Combining

Chapter 3:-Smart Antenna.

3.1:- Introduction of Smart Antenna

3.2:- History of Smart Antenna

3.3:- Types of Smart Antenna

3.4:- Working of Smart Antenna

3.5:- Categories of Smart Antenna.

3.6- Function of Smart Antenna

3.6.1:- Beamforming

3.6.2:- Direction of Arrival(DOA)

3.7:- Parameters affecting Antenna performance2

3.8:- Applications of Smart Antenna.

3.9:- Advantages and Disadvantages of Smart Antenna.

3.10:- Features and Benefit of Smart Antenna

Chapter 4:- Summary

References

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Chapter 1

IntroductionWireless Communication is growing with a very rapid rate for several years. The progress in radio technology enables new and improved services. Current wireless services include transmission of voice, fax and low-speed data. More bandwidth consuming interactive multimedia services like video-on demand and internet access will be supported in the future.

Wireless systems that enable higher data rates and higher capacities are a pressing need. Wireless networks must provide these services in a wide range of environments, dense urban, suburban, and rural areas.Because the available broadcast spectrum is limited, attempts to increase traffic within a fixed bandwidth create more interference in the system and degrade the signal quality.

The solution to this problem is SMART ANTENNA. Today's modern wireless mobile communications depend on adaptive "smart" antennas to provide maximum range and clarity. With the recent explosive growth of wireless applications, smart antenna technology has achieved widespread commercial and military applications.

There is an ever-increasing demand on mobile wireless operators to provide voice and high-speed data services. At the same time, operators want to support more users per basestation in order to reduce overall network cost and make the services affordable to subscribers. As a result, wireless systems that enable higher data rates and higher capacities have become the need of the hour.

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Chapter 2

Antenna and Antenna System

2.1 – Antenna

An antenna (or aerial) is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, radar, and space exploration. Antennas are most commonly employed in air or outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances.

Physically, an antenna is simply an arrangement of one or more conductors, usually called elements in this context. . In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. In reception, the inverse occurs: an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna's terminals. Some receiving antennas (such as parabolic types) incorporate shaped reflective surfaces to collect EM waves from free space and direct or focus them onto the actual conductive elements.

There are two fundamental types of antenna directional patterns, which, with reference to a specific three dimensional (usually horizontal or vertical) plane are either:

1. Omni-directional (radiates equally in all directions), such as a vertical rod.

2. Directional (radiates more in one direction than in the other).

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2.1.1- Omnidirectional Antenna

Omni-directional usually refers to all horizontal directions with reception above and below the antenna being reduced in favor of better reception (and thus range) near the horizon .

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.

Figure 2.1:- Omnidirectional Antenna and Coverage Patterns

Given this limitation, omnidirectional strategies attempt to overcomeenvironmental challenges by simply boosting the power level of the signals broadcast. In a setting of numerous users (and interferers), this makes a bad situation worse in that the signals that miss the intended user become interference for those in the same or adjoining cells.In uplink applications (user to base station), omnidirectional antennas offer no preferential gain for the signals of served users. In other words,

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users have to shout over competing signal energy. Also, this single-element approach cannot selectively reject signals interfering with those of served users and has no spatial multipath mitigation or equalization capabilities.

2.1.2- Directional Antenna

A "directional" antenna usually refers to one focusing a narrow beam in a single specific direction. A single antenna can also be constructed to have certain fixed preferential transmission and reception directions. As an alternative to the brute force method of adding new transmitter sites, many conventional antenna towers today split, or sectorize cells. A 360° area is often split into three 120° subdivisions, each of which is covered by a slightly less broadcast method of transmission.

All else being equal, sector antennas provide increased gain over a restricted range of azimuths as compared to an omnidirectional antenna. This is commonly referred to as antenna element gain and should not be confused with the processing gains associated with smart antenna systems.

While sectorized antennas multiply the use of channels, they do not overcome the major disadvantages of standard omnidirectional antenna broadcast such as co-channel interference.

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Figure 2.2 -Directional Antenna and Coverage Pattern

Chapter 3

Smart Antenna

3.1- Introduction of Smart Antenna

Contrary to the name smart antennas consist of more than an antenna. “A Smart Antenna is an antenna system which dynamically reacts to its environment to provide better signals and frequency usage for wireless communications”. There are a variety of smart antennas which utilize different methods to provide improvements in various wireless applications. This report aims to explain the main types of smart antennas and there advantages and disadvantages.

The concept of using multiple antennas and innovative signal processing to serve cells more intelligently has existed for many years. In fact, varying degrees of relatively costly smart antenna systems have already been applied in defense systems. Until recent years, cost barriers have prevented their use in commercial systems. The advent of powerful low-cost digital signal processors (DSPs), general-purpose processors (and ASICs), as well as innovative software-based signal-processing techniques (algorithms) have made intelligent antennas practical for cellular communications systems.

Today, when spectrally efficient solutions are increasingly a business imperative, these systems are providing greater coverage area for each cell site, higher rejection of interference, and substantial capacity improvements.

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Fig 3.1:- Smart Antenna System 

Figure 3.2- Block Diagram of Smart Antenna

3.2- History of Smart Antenna

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Early smart antennas were designed for governmental use in military applications, which used directed beams to hide transmissions from an enemy. Implementation required very large antenna structures and time-intensive processing and calculation.

As personal wireless communications began to emerge, it was evident that interference in wireless networks was limiting the total number of simultaneous users the network could handle before unacceptable call quality and blocking occurred. Since the narrow beams of the early governmental smart antennas created less overall interference, researchers began to explore the possibility of extending the use of smart antennas to reduce overall network interference in commercial wireless networks, thus increasing the total number of users a wireless system could handle in a given block of spectrum. But the hardware and processing technologies required to perform the complex calculations in the very small spaces of time available in personal wireless communications would prove to be a hurdle that was extremely difficult to overcome. A few select companies have successfully developed and introduced smart antenna technologies into commercial wireless networks.

Antennas were used in 1888 by Heinrich Hertz (1857-1894) to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. Hertz placed the emitter dipole in the focal point of a parabolic reflector.

The origin of the word antenna relative to wireless apparatus is attributed to Guglielmo Marconi. In 1895, while testing early radio apparatus in the Swiss Alps ,Marconi experimented with early wireless equipment.

A 2.5 meter long pole, along which was carried a wire, was used as a radiating and receiving aerial element . Until then wireless radiating transmitting and receiving elements were known simply as aerials or

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terminals. Marconi's use of the word antenna (Italian for pole) would become a popular term for what today is uniformly known as the antenna.

Smart Antennas Today

Today, smart antennas have been widely deployed in many of the top wireless networks worldwide to address wireless network capacity and performance challenges.

Several different versions of smart antennas are either in development or available on the market today. Appliqué smart antenna systems can be added to existing cell sites, enabling software-controlled pattern changes or software-optimized antenna patterns that have produced capacity increases of up to 35-94% in some deployments. Appliqué smart antenna systems provide greater flexibility in controlling and customizing sector antenna pattern beamwidth and azimuthal orientation over that of standard sector antennas.

A second approach, embedded smart antennas, uses adaptive array processing within the channel elements of a base station. The smart antenna processing takes place in the base station signal path, using a custom, narrow beam to track each mobile in the network. Embedded smart antenna system trials have been proven to deliver 2.5-3 times the capacity of current 2-2.5G base stations.

3.3- Types of Smart Antenna

The following are distinctions between the two major categories of smart antennas regarding the choices in transmit strategy:

1).Adaptive array - an infinite number of patterns (scenario-based) that are adjusted in real time .

2).Switched beam - a finite number of fixed, predefined patterns or combining strategies (sectors).

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3.4-Working of Smart AntennaTraditional switched beam and adaptive array systems enable a base station to customize the beams they generate for each remote user effectively by means of internal feedback control. Generally speaking, each approach forms a main lobe toward individual users and attempts to reject interference or noise from outside of the main lobe.

Listening to the Cell (Uplink Processing)

It is assumed here that a smart antenna is only employed at the base station and not at the handset or subscriber unit. Such remote radio terminals transmit using omnidirectional antennas, leaving it to the base station to separate the desired signals from interference selectively.Typically, the received signal from the spatially distributed antenna elements is multiplied by a weight, a complex adjustment of an amplitude and a phase. These signals are combined to yield the array output. An adaptive algorithm controls the weights according to predefined objectives. For a switched beam system, this may be primarily maximum gain; for an adaptive array system, other factors may receive equal consideration. These dynamic calculations enable the system to change its radiation pattern for optimized signal reception.Speaking to the Users (Downlink Processing)

The task of transmitting in a spatially selective manner is the major basis for differentiating between switched beam and adaptive array systems. As described below, switched beam systems communicate with users by changing between preset directional patterns, largely on the basis of signal strength. In comparison, adaptive arrays attempt to understand the RF environment more comprehensively and transmit more selectively.The type of downlink processing used depends on whether the communication system uses time division duplex (TDD), which transmits and receives on the same frequency (e.g., PHS and DECT) or frequency division duplex (FDD), which uses separate frequencies for transmit and

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receiving (e.g., GSM). In most FDD systems, the uplink and downlink fading and other propagation characteristicsmay be considered independent, whereas in TDD systems the uplink and downlink channels can be considered reciprocal. Hence, in TDD systems uplink channel information may be used to achieve spatially selective transmission. In FDD systems, the uplink channel information cannot be used directly and other types of downlink processing must be considered.

3.5- Categories of Smart Antenna

A smart antenna is a digital wireless communications antenna system that takes advantage of diversity effect at the source (transmitter), the destination (receiver), or both. Diversity effect involves the transmission and/or reception of multiple radio frequency (RF) waves to increase data speed and reduce the error rate.

In conventional wireless communications, a single antenna is used at the source, and another single antenna is used at the destination. This is called SISO (single input, single output). Such systems are vulnerable to problems caused by multipath effects. When an electromagnetic field (EM field) is met with obstructions such as hills, canyons, buildings, and utility wires, the wavefronts are scattered, and thus they take many paths to reach the destination. The late arrival of scattered portions of the signal causes problems such as fading, cut-out (cliff effect), and intermittent reception (picket fencing). In a digital communications system like the Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of smart antennas can reduce or eliminate the trouble caused by multipath wave propagation.

Smart antennas fall into three major categories:--

1). SIMO (single input, multiple output)

2). MISO (multiple input, single output)

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3). MIMO (multiple input, multiple output).

SIMO

SIMO (single input, multiple output) is an antenna technology for wireless communications in which multiple antennas are used at the destination (receiver). The antennas are combined to minimize errors and optimize data speed. The source (transmitter) has only one antenna. SIMO is one of several forms of smart antenna technology, the others being MIMO (multiple input, multiple output) and MISO (multiple input, single output).

In digital communications systems such as wireless Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas at the destination can reduce the trouble caused by multipath wave propagation.

SIMO technology has widespread applications in digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications. An early form of SIMO, known as diversity reception, has been used by military, commercial, amateur, and shortwave radio operators at frequencies below 30 MHz since the First World War.

MISO

MISO (multiple input, single output) is an antenna technology for wireless communications in which multiple antennas are used at the source (transmitter). The antennas are combined to minimize errors and optimize data speed. The destination (receiver) has only one antenna. MISO is one of several forms of smart antenna technology, the others being MIMO (multiple input, multiple output) and SIMO (single input, multiple output).

In digital communications systems such as wireless Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas, along with the transmission of multiple

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signals (one for each antenna) at the source, can reduce the trouble caused by multipath wave propagation.

MISO technology has widespread applications in digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications.

MIMO

MIMO (multiple input, multiple output) is an antenna technology for wireless communications in which multiple antennas are used at both the source (transmitter) and the destination (receiver). The antennas at each end of the communications circuit are combined to minimize errors and optimize data speed. MIMO is one of several forms of smart antenna technology, the others being MISO (multiple input, single output) and SIMO (single input, multiple output).

In digital communications systems such as wireless Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas, along with the transmission of multiple signals (one for each antenna) at the source and the destination, eliminates the trouble caused by multipath wave propagation, and can even take advantage of this effect.

MIMO technology has aroused interest because of its possible applications in digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications.

3.6- Function of Smart Antenna

Smart antennas (also known as adaptive array antennas, multiple antennas and recently MIMO) are antenna arrays with smart signal processing algorithms used to identify spatial signal signature such as the direction of arrival (DOA) of the signal, and use it to calculate

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beamforming vectors, to track and locate the antenna beam on the mobile/target.

Smart antennas have two main functions: DOA estimation and Beamforming.

3.6.1- Beamforming

Beamforming is a signal processing technique used with arrays of transmitting or receiving transducers that control the directionality of, or sensitivity to, a radiation pattern. When receiving a signal, beamforming can increase the receiver sensitivity in the direction of wanted signals and decrease the sensitivity in the direction of interference and noise. When transmitting a signal, beamforming can increase the power in the direction the signal is to be sent. The change compared with an omnidirectional receiving pattern is known as the receive gain (or loss). The change compared with an omnidirectional transmission is known as the transmission gain. These changes are done by creating beams and nulls in the radiation pattern. In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system.

Beamforming can be done with either radio or sound waves, and can also be thought of as spatial filtering. As an everyday analogy, the human brain uses a form of signal processing on its two sound transducers (ears) and determines where the sound came from (sound localization). In the comparable beamforming analogy, digital computers use signal processing on an array of two (or generally more) electromagnetic sound transducers (microphones) to determine the direction of maximum signal strength, and thus the likely origin of the sound. A microphone with a cord A microphone, sometimes called a mic (pronounced mike), is a device that converts sound into an electrical signal. In telecommunications, and particularly in radio, signal strength is the measure of how strongly a transmitted signal is being received, measured, or predicted, at a

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reference point that is a significant distance from the transmitting antenna.

Beamforming takes advantage of interference to change the directionality of the array. When transmitting, a beamformer controls the phase and relative amplitude of the signal at each transmitter, in order to create a pattern of constructive and destructive interference in the wavefront. When receiving, information from different sensors is combined in such a way that the expected pattern of radiation is preferentially observed. Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right).

In the receive beamfomer the signal from each antenna may be amplified by a different "weight." Different weighting patterns (eg Dolph-Chebyshev) can be used to achieve the desired sensitivity patterns. . A main lobe is produced together with nulls and sidelobes. As well as controlling the main lobe width (the beam) and the sidelobe levels, the position of a null can be controlled. This is useful to ignore noise or jammers in one particular direction, while listening for events in other directions. A similar result can be obtained on transmission. Jammer can refer to: A device used in electronic warfare to inhibit or halt the transmission of signals.

Figure3.5:- BeamForming Lobe.

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Figure3.6:- Figure show pattern of Beamforming

Beamforming techniques can be broadly divided into two categories: A).Conventional (fixed) beamformers or switched beam smart

antennas. B).Adaptive beamformers or adaptive array smart antennas

Conventional beamformers use a fixed set of weightings and time-delays (or phasings) to combine the signals from the sensors in the array, primarily using only information about the location of the sensors in space and the wave directions of interest. In contrast, adaptive beamforming techniques, generally combine this information with properties of the signals actually received by the array, typically to improve rejection of unwanted signals from other directions. This process may be carried out in the time or frequency domains. Smart Antenna refers to a system of antenna arrays with smart signal processing algorithms that are used to identify the direction of arrival (DOA) of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on the mobile/target. ... Smart Antenna refers to a system of antenna arrays with smart signal processing algorithms that are used to identify the direction of arrival (DOA) of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on the mobile/target. ...

As the name indicates, an adaptive beamformer is able to adapt automatically its response to different situations. Some criterion has to be set up to allow the adaption to proceed such as minimising the total noise

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output. Because of the variation of noise with frequency, in wide band systems it may be desirable to carry out the process in the frequency domain. An adaptive beamformer is signal processing system often used with an array of radar antennae (or phased array) in order to transmit or receive signals in different directions without having to mechanically steer the array. ... Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency.

3.6.2- Direction of Arrival(DOA)

Direction of arrival(DOA) denotes the direction from which usually a propagating wave arrives at a point, where usually a set of sensors are located. This set of sensors forms what is called a sensor array. Often there is the associated technique of beamforming which is estimating the signal from a given direction. Various engineering problems addressed in the associated literature are as follows: A wave crashing against the shore A wave is a disturbance that propagates. Beamforming is the process of delaying the outputs of the sensors in an arrays aperture and adding these together, to reinforce the signal with respect to noise or waves propagating in different directions. Find the direction relative to the array where the underwater sound

source is located. Direction of different sound sources around you are also located by you

using a process similar to those used by the algorithms in the literature.

Radio telescopes use these techniques to look at a certain location in the sky.

Recently beamforming has also been used in RF applications such as wireless communication. Compared with the spatial diversity techniques, beamforming is preferred in terms of complexity. On the other hand beamforming in general has much lower data rates.In

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multiple access channel(CDMA,FDMA,TDMA) beamforming is necessary & sufficient.

The smart antenna system estimates the direction of arrival of the signal, using any of the techniques like MUSIC (Multiple Signal Classification) or ESPRIT (Estimation of Signal Parameters via Rotational Invariant Techniques) algorithms,Matrix Pencil method or their derivatives. They involve finding a spatial spectrum of the antenna/sensor array, and calculating the DOA from the peaks of this spectrum. MUSIC involves calculation of eigenvalues and eigenvectors of an autocorrelation matrix of the input vectors from the receiving antenna array. These calculations are computationally intensive. Matrix Pencil is very efficient in case of real time systems, and under the correlated sources. In mathematics, a number is called an eigenvalue of a matrix if there exists a nonzero vector such that the matrix times the vector is equal to the same vector multiplied by the eigenvalue.In linear algebra, the eigenvectors (from the German eigen meaning own) of a linear operator are non-zero vectors which, when operated on by the operator, result in a scalar multiple of themselves.

3.7- Parameters affecting Antenna performance

There are several critical parameters affecting an antenna's performance that can be adjusted during the design process. These are resonant frequency, impedance, gain, aperture or radiation pattern, polarization, efficiency and bandwidth. Transmit antennas may also have a maximum power rating, and receive antennas differ in their noise rejection properties. All of these parameters can be measured through various means.

3.7.1- Resonant frequency

The "resonant frequency" and "electrical resonance" is related to the electrical length of an antenna. The electrical length is usually the

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physical length of the wire divided by its velocity factor (the ratio of the speed of wave propagation in the wire to c0, the speed of light in a vacuum). Typically an antenna is tuned for a specific frequency, and is effective for a range of frequencies that are usually centered on that resonant frequency. However, other properties of an antenna change with frequency, in particular the radiation pattern and impedance, so the antenna's resonant frequency may merely be close to the center frequency of these other more important properties.

Antennas can be made resonant on harmonic frequencies with lengths that are fractions of the target wavelength. Some antenna designs have multiple resonant frequencies, and some are relatively effective over a very broad range of frequencies. The most commonly known type of wide band aerial is the logarithmic or log periodic, but its gain is usually much lower than that of a specific or narrower band aerial.

3.7.2- Gain

Gain as a parameter measures the efficiency of a given antenna with respect to a given norm, usually achieved by modification of its directionality. An antenna with a low gain emits radiation with about the same power in all directions, whereas a high-gain antenna will preferentially radiate in particular directions. Specifically, the Gain, Directive gain or Power gain of an antenna is defined as the ratio of the intensity (power per unit surface) radiated by the antenna in a given direction at an arbitrary distance divided by the intensity radiated at the same distance by a hypothetical isotropic antenna.

The gain of an antenna is a passive phenomenon - power is not added by the antenna, but simply redistributed to provide more radiated power in a certain direction than would be transmitted by an isotropic antenna. If an antenna has a gain greater than one in some directions, it must have a gain less than one in other directions, since energy is conserved by the antenna. An antenna designer must take into account the application for

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the antenna when determining the gain. High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully in a particular direction. Low-gain antennas have shorter range, but the orientation of the antenna is relatively inconsequential. For example, a dish antenna on a spacecraft is a high-gain device that must be pointed at the planet to be effective, whereas a typical Wi-Fi antenna in a laptop computer is low-gain, and as long as the base station is within range, the antenna can be in any orientation in space. It makes sense to improve horizontal range at the expense of reception above or below the antenna. Thus most antennas labelled "omnidirectional" really have some gain.

3.7.3- Radiation pattern

The radiation pattern of an antenna is the geometric pattern of the relative field strengths of the field emitted by the antenna. For the ideal isotropic antenna, this would be a sphere. For a typical dipole, this would be a toroid. The radiation pattern of an antenna is typically represented by a three dimensional graph, or polar plots of the horizontal and vertical cross sections. The graph should show sidelobes and backlobes, where the antenna's gain is at a minima or maxima.

3.7.4- Impedance

As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source[5], forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences

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at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

3.7.5- Efficiency

Efficiency is the ratio of power actually radiated to the power put into the antenna terminals. A dummy load may have an SWR of 1:1 but an efficiency of 0, as it absorbs all power and radiates heat but not RF energy, showing that SWR alone is not an effective measure of an antenna's efficiency. Radiation in an antenna is caused by radiation resistance which can only be measured as part of total resistance including loss resistance. Loss resistance usually results in heat generation rather than radiation, and reduces efficiency. Mathematically, efficiency is calculated as radiation resistance divided by total resistance.

3.7.6- Bandwidth

The bandwidth of an antenna is the range of frequencies over which it is effective, usually centered on the resonant frequency. The bandwidth of an antenna may be increased by several techniques, including using thicker wires, replacing wires with cages to simulate a thicker wire, tapering antenna components (like in a feed horn), and combining multiple antennas into a single assembly and allowing the natural impedance to select the correct antenna. Small antennas are usually preferred for convenience, but there is a fundamental limit relating bandwidth, size and efficiency.

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3.7.7- Polarization

The polarization of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation. It has nothing in common with antenna directionality terms: "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. "Electromagnetic wave polarization filters" are structures which can be employed to act directly on the electromagnetic wave to filter out wave energy of an undesired polarization and to pass wave energy of a desired polarization.

Reflections generally affect polarization. For radio waves the most important reflector is the ionosphere - signals which reflect from it will have their polarization changed unpredictably. For signals which are reflected by the ionosphere, polarization cannot be relied upon. For line-of-sight communications for which polarization can be relied upon, it can make a large difference in signal quality to have the transmitter and receiver using the same polarization; many tens of dB difference are commonly seen and this is more than enough to make the difference between reasonable communication and a broken link.

3.7.8- Transmission and reception

All of the antenna parameters are expressed in terms of a transmission antenna, but are identically applicable to a receiving antenna, due to reciprocity. Impedance, however, is not applied in an obvious way; for impedance, the impedance at the load (where the power is consumed) is most critical. For a transmitting antenna, this is the antenna itself. For a receiving antenna, this is at the (radio) receiver rather than at the antenna. Tuning is done by adjusting the length of an electrically long linear antenna to alter the electrical resonance of the antenna.

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Antenna tuning is done by adjusting an inductance or capacitance combined with the active antenna (but distinct and separate from the active antenna). The inductance or capacitance provides the reactance which combines with the inherent reactance of the active antenna to establish a resonance in a circuit including the active antenna. The established resonance being at a frequency other than the natural electrical resonant frequency of the active antenna. Adjustment of the inductance or capacitance changes this resonance.

Antennas used for transmission have a maximum power rating, beyond which heating, arcing or sparking may occur in the components, which may cause them to be damaged or destroyed. Raising this maximum power rating usually requires larger and heavier components, which may require larger and heavier supporting structures. This is a concern only for transmitting antennas, as the power received by an antenna rarely exceeds the microwatt range.

Antennas designed specifically for reception might be optimized for noise rejection capabilities. An antenna shield is a conductive or low reluctance structure (such as a wire, plate or grid) which is adapted to be placed in the vicinity of an antenna to reduce, as by dissipation through a resistance or by conduction to ground, undesired electromagnetic radiation, or electric or magnetic fields, which are directed toward the active antenna from an external source or which emanate from the active antenna. Other methods to optimize for noise rejection can be done by selecting a narrow bandwidth so that noise from other frequencies is rejected, or selecting a specific radiation pattern to reject noise from a specific direction, or by selecting a polarization different from the noise polarization, or by selecting an antenna that favors either the electric or magnetic field.

For instance, an antenna to be used for reception of low frequencies (below about ten megahertz) will be subject to both man-made noise from motors and other machinery, and from natural sources such as lightning.

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Successfully rejecting these forms of noise is an important antenna feature. A small coil of wire with many turns is more able to reject such noise than a vertical antenna. However, the vertical will radiate much more effectively on transmit, where extraneous signals are not a concern.

3.8- Application of Smart Antenna

Smart Antenna is used in number of fields. It has number of Applications. Here are some of the fields where Smart Antenna used:-

1). MOBILE COMMUNICAION.

2).WIRELESS COMMUNICATION.

3). RADAR.

4).SONAR

APPLICATION OF SMART ANTENNAS TO MOBILE COMMUNICATIONS SYSTEMS

Smart or adaptive antenna arrays can improve the performance of wireless communication systems. An overview of strategies for achieving coverage, capacity, and other improvements is presented, and relevant literature is discussed. Multipath mitigation and direction finding applications of arrays are briefly discussed, and potential paths of evolution for future wireless systems are presented. Requirements and implementation issues for smart antennas are also considered. Smart antennas are most often realized with either switched-beam or fully adaptive array antennas. An array consists of two or more antennas (the elements of the array) spatially arranged and electrically interconnected to produce a directional radiation pattern. In a phased array the phases of the exciting currents in each element antenna of the array are adjusted to change the pattern of the array, typically to scan a pattern maximum or null to a desired direction.

A smart antenna system consists of an antenna array, associated RF hardware, and a computer controller that changes the array pattern in

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response to the radio frequency environment, in order to improve the performance of a communication or radar system.Switched-beam antenna systems are the simplest form of smart antenna. By selecting among several different fixed phase shifts in the array feed, several fixed antenna patterns can be formed using the same array. The appropriate pattern is selected for any given set of conditions. An adaptive array controls its own pattern dynamically, using feedback to vary the phase and/or amplitude of the exciting current at each element to optimize the received signal.Smart or adaptive antennas are being considered for use in wirelesscommunication systems. Smart antennas can increase the coverage and capacity of a system. In multipath channels they can increase the maximum data rate and mitigate fading due to cancellation of multipath components. Adaptive antennas can also be used for direction finding, with applications including emergency services and vehicular trafficmonitoring. All these enhancements have been proposed in the literature and are discussed in this paper. In addition, possible paths of evolution, incorporating adaptive antennas into North American cellular systems, are presented and discussed. Finally, requirements for future adaptive antenna systems and implementation issues that willinfluence their design are outlined.

Range extensionIn sparsely populated areas, extending coverage is often more important than increasing capacity. In such areas, the gain provided by adaptive antennas can extend the range of a cell to cover a larger area and more users than would be possible with omnidirectional or sector antennas.

Interference reduction and rejection In populated areas, increasing capacity is of prime importance. Two related strategies for increasing capacity are interference reduction on the downlink and interference rejection on the uplink. To reduce interference,

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directional beams are steered toward the mobiles. Interference to co-channel mobiles occurs only if they are within the narrow beamwidth of the directional beam. This reduces the probability of co-channel interference compared with a system using omnidirectional base station antennas.Interference can be rejected using directional beams and/or by forming nulls in the base station receive antenna pattern in the direction of interfering co-channel users.Interference reduction and rejection can allow N c (which is dictated by co-channel interference) to be reduced, increasing the capacity of the system. Interference reduction can be implemented using an array with steered or switched beams. By using directional beams to communicate with mobiles on the downlink, a base station is less likely to interfere with nearby co-channel base stations than if it used an omnidirectional antenna.There will be a small percentage of time during which co-channel interference is strong, e.g., when a mobile is within the main beam of a nearby co-channel base station.This can be overcome by handing off the mobile within its current cell to another channel that is not experiencing strong co-channel interference.

3.9- Advantages and Disadvantages of Smart Antenna.

Advantages

Increased number of users

Due to the targeted nature of smart antennas frequencies can be reused allowing an increased number of users. More users on the same frequency space means that the network provider has lower operating costs in terms of purchasing frequency space.

Increased Range

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As the smart antenna focuses gain on the communicating device, the range of operation increases. This allows the area serviced by a smart antenna to increase. This can provide a cost saving to network providers as they will not require as many antennas/base stations to provide coverage.

Geographic Information

As smart antennas use ‘targeted’ signals the direction in which the antenna is transmitting and the gain required to communicate with a device can be used to determine the location of a device relatively accurately. This allows network providers to offer new services to devices. Some services include, guiding emergency services to your location, location based games and locality information.

Security

Smart antennas naturally provide increased security, as the signals are not radiated in all directions as in a traditional omni-directional antenna. This means that if someone wished to intercept transmissions they would need to be at the same location or between the two communicating devices.

Reduced Interference

Interference which is usually caused by transmissions which radiate in all directions are less likely to occur due to the directionality introduced by the smart antenna. This aids both the ability to reuse frequencies and achieve greater range.

Increased bandwidth

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The bandwidth available increases form the reuse of frequencies and also in adaptive arrays as they can utilize the many paths which a signal may follow to reach a device.

Easily integrated

Smart antennas are not a new protocol or standard so the antennas can be easily implemented with existing non smart antennas and devices.

Disadvantages

Complex

A disadvantage of smart antennas is that they are far more complicated than traditional antennas. This means that faults or problems may be harder to diagnose and more likely to occur.

More Expensive

As smart antennas are extremely complex, utilizing the latest in processing technology they are far more expensive than traditional antennas. However this cost must be weighed against the cost of frequency space.

Larger Size

Due to the antenna arrays which are utilized by smart antenna systems, they are much larger in size than traditional systems. This can be a problem in a social context as antennas can be seen as ugly or unsightly.

Location

The location of smart antennas needs to be considered for optimal operation. Due to the directional beam that ‘swings’ from a smart antenna locations which are optimal for a traditional antenna are not for a smart antenna. For example in a road context, smart antennas are better

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situated away from the road, unlike normal antennas which are best situated along the road.

3.11- Features and Benefit of Smart Antenna

Feature of Smart Antenna

1).Signal gain - Inputs from multiple antennas are combined to optimize available power required to establish given level of coverage.

2).Interference Rejection - Antenna pattern can be generated toward cochannel interference sources, improving the signal-to-interference ratio of the received signals.

3).Spatial diversity-Composite information from the array is used to minimize fading and other undesirable effects of multipath propagation.

4).Power efficiency- Combines the inputs to multiple elements to optimize available processing gain in the downlink (toward the user)

Benefit of Smart Antenna

1).Better range/coverage- Focusing the energy sent out into the cell increases base station range and coverage. Lower power requirements also enable a greater battery life and smaller/lighter handset size.

2).Increased capacity- Precise control of signal nulls quality and mitigation of interference combine to frequency reuse reduce distance (or cluster size),improving capacity. Certain adaptive technologies (such as space division multiple access) support the reuse of frequencies within the same cell.

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3).Multipath rejection- Can reduce the effective delay spread of the channel, allowing higher bit rates to be supported without the use of an equalizer.

4).Reduced expense- Lower amplifier costs, power consumption, and higher reliability will result.

Chapter 4

Summary

This report aims to explain the basic concept of Smart Antenna and some of its Application.

First Question arises What is Smart Antenna?

A smart antenna combines an antenna array with a digital signal-processing capability to transmit and receive in an adaptive, spatially sensitive manner. Or In other words Smart Antenna is an Array of antenna which is used to optimize its reception and transmit pattern.

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There are two types of Smart Antenna:-

1). Switched Beam- 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.

2). Adaptive Array- Adaptive antenna technology represents the most

advanced smart antenna approach to date. the adaptive system takes advantage of its ability to effectively locate and track various types of signals to dynamically minimize interference and maximize intended signal reception.

Both systems attempt to increase gain according to the location of the user; however, only the adaptive system provides optimal gain while simultaneously identifying, tracking, and minimizing interfering signals.

Smart antenna works in two processes . First one is Uplinking and second one is Downlinking

There are 2 categories of Smart Antenna:-

1). SIMO(Single Input Multiple Output)

2). MISO(Multiple Input Single Output)

3).MIMO(Multiple Input Multiple Output)

Basically Smart antenna has two functions :-

1).Beamforming-

2).Dirrection of Arrival

Smart antenna is used in various fields the most important is named below:-

1). Mobile Communication

2). Wireless Communication

3). RADAR

4).SONAR

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There are some of the factors which affects the performance of Smart Antenna . These factors reduces the Quality of Smart Antenna.Factors are:-

1).Resonant Frequency

2).Gain

3).Impedance

4).Bandwidth

5).Polarization

6).Transmission and Reception

Merits of Smart Antenna

1). Increased number of users.

2). Increased Range

3). Security

4). Reduced Interference.

Demerits of Smart Antenna:-

1). Complex

2). Expensive

3). Large Size

4). Location

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References

1).www.wikipedia.com

2).www.statemaster.com

3).www.iec.org

4).http://www.iec.org/online/tutorials/smart_ant/

5).W. L. Stutzman and G. A. Thiele, Antenna theory and Design, John Wiley & Sons, New York, 1981.6). D. Johnson and D. Dudgeon, Array Signal Processing, Prentice-Hall, Englewood Cli_s, NJ, 19937). http://www.smartanteenas.googlepages.com

8). Michael Chryssomallis “Smart antennas” IEEE antenna and propagation magazine” Vol 42 No 3 pp 129-138, June 2000.9). D. Johnson and D. Dudgeon, Array Signal Processing, Prentice-Hall, Englewood Cli_s, NJ, 199310). Special issue on blind identi_cation and estimation," IEEEProceedings, mid-1998 .11). R Kronberger,H Lindermerier,J Hopf “Smart antenna applications on vehicles with low profile array antenna” Proc IEEE Vol 53 pp1-3 September 2003.

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