Showing posts with label Survey. Show all posts
Showing posts with label Survey. Show all posts

Thursday, 7 September 2017

Ekahau’s “Game Changer”: Your New Survey BFF

The phrase “game changer” is banded around a great deal by our good friends in sales and marketing. It seems to accompany  just about every new product or service that they may introduce. Being a techie (and a rather reserved Brit), I’m not one for throwing around such emotional, bombastic language lightly. But after having been given early access to a new product from Ekahau, I’m going to say it: yes…this is a “game changer”. Read on to find out why…


(Download a PDF of this article here)

Background

If you’re a current user of Ekahau Site Survey (or any wireless survey product come to think of it), you’ll be familiar with the ritual of assembling your survey dongle collection each time you need to perform a wireless survey.

To correctly survey, you’ll need at least two dongles gathering Wi-Fi RF data (one per band), together with one or two spectrum analysis dongles scanning both bands of the Wi-Fi spectrum.

In most cases, all of the dongles are invariably connected to USB ports of your survey laptop or tablet. But hold on…does your laptop even have that many USB ports..? No? Ah…so you’ll need a USB hub to ensure you have enough USB ports. Hmmmm…but how do you carry a USB hub festooned with adapters AND your laptop during the survey…? Well, we’re all highly skilled engineers - we can fashion something with a Velcro fixing, or maybe some carefully crafted wire twists, or even buy a cleverly designed hub holder.


Whatever your survey multi-dongle solution, it’s likely to end up looking something like this:

Figure 1 - Say goodbye to your dongle forest?

Ok, so we’ve cleverly managed to attach our survey-dongle paraphernalia to our laptop and we’re ready to survey! However, we’d better not hang around whilst doing our survey. All of those power-hungry  USB devices are going to be sucking the juice out of our laptop battery at a rate of knots, significantly shortening the amount of time we have before our laptop battery is exhausted under the strain of these unwelcome power-leeches.

Prior to commencing our survey we also, finally, have to offer up a prayer to the gods of Wi-Fi. We pray that our dongles are fully functioning, have incurred no damage from rattling around in our laptop bag and will serve us faithfully until the end of our survey. We also pray that dongles sticking out at right angles from our laptop are not going to be snapped off by one of the many employees we’ll be trying to avoid, not to mention the many other obstacles we may not notice while focused on our laptop screen (you know the ones…filing cabinets, coat stands, cubicle partitions, door frames…etc. etc.)

A Better Way

Well, I’m here to tell you that there is a new product available from Ekahau that will solve all of these issues…and more! I’ve seen the future folks in the shape of their new “Sidekick” appliance, and it could well be your new survey BFF (Best Friend Forever).

Our friends at Ekahau have put their thinking caps on and created an industry-first for the wireless surveying world. They’ve created a new “one-stop-shop” appliance for all your survey needs. They have designed and created an appliance that will replace all of your survey adapters with a single device that you simply sling over your shoulder. Imagine that! A device that replaces your spectrum and Wi-Fi dongles in a single unit! And, it gets better…imagine that it was self-powered to save your laptop battery AND only needed a single USB connection to your survey laptop or tablet!!! Excited yet..? :)

The Ekahau Sidekick

Ekahau have long been known as a very responsive company who actively solicit feedback from their customers. Not only do they solicit feedback, they actually act on it and incorporate the suggestions received in to their product. They’re also incredibly innovative, ploughing new features in to their product at rapid pace.

The new Sidekick device is a significant departure for Ekakau. They have moved from the realms of pure software development in to hardware. The new device has been designed and manufactured by Ekahau to meet the growing requirements in complexity of hardware required to effectively and efficiently perform wireless site surveys. Rather than requiring survey engineers to precariously balance a laptop festooned with a variety of dongles at all angles, they have come up with a device that is easy to use and simplifies the whole survey process.

Figure 2 – Yep, here it  is: The Sidekick
The unit itself is unlike anything you may will used for surveying before. It’s probably slightly larger than one of those larger lithium batteries you may use to charge your laptop or tablet (It comes in at just over 6.5 inches square). It’s also a similar weight. But, as it’s slung over your shoulder during use, its size and weight are not too much of an issue. 

Figure 3 - SK with standard CD case for reference

I was provided with a pre-production prototype for my assessment. I decided to put it on the scales to see how it measures up. I believe the final production model will be of similar specification:

Figure 4 - The SK weighs in at around 2lb 5oz (including strap)
Weighing in at just over 2 pounds (including the shoulder strap), it may sound like it’s a whole lot heavier that a handful of dongles, but imagine having the option of a lighter laptop with smaller batteries, or even using a Windows tablet for your survey work. Slinging the Sidekick over your shoulder and having a lighter survey platform feels like a very attractive proposition!

Figure 5 - The Sidekick artfully modelled by a very attractive model who is available for swimwear shoots

How Do I Use It?

As a techie, I must admit to having found the SK disappointingly easy to use   It literally is just a case of powering up the SK, connecting it via a single USB cable to your laptop and firing up your copy of Ekahau ESS. That’s it. Throw the SK over your shoulder and start surveying. You use ESS in exactly the same way as you’ve always used it. The adapters built-in to the SK are shown on the ESS GUI in the same way as the external adapters you will have used previously. Instead of having 2 spectrum adapters, a single dual-band spectrum adapter is included. The SK adapter display in ESS is shown below.
Figure 6 - SK adapters shown in ESS
In addition to the adapter indicators you’re used to seeing in ESS, the other addition you may notice is the battery indicator that shows how much charge the SK has left. I believe the SK is rated to perform for at least 8 hours of survey time. During my testing I didn’t get an opportunity to survey for extended periods, but I left mine switched on all day with ESS running and it lasted well over 8 hours.

The adapter configuration controls are the same as you usually expect to see in ESS, but there are new names for the SK adapters and we now only have a single, dual band spectrum adapter. 

Figure 7 - The usual adapter controls but with the SK adapters now available
Beyond these updates, ESS looks almost unchanged in terms of the user experience of driving the ESS application itself.

Figure 8 - ESS when using the Sidekick - no real change here

 

What’s Inside?

You may well be wondering what’s inside this new box of tricks. I don’t have any technical specs for the unit, but I can tell you what I’ve observed and managed to wheedle out of the Ekahau team.

 For Wi-Fi signal scanning, there are two adapters. One will generally run on the 2.4GHz band, and the other on the 5GHz band – this is the default behaviour when you fire up ESS with the Sidekick. These are built-in to the unit – there are no external antennas, dongles or other external attachments. I was concerned about their location and the effects of RF shielding due to internal components etc. on their performance, but am assured they are around the edge of the casing to ensure there are no propagation issues.

In addition to the Wi-F NICs, there is spectrum analysis “capability” of some type. This is another of the huge “wins” that the SK provides. Previously, spectrum scanning has been limited to the output of Metageek DBx adapters. Although they do a fine job, ESS has always been limited to the data resolution that they are able to provide. The new spectrum capability provides much higher resolution of both bands. This is obviously due to the new custom hardware that Ekahau have developed and that they now have the power to control. It’s immediately obvious from looking at the scan rates available that this is a massively enhanced capability.

I have no idea what the roadmap for this product entails, but I’d be surprised if it didn’t involve further significant enhancements in the area of spectrum analysis. The processing power that is now obviously available must provide significant options in this area.      
  
As mentioned previously, the SK is self-powered, so obviously has a pretty capable internal battery. Beyond this rudimentary analysis of the internals, I have little additional information. It also obviously has significant processing capability, but no details were available to me.

 

What does it look like?

I was provided with a beta unit for my assessment and testing. I believe the final production units will be very similar, so though it would be nice to provide a few close-up shots so that you can see what this baby looks like close up:

Figure 9 - USB cable connection, charging socket, charge indicator and heatsink (top)

Figure 10- On/off button, power on/off indicator & activity indicator
Figure 11 - Rear of Sidekick showing strap attachment options

Pros

I’ve already touched on some of the advantages that the SK will bring to my own surveying work, but I think it’s worth listing them all:
  • The SK is self-powered unit that is independent of the survey laptop. This means there will be no drain on laptop battery from the 4 passive adapters generally needed for surveying (i.e. 2 x NIC-300 & 2 x DBx). This is going to mean a much improved laptop battery life. I guess you can survey for longer with your current laptop or move to a lighter laptop or maybe even a Windows tablet?

  • The Sidekick is very easy to use. There’s no USB hub requirement and no plugging adapters in & out. You literally just plug the SK in to a USB port on your laptop and you’re good to go. No more bags of adapters, cables and velcro strips, just one unit to plug in to your survey laptop.

  • The SK has 2 matched Wi-Fi adapters that are very similar to each other in terms of tolerance and performance. When using external adapters, even adapters of the same brand and model may vary by several dB in terms of the measurements that they report. This is due to the wide tolerances that are accepted as part of their manufacturing process. This can lead to inconsistent results depending on which adapters you or your team may use. The SK adapters are manufactured to much tighter tolerances, meaning that results are subject to far less variation compared to their off-the-shelf low-tolerant counterparts. This will allow for survey data to be comparable between surveys performed by different teams or individuals (as long as they were using a Sidekick unit). I wrote at some length about this is an article earlier this year, which I suggest you check out (http://bit.ly/Survey_CESN). For me this is one of the major game-changers that the SK provides, though many folks involved in surveying are not even aware of this issue

  • Spectrum analysis is significantly improved when using the SK compared to DBx adapters. Data resolution is massively improved which makes the ESS/SK combo a dammed fine Spectrum  Analyser in its own right, comparable with other Spectrum Analyzers at the higher end of the Wi-Fi Spec An market.

  • The ESS/SK combo provides an easier, less obtrusive survey experience. If you compare the current experience of surveying with a multitude of antennas sticking out of your laptop at a variety of angles, it provides a huge improvement in the ease of surveying. There is no more dodging obstructions, snagging passers-by or snapping off USB NICs as you mis-judge a door width. Your survey setup is far less obtrusive and easier to manoeuvre. It will attract far less attention (and accompanying inane questioning about whether you are going to improve cell phone coverage) when walking the length and breadth of any facility you are surveying.

    Cons

    In addition to the benefits that it brings to the party, there are also obviously other, new aspects to consider with the introduction of the Sidekick unit.

    • Cost: Wireless surveying (certainly in the UK anyhow) is an activity that seems to be constantly subject to significant pressure in terms of the pricing of services. Organizations generally seem reticent to invest in the time that’s required to perform a comprehensive survey. They generally want it done quickly and as cheaply as possible. The organizations who provide surveying services are often expected to invest heavily in their survey equipment and software and still work at very low margins for the services they provide. The pricing of the Sidekick unit will be very important to these organizations. On top of the existing costs they incur, the SK may be quite a challenging investment for these organizations, particularly if they have sizeable engineering teams.
    • Hardware Support: Providing rapid support for the SK hardware will be a key requirement for those who make the investment in the hardware. If the unit should fail, then getting a replacement to avoid lost productivity time will be paramount. For those who are existing ESS users, they will no doubt be able to fall back to their existing dongles in the interim. However, new users without backup hardware will need to be confident that they can get a replacement unit promptly if required. Having only the SK for surveying represents a potential single point of failure that wasn’t quite so much of a concern previously.
    • Weight: The SK unit weighs in a just over 2 pounds. This isn’t a significant weight, but when you’re walking, potentially miles per day, then any additional weight is potentially unwelcome – it all adds up! My own opinion on this is that over time this will become less of a consideration. As survey laptops or tablets are refreshed, then the option of using tablets or laptops with smaller (and hence lighter) batteries will be leveraged, meaning that the overall load carried by the surveyor will be very similar to the current survey kit. If you add in the fact that the SK can be carried over the should or perhaps in a back-pack or on a belt, it feels as though the better distribution of load is, in-fact, a longer-term net benefit.
    • New Product Line: I am not, by nature, an early adopter. I like my hardware and software to be relatively mature before taking the plunge with anything new. I’ve have been stung too many times by “the latest & greatest’ offerings from larger organizations who really should do an awful lot better. Ekahau have a very good history of rapid, stable software development. Sure, they’ve had their issues, but I’ve always been able to get a workaround or fix in very reasonable timescales. However, Ekahau is known as  a software company who leverage 3rd party hardware to gather data from the “real world”. As well as introducing a brand new paradigm in terms of wireless surveying, they are also re-inventing themselves as a hardware company too. I’m not aware that they have done this through acquisition, so I assume they are creating this hardware for themselves…for the first time. The pre-production unit I was supplied performed very well. There were some issues with one or two aspects of its operation (which I’m assured will be fixed by the time it leaves the factory gates), but in the main it felt solid & reliable. Ekahau will no doubt learn a few lessons with their initial foray in to hardware development and supply, but it feels like they have done a pretty reasonable job.
    • Heat: The SK has the capability to kick out some pretty significant heat during operation. Once it has been fired up for a few minutes, the cleverly located heat-sink gets pretty warm to the touch – not enough to burn, but you could warm your hands very quickly on a cold day. This is obviously one of the trade-offs of having a self-contained piece of high-performance hardware with a high capacity battery built-in. Ekahau have done a superb job of dissipating the heat using the heatsink located on the top face of the unit. The heatsink is in the centre of the top-most face that faces away from the body of the survey engineer. Its centralized position also ensures it has minimal impact on the antennas that are located around the edges of the SK casing.

    The Future

    With the ground-breaking shift that the Sidekick provides for Wi-Fi surveying, I can’t help but think about future possibilities that it might provide. I have no concrete inside information about how the product will develop in the future, but the shift from a handful of off-the-shelf passive components to a custom-designed, self-powered device with processing capabilities obviously opens up some mouth-watering possibilities.

    The leap in capabilities around spectrum analysis is an obvious area where the product could be improved to match the capabilities of competing products. Fingerprinting of non-Wi-Fi signals to identify specific types of interferers is an obvious enhancement that would continue the “game-changing” meme for this product.

    Once you start to consider the possible applications that a self-contained, high spec unit like the SK could theoretically provide, some very exciting possibilities spring to mind. The possibilities around data storage, of new applications running on the device or perhaps offloading of some tasks to the SK unit provide some exciting possibilities for the future. It raises the question of whether lower-spec of even new form-factor survey devices could be a future option.

    This really feel likes a huge gamechanger in the market place. Obviously, in reality, the market will determine whether there is an appetite for such a device. As a Wi-Fi enthusiast, the SK is a very exciting addition to our arsenal of Wi-Fi test equipment. But, it will subject to the economic realities and the sometimes-harsh fickleness of real-world commercial organizations. There will be many “techies” like myself who will love this new concept from day one of its release. But, it will be down to the SK itself to deliver enough ROI for organizations to be willing to make the investment if it is to survive long term.

    References:


    Disclosure: I was loaned an evaluation pre-production beta unit for this review. No compensation was received for this article (though discounts or hardware donations would be most welcome  :) ).

    Saturday, 13 May 2017

    Preserving Your Survey Gear: Hub Holster

    If you carry out wireless survey activities, you’ll be painfully aware how much your precious survey kit cost you. And, I’m pretty sure you want to keep it in pristine, working condition. Here is a great little add-on for your kit that can help preserve your survey laptop and your survey wireless NICs.

    The Problem

    Yes, I know it’s not fashionable to use the word “problem” anymore, but if you’ve ever been surveying on site and had a passing pedestrian or unexpected filing cabinet damage one of your wireless survey NICs, then you know that it’s a “problem”.

    Side_Dongles.jpg
    Fig.1 - This is never going to end well...

    When performing on-site surveys to measure Wi-Fi network coverage or performance, there is generally a requirement to have one or more wireless NICS or dongles attached to a survey laptop. These cards gather data to feed into survey software as a survey engineer moves around a coverage area.

    However, plugging the cards into the standard USB ports on your laptop can mean that they are protruding from the sides of your laptop, making them fair game for getting bent or ripped out by unseen items of furniture and passers-by. Also, many laptops may not have a sufficient number of USB ports for survey purposes. Many survey engineers have taken the sensible step of getting hold of a USB hub and mounting it on the lid of their survey laptop to keep things out of harm’s way and provide sufficient USB ports for their requirements .

    Attaching a USB hub to the laptop can be something of a challenge. Well-known methods include gluing velcro strips onto your survey laptop lid and using wire twists that have been fashioned into a supporting loop. Neither are particularly “robust” over time when used on a frequent basis.   

    The Solution

    Enter the “Hub Holster” to save the day!

    The Hub Holster is a great solution to mitigate issues around securing your USB hub to your survey laptop. It allows USB hub mounting without any of the glue or other damaging attachment methods. It simply clips onto your laptop screen, providing a firm, robust support bracket for a USB hub during surveys.

    HH_Dongles.jpg
    Fig. 2 -  A handsome, practical solution for fixing your USB hub

    Hub Holsters are produced by Robert Boardman. As each laptop model has slightly different dimensions in terms of screen thickness, bezel size etc., Rob produces a range of his 3D printed brackets for various laptop models and a range of commonly used USB hubs. If you send him the dimensions for your laptop screen he can even print you a custom Hub Holster for your particular laptop (which he did for me!).

    I bought a pair of Hub Holsters for my Macbook Pro and my Lenovo laptop and they are excellent.

    HH.jpg
    Fig. 3 - This is what they look like out of the packet

    I personally think the Hub Holster is a very worthwhile investment. No more sagging velcro mounts, no more glue on your laptop lid, no more NICs sticking out at 90 degrees and no more twisty bits of wire to try and hang the hub on your laptop lid. And, far less chance of any damage to your precious survey kit. For more info, please see the links provided below (and order yourself a couple...trust me):

    References
    HH_No_Dongles.jpg
    Fig. 4 - One more pic, this time without the dongles

    Wireless Engineer Locator Tool

    If you’re looking for a wireless survey engineer for a forthcoming Wi-Fi network project, or you’re a wireless survey engineer who’d like to snag a few new customers, here is a great site you’ll want to check out!

    I was lucky enough to attend the Wireless LAN Professionals Conference in February of this year (2017). Among the feast of Wi-Fi presentations and products was a very nice survey kit offering from a company I’d not heard of before called HiveRadar. They offer a complete survey kit in a flight case for survey engineers. The beauty of this kit is that it has everything you need to perform an on-site, “AP on a Stick” survey packed into one, robust flight case (yes...even the survey pole!). If you’re a Wi-Fi engineer, this is certainly an offering you will appreciate, particularly if you have to do plenty of plane journeys.


    Fig1. Engineer Locator

    However, in addition to their great products, one thing that really caught my eye was an “engineer locator” tool that is available on their web site. The locator shows a map of the world, with little “HiveRadar” pins sprinkled across various countries. Each pin represents the location of a wireless engineer. If you click on any of the pins, you can access the engineer details, including their bio, qualifications, experience, and vendor expertise. It also provides a  contact form so that you can get in touch directly with the engineer so that perhaps you can talk to them about possible engagements etc.

    Engineer_Locator_Details.png
    Fig2. Engineer Details

    If you’re a wireless engineer, you might assume that this superb service is only available to HiveRadar customers. But, no, you’d be wrong! HiveRadar make this service available to any wireless engineer (for free!) who’d like to submit their details and sign-up. There is a slight delay between sign-up and appearing on the locator page, but I assume this is due to a checking process.

    If you’re a wireless engineer, I’d strongly recommend you get along to the HiveRadar site and register yourself on their locator page - who knows who may be looking to get hold of your services!?. Similarly, if you’re looking for a wireless engineer to help you out with your next Wi-Fi project, this is a great place to check out engineering talent in your area.  

    References:

    Tuesday, 28 March 2017

    Cell Edge Specification Notation (CESN)


    When it comes to designing WLAN RF environments, everyone seems to have their favourite cell edge signal level that they like to shoot for. Common figures include -67dBm for voice grade WLANs, maybe -60dBm for higher 802.11ac speeds and perhaps -72dBm for general data traffic coverage. Each vendor and wireless consultant seems to have their own preferred cell edge design target that will vary with WLAN requirements. However, these figures are meaningless without some type of explanation or context. If you rely solely on these types of figures, you are very likely designing incorrectly....

    Background
    Around 18 months ago, I was involved in a project that required the deployment of a new wireless LAN network at many sites around the globe. The project required that all sites would be subject to the same standard of RF parameters to provide a consistent design approach at all sites.

    A team was sent to the first site to perform an “AP on a stick” survey using an AP of the same model that would be deployed for the final solution. The results from the survey report looked very good - we were hitting the coverage and capacity levels we were hoping for. We had a well defined threshold for (amongst other parameters) the cell edge signal level we wanted to achieve (let’s call it -62dBm).

    Another team was sent to a second site in another part of the globe to perform another survey, using the same survey thresholds. They were using the same survey software, the same type of survey AP (with the same settings) and were working to the same cell edge figure of -62dBm.

    Both buildings were primarily large, modern, open plan offices.

    However, the results in the two survey reports were hugely different in terms of the cell coverage achieved for the same AP transmit power. The physical cell size for each AP cell (at the same cell edge threshold) in the second survey was 50% or less of that observed in the first survey. We would would need twice as many APs for the second site even though they were being designed to the same RF standard.

    This couldn’t be right..could it? Two surveys done with the same software, in similar environments, using the same survey thresholds with twice as many APs required in one survey compared to the other? Something just didn't make sense. We would expect similar AP cell sizes and similar AP densities at both sites.

    After lots of head-scratching, configuration checking and re-surveying the culprit of the huge difference in survey results came to light: the two teams had surveyed with different wireless NICs in their survey rig. One had used Proxim adapters, while the second team had used Netgear adapters. Both were valid adapters supported by the survey software, but they gave wildly different survey results due to their different RF characteristics.  

    Which adapters were giving the correct results? In the absence of any other data, then they were both, arguably, correct.

    Which Clients Are You Designing For?
    The fundamental flaw in this survey approach was the lack of specification of the wireless NIC to be used to perform the survey.

    Each model of wireless NIC is likely to have very different RF characteristics in terms of antenna capabilities and RF sensitivity. As a minimum, the model of wireless NIC to be used for the surveys should have been specified. This would have perhaps at least ensured that the surveys would achieve reasonably comparable results and a more consistent RF design.

    (Note: even models of the same wireless NIC may vary from device to device due to manufacturing tolerances, so there will still be a variation of a few dB between devices)

    The solution to this issue was to ensure that all survey teams used the same type of Proxim adapter. The results from the different survey teams were far more comparable once this standard approach had been agreed.

    However, even this approach had flaws. The survey cell-edge threshold was provided by a 3rd party, based on their previous general design experience. A better approach would have been to design for the RF behaviour of a specific device or devices, based on customer requirements.

    The best-practice approach is to understand the behaviour of one or more of the clients that will use the wireless LAN and tailor the RF environment for those devices (as closely as possible). This is incredibly difficult to achieve in the real world, as there are likely to be many different types of client with a variety of RF capabilities and behaviours. The choice of which RF characteristics to design for will have to be a judgement call based on business requirements and priorities.

    Compensation
    Once a decision has been made around which device will be used for the design decisions, then the RF survey criteria will need to be decided.

    As an example, let’s assume that the primary device on our WLAN is an Apple iPad Mini 4, as we have many deployed across our network for a mission critical service . It also happens (in this theoretical scenario) that a few other devices on our proposed WLAN will have quite similar characteristics, so this RF design will suit quite a few other devices too.

    We have also seen from a vendor wireless design guide that a useful cell edge design threshold is -70dBm for Apple devices. Therefore, we will use this as our cell edge threshold.

    However, we will be performing our survey with a Proxim wireless NIC. The iPad Mini 4 is not able to run our wireless survey software, so we have to run it on our laptop with the Proxim adapter.

    We suspect our Proxim adapter is going to have very different RF characteristics to our iPad Mini 4. But, we want to design our WLAN network with cell edges of -70dBm, as seen by an iPad Mini 4 (not a Proxim adapter).  Cell sizes at -70dBm for a Proxim adapter are likely to be very different to those of an iPad Mini 4.

    Therefore, we need a way for the Proxim adapter to see the RF world in a similar way to the iPad Mini4. This is generally done using a “compensation” technique.

    In summary, when we compensate for our survey adapter in a survey report, we add (or subtract) a dB  offset to/from our survey data to account for the different in the survey NIC and the required client that we are trying to emulate.

    For instance, we might set up a test access point and measure the signal level we observe at a distance of 6 metres (20 feet) with the Proxim adapter. We would then measure the signal level with a wireless client (e.g. our iPad Mini 4) at the same distance. The difference between the two signals observed is the offset we need to apply to our survey data.  

    As an example, if the survey NIC showed a signal level that was 5dB stronger than the client, we would have to apply an offset of 5dB to signal levels in the survey data. If we were aiming for the -70dBm cell edge we previously discussed, the cell edge shown in our report would be -65dBm, as we know that this would be observed as -70dBm by our wireless client.

    Signal Level Specification
    Hopefully, the discussions above will underline need for some form of context or reference when specifying a signal level for an RF design cell edge. Simply stating that we need to: “design for voice to cell edge of -67dBm” is meaningless without further information. The key piece of information missing is the specification of which device observes the cell edge.

    There is a common (often unspoken) rule around cell-edge signal level specifications among wireless LAN pros. A signal level is generally accepted to be that observed by the client device that is in-use. For instance, if a design guide specifies that a cell edge of -67dBm for voice handsets be used, experienced WLAN pros will assume that this signal level is measured with the actual voice handset.

    However, this assumption is not widely understood or is often unknown. Many people performing a wireless design will not even consider that there may be a difference between their survey rig and the clients that will use the final deployed WLAN.

    I believe there needs to be a better, unambiguous way to specify signal levels, particularly for cell edge measurements in WAN survey work.

    Signal Level Notation
    SIgnal levels need to be expressed in a less ambiguous format. The information about the expectation of how the signal level is to be measured needs to be embedded in a standardized notation.

    If we consider the case of “AP on a stick” surveys, we have two methods of specifying the cell edge signal we’d like to aim for:

    • A signal level as seen by a specific client type (e.g. -70dBm as seen by an Apple iPad Mini 4)
    • A raw signal level value that we’d like to use with our survey adapter (e.g. we know that our adapter works well for many Apple devices at -65dBm from previous work or compensation testing, so we’d like to use that specific value)

    We may also have a third method of specifying signal levels if performing predictive modelling with a wireless survey tool. Predictive models will generally provide “raw” signal levels based on Free Space Loss, which will not account for an adapter or client type. With some of our own real-world vs predictive testing, we may be able to specify a suitable predictive signal level which is suitable for our purposes.

    To meet each of these three scenarios, I’d like to propose the following notation specification:

    <signal level in dBm> (<measurement type>: “<device type”)

    The ‘measurement types’ would be specified as:

    UC = Un-compensated
    CF = Compensated For
    PM = Predictive Model

    Here are three signal levels, specified using the proposed notation:

    • -65dBm (UC: “Ekahau USB-300”)
    • -65dBm (CF: “Apple iPad Mini 4”)
    • -65dBm (PM: “FSPL”)

    These translate to

    • -65dBm (UC: “Ekahau USB-300”) : a signal level of -65dBm that is a raw (un-compensated) measurement made with an Ekahau USB-300 NIC
    • -65dBm (CF: “Apple iPad Mini 4”): a signal level that has been compensated for a value that would appear as -65dBm to an iPad Mini 4 device
    • -65dBm (PM: “FSPL”): a signal level that uses a free space loss measurement as represented in a predictive model.

    Conclusion
    RF design for wireless LANs  is a complex topic, which is very difficult to “get right” in the real world.

    However, it is very easy to “get it wrong” through simple misunderstandings and the lack of standardized reference points for RF measurements.

    Although the proposed signal level notation adds a little more complexity to the mix when creating an RF design, it does removes a level of ambiguity from signal level specifications. This will hopefully provide a more consistent WLAN design methodology across the industry.

    I’d be very interested to hear your thoughts on this.