seminar on smart antenna systems

Smart Antenna Systems

A

Seminar Report

On

SMART ANTENNA

SYSTEMS

By

ASHOK BEHURIA

B211010


A

Seminar Report

On

SMART ANTENNA

SYSTEMS

In partial fulfillment of requirements for the degree of

Bachelor of Engineering In

Electronics & Telecommunication Engineering

SUBMITTED BY:

Ashok Behuria Under the Guidance of

Prof. A.Kar


CERTIFICATE

Certified that seminar work entitled “SMART ANTENNA SYSTEMS” is a bonafide

work carried out in the seventh semester by “Ashok Behuria” in partial fulfilment for the award

of Bachelor of Technology in Electronics and Telecommunication Engineering from International

Institute of Information Technology Bhubaneswar during the academic year 2014-2015.

SIGNATURE

Name of Student

SIGNATURE

Name of SEMINAR CO_ORDINATOR

SIGNATURE

BRANCH CO ORDINATOR


ACKNOWLEDGEMENT

I express my deep sense of gratitude to my seminar in charge Mr. A.Kar, ETC

faculty Mr. Bijayananda Patnaik and ETC branch HOD Mr. Harish Kumar

Sahoo who with their critical acumen, indomitable energy and versatility has

supervised me and guided me all through my learning venture. But for deft

guidance, this report would not have seen the light of the day.

I wish to extend my warm thanks to the library as well as to my co-mates who

have promptly and readily provided me with ample materials to carry out my

report.

Lastly, I would thank the ETC branch faculties for their continuous support and

encouragement who gave their valuable time in explaining me details regarding

all the working systems of the smart antennas with their proper flowcharts and

layouts.


Contents

Particulars Page No.

Abstract 2

Introduction 2

Smart Antenna Systems 3

Overview 3

Relative Benefits/Trade-offs of Switched Beam and Adaptive Array Systems

6

The Goals Of A Smart Antenna System 9

The Architecture Of Smart Antenna Systems 10

Basic Working Mechanism 12

Who Can Use Smart Antenna Technology? 13

Adaptation Algorithms 14

Benefits Of Smart Antenna Technology 14

Discussion 15

Future Scope 15

Conclusion 16

References 17



Abstract

The adoption of smart / adaptive antenna techniques in future wireless systems is expected to

have a significant impact on the efficient use of the spectrum, the minimization of the cost of

establishing new wireless networks, the optimization of service quality and realization of

transparent operation across multi technology wireless networks. This seminar report presents

brief account on smart antenna (SA) system. SAs can place nulls in the direction of

interferers via adaptive updating of weights linked to each antenna element. SAs thus cancel

out most of the co-channel interference resulting in better quality of reception and lower

dropped calls. SAs can also track the user within a cell via direction of arrival algorithms.

This report explains the architecture, evolution and how the smart / adaptive antenna differs

from the basic format of antenna. The report further explains about the radiation pattern of

the antenna and why it is highly preferred in its relative field. The capabilities of smart /

adaptive antenna are easily employable to Cognitive Radio and OFDMA system.

1. Introduction

In view of explosive growth in the number of digital cellular subscribers, service providers

are becoming increasingly concerned with the limited capacities of their existing networks. In

a cellular system, omni-directional antennas have traditionally been used at base stations to

enhance the coverage area of the base stations but it also leads a gross wastage of power that

in-fact is the main cause of co-channel interference at neighbouring base stations. The

sectoring concept with diversity system exploits space diversity and results in improve

reception by counteracting with negative effects of multipath fading. Adaptive /smart antenna

technology represents the most advanced smart antenna approach to date. Using a variety of

new signal-processing algorithms, 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 adaptive / smart 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.

This concern has led to the deployment of smart antenna systems throughout major

metropolitan cellular markets. These smart antenna systems have typically employed multi

beam technologies, which have been shown, through extensive analysis, simulation, and

experimentation, to provide substantial performance improvements in FDMA, TDMA and

CDMA networks. Multi beam architectures for FDMA and TDMA systems provide the

straight-forward ability of the smart antenna to be implemented as a non-invasive add-on or

appliqué to an existing cell site, without major modifications or special interfaces.


2. Smart Antenna Systems

Definition

First Definition A smart antenna is a phased or adaptive array that adjusts to the environment. That is, for the

adaptive array, the beam pattern changes as the desired user and the interference move, and

for the phased array, the beam is steered or different beams are selected as the desired user

moves. Phased array or multi beam antenna consists of either a number of fixed beams with

one beam turned on towards the desired signal or a single beam (formed by phase adjustment

only) that is steered towards the desired signal.

Adaptive antenna array is an array of multiple antenna elements with the received signals

weighted and combined to maximize the desired signal to interference and noise (SINR)

ratio. This means that the main beam is put in the direction of the desired signal while nulls

are in the direction of the

interference.

Second Definition A smart antenna system combines multiple antenna elements with a signal processing

capability to optimize its radiation and/or reception pattern automatically in response to the

signal environment.

Smart antenna systems are customarily categorized as either switched beam or adaptive array

systems.

Third Definition Smart Antennas are arrays of antenna elements that change their antenna pattern dynamically

to adjust to the noise, interference in the channel and mitigate multipath fading effects on the

signal of interest.

The difference between a smart (adaptive) antenna and “dumb” (fixed) antenna is the

property of having an adaptive and fixed lobe-pattern, respectively. The secret to the smart

antennas’ ability to transmit and receive signals in an adaptive, spatially sensitive manner is

the digital signal processing

capability present. An antenna element is not smart by itself; it is a combination of antenna

elements to form an array and the signal processing software used that make smart antennas

effective. This shows that smart antennas are more than just the “antenna”, but rather a

complete transceiver concept.

3. Overview A smart antenna consists of several antenna elements, whose signal is processed adaptively in

order to exploit the spatial domain of the mobile radio channel. The smart antenna technology

can significantly improve wireless system performance and economics for a range of

potential users. It enables operators of PC's cellular and wireless local loop networks to

realize significant increase in signal quality, network capacity and coverage.

What Is a Smart Antenna System?

In truth, antennas are not smart antenna systems are smart. Generally co-located with a base

station, a smart antenna system combines an antenna array with a digital signal-processing

capability to transmit and receive in an adaptive, spatially sensitive manner. Such a

configuration dramatically enhances the capacity of a wireless link through a combination of


diversity gain, array gain and interference suppression. Increased capacity translates to higher

data rates for a given number of users or more users for a given data rate per user. In other

words, such a system can automatically change the directionality of its radiation patterns in

response to its signal environment. This can dramatically increase the performance

characteristics (such as capacity) of a wireless system.

Multipath of propagation are created by reflections and scattering. Also, interference signals

such as that produced by the microwave oven are superimposed on the desired signals.

Measurements suggest that each path is really a bundle or cluster of paths, resulting from

surface roughness or irregularities. The random gain of the bundle is called multipath fading.

This is a new and promising technology in the field of wireless and mobile communications

in which capacity and performance are usually limited by two major impairments multipath

and co-channel interference. Multipath is a condition that arises when a transmitted signal

undergoes reflection from various obstacles in the environment. This gives rise to multiple

signals arriving from different directions at the receiver. Smart antennas (also known as

adaptive array antennas and multiple antennas) are antenna arrays with smart signal

processing algorithms to identify spatial signal signature such as the Direction of arrival

(DOA) of the signal and use it to calculate beam forming vectors, to track and locate the

antenna beam on the mobile targets. The antenna could optionally be any sensor. Smart

antenna techniques are used notably in acoustic signal processing, track and scan Radar,

Radio astronomy and Radio Telescopes and mostly in Cellular Systems like W-CDMA and

UMTS.

How Many Types of Smart Antenna Systems Are There?

Terms commonly heard today that embrace various aspects of a smart antenna system

technology include intelligent antennas, phased array, SDMA, spatial processing, digital

beam forming, adaptive antenna systems, and others. Smart antenna systems are customarily

categorized, however, as either switched beam or adaptive array systems.

The following are distinctions between the two major categories of smart antennas regarding

the choices in transmit strategy:

Switched Beam—a finite number of fixed, predefined patterns or combining

strategies (sectors)

Adaptive Array—an infinite number of patterns (scenario-based) that are adjusted in

real time.


What Are Switched Beam Antennas? 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.

Instead of shaping the directional antenna pattern with the metallic properties and physical

design of a single element (like a sectorized antenna), switched beam systems combine the

outputs of multiple antennas in such a way as to form finely sectorized (directional) beams

with more spatial selectivity than can be achieved with conventional, single-element

approaches fig (1).

What Are Adaptive Array Antennas? Adaptive antenna (fig 2) technology represents the most advanced smart antenna approach to

date. Using a variety of new signal-processing algorithms, 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.

A third type of system is

Dynamically-Phased Arrays


The beams are predetermined and fixed in the case of a switched beam system. A user may

be in the range of one beam at a particular time but as he moves away from the center of the

beam and crosses over the periphery of the beam, the received signal becomes weaker and an

intra cell handover occurs.

But in dynamically phased arrays, a direction of arrival (DoA) algorithm tracks the user’s

signal as he roams within the range of the beam that’s tracking him. So even when the intra-

cell handoff occurs, the user’s signal is received with an optimal gain. It can be viewed as a

generalization of the switched lobe concept where the received power is maximized.

Comparison Between Switched Beam And Adaptive Array Systems Switched Beam System. (a) It uses multiple fixed directional beams with narrow beam widths.

(b) The required phase shifts are provided by simple fixed phase shifting networks like the

butler matrix.

(c) They do not require complex algorithms; simple algorithms are used for beam selection.

(d) It requires only moderate interaction between mobile unit and base station as compared to

adaptive array system.

(e) Since low technology is used, it has lesser cost and complexity.

(f) Integration into existing cellular system is easy and cheap.

(g) It provides significant increase in coverage and capacity compared to conventional

antenna based systems.

(h) Since, multiple narrow beams are used, frequent intra-cell hand-offs between beams have

to be handled as mobile moves from one beam to another.

(j) It cannot distinguish between direct signal and interfering and/or multipath signals, this

leads to undesired enhancement of the interfering signal more than the desired signal.

(k) Since, there is no null steering involved, switched beam systems offer limited co-channel

interference suppression as compared to the adaptive array systems.

Adaptive Array System. (a) A complete adaptive system; steers the beam towards desired signal of interest and places

nulls at the interfering signal directions.

(b) It requires implementation of DSP technology.

(c) It requires complicated adaptive algorithms to steer the beam and the nulls.

(d) It has better interference rejection capability compared to Switched beam systems.

(e) It is not easy to implement in existing systems i.e. up-gradation is difficult and expensive.

(f) Since, continuous steering of the beam is required as the mobile moves; high interaction

between mobile unit and base station is required.

(g) Since, the beam continuously follows the user; intra-cell hand-offs are less.

(h) It provides better coverage and increased capacity because of improved interference

rejection as compared to the Switched beam systems.

(j) It can either reject multipath components or add them by correcting the delays to enhance.

4. Relative Benefits/Trade-offs of Switched Beam and Adaptive Array Systems

Integration- Switched beam systems are traditionally designed to retrofit widely deployed cellular

systems. It has been commonly implemented as an add-on or appliqué technology that


intelligently addresses the needs of mature networks. In comparison, adaptive array systems

have been deployed with a more fully integrated approach that offers less hardware

redundancy than switched beam systems but requires new build-out.

Range/coverage- Switched beam systems can increase base station range from 20 to 200 percent over

conventional sectored cells, depending on environmental circumstances and the

hardware/software used. The added coverage can save an operator substantial infrastructure

costs and means lower prices for consumers. Also, the dynamic switching from beam to beam

conserves capacity because the system does not send all signals in all directions. In

comparison, adaptive array systems can cover a broader, more uniform area with the same

power levels as a switched beam system.

Interference suppression-Switched beam antennas suppress interference arriving from directions away from the active

beam's center. Because beam patterns are fixed, however, actual interference rejection is

often the gain of the selected communication beam pattern in the interferer's direction. Also,

they are normally used only for reception because of the system's ambiguous perception of

the location of the received signal (the consequences of transmitting in the wrong beam being

obvious). Also, because their beams are predetermined, sensitivity can occasionally vary as

the user moves through the sector.

Switched beam solutions work best in minimal to moderate co-channel interference and have

difficulty in distinguishing between a desired signal and an interferer. If the interfering signal

is at approximately the center of the selected beam, and the user is away from the center of

the selected beam, the interfering signal can be enhanced far more than the desired signal. In

these cases, the quality is degraded for the user.

Adaptive array technology currently offers more comprehensive interference rejection. Also,

because it transmits an infinite, rather than finite, number of combinations, its narrower focus

creates less interference to neighbouring users than a switched-beam approach.

Spatial division multiple access (SDMA)- Among the most sophisticated utilizations of smart antenna technology is SDMA, which

employs advanced processing techniques to, in effect, locate and track fixed or mobile

terminals, adaptively steering transmission signals toward users and away from interferers.

This adaptive array technology achieves superior levels of interference suppression, making

possible more efficient reuse of frequencies than the standard fixe hexagonal reuse patterns.

In essence, the scheme can adapt the frequency allocations to where the most users are

located.

Fig 3 Smart Antenna Technology


Signal Propagation- Multipath And Co-channel Interference –

A Useful Analogy for Signal Propagation Envision a perfectly still pool of water into which a

stone is dropped. The waves that radiate outward from that point are uniform and diminish in

strength evenly. This pure omnidirectional broadcasting equates to one caller's signal—

originating at the terminal and going uplink. It is interpreted as one signal everywhere it

travels.

Picture now a base station at some distance from the wave origin. If the pattern

remains undisturbed, it is not a challenge for a base station to interpret the waves. But as the

signal's waves begin to bounce off the edges of the pool, they come back (perhaps in a

combination of directions) to intersect with the original wave pattern.

As they combine, they weaken each other's strength. These are multipath interference

problems. Now, picture a few more stones being dropped in different areas of the pool,

equivalent to other calls starting. How could a base station at any particular point in the pool

distinguish which stone's signals were being picked up and from which direction? This

multiple-source problem is called co-channel interference. These are two-dimensional

analogies; to fully comprehend the distinction between callers and/or signal in the earth's

atmosphere, a base station must possess the intelligence to place the information it analyses

in a true spatial context. Multipath is a condition where the transmitted radio signal is

reflected by physical features/structures, creating multiple signal paths between the base

station and the user terminal.

Problems Associated with Multipath One problem resulting from having unwanted reflected signals is that the phases of the waves

arriving at the receiving station often do not match. The phase of a radio wave is simply an

arc of a radio wave, measured in degrees, at a specific point in time.

Conditions caused by multipath that are of primary concern are as follows:

Fading- When the waves of multipath signals are out of phase, reduction in signal strength

can occur. One such type of reduction is called a fade; the phenomenon is known as

"Rayleigh fading" or "fast fading."

A fade is a constantly changing, three-dimensional phenomenon. Fade zones tend to be small,

multiple areas of space within a multipath environment that cause periodic attenuation of a

received signal for users passing through them. In other words, the received signal strength

will fluctuate downward, causing a momentary, but periodic, degradation in quality.

Phase cancellation- When waves of two multipath signals are rotated to exactly 180° out

of phase, the signals will cancel each other. While this sounds severe, it is rarely sustained on

any given call (and most air interface standards are quite resilient to phase cancellation). In

other words, a call can be maintained for a certain period of time while there is no signal,

although with very poor quality. The effect is of more concern when the control channel

signal is cancelled out, resulting in a black hole, a service area in which call set-ups will

occasionally fail.

Delay spread- The effect of multipath on signal quality for a digital air interface (e.g.,

TDMA) can be slightly different. Here, the main concern is that multiple reflections of the

same signal may arrive at the receiver at different times. This can result in inter symbol


interference (or bits crashing into one another) that the receiver cannot sort out. When this

occurs, the bit error rate rises and eventually causes noticeable degradation in signal quality.

While switched diversity and combining systems do improve the effective strength of the

signal received, their use in the conventional macro cell propagation environment has been

typically reverse-path limited due to a power imbalance between base station and mobile

unit. This is because macro cell-type base stations have historically put out far more power

than mobile terminals were able to generate on the reverse path.

Co-channel interference- One of the primary forms of man-made signal degradation

associated with digital radio, co-channel interference occurs when the same carrier frequency

reaches the same receiver from two separate transmitters. Figure 13. Illustration of Co-channel Interference in a Typical Cellular Grid

As we have seen, both broadcast antennas as well as more focused antenna systems scatter

signals across relatively wide areas. The signals that miss an intended user can become

interference for users on the same frequency in the same or adjoining cells. While sectorized

antennas multiply the use of channels, they do not overcome the major disadvantage of

standard antenna broadcast—co-channel interference. Management of co-channel

interference is the number-one limiting factor in maximizing the capacity of a wireless

system. To combat the effects of co-channel interference, smart antenna systems not only

focus directionally on intended users, but in many cases direct nulls or intentional non-

interference toward known, undesired users.

5. The Goals Of A Smart Antenna System The dual purpose of a smart antenna system is to augment the signal quality of the radio-

based system through more focused transmission of radio signals while enhancing capacity

through increased frequency reuse.

Table 1 : Features and Benefits of Smart Antenna Systems

Feature Benefit Signal Gain—Inputs from multiple antennas are combined to optimize available power required to establish given level of coverage.

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.

Interference Rejection—Antenna pattern can be generated toward co-channel interference sources, improving the signal-to-interference ratio of the received signals.

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 (i.e., space division multiple access) support the reuse of frequencies within the same cell.

Spatial Diversity—Composite information from the array is used to minimize fading and other undesirable effects of multipath propagation.

Multipath Rejection—It can reduce the effective delay spread of the channel, allowing higher bit rates to be supported without the use of an equalizer, improved bit error rate (due to decreased amount of Multi-path and ISI).

SDMA- SDMA continually adapts to the radio environment through intelligent / smart

Providing each user with uplink and downlink signals of the highest possible quality and can


antenna. adapt the frequency allocation to where the most users are located.

Power Efficiency—combines the inputs to multiple elements to optimize available processing gain in the downlink (toward the user)

Reduced Expense—Lower amplifier costs, power consumption, and higher reliability will result. Lower power consumption reduces not only interferences but also reduces RF pollution (ease health hazard). It will also result in reduction of scares energy resource (diesel consumption) and save foreign currency.

6. The Architecture Of Smart Antenna Systems How Do Smart Antenna Systems Work? Traditional 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.

Fig:4 Antenna Array What Makes Them So Smart? A simple antenna works for a simple RF environment. Smart antenna solutions are required

as the number of users, interference, and propagation complexity grow. Their smarts reside in

their digital signal-processing facilities. Like most modern advances in electronics today, the

digital format for manipulating the RF data offers numerous advantages in terms of accuracy

and flexibility of operation. Speech starts and ends as analog information. Along the way,

however, smart antenna systems capture, convert, and modulate analog signals for

transmission as digital signals and reconvert them to analog information on the other end. In

adaptive antenna systems, this fundamental signal-processing capability is augmented by

advanced techniques (algorithms) that are applied to control operation in the presence of

complicated combinations of operating conditions. The benefit of maintaining a more focused

and efficient use of the system's power and spectrum allocation can be significant.

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 omni-directional 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

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 use

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 to transmit and receive the signal (e.g. GSM).

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. Direction of arrival (DOA) Estimation- The smart antenna system estimates the

direction of arrival of the signal, using techniques such as Multiple Signal Classification

(MUSIC), estimation of signal parameters via rotational invariance techniques (ESPRIT)

algorithms, Matrix Pencil method or one of their derivatives. They involve findings of a

spatial spectrum of the antenna/sensor array and calculating the DOA from the peaks of this

spectrum. These calculations are computationally intensive. Matrix Pencil is very efficient in

case of real time systems and under the correlated sources.

Beam forming- It is the method used to create the radiation pattern of the antenna array by

adding constructively the phases of the signals in the direction of the targets/mobiles desired

and nullifying the pattern of the targets/mobiles which are undesired/interfering targets. This

can be done with a simple FIR tapped delay line filter. The weights of the FIR filter may also

be changed adaptively and used to provide optimal beam forming and actual beam pattern

formed. Typical algorithms are the steepest descent and LMS algorithms. There is an ever-

increasing demand on mobile wireless operators to provide voice and high-speed data

services. At the same time, these operators want to support more users per base station to

reduce overall network costs and make the services affordable to subscribers. As a result,

wireless systems that enable higher data rates and higher capacities are a pressing need.

Smart Antenna System – Beam forming

Fig:5 Smart Antenna System


Advantage of Beam Forming - There are following advantages of Beam forming:-

(a) Processing Speed. Smart Antenna technology requires high processing bandwidth with

computational speeds approaching several billion Multiply and Accumulate (MAC)

operations per second. Such computationally demanding applications quickly exhaust the

processing capabilities of digital signal processors. Enhanced DSP blocks and Tri-Matrix

memory provide throughputs in excess of 50 GMACs, offering a high-performance platform

for beam forming applications.

(b) Flexibility. There are a number of beam forming architectures and adaptive algorithms

that provide good performance under different scenarios such as transmit-receive adaptive

beam forming and transmit-receive switched beam forming. With embedded processors and

easy-to-use development tools such as DSP Builder. It offers a high degree of flexibility in

implementing various adaptive signal processing algorithms.

(c) Lower Risk. The standards for next-generation networks are continuously evolving and

this creates an element of risk for beam forming implementation. Transmit beam forming for

example, utilizes the feedback from the mobile terminals. The number of bits provided for

feedback in the standards can determine the beam forming algorithm that is used at the base

station. Moreover, future base stations are likely to support transmit diversity including

space-time coding and Multiple-Input Multiple-Output (MIMO) technology. They reduce the

risk involved with designing for evolving industry standards while providing the option for

the gradual deployment of additional transmit diversity schemes.

(d) Cost Reduction Path. Mobile wireless service providers would likely to deploy smart

antennas technology initially at certain "hot spots" such as densely populated urban areas

where there is more demand for high-speed wireless data services. The high NRE costs and

long development cycles associated with ASICs cannot be justified for such low volume

requirements. It offers a seamless migration process that supports the high-density FPGAs

and can offer up to 70 percent cost reduction for relatively low Minimum Order Quantities

(MOQs).

7. Basic Working Mechanism A smart antenna system can perform the following functions:-

(a) First, the direction of arrival of all the incoming signals including the interfering signals

and the multipath signals are estimated using the Direction of Arrival algorithms.

(b) Secondly, the desired user signal is identified and separated from the rest of the unwanted

incoming signals.

(c) Lastly, a beam is steered in the direction of the desired signal and the user is tracked as he

moves while placing nulls at interfering signal directions by constantly updating the complex

weights.

Spatial Division Multiple Access (SDMA) Among the most sophisticated utilizations of smart antenna technology is SDMA, which employs

advanced processing techniques to, in effect, locate and track fixed or mobile terminals, adaptively

steering transmission signals toward users and away from interferers. This adaptive array technology

achieves superior levels of interference suppression, making possible more efficient reuse of

frequencies than the standard fixed hexagonal reuse patterns. In essence, the scheme can adapt the

frequency allocations to where the most users are located. Because SDMA employs spatially selective

transmission, an SDMA base station radiates much less total power than a conventional base station.


One result is a reduction in network-wide RF pollution. Another is a reduction in power amplifier

size. First, the power is divided among the elements, and then the power to each element is

reduced because the energy is being delivered directionally. With a ten-element array, the amplifiers

at each element need only transmit one-hundredth the power that would be transmitted from the

corresponding single antenna system.

Utilizing highly sophisticated algorithms and rapid processing hardware, spatial processing takes the

reuse advantages that result from interference suppression to a new level. In essence, spatial

processing dynamically creates a different sector for each user and conducts a frequency/channel

allocation in an ongoing manner in real time.

Adaptive spatial processing integrates a higher level of measurement and analysis of the scattering

aspects of the RF environment. Whereas traditional beam-forming and beam-steering techniques

assume one correct direction of transmission toward a user, spatial processing maximizes the use of

multiple antennas to combine signals in space in a method that transcends a one user-one beam

methodology.

Fig:6 SDMA technology(general and actual mechanism)

8. Who Can Use Smart Antenna Technology? Smart antenna technology can significantly improve wireless system performance and

economics for a range of potential users. It enables operators of PCS, cellular, and wireless

local loop (WLL) networks to realize significant increases in signal quality, capacity, and

coverage.

Operators often require different combinations of these advantages at different times. As a

result, those systems offering the most flexibility in terms of configuration and upgradeability

are often the most cost-effective long-term solutions.

Applicable Standards Smart antenna systems are applicable, with some modifications, to all major wireless protocols

and standards, including those in Table 2. Table 2. Applicable Standards

Access methods Analog —frequency division multiple access (FDMA) (e.g., AMPS, TACS, NMT)

Digital—time division multiple access (TDMA) (e.g., GSM, IS–136); code division multiple access (CDMA) (e.g., IS–95)

Duplex methods frequency division duplex (FDD); time division duplex (TDD)


9. Adaptation Algorithms Continuous Adaptation: Automatically adjust weights as the incoming data is

sampled and updates it such that it converges to an optimal solution, uses a reference

signal.

E.g. The Least Mean Square algorithm (LMS), The Recursive Least Square algorithm

(RLS).

Blind Adaptive algorithm: Adjustment of weights without the benefit of reference

signal information.

E.g. The Constant modulus algorithm (CMA).

LMS algorithm generates better main lobes in desired user direction but do not nullify

co channel interference.

Interference rejection is better in CMA because nulls are produced towards

interfering signals. Hence nullifies co channel interference but bears maximum errors.

RLS algorithm has better response towards co channel interference, generates better

main lobe in desired direction and has faster convergence rate than LMS, hence the

best of all.

10. Benefits Of Smart Antenna Technology There are large number of benefits of Smart Antennas, some of them are enumerated below

as:

(a) Reduction in Co-Channel Interference. Smart antennas have a property of spatial

filtering to focus radiated energy in the form of narrow beams only in the direction of the

desired mobile user and no other direction. In addition, they also have nulls in their radiation

pattern in the direction of other mobile users in the vicinity. Therefore, there is often

negligible co-channel interference.

(b) Range Improvement. Since, smart antennas employs collection of individual elements in

the form of an array they give rise to narrow beam with increased gain when compared to

conventional antennas using the same power. The increase in gain leads to increase in range

and the coverage of the system. Therefore, fewer base stations are required to cover a given

area.

(c) Increase in Capacity. Smart antennas enable reduction in co-channel interference which

leads to increase in the frequency reuse factor means smart antennas allow more users to use

the same frequency spectrum at the same time bringing about tremendous increase in

capacity.

(d) Reduction in Transmitted Power. Ordinary antennas radiate energy in all directions

leading to a waste of power. Comparatively, smart antennas

radiate energy only in the desired direction. Therefore, less power is required for radiation at

the base station. Reduction in transmitted power also implies reduction in interference

towards other users.

(e) Reduction in Handoff. To improve the capacity in a crowded cellular network, congested

cells are further broken into micro cells to enable increase in the frequency reuse factor. This

results in frequent handoffs as the cell size is smaller. Using smart antennas at the base

station, there is no need to split the cells as the capacity is increased by using independent

spot beams.


11. Discussion

The above capability of adaptive / smart antennas clearly indicates without doubts that smart

antenna can be easily replaced with traditionally used existing antennas (omni directional,

sectored antenna with diversity concept). Use of adaptive antenna in existing systems will

reduce power consumption and interference while enhancing spectral density in wireless

system which is the dire need of wireless communication systems. Health hazard is being

considered the main factor in RF communication which will also be taken care of by use of

smart antenna as less RF pollution is created with the use of smart / adaptive antenna. Latest

studies in INDIA indicates that most of the subsidies on diesel is being consumed by cellular

vendors for running more than 4 lacs base stations in the country which is much more in

comparison to farmers diesel consumption (this subsidy was meant for farmers and poor

people only). The use of smart antenna will reduce diesel consumption in cellular

communication drastically. The capabilities of smart antenna have been proved beyond doubt

through analysis, simulation and deployment. With the inclusion of nanotechnology devices

the capability of adaptive antenna will increase manifold.

12. Future Scope MIMO systems employing smart antennas that fulfill IMT-advanced requirements is

the core of 4G systems with 1Gbit/s data rate and freq 20-100MHz.

MIMO systems fulfilling beyond IMT-advanced standard forms the 5G systems with

more than 10 Gbit/s data rate and with a frequency of 200MHz.

Use of multiple smart antennas in mobile handsets to achieve much better

performance.

Smart antenna based on UWB technology to detect malignant tumors.


13. Conclusion

Smart Antennas have been tested in a variety of field locations with promising results. The

new antenna has demonstrated a considerable advantage over various indoor antennas with

no amplification and the set-top UHF loop/VHF rod antenna combination with built-in

amplification. In a few locations, Smart Antennas may be unable to automatically optimize

the signal. A simple antenna works for a simple RF environment. Smart antenna solutions are

required as the number of users, interference and propagation complexity grows. Their

smartness resides in their digital signal processing facilities. Like most modern advances in

electronics today, the digital format for manipulating the RF data offers numerous advantages

in terms of accuracy and flexibility of operation. Speech starts and ends as analog

information. Along the way, however, Smart Antenna systems capture, convert and modulate

analog signals for transmission as digital signals and reconvert them to analog information on

the other end. In adaptive antenna systems, this fundamental signal-processing capability is

augmented by advanced techniques (algorithms) that are applied to control operation in the

presence of complicated combinations of operating conditions.

The dual purpose of a smart antenna system is to augment the signal quality of the radio-

based system through more focused transmission of radio signals while enhancing capacity

through increased frequency reuse. The technology of smart or adaptive antennas for mobile

communications has received enormous interest worldwide in recent years. In the Smart

antenna, different levels of intelligence are introduced, ranging from simple switching

between predefined beams to optimum beam forming. The principle reason for evolution of

Smart Antennas is the possibility for a large increase in capacity, an increase of three times

for TDMA systems and five times for CDMA systems has been reported. Other advantages

include increased range and the potential to introduce new services. Major drawbacks and

cost factors include increased transceiver complexity and more complex radio resource

management. In the Smart antenna, special attention is given to the critical factors and

technological challenges, including achieving equal performance on uplink and downlink as

well as real-time calibration of the receiver and transmitter chains.


14. References

1) R. H .Roy, “An overview of smart antenna technology and its application on wireless communication systems,” Proc .IEEE conf.personal wireless comm.,2007, pp. 234 – 238

2) Chryssomallis, M., 2008. Smart antennas , IEEE Antennas and Propogation Magazine, 42(3): 129 -136

3) S. F. Shaukat , Mukhtar ul Hassan, R. Farooq, H. U. Saeed and Z. Saleem, “Sequential studies of beam forming algorithms for smart antenna systems”, world applied sciences journal , vol .6, no. 6, pp 754-758,2009

4) http://www.iec.org 5) http://www.smartantennas.googlepages.com 6) S.F. Shaukat, Mukhtar ul Hassan, R. Farooq, H.U. Saeed and Z.Saleem,

"Sequential Studies of Beam forming Algorithms for Smart Antenna Systems", World Applied Sciences Journal, Vol. 6, no. 6, pp 754-758, 2009.

7) Luca Bencini, Giovanni Collodi, Divide Di Palma, Gianfranco Manes, Antonio Manes,” An Energy Efficient Cross Layer Solution based on Smart Antennas for Wireless Sensor Network Applications” ,IEEE, COMPUTER SOCIETY, SENSOR COM, Fourth International Conference on Sensor Technologies and Applications. 2010, pp 232- 237.

8) Sultan Budhwani, Mahasweta Sarkar and Santosh Nagaraj “A MAC Layer Protocol for Sensor Networks using Smart Antennas”, IEEE International Conference on Sensor Networks, Ubiquitous, and Trustworthy Computing, 2010, pp 261-267.

9) Chryssomallis, M., 2008. Smart antennas, IEEE Antennas and Propagation Magazine, 42(3): 129- 136.

10) Jensen M and J. W. Wallance, “A review of antennas and propagation for MIMO wireless systems”, IEEE Transaction of Antennas and propagation, vol. 52, pp. 2810-2824, 2004.