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WN Blog 024 – RF Math

Hey!

Welcome to our latest blog – this time we are taking it back to some RF fundamentals and more specific – RF Math!

Since we started our Podcast & Blog, we have had requests from people to cover beginner level WiFi basics, which we will be doing with a series of blogs & podcasts coming up in the future but today let’s make a start with understanding some RF Maths.

You might be wondering why do I need to learn RF maths? I had enough of Maths when I was at school – I don’t want to have to do it all again! Well RF maths is important in WiFi because we typically measure WiFi in dBm & dBm means dB scale relative to mW. For example, when looking at your RSSI (Received Signal Strength Indicator) in dBm it would look something like this “-50dBm”.

WinFi RSSI

Now I am no maths expert at all, so luckily there is a relatively simple rule we can follow to pretty much work out all RF maths.

This is the rule of “10s & 3s”

Below is a table, on one side we have dBm and on the other we have mW. Now whatever we do on one side of the table we must do on the other side of the table. If you + (add) in dBs, then we X (times) in mW. If we – (minus) in dBs, then we / (divide) in mW. 10 in dBs is 10 in mW and the only thing that is a little bit tricky to remember is 3 in dBs is 2 in mW.

dBm mW
+ X
/
10 10
3 2

This table below might help paint a bit of clearer picture, for example if we increase the signal strength by +3dBs we then have 2 x the power. If our signal strength decreases by -10dBs we then have 1/10th of the power that we had.  

dBm Power
+3dB 2x Power
-3dB ½ Power
-10dB 1/10th Power
+10dB 10x Power

Starting to make a bit of sense? If not, do not worry as we have plenty more examples below that will help you have a better understanding of how this works & we have even thrown in a little quiz for you guys!

When we are doing RF math, we always start with 0dBm & 1mW at our starting point.

In the example below, we are converting dBm to mW & our aim is to work out what 13dBm would be in mW.

Remembering that we always start from 0dBm, we first would add +10db and then add another +3dBs to get to 13dBm. Now to convert that to mW & remembering that we always start from 1mW, we first x 10 and then x 2. Which would mean our calculation would be “1 x 10 x 2” and then equals 20mW.

RF Math Example 1

Let’s move on to another example. This time, how do we convert 36dBm into mW. See in the image below, in dB we +10 +10 +10 +3 +3 to get to 36 so that means in mW we x10 x10 x10 x2 x2 which = 4000mW.

RF Math Example 2

A very strong signal in WiFi & typically the highest you will see is -30dBm. Let’s work out in mW what is considered a very high RSSI if WiFi. Remember we start from 0dBm, so -10 -10 -10 will get us to -30dBm. Which means in mW we / 10 / 10 / 10 – so our calculations will be 1 / 10 / 10 / 10 which equals 0.001mW! Wow, so an extremely good strong signal in WiFi has a power level of 0.001mW?! That’s impressive!

RF Math Example 3

Let’s move on to another example, this time -53dBm (still a very good signal strength in WiFi). To get to -53 from 0 we need to – 10 – 10 – 10 – 10 – 10 – 3. Which in mW would be / 10 / 10 / 10 / 10 / 10 / 2. That means our calculations would 1 / 10 / 10 / 10 / 10 / 10 / 2 which equals 0.000005mW.

RF Math Example 4

Are you starting to see why we do not measure RSSI in mW? Imagine having to go back to the customer and say, “oh yes Mr. Customer your signal strength here is very good, its actually 0.000005mW!” I think being able to say that the RSSI is -53dBm is much easier 😊

I have put together another table below of some additional dBm conversions to mW and to Watts for your comparison.  

RF Math Examples Table

Hopefully after those few conversions we have worked out together you guys are ready for a little quiz & to work out some dBm to mW yourselves! Now, I will put the answers to the dBm levels below at the bottom of the blog but do not cheat! Work these ones out yourself using the 10s & 3s rule as well at the examples above and see what answers you come up with!

Quiz dBm to mW:

RF Math Quiz

Now that we are all RF Math WiFi Ninjas lets take this another step & take into consideration what happens when WiFi passes through walls. Some typical wall type materials we see in the wild & how they attenuate the WiFi signal.

If we first look at what wall is most commonly used internally in buildings, which is “drywall”. On average typically drywall will have an attenuation level of 3dBs. So that means when WiFi signals pass through the drywall we will lose -3dBs & losing -3dBs means that we now have half the power we originally did. Looking at the image below we can see an AP on the left-hand side where client A has an RSSI of -49dBm, but on the other side of the drywall, client B has an RSSI of -52dBm.

RF Math Dry Wall Example

Moving on to another type of wall that is commonly used on the exterior of buildings, “brick wall”. A brick wall typically has an attenuation of 10dBs, so this means when WiFi signals pass through a brick wall they will lose -10dBs, therefore we will now have 1/10th of the power we originally had before passing through the brick wall. Looking at the image below we can see an AP on the left-hand side where client A has an RSSI of -49dBm, but on the other side of the brick wall client B has an RSSI of -50dBm. 

RF Math Brick Wall Example

The final concept that we would like to explain to you is something called “Free Space Path Loss) aka – FSPL. What we need to remember with FSPL is that when you double the distance, you quarter the power. That will mean at double the distance we will need to half the original power and then half it again. To half the power in WiFi, we need to -3dB.

In the example image below, we are using the example of at 1m distance from the AP, we have an RSSI of -30dBm, we then move to 2m distance which is double 1m so we need to quarter the power which means -3 + -3 so at 2m our RSSI should be -36dBm. You can see / work out for yourself how we got to that RSSI at 4m & 8m 😉

Free Space Path Loss Example

Here are the calculations and answers to the quiz above:

27dBm = 0 +10 + 10 + 10 – 3 = 27 so 1 x 10 x 10 x 10 / 2 = 500mW

45dBm = 0 +10 + 10 + 10 + 3 + 3 + 3 + 3 + 3 = 45 so 1 x 10 x 10 x 10 x 2 x 2 x 2 x 2 x 2 = 32,000 mW

39dBm = 0 – 10 – 10 – 10 – 3 – 3 – 3 = 39 so 1 / 10 / 10 / 10 / 2 / 2 / 2 = 0.000125mW

57dBm = 0 – 10 – 10 – 10 – 10 – 10 – 10 + 3 = 57 so 1 / 10 / 10 / 10 / 10 / 10 / 10 x 2 = 0.000002mW

How many did you get right? Let us know 😀

That concludes our RF Maths blog, we hope you found it useful if you are a WiFi beginner or even if you are more experienced and just needed a little refresh 😊

Tons of Love,

WiFi Ninjas x

WN Blog 018 – WiFi Design Day 2019 Experience

Hey!

I have just recently attended the Ekahau & Open Reality WiFi Design Day 2019 at the ICC in Birmingham and thought I would do a blog post to summarise my experience and thoughts.

This was my 3rd year in a row attending from the 1st one back in 2017 at the Churchill War Rooms, to the Barbican centre and then the ICC in Birmingham  – this year I was attending as a speaker for the first time.

I really feel that there is no other event like this in the UK where you get the exposure to such a wealth of fantastic speakers, the opportunity to network with like-minded individuals & they throw in food + beers! For what is very little expense in comparison.

Big thanks to all the people over at Ekahau & Open Reality for the event but I want to say to Sam Cobley and Matt Cavill imparticular a huge thanks to these guys as I know how much personal time & effort they put into this event to make sure it’s always a massive success.  

I will cover & highlight some of the presentations from the day below but disclaimer – I have not included every presentation from the day here as I did not attend them all!

When I first arrived at the ICC in Birmingham it wasn’t too difficult to work out where I needed to go from this nice display.

Arrival Display
Arrival Display

The line up for the day’s action, we took the liberty of highlighting what the people were saying was the most exciting & anticipated presentation of the day:

Presentation Timetable
Presentation Timetable

My 3rd year attending, first time speaking lanyard – a special day for me personally 🙂

Matt Lanyard
Matt Lanyard

I took this photo at what is arguably the most important part of the day – coffee time! We WiFi pros need that coffee first thing in the morning but it was equally as great to see that so many people were in attendance given the typically bad English weather that had caused extensive flooding & travel nightmares.

Coffee Time
Coffee Time

With nearly 300 tickets sold, we can see a packed crowd here and just how popular these WiFi Design days are becoming!

WDD Crowed Shot
WDD Crowed Shot
Mikko Lauronen
Mikko Lauronen

Anssi & Mikko kicked off the day by showing us some extremely cool & exciting new features that will be coming out very soon with Ekahau. You will now be able to moonwalk, drink a beer and survey – all at the same!

Ekahau never fails to amaze me with the innovations of the products they offer to us as WiFi Engineers and there is absolutely no way I would be able to do my job as effectively without having Ekahahu in my tool kit. 

Anssi Presenting
Anssi Presenting
David Corbett
David Corbett

David Corbett gave us an interesting insight into the NHS Free WiFi rollout and how important WiFi really is seen now and no more as a “nice to have”.  How much of a benefit & positive experience it brings to not only patients that use the WiFi extensively whilst at the hospital to stay in contact with loved ones but also for staff how much it is helping them also.

David Corbett Presenting
David Corbett Presenting
Keith Parsons
Keith Parsons

Next up to present was the original WiFi Legend himself, Mr. Keith Parsons! Keith took us through some tips, techniques, tools for troubleshooting WLANs. I have been lucky enough to be on one of Keith’s’ training courses, as well as seeing him present in person. There are few better in the WiFi industry than Keith and for him to share his knowledge and tips with us is one of the best parts of the day for me.

A couple of tips if you are at one of Keith’s presentations – make sure to put your phone on silent and ask permission if you want to record him, personally I would just suggest you sit back, enjoy and try to take in as much information as possible!

Keith Parsons Presenting
Keith Parsons Presenting

Keith also revealed some new training courses that are going to be available from the ECSE / WLAN Pros next year. ECSE Troubleshooting & ECSE Advanced – as well as offering the original ECSE Design still.

If like me you wanted to know when the next opportunity would be to go on one of these amazing training courses – here are some of the dates for 2020:

ECSE Training Dates
ECSE Training Dates
Mark O'Leary
Mark O’Leary

Mark gave us an insight into Eduroaming, from how it is deployed to how many unique devices they are seeing on the Eduroam network – Pretty impressive. This is a great concept and something I personally really want to see more of in the WiFi industry. Cisco is doing something very similar called “Open Roaming” where the handoff from 4/5G to WiFi is completely seamless and requires no interaction from the end-user – just how WiFi should be in my opinion.

Mark O'Leary Presenting
Mark O’Leary Presenting

Keeping up with the theme from last year where I featured on the WiFi design day YouTube video for feedback on the day – I was more than happy to get back in front of the camera again to tell everyone what a great day I had and why.

Matt Youtube
Matt YouTube Video

This was now after the lunch and the two breakout sessions or “tracks” started.

I attended track 2 as this was also where we would be presenting 🙂

First up was Nick Turner / Dick Burner – giving us a live demo of some of the new Ekahau features.

Nick Turner Presenting
Nick Turner Presenting
Andrew McHale
Andrew McHale

Next up in track 2 was the voice master, Andrew McHale. It is always a pleasure and insightful to listen to Andrew’s tips on voice for wireless – there is no doubt that he is one of the leading experts in the industry when it comes to the subject – so even though this was the 327273th time we had heard Andrew talk about voice over wireless – it was still amazing & extremely mind-blowing hearing Andrews knowledge of this subject.

I have highlighted my favourite tip from Andrews slide here 😀

Andrew McHale Presenting
Andrew McHale Presenting
WiFi Ninjas
WiFi Ninjas

This was mine & Mac’s first time presenting at the WiFi design day and we decided to talk about what we think is the most exciting thing about WiFi – RTLS! (Real-time location services) We first went through some theory on what is RTLS, different methods & techniques, etc and then had some real-world demos + testing that we had been doing throughout the year.

WiFi Ninjas Presenting
WiFi Ninjas Presenting
WiFi Ninjas Presenting 2
WiFi Ninjas Presenting 2
Jim Vajda
Jim Vajda

We then headed back into the main hall where Jim took us through an alternative view of what the 7Signal portfolio could bring to us by not using the WiFi monitoring tool for monitoring the WiFi – but using it to help us with designing WiFi. 

Jim Vajda Presenting
Jim Vajda Presenting
Peter MacKenzie
Peter MacKenzie

The last presenter of the day was the Magician himself, Mr. Perter Mackenzie. The topic for Peter’s presentation was roaming analysis – where Peter covered the different methods & amendments available to help clients roam whilst giving us a deep dive view into the packets of how all of this happens.

This would have seemed like quite a dark art to me if I hadn’t have had the pleasure of sitting one of Peter’s CWAP courses this year so thankfully I could understand at least some of what Peter was saying :D.

Anyone thinking about going for their CWAP or just want to get a better understanding of how this fantastic protocol works, then I highly recommend you take one of Peters’s courses if you get the chance to.

Peter MacKenzie Presenting
Peter MacKenzie Presenting

Peter finished his presentation off by mentioning the WLA, all the great things they have coming up but also about the UK WiFi Guys Slack Chat.

This a great form of community and communicating with fellow WiFi pros in the UK – if you are not in the UK WiFi Guys Slack chat and would like to be, you can reach out to @WiFiNigel on twitter to get added.

This was a fantastic selfie that WiFi Nigel took, really catching his best angle here I think :D.  

WiFi Nigel Selfie 2
WiFi Nigel Selfie

We finished the day off with a round table where some of the presenters were invited back on stage to take questions from the crowd & any questions that came in online. We were extremely honored to be invited back up to be on the round table to sit up there with some true WiFi legends and, Andrew McHale ;).

WiFi Round Table
WiFi Round Table

The only slightly negative feedback / constructive criticism was, and this is my completely unbiased opinion but I think that next year Open Reality / Ekahau should give the WiFi Ninjas a longer time slot and be on the main stage 😉

One final warning/ tip:  if you go out with Alan Blake the night before a conference, you will have one of the best nights out you have ever had, but prepare appropriately for the hangover the next day. I would still highly recommend this experience to anyone as Alan is one of the most fun & nicest people I have met – who I always look forward to seeing at these events.

Alan Blake & Co.
Alan Blake & Co.

I hope you enjoyed my summary of the 2019 WiFi Design day, if you were there and would like to leave your feedback also – please feel free to post a comment below as I am sure the guys at Open Reality & Ekahau would love to know.

Lots of love,

Matt

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