ALL ABOUT WIRELESS CONNECTIVITY
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Wireless as a technology has matured from a cutting edge “only-to-be-used-in-an-emergency” technology into a mainstream, and in many cases, primary means of providing connectivity.
Within any given metropolitan, suburban or rural area, broadband wireless access is by far the easiest and most cost-effective way to implement your high-performance network. Whether you’re creating a network from scratch, or need to augment or replace your existing wireline links, broadband wireless access is the most reliable and cost-effective, high-speed data networking alternative you should know more about.
There is an obvious and increasing need for bandwidth. Multimedia content, such as Video, Music, Clips or Movies have been feeding this intrinsic infatuation for more capacity. This phenomenon has materialised all around the globe.
Understanding Line of Sight in Wireless Networks
A clear line of sight (LoS) is one of the most important conditions for creating reliable wireless links. All wireless signals are attenuated when they encounter obstructions. The goal for every network designer is to reduce the amount of attenuation by deploying clear LoS links.
Despite what the term LoS implies-the ability to see from point A to point B without any obstructions, wireless line-of-sight requires more than being able to easily see from one location to another. Wireless signals travel in waves, not straight lines, which mean that the signal is radiated outwards from the antenna-not linearly.
Find below the main differences between LoS, nLoS and NLoS.
As you can see, the wireless equipment radiates out wider than a visual LoS. Therefore, there is a greater chance that the signal can be obstructed by objects as it travels to the end destination. Each link requires its evaluation to determine whether a clear LoS can be achieved.
By understanding and calculating what is known as the Fresnel Zone, you can decide if your proposed wireless link will have sufficient signal strength for a reliable connection.
The fresnel zone is a method of calculating the amount of anticipated clearance needed to prevent a wireless signal from being attenuated by an object in the path between the link.
The equation for calculating the required fresnel zone is:
To ensure an adequate connection, at least 60% of the calculated fresnel zone must be free from obstructions.
Types of Wireless Internet Links
Point-to-point links typically provide an Internet connection where such access isn’t otherwise available. One side of a point-to-point link will have an Internet connection, while the other uses the link to reach the Internet. If the main building has an unobstructed view of the remote site, a point-to-point connection can be used to link the two together. This can augment or even replace existing dial-up links. With proper antennas and a clear line of sight, reliable point-to-point links over thirty kilometres are possible.
Of course, once a single point-to-point connection has been made, more can be used to extend the network even further. If the remote building in our example is at the top of a tall hill, it may be able to see other important locations that can’t be seen directly from the central campus. By installing another point-to-point link at the remote site, another node can join the network and make use of the central Internet connection.
Point-to-point links don’t necessarily have to involve Internet access. Suppose you have to physically drive to a remote weather monitoring station, high in the hills, to collect the data which it records over time. You could connect the site with a point-to-point link, allowing data collection and monitoring to happen in realtime, without the need to travel to the site. Wireless networks can provide enough bandwidth to carry large amounts of data (including audio and video) between any two points that have a connection to each other, even if there is no direct connection to the Internet.
The next most commonly encountered network layout is point-to-multipoint. Whenever several nodes are talking to a central point of access, this is a point-to-multipoint application. The typical example of a point-to-multipoint layout is the use of a wireless access point that provides a connection to several laptops. The laptops do not communicate with each other directly but must be in the range of the access point to use the network.
Point-to-multipoint networking can also apply to an example at a university. Suppose the remote building on top of the hill is connected to the central campus with a point-to-point link. Rather than setting up several point-to-point links to distribute the Internet connection, a single antenna could be used that is visible from several remote buildings. This is a classic example of a wide area point (remote site on the hill) to multipoint (many buildings in the valley below) connection.
Using Repeaters – for long-range connectivity
The most critical component to building long-distance network links is the line of sight (often abbreviated as LOS). Terrestrial microwave systems simply cannot tolerate large hills, trees, or other obstacles in the path of a long-distance link. You must have a clear idea of the lay of the land between two points before you can determine if a link is even possible But even if there is a mountain between two points, remember that obstacles can sometimes be turned into assets. Mountains may block your signal, but assuming power can be provided they also make very good repeater sites. Repeaters are nodes that are configured to rebroadcast traffic that is not destined for the node itself. In a mesh network, every node is a repeater. In a traditional infrastructure network, nodes must be configured to pass along traffic to other nodes.
A repeater can use one or more wireless devices. When using a single radio (called a one-arm repeater), overall efficiency is slightly less than half of the available bandwidth, since the radio can either send or receive data, but never both at once. These devices are cheaper, simpler, and have lower power requirements. A repeater with two (or more) radio cards can operate all radios at full capacity, as long as they are each configured to use nonoverlapping channels. Of course, repeaters can also supply an Ethernet connection to provide local connectivity.
Typically, repeaters are used to overcome obstacles in the path of a long-distance link. For example, there may be buildings in your path, but those buildings contain people. Arrangements can often be worked out with building owners to provide bandwidth in exchange for roof rights and electricity. If the building owner isn’t interested, tenants on high floors may be able to be persuaded to install equipment in a window.
If you can’t go over or through an obstacle, you can often go around it. Rather than using a direct link, try a multi-hop approach to avoid the obstacle.
Voice telephony has been the main option for providing access to telecommunications in rural areas. Today, a wide variety of new applications such as e-mail, e-commerce, tele-education, telehealth, and telemedicine, among others, has made access to interactive multimedia services as important as – maybe even more important than – voice connectivity alone.
Since each rural district or community requires a different mix of voice, text, image, video and audio communications to best meet its needs, telecommunication network operators must be able to support the widest possible range of services and/or applications and different bandwidth levels at a reasonable cost. The Internet (with the unavailability of an IP network in a rural area) is the most widely used platform used to deliver multimedia applications in rural areas of developing countries.
VSAT is often referred to as a long fat pipe network. This term refers to factors that affect TCP/IP performance on any network that has relatively large bandwidth, but high latency. Most Internet connections in Africa and other parts of the developing world are via VSAT. The high latency in satellite networks is due to the long distance to the satellite and the constant speed of light. This distance adds about 520 ms to a packets round-trip time (RTT), compared to a typical RTT between SA and Europe of about 140 ms.
Licensed vs. Unlicensed Products and Bands
Sub Technologies within the greater wireless market
There are two broad subsections within the greater wireless access technology family, simply unlicensed products and licensed products.
Both have a vital role to fulfil and are viable technologies but they must be applied to the correct requirement. Unlicensed wireless circuits may be deployed by any ECNS license holder as long as the equipment is type-approved and ICASA regulations such as EIRP power outputs are adhered to. This means that any ECNS holder may offer connectivity using unlicensed wireless technologies.
The biggest disadvantage of using unlicensed technologies is simply the risk of interference from other devices using the same unregulated piece of spectrum. The choice to use unlicensed spectrum is one the service providers need to make, in areas where the noise floor is low (number of other devices in the area using the same spectrum) this becomes a good option. In areas where the noise floor is currently high or is likely to become high soon, this becomes a poor option.
The biggest advantage of using unlicensed technology is the relatively low cost. The attractiveness of the low cost makes sense in the correct area but the short term benefits of low cost are not worth the risk in areas with a high noise floor. Anywhere in Gauteng, an unlicensed link may be a perfect option for a very small business using data services only but certainly not for anything bigger than a very small business. In the middle of Burgersfort, it may make sense for a big company to make use of unlicensed technology.
These important choices need to be made by the service providers and need to be understood by their customers. In areas with a relatively high noise floor licensed technologies are the only viable option. The good news here is that the cost of licensed band hardware is dramatically decreasing and the cost of the spectrum to run a licensed wireless link is also decreasing.
Microwave links are available in both licensed and unlicensed frequency bands from 2.4 GHz to 86 GHz. Depending on the application distance, required link capacity, geographic considerations and spectral requirements, each band is suited to particular distances and traffic types.
– The unlicensed frequency bands tend to be used where the networks provide a best-effort type of service at low cost such as Internet Service Providers (ISPs).
– Licensed bands are used in preference where the operator requires guaranteed performance (minimal interference problems from other users).
– In some special cases, the bands are allocated to particular user classes such as the 4.5 GHz band for military use.
Advantages and Disadvantages
For Microwave and Millimetre-wave link applications, there are several advantages and disadvantages as summarised below.
Microwave (2 to 38 GHz)
– 10 to 800 Mbps or 1 to 10 x STM1 (N+1)
– Beyond 50 km (clear line of sight required)
– Distance is dependant on link capacity
– All links offer SNMP based element management and integration into a network management system
– Guaranteed interference & regulatory protection
– Installation time – number of days (usually 1 to 5 days)
– Cost of ownership – medium to high (capacity dependent)
– Long distances possible with multiple hops (beyond 1000 km)
– Robust – protected mode in a licensed band
– Finite licensed band spectrum – requires spectrum management & RF Planning
– Requires line of sight between endpoints
– Requires antenna mounting/mast at each site
millimetre-wave (71 to 86 GHz band)
– Up to 2.5 Gbps (10 Gbps possible in the future)
– Up to 5 km
– All links offer SNMP based element management and integration into a network management system
– Not heavily regulated – ‘light licensing’
– Installation time – hours/days
– Cost of ownership – medium to high
– Robust – protected mode
– Limited distance
– Annual license fees for spectrum
There is a lot of false information and quick fixes on the internet on how to install a Wireless Link, however, this is usually provided by private individuals or companies that focus on personal connectivity that may not be as important as connectivity for Business.
WhichVoIP.co.za called on leading Wireless Internet Service Provider Comsol Wireless Solutions to clarify and provide the top factors to keep in mind when installing a Wireless Link. Thanks, Comsol!
There is a lot of variance in the cost of radio equipment, as in all IT areas. Each also has its place in the eco-system of networks. Unfortunately, the differences in equipment are not always evident to the end-user and service providers often use sub-par equipment in the interest of keeping costs low and being price competitive.
The suggestion would be to ensure that you understand the equipment being proposed, not only for the CPE but more importantly the Core.
Do some research on the equipment and understand the inherent quality or limitations.
Most vendors have approved antenna designs that meet their RF parameters, thus it’s very difficult to compare one antenna to the next. What should be considered are the following:
– Construction quality
– Metal choice
– Corrosion prevention
– Antenna Bracket
– Characteristics (focus and radiation pattern)
Choosing the right bracket for installation is vital as it impacts the link quality and longevity. Brackets are chosen based on:
– Pole selection
– Wind loading
– Equipment weight
– Installation placement
Ensure that your SP installs an appropriately strong bracket for your location as a weak bracket is quite often the main cause for alignment issues and property damage.
Steer clear of the following metals (for poles and brackets):
– Mild steel (Painted or not)
– Electroplated Galvanised steel
– Stainless Steel (Unless installed correctly)
Stainless steel is notorious for causing galvanic corrosion and suffering from galling.
– Powder-coated ferrous metals
Selecting the correct pole for the installation is vital as, along with the bracket, it affects the stability of the solution. In general, most poles are made of aluminium but the important factors are:
– Wall thickness
For stability, we recommend a minimum of:
50mm diameter with 5mm wall thickness.
The longer the pole the more inherently unstable the solution becomes, this due to the wind loading of the antenna causing the pole to sway in the wind.
This sway results in link loss as well as pole and bracket fatigue that might result in breakage.
Poles longer than 2m needs to be supported by wire stays and need to have an increased pole diameter.
Indoor cabling is not designed to withstand outdoor conditions. But more often than not installers make use of them due to their lower cost and easier installation.
But invariably they will perish and fail to result in outages, thus insist on outdoor screened cabling for power and data.
Here are a few points to consider when looking at the quality of installations:
Cables should be installed in:
Bosal or PVC piping
Not glued to walls or poles
On wire mesh grids supported by concrete/brick supports for horizontal runs
Cables should be cable tied at least every 50cm to secure them
At no point must water be able to run down the cables entering either :
– Indoors (via a drilled hole)
Entry points must be sealed.
The cable is not allowed to hang horizontally unsupported
Cables are not allowed to lie directly on a roof or other flat structures that may allow prolonged water buildup around them.
Cables entry points should be weatherproofed with butyl based sealants
All equipment including cables must be labelled
Fastening relates to:
– Brackets to walls
– Brackets to poles
– Antennas to poles
– Cables to poles
– Cables to the walls
There is lots of variation in installation techniques of the above. But in general the installations should:
– Maximise stability (i.e. minimize movement)
– Minimise impact on the surroundings
– Maximise maintainability
– Maximise longevity
Equipment installed outside high on a building or pole is exposed to various conditions that could result in electrical damage. Earthing is thus required to:
– Secure equipment against static discharge
– Secure against lightning strikes
– Secure the premises from Potential difference between the inside and outside of the facility
The majority of radios that would be installed at Access locations would be of the Integrated-type. This implies that the radios and the WAN/LAN ports are integrated on the same device. Often this also includes the antenna.
To power the radios, POE (Power Over Ethernet) injectors introduce both data and power over the data cables to the radios installed outside.
As a result, these POE units are often the items damaged by surge or other factors and as such need to be easily accessible and interchangeable.
There are three types of surge that can be secured against:
– Power Surge (transferred from the mains to the radios)
– Lighting Surge (direct strike to radios transferred to the mains)
– Induction Surge (strike in proximity inducing a current, either mains to radios or radios to mains)
Surge protection is expensive and thus often left out. The customer should be aware of the cost and the impact that a surge can have and then asses the need thereof.
Types of Antennas
A classification of antennas can be based on:
- Frequency and size
Antennas used for HF are different from antennas used for VHF, which in turn are different from antennas for microwave. The wavelength is different at different frequencies, so the antennas must be different in size to radiate signals at the correct wavelength. We are particularly interested in antennas working in the microwave range, especially in the 2.4 GHz and 5 GHz frequencies. At 2.4 GHz the wavelength is 12.5 cm, while at 5 GHz it is 6 cm.
Antennas can be omnidirectional, sectorial or directive.
Omnidirectional antennas radiate roughly the same pattern all around the antenna in a complete 360° pattern. The most popular types of omnidirectional antennas are the dipole and the ground plane. Sectorial antennas radiate primarily in a specific area. The beam can be as wide as 180 degrees, or as narrow as 60 degrees. Directional or directive antennas are antennas in which the beamwidth is much narrower than in sectorial antennas.
They have the highest gain and are therefore used for long-distance links. Types of directive antennas are the Yagi, the biquad, the horn, the helicoidal, the patch antenna, the parabolic dish, and many others.
- Physical construction
Antennas can be constructed in many different ways, ranging from simple wires to parabolic dishes, to coffee cans.
Antennas based on parabolic reflectors are the most common type of directive antennas when a high gain is required. The main advantage is that they can be made to have gain and directivity as large as required. The main disadvantage is that big dishes are difficult to mount and are likely to have large windage.
Dishes up to one meter are usually made from solid material. Aluminium is frequently used for its weight advantage, its durability and good electrical characteristics. Windage increases rapidly with dish size and soon becomes a severe problem. Dishes which have a reflecting surface that uses an open mesh are frequently used. These have a poorer front-to-back ratio but are safer to use and easier to build. Copper, aluminium, brass, galvanized steel and iron are suitable mesh materials.
The BiQuad antenna is simple to build and offers good directivity and gain for Point-to-Point communications. It consists of two squares of the same size of 1⁄4 wavelength as a radiating element and a metallic plate or grid as a reflector.
This antenna has a beamwidth of about 70 degrees and a gain in the order of 10-12 dBi. It can be used as a stand-alone antenna or as a feeder for a Parabolic Dish. The polarization is such that looking at the antenna from the front of the squares are placed side by side the polarization is vertical.
1/4 wavelength ground plane
The 1⁄4 wavelength ground plane antenna is very simple in its construction and is useful for communications when size, cost and ease of construction
are important. This antenna is designed to transmit a vertically polarized signal. It consists of a 1⁄4 wave element as half-dipole and three or four 1⁄4 wavelength ground elements bent 30 to 45 degrees down. This set of elements, called radials, is known as a ground plane.
This is a simple and effective antenna that can capture a signal equally from all directions. To increase the gain, the signal can be flattened out to take away focus from directly above and below and providing more focus on the horizon. The vertical beamwidth represents the degree of flatness in the focus. This is useful in a Point-to-Multipoint situation if all the other antennas are also at the same height. The gain of this antenna is in the order of 2 – 4 dBi.
A basic Yagi consists of a certain number of straight elements, each measuring approximately half wavelength. The driven or active element of a Yagi is the equivalent of a centre-fed, half-wave dipole antenna. Parallel to the driven element and approximately 0.2 to 0.5 wavelength on either side of it are straight rods or wires called reflectors and directors, or simply passive elements. A reflector is placed behind the driven element and is slightly longer than half wavelength; a director is placed in front of the driven element and is slightly shorter than half wavelength.
A typical Yagi has one reflector and one or more directors. The antenna propagates electromagnetic field energy in the direction running from the driven element toward the directors and is most sensitive to incoming electromagnetic field energy in this same direction. The more directors a Yagi has, the greater the gain. As more directors are added to a Yagi, it, therefore, becomes longer. Following is the photo of a Yagi antenna with 6 directors and one reflector.
Yagi antennas are used primarily for Point-to-Point links, have a gain from 10 to 20 dBi and a horizontal beamwidth of 10 to 20 degrees.
Sector or Sectorial antennas
Are widely used in cellular telephony infrastructure and are usually built adding a reflective plate to one or more phased dipoles. Their horizontal beamwidth can be as wide as 180 degrees, or as narrow as 60 degrees, while the vertical is usually much narrower. Composite antennas can be built with many Sectors to cover a wider horizontal range (multi-sectorial antenna).
Many other types of antennas exist and new ones are created following the advances in technology, such as Horn, Panel or Patch antennas which are Solid flat panels used for indoor coverage, with a gain up to 20 dB.
Questions to ask when evaluating a Wireless provider
Wireless as a technology has matured from a cutting edge “only-to-be-used-in-an-emergency” technology into a mainstream, and in many cases, primary means of providing connectivity. With this big change in the Telecommunications landscape, it becomes very important to carefully consider which wireless provider to engage with. Unlike a medium such as fibre, wireless technology has many different facets, brands and options. Choosing the wrong brand or wrong sub technology within the greater wireless umbrella can have dire consequences for an organisation that heavily relies on its connectivity.
With the explosion of connectivity requirements over the past 15 years, a wide range of wireless manufacturers has entered the worldwide market. As with any product, some of these brands are excellent, they make truly world-class products, are flexible in terms of customizing their products to meet different requirements and have their manufacturing process “down pat”.
The sad converse is the worrying number of wireless manufacturers currently peddling a product that is badly designed and constructed and their tunnel vision to move as many boxes as possible as opposed to contributing to a sustainable market place.
Bearing the earlier point in mind most of these manufacturers fit into the unlicensed product category. In many cases, these so-called “cheap and nasty” products have the same look and feel as the more expensive and reliable products and even produce specification sheets that closely mirror the higher-end products. A few key things to always check:
Is the product standards-based or proprietary?
Proprietary simply means that the manufacturer has specially designed its operating intelligence. This intelligence assists with ensuring that the product operates as well as it can when interference becomes an issue. Cheap Wi-Fi devices being used for outdoor applications are the best example of non-proprietary products that may cause issues.
Is the product’s mechanics in order?
Any outdoor product housed in a cheap plastic enclosure/covering should raise suspicions. If the internal workings of the wireless device are meaningful the manufacturer will protect these with the housing, if the components are cheap there will be no motivation to substantially protect them.
Is the product spectrally efficient?
This may seem like a mouthful but it simply means “does the product require a lot of spectrum to work”. The simple rule is that the more spectrally efficient the product the more likely it is to work when the noise floor rises. Cheap modified Wi-Fi devices sometimes need 20-40Mhz on the spectrum to offer the capacity advertised, this inefficiency will eventually lead to link failure. Unlicensed products that have spectral efficiency down to 5Mhz are more likely to work in high noise areas.
Service Level Agreement
Finally and possibly the best way for an end-user to protect itself against rouge products, Ask the service provider for a watertight SLA. Many service providers peddling the cheap and nasty hardware will be reticent to offer an SLA with penalties if they are aware of the deficiencies of the products they are using. Bearing all of this in mind on the upside there are some fantastic wireless brands in the marketplace, it would be a good idea to do some quick research on the company who manufactures the hardware, this can often indicate their strength and longevity.
– Thanks to Comsol Wireless Solutions for this contribution.
Other questions to ask your potential provider
Evaluate service provider and system integrator capabilities in terms of breadth of services and flexibility of offerings
There is real value to a business when it selects a range of services from one provider. It is also sensible to use the same circuits/network to provide other services. Remember, the cost of managing separate suppliers is much higher than dealing with one.
Ensure that the vendor is financially stable and committed to the business over the long haul
There are a large number of providers in this market. Some have significant venture capital funding that has to be repaid, often by selling the business on. A large proportion of the rest are operating on a shoestring and some fail every year. Both of these situations leave you exposed to the risk of no services or one that is altered and not fit for purpose.
Tour the company’s network management facility and meet the people who will monitor the network
Take advantage of any offers to visit the service provider’s data centre and/or network management centre. Some companies will be proud of their facilities because they know that the investments they have made are about servicing the customer.
Select a service provider that has business continuity and disaster recovery capabilities
Some providers cut corners, especially when they are in a setup or rapid growth phase. They don’t have the resources to deploy services at two or more data centres. They have single points of failure in their hardware, software or network. Building resilience into the platform adds cost initially but it is vital to ensure that the service is always available. If an entire data centre is lost, what happens to the customer data, call recordings, voicemails? If these are important to you, they should be important to the service provider.
Go for a service provider that has made considerable investments in the technology and support services
Ask the provider how much has been invested in the infrastructure. Some will have invested very little and some may have invested vast sums. If it is too little the service is likely to be poor. If it is very high the price is likely to be high, or they need to add huge numbers quickly which will probably mean a poor service as well.