Hello. Now, knowing which device types will be used in your wireless network matters. You see all devices differ in the following two important ways. They differ in our antenna and how it receives circuitry. And they’re different in their BSF selection and merman algorithms. Now, in this video I’m going to focus on one important difference between devices. And that is they receive signal strength. You see different devices in the same location, will have the same signal at differing signal levels. And that’s due to different and antennas and area of circuitry.
For example, I know my iPhone typically receives signals 10dB less than my laptop. 10dB, that’s 10 times less power. So why the difference? Why such a big difference? Well, one reason is my laptop has antennas built into the side of the screen, which have a positive receive gain. Whereas, my phone on the other hand, has a circuit board printed antenna, which is bent to fit into the product. Now, I’m sure you don’t want to carry around an iPhone, which looks a bit like this. Now, while this phone with an external antenna would be able to receive signal strength similar to my laptop, it doesn’t look very good, does it? And it doesn’t really fit nicely into my pocket. You see here is what an actual iPhone wifi antenna looks like. You can see how it’s been bent to fit into the casing of the phone. And antennas like this end up with a negative gain.
Now, to demonstrate a difference between different devices, a few years ago I did some testing. And I had an iPhone, a Samsung Galaxy phone, and a Lenovo laptop. And I placed all devices in the same location with a clear line of sight to the access point. And I recorded their average received signal strength for both the 2.4 and five gigahertz radios for each device. And then this is what results I got. So for the Lenovo laptop, it could receive the AP2.4 gigahertz signal at minus 49dBM. And the five gigahertz, it received at minus 52dBM. If we compare that to the Samsung Galaxy phone in 2.4 gigahertz, it was receiving the access point signal at minus 66dBM. That’s a 17dB difference to the laptop. And when we look at the five gigahertz band, it was receiving that at minus 56dBM, which is only a four dB difference.
Looking at the iPhone in 2.4 gigahertz band, it was receiving a single at minus 58dBM. A nine dB difference to the laptops nine dB less. On the five gigahertz band however, it was receiving the signals at minus 69dB. That’s a 17dB difference. So do you see how much difference there is between differing devices, even when they’re placed in the same location? So why does all its matter? Well, let’s say we’re designing a wireless land to have a primary signal strength of minus 67dBM. Well, the obvious question is minus 67dBM as seen by which device? Because to design a minus 67dBM network for my laptop will likely need fewer APs than for my iPhone. So when we’re designing to make 67dBM, we can only do that for one device in a given area. So which device do you pick?
Well, this is where we need to identify something we call the LCMI. Least capable most important device. Now, LCMI is as much of a thinking process as it is a designation of an individual device. For example, when looking at my iPhone and laptop, again, the least capable in terms of how they receive a wifi signal is my iPhone. So if we design for the iPhone device, I can probably also guarantee that laptop will also have enough signal strength. But see we don’t always just pick the least capable. We need to also consider the most important device too. Let me give you an example. Let’s say our least capable device might be Bob’s eight year old iPhone, which he dropped on a night out. And now it early connects to wifi, if it’s within four meters of an access point. Now, Bob’s phone is definitely the least capable. But if we design to that device, we’re going to end up with access points every four meters. And all other devices are going to receive loads of co-channel and adjacent channel interference.
Yes, we might give Bob a great wifi experience, but at the expense of everyone else. Now, you see in this scenario, Bob needs to just get a new phone, doesn’t he? And we need to consider which devices are most important to us. So what are examples of most important devices? Well, in an office environment that might be corporate laptops. In a warehouse, it might be barcode scanners or picking devices. What we need to do is create a list of the most important devices and then look at which of these is the least capable. Now, we might come up with a minimum signal level, which we know will work for all our most important devices. For example, we might say we will design for NEG 65dBM knowing that some devices will receive a signal a little bit above that level and some will receive it below.
But all devices will receive a signal that will allow them to operate at a high data rate and receive a good user experience. Let me give you a real life example of this LCMI thinking process. Now, I was designing a wireless network for a UK retailer who had identified their most important device was a Zebra TC70 hand held barcode scanner. Now, when we were monitoring how this device was used by different colleagues, we found out that the colleagues would use this device in conjunction with wireless’s printers. So the way it would work was they would take a zebra TC70 scanner, and they would scan a barcode on the printer, and that would make a connection or a pairing between the scanner and the printer. That way when they were on the shop floor, when they were scanning a product, they could then print a label out for that product on the printer.
Now, both of these devices connected to this network. And one problem was if the printer lost connectivity, you’d get an error on the scanner saying lost connection to the printer. And you couldn’t move on until the printer was reconnected to the network. So there was this relationship between the two. One device relied on the other. So which was the least capable? Well, the least capable by far was the printer. They were very old devices. They were 2.4 gig only. And they needed a really, really strong signal strength. If you looked at compared, say, a printer to my laptop, it was about 20dB less with how they saw signal strengths. So they needed a very, very strong 2.4 gig signal. And they needed a very strong secondary 2.4 gig signal to be able to roam.
Now, the TC70 scanners were capable of for using the five gigahertz band and generally did connect on the five gigahertz band. So in this scenario, what we ended up doing was designing the 2.4 gig band for the printers, a very strong 2.4 gigahertz signal everywhere. But we designed the five gigahertz band to the TC70’s. And therefore, ensuring that both of these devices got the wireless experience they required.
You see, it’s important to understand the correct signal strength offsets between different devices. And that also includes actually our survey devices. For example, let’s consider Stanley here. He’s confirming he has a great signal strength, but using a USB wireless adapter with external antennas. And these antennas have a really, really high antenna gain. But the problem here is that Stanley’s device is nothing like the devices the end users of the system will be using. Misty, on the other hand, is testing different corporate devices to identify the different signal strength offsets. These offsets can then be used in the error of design and validation stages. So thank you for taking the time to watch this video all about the LCMI. The least capable, most important device. Goodbye, for now.