Wessex Internet utilises a technology called Fixed Wireless Access for the predominant means of connecting customers to the Internet. This technology is not too dissimilar to your indoor Wi-Fi in your home or business. In fact, it uses the same frequency bands you find on modern 802.11n or 802.11ac indoor Wi-Fi Hubs, specifically 5GHz, and the power is not much more either.
Some people think that this technology is dangerous and has links to health problems, however following many scientific studies conducted to date, these links are unfounded.
This article is specifically technical and scientific due to the nature of it. If you have more technical questions, please consult an expert on Fixed Wireless Access, Ofcom, or the higher education authorities who may be able to assist you further.
Wessex Internet complies with the rules and stipulations set by the UK authorities, including Ofcom and thus the EU as well.
- The power we are allowed to use by Ofcom is considerably less than mobile phone towers. A maximum of 4W EIRP. EIRP is radio power - losses + antenna gain. The actual power the radio uses is considerably less than 4W as we have to factor in the antenna gain.
- The radio waves we use are in the 5GHz band. This band is attenuated/blocked more easily than lower frequencies such as mobile phones (0.8GHz or 800MHz).
- The directivity/antenna gain of the outdoor customer equipment, our backhaul point-to-point long-distance links as well as our base stations are very high. This means that the signal is concentrated in a particular direction and not spilling all over the place unnecessarily.
- Customer dishes are usually located high up on a roof, chimney, or wall, and in combination with the high gain antenna, the signal is directed in a specific direction. Due to this, extremely small amounts if any signal makes it's way inside the property. A combination of the antenna gain and the attenuation of the signal ensures this.
- The wireless signal strength is subject to the inverse square law. This means that if the distance from the antenna is doubled, the signal strength decreases by a factor of 4 (2 raised to the sector power). If the distance then triples, the strength decreased by a factor of 9 (3 raised to the second power). This means the signal strength received at your home or business from a nearby base station is going to be measured in the region of 0.000000009W (-60dBm). By comparison GPS signals are
- Compared to other wireless signals such as mobile phone, TV, radio, the power we are allowed to use on our base station is considerably smaller. A mobile phone tower may have an EIRP of 61dBm = 1258W, whereas we are allowed to use a maximum of 36dBm EIRP = 4W.
- The frequencies we use, in the 5GHz band, are the same used on modern indoor Wi-Fi hubs, such as the BT Home Hub, and other 802.11n and 802.11ac dual band routers.
- Although some people describe our signals as being microwave, this essentially is a broad description of the wavelength of the wireless signals. However micro is not meant to describe the wavelength in the micrometer range, it covers the range from 300MHz to 300GHz (100cm to 0.1cm). It's not a microwave oven!
- The radio waves we use are non-ionising radiation. Ionising radiation describes any type of electromagnetic radiation that does not carry enough energy to ionize atoms or molecules, that is, to completely remove an electron from an atom or molecule. Examples of non-ionising radiation include radio, microwave, infra-red and visible light. Ionising radiation includes UV rays, X-rays and Gamma-rays.
Power and EIRP
Ofcom (the telecoms regulator) limits the amount of 'power' that we can use on our equipment.
We are limited to 1W (Watt) EIRP for equipment operating in the 5.5 - 5.735GHz band, and 4W EIRP for the 5.735GHz - 5.850GHz band. These are called Band B and Band C respectively.
- Band B: 1W of EIRP
- Band C: 4W of EIRP
Band B is what we typically use for the wireless-radios installed on customer properties. Band B affords us enough EIRP to reach customers around 8km from our base stations.
Band C is typically used for the long-range point-to-point backhaul links that connect our base stations to our core network. This is because the higher EIRP allows us to have longer links.
The key to EIRP is that it is this that the power above is based on, so we are limited to 1W and 4W EIRP respectively.
EIRP is calculated as EIRP = Radio Power - Losses + Antenna Gain
Therefore, as EIRP is a calculation of radio power + antenna gain, this actually means that the radio power is considerably less than 1W or 4W.
dBm and dBi
There are a number of ways to represent EIRP, antenna gain and power output, however the most common way of expressing the measurements are in dBm for power output and dBi for antenna gain.
- dBi = dB(isotropic) – the forward gain of an antenna compared with the hypothetical isotropic antenna, which uniformly distributes energy in all directions.
- dBm = decibel-milliwatts is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW).
We use dBm for representing power output due to it's logarithm scale. We can use Watts, however the numbers become so small, it's better to use dBm.
dBm to Watts
- 4W = 36dBm (the maximum EIRP we're allowed to use in Band C)
- 2W = 33dBm
- 1W = 30dBm (the maximum EIRP we're allowed to use in Band B)
- 0.5W = 27dBm
- 0.2W = 23dBm (the maximum EIRP allowed to use in Band A - indoor 5GHz Wi-Fi APs use this)
- 0.0031W = 5dBm (the actual output power from the most common customer outdoor radio transceiver)
- 0.001W = 0dBm (the maximum EIRP allowed for a 2.4GHz common indoor Wi-Fi access point)
- 0.000000009W = -60dBm (a typical good received signal strength at the customer's Wessex Internet outdoor receiver)
- 0.00000000001W = -80dBm (the limit of an adequete recieved signal strength for a Wi-Fi conencted device such as a laptop, phone or tablet)
Example EIRP calculations
- Base Station Sector: 9dBm - 1dBm + 21dBi = 30dBm
- Customer radio: 5dBm - 0dBm + 25dBi = 30dBm
- Long-range point-to-point backhaul link: 0dBm - 1dBm + 36dBi = 36dBm
Format above is EIRP = Radio Power - Losses + Antenna Gain.
If you have any further questions, you can contact our support team at firstname.lastname@example.org and we can try to answer any further questions you may have.