A lot of users are moving to 300meg 11n outdoor WiFi links under the impression that this is going to give them a super-fast data link. However the truth is that 300meg 11n does not mean 300meg data throughput or even 150meg! The rough rule-of-thumb for a WiFi link used to be take the PHY rate (300meg for example) and divide by two to get the true data throughput. For example old fashioned 54meg 11g WiFi used to give about 25meg true TCP throughput. So it would be nice to think that 300meg 11n would give you 150meg throughput. Unfortunately this just isn’t true. There are a number of reasons for this but two stick out in particular:
1. WiFi channel space:
In order for a 300meg 11n WiFi link to run at 300meg you need channel space for four 20meg wide channels (actually running as 2x40meg wide streams). That’s 80meg of channel space. The only way you can get that in the 2.4GHz WiFi band is to grab ALL of the spectrum: That’s every single channel. This assumes that there are zero other users out there in using 2.4GHz – in reality this just doesn’t happen. The chances of the complete 2.4GHz spectrum being available for your 300meg link is pretty much zero! In fact, in the 2.4GHz band you’ll be lucky if you can even get one 20meg channel to your self!
So what about the 5GHz bands? Well Band C’s out ’cause although there’s 105meg of free channel space there it’s got a notch in the middle so in actual fact you’ve got 70meg, then a gap and then 35meg. So there’s nowhere to put two 40meg wide channels. So then there’s Band B in the 5GHz. Well Band B is the 5470 to 5725MHz range. So lots of channel space there. Well there is at the moment. The problem is that most outdoor wifi links are usually running on Band B (the professionals have been switching over to Band B post haste over the last few years) so it’s starting to get a bit congested there. At the moment Band B’s your best bet but, the way things are going (and the launch of 802.11ac where a single 5GHz wifi link uses ALL of the channels in one go isn’t going to help!), it won’t be long before that starts to suffer.
As I’ve discussed elsewhere, TP (Twisted Pair) Homeplug products are networking products which allow Homeplug networking down standard twisted pair wire. The advantages of Homeplug over more dedicated cabling, compared to over active mains cables (which is the type of Homeplug networking 99.9% of users know of), are much higher data transmission rates and longer cable runs. The electrical noise invariably present on normal mains wiring and the complications present in how the cable is distributed (spurs, consumer units etc) often limits the effective data speed and also restricts the length of cable runs you can get away with. But Homeplug over twisted pair wire, with it’s simpler, cleaner interconnect can, for example, give TCP data throughputs in excess of 25Mbps with cable runs of 500m. In our own office testing we got speeds from 95Mbps (the theoretical limit for the devices) with a short cable, down to 15Mbs with a 700m run.
Direct (4m of twisted pair) 95Mbps
200m twisted pair 71Mbps
500m twisted pair 25Mbps
700m twisted pair 15Mbps
Applications for TP Homeplug are anywhere where there is the option of using a single pair of twisted cable as the infrastructure. This can, for example, be a used or unused wire pair in multi-pair telephone cable, an unused wire pair in alarm cable, or an unused pair in network cable.
If you are having trouble getting a HomePlug setup to deliver the through-put that you need, or if you are trying to determine what you can expect from some products that you are thinking of buying, then the following notes may help.
There are four main considerations that affect the performance of a HomePlug system:
The distance between the pair of devices
The complexity of the building’s mains wiring
Electrical noise generated by other mains powered equipment
Understanding the headline speed of the standard
Before we look at these points in detail we’ll have a quick look at the technology in general.
To try and clarify factors that you need to consider when planning on using an external antenna for your 4G/LTE broadband connection.
With 4G (LTE) services starting to come onto the UK market a lot of users are finding that they are achieving download speeds that are lower than they were expecting to get. Often this can be due to poor reception however there are other factors that need to be understood which can affect the broadband speed.
Hopefully this short article will help explain the implications and considerations the user needs to examine before they can decide the best course of action.