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Buyer's Guide to Linking Buildings (or anything!) Wirelessly - Point to Point Bridging

Hello and welcome to our guide on wireless point to point bridging. The idea is to take an existing network and link it to another network wirelessly without having to dig up the ground and lay a physical data cable. This could be a network that is connected or disconnected from the internet.

So what should you look for in your wireless point to point or PtP bridge?

Line of Sight

When you call WifiGear about a wireless bridge, the first thing we will ask you is 'do you have line of sight?'

What do we mean by this? It's not quite what you think - 'can I see the place I want to shoot my signal to'. Wireless radio signals are 3D shapes, they normally look like streched out rugby balls. If anything gets in the way of the radio waveform, it'll affect your signal strength and data rates.

All radios require line of sight, if you don't have this, you'll need to get it via a taller mast or a repeater. If anything gets in the way, you'll lose data.

Range

Point to Point links vary in range, you can get links from 20-30 meters all the way up to around 12+km given good conditions. Longer links require specialised licensed frequencies and equipment, but also need to take into account the curvature of the earth. This is because wireless links are directly straight and the Earth is not, creating a 'hump' in the centre of the link which means you'll need more height on the mountings.

IP Rating - Dust and Water

IP rating is short for 'Ingress Protection' or the ability of a device to lock out dust and water. After the term 'IP' there are two numbers, the first is protection against solids, the second is protection against liquids. Be aware that any electronic device that isn't officially 'IP Rated' should not be relied on for a 'business critical' link.

Frequency - 5GHz, 60GHz?

Wireless Point to Point bridges can use almost any frequency. 2.4GHz, 5GHz, 60GHz, 80GHz and then you've got Free Space Optics or Laser Links. How do you know what's right for you?

If you live in a highly rural area with no interference, you can use 2.4GHz. The only reason we still don't use it is due to the congestion of the frequency.

If you're a small business or home user, it's likely you'll want to use 5GHz unless you're in a very busy area (central London) where 5GHz is a busy network.

If you're a small business, enterprise or have a 'business critical' link over 1km or so, you'll want to look into 60GHz and microwave technology.

Frequency Guidelines:
  • 2.4GHz max speeds: ~170Mbps (15km max)
  • 5GHz max speeds: 700+Mbps (12km max)
  • 60GHz max speeds: 5Gbps (1.5Km max)
  • Laser max speeds: 10+Gbps (350m max)

Some frequencies are licensed such as 24Ghz and 60GHz, you'll find licensing plans on the products you look into.

Full Details can be found here: http://static.ofcom.org.uk/static/spectrum/fat.html

Fresnel Zone

We referenced this briefly with the stretched 'rugby ball' analogy. Essentially when you shoot a wireless signal it takes a 3 dimensional shape, you're shooting two beams of radio waves at each antenna.

Imagine the shape as a thin cone that shoots out from your master radio to the other 'client' radio head, the cone meets in the middle and then tapers back to the recieving radio.

If anything intersects this 3 dimensional path, you'll lose signal, packets and throughput (Mbps)

Throughput

Simply put, this is the amount of data that will be fired across the air (transmitting and recieving) in both directions. For example a link may be 170Mbps total, 85Mbps download and 85Mbps upload.

You need to figure out how much data you need for your purpose. For example a single HD camera may need to push 4Mbps of data across the link. You might think you can put 20 cameras on an 85Mbps link, but be aware that wireless links are not usually 'perfect' so you will want to leave some 'headroom' to allow for weather conditions and alignment.

Wi-Fi Protocol

Wireless Protocols such as 802.11ac and 802.11n dictate the total throughput that can be achieved and how complicated the waveform is. 802.11n products such as the Ligowave 5-20n can push 170Mbps but 802.11ac products can push up to 700+ Mbps if configured correctly and pushed to the limit.

802.11ac introduced a much higher complexity to the waveform including an extra channel for a larger bandwidth and 256 QAM instead of 64 QAM (QAM - Quadrature Amplitude Modulation).

It's important to note that 802.11ac is a 5GHz *only* frequency.

Quality of Service

QoS is an idea that sparked lots of proprietary protocols. The idea is that some data should be prioritized above other data in order to get mission critical or sensitive application data across the link first, before other data.

This is especially important for video and voice data. The packets themselves cannot afford to be dropped and re-sent and they must be sent in the correct order to maintain the integrity of the data.

This idea ensures that information who's data is easily lost is 'core', any other data that is not business critical may be subject to a 'second class' service level.

Antenna Gains, Antenna Shapes

Point to Point links can be made from many types of radios. Along with the frequency, the power and/or gain of the antenna must be taken into account.

How far are you planning on firing your link? Is it a short range link? Then perhaps consider the Ligowave DLB 5-15n radio. Need to shoot a couple of kilometers? Then you're better off with the 5-20n.

You can often find the 'gain' of the antenna within the product name on Ligowave products. 5-15n stands for 5GHz, 15dBi, 802.11n.

The higher the gain, the harder the radio waves are 'projected' and the thinner the beamwidth will be, you can find yourself with problems when trying to deliver high dBi at close ranges.

AES Encryption

Available on most wireless links as standard. 'Advanced Encryption Standard' is an extension to the standard WPA2 protocol across the air for an added layer of security.

Siklu Wireless Links offer higher levels of AES encryption for high security links such as for governments and military use.

Protocols such as iPoll and AirMAX

Many wireless links have proprietary protocols to try to ensure their QoS voice and video prioritisation such as 'AirMAX' from Ubiquiti. 'iPoll is Ligowave's protocol which not only increases quality of service but additionally optimises Point to Multi-Point links - such as 4 subscriber 'client' units all shooting data back to a large sector 'base station'.

TDD, FDD - Time Division Duplex, Full Division Duplex

Simply put, this refers to the way each radio speaks to the other. Imagine you're holding a handheld radio.

If you hold the button down, you can speak but you cannot hear. You let go and let the other radio speak to you. - This is Time Division Duplex.

Full Division Duplex is when both radios can speak at the same time and hear each other at the same time. This usually doubles the throughput capabilities.

Alignment

Ensuring a precise alignment will give you the best possible throughput that your device is capable of.

Alignment can be affected by heavy weather - wind, heavy rain and sometimes even wildlife. Ensure your links are secure with sturdy poles and mounting brackets!

Mounting

Really this is the same as the above, not all brackets are created equal and you'll find that you can't get a link in some situations without fine alignment on the mount.

Spending out a little more on a heavy duty precision mount on a 60GHz link could prevent you having to attend a call out to re align your radio saving you several hours.

Interference Mitigation

Many Manufacturers will have coded specific software for their hardware that mitigates against interference, such as Siklu's weather mitigation protocols (link slows down to preserve integrity of high priority data).

Additionally you can ensure you're mitigating your own co-channel interference by not installing 20 5GHz radios on one mast, 3 of which are on the same channel.

Point to Point Wireless Applications:

  • Live and recorded video via CCTV feeds
  • Agricultural data analytics
  • Networking between two buildings, linking buildings, for permanent or redundancy purposes
  • Internet connectivity for temporary sites
  • Lease line replacement (can't dig a fiber trench)
  • Difficult terrain preventing you from running cable
  • Smart city infrastructure - no need to dig up ground to fix fiber lines
  • Audio visual installations and events
  • Setting up affordable and fast internet access (Wireless ISP) to your town (where fiber is not available)
  • Short distance forex trading (wifi bridges are actually lower latency than fiber)