How To Make A Reliable Wireless Link
No Internet Access?
- Internet Connection not available
- Internet access has poor quality service
- No local supplier for land line ADSL access
- Mobile access quality is poor or to expensive for serious use
- other options but very expensive alternatives
What to Consider to Create a Reliable Wifi Link
Wifi Link Transmit Power and Receiver Sensitivity
These days we all assume we have access to the Internet and therefore nobody really addresses what is for many a real problem – Still, for lots of people there is “No easy or cheap way to get Internet access!”
ADSL/Cable verses Mobile Internet Access
Many people live in rural communities in many parts of the so called civilised world but there are problems, even today, with just getting normal telephone lines. Of course the growth of the mobile networks is removing the need for such fixed lines.
You then find that even the new mobile networks are not perfect. There are thousands of places where mobile signals are either non-existent or of such poor quality that they are next to useless, especially for Internet access. And once again we find the problem more prevalent in rural locations for much the same reasons as for fixed lines.
Poor Quality Internet Access
Where some kind of advertised facilities exist there may still be problems with the link quality and speed whether the supplier provides an ADSL connection to the Internet or a mobile Internet access like GPRS or 3G. For most people using land line based telephone based Internet access is the most accessible and cheaper option when available. But depending on your local supplier you will get a mixture of quality access and value for money. Similar arguments apply to mobile Internet access when available but Internet access in mobile networks is much more costly for serious Internet access.
Apart from the people affected from the situation described above, what about the people with no access at all. How can they get connected to the Web? From all this we can reasonable ask “How To Make A Reliable Wireless Link”.
Using a Wifi link to gain Internet Access
It is possible where at least, there is some reasonable Internet access nearby, to share that Internet access over WIFI. It is a question of choosing suitable WIFI Kits and components for the expected range and planned use of your Wifi connection. You may want to create a local Wifi Access point (hot spot) or create a point to point Wifi link over many kilometers. With a point to point link you can create a wireless bridge to share your Internet connection or to share somebody else’s Internet connection in your location.
Different Wifi Connections need Different Wifi Kits
If you create a shared AP within a local community it is likely you will need to employ a suitable omnidirectional external antenna with sufficient gain to reach your intended clients.
In the case where you are creating a point to point link over considerable distance you will need to choose from a selection of directional grid, panel or Yagi antennas to get the best signal results. Our on-line store includes many of these Wifi kits designed for a variety of needs and different ranges.
Designing A Point to Point Link over many kilometers
There are many factors affecting the design of point to point Wifi not least of which is the availability of line of sight between antennas and how to find the desired access point. It is vital where possible to get the most direct and un-obstructed view between antennas, even if it means mounting antennas higher than planned. Obstructions with long distance Wifi can gravely affect the system signal quality.
We have provided a set of on-line tools that you may freely use to help address these issues like the…
- Link Budget Calculator
- Wifi Link Reliability Calculator
- Fresnel Radius Calculator
- Decibels to Milliwatts Converter
- Signal loss due to Diffraction by Obstacles
- WiFi Free Space Loss Calculator
- Wireless Link Reliability Calculator
Planning a point to point Wifi link
We discuss in our article about wifi link budget calculator the concepts involved in creating such links and how it is helpful to understand the equations the calculator uses to work out what equipment components will satisfy your needs. To summarise these concepts we will only list the considerations needed here but we give you yet another super tool to work all the things out for you before you go ahead and buy wifi kits.
Things to consider to set up a Wireless Link
- You have a wireless transmitter and receiver on both ends of the wireless link
- The power of the transmitter will affect the effective range of the wifi signal – more power = more range
- The sensitivity of the wireless receivers effects the effective range of the wifi signal – more sensitivity = more range
Effects of Wifi Link Distance and Transmit Frequency
- Radio signals get weaker as you move away from their source. If you move twice the distance away from your current position you will only get 1/4 of the signal power you had in the first position. The name for this natural phenomena is called the “Free Space Loss”.
- The signal power collected by an antenna is affected by the wavelength of the signal. The antenna aperture is a kind of measure that describes the ability of an antenna to pick up the signal. If you think of it like a door open or closed you get the idea, the more the door is open the more signal comes in. Because frequency is related to wavelength by the fundamental relationship (frequency = speed of light/wavelength) some people confuse the loss of signal at an antenna is the direct result of frequency but this is not really true. It is the geometry of the antenna design in relationship to the wavelength of the radio signal that effects the antenna efficiency.
- It just so happens that frequency is related to wavelength But having made that point if you increase the frequency (shorten the wavelength) radio signals do not go as far anyway by natural defraction effects in the atmosphere. Wifi normally works at the popular 2400 Mhz frequency. But in urban situations this band is becoming more congested with same and cross channel interference. For this reason Wifi is also available at 5000 Mhz which is less congested from an interference point of view and offers the potential for higher bandwidth and non overlapping channels. But this all comes at a cost. Wifi signal propagation decrease with increased frequency. So you need more signal power and antenna gain to do wifi in the 5000 Mhz band that may be possible at 2400 Mhz.
- Bear in mind 2400 Mhz is more than likely to be the first choice for a point to point link. But with more cross channel interference and fading effects depending on the location of your link this could present a problem. In rural areas it could be fine but in an inner city location the link might be better run on 5000 Mhz. depending on intended use and equipment capacity to work at this frequency.
- When you send high frequency signals like Wifi through connectors and specially designed cables you loose some signal power. The longer these cables and the more connectors the bigger the losses. So you should strive to keep these looses to a minimum.
- Added to the above there are now new mobile Wifi devices operating at the 5000 Mhz frequency. Typically new features and signal speed advantages are now offered by the likes of I phone 5/5s and Apple IOS 6/7 and the latest Android smart phones.
Method to Power Wireless Cards
Where possible use POE cables to power your wireless cards. They provide both power to the transmitter/receiver and wifi signal down the same ethernet connection cable. These cables can safely send power and signal without significant loss for 100 meters and more. USB cables by design are limited to short (6 meter) cable lengths for USB 2 standards although they too can power devices and get signals down the same wire.
Wifi Signal Loss by Natural Effects and Obstacles
- Radio signals spread out and in point to point applications we can see this effect. We discuss this in our article about the Fresnel Radius effect. We want to mount our antennas so that this effect is compensated for and we don’t loose any more signal.
- The common Wifi frequency 2400 Mhz is in the same range as domestic microwave ovens. These frequencies were chosen because water freely absorbs this (electromagnetic) energy and creates the heat we see in items cooked in a microwave oven. So in general it is a good thing to keep Wifi equipment away from such devices.
- Because Wifi is easily absorbed by water and trees are full of the stuff, trees are a real signal blocker where wifi is concerned. So make sure your wifi links avoid natural obstructions like these.
Wifi Antennas – Critical Part of Wifi Link Design
Antennas are designed to distribute radio signal energy to the places its needed. They are in a way like optical lenses focussing beams of radio signals. They have the ability to stretch the influence of a radio transmission much further and much more directed than having simple pieces of wire at the end of your radio transmitter. Antenna selection is an important aspect of link design and you should see the antennas and their function as a vital and critical component in the whole link design. You can find information on antennas elsewhere on this blog.
Wifi Link Quality – What Kind of Traffic do you want your link to Support
- What link quality are you expecting to get from your link and will it service the number of users you expect to use the link
- What type of use are you expecting the link to do. Are you expecting concurrent video streaming from all your users at the same time? That is a different prospect than normal web and chat access.
- With increasing link speed protocols and the capacities offered by the Wifi standards like 802.11n and the even newer 802.11a. user demand and expectations for more capacity will increase. But there is a direct relationship between link quality and speed for a given link. The rule is, the better the signal to noise ratio of a channel and the wider the channel bandwidth the higher the effective data rate that channel will provide. Meaning more real information per second.
- Have you allowed for some signal losses and given some thought to weather effects like rain, mist, fog. What about wind loading on your antenna and how it effects the received signal
- Above all then, the only sensible and overriding advice we can offer is to get the best present technical equipment specifications available that match your budget and project needs.
Wifi Point to Point Link Reliability Tester
We developed a new tool for testing point to point links. This tool does link budget calculations for both ends of the link at the same time. There are lots of set-up options at both ends to give you an idea of your link viability with the equipment you intend to use and also the environment conditions. This is a really handy tool. See it here…Wifi point to point link reliability tester