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good afternoon this is Kyle Walsh with RCR wireless news thank you for attending interference hunting for improved quality of experience presented by rohde & schwarz our presenter today is Paul Dennis house key Application Engineer at Rodian Schwartz just a reminder that within 24 hours of this webinar we will provide you with a link to the on-demand version of today’s webinar during the webinar we encourage you to submit questions via the control panel which will then be answered towards the end of the presentation with that being said I’d like to turn the presentation over to Paul well thank you very much hello everyone my name is Paul Danis house Kiana and applications engineer for Orion Schwarz and I’ll be presenting today is interference hunting for improved quality of experience now obviously the first thing I’d like to talk about I’d like to define what Eve experienced quality of experience essentially is defined as the performance of a system as seen or perceived by the end users or customers now as our vers RF performance engineers or people involved in RF at a technical level we tend to think of radio frequency interference and quality of service in terms of statistics so things like our SSI signal to noise ratio bit error rates we tend to think of quality of service in terms of actual metrics KPIs that we can measure the reality is however that users are usually not particularly concerned with these type of metrics they’re interested in things such as voice quality or data throughput so it’s important for us to begin by understanding that users don’t necessarily see these parameters or don’t perceive them as something that’s important while we may be very concerned with what the noise floor is in a certain part of town this is not something that the users normally see and perceive now there are number of different parameters that are important that are related to quality of experience so I’d like to talk about each one of them briefly one is coverage of service availability this is essentially where you have coverage or where you’re able to use a wireless service a wireless service could be the best service in the world but if you’re unable to actually use that service it’s really not much for use to you there’s reliability of the system system availability this is how well the system works especially under adverse conditions as we go further through the presentation you’ll see that by adverse conditions what we really are referring mostly to is interference here and the last one is performance that is the actual throughput of data voice quality and other metrics like that and these tied together to build what the user perceives as quality of experience now what impacts quality of experience they’re basically three main areas that impact how a user sees quality of experience and these are services and applications devices and the network itself now the network is an easy part for most of us to understand the network is the infrastructure that provides the wireless services the service providers these would be of course base stations etc on the device side these are the user devices again in a cellular networking environment these would be phones uese user equipment and then services an application probably deserves a little bit more explanation these are the applications actually running on the device or on the phone and their interactions between all three of these for example it’s very clear to most people probably on this webinar the interaction between the device and the network does the phone talk to the network do they interoperate properly over different vendors different supplier choose that are involved in the communication between those two that will impact quality of experience likewise there’s an interaction between the network and the service and application there are some applications that may be very bandwidth intensive or they put special loads on the network and these have to be considered as well there’s also an interaction between the service and applications in the device and again this is how well the device runs certain applications or the impact that certain applications have on devices battery life would be a good example of this where all three of these areas come together is where we define quality of experience and to give you a practical example of this volte voice over LTE is an example of where all three of these components is very important in quality of experience for example if you want to have a volte call you’re going to need a network that can support volte that can do prioritization if necessary you need devices that can support it because not all devices are created equal and you also need services and applications running on the UE in this case the Bolton and Annie they can will not be equal all of these together will contribute into what we consider to be quality of experience this is very important for the user now for this presentation for this webinar we’re going to be concentrating mostly on the per devices and networks since again it’s people working in doing interference signing in an RF environment this is where we have the most opportunity to find improvements or to come back problems in the network so why is quality of experience important I would like to talk about again mostly from a cellular networking point of view but it can be applied to other ones as well why is quality of service important quality of service is basically the quality of experience rather is basically the prime differentiator in commercial networks in the days before for example LT we had different radio access technologies 3G you could have WCDMA you could have UMTS what we have now with a lot of people moving towards LTE or essentially everyone moving towards LTE is that

we’re essentially using the same radio access technology so what makes provider a or equipment vendor a better than provider equipment vendor B it’s going to be quality of experience these will affect how people make decisions about what’s a good and a bad network whether they’re happy with a service etc this also applies to non commercial networks for example for government military Public Safety applications what you’ll see is the quality of services vary or quality of experience is very important here as well and their two main factors that go into quality of experience again from an RF and interference funding level and that system or device design and resource planning’s as well as the RF environment and again our webinar today is going to focus mostly on the RF environment component so why is interference something important for quality of experience well interference affects quality of experience by degrading the RF environment of wireless systems a wireless system obviously that has to operate in a degraded environment will have a poor quality of experience normally speaking than one that has an ideal RF environment as all of you probably know spectrums are very expensive and very limited resource there’s only so much spectrum and there’s a limit to how much information can be pushed over a certain bandwidth with a certain noise for a certain signal-to-noise ratio and therefore it’s imperative that we use this spectrum efficiently resolving interferences generally I would say always but I’ll say generally here almost always more cost-effective than we if we try to increase performance there are some cases in which if you have poor coverage or you have interference issues you overcome by essentially more infrastructure more towers bigger antennas more gain etc however there are many cases in which interference is at such a level or so severe that no amount of infrastructure changes can overcome it and in this case there will be a definite negative impact the quality of experience if interference is in fact present now LTE I’d like to talk about because LTE is really raised the bar for interference and the levels of interference that are tolerable many of you may have worked on older 2 or 3G cellular networks this also applies to older analog radio networks if you’re in a public safety role for example and have used analog trunking radios versus something digital like P 25 LT has raised the bar for interference because first of all it’s become very widely deployed LTE is being used by network operators it’s being used by military government Public Safety etc and it’s become a worldwide standard you have to assume that you can have LTE access for radios all over the world and it’s rapidly becoming that way in pretty much every place that you would visit the downside to LTE is of course that it requires a much cleaner RF environment compared to 2 and 3G technologies that were more robust in the face of interference LTE has a much lower tolerance if you will for interference because again LTE in order to provide the higher speeds higher data rates put shorter round-trip times it requires a much cleaner RF environment so interferes that might have been and not have been an issue for older and cellular networks are now a much bigger issue for LTE in other words we have interference at levels that might not have bothered us in previous technologies there are other aspects the LTE that are also important for example use of remote radio heads and doing interference hunting prior to the use of remote radio heads one could often go to the e note B or rather the space station and plug into the RF sniff report and actually look at the spectrum as seen by the antennas mounted on the top of a tall tower with gain unfortunately with a remote radio head which is at the top of the tower and which feeds the rest of the network through a fiber optic cable we no longer have that access to the RF we can no longer see the RF at the power saw and what this often forces us to do is to drive the area we can no longer say what does this look like we have to actually go out in the field in the area that’s being covered by that cell or by that sector and drive the area there’s also some challenges with regards to the next version of LTE LTE advanced one of the big characteristics of which is carrier aggregation we’re going to see spectrum being used and chunks or blocks that are aggregated together to provide higher throughput and what this means is that interference can affect our overall throughput even though maybe they may be located in different frequency ranges different aggregated carriers so what are common sources of interference one of the things that I enjoy the most about interference hunting is it’s the variety of devices that can cause interference anyone who’s done interference hunting for a long period of time knows that there’s almost an endless supply of devices that will cause interference but there are several common causes of interference I’d like to mention the first one the most important one I think is other wireless services the sad truth is that in many cases it’s one wireless service interfering with another not usually intentionally but these kind of things do in fact happen their basic sort of RF characteristics or phenomenon such as harmonics and inner modulation these are our common sources of interference especially when you have high powered transmitters or transmitters in close physical proximity faulty or misconfigured repeaters and amplifiers this is the bi-directional amplifier which has caused many problems in cellular networks or other types of amplifiers that misbehavior can cause huge increases in the noise floor over many tens of megahertz or it can cause

signals that drift or wander over a certain frequency range and therefore can be very difficult to locate or analyze this emissions is any radiation from an electronic device it’s not intentional almost all electronics generate some radio frequency signals at certain frequencies this would be the classic case of a plasma TV for example which generates signals that interfere with a cellular uplink one of the things that’s also come up recently in terms of spurious emissions is lighting ballast there’s certain fluorescent lighting balance unfortunately that generate unacceptable levels of RF noise at frequencies used by many network providers one very interesting and I think perhaps underestimated source of egress or source of interference has been cable leakage or egress cable television systems as you probably know use the same frequencies that cellular providers use for 700 megahertz and what that’s meant is that signals that egress or leak from acid I cable TV system can cause problems to cellular networks this is not an issue before because there was very little frequency overlap between the systems and also because again the slower and lower order modulation of previous cellular systems was more immune to this type of interference you can also have unlicensed wrong band operations it’s always amazing to me how many will transmit on frequencies that don’t belong to them this does continue to go on and Alaska jammers or malicious interference there is of course though uh of people out there who have jammers or other devices intentionally disrupting communications and these obviously are a pretty severe source of interference because they’re intended to interfere so there are two steps and interference hunting the first step in interference hunting is identifying that interference as present at all and then trying to identify what that interference looks like this is normally done by actually viewing the spectrum itself the next step is of course finding the interference we need to know where the interference is coming from that is which direction which bearing is we’ll talk about and also what kind of device is generating the interference identifying interferences obviously the first step in this you might have to know that interference is happening that the problem is external for example of the system you it’s helpful to know what the interference looks like but that by itself is not sufficient in order to successfully hunt and resolve interference you have to physically find the source you have to be able to actually put your finger on it and pull the plug so to speak it’s usually not sufficient to say it’s somewhere within this building you actually have to say it’s coming from this particular box now the size the shape the location the behavior the interference can give you strong hints as to it so it’s an example here on this slide you’ll see a picture of cable television egress cable television egress as I mentioned the previous slide is one cable television signals leaked into the over-the-air environment and the good news is it’s very easy to recognize if you look at this slide you’ll see these six megahertz wide qualm haystacks and they’re pretty regularly spaced and you can see that they have but they’re always on and they are very very unique in terms of their spectral pattern if you were to have an interferer for example in your uplink band and you saw this this would be a huge hint as to what you have to look for because obviously there are a limited number of devices from which cable signals can escape so if you see that say interfere looks like what you see here on the screen shot you can limit your interference hunting activities of things like cables amplifiers repeaters pedestals and not worry so much about LCD billboards or other such devices I’d like to talk about interference hunting tools I mean one of the things that’s important about to understand about RF is it’s something that we cannot have human beings normally sense without instruments so in order to do interference you will need some kind of instruments that can sense RF and give you information about it there’s several specialized tools that are used in interference hunting one of them is spectrum analyzers or monitoring receivers I’ll talk about the difference between those in a minute directional antennas is an extremely important component interference hunting it be very difficult to do interference hunting without a directional antenna there’s also direction-finding systems these are systems that allow you to locate and interfere by simply giving it the frequency and perhaps some other parameters of the interfere and knowledge bases one thing that I think is underestimated in terms of tools or resources for people doing interference hunting is the vast body of knowledge that already exists in terms of interferes what they look like where they are and how to resolve them another very important aspect in terms of interference hunting is having a good practical knowledge of certain things RF in general is very important but propagation I think is key knowing how signals travel how they can get into or out of structures or out of enclosures is very important being aware of what’s where inspect from the allocations what kind of signals might use the 800 megahertz this is very important as well and also methodologies as just like all other technologies as interference hunting has evolved over time some methodologies that may have worked for older technologies no longer work and their continual advancements in the field as well see there are new methodologies and new tools coming out and these are things that can be very helpful in resolving interference let me talk for a moment but spectrum analyzers versus monitoring receivers there is a difference between them it’s often very difficult to tell what they are by looking at them the spectrum analyzer is probably the tool that many of you are familiar with it’s based on the heterodyne or swept architecture slipt principle if you have a device that has

a sweep time then that is a heterodyne based instrument essentially it sweeps a small window a resolution bandwidth if you will across an area of spectrum and it displays what that spectrum looks like this is the traditional way of doing it it works very well makes very precise measurements there are some limitations and using spectrum analyzers for doing interference hunting generally they tend to be much slower than a monitoring receiver and they may have or rather they may not have certain features that you may find in a dedicated monitoring receiver on the other hand spectrum analyzers also tend to be general-purpose pieces of equipment so they can be applied in a wide range of applicants there now as interference has grown in importance you’ve also seen the development of new tools called monitoring receivers these are not the traditional heterodyne swept receivers or instruments that you may be used to these are actually based on an FFT architecture where they take a block of spectrum digitize it do a Fourier transform and then output the results this means that they’re very very fast and as we’ll see in a few later slides speed is very important at interference hunting for a variety of reasons and typically these are single purpose instruments whereas a spectrum analyzer may be applied for many different tasks monitoring receivers tend to be purposed based and designed for interference hunting and spectral monitoring I’d like to talk and spend a little bit time on this slide because I think it’s an important slide is the importance of speed and interference hunting I’m often asked by people why is speed important an interference hunting and I think there are some misconceptions about this obviously if you’re looking for a bursty or intermittent signal one is very short duration very very quick pulses then you would need a very fast instrument in order to be able to see that signal that however is typically not a large source of interference and most networks if signal is on the only on really on in the air for say 10 milliseconds every not on the air long enough to be an interference I mean interfere why then is speed important and interference hunting especially if we’re looking at for example a CW a continuous wave interfere something that’s on the air all the time in this case as well speed is very important the reason the speed is important in interference hunting is essentially twofold one is that the faster an instrument response to signals the more quickly you can move past that signal and not miss it and let me give an example of what I mean by this the example of LTE the lower layer and lower level interferes which means we can’t see it very well we may not have access to the actual antenna system to be able to see it the way the tower sees it so essentially forced to drive the area now this is a low level interfere and we’re driving the area at a reasonable speed of a speed say 30 40 50 miles an hour and we pass by it a slower instrument may not be able to see that interfere at all so this would require us to either a read rive the area in hopes that we hit it the next time or drive much more slowly perhaps at an unnaturally slow rate in the hopes that we’ll pass by the interfere the other way that speed is important in interference hunting is the so what I will call the last 100 yards dilemma usually what will happen is you will be able to get down to an area of maybe 100 yards or so and then have to manually sweep the area with a handheld antenna again if the instrument responds quickly then you’ll get an indication with the instrument say for example an audible tone or you’ll see a change in level on the display as soon as that antennas pointed at the device that’s generating the interference on the other hand with a slower instrument you will have trouble doing this because you’ll have to move the antenna much more slowly and as anyone who’s done interference hunting knows time is essentially money and interference hunting as well you need to be able to resolve the interfere as quickly as possible now I’d like to talk about directional antennas I’d people asked me if it’s possible to do interference hunting without a directional antenna and my answer quite frankly is no it’s really a very very important component of interference hunting there are two general types of antennas that are used handheld antennas that are used in interference hunting Yogi’s and what I’m going to call generically wideband antennas yagi antenna there’s a picture here on this slide they generally have very good directionality they have a very tight beam which if you you point it towards the source of interference you get a much stronger response than if it’s pointed away and then the gain is relative to the number of elements that it has in it and these antennas work for very well they tend to be very low cost and again good directionality and good gain but that comes as everything does with the cost essentially most yagi antennas are what I like to refer to as deaf outside of their specified frequency range so a yagi antenna that’s tuned for example for 850 megahertz may work reasonably well at 800 and 900 megahertz but probably doesn’t work very well at all at 700 or a gig and is almost completely deaf when you get to say 400 megahertz this is the drawback of using band matched antennas that if you’re in the band of operation they work very very well once you get outside of that band they were less well why is this important well interference issues are often multi band for example harmonics the harmonic of course is a whole number multiple in frequency of a certain fundamental signal I may see an interfere at say 800 megahertz that’s actually the fourth harmonic of a signal at 200 megahertz and of course the 200 megahertz signal will be stronger and will be easier to do direction find your locating on because it’s higher

amplitude if I have an antenna that’s only tuned for 800 and I try to look for something at 200 that’s problematic because I have the quote/unquote wrong antenna likewise you’ll see some amplifiers bi-directional amplifiers used in cellular systems often maybe multi band so you may have an amplifier that’s causing wide raises at both 850 and 1900 spurious emissions also can occur at a wide range of frequencies and there are wideband noise sources jammers are an excellent example of a very wideband noise source that may extend over several hundred megahertz another aspect is spectral reforming at 700 megahertz exists because UHF TV channels were vacated from that frequency range and we’re going to see more of this as time goes on this means that you have to be prepared as an interference hunter to look at various frequencies different frequency bands possibly separated by many tens or hundreds of megahertz antenna per band at that point becomes cumbersome and problematic if you have to support seven or eight bands it’s really not practical to bring with you seven or eight yagi antennas in the field now there are tenets that are wideband antennas there’s a picture of one here these often work on different physical designs for example a long periodic versus a yagi antenna wide band or multi band antennas allow operation generally of a much wider frequency range now again there is a drawback to a wider frequency range in that their beam width tends to be wider they’re not as laser focused so the yagi antenna might be but again the trade-off is that it requires you to only bring one antenna with you instead of five six the situation will determine which antenna combination is most appropriate for a given task now with regards to direction finding there’s two major steps in radio location or correction finding and what I will call the geographic part in the local park the geographic part is where you essentially drive around typically and try to get within let’s say a hundred yards maybe 50 yards of the interfering source so you want to have a general idea it’s coming from this building it’s coming from this set of apartment it’s coming from this set of acute ility poles and then there’s a local part where you actually have to go and figure out exactly what point down to the inch down to the device that’s generating the interference and these require different approaches typically for usually in the geographic approach you drive an area looking for issues and you’ll take bearings you’ll say I think the interfere is that way or this way it has a bearing as a direction that it’s located in and these bearings of directions can be German Daz will see manually or in an automated method then there’s the local park where you actually walk the area holding a handheld directional antenna and sweep the area looking for the device or the point of what you see the maximum level of the interfere and hopefully that’s the device that you’re looking for now there’s two methods of getting bearings I mentioned before that the geographic part involves taking bearings there’s two methods of doing this one is the manual method and one is the automatic mintage so the manual method of taking bearing essentially the operator you are holding a directional antenna this is a yoggi maybe this is a wideband depending on what you’re doing and you move the antenna around until you get the maximum signal level that’s typically the way that it’s done a bearing will in this way will then be plotted or saved and used in triangulation there’s also an automatic method of getting bearings where you have an instrument a system that you input a frequency in it automatically based on characteristics of the incoming signal it automatically computes the bearing line and then plots a line towards where the source of the signal or plots align towards the source of the signal and I’ll talk a little bit more about these in the next few slides now a bearing by itself a single bearing is useful in the sense that it points you in the right direction but it also has a limitation that it only tells you the direction it doesn’t tell you how far away the interfere is I’m guessing many people on this call of hand the experience that they do interference hunting of knowing that the interfere is in a certain direction and driving and driving and driving and driving and finding out that it’s ten or fifteen miles away this is what we would like to avoid and one way that we can avoid this is by taking multiple bearings ideally what you would do in this bearing based method of Direction finding of geographic Direction finding is you go to a location and take aberrant you say that the transmitter is in this certain direction then you go to some other location ideally like to try to get around where you think the interfere is take another bearing and he continued to take a certain number of bearings and hope that these cross in one location and this would be triangulation typically you need at least two or three lines to do triangulation more is better up to a certain point but there are some limitations on the triangulation approach in terms of taking bearings first of all the quality of your triangulation the point that’s calculated to be the likely source of the emitter that point accuracy is going to be based on the accuracy of the bearings that you take if you take very good bearings you should have a very good translation point less accurate bearings a left accurate triangulation point and again one way that you can overcome this is by taking a large number of bearings and discarding what I will call Flyers bearings that obviously make no sense at all sometimes you’ll get in a position you’ll take a bearing and it’s pointing completely in the opposite direction from all the other bearings and this is where the certain amount of experience and human intelligence is required this would work very well and would lead us to a large number of interfering sources with one exception and that’s the problem with multipath multipath as the name implies is where a signal takes

multiple paths to get from transmitter to receiver for example many of you may have sat in traffic at a traffic light lifting listening to an FM radio station that sounds a little bit not so good and you move the car and forward a few inches and it clears up why it’s multipath you’ve moved far enough that you’ve cancelled out the effect of receiving this radio signal from multiple directions with slightly different time delays now multipath is a fairly substantial issue for interference hunting in urban areas because in urban areas where you have lots of buildings or other structures which will reflect radio frequency signals you’ll receive the signal from multiple directions and therefore it’s very difficult to know which direction the transmitter is actually located in multipath is a problem for both manual and automatic bearing based direction finding the good news is of course the multipath although it’s makes your life much more difficult in terms of direction finding doesn’t really impact your ability to do analysis of signals if you want to know what does the interference look like what is the level of the interference what are the particular spectral characteristics the bandwidth with the interference multipath will not affect us at all but for Direction finding this can vastly complicate our lives and that’s why it’s imperative that we find ways to deal with multipath so for doing fixed location bearings and by fixed location and bearings I mean for example standing in a location and moving our antenna or putting a system in a certain location having it getting bearing it is fixed location bearings how do we minimize the effects of multipath the best way to do this is by carefully choosing your bearing locations you don’t want to choose a location to take a bearing that say between two tractor trailers because I can tell you exactly where your bearing will come from it will come from the gap between the two tractor trailers what you want is location that minimize the effects of multipath and in urban or semi urban environments these locations are typically away from obstructions obstructions being building the vehicles etc they’re away from metallic structures again vehicles I don’t underestimate the ability of vehicles or other metallic structures to reflect radio frequency energy another very common metallic structure that most people don’t see as metallic are tinted windows which are tinted by having very small fragments of metal embedded in them so these axes again is giant pieces of metal from a radio and generally speaking Haier is always better if you’re in urban area getting on the roof is an excellent solution if you’re trying to take bearings you may or may not have access to the roofs of the buildings that you want to be on parking garages are an excellent way to do this as well unfortunately despite all this in many cases you may not have access to a good bearing location you may not have access to rooftops or buildings the geography of the area may be prohibitive so it’s not always possible to overcome these challenges when you’re doing fix two bearings so one solution that people have is to do vehicle based bearings they will drive around and take bearings volley motion and I we teach an interference ending classic Rodian Schwartz and one piece of advice I give my students is don’t drive around and stick the antenna out the window and try to get a decent bearing and of course I do that myself and everyone else does that because frankly there’s not much of a better solution when you’re trying to do vehicle based bearings with a handheld antenna driving around with a yogi or other antenna on top of the roof as in this picture or pointed out of the window is really not a great solution one of the problems you have is these antennas are of course highly directional so if I’m driving down the street and pointing my antenna out of the passenger side and the interferer is actually on the driver’s side I’m going to run into some issues because the null make it unable for me to feed the interfere even though I may have driven almost directly past it there are also safety issues it’s generally not a good idea to be trying to drive and hold a directional antenna out of the window and manipulate an instrument and look at it all at the same time so again not an optimal solution in many cases and as I mentioned before vehicles are one of the things that can reflect radio signals they will attenuate radio signals so in vehicle based bearings when you’re driving around with that directional antenna you often have to stop exit move away from the vehicle because again the vehicle will act as a large reflector of radio frequency energy to get an accurate bearing and now you’re back to the same fixed a bearing location issue you have before so what do we do about all this there are a number of ways that we can overcome path and multipath based bearing issues one methodology that we’ve already kind of alluded to an a manual method is it take lots of bearings if I go to many good or reasonably good bearing locations and I take bearings to try to locate the source of the interference then I I’m kind of rough triangulation the problem is that in many environments for example in urban areas you may not hear almost from any locations so you may have the vast majority of your bearings being Flyers also because if we do this with a manual bearing methodology where we’re actually moving the antenna and looking at our instrument or listening to a tone in order to figure out the source of the signal we introduce a certain amount of human error and this is a problem as well now what we can do is we can use an automatic direction-finding system preferably one that’s relatively immune to multipath and take very large number of bearings I don’t know anyone who does interference coming who would take three or four thousand bearings on a certain transmitter that’s impractical for a number of reasons but this is not a

problem for a automated system take many many bearings keep in mind that example of sitting at a stop light and creeping the car forward to get better FM radio reception that every time we move even a very small distance we changed the multipath parameters we change the multipath profile if you will so that we actually get a different set of multipath parameters different impairments at every different location that we’re at if we could somehow take very large numbers of bearings and then put them through a mathematical algorithm we could subtract out to a large extent the effect of multipath that’s again a map would get very cluttered with three or four thousand bearings on it at a time so often the way that systems like this work are by plotting what I would call for one of a better word probability clouds so we can anticipate statistically and based on probability and mathematical algorithms the probable location of the emitter and then assuming we have enough data and we have enough confidence that data such a system would also allow us to locate the transmitter again by taking extremely large and by extremely large I mean on the order of thousands and tens of thousands of bearings unique bearings and then run those through an algorithm in real time and plot the result now excuse me how would we implement this type of system well to ensure that we have a large number of unique bearings as I mentioned before you need to do something where the vehicle or the system is in motion it makes no sense at all to sit in one location take 3,000 identical bearings so any kind of system that would do this again the same way that a human would do it with a handheld antenna by picking different locations is by moving around if you move to different locations each bearing you have will have different multipath characteristics and therefore you’ll be able to locate a transmitter more reliably because you have a larger body of days again to take bearings in an automatic versus a manual method you need some kind of antenna or methodology that can look at the incoming signal and make a determination of its bearing based solely on the characteristics of the incoming signal now there different radio finding methodologies that do this one for example would be correlative interferometry that’s a system in which the phase of the incoming signals compare two different antennas there are other systems you may have heard of Doppler systems etc but generally correlative interferometry has been used in most attempts to overcome multipath simply because of the large number of antennas that are in an interferometer will tend to cancel out some multipath issues and this allows for a smaller more portable factor well there are systems for example that use these methodologies these systems can become prohibitively large physically to large amount on a vehicle so again there’s a bit of a compromise involved in terms of trying to have a system that’s small enough to be practical but also still has adequate results and what’s really important I think especially with regards to LTE if you go back to the slide where I originally mention the different types of interferes we don’t really know what kind of interferes we’ll be dealing with for example we may have narrowband interfere and interferes we may have interferes that are noise like for example jammers or oscillating amplifiers we may have interferes that are constant signals we have interferes that are bursty your nutriment signals so ideally we need a system that’s able to deal with all of these different types of signals calculate the same parameters based on any type of signal and then yield results now one thing that I think is continually underestimated in terms of interference hunting is the importance of knowledge bases and knowledge sharing and I’d like to explain what I mean by that one of the things that we’ve seen over and over again is that interference problems tend to reoccur you tend to see if you’ve done interference hunting for a number of years the same kinds of things happen again and again I’ve been asked sometimes when I’m out in the field how do you know that it’s this and I tell them well I’ve seen it before that works great if you have seen it before it’s not so good if it’s your first time seeing it so one of the things that I highly encourage all of the people that I work with in anyone involved in interference hunting is to share knowledge to develop knowledge bases interference hunting knowledge is not something that’s necessarily confined confined to a certain organization or to a certain market segment as an excellent cable egress again previously cable systems and wireless communication systems did not have significant overlap in terms of frequency and so these groups never had to work with each other now that you have issues with cable egress you have a need to share information about what kind of devices cause leakage what does this leakage look like what are acceptable not acceptable not simply between companies doing the same kinds of things but between different companies documentation is very critical in the terms of resolving interference if you have known interference sources for example if you have pictures or screenshots I often have customers of mine send me pictures and say you know what this is this could be very helpful to have a reference library of them one thing that’s often useful interference hunting is audio demodulation being able to actually listen to signals that may be audio demodulated because again after a while you tend to hear the same types of signals and go oh I know what that is I’ve seen or heard this before one other thing that’s important especially in our

rapidly changing wireless environment is a need to have a knowledge of what should be in a certain frequency range I’ve had many issues I’ve seen for example at 1800 megahertz that were harmonics of devices that were down at 900 megahertz in the I FM bam so knowing what frequencies normally have what kind of signals and also knowing the harmonics very quickly being able to very quickly do the math and figure out what a harmonics of a signal it’s often a very useful tool in troubleshooting interference issues and again you really want this information to be accessible wherever and whenever you are running back to the office to look something up is usually not an optimal way of doing things so ideally what you would want to do is have some way of carrying this information in the field with you and if there’s anything I can recommend is that set up some system for sharing information about interference between different groups or individuals because I guarantee that it’s the rare issue that only comes up one time I’d like to give an example here just briefly how this knowledge base will be useful on the previous slide I showed a screenshot of a bi-directional amplifier this is from our interference hunting app that we have for mobile phones that is a reference app and I was recently I probably shouldn’t say where I was but I was recently in a location where I saw the screenshot that you see here on the left a very broad noise like signal it’s about 35 megahertz wide and it’s negative 77 DBM which is horrific and I looked at the signal with a customer that I was with and I said that’s a PDA and they said how do you know and of course I told them well I’ve seen it before and at this point I pulled out my screenshots I said see doesn’t it look exactly like this and you looked at it agreed that it was now why is this useful well it’s useful because if you know something about bi-directional amplifiers or done with this or sharing your knowledge properly you know that typically these systems involve two antennas a donor antenna on the outside of the building and another intent on the inside so the signals picked up amplified and then put into the building and then vice versa well once I saw the screenshot I knew immediately what I was looking for most likely I was looking for a small yagi mounted on the corner of a building and pointed at the nearest space station and as you can see from the picture here on the right that’s exactly what we found so having this knowledge base being able to look at spectrum reviewable to compare spectrum to known issues can give you a huge hint as to what you’re looking for and greatly accelerate your interference hunting activities so in summary what I’d like to mention again at reiterate is that rapid detection location and resolution of interference issues is a critical component in delivering quality of experience again customers don’t know and typically don’t care about things like our SSI or signal to noise or noise for things like that what they’re interested in is how does their phone work how does their radio work how does their data communication system work and Wireless used to be if you went back maybe 10 20 years a nice to have it’s wireless and now become a must-have in many cases so any disruption to a wireless system any degradation of a wireless system isn’t really irritating it can be essentially interfering with a mission critical application likewise as we see a LT is a prime example of this the types of interference that we’re seeing and the levels of it of interfering signals that actually caused problems is changing LTE again has been raising the bar on interference and this means that we typically need faster instruments we need different types of systems and we also need new methodologies in order to keep pace with these and be able to deliver the quality of experience that customers or users expect from the system and again the last point again which I really can’t stress enough is that the ability to share and leverage interference on experience is absolutely critical we’ll usually they’re people within your organization or across organizations who have seen what you’ve seen before know what kind of device is generated know how to resolve it so I could give you a huge list of times and that I’ve been out interference humming Athena’s signal said hey I wonder if someone else has seen this run it by my colleagues and have them say yes you’re looking for a XYZ brand device and it greatly simplifies and greatly improves the efficiency of any interference hunting activity that you’re involved on so that brings us to the end of the slide presentation if you have questions or comments you’ll see my contact information below and I believe at this point we’re going to turn it open to questions thanks Paul yeah we we’ve had a few questions come in during the webinar and once again we do encourage you to submit those questions you can submit them right here and we’ll try and get to them today and any others who we can follow up after the webinar the first question that we had come in today was what will be the impact of small cells on the nature of interference humming that’s a really good question small cells of courses where we try to actually reduce the size of cells these may be femtocells he’s bet you install in your house they may be smaller size cells that are used indoors the basic fundamentals of interference hunting remain unchanged you’ll still need to use the same tools and methodologies for small cells you would use for larger macro cells my personal feeling from what I’ve seen so far with small cells is that of course a smaller cells as they’re more distributed brings up the possibility of having more localized sources of interference a very weak interfere that might not have expect a macro sized cell

a normal sized cell if it’s in close proximity to a small cell will obviously cause greater interference issues there are other issues of course involved in terms of dimensioning a network planning but in terms of sheer interference hunting small cells the approach for doing interference hunting is really not that much different for large cells great one other question we had are is what are the major sources of interference impacting le LTE today and what about with LTE advanced how does that differ well LT I’ll take the second part first LTE advanced and lt are essentially the same thing and in many regards from interviewing interference sending point of view LTE advanced the main thing that you’ll see differently is carrier aggregation the downlink signal etc and the uplink signals are essentially the same carrier it’s a released ten feature in LTE and what this really means is that you’re will have different bandwidth segments different carriers being bonded together being aggregated together and therefore if you have an overall drop in throughput or system performance it could be due to interferes any one of those component carriers that make up your carrier aggregated LTE now in terms of the major interference sources for LTE from my own experience doing field work I would say the major interferes it depends on the frequency band most of the LTE in United States is currently at seven huh but you’ll see at 700 megahertz again in my experience I’ve been cable egress surprisingly so to me but it’s been a very big issue in many places you also see issues with bi-directional amplifiers that old and then there because 700 megahertz was used for other things before LT was deployed there there believe it or not years later still are many people using devices and that frequency range that should have left it long ago wireless microphones is an excellent example of this and here’s a case where audio demodulation is very important I tell people if you see a narrowband interfere always try to demodulate it because if it is audio and you are able to listen to it gives you an enormous clue as to what the source of the interfere will be other questions all right yep one more coming in is how well do direction-finding tools work on the wideband interferes direction for any tools to work well there’s two kinds of direction-finding tools one of course is the manual – hand-held antenna the directional antenna and that in that case doesn’t really matter too much if it’s wide band or narrow band now for automatic direction-finding systems there various technologies that are used for automatic direction-finding systems some of the ones that you may be familiar with or for example dapper watson-watt timed Toa time difference of arrival correlative interferometry etc these different technologies handle different types of signals differently for example doppler bae systems the old doppler DF tape systems work reasonably well for a narrowband FM modulated CW types signal they don’t work at all for wideband or noise like signals on the other hand other systems for example like correlative interferometry work on wideband signals as well because they’re only measuring phase differences so it really depends strongly on the interference type or the type of signal you’re looking at for handhelds not so much of a difference for automatic direction-finding system the type of signal that you’re looking for one other question can you explain why measurement speed is important when looking at bursty signals well as I mentioned before there’s in my mind a little bit of a misconception about measurement speed obviously if you’re looking at a bursty signal say that you’re looking at a frequency hopping signal or a signal very short duration if you have an instrument that’s not fast enough to see it then you won’t see it and that’s obviously the big problems for bursty signals measurement speed is absolutely critical and if you’re in a military or government or signals intelligence of type application where you’re trying to pick up signals that don’t necessarily want to be picked up then obviously here you would need an instrument that’s fast and has that kind of speed now for bursty signals that are interfering signals there may be short signals again speed is important because you have a limited window in which you can see it especially if you’re in motion very few of us have the leisure of seeing in our office and rotating an antenna and finding an interferer typically we have to be out in the field moving around often in a vehicle maybe moving in a tent or rapidly and we’d like a system that responds to that signal as quickly as possible so this is the other aspect of speed that you can see short duration signals but again that it also will respond quickly to signals that may only be visible for a short period of time even though in some cases those signals may be continuous wave type signals this next question seems to be somewhat related to the last one so when you find a signal outside and it happens to be inside a huge building is there tools or processes to find a signal within a huge building yes the first the solution is to get inside of the huge building so I’m actually very surprised at the timber I mean that only half jokingly I’m always surprised of the number of people who will let strange people holding directional antennas and equipment walk into their buildings and walk around with them I very rarely been denied entry into a building when I’ve been doing interference hunting and usually that was for a good reason there if you have an instrument that’s sufficiently sensitive and that is a sufficiently

advanced often you can actually walk around the building and have a very good idea of where the signals coming from inside the building I was recently doing some interference setting where we had signals coming from a large building what it was a health club and I could actually walk around the building with my instrument and say it’s coming from the second floor the back left corner of this building again using a suitably directional antenna and carefully looking at the levels on my instrument and sure enough it was a lighting ballast that was being used in a basketball court in that part of the building so often you can narrow it down to a certain point in the building even from outside the building if you have a sufficiently sensitive instrument but ultimately nothing replaces being able to actually access the building and walk around inside of it and if you’re a wireless operator for example you typically can use your badge people know who you are and can access the building and look around and again of the worst case scenarios and sometimes you have to involve the FCC in order to get access to the building but being able to narrow it down to a certain area of the building is very helpful it’s also very helpful to be able to explain the people who are in charge of that building or maybe limiting access to that building what your needs are I often find it very helpful to approach a person and show them exactly what we’re doing spend the time 10 15 minutes to show them what I’m looking for on my instrument and then actually most of them take an interest in it and will actually go around with you because they’re just curious as to how this actually works so again the best way is access to the building although if you have a sufficiently sensitive instrument you should be able to determine a rough location even from outside of the building great what is the benefit of a leftie based architecture sorry well FFT based architecture has had a couple of different benefits one benefit is speed that’s the biggest benefit anyone who’s ever seen an FFT and ahead of a dine based instrument placed side by side with identical parameters usually the reaction is Wow because again F of T is a next-generation architecture of fuel it’s something that’s substantial step up in terms of sophistication from a swept analyzer and it’s much much faster many people never seen one before are frankly amazed at how quickly they operate and how well they work fft based analyzers also have some advantages in terms of immunity to overload because again of the architecture the whole load is not being applied to the front end and they also tend in my opinion and I use both spectrum analyzers and FFT based analyzers they can it be easier to use if you’ve used a traditional spectrum analyzer you know that you have issues with what is the correct resolution bandwidth and choose what is correct video that’s right the sweep time etc etc in FFT based in texture doesn’t have a sweep time it doesn’t have a strictly speaking a resolution bandwidth so in that case I think that there are two advantages really in FFT is one is of course speed and that’s the big one but the other one is ease of operation especially for someone who has not already been using a spectrum analyzer and it’s coming fresh to this so many people our next question all right for say the hobbyists or the non CRO are there any good interference hunting or mapping smartphone apps out there that you’re familiar with I’m sorry play the first part of it again so for like a hobbyist or non Pro are there any interference hunting mapping smartphone apps well interference something mapping by itself there plenty of maps where you can map all kinds of things at all kinds of markers for the hobbyist I’m an amateur radio operator myself have been for 20 years so ultimately you the trick is not so much the mapping application because again there are lots of free applications for mapping the trick is having it advice that can actually sense the interference and give you a meaningful readings so that you can actually go around and make measurements what I actually have found it’s interesting is I have encountered several people trying to use hobbyist type devices to do serious interference hunting and that has never really ended well and that has efficient horsepower to do it now in the hobbyist side could you do it depends on the signal type of what have you it’s not so much the mapping is making sure that you have a receiver that’s suitably sensitive and suitably fast for finding the kind of interfere or the kind of signal that you’re looking for yep we have another one coming in does Rorion Schwartz offer a portable monitoring receiver yes we do but I would say if you’re interested in that to take flying or visit our website we’d be happy to talk about about that later okay another one coming in is what does BDA mean aha PD I’m sorry that’s my fault B D is a bi-directional amplifier you may hear these refer the FCC for a reason I’m not completely sure about very unscientifically refers to them as signal boosters if you go to the FCC website they call them signal boosters and say that you live in an area where you have poor cellphone reception or you learn a structure say a concrete building where you have poor cellphone reception one Willie that you can improve your reception is by having a BDA a bi-directional amplifier in other words you have an outside antenna a donor in town that picks up the signals from the base station amplifies them this is the amplifier part of it and and it injects those signals into the building so your phone actually gets a higher gets more bars essentially on the return path it picks up the uplink signals from your phone amplifies them and transmits them back to the base station again usually using a small externally mounted yagi antenna and this is the bi-directional part it amplifies both the signals going to the downlink

and the signals going in the uplink and if these are installed properly they work very well as a matter of fact the wireless network operators will install them current law allows people also to buy their own Wilson’s there’s other brands and install them themselves the problem that you have typically with bi-directional amplifiers is when they’re installed improperly if there’s insufficient separation between the two antennas you can have a situation in which the signal oscillates that picture I showed on one of the slides of the you sort of birthday cake looking hump this is a perfect example of an oscillating BDA and the problem is of course once it starts oscillating it raises the noise for so high in the uplink that the tower can no longer hear the phones at all anymore and this is one of the top issues I’ve seen I hardly a week goes by where I don’t see a malfunctioning BDA and you will see them in a variety of places people put them on buildings people put them on homes we see them on boats where people think they can improve their cellular coverage by having one on a boat and unless you have a very large boat it’s hard to get that at the sufficient antenna separation between them so that’s what PDAs are and that is one of the big issues that we see an interference honey okay great well I think that about does it for time I want to thank Paul Dennis house key from rohde & schwarz is any closing comments you want to make before we close this out no except that I think that interference hunting is time design is becoming a more and more important aspect RF performance engineering and RF engineering in general and frankly I think that if you get involved in interference hunting and take the time to learn about the different types of interferes and RF and the instruments and tools that it actually can be very enjoyable I think one of the best parts of my job is actually going out and doing interference in the field alright thank you Paul and thank you to our attendees in just a reminder within 24 hours we will get a none demand version of this webinar for you for your reference and if you have any questions just follow up with us and we thank you for attending thank you everyone

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