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An Introduction to 5GHz Technology

5GHz Wireless Networking is a quickly emerging technology that is becoming popular over the long existing 2.4GHz technology that we are all accustomed to. It uses the same concepts and methods as the 802.11g, 2.4GHz wireless standard but instead operates in 2 unlicensed and 1 licensed frequency bands within the 5GHz Wireless Networking range, also utilising OFDM technology throughout the whole speed scales rather than just above 20Mbps and MIMO (Multiple-In-Multiple-Out) technology. By using operating frequencies within the 5GHz Wireless Networking bands, you are provided with a range of significant advantages over equipment operating at 2.4GHz, a selection of these are as follows:

  • Unlike the 5GHz Wireless Networking band, the 2.4GHz band is so heavily used to the point of being over crowded, Signal Quality degradation caused by such conflicts can cause frequently dropped connections and unreliability of service. The greater amount of channels that are non-overlapping (4 to 8 times more) in the 5GHz Wireless Networking band provides more scope for the total number of wireless devices operating within close proximity without interference.
  • The 5GHz Wireless Networking band has higher output power limits on equipment and better NLOS (Non-Line-of-Site) Scatter capabilities increases the penetrative effect through buildings relative to 2.4GHz.
  • 5GHz Wireless Networking devices use OFDM over the entire speed range from 1Mbps upwards which greatly reduces the effect of NLOS, RF path signal interference that can occur indoors, slowing down your wireless network and causing it to become unreliable.
  • There is very minimal signal absorption by Water in the 5GHz Wireless Networking frequency bands which means the RF signal can penetrate wet objects a multitude of times greater than a 2.4GHz transmitter. Damp objects such as walls, high water content objects such as people and also rain can cripple 2.4GHz networks whereas 5GHz examples are almost not affected.

However, there are drawbacks to using this technology. The theoretical overall range of 5GHz is less than that of 2.4GHz when operating at the same output power as the Free Space Loss for the 5GHz frequency bands are calculated to be around 6dB poorer. This is due to the signals not being able to penetrate as far through walls and solid objects in their paths. The resulting range becomes only half as much and therefore higher power levels must be used if operating distances are to be made equal; this is ultimately not an issue as the regulated power levels of 5GHz equipment is much higher than that of 2.4GHz and so the problem is negated.

As a result, this is why 5GHz is quickly becoming popular and looks to be turning into the new standard when installing Near-Line-of-Site, Point-to-Point applications between buildings and also Wireless Networks within home and office spaces both small and large.

Typical Applications of 5GHz Technology

5GHz WLAN connections are used around the home and offices to eliminate the use of cables when sharing printers, scanners, and high speed internet connections. In the home or small-office-home-office areas, devices such as 5GHz Wi-Fi Routers and higher end, 5GHz Access Points can be used to create building wide internet and Wireless Network access with strong signal qualities with good interior ranges. The main advantage of a 5GHz WLAN is that they are simple to set up and require only one access point connected directly to the internet through the router. Once a machine is connected to that wireless network, it can access the web and other connected devices from anywhere within the router's range.

Point-to-Point Wireless Ethernet Bridges refer to the implementation of Fixed Wireless Data links between just two computers or networks at more distant locations where higher end, more expensive equipment can be used with high gain antennas. These wireless networks can span areas over long distances which are achieved by using dedicated 5GHz Wireless Networking signals over paths that can even be NLOS (Non-Line-of-Site) and are often utilised in towns and cities to connect office buildings to a network without having to install an expensive cabled connection. 5GHz Ethernet Bridges are especially popular in shorter Point-to-Point Links between two locations as they provide high throughput speeds, good reliability with relatively low chances of being degraded by signal interference.

Performance

The 802.11 family, which governs the 5GHz frequency band, consists of a series of over-the-air modulation techniques that use the same basic protocol. These are those defined by the 802.11a and 802.11n protocols.

You can see in the table below the varying performance of the 2 standards:

802.11 network standards

802.11 Protocol Release Bandwidth (MHz) Data rate per stream (Mbps) Allowable MIMO streams Modulation Approximate indoor range (m) Approximate outdoor range (m)
a Sep-99 20 Up to 54 1 OFDM 35 120
n Oct-09 20 Up to 72.2 4 OFDM 70 250
40 Up to 150 70 250

The Data Transfer Rates that are advertised are usually slightly less when put in practice for several reasons, each data packet includes more data that what you are trying to transfer such as MAC, IP and TCP headers, checksum and preambles etc, also transmitters wait for a short interval between sending or receiving data packets to see if other networks are trying to use the same channel and finally, when each packet is received a small acknowledgement packet is sent to the location that it was sent from.

All of these have a slight effect on maximum throughput speed and therefore the suggested 'real' speeds of the standards could be said to be as follows (please note that throughput speed will vary for each individual wireless network set up so these figure should only be taken as a rough guide):

802.11 network standards

802.11 Protocol Advertised Speed (Mbps) Real World Throughput Speed (Mbps)
802.11a 54 ≈ 27.5
802.11a MIMO 108 ≈ 49
802.11n 300 ≈ 74
802.11n 600 ≈ 144

The UK has specific regulations as to the operating frequencies at which you can use your 5GHz Wireless Networking equipment. There are 3 bands called Band A, B and C which operate on the frequencies shown in the table below:

Band (A, B, C) Frequency (GHz) Channel Maximum EIRP License Regulations

A

(5.18GHz to 5.32GHz)

5.180 36 0.2W License Free Operation
5.200 40
5.220 44
5.240 48
5.260 52
5.280 56
5.300 60
5.320 64

B

(5.5GHz to 5.7GHz)

5.500 100 1W License Free Operation
5.520 104
5.540 108
5.560 112
5.580 116
5.600 120
5.620 124
5.640 128
5.660 132
5.680 136
5.700 140

C

(5.745GHz to 5.805GHz)

5.745 149 4W License Required for Operation
5.765 153
5.785 157
5.805 161

Band A (5.150-5.350GHz)

All devices must comply with ERC Decision 99(23) and IR 2006 which includes TPC (Transmit Power Control) and DFS (Dynamic Frequency Selection), be part of a mobile/nomadic wireless network (i.e. WLAN applications), have a maximum EIRP of 0.2W (200mW) and must be for indoor use only.

Band B (5.470-5.725GHz)

All devices must comply with ERC Decision 99(23) and IR 2006 which includes TPC (Transmit Power Control) and DFS (Dynamic Frequency Selection), have a maximum EIRP of 1W with indoor and outdoor use being permitted. Please note that maximum power levels are much lower than those allowed in Band C.

Band C (5.725-5.850GHz)

All devices must comply with IR 2007, have a maximum EIRP of 4W with a PSD not exceeding 23dBm/MHz, have TPC (Transmit Power Control) and DFS (Dynamic Frequency Selection) and is only to be used in Fixed Service Operations applications (i.e. Point-to-Point links between 2 stationary locations).

Note: The frequency ranges and bands that are regulated in the UK are different to those found in the USA. Also, maximum output power of American equipment is 4 times less than that of the regulations in the UK. Therefore, for legality issues and optimum 5GHz Wireless Networking performance, it is critical that you do not purchase products intended for the US market for use within the UK.

Technical Discussion

OFDM

OFDM(Orthogonal Frequency Division Multiplexing) is a technology that can be used by your 5GHz Wireless Networking equipment to reduce loss in signal. The increased scatter property found with 5GHz Wireless Networking can cause problems with regards to signal quality due to an effect where signals that are being reflected off objects, such as walls, can be out of phase with each other. This can cause the overlapping waves in question to either enlarge the signal amplification or can completely cancel out each other. Also the times at which the reflected signals reach the receiver are different due to the varying distances in the RF Paths they have travelled to get there. The spread in the delay between the signals creates ISI (Intersymbol Interference) which is a situation in which the delayed signals begin to corrupt the symbols travelling on a shorter RF Path. OFDM can cure this by introducing 52 subcarrier channels within each 20MHz channel that send and receive date simultaneously in parallel with each other. The many, smaller channels ensure that more data can be transferred with lower levels of loss due to signal interference.

Scatter

Compared to 2.4GHz, 5GHz Wireless Networks have much better Non-Line-of-Site capabilities due to their increased Scatter performance resulting in the fact that they can be used in environments where there may be an amount of objects between the device locations. They do this by reflecting its signal off surrounding buildings to pass the obstructions in the direct line of site. Scatter performance is proportional to signal wavelength and due to the 5GHz Wireless Networking wave signals having smaller wavelengths than 2.4GHz waves, the Scatter performance is at least 19 times better.

Water

Water is a great absorber of 2.4GHz RF Signal, this is due to the chemical makeup of water between its Oxygen and Hydrogen bonds. Oppositely, 5GHz RF Signal is only very slightly absorbed by water. This means that 5GHz Wireless Networking devices can penetrate high water content objects such as damp walls, people and is also not affected as drastically in rainy conditions.

Fresnel Zones

Fresnel Zones are described as the circular cross sections between two wireless devices that must clear of any objects to avoid any degradation in signal quality. As the size of the Fresnel Zone is proportional to the wavelength of the signal, it is found that the larger the wavelength the bigger the Fresnel Zone (the area that must be clear). To avoid any complex calculations, the size of the 5GHz Fresnel Zone is about half that of 2.4GHz meaning that less free space is required between the two points. For more information, please refer to our "Fresnel Zones" article.

Simple Fresnel Diagram

Free Space Loss & Output Power

These two go hand in hand when discussing 5GHz Wireless devices as Free Space Loss is the one area where they do not perform as well as 2.4GHz devices. As mentioned previously in this article, 5GHz Wireless Networking devices suffer around 6dB worse off which means the signal will only travel about half as far at the same output power of a 2.4GHz device (assuming antenna gain, receiver sensitivity etc. is the same) but this is counteracted by the regulations of the 5GHz Wireless Networking devices being able to operate at much high power levels. 2.4GHz equipment is limited to 0.1W (20dB) whereas 5GHz Band, C equipment can go all the way up to 4W (36dB)... 40 times more powerful. Even with the 6dB extra loss due to Free Space Loss, the potential extra range for 5GHz Wireless Networking devices can be up to 100% further.

In summary, 5GHz looks as though it will, in general, outperform 2.4GHz equipment in nearly all areas. In Point-to-Point, Non Line of Site applications 5GHz Wireless Networks seem to be much better suited, and with technology such as OFDM and high power levels, when equipped with a directional, high gain antenna, ranges of more than 10km can be achieved. When regarding interior applications, better scatter properties and high penetrative effect give great improvements for home, office and enterprise Networks.

The main drawback with 5GHz Wireless Networking as a solution is the increased price over 2.4GHz equipment. Nevertheless, as popularity rises and uptake increases the prices should become very competitive but even in the current market, 5GHz already seems to be a popular solution.

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