~ 1 ~ SMART ANTENNA SYSTEM INTRODUCTIONIn mobile communication systems, capacity and performance are usually limited by two majorimpairments.Theyaremultipathandco-channelinterference.Multipathisacondition whichariseswhenatransmittedsignalundergoesreflectionfromvariousobstaclesinthe propagation environment. This gives rise to multiple signals arriving from different directions. Sincethemultipathsignalsfollowdifferentpaths,theyhavedifferentphaseswhentheyare arrive at the receiver. The result is degradation in signal quality when they are combined at the receiverdueto thephasemismatch.Co-channelinterferenceistheinterferencebetweentwo signals that operate at the same frequency. In cellular communication the interference is usually caused by a signal from a different cell occupying the same frequency band. All these defects can be rectified with the use of smart antenna[6]. WHAT IS SMART ANTENNA? Smartantennaisoneofthemostpromisingtechnologiesthatwillenableahigher capacityinwirelessnetworksbyeffectivelyreducingmultipathandco-channelinterference. This is achieved by focusing the radiation only in the desired direction and adjusting itself to changingtrafficconditionsorsignalenvironments. Smartantennasemployaset ofradiating elements arranged in the form of an array. The signals from these elements are combined to form a movable or switchable beam pattern that follows the desired user. In a Smart antenna system thearraysbythemselvesarenotsmart,itisthedigitalsignalprocessingthatmakesthem smart[2]. The process of combining the signals and then focusing the radiation in a particular direction is often referred to as digital beamforming Beam forming is the term used to describe the application of weights to the inputs of an array of antennas to focus the reception of the antenna array in a certain direction, called the look direction or the main lobe. More importantly, other signals of the same carrier frequency from other directions canbe rejected. These effects are all achieved electronically andno physical movement of the receiving antennas is necessary. In addition, multiple beam formers focused in different directions can share a single antenna array one set of antennas can service multiple calls of the same carrier[3]. WHAT MAKES THEM SO SMART? AsimpleantennaworksforasimpleRFenvironment.Smartantennasolutionsare required as the number of users, interference, and propagation complexity grow. Their smarts resideintheirdigitalsignal-processingfacilities.Likemostmodernadvancesinelectronics today, the digital format for manipulating the RF data offers numerous advantages in terms of ~ 2 ~ accuracy and flexibility of operation. Speech starts and ends as analog information. Along the way,however,smartantennasystemscapture,convert,andmodulateanalogsignalsfor transmission as digital signals and reconvert them to analog information on the other end[1]. In adaptive antenna systems, this fundamental signal-processing capability is augmented byadvancedtechniques(algorithms)thatareappliedtocontroloperationinthepresenceof complicated combinations of operating conditions[1]. GOAL OF SMART ANTENNA Better range/coverage- Focusing the energy sent out into the cell increases base station rangeandcoverage.Lowerpowerrequirementsalsoenableagreaterbatterylifeand smaller/lighter handset size. Increasecapacity-Precise control of signal nulls quality and mitigation of interference combine to frequency reuse reduce distance (or cluster size), improving capacity. Certain adaptivetechnologies(suchasspacedivisionmultipleaccess)supportthereuseof frequencies within the same cell. Multipathrejection-canreducetheeffectivedelayspreadofthechannel,allowing higher bit rates to be supported without the use of an equalizer. Reduce expense-Lower amplifier costs, power consumption, and higher reliability will result[4]. FEATURES OF SMART ANTENNA The dual purpose of a smart antenna system is to augment the signal quality of the radio-basedsystemthroughmorefocusedtransmissionofradiosignalswhileenhancingcapacity throughincreasedfrequencyreuse.Morespecifically,thefeaturesofsmartantennasystem include: Highersignalgain- Inputs from multiple antennas are combined to optimize available power required to establish given level of coverage. Betterinterferencerejection-Antennapatterncanbegeneratedtowardcochannelinterference sources, improving the signal to interference ratio of the received signals. Spatial diversity- Composite information from the array is used to minimize fading and other undesirable effects of multipath propagation. Good powerefficiency- combines the inputs to multiple elements to optimize available processing gain in the downlink (toward the user)[4]. TYPES OF SMART ANTENNA There are basically two approaches to implement antennas that dynamically change their antennapatterntomitigateinterferenceandmultipathaffectswhileincreasingcoverageand range. They areSwitched beamAdaptive Arrays ~ 3 ~ SWITCHED BEAM SYSTEM TheSwitchedbeamapproachissimplercomparedtothefullyadaptiveapproach.It providesaconsiderableincreaseinnetworkcapacitywhencomparedtotraditional omnidirectionalantennasystemsorsector-basedsystems.Inthisapproach,anantennaarray generatesoverlappingbeamsthatcover thesurroundingareaasshowninfigure1.Whenan incomingsignalisdetected, thebasestationdeterminesthebeamthatisbestalignedinthe signal-of-interest direction and then switches to that beam to communicate with the user. This type of adaptive technique actually does not steer or scan the beam in the direction ofthedesiredsignal.Switchedbeamemploysanantennaarraywhichradiatesseveral overlapping fixed beams covering a designated angular area. It subdivides the sector into many narrow beams. Each beam can be treated as an individual sector serving an individual user or a group of users. Consider a traditional cellular area that is dividedinto three sectors with 120 degree angular width, with each sector served by six directional narrow beams. The spatially separated directionalbeamsleads to increaseinthe possible reuse of afrequency channelby reducingpotentialinterferenceandalsoincreasestherange.Theseantennasdonothavea uniform gain in all directions but when compared to a conventional antenna system they have increased gain in preferred directions. The Switched beam antenna has a switching mechanism thatenablesittoselectandthenswitchtherightbeamwhichgivesthebestreceptionfora mobile user under consideration. The selection is usually based on maximum received power for that user. Note that same beam can be used both for uplink and downlink communication[7]. (a)Fig 1: Beam formation for switched beam antenna system ~ 4 ~ ADAPTIVE ARRAY SYSTEM The Adaptive array system is the smarter of the two approaches. This system tracks the mobile user continuously by steering the main beam towards the user and at the same time forming nulls in the directions of the interfering signal as shown in figure 2. Like switched beam systems, they also incorporate arrays. Typically, the received signal from each of the spatially distributed antenna elements is multiplied by a weight. The weights are complex in nature and adjust theamplitudeandphase.Thesesignalsarecombinedtoyieldthearrayoutput.These complex weights are computed by a complicated adaptive algorithm, which is pre-programmed into the digital signal-processing unit that manages the signal radiated by the base station[7]. From the previous discussionit was quite apparent that switchedbeamsystems offer limited performance enhancement when compared to conventional antenna systems in wireless communication. However, greater performance improvements can be achieved by implementing advanced signal processing techniques to process the information obtained by the antenna arrays. Unlike switched beam systems, the adaptive array systems are really smart because they are able to dynamically react to the changing RF environment. They have a multitude of radiation Fig 2: Beam formation for adaptive array antenna system patternscomparedtofixedfinitepatternsinswitchedbeamsystemstoadapttotheever-changing RF environment. An Adaptive array, like a switched beam system uses antenna arrays but it is controlled by signal processing. This signal processing steers the radiation beam towards a desired mobile user, follows the user as he moves, and at the same time minimizes interference arising from other users by introducing nulls in their directions. This is illustrated in a simple diagram shown below in figure 2. ~ 5 ~ The adaptive array systems are really intelligent in the true sense and can actually be referred to as smart antennas. The smartness in these systems comes from the intelligent digital processor thatisincorporatedinthesystem.Theprocessingismainlygovernedbycomplex computationally intensive algorithms. COMPARISON BETWEEN SWITCHED BEAM AND ADAPTIVE ARRAY SYSTEM Switched beam systemIt uses multiple fixed directional beams with narrow beamwidths.The required phase shifts are provided by simple fixed phase shifting networks like the butler matrix.Theydonotrequirecomplexalgorithms;simplealgorithmsareusedforbeam selection.Itrequiresonlymoderateinteractionbetweenmobileunitandbasestationas compared to adaptive array system.Since low technology is used it has lesser cost and complexity.Integration into existing cellular system is easy and cheap.Itprovidessignificantincreaseincoverageandcapacitycomparedconventional antenna based systems.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.It cannot distinguish between direct signal and interfering and/or multipath signals, this leading to undesired enhancement of the interfering signal more than the desired signal.Since there is no null steering involved; Switched beam systems offers limited co-channel interference suppression as compared to the adaptive array system[7]. Adaptive array systemA complete adaptive system; steers the beam towards desired signal-of-interest and places nulls at the interfering signal directions.It requires implementation of DSP technology.It requires complicated adaptive algorithms to steer the beam and the nulls.It has better interference rejection capability compared to Switched beam systems.Itisnoteasytoimplementinexistingsystems,i.e.upgradationisdifficultand expensive.Sincecontinuoussteeringofthebeamisrequiredasthemobilemoves;high interaction between mobile unit and base station is required.Since the beam continuously follows the user; intra-cell hand-offs are less.It provides better coverage and increased capacity because of improved interference rejection as compared to the Switched beam system.It can either reject multipath components or add them by correcting the delays to enhance the signal quality[7]. ~ 6 ~ BASIC WORKING MECHANISM OF SMART ANTENNA A smart antenna system can perform the following functions: first the direction of arrival ofalltheincomingsignalsincludingtheinterferingsignalsandthemultipathsignalsare estimatedusingtheDirectionofArrivalalgorithms.Secondly,thedesiredusersignalis identified and separated from the rest of the unwanted incoming signals. 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[7].As discussed previously in the section of phased arrays it is quite evident that the direction of radiation of the main beam in an array depends upon the phase difference between the elements of the array. Therefore it is possible to continuously steer the main beam in any direction by adjusting the progressive phase difference between the elements. The same concept forms the basis in adaptive array systems in which the phase is adjusted to achieve maximum radiation in the desired direction. To have a better understanding of how an adaptive array system works, let us consider a typical adaptive digital beamforming network shown below in figure 3. Fig3. Block diagram of adaptive array systems In a beamforming network typically the signals incident at the individual elements are combined intelligently to form a single desired beamformed output. Before the incoming signals areweightedtheyarebroughtdowntobasebandorintermediatefrequencies(IFs).The receiversprovidedattheoutputofeachelementperformthenecessaryfrequencydown conversion. Adaptive antenna array systems use digital signal processors (DSPs) to weight the incoming signal. Therefore it is required that the down-converted signal be converted into digital format before they are processed by the DSP. Analog-to-digital converters (ADCs) are provided for this purpose. For accurate performance, they are required to provide accurate translation of the RF signal from the analog to the digital domain. The digital signal processor forms the heart of the system, which accepts the IF signal in digital format and the processing of the digital data ~ 7 ~ is driven by software. The processor interprets the incoming data information, determines the complexweights(amplificationandphaseinformation)andmultipliestheweightstoeach element output to optimize the array pattern. The optimization is based on a particular criterion, which minimizes the contribution from noise and interference while producing maximum beam gain at the desired direction. There are several algorithms based on different criteria for updating and computing the optimum weights. BENEFITS OF SMART ANTENNA TECHNOLOGY Reduction in co-channel interferenceSmart antennas has 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[7]. Range improvement Since smart antennas employs collection of individual elements in the form of an array theygiverisetonarrowbeamwithincreasedgainwhencomparedtoconventionalantennas 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. Increase in capacitySmart antennas enable reduction in co-channel interference, which leads to increase in the frequency reuse factor. That is smart antennas allow more users to use the same frequency spectrum at the same time bringing about tremendous increase in capacity. Reduction in transmitted powerOrdinaryantennasradiateenergyinalldirectionsleadingtoawasteofpower. Comparatively smart antennas radiate energy only in the desired direction. Therefore less power isrequiredforradiationatthebasestation.Reductionintransmittedpoweralsoimplies reduction in interference towards other users.

Reduction in handoffTo improve the capacity in a crowded cellular network, congested cells are further broken intomicrocellstoenableincreaseinthefrequencyreusefactor.Thisresultsinfrequent handoffs, as the cell size is smaller. Using smart antennas at the base station, there is no need to splitthecellssincethecapacityisincreasedbyusingindependentspotbeams.Therefore, handoffs occur rarely, only when two beams using the same frequency cross each other. Mitigation of multipath effectsSmart antennas can either reject multipath components as interference, thus mitigating its effects in terms of fading or it can use the multipath components and add them constructively to enhance system performance. ~ 8 ~ 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 devicerelativelyaccurately.Thisallowsnetworkproviderstooffernewservicestodevices. 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 directionsasina traditional omni-directional antenna. Thismeans thatifsomeone wished to intercepttransmissionstheywouldneedtobeatthesamelocationorbetweenthetwo communicating devices[6]. CompatibilitySmart antenna technology can be applied to various multiple access techniques such as TDMA,FDMA,andCDMA.Itiscompatiblewithalmostanymodulationmethodand bandwidth or frequency band. DISADVANTAGES OF SMART ANTENNAS 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 theyarefarmoreexpensivethantraditionalantennas.Howeverthiscostmustbeweighed 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 location which are optimal for a traditional antenna are not for a smart antenna. For example in a road context, smart antennas are better situated away from the road, unlike normal antennas which are best situated along the road[6]. ~ 9 ~ APPLICATIONS Smart antennas can be used for virtually any application that involves radio signals. They aremostcommonlyusedindomesticandcommercialwirelesscomputernetworks.Smart antennas also give remote controlled vehicles better range. As smart antennas have become more popularinrecentyears,televisionnetworksandradiobroadcastershaveslowlyincorporated them into their telecommunication systems. Additionally, smart antennas are used in RADAR and astronomy[5]. CONCLUSION Inconclusiontothisseminarreport,SmartAntenna systemsaretheantennaswith intelligence and the radiation pattern can be varied without being mechanically changed. With appropriateadaptivealgorithmssuchasRecursiveLeastSquareAlgorithm efficientbeam formingcanbeobtained.AsthesystemusesaDSPprocessorthesignalscanbeprocessed digitally and the performance is with a high data rate transmission and good reduction of mutual signalinterference. Smart antennasvastlyimprove the efficiency of wireless transmission and arelikelytobecomethestandardinuseforconnectionsbetweenwirelessdevices.Asthe technologybecomescheaperitislikelythatalldeviceswillutilisesmartantennas.This transitioncouldbecomparedtotheuseofhubsinwiredcomputernetworksandthere replacement with switching technology as the costs of implementation reduced[6]. REFERENCES [1] Salvatore Bellofiore, Constantine A. Balanis, Jeffrey Foutz and Andreas S. Spanias, Smart-Antenna systems for mobile communication networks [2] Smart Antenna, http://en.wikipedia.org/wiki/Smart_antenna [3] Smart Antennas- Beamforming, http://www.altera.com/end-markets/wireless/advanced- dsp/beamforming/wir-beamforming.html [4] Smart Antenna Systems, http://111.93.135.184/quality/TelecomBasics%5Csmart_ant.pdf [5] What is smart antenna?, http://www.tech-faq.com/what-is-a-smart-antenna.html [6] Smart Antennas http://robotification.com/2007/06/15/smart-antennas/ [7]SmartAntennaTechnology,http://etd.lib.fsu.edu/theses/available/etd-04092004-143712/unrestricted/Ch_4smartantennatechnology.pdf